SpaceX Further Improves the Raptor 3 Engine

35 thoughts on “SpaceX Further Improves the Raptor 3 Engine”

1. Look at the increase in thrust and thrust weight with increased chamber pressure. It’s really a big increase. More than I would have thought. So I look at the 400 bar and then thought,”don’t hydraulic lines routinely go higher?”. So I looked that up and found “…The accepted international standard for maximum working pressure in the high-pressure hydraulic tools industry is 700 Bar (10,000 PSI). …”

   https://www.allphasehydraulics.com/what-is-maximum-hydraulic-pressure-and-why-is-it-important/

   So this pressure is for everyday stuff that has to handle a lot of stress for a good while and be safe. Now I know it’s not at the high end temperature they are using, nor is it subjected to the low end temps, but it does, as a rough guide, tell you they have a good bit of leeway for safety.

   The power they are getting from this is frightening and wondrous.

2. Musk is really on the cheap side!

   Zinc coated clamping screw to fix the engine on a filthy pallet.

3. Would it be too much to ask for the successful orbiting BEFORE changing everything?

   • Starship will reach orbit. It may not be this next launch but one of the next three launches but it will happen.

4. Great article. It’s amazing how quickly they’ve come along. Tremendous engineering@

5. *tonnes. Tons are imperial units, 9000 tons = 180 million pounds. 9000 tonnes = 19.8 million pounds.

   • 9000 tons are 18 million lbs; 9000 tonnes is heavier, 1 kilo = 2.2 lbs.

6. So how does it work? More thrust means you can reduce the number of rocket engines, save weight and still get to orbit, thus allowing more payload? Because the tanks can only hold the amount of fuel that is in them now, so you cannot increase the impulse.
   In that case, they would have to plan a reduction of the number of engines, right? But so far, I nobody is speculating about a reduction of engines. Am I missing something?

   • Higher acceleration, especially while the rocket is full and heavy, means less fuel is burned counteracting gravity.

   • More thrust per engine means increased efficiency and a better thrust/weight ratio. This will improve the specific impulse, which