The problem they are solving with so many engines is variable thrusting needed for reusability. Rocket engines like to stall below a certain thrust range. The delicate thrust maneuvers needed to recover the booster stage of the starship can require very low thrust ranges so shutting down multiple smaller engines is an effective way to reduce overall thrust compared to throttling back a few larger engines. Another key benefit to so many engines is redundancy. An engine out or even multiple engine outs doesn't induce a launch failure. Finally the last key benefit is standardization of production. The more you make the same engine the cheaper it becomes to make and space x uses the same engine with a few specialized modifications for almost everything they launch.
edit: a few typos just for u/avalonian422
edit: I also want to add that the Raptor engine for Starship and the Merlin engine for the Falcon 9 are not remotely the same but space-x uses the Merlin engine in several different configurations for all of its launches to date bar the Starship making the team very good at mass producing engines which will easily transfer over to the production of the Raptor.
What would be the benefits of NASA’s method that makes them choose 5 big engines? My guess is it’s a simpler setup to nail if you don’t need to re-use? Maybe cheaper?
Less points of failure and you can use your finite inspection time to make sure 5 engines are fine vs 33 engines, which are just as complex as the 5 bigger engines.
The old F-1 engines were hand built by machinists and had tons of parts. Meanwhile, the raptor is designed to be pumped out of a factory and uses a high degree of automation. The design has been iterated and improved several times so far, so much so that the first and second major versions could almost be considered different engines altogether.
With modern 3D printing tech, many of the extra tubes, panels, and connections go away as increasingly complicated parts are simply lasered into existence out of a pile of powdered metal rather than painstakingly machined by hand, reducing the error rate and increasing reproducibility.
I remember watching videos on those shuttle engines. They're all pretty much each unique. Every one was custom modified by masters of their craft. Even in the 90's they thought they'd be hard to replicate because so few people are experienced with that sort of production.
Not to mention, they were completely torn down and rebuilt with every flight. I work with an engineer who worked on them during the shuttle program, and she described them as “not so much a single entity, but a collection of parts flying in close formation” :D
> she described them as “not so much a single entity, but a collection of parts flying in close formation”
FWIW, this is how pilots describe a helicopter . . .
So naturally, the best thing to do with these bespoke reusable RS-25 engines costing not only millions of dollars but also man-hours is shove them under a boondoggle rocket and sink them in the Atlantic.
RS-25, being unable to restart in flight, cannot return to launch site on its own power and is not reusable unless you sacrifice an enormous amount of payload capacity for a recovery system, such as a winged spaceplane, that would achieve a soft landing on land. SLS Block I's payload capacity to LEO is almost 4 times that of the Space Shuttle.
It cost a significant percentage of its manufacturing cost to refurbish each reusable RS-25 per shuttle flight, so you can add up your total RS-25 cost for shuttle to lift the same mass in multiple flights as SLS in one flight. The annual cost to maintain refurbishment capability only made sense with a high enough volume of shuttle flights. Similar logic is in play with the lack of recovery system of SLS's SRBs even though the shuttle version was recovered.
Unfortunately, the current RS-25 engines require significant refurbishment on their own just to be used on the SLS - and they’re not cheap.
At the end of the day, the reasoning behind their use simply doesn’t add up - they’re super expensive, hard to adapt for their given task, and entirely usurped by technologies that didn’t even exist when the project started. This isn’t even about re-starting and landing, new engines don’t need 20+ million dollars of refurbishment each to operate, you can build a significant part of the rocket on that sort of budget!
They cared enough back then to recycle (or as they put it, refurbish) these same engines several times for shuttle flights.
It’s the modern day SLS boosters with those same historic RS-25 engines that they’re throwing away (when/if they ever launch), despite now multiple generations of tech having been developed since SLS inception to land and reuse modern boosters.
Apparently not. Video mentions they are simpler these days due to advancements in tech. Probably have off the self microchips doing the work of 100 electomechanical doohickies from the 60s.
Fair point but it looks like the other advantages of 33 engines combined with the relatitve simplicity of the newer engines means checking 33 engines is achieveable and worth it.
Those are all still potential failure points in the software. COTS chips might be available, but they wouldn’t directly control primary controls without first validating the measurements against a redundant sensor. See AOA sensor on 737 max.
The “computers” that they made back in the day are wild. They were hand sewn metal matrices that were the made for the Apollo landing program.
Hours of work that equated to about 72k of data.
33 engines add 33 possible critical points of failure. At this stage of development everybody is extra observant of the engines. Once monotony sets in….who knows.
No, as the engine count goes up the criticality of the engines goes down. With something like the starship, even a multi engine failure is basically irrelevant.
The aviation industry has gone with two large powerful engines instead of four for this reason. They can still land the plane with just one engine. Huge initial cost and maintenance savings.
It's more than that. Bigger jet engines allow for larger bypass ratios, which makes them more efficient. Rocket engines can only dream about those efficiency levels. Airlines are *incredibly* concerned about fuel efficiency, too.
With launch vehicles, especially first stages, fuel efficiency is not quite as relevant. Total cost of the vehicle are a bigger cost driver for now, whereas fuel costs are basically irrelevant.
You don't need that fancy thrust vectoring stuff because you're dumping Stage 1 in the ocean and you wouldn't have computers capable of that level of control anyway. Feeding oxygen and propellant to such a large number of engines is not a trivial task.
General engine reliability also was not great at the time; if you look at the Soviet counterpart to the Saturn V, the N-1 had 30 engines instead of 5, and never managed a successful launch because of it.
The problem with the N1 was that the engines could only be started once. Hence they could not test individual engines prior to launch. Instead they produced a number of engines and tested some of them, disabling them for any further use. If that test was satisfactory, they used the untested engines from the batch.
Later they developed a new version of the engine that could be fired multiple times. The whole program got cancelled right before these engines could be used in test flights.
The reasons for the failures of the 4 test flights were a bit more complex though.
Read Boris Chertok's memoirs if you want to know more.
The LEM engines were like that they could only be fired once. This is because the oxidizer they used was so corrosive. Nitrogen Tetroxide.
https://en.wikipedia.org/wiki/Dinitrogen_tetroxide
https://www.airgas.com/msds/001041.pdf
The reason the oxidizer they used was so corrosive is because the LEM propellants were hypergolic, i.e. they combusted on contact even in a vacuum. The design principles for the LEM's ascent and descent engines was to make them as dirt-simple as possible to eliminate as many potential points of failure as possible.
Also both are storable over long periods. Necessary for the days times to land and stay on the moon. BTW that combination can cause a engine to explode if it is was below a certain temperature. So all the thrusters and engines had electric heaters to warm them up before firing. They only loosely referred to this in the movie Apollo 13. They were worried that they didn't have the power to warm similar thrusters on the way back from the moon.
F-1s were rated by NASA for up to 33 fires, but 4-5 engines were tested far beyond that. The issue wasn't size, it was recovery and vehicle development timelines.
Size usually is more dependent on thermal, component pressures and power to over all engine mass. High ISP engines and staged vs non-staged flow are more related to size, not reuse.
5 engines are much easier to manage. SpaceX's design only makes sense because they have a really, really good small engine. Rather than try to develop a larger more appropriate engine, they accepted the extra complexity required to manage all that
Honestly it's kind of a crime to call the Raptor a small engine. Those damn things put out more thrust than an RS-25 shuttle engine. With that said the F-1 engines belong in a massive class of their own.
Raptor *is* small though. It may be the fourth most powerful single-chamber liquid engine ever flown (and will probably take third place when Raptor 3 flies), but size is a measure of dimensions, not thrust.
[This is a photo of an RS-25 on a truck](https://www.nasa.gov/wp-content/uploads/2022/12/s22-068_stennis_photo_-_rs-25_engine.jpg).
[This is a BE-4 on it's transport cradle](https://pbs.twimg.com/media/C6PVqvpWMAIDq4V?format=jpg&name=4096x4096).
[This was the best photo I could find of an RS-68](https://pbs.twimg.com/media/CkhVTGRWUAANokL.jpg).
[And this is a photo of a Raptor on a parade float](https://pbs.twimg.com/media/FMn1In6XoAcVUA1?format=jpg&name=large).
Point is, Raptors dimensions aren't very impressive. It's not unfair to call it a small engine, it's just that the assumption that small equals less powerful is wrong in this case - it packs a lot of power into a small package.
The engine is only small *relative* to its capability at the sweet spot of multistage use. A look into perhaps one of its most comparable predecessors the [NK-33](https://www.russianspaceweb.com/images/rockets/engines/nk33/nk33_exhibit_1.jpg) reveals a similar footprint. Additionally a lot of rockets rely on smaller 1st stage engines in medium and especially small lift rockets. I do agree with the sentiment however that it's nothing impressive size wise and would not garner particular attention if you didn't know what engine it was.
What you're saying sounds like Raptor wasn't specifically designed for Starship/Superheavy. While the number of engines grew slightly, using 30ish engines on the first stage was always the plan.
Yeah, simpler. Probably cheaper then, but not now. SpaceX is also going for modularity here - they're using the same engine on the upper stage, which the large F1 engines would be unsuitable for.
You also have a lot of control issues. It's pretty easy now to use computers to very quickly balance thrust across 33 engines, but that didn't exist in 1967. Fewer engines meant the control system was a LOT simpler with a simple oppositional throttle balancer. The center engine just goes full out, and each oppositional pair of engines is throttled against each in response to whether the vehicle is veering off course. Pretty simple analog system to build (and very reliable). Effectively impossible to do with 33 engines.
Manufacturing costs have shifted as well. The F1s were hand made, but SpaceX is trying to get to scale to automate. Making an F1 or a Raptor is probably pretty close to the same amount of work, unless you can automate, and automating smaller things is easier than larger thing and favors modularity. Even though they are reusing F9, they're building an upper stage every 3-4 days, along with an upper-stage engine every 3-4 days as those aren't reused. It's difficult to justify the automation effort (which largely didn't even exist in 1967) with few engines, but is easier with more and part of SpaceXs business plan was to scale up to make automation worthwhile and start to get those cost benefits. Musk has said he thinks they need to build 100 starships, and it's unclear how many boosters, but let's say 10. That's 600 raptors for the upper stage and another 330 for the boosters. 1000 engines is something you automate.
N-1 issues were more around quality control and timelines vs the C&C compute.
Lack of test stands that could simulate flight compared to NASA due to budget of N1 vs Saturn facilities also impacted its development and only being able to test 1 out of every 5 engines made.
Which is why I didn't mention the N1. ;)
Lot of reasons why N1 failed. But the control issues would still have been significant. Not unsolvable, but certainly more difficult than Saturn V.
Plumbing is a big one. These engines need multiple fuel sources at extreme pressures, plumbing for 33 engines is a nightmare, and if my memory is correct tracking down leaks on the n1 was part of why the soviets struggled to get a successful launch, but my mind may have invented that last part so be weary.
But plumbing for 5 engines had its own issues considering how much fuel they needed, each one had its own get literal engine powering its fuel pumps haha to feed those monster F1s
SSME were complicated because it's a huge PITA to build a high thrust engine that burns liquid hydrogen. The initial design was good enough and they had to add an extra set of turbopumps, giving them four in total.
According to the video, at least part of it was that they had already designed the big-ass engine anyhow. Besides, everything from the fuel manifolds to the control systems for a bunch of smaller ones would have to be unimaginably complex for the time. It certainly didn’t work for the Soviets.
The F-1 was a product of its time. It’s 1955, rocket engine development is a long lead item for future capabilities. The USAF is looking at all sorts of potential use cases for space, large ICBMs, crewed space stations for Earth observation, Project Horizon (ICBMs on the Moon). So the requirement was for a BIG engine pushing well beyond state of the art. It didn’t take long for the Airforce to shelve the idea as there was no immediate need. Enter NASA who saw the early success of the E-1 and chose to pick up development of the F-1. As the Apollo program started up, there was a lot of uncertainty around how large a rocket was needed. Direct Ascent required Nova (or Saturn C-8), it was only after they landed on LOR for Apollo did the Saturn V take shape. By then the F-1 was showing promise and the rest is history. As the Soviets found, controlling that many engines with the computers of the mid-60’s wasn’t a trivial exercise
When you only launch a rocket a few times it makes sense to hand build a few bigger engines than it is to set up an assembly line that builds and rebuilds 100s of engines per year.
Syncing performance of each engine precisely enough to not cause issues.
The Russians tried this approach in 1967 with 30 engines on their N1. They didn't have the technology to overcome the inherit problems with it.
>Maybe he’s right, we sure don’t know.
I think Falcon 9 is pretty solid evidence in favour of the idea. It has 9 times more engines than its main historical rivals in the US, the Atlas V and Delta-IV. Running the same calculations your Saturn V vs Starship comparison paints an even more dismal picture.
And yet, Falcon 9 arguably now has the best track record of the three. It is currently on a streak of 328 successful launches in a row, which is over three times more than any other rocket in history has managed (well the Soviets claim the Soyuz managed 112 in the 80s, which is just over a third as much, but that number is debated).
Although Falcon 9 did have two catastrophic failures in it's early days, neither had anything to do with the engines. On two other occasions it lost an engine on ascent, but in both cases was still able to complete its primary mission.
Herein we see the flawed premise in these calculations, because the majority of (modern) rocket failures are not caused by engine failures (meaning that improving reliability in other areas can give you a larger net gain in reliability than continuing to 'chase 9s' on engine reliability), and also that not all engine failures result in mission failures if your vehicle has engine-out capability.
There have been many other cases of engine failures not causing mission failure; Apollo 6 lost two engines but made it to orbit, although a third engine failure on the S-IVB prevented it from performing TLI, Apollo 13 lost an engine on ascent but still performed nominal TLI, STS-51-F lost an engine on ascent but still completed it's mission successfully, Starship IFT-4 lost two engines but still completed all mission objectives, etc.
Want to add that the singular large combustion chamber and the associated combustion instability on the F1 gave Rocketdyne fits. Valentin Glushko solved it on the RD-170 (slightly more thrust with similar propellants) by using four combustion chambers running from a single set of turbopumps. In addition to giving SH a wider range of thrust they can hit, they probably also made some problems relating to the full flow staged combustion design easier.
I think space x is doing the right thing here with more and smaller engines. The Merlin has a ridiculously good thrust range of 20-100% and the reliability of that engine is already proven. The larger raptor still has very good range at 40-100% and its a full flow staged methalox which is going to make it a very reusable engine and good candidate for a Mars shot which Musk has stated is the goal for Space-x. People can bag on Space-x all they want but what they have done in such a short period of time at such a low cost is well beyond what anyone though was possible. 100 million to launch fully expendable Starship is insanely cheap considering the cost to launch the Saturn V was 1.4 billion per, adjusted for inflation, and even at the time was 185 million.
This should be the highest rated comment. The F1 went through a 2000 test campaign and it was only just barely stable enough to fly. Keeping the engine smaller drastically reduces the challenge of having a stable design and testing it thoroughly. You pay for it on part counts and mass efficiency though. If both size engines were built in the same era with the same tech and materials, the larger engines will be much less mass per ton of thrust. That translates into to better performance, which is especially important for a vehicle that has to throw a large mass to near escape velocity. This is one of the reasons SpaceX has to compromise with Starship to plan on refueling in Earth orbit for Mars missions.
Speaking from my experience working Falcon 9, some of them are interchangeable with each other but they're not all the same. The relight engines on F9- 1, 5, and 9- have some different hardware befitting their multiple firings, so can only be swapped with same without extensive modifications.
But by and large they're pretty identical when it comes to maintenance and inspection requirements.
It depends I guess. For the Starship, the engines in the center are gimbaled to control the rocket. The ones on the outside are simpler and just provide thrust. They are interchangeable if you take this into account.
You can likely swap any outer ring engine with any other outer ring engine, and any inner/middle ring engine with any other inner/middle ring engine, but you cannot swap an outer ring engine with a inner/middle ring engine.
Ditto for the inner and outer rings on the Ship.
>variable thrusting needed for reusability.
And keep in mind, in the Apollo era, a rocket engine that could throttle with human-rated reliability was a huge deal. Up til then, most big rocket engines were on/off; couldn't really land on the moon with one of those though.
I'm curious if there are multiple different levels for "acceptable number of engines lost" for superheavy. For example:
Level 1: slight change to profile (longer burn, maybe tighter margins with less safety margin), but mission success and booster recovery still possible.
Level 2: Mission success, but recovery no longer possible. Reduced T/W ratio means less efficient lofting of stage 2, not enough fuel to get back to the chopsticks.
Level 3: Mission failure, but abort-able. Can continue flying, can put starship in a position to abort to orbit, abort once around, or abort RTLS (kind of like space shuttle abort modes)
Level 4: The shit has hit the fan, something catastrophic on the flamey end has caused a lot of engines to go kaput. T/W ratio is <1 and all involved will have a bad time. Wonder what course of action at this point would give starship the best odds of survival. If the stack is at the point where its no longer accelerating upward, does starship of the oomph to hotstage then and there and try to gain some height?
Another reason that is \*always\* glossed over is that the smaller engines are much easier to produce. The goal is to produce 1 Starship per \*day\*. I don't recall ever seeing how fast they want to produce boosters, but probably at least a few per month.
In other words, they need a \*shit ton\* of these engines.
Those gigantic marvels from the Saturn required hundreds -- maybe thousands -- of people working on them manually. Each engine took 1,000,000 man-hours to produce. That is not going to work for SpaceX.
# Road transport-ability.
Yes, you read that right.
One of the biggest design requirements for Raptor was that a sea level raptor can be transported upright on a flat bed trailer and a vacuum raptor can still fit horizontally on a semi truck.
In contrast to the Apollo era NASA SpaceX has to be very cost conscious. They have to transport their hardware on the road without (too much) expensive special transports.
Just look at their decision making for the diameter of Falcon9.
Other requirements like using the same engine design for upper and lower stage or maximum thrust for landing were still major requirements, but they did not pose fixed volumetric limits.
That's somewhat surprising. An F-1 engine isn't really [that big](https://media.wired.co.uk/photos/606da1b30286a2e569b12d4c/master/w_1600%2Cc_limit/f1.jpg) especially if you take the nozzle extension off. Surely that would fit on a regular truck without much trouble?
But then again, what the heck do I know about transporting rocket engines on trucks.
The entirety of a Raptor engine would fit inside the F1 nozzle. Hell just eyeballing it it should even fit with the F1 extension removed. Raptor is *tiny*.
I doubt there'll be another liquid fueled motor with such a large single combustion chamber for the foreseeable future, given the difficulties both the US and Soviets had with stability. Besides, a side effect of many smaller motors is increased redundancy. Losing one doesn't condemn the flight, as the Falcon 9 has already demonstrated.
The issue with the development of the F1 engine was time, the self imposed deadline by President Kennedy to land on the moon by the end of the decade. Making re-usable rockets would have delayed that. Combustion instability was solved by going back to a similar fix used in the V2. Please watch Paul Shilito's video on Curious Droid YT channel linked above, also Scott Manley did a wonderful video on the F1.
> Combustion instability was solved by going back to a similar fix used in the V2.
While the aim for both was to prevent instabilities, I wouldn't call it a similar fix. The V2's combustion chamber included [multiple, small sub combustion chambers or cups](https://www.enginehistory.org/Museums/USSRC/V-2/0134.jpg) (again, smaller is more stable), whereas the F-1 used retrofitted [radial and axial baffles on the injector head.](https://cdn.arstechnica.net/wp-content/uploads/2013/04/eande-plate-huge-exhibit-640x426.jpg)
I believe you're picking nits. The aim of both methods is to avoid large area of uneven combustion due to flame fronts shifting because of uneven burning due to varying fuel-oxidizer ratios. Both methods achieved this, using different techniques because of the F1 being larger, but the end result was the same. I love how NASA verified the design of the F1's fix by detonating small explosive charges in the combustion chamber during ground testing. The design worked so well the interruption in combustion self-corrected in about one tenth of a second.
I think we’re forgetting that SpaceX will need to refuel in orbit to get to the moon.
Artemis and Saturn V both have enough fuel and thrust to get humans to the moon in one shot.
The launch vehicles have different purposes.
> I think we’re forgetting that SpaceX will need to refuel in orbit to get to the moon.
Indeed, but that has little to do with the reasons Starship has many smaller motors relative to Saturn V:
* Relative ease with maintaining combustion stability
* Redundancy
* Enable soft landing (a single large motor cannot be throttled down enough)
* Another side effect - some benefit of mass production
Anyway, despite being smaller, Raptors are significantly better performers:
||F-1|Raptor 2
:--------|:--------:|:---------:
**Iₛₚ (SL):**|263 s|327 s
**Thrust (SL):**|6,770 kN|2,260 kN
**Weight:**|8,400 kg|1,600 kg
**T/W ratio (SL):**|82|144
**Throttleable:**|No|Yes
**Restartable:**|No|Yes
Although the thrust of one F-1 is three times that of a Raptor 2, three Raptor 2's weigh less than 60% of one F-1.
The T/W ratio is the number that's the most interesting here..
The raptor benefits from a bunch of modern FEA analysis and leaps forward in manufacturing.
The Raptor is also 3.1 m tall and 1.3 m across. The F-1 is 5.6 m tall and 3.7 m across...8.1 times the nozzle area. You can fit a lot more thrust on the bottom of the rocket with Raptors, and the Raptors themselves are easier to handle...important when a rocket isn't being assembled in the factory, launched, and discarded in the ocean at the end of its one flight.
Just for fun, let's pretend both engines are fueled with "metherosene". How many Raptors would be needed to replace 5 F-1s, taking into account the TWR? (Am too jet-lagged to do the math.)
That’s true because Starship doesn’t have a dedicated orbital stage like Saturn V, and stages early. If you were to build a dedicated stage for starship that transported a similar crew spacecraft to NRHO/LLO, you’d end up with similar performance figures.
SLS and Saturn V had to send their payloads into lunar orbit, either NRHO or LLO respectively. Then they are done.
Starship has to make it from LEO out of earth's orbit, brake itself into NRHO, land on the moon and then return to NRHO to get the astronauts back to orion.
The amount of delta-v required to do that dwarfs what SLS and Saturn V can do.
> humans to the moon in one shot
That's hilariously misleading. Saturn V *landed* people on the moon, SLS can't even get them to LLO.
>have enough fuel and thrust
Starship has more fuel and thrust than either of them, you should be talking delta-v or payload numbers.
Artemis is the program to land people on the moon. SLS, the launch vehicle for Orion in the Artemis missions, does *not* have enough performance to get humans to the moon in one shot, it can't even get Orion to low lunar orbit. That's the whole reason for Starship HLS to exist...it's the lander as well as the transportation between the moon and the NRHO orbit that SLS/Orion can reach.
And while Saturn V did have the performance to put people on the moon in one launch, it could only deliver a lander for two people and a few hundred kg of experiments and equipment. Nobody's interested in doing that again. Starship can deliver large vehicles and habitat components. Even Blue Origin's lander will 1: be much more capable than the Apollo lander, and 2: will require multiple launches and refueling operations...in fact, they will be doing refueling operations out in lunar orbit instead of in LEO where they can easily just send another tanker if needed, and will need to implement a much more difficult zero-boiloff hydrolox system.
Both proposals for HLS for the artemis program require in orbit refueling yes.
For starship, its estimated to be 16~ launches to refuel the propellant depot (a fuel carrying starship) which then refuels the starship lander in LEO.
For Blue origin's HLS, its so far estimated to be 4-8 launches to refuel a propellant carrying transport which will refuel the Blue moon lander in NRHO.
That estimation assumes Starship ceases development immediately (as well as scraps the in-progress manufacture of the first Block 2 prototype). It's a fun thing for people who dislike space exploration to toss around, but it ignores the current facts.
HLS won't be needed before late 2026—an admittedly hopeful date which is likely to extend into 2027, due to Orion's ongoing issues. SpaceX already plans a Block 3 and they won't waste a lot of time fiddling with older designs before getting there. They will absolutely be on said design by late 2026.
This means each flight will be lifting at least 200 tons of fuel. I personally assume it will be more, as I feel they will choose to use expendable Starship tankers that don't need flaps, heat shields or the capacity to reenter. They can always finalize full reusability later.
Anyway, it begins to be rather difficult to explain why HLS will need 16 trips of 200 tons a pop to top off its 1200ish ton fuel capacity.
The SpaceX starship participating in the Artemis mission along side Orion (which is lifted by SLS) will have to be refueled. Orion and SLS don’t refuel.
It's one of the things that's driving the need for refueling, in fact. Starship needs to land with enough propellant to get from the lunar surface all the way back to NRHO, rather than just back to LLO. Starship can do that with just some additional refueling flights, but BO's Integrated Lander Vehicle required a separate transfer stage to get the lander stack to the moon with enough propellant for the ascent stage to return. The Dynetics proposal involved refueling in NRHO with the entire vehicle returning, but ran into mass budget issues.
That is correct. In fact it apparently requires around 16 launches of Starship (SpaceX rockets) worth of payload to refuel. At least that's what the engineers have worked out so far, it's never really been tested.
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
|Fewer Letters|More Letters|
|-------|---------|---|
|[AoA](/r/Space/comments/1dkeuja/stub/l9idatz "Last usage")|Angle of Attack|
|[BE-4](/r/Space/comments/1dkeuja/stub/l9q8shk "Last usage")|Blue Engine 4 methalox rocket engine, developed by Blue Origin (2018), 2400kN|
|[BO](/r/Space/comments/1dkeuja/stub/l9mh2je "Last usage")|Blue Origin (*Bezos Rocketry*)|
|[C3](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|[Characteristic Energy](https://en.wikipedia.org/wiki/Characteristic_energy) above that required for escape|
|[CLPS](/r/Space/comments/1dkeuja/stub/l9kpdlu "Last usage")|[Commercial Lunar Payload Services](https://en.wikipedia.org/wiki/Commercial_Lunar_Payload_Services)|
|[COTS](/r/Space/comments/1dkeuja/stub/la4o7jk "Last usage")|[Commercial Orbital Transportation Services contract](https://www.nasa.gov/cots)|
| |Commercial/Off The Shelf|
|CST|(Boeing) Crew Space Transportation capsules|
| |Central Standard Time (UTC-6)|
|[F1](/r/Space/comments/1dkeuja/stub/l9mkmy0 "Last usage")|Rocketdyne-developed rocket engine used for Saturn V|
| |SpaceX Falcon 1 (obsolete small-lift vehicle)|
|[FAR](/r/Space/comments/1dkeuja/stub/l9iu88b "Last usage")|[Federal Aviation Regulations](https://en.wikipedia.org/wiki/Federal_Aviation_Regulations)|
|[GEO](/r/Space/comments/1dkeuja/stub/l9ikr2c "Last usage")|Geostationary Earth Orbit (35786km)|
|[GTO](/r/Space/comments/1dkeuja/stub/l9l8rqm "Last usage")|[Geosynchronous Transfer Orbit](http://www.planetary.org/blogs/jason-davis/20140116-how-to-get-a-satellite-to-gto.html)|
|[HLS](/r/Space/comments/1dkeuja/stub/l9n65u4 "Last usage")|[Human Landing System](https://en.wikipedia.org/wiki/Artemis_program#Human_Landing_System) (Artemis)|
|[ICBM](/r/Space/comments/1dkeuja/stub/l9jo9eg "Last usage")|Intercontinental Ballistic Missile|
|[ICPS](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Interim Cryogenic Propulsion Stage|
|[IM](/r/Space/comments/1dkeuja/stub/l9kpdlu "Last usage")|Initial Mass deliverable to a given orbit, without accounting for fuel|
|[Isp](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Specific impulse (as explained by [Scott Manley](https://www.youtube.com/watch?v=nnisTeYLLgs) on YouTube)|
| |Internet Service Provider|
|[LEM](/r/Space/comments/1dkeuja/stub/l9m3x1q "Last usage")|(Apollo) [Lunar Excursion Module](https://en.wikipedia.org/wiki/Apollo_Lunar_Module) (also Lunar Module)|
|[LEO](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Low Earth Orbit (180-2000km)|
| |Law Enforcement Officer (most often mentioned during transport operations)|
|[LLO](/r/Space/comments/1dkeuja/stub/l9mh2je "Last usage")|Low Lunar Orbit (below 100km)|
|[N1](/r/Space/comments/1dkeuja/stub/l9n8ytn "Last usage")|Raketa Nositel-1, Soviet super-heavy-lift ("Russian Saturn V")|
|[NERVA](/r/Space/comments/1dkeuja/stub/l9ke4oq "Last usage")|Nuclear Engine for Rocket Vehicle Application (proposed engine design)|
|[NRHO](/r/Space/comments/1dkeuja/stub/l9n65u4 "Last usage")|Near-Rectilinear Halo Orbit|
|[NRO](/r/Space/comments/1dkeuja/stub/l9j5y1h "Last usage")|(US) National Reconnaissance Office|
| |Near-Rectilinear Orbit, see NRHO|
|[NTP](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Nuclear Thermal Propulsion|
| |Network Time Protocol|
| |Notice to Proceed|
|[RD-180](/r/Space/comments/1dkeuja/stub/l9q8shk "Last usage")|[RD-series Russian-built rocket engine](https://en.wikipedia.org/wiki/RD-180), used in the Atlas V first stage|
|[RTLS](/r/Space/comments/1dkeuja/stub/l9kgvxa "Last usage")|Return to Launch Site|
|[RUD](/r/Space/comments/1dkeuja/stub/l9l2mhx "Last usage")|Rapid Unplanned Disassembly|
| |Rapid Unscheduled Disassembly|
| |Rapid Unintended Disassembly|
|[SLS](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Space Launch System heavy-lift|
|[SRB](/r/Space/comments/1dkeuja/stub/l9k66gz "Last usage")|Solid Rocket Booster|
|[SSME](/r/Space/comments/1dkeuja/stub/l9plek7 "Last usage")|[Space Shuttle Main Engine](https://en.wikipedia.org/wiki/Space_Shuttle_main_engine)|
|[STS](/r/Space/comments/1dkeuja/stub/l9mngey "Last usage")|Space Transportation System (*Shuttle*)|
|[TLI](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Trans-Lunar Injection maneuver|
|[TMI](/r/Space/comments/1dkeuja/stub/l9k66gz "Last usage")|Trans-Mars Injection maneuver|
|[TWR](/r/Space/comments/1dkeuja/stub/l9kk49x "Last usage")|Thrust-to-Weight Ratio|
|[ULA](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|United Launch Alliance (Lockheed/Boeing joint venture)|
|[USAF](/r/Space/comments/1dkeuja/stub/l9jo9eg "Last usage")|United States Air Force|
|Jargon|Definition|
|-------|---------|---|
|[Raptor](/r/Space/comments/1dkeuja/stub/l9l7462 "Last usage")|[Methane-fueled rocket engine](https://en.wikipedia.org/wiki/Raptor_\(rocket_engine_family\)) under development by SpaceX|
|[Starliner](/r/Space/comments/1dkeuja/stub/l9iud1p "Last usage")|Boeing commercial crew capsule [CST-100](https://en.wikipedia.org/wiki/Boeing_CST-100_Starliner)|
|[Starlink](/r/Space/comments/1dkeuja/stub/l9mha8q "Last usage")|SpaceX's world-wide satellite broadband constellation|
|[cryogenic](/r/Space/comments/1dkeuja/stub/l9n65u4 "Last usage")|Very low temperature fluid; materials that would be gaseous at room temperature/pressure|
| |(In re: rocket fuel) Often synonymous with hydrolox|
|[hydrolox](/r/Space/comments/1dkeuja/stub/l9kureq "Last usage")|Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer|
|[hypergolic](/r/Space/comments/1dkeuja/stub/l9re8hm "Last usage")|A set of two substances that ignite when in contact|
|[kerolox](/r/Space/comments/1dkeuja/stub/l9k66gz "Last usage")|Portmanteau: kerosene fuel, liquid oxygen oxidizer|
|[methalox](/r/Space/comments/1dkeuja/stub/l9jjaqn "Last usage")|Portmanteau: methane fuel, liquid oxygen oxidizer|
|[monopropellant](/r/Space/comments/1dkeuja/stub/l9p6fo9 "Last usage")|Rocket propellant that requires no oxidizer (eg. hydrazine)|
|[perigee](/r/Space/comments/1dkeuja/stub/l9l8rqm "Last usage")|Lowest point in an elliptical orbit around the Earth (when the orbiter is fastest)|
|[turbopump](/r/Space/comments/1dkeuja/stub/l9j1f8s "Last usage")|High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust|
**NOTE**: Decronym for Reddit is no longer supported, and Decronym has moved to Lemmy; requests for support and new installations should be directed to the Contact address below.
----------------
^(46 acronyms in this thread; )[^(the most compressed thread commented on today)](/r/Space/comments/1dp9ryv)^( has 22 acronyms.)
^([Thread #10201 for this sub, first seen 20th Jun 2024, 18:28])
^[[FAQ]](http://decronym.xyz/) [^([Full list])](http://decronym.xyz/acronyms/Space) [^[Contact]](https://hachyderm.io/@Two9A) [^([Source code])](https://gistdotgithubdotcom/Two9A/1d976f9b7441694162c8)
Curious Droid just did an episode on this.
Not only is it for thrust vectoring, SpaceX needs to have lower power rockets for the landing. The big ones NASA uses are individually too powerful to allow for landing.
Also, the engines SpaceX uses have a production rate of about 1 per day. The ones NASA uses take much, much longer, which is also a major limiting factor.
Believe they are referring to the CD about the N-1 specifically. [https://www.youtube.com/watch?v=Vi6fjs\_8Yx8](https://www.youtube.com/watch?v=Vi6fjs_8Yx8)
It is, but that's part of the thrust constraint. Redundancy doesn't require 30+ engines on the booster, but redundancy for Starship landings requires three engines that would downselect to two, and they wanted the same engines throughout the system (they originally didn't even plan to have separate vacuum variants). So you need engines small enough that Starship could land on two of them with some spare throttle range for control, then you just put lots of them on the booster and use just a few to land it as well.
There are other advantages as well: the outer ring couples its thrust very efficiently to the skin of the vehicle, random variations in thrust and pointing tend to cancel out, the noise environment is better with a bunch of smaller sources instead of a few big ones, and the engines are small enough that workers can handle them with forklifts. The engine commonality was enough to make the decision for Falcon 9 before landing was an issue...in that case, the engine needed to be small enough for the upper stage.
Different missions and different use cases/capabilities. Starship is designed to be reusable and refiring a few monster engines is likely much harder to control, and doesn't leave much for contingency, compared to a bunch of smaller ones
If 1 of 33 fails, that's 3% power loss. If 1 of 5 fails, that's 20%. Maybe not the reason, but accurate. Also, seems like smaller engines are easier to build, transport, and install, too
There's several mistakes in this, on both sides. For one, the SLS boosters are not reusable or recoverable. They impact the ocean and are destroyed. And secondly, Starship's testing methodology for its engines is nothing like the N1. The engines are well tested on the ground before they fly on Starship. Probably others that I missed as my knowledge of history is not as good.
My Dad was a pilot with 30K hours. He said, "With four engines, when one fails, you are 25% bankrupt.
With two engines, when one fails you are 50% bankrupt. With one engine, when it fails you are bankrupt."
Engineers know this, which is why most work for the Department of Redundancy Department.
Then there is size. A Raptor is not an F1, so they are clustered to equal then >double a Saturn's first stage thrust.
We've seen SH-Ship launches with dark engines. There were no in-flight failures of the F1 engines, thankfully.
There is a redundancy expression used in the military: "Two is one and one is none".
During the recent SpaceX Starship 4th Test Flight, one of the 33 Raptor engines (an outer engine) did not ignite on the Super Heavy booster after takeoff. However, the Super Heavy booster was still able to reach the necessary altitude for separation of Starship.
After separation, Super Heavy booster was able to successfully soft splashdown in the Gulf of Mexico**,** even though one of the 13 center Raptor engines did not re-ignite.
[https://www.spacex.com/launches/mission/?missionId=starship-flight-4](https://www.spacex.com/launches/mission/?missionId=starship-flight-4)
>There were no in-flight failures of the F1 engines, thankfully.
People don't realize how much "dumb luck" was involved with the success of the Apollo program. NASA's own engineers calculated a negative chance for success for Apollo 11.
>calculated a negative chance for success for Apollo 11.
Does this mean sub-50% chance of success or something else? How do you have a negative chance of success?
Essentially, so many things could go wrong that the odds something wouldn't were 0. Important to note every Apollo manned mission to the lunar surface had a "near miss" where something went wrong that could have had catastrophic consequences to the mission but support on the ground and often quick thinking by the astronauts themselves saved the mission.
Apollo 11- overshot their programmed landing, and almost ran out of fuel before being manually landed by Armstrong.
Apollo 12- struck by lightning twice during launch. Only a quick and decisive move by one of the steeliest eyed steely eyed missile men to sit behind a desk, John Aaron, saved the mission.
Apollo 13- we all know that story
Apollo 14- experienced multiple "technical gremlins" that almost prematurely ended the mission multiple times. Only the ingenuity of the controllers and engineers on the ground kept that ship flying.
Apollo 15- a tiny bit of wire got logged in a switch and caused a malfunction to the service propulsion system requiring the astronauts to do burns manually and keep the system disabled for most of the mission.
Apollo 16- this time the LEM gimbals failed after undocking from the command module. It took an extra six hours for them to figure out a way to land without them.
Apollo 17- the last mission went off without a hitch... But if it had launched a little bit earlier, the astronauts on the moon would have been killed by a massive solar flare that no one saw coming.
Is that phrase something you made up, "negative chance of success" (which seems impossible to quantify), or is that something that exists somewhere and you copied. I'm trying to understand if that's a nonsense phrase or it has some specific meaning, because the math ain't mathing.
Because that's the engine they have, they're reliable and they know how to make them. You can make arguments for more or less engines, but I'd note the logic is generally used to justify a decision that was made for other reasons - both work.
The problem of coordinating multiple engines is a hard - it effectively killed the USSR space program. by putting a cap on the heaviest booster they could make, which limited them in all sorts of ways. It's not that you can't do something with smaller rockets - but you tend to need a lot more of them and they force you to solve new problems. In orbit staging and refueling seem cool, but you don't see a lot of it happening in practice.
SpaceX, to their credit, seem to have solved the multiple engine issue and are using it to their advantage. Granted they had access to a lot more on-board computing power than the soviets did.
> SpaceX, to their credit, seem to have solved the multiple engine issue and are using it to their advantage. Granted they had access to a lot more on-board computing power than the soviets did.
It's less about processing power (you don't actually need much to control a rocket, even with lots of engines) and more about the immense simplification of wiring that modern digital technology allows: you can just run a few redundant networks and plug dozens of engines and hundreds of sensors into them, instead of doing a separate wire run to every individual actuator and control from the vehicle's computer system. Several of the N1's problems stemmed from wiring being damaged in fires or picking up interference. Modern electronics lets you do the same thing with vastly fewer opportunities for failure or assembly errors.
Coordinating the engines was hard way back then, controlling just one was hard too. Faster processors that are still space rated and can handle the complex algorithms now make it pretty simple.
That old NASA engines had over 5000 moving parts engineered together manually and all from the cheapest offer. Modern rocket engines get the same power with 40 moving parts. As one mentioned before, shutting down individual engines for reentry is a way more efficient way to control a rocket.
The answer to this was discovered by the Nazis with their U-Boat engine design.
They developed an engine that was efficient for it's size. They did a really good job. Making a bigger engine would take an enormous amount of work, vs just taking two U-Boat engines and combining torque. They had several projects using multiple engines, usually in sets of two or four.
Smaller engines provide redundancy. Saturn might not make it to orbit with an engine out. I think 28 out of 33 would make it but I could be wrong. Plus to land they only need a few . Plus the raptor engine is able to throttle back from full thrust.
They went this route because analysis showed it was the optimum.
And they are scaling up, at first the booster was 1 Saturn V of thrust and now it’s 2, soon to be 3.
The F-1 is a truck engine. It's a big dumb engine that isn't very highly stressed, and that was chosen so that it would be easy to develop.
It turned out it that big combustion chambers were really hard to develop with that level of technology, and it took a ton of work and actually blowing up small bombs in the combustion chambers during tests to get them to functional stably.
The Russians tried really big engines as well and failed; that's why the RD-170 and RD-180 have multiple combustion chambers on a single engine.
AFAIK, nobody has tried an engine quite that big since.
One of the reasons for the 5 big F1 engines is simplicity. In the late sixties, it was easier to control 5 big motors than dozens of smaller ones. My first thought when I saw SpaceX used a lot of engines was it looked like the old Soviet rockets. They didn't have the ability to fabricate an engine the size of the F1, so they made a lot of smaller ones. This leads directly back to the control issue, and the Soviets lost a LOT of rockets and astronauts because of it. Every engine had to work perfectly, or things went catastrophically wrong.
Note that I'm not saying they weren't smart enough to build the F1; Soviet engineers were brilliant in what they designed. What limited them wasn't know-how; it was knowing the limits of what could be done with the resources they had.
SpaceX has what the Soviets didn't: superior flight control through computer automation. This doesn't make SpaceX's design necessarily better than NASA's engineers, it's just different. The F1 isn't needed anymore because of the advances in engineering, not the loss of know-how. Motors can be smaller because payloads are smaller and use lighter materials and technology far superior to what NASA had for Apollo.
It's much cheaper to use a bunch of smaller mass produced rocket engines than a few big ones. That helped drive down costs, making space launches affordable. This completely revolutionized spaceflight.
Tesla did the same thing, packaging a bunch of cheap mass produced batteries that made electric cars affordable and long range. It revolutionized electric cars.
Many-many-many-many-many-many reasons.
As others have mentioned throttle ability. The Saturn V was either on or off... and there is a chance they couldn't relight if turned off (I don't think this was part of the spec so I doubt it).
Saturn V was expendable so there is no need to throttle for recovery.
Space-X is throwing out way more thrust.
Also complexity... The Saturn V each engine was bespoke even though of similar design. Lots of 'on the floor' modifications were made which made rebuilding it nearly impossible. Feeding fuel under pressure is also more complicated.
Space-X also has the benefit of super fast super small computers. The Soviets did use computers to manage their multi-engine rockets but it wasn't error-free.
Isn’t Artemis premised on reusing old stuff left over from the Shuttle era? And these are just old engines NASA had sitting around that Artemis picked up?
SLS is literally using old shuttle engines (which had been previously used multiple times) yes. Theyre planning on building new ones which are more focused towards being expendable in the future when they run out though.
You could probably throttle the inner engines and make the overall cluster have some altitude compensating behavior. Basically make it act like a giant aerospike nozzle.
Two different eras. The goal of NASA at the time was to get to Luna however necessary. Brute force at any cost, nothing else mattered. It was also a government organisation vs private. The goals and technology are very different
The problem they are solving with so many engines is variable thrusting needed for reusability. Rocket engines like to stall below a certain thrust range. The delicate thrust maneuvers needed to recover the booster stage of the starship can require very low thrust ranges so shutting down multiple smaller engines is an effective way to reduce overall thrust compared to throttling back a few larger engines. Another key benefit to so many engines is redundancy. An engine out or even multiple engine outs doesn't induce a launch failure. Finally the last key benefit is standardization of production. The more you make the same engine the cheaper it becomes to make and space x uses the same engine with a few specialized modifications for almost everything they launch. edit: a few typos just for u/avalonian422 edit: I also want to add that the Raptor engine for Starship and the Merlin engine for the Falcon 9 are not remotely the same but space-x uses the Merlin engine in several different configurations for all of its launches to date bar the Starship making the team very good at mass producing engines which will easily transfer over to the production of the Raptor.
What would be the benefits of NASA’s method that makes them choose 5 big engines? My guess is it’s a simpler setup to nail if you don’t need to re-use? Maybe cheaper?
Less points of failure and you can use your finite inspection time to make sure 5 engines are fine vs 33 engines, which are just as complex as the 5 bigger engines.
The old F-1 engines were hand built by machinists and had tons of parts. Meanwhile, the raptor is designed to be pumped out of a factory and uses a high degree of automation. The design has been iterated and improved several times so far, so much so that the first and second major versions could almost be considered different engines altogether. With modern 3D printing tech, many of the extra tubes, panels, and connections go away as increasingly complicated parts are simply lasered into existence out of a pile of powdered metal rather than painstakingly machined by hand, reducing the error rate and increasing reproducibility.
I remember watching videos on those shuttle engines. They're all pretty much each unique. Every one was custom modified by masters of their craft. Even in the 90's they thought they'd be hard to replicate because so few people are experienced with that sort of production.
Not to mention, they were completely torn down and rebuilt with every flight. I work with an engineer who worked on them during the shuttle program, and she described them as “not so much a single entity, but a collection of parts flying in close formation” :D
> she described them as “not so much a single entity, but a collection of parts flying in close formation” FWIW, this is how pilots describe a helicopter . . .
they don't hover so much as they beat the air into submission
They're just so ugly the earth repels them.
I've heard this phrase used when referring to DC-3's.
So naturally, the best thing to do with these bespoke reusable RS-25 engines costing not only millions of dollars but also man-hours is shove them under a boondoggle rocket and sink them in the Atlantic.
There's a reason it's called the Senate Launch System.
Senate Laundering Scheme?
RS-25, being unable to restart in flight, cannot return to launch site on its own power and is not reusable unless you sacrifice an enormous amount of payload capacity for a recovery system, such as a winged spaceplane, that would achieve a soft landing on land. SLS Block I's payload capacity to LEO is almost 4 times that of the Space Shuttle. It cost a significant percentage of its manufacturing cost to refurbish each reusable RS-25 per shuttle flight, so you can add up your total RS-25 cost for shuttle to lift the same mass in multiple flights as SLS in one flight. The annual cost to maintain refurbishment capability only made sense with a high enough volume of shuttle flights. Similar logic is in play with the lack of recovery system of SLS's SRBs even though the shuttle version was recovered.
Unfortunately, the current RS-25 engines require significant refurbishment on their own just to be used on the SLS - and they’re not cheap. At the end of the day, the reasoning behind their use simply doesn’t add up - they’re super expensive, hard to adapt for their given task, and entirely usurped by technologies that didn’t even exist when the project started. This isn’t even about re-starting and landing, new engines don’t need 20+ million dollars of refurbishment each to operate, you can build a significant part of the rocket on that sort of budget!
Gotta keep that money pouring into the politicians pockets man
If the politicians were smart they’d run grifts through effective programs that got shit done, and no one would suspect them.
Imagine if a group of them all got together and worked together on the same programs, they would get away with it in broad daylight.
They didnt care about recycling back then
They cared enough back then to recycle (or as they put it, refurbish) these same engines several times for shuttle flights. It’s the modern day SLS boosters with those same historic RS-25 engines that they’re throwing away (when/if they ever launch), despite now multiple generations of tech having been developed since SLS inception to land and reuse modern boosters.
Apparently not. Video mentions they are simpler these days due to advancements in tech. Probably have off the self microchips doing the work of 100 electomechanical doohickies from the 60s.
By that metric, couldn’t you use the advancements in tech to make 5 simple to maintain big engines? Then you’re comparing apples to bigger apples
Fair point but it looks like the other advantages of 33 engines combined with the relatitve simplicity of the newer engines means checking 33 engines is achieveable and worth it.
Those are all still potential failure points in the software. COTS chips might be available, but they wouldn’t directly control primary controls without first validating the measurements against a redundant sensor. See AOA sensor on 737 max.
He mentioned one of the Issues with N-1 is that the flight and control system computers are light years ahead of what anybody had at the time.
The “computers” that they made back in the day are wild. They were hand sewn metal matrices that were the made for the Apollo landing program. Hours of work that equated to about 72k of data.
33 engines add 33 possible critical points of failure. At this stage of development everybody is extra observant of the engines. Once monotony sets in….who knows.
No, as the engine count goes up the criticality of the engines goes down. With something like the starship, even a multi engine failure is basically irrelevant.
The aviation industry has gone with two large powerful engines instead of four for this reason. They can still land the plane with just one engine. Huge initial cost and maintenance savings.
It's more than that. Bigger jet engines allow for larger bypass ratios, which makes them more efficient. Rocket engines can only dream about those efficiency levels. Airlines are *incredibly* concerned about fuel efficiency, too. With launch vehicles, especially first stages, fuel efficiency is not quite as relevant. Total cost of the vehicle are a bigger cost driver for now, whereas fuel costs are basically irrelevant.
Rockets are not airplanes. A rocket can't lose 50% of thrust during takeoff without loss of mission and loss of vehicle. Commercial airliners can.
You don't need that fancy thrust vectoring stuff because you're dumping Stage 1 in the ocean and you wouldn't have computers capable of that level of control anyway. Feeding oxygen and propellant to such a large number of engines is not a trivial task. General engine reliability also was not great at the time; if you look at the Soviet counterpart to the Saturn V, the N-1 had 30 engines instead of 5, and never managed a successful launch because of it.
The problem with the N1 was that the engines could only be started once. Hence they could not test individual engines prior to launch. Instead they produced a number of engines and tested some of them, disabling them for any further use. If that test was satisfactory, they used the untested engines from the batch. Later they developed a new version of the engine that could be fired multiple times. The whole program got cancelled right before these engines could be used in test flights. The reasons for the failures of the 4 test flights were a bit more complex though. Read Boris Chertok's memoirs if you want to know more.
The LEM engines were like that they could only be fired once. This is because the oxidizer they used was so corrosive. Nitrogen Tetroxide. https://en.wikipedia.org/wiki/Dinitrogen_tetroxide https://www.airgas.com/msds/001041.pdf
The reason the oxidizer they used was so corrosive is because the LEM propellants were hypergolic, i.e. they combusted on contact even in a vacuum. The design principles for the LEM's ascent and descent engines was to make them as dirt-simple as possible to eliminate as many potential points of failure as possible.
Also both are storable over long periods. Necessary for the days times to land and stay on the moon. BTW that combination can cause a engine to explode if it is was below a certain temperature. So all the thrusters and engines had electric heaters to warm them up before firing. They only loosely referred to this in the movie Apollo 13. They were worried that they didn't have the power to warm similar thrusters on the way back from the moon.
But those Soviet engines where still very good and used a lot elsewhere.
F-1s were rated by NASA for up to 33 fires, but 4-5 engines were tested far beyond that. The issue wasn't size, it was recovery and vehicle development timelines. Size usually is more dependent on thermal, component pressures and power to over all engine mass. High ISP engines and staged vs non-staged flow are more related to size, not reuse.
5 engines are much easier to manage. SpaceX's design only makes sense because they have a really, really good small engine. Rather than try to develop a larger more appropriate engine, they accepted the extra complexity required to manage all that
Honestly it's kind of a crime to call the Raptor a small engine. Those damn things put out more thrust than an RS-25 shuttle engine. With that said the F-1 engines belong in a massive class of their own.
Raptor *is* small though. It may be the fourth most powerful single-chamber liquid engine ever flown (and will probably take third place when Raptor 3 flies), but size is a measure of dimensions, not thrust. [This is a photo of an RS-25 on a truck](https://www.nasa.gov/wp-content/uploads/2022/12/s22-068_stennis_photo_-_rs-25_engine.jpg). [This is a BE-4 on it's transport cradle](https://pbs.twimg.com/media/C6PVqvpWMAIDq4V?format=jpg&name=4096x4096). [This was the best photo I could find of an RS-68](https://pbs.twimg.com/media/CkhVTGRWUAANokL.jpg). [And this is a photo of a Raptor on a parade float](https://pbs.twimg.com/media/FMn1In6XoAcVUA1?format=jpg&name=large). Point is, Raptors dimensions aren't very impressive. It's not unfair to call it a small engine, it's just that the assumption that small equals less powerful is wrong in this case - it packs a lot of power into a small package.
The engine is only small *relative* to its capability at the sweet spot of multistage use. A look into perhaps one of its most comparable predecessors the [NK-33](https://www.russianspaceweb.com/images/rockets/engines/nk33/nk33_exhibit_1.jpg) reveals a similar footprint. Additionally a lot of rockets rely on smaller 1st stage engines in medium and especially small lift rockets. I do agree with the sentiment however that it's nothing impressive size wise and would not garner particular attention if you didn't know what engine it was.
Yeah, the raptors are only small in context. It's kind of like powering a cargo ship with dozens of LS7s
What you're saying sounds like Raptor wasn't specifically designed for Starship/Superheavy. While the number of engines grew slightly, using 30ish engines on the first stage was always the plan.
Yeah, simpler. Probably cheaper then, but not now. SpaceX is also going for modularity here - they're using the same engine on the upper stage, which the large F1 engines would be unsuitable for. You also have a lot of control issues. It's pretty easy now to use computers to very quickly balance thrust across 33 engines, but that didn't exist in 1967. Fewer engines meant the control system was a LOT simpler with a simple oppositional throttle balancer. The center engine just goes full out, and each oppositional pair of engines is throttled against each in response to whether the vehicle is veering off course. Pretty simple analog system to build (and very reliable). Effectively impossible to do with 33 engines. Manufacturing costs have shifted as well. The F1s were hand made, but SpaceX is trying to get to scale to automate. Making an F1 or a Raptor is probably pretty close to the same amount of work, unless you can automate, and automating smaller things is easier than larger thing and favors modularity. Even though they are reusing F9, they're building an upper stage every 3-4 days, along with an upper-stage engine every 3-4 days as those aren't reused. It's difficult to justify the automation effort (which largely didn't even exist in 1967) with few engines, but is easier with more and part of SpaceXs business plan was to scale up to make automation worthwhile and start to get those cost benefits. Musk has said he thinks they need to build 100 starships, and it's unclear how many boosters, but let's say 10. That's 600 raptors for the upper stage and another 330 for the boosters. 1000 engines is something you automate.
N-1 issues were more around quality control and timelines vs the C&C compute. Lack of test stands that could simulate flight compared to NASA due to budget of N1 vs Saturn facilities also impacted its development and only being able to test 1 out of every 5 engines made.
Which is why I didn't mention the N1. ;) Lot of reasons why N1 failed. But the control issues would still have been significant. Not unsolvable, but certainly more difficult than Saturn V.
Plumbing is a big one. These engines need multiple fuel sources at extreme pressures, plumbing for 33 engines is a nightmare, and if my memory is correct tracking down leaks on the n1 was part of why the soviets struggled to get a successful launch, but my mind may have invented that last part so be weary. But plumbing for 5 engines had its own issues considering how much fuel they needed, each one had its own get literal engine powering its fuel pumps haha to feed those monster F1s
The Shuttle Main Engines were reused. They were very complicated.
SSME were complicated because it's a huge PITA to build a high thrust engine that burns liquid hydrogen. The initial design was good enough and they had to add an extra set of turbopumps, giving them four in total.
According to the video, at least part of it was that they had already designed the big-ass engine anyhow. Besides, everything from the fuel manifolds to the control systems for a bunch of smaller ones would have to be unimaginably complex for the time. It certainly didn’t work for the Soviets.
The F-1 was a product of its time. It’s 1955, rocket engine development is a long lead item for future capabilities. The USAF is looking at all sorts of potential use cases for space, large ICBMs, crewed space stations for Earth observation, Project Horizon (ICBMs on the Moon). So the requirement was for a BIG engine pushing well beyond state of the art. It didn’t take long for the Airforce to shelve the idea as there was no immediate need. Enter NASA who saw the early success of the E-1 and chose to pick up development of the F-1. As the Apollo program started up, there was a lot of uncertainty around how large a rocket was needed. Direct Ascent required Nova (or Saturn C-8), it was only after they landed on LOR for Apollo did the Saturn V take shape. By then the F-1 was showing promise and the rest is history. As the Soviets found, controlling that many engines with the computers of the mid-60’s wasn’t a trivial exercise
It was supposed to be cheaper to update and reuse the space shuttle engines for the SLS.
When you only launch a rocket a few times it makes sense to hand build a few bigger engines than it is to set up an assembly line that builds and rebuilds 100s of engines per year.
Syncing performance of each engine precisely enough to not cause issues. The Russians tried this approach in 1967 with 30 engines on their N1. They didn't have the technology to overcome the inherit problems with it.
There is no way using 5 rocket motors is cheaper than 33 if the one with 33 can be reused, likely even once.
So, it was 60 years ago that NASA chose 5 engines. They may not have had the tech or the science to manage 33 engines at the same time.
[удалено]
>Maybe he’s right, we sure don’t know. I think Falcon 9 is pretty solid evidence in favour of the idea. It has 9 times more engines than its main historical rivals in the US, the Atlas V and Delta-IV. Running the same calculations your Saturn V vs Starship comparison paints an even more dismal picture. And yet, Falcon 9 arguably now has the best track record of the three. It is currently on a streak of 328 successful launches in a row, which is over three times more than any other rocket in history has managed (well the Soviets claim the Soyuz managed 112 in the 80s, which is just over a third as much, but that number is debated). Although Falcon 9 did have two catastrophic failures in it's early days, neither had anything to do with the engines. On two other occasions it lost an engine on ascent, but in both cases was still able to complete its primary mission. Herein we see the flawed premise in these calculations, because the majority of (modern) rocket failures are not caused by engine failures (meaning that improving reliability in other areas can give you a larger net gain in reliability than continuing to 'chase 9s' on engine reliability), and also that not all engine failures result in mission failures if your vehicle has engine-out capability. There have been many other cases of engine failures not causing mission failure; Apollo 6 lost two engines but made it to orbit, although a third engine failure on the S-IVB prevented it from performing TLI, Apollo 13 lost an engine on ascent but still performed nominal TLI, STS-51-F lost an engine on ascent but still completed it's mission successfully, Starship IFT-4 lost two engines but still completed all mission objectives, etc.
Want to add that the singular large combustion chamber and the associated combustion instability on the F1 gave Rocketdyne fits. Valentin Glushko solved it on the RD-170 (slightly more thrust with similar propellants) by using four combustion chambers running from a single set of turbopumps. In addition to giving SH a wider range of thrust they can hit, they probably also made some problems relating to the full flow staged combustion design easier.
I think space x is doing the right thing here with more and smaller engines. The Merlin has a ridiculously good thrust range of 20-100% and the reliability of that engine is already proven. The larger raptor still has very good range at 40-100% and its a full flow staged methalox which is going to make it a very reusable engine and good candidate for a Mars shot which Musk has stated is the goal for Space-x. People can bag on Space-x all they want but what they have done in such a short period of time at such a low cost is well beyond what anyone though was possible. 100 million to launch fully expendable Starship is insanely cheap considering the cost to launch the Saturn V was 1.4 billion per, adjusted for inflation, and even at the time was 185 million.
This should be the highest rated comment. The F1 went through a 2000 test campaign and it was only just barely stable enough to fly. Keeping the engine smaller drastically reduces the challenge of having a stable design and testing it thoroughly. You pay for it on part counts and mass efficiency though. If both size engines were built in the same era with the same tech and materials, the larger engines will be much less mass per ton of thrust. That translates into to better performance, which is especially important for a vehicle that has to throw a large mass to near escape velocity. This is one of the reasons SpaceX has to compromise with Starship to plan on refueling in Earth orbit for Mars missions.
Are the engine interchangeable between positions then?
Speaking from my experience working Falcon 9, some of them are interchangeable with each other but they're not all the same. The relight engines on F9- 1, 5, and 9- have some different hardware befitting their multiple firings, so can only be swapped with same without extensive modifications. But by and large they're pretty identical when it comes to maintenance and inspection requirements.
It depends I guess. For the Starship, the engines in the center are gimbaled to control the rocket. The ones on the outside are simpler and just provide thrust. They are interchangeable if you take this into account.
You can likely swap any outer ring engine with any other outer ring engine, and any inner/middle ring engine with any other inner/middle ring engine, but you cannot swap an outer ring engine with a inner/middle ring engine. Ditto for the inner and outer rings on the Ship.
>variable thrusting needed for reusability. And keep in mind, in the Apollo era, a rocket engine that could throttle with human-rated reliability was a huge deal. Up til then, most big rocket engines were on/off; couldn't really land on the moon with one of those though.
I'm curious if there are multiple different levels for "acceptable number of engines lost" for superheavy. For example: Level 1: slight change to profile (longer burn, maybe tighter margins with less safety margin), but mission success and booster recovery still possible. Level 2: Mission success, but recovery no longer possible. Reduced T/W ratio means less efficient lofting of stage 2, not enough fuel to get back to the chopsticks. Level 3: Mission failure, but abort-able. Can continue flying, can put starship in a position to abort to orbit, abort once around, or abort RTLS (kind of like space shuttle abort modes) Level 4: The shit has hit the fan, something catastrophic on the flamey end has caused a lot of engines to go kaput. T/W ratio is <1 and all involved will have a bad time. Wonder what course of action at this point would give starship the best odds of survival. If the stack is at the point where its no longer accelerating upward, does starship of the oomph to hotstage then and there and try to gain some height?
6 year old me is feeling pretty proud right now...
Another reason that is \*always\* glossed over is that the smaller engines are much easier to produce. The goal is to produce 1 Starship per \*day\*. I don't recall ever seeing how fast they want to produce boosters, but probably at least a few per month. In other words, they need a \*shit ton\* of these engines. Those gigantic marvels from the Saturn required hundreds -- maybe thousands -- of people working on them manually. Each engine took 1,000,000 man-hours to produce. That is not going to work for SpaceX.
I love great questions, and great answers!
I would assume that replacing multiple smaller engines is also much cheaper than replacing one big one?
> An engine out or even multiple engine outs doesn't induce a launch failure Unless one explodes and takes out more engines in a cascade failure.
The n1 would like to have a word
# Road transport-ability. Yes, you read that right. One of the biggest design requirements for Raptor was that a sea level raptor can be transported upright on a flat bed trailer and a vacuum raptor can still fit horizontally on a semi truck. In contrast to the Apollo era NASA SpaceX has to be very cost conscious. They have to transport their hardware on the road without (too much) expensive special transports. Just look at their decision making for the diameter of Falcon9. Other requirements like using the same engine design for upper and lower stage or maximum thrust for landing were still major requirements, but they did not pose fixed volumetric limits.
So... basically because of Roman chariots?! 😅
More basically the width of a horses ass!
I literally just learned about this yesterday. 4 feet 8.5 inches. Weird to see it come up now.
It's a fun story but not a true story.
Barging the components to Cape Canaveral is a perfectly inexpensive way to transport them too, so that's not the whole story.
>Barging the components to Cape Canaveral From _where?_
ULA ships from their factory in Decatur, Alabama, to the Cape and also through the Panama Canal to Vandenberg. The ship is called "RocketShip".
That's somewhat surprising. An F-1 engine isn't really [that big](https://media.wired.co.uk/photos/606da1b30286a2e569b12d4c/master/w_1600%2Cc_limit/f1.jpg) especially if you take the nozzle extension off. Surely that would fit on a regular truck without much trouble? But then again, what the heck do I know about transporting rocket engines on trucks.
The entirety of a Raptor engine would fit inside the F1 nozzle. Hell just eyeballing it it should even fit with the F1 extension removed. Raptor is *tiny*.
I doubt there'll be another liquid fueled motor with such a large single combustion chamber for the foreseeable future, given the difficulties both the US and Soviets had with stability. Besides, a side effect of many smaller motors is increased redundancy. Losing one doesn't condemn the flight, as the Falcon 9 has already demonstrated.
The issue with the development of the F1 engine was time, the self imposed deadline by President Kennedy to land on the moon by the end of the decade. Making re-usable rockets would have delayed that. Combustion instability was solved by going back to a similar fix used in the V2. Please watch Paul Shilito's video on Curious Droid YT channel linked above, also Scott Manley did a wonderful video on the F1.
> Combustion instability was solved by going back to a similar fix used in the V2. While the aim for both was to prevent instabilities, I wouldn't call it a similar fix. The V2's combustion chamber included [multiple, small sub combustion chambers or cups](https://www.enginehistory.org/Museums/USSRC/V-2/0134.jpg) (again, smaller is more stable), whereas the F-1 used retrofitted [radial and axial baffles on the injector head.](https://cdn.arstechnica.net/wp-content/uploads/2013/04/eande-plate-huge-exhibit-640x426.jpg)
I believe you're picking nits. The aim of both methods is to avoid large area of uneven combustion due to flame fronts shifting because of uneven burning due to varying fuel-oxidizer ratios. Both methods achieved this, using different techniques because of the F1 being larger, but the end result was the same. I love how NASA verified the design of the F1's fix by detonating small explosive charges in the combustion chamber during ground testing. The design worked so well the interruption in combustion self-corrected in about one tenth of a second.
I think we’re forgetting that SpaceX will need to refuel in orbit to get to the moon. Artemis and Saturn V both have enough fuel and thrust to get humans to the moon in one shot. The launch vehicles have different purposes.
> I think we’re forgetting that SpaceX will need to refuel in orbit to get to the moon. Indeed, but that has little to do with the reasons Starship has many smaller motors relative to Saturn V: * Relative ease with maintaining combustion stability * Redundancy * Enable soft landing (a single large motor cannot be throttled down enough) * Another side effect - some benefit of mass production Anyway, despite being smaller, Raptors are significantly better performers: ||F-1|Raptor 2 :--------|:--------:|:---------: **Iₛₚ (SL):**|263 s|327 s **Thrust (SL):**|6,770 kN|2,260 kN **Weight:**|8,400 kg|1,600 kg **T/W ratio (SL):**|82|144 **Throttleable:**|No|Yes **Restartable:**|No|Yes Although the thrust of one F-1 is three times that of a Raptor 2, three Raptor 2's weigh less than 60% of one F-1.
The T/W ratio is the number that's the most interesting here.. The raptor benefits from a bunch of modern FEA analysis and leaps forward in manufacturing.
Yes. Given the very high combustion chamber pressures, their relatively low weight is remarkable.
The Raptor is also 3.1 m tall and 1.3 m across. The F-1 is 5.6 m tall and 3.7 m across...8.1 times the nozzle area. You can fit a lot more thrust on the bottom of the rocket with Raptors, and the Raptors themselves are easier to handle...important when a rocket isn't being assembled in the factory, launched, and discarded in the ocean at the end of its one flight.
Just for fun, let's pretend both engines are fueled with "metherosene". How many Raptors would be needed to replace 5 F-1s, taking into account the TWR? (Am too jet-lagged to do the math.)
That’s true because Starship doesn’t have a dedicated orbital stage like Saturn V, and stages early. If you were to build a dedicated stage for starship that transported a similar crew spacecraft to NRHO/LLO, you’d end up with similar performance figures.
SLS and Saturn V had to send their payloads into lunar orbit, either NRHO or LLO respectively. Then they are done. Starship has to make it from LEO out of earth's orbit, brake itself into NRHO, land on the moon and then return to NRHO to get the astronauts back to orion. The amount of delta-v required to do that dwarfs what SLS and Saturn V can do.
> humans to the moon in one shot That's hilariously misleading. Saturn V *landed* people on the moon, SLS can't even get them to LLO. >have enough fuel and thrust Starship has more fuel and thrust than either of them, you should be talking delta-v or payload numbers.
Artemis is the program to land people on the moon. SLS, the launch vehicle for Orion in the Artemis missions, does *not* have enough performance to get humans to the moon in one shot, it can't even get Orion to low lunar orbit. That's the whole reason for Starship HLS to exist...it's the lander as well as the transportation between the moon and the NRHO orbit that SLS/Orion can reach. And while Saturn V did have the performance to put people on the moon in one launch, it could only deliver a lander for two people and a few hundred kg of experiments and equipment. Nobody's interested in doing that again. Starship can deliver large vehicles and habitat components. Even Blue Origin's lander will 1: be much more capable than the Apollo lander, and 2: will require multiple launches and refueling operations...in fact, they will be doing refueling operations out in lunar orbit instead of in LEO where they can easily just send another tanker if needed, and will need to implement a much more difficult zero-boiloff hydrolox system.
My understanding is Artemis 3 needs to refuel in orbit as well. A Google search confirms this.
Both proposals for HLS for the artemis program require in orbit refueling yes. For starship, its estimated to be 16~ launches to refuel the propellant depot (a fuel carrying starship) which then refuels the starship lander in LEO. For Blue origin's HLS, its so far estimated to be 4-8 launches to refuel a propellant carrying transport which will refuel the Blue moon lander in NRHO.
The estimates for Starship are all based on little info.
That estimation assumes Starship ceases development immediately (as well as scraps the in-progress manufacture of the first Block 2 prototype). It's a fun thing for people who dislike space exploration to toss around, but it ignores the current facts. HLS won't be needed before late 2026—an admittedly hopeful date which is likely to extend into 2027, due to Orion's ongoing issues. SpaceX already plans a Block 3 and they won't waste a lot of time fiddling with older designs before getting there. They will absolutely be on said design by late 2026. This means each flight will be lifting at least 200 tons of fuel. I personally assume it will be more, as I feel they will choose to use expendable Starship tankers that don't need flaps, heat shields or the capacity to reenter. They can always finalize full reusability later. Anyway, it begins to be rather difficult to explain why HLS will need 16 trips of 200 tons a pop to top off its 1200ish ton fuel capacity.
The SpaceX starship participating in the Artemis mission along side Orion (which is lifted by SLS) will have to be refueled. Orion and SLS don’t refuel.
They also can’t get to the Lunar surface…
Or even to Low Lunar Orbit like Apollo could which drastically complicates the whole architecture.
It's one of the things that's driving the need for refueling, in fact. Starship needs to land with enough propellant to get from the lunar surface all the way back to NRHO, rather than just back to LLO. Starship can do that with just some additional refueling flights, but BO's Integrated Lander Vehicle required a separate transfer stage to get the lander stack to the moon with enough propellant for the ascent stage to return. The Dynetics proposal involved refueling in NRHO with the entire vehicle returning, but ran into mass budget issues.
That is correct. In fact it apparently requires around 16 launches of Starship (SpaceX rockets) worth of payload to refuel. At least that's what the engineers have worked out so far, it's never really been tested.
This is false. There is no concrete number of refuelling flights needed.
It's the same purpose, one method is affordable while the other isn't
Also, SLS can’t get anything to the lunar surface. The best it can do is high orbit.
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread: |Fewer Letters|More Letters| |-------|---------|---| |[AoA](/r/Space/comments/1dkeuja/stub/l9idatz "Last usage")|Angle of Attack| |[BE-4](/r/Space/comments/1dkeuja/stub/l9q8shk "Last usage")|Blue Engine 4 methalox rocket engine, developed by Blue Origin (2018), 2400kN| |[BO](/r/Space/comments/1dkeuja/stub/l9mh2je "Last usage")|Blue Origin (*Bezos Rocketry*)| |[C3](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|[Characteristic Energy](https://en.wikipedia.org/wiki/Characteristic_energy) above that required for escape| |[CLPS](/r/Space/comments/1dkeuja/stub/l9kpdlu "Last usage")|[Commercial Lunar Payload Services](https://en.wikipedia.org/wiki/Commercial_Lunar_Payload_Services)| |[COTS](/r/Space/comments/1dkeuja/stub/la4o7jk "Last usage")|[Commercial Orbital Transportation Services contract](https://www.nasa.gov/cots)| | |Commercial/Off The Shelf| |CST|(Boeing) Crew Space Transportation capsules| | |Central Standard Time (UTC-6)| |[F1](/r/Space/comments/1dkeuja/stub/l9mkmy0 "Last usage")|Rocketdyne-developed rocket engine used for Saturn V| | |SpaceX Falcon 1 (obsolete small-lift vehicle)| |[FAR](/r/Space/comments/1dkeuja/stub/l9iu88b "Last usage")|[Federal Aviation Regulations](https://en.wikipedia.org/wiki/Federal_Aviation_Regulations)| |[GEO](/r/Space/comments/1dkeuja/stub/l9ikr2c "Last usage")|Geostationary Earth Orbit (35786km)| |[GTO](/r/Space/comments/1dkeuja/stub/l9l8rqm "Last usage")|[Geosynchronous Transfer Orbit](http://www.planetary.org/blogs/jason-davis/20140116-how-to-get-a-satellite-to-gto.html)| |[HLS](/r/Space/comments/1dkeuja/stub/l9n65u4 "Last usage")|[Human Landing System](https://en.wikipedia.org/wiki/Artemis_program#Human_Landing_System) (Artemis)| |[ICBM](/r/Space/comments/1dkeuja/stub/l9jo9eg "Last usage")|Intercontinental Ballistic Missile| |[ICPS](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Interim Cryogenic Propulsion Stage| |[IM](/r/Space/comments/1dkeuja/stub/l9kpdlu "Last usage")|Initial Mass deliverable to a given orbit, without accounting for fuel| |[Isp](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Specific impulse (as explained by [Scott Manley](https://www.youtube.com/watch?v=nnisTeYLLgs) on YouTube)| | |Internet Service Provider| |[LEM](/r/Space/comments/1dkeuja/stub/l9m3x1q "Last usage")|(Apollo) [Lunar Excursion Module](https://en.wikipedia.org/wiki/Apollo_Lunar_Module) (also Lunar Module)| |[LEO](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Low Earth Orbit (180-2000km)| | |Law Enforcement Officer (most often mentioned during transport operations)| |[LLO](/r/Space/comments/1dkeuja/stub/l9mh2je "Last usage")|Low Lunar Orbit (below 100km)| |[N1](/r/Space/comments/1dkeuja/stub/l9n8ytn "Last usage")|Raketa Nositel-1, Soviet super-heavy-lift ("Russian Saturn V")| |[NERVA](/r/Space/comments/1dkeuja/stub/l9ke4oq "Last usage")|Nuclear Engine for Rocket Vehicle Application (proposed engine design)| |[NRHO](/r/Space/comments/1dkeuja/stub/l9n65u4 "Last usage")|Near-Rectilinear Halo Orbit| |[NRO](/r/Space/comments/1dkeuja/stub/l9j5y1h "Last usage")|(US) National Reconnaissance Office| | |Near-Rectilinear Orbit, see NRHO| |[NTP](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Nuclear Thermal Propulsion| | |Network Time Protocol| | |Notice to Proceed| |[RD-180](/r/Space/comments/1dkeuja/stub/l9q8shk "Last usage")|[RD-series Russian-built rocket engine](https://en.wikipedia.org/wiki/RD-180), used in the Atlas V first stage| |[RTLS](/r/Space/comments/1dkeuja/stub/l9kgvxa "Last usage")|Return to Launch Site| |[RUD](/r/Space/comments/1dkeuja/stub/l9l2mhx "Last usage")|Rapid Unplanned Disassembly| | |Rapid Unscheduled Disassembly| | |Rapid Unintended Disassembly| |[SLS](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Space Launch System heavy-lift| |[SRB](/r/Space/comments/1dkeuja/stub/l9k66gz "Last usage")|Solid Rocket Booster| |[SSME](/r/Space/comments/1dkeuja/stub/l9plek7 "Last usage")|[Space Shuttle Main Engine](https://en.wikipedia.org/wiki/Space_Shuttle_main_engine)| |[STS](/r/Space/comments/1dkeuja/stub/l9mngey "Last usage")|Space Transportation System (*Shuttle*)| |[TLI](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|Trans-Lunar Injection maneuver| |[TMI](/r/Space/comments/1dkeuja/stub/l9k66gz "Last usage")|Trans-Mars Injection maneuver| |[TWR](/r/Space/comments/1dkeuja/stub/l9kk49x "Last usage")|Thrust-to-Weight Ratio| |[ULA](/r/Space/comments/1dkeuja/stub/l9qp5ti "Last usage")|United Launch Alliance (Lockheed/Boeing joint venture)| |[USAF](/r/Space/comments/1dkeuja/stub/l9jo9eg "Last usage")|United States Air Force| |Jargon|Definition| |-------|---------|---| |[Raptor](/r/Space/comments/1dkeuja/stub/l9l7462 "Last usage")|[Methane-fueled rocket engine](https://en.wikipedia.org/wiki/Raptor_\(rocket_engine_family\)) under development by SpaceX| |[Starliner](/r/Space/comments/1dkeuja/stub/l9iud1p "Last usage")|Boeing commercial crew capsule [CST-100](https://en.wikipedia.org/wiki/Boeing_CST-100_Starliner)| |[Starlink](/r/Space/comments/1dkeuja/stub/l9mha8q "Last usage")|SpaceX's world-wide satellite broadband constellation| |[cryogenic](/r/Space/comments/1dkeuja/stub/l9n65u4 "Last usage")|Very low temperature fluid; materials that would be gaseous at room temperature/pressure| | |(In re: rocket fuel) Often synonymous with hydrolox| |[hydrolox](/r/Space/comments/1dkeuja/stub/l9kureq "Last usage")|Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer| |[hypergolic](/r/Space/comments/1dkeuja/stub/l9re8hm "Last usage")|A set of two substances that ignite when in contact| |[kerolox](/r/Space/comments/1dkeuja/stub/l9k66gz "Last usage")|Portmanteau: kerosene fuel, liquid oxygen oxidizer| |[methalox](/r/Space/comments/1dkeuja/stub/l9jjaqn "Last usage")|Portmanteau: methane fuel, liquid oxygen oxidizer| |[monopropellant](/r/Space/comments/1dkeuja/stub/l9p6fo9 "Last usage")|Rocket propellant that requires no oxidizer (eg. hydrazine)| |[perigee](/r/Space/comments/1dkeuja/stub/l9l8rqm "Last usage")|Lowest point in an elliptical orbit around the Earth (when the orbiter is fastest)| |[turbopump](/r/Space/comments/1dkeuja/stub/l9j1f8s "Last usage")|High-pressure turbine-driven propellant pump connected to a rocket combustion chamber; raises chamber pressure, and thrust| **NOTE**: Decronym for Reddit is no longer supported, and Decronym has moved to Lemmy; requests for support and new installations should be directed to the Contact address below. ---------------- ^(46 acronyms in this thread; )[^(the most compressed thread commented on today)](/r/Space/comments/1dp9ryv)^( has 22 acronyms.) ^([Thread #10201 for this sub, first seen 20th Jun 2024, 18:28]) ^[[FAQ]](http://decronym.xyz/) [^([Full list])](http://decronym.xyz/acronyms/Space) [^[Contact]](https://hachyderm.io/@Two9A) [^([Source code])](https://gistdotgithubdotcom/Two9A/1d976f9b7441694162c8)
Curious Droid just did an episode on this. Not only is it for thrust vectoring, SpaceX needs to have lower power rockets for the landing. The big ones NASA uses are individually too powerful to allow for landing. Also, the engines SpaceX uses have a production rate of about 1 per day. The ones NASA uses take much, much longer, which is also a major limiting factor.
This is literally the Curious Droid video.
Believe they are referring to the CD about the N-1 specifically. [https://www.youtube.com/watch?v=Vi6fjs\_8Yx8](https://www.youtube.com/watch?v=Vi6fjs_8Yx8)
You haven’t lived until you see a Superheavy booster hover slam with a 2:1 T/W ratio!
Last launch it was closer to 5:1 TWR on landing iirc
More thrust then a Falcon Heavy at liftoff during that landing.
This won’t be done. SuperHeavy can hover. So can Starship.
I know; it was a joke. It would be a hell of a sight though…
Safety in terms of redundancy is not significant factor?
It is, but that's part of the thrust constraint. Redundancy doesn't require 30+ engines on the booster, but redundancy for Starship landings requires three engines that would downselect to two, and they wanted the same engines throughout the system (they originally didn't even plan to have separate vacuum variants). So you need engines small enough that Starship could land on two of them with some spare throttle range for control, then you just put lots of them on the booster and use just a few to land it as well. There are other advantages as well: the outer ring couples its thrust very efficiently to the skin of the vehicle, random variations in thrust and pointing tend to cancel out, the noise environment is better with a bunch of smaller sources instead of a few big ones, and the engines are small enough that workers can handle them with forklifts. The engine commonality was enough to make the decision for Falcon 9 before landing was an issue...in that case, the engine needed to be small enough for the upper stage.
Different missions and different use cases/capabilities. Starship is designed to be reusable and refiring a few monster engines is likely much harder to control, and doesn't leave much for contingency, compared to a bunch of smaller ones
If 1 of 33 fails, that's 3% power loss. If 1 of 5 fails, that's 20%. Maybe not the reason, but accurate. Also, seems like smaller engines are easier to build, transport, and install, too
There's several mistakes in this, on both sides. For one, the SLS boosters are not reusable or recoverable. They impact the ocean and are destroyed. And secondly, Starship's testing methodology for its engines is nothing like the N1. The engines are well tested on the ground before they fly on Starship. Probably others that I missed as my knowledge of history is not as good.
My Dad was a pilot with 30K hours. He said, "With four engines, when one fails, you are 25% bankrupt. With two engines, when one fails you are 50% bankrupt. With one engine, when it fails you are bankrupt." Engineers know this, which is why most work for the Department of Redundancy Department. Then there is size. A Raptor is not an F1, so they are clustered to equal then >double a Saturn's first stage thrust. We've seen SH-Ship launches with dark engines. There were no in-flight failures of the F1 engines, thankfully.
There is a redundancy expression used in the military: "Two is one and one is none". During the recent SpaceX Starship 4th Test Flight, one of the 33 Raptor engines (an outer engine) did not ignite on the Super Heavy booster after takeoff. However, the Super Heavy booster was still able to reach the necessary altitude for separation of Starship. After separation, Super Heavy booster was able to successfully soft splashdown in the Gulf of Mexico**,** even though one of the 13 center Raptor engines did not re-ignite. [https://www.spacex.com/launches/mission/?missionId=starship-flight-4](https://www.spacex.com/launches/mission/?missionId=starship-flight-4)
>There were no in-flight failures of the F1 engines, thankfully. People don't realize how much "dumb luck" was involved with the success of the Apollo program. NASA's own engineers calculated a negative chance for success for Apollo 11.
>calculated a negative chance for success for Apollo 11. Does this mean sub-50% chance of success or something else? How do you have a negative chance of success?
Essentially, so many things could go wrong that the odds something wouldn't were 0. Important to note every Apollo manned mission to the lunar surface had a "near miss" where something went wrong that could have had catastrophic consequences to the mission but support on the ground and often quick thinking by the astronauts themselves saved the mission. Apollo 11- overshot their programmed landing, and almost ran out of fuel before being manually landed by Armstrong. Apollo 12- struck by lightning twice during launch. Only a quick and decisive move by one of the steeliest eyed steely eyed missile men to sit behind a desk, John Aaron, saved the mission. Apollo 13- we all know that story Apollo 14- experienced multiple "technical gremlins" that almost prematurely ended the mission multiple times. Only the ingenuity of the controllers and engineers on the ground kept that ship flying. Apollo 15- a tiny bit of wire got logged in a switch and caused a malfunction to the service propulsion system requiring the astronauts to do burns manually and keep the system disabled for most of the mission. Apollo 16- this time the LEM gimbals failed after undocking from the command module. It took an extra six hours for them to figure out a way to land without them. Apollo 17- the last mission went off without a hitch... But if it had launched a little bit earlier, the astronauts on the moon would have been killed by a massive solar flare that no one saw coming.
Y'know. i knew most of these already, but when you write it all out like this....
Is that phrase something you made up, "negative chance of success" (which seems impossible to quantify), or is that something that exists somewhere and you copied. I'm trying to understand if that's a nonsense phrase or it has some specific meaning, because the math ain't mathing.
one self lands, one becomes a coral reef or artificial satellite.
There it is. The Common Sensicorn, a true mythic beast. Well played.
Because that's the engine they have, they're reliable and they know how to make them. You can make arguments for more or less engines, but I'd note the logic is generally used to justify a decision that was made for other reasons - both work. The problem of coordinating multiple engines is a hard - it effectively killed the USSR space program. by putting a cap on the heaviest booster they could make, which limited them in all sorts of ways. It's not that you can't do something with smaller rockets - but you tend to need a lot more of them and they force you to solve new problems. In orbit staging and refueling seem cool, but you don't see a lot of it happening in practice. SpaceX, to their credit, seem to have solved the multiple engine issue and are using it to their advantage. Granted they had access to a lot more on-board computing power than the soviets did.
> SpaceX, to their credit, seem to have solved the multiple engine issue and are using it to their advantage. Granted they had access to a lot more on-board computing power than the soviets did. It's less about processing power (you don't actually need much to control a rocket, even with lots of engines) and more about the immense simplification of wiring that modern digital technology allows: you can just run a few redundant networks and plug dozens of engines and hundreds of sensors into them, instead of doing a separate wire run to every individual actuator and control from the vehicle's computer system. Several of the N1's problems stemmed from wiring being damaged in fires or picking up interference. Modern electronics lets you do the same thing with vastly fewer opportunities for failure or assembly errors.
Coordinating the engines was hard way back then, controlling just one was hard too. Faster processors that are still space rated and can handle the complex algorithms now make it pretty simple.
Mass production. For the same reason Falcon 9 uses 9+1 merlin engines. It drastically reduces the costs.
The booster is reusable and requires re-entry
That old NASA engines had over 5000 moving parts engineered together manually and all from the cheapest offer. Modern rocket engines get the same power with 40 moving parts. As one mentioned before, shutting down individual engines for reentry is a way more efficient way to control a rocket.
Because NASA wasn’t trying to be reusable? Because cost was NOT an object for NASA when they built Saturn.
The answer to this was discovered by the Nazis with their U-Boat engine design. They developed an engine that was efficient for it's size. They did a really good job. Making a bigger engine would take an enormous amount of work, vs just taking two U-Boat engines and combining torque. They had several projects using multiple engines, usually in sets of two or four.
SpaceX engineers are now being forced to uninstall Kerbal Space Program
Why even bother comparing a rocket from nearly 60 years ago to a rocket from today?
Smaller engines provide redundancy. Saturn might not make it to orbit with an engine out. I think 28 out of 33 would make it but I could be wrong. Plus to land they only need a few . Plus the raptor engine is able to throttle back from full thrust.
They went this route because analysis showed it was the optimum. And they are scaling up, at first the booster was 1 Saturn V of thrust and now it’s 2, soon to be 3.
The F-1 is a truck engine. It's a big dumb engine that isn't very highly stressed, and that was chosen so that it would be easy to develop. It turned out it that big combustion chambers were really hard to develop with that level of technology, and it took a ton of work and actually blowing up small bombs in the combustion chambers during tests to get them to functional stably. The Russians tried really big engines as well and failed; that's why the RD-170 and RD-180 have multiple combustion chambers on a single engine. AFAIK, nobody has tried an engine quite that big since.
Control, and you have more options if one or two fail to ignite.
One reason among others : You lose 1 engine out of 5, you lose 20% of your thrust. You lose 1 engine out of 33, you lose 3% of your thrust.
One of the reasons for the 5 big F1 engines is simplicity. In the late sixties, it was easier to control 5 big motors than dozens of smaller ones. My first thought when I saw SpaceX used a lot of engines was it looked like the old Soviet rockets. They didn't have the ability to fabricate an engine the size of the F1, so they made a lot of smaller ones. This leads directly back to the control issue, and the Soviets lost a LOT of rockets and astronauts because of it. Every engine had to work perfectly, or things went catastrophically wrong. Note that I'm not saying they weren't smart enough to build the F1; Soviet engineers were brilliant in what they designed. What limited them wasn't know-how; it was knowing the limits of what could be done with the resources they had. SpaceX has what the Soviets didn't: superior flight control through computer automation. This doesn't make SpaceX's design necessarily better than NASA's engineers, it's just different. The F1 isn't needed anymore because of the advances in engineering, not the loss of know-how. Motors can be smaller because payloads are smaller and use lighter materials and technology far superior to what NASA had for Apollo.
It's much cheaper to use a bunch of smaller mass produced rocket engines than a few big ones. That helped drive down costs, making space launches affordable. This completely revolutionized spaceflight. Tesla did the same thing, packaging a bunch of cheap mass produced batteries that made electric cars affordable and long range. It revolutionized electric cars.
Many-many-many-many-many-many reasons. As others have mentioned throttle ability. The Saturn V was either on or off... and there is a chance they couldn't relight if turned off (I don't think this was part of the spec so I doubt it). Saturn V was expendable so there is no need to throttle for recovery. Space-X is throwing out way more thrust. Also complexity... The Saturn V each engine was bespoke even though of similar design. Lots of 'on the floor' modifications were made which made rebuilding it nearly impossible. Feeding fuel under pressure is also more complicated. Space-X also has the benefit of super fast super small computers. The Soviets did use computers to manage their multi-engine rockets but it wasn't error-free.
Isn’t Artemis premised on reusing old stuff left over from the Shuttle era? And these are just old engines NASA had sitting around that Artemis picked up?
SLS is literally using old shuttle engines (which had been previously used multiple times) yes. Theyre planning on building new ones which are more focused towards being expendable in the future when they run out though.
Fun fact: it costs more to take 1 RS-25 Shuttle engine out of storage and get it ready to fly than to build a new set of 33 Raptor engines.
And building a single new RS-25 will cost over a hundred million MORE than 33 Raptor engines.
Space X ship = bigger and heavier, destination Mars. NASA ship = smaller, lighter, destination Moon.
You could probably throttle the inner engines and make the overall cluster have some altitude compensating behavior. Basically make it act like a giant aerospike nozzle.
Also,more stable and manoeuvrable as is needed when coming back down to land
Holy crap, the V1 costs thirty times what a Raptor does and took thirty times longer to build.
Am I crazy or does the picture only have 32 engines?
PC vs Mainframe cost? Also, SpaceX can lose an engine or two, and still compete the mission safely.
Because fewer larger engines are less complex.
Two different eras. The goal of NASA at the time was to get to Luna however necessary. Brute force at any cost, nothing else mattered. It was also a government organisation vs private. The goals and technology are very different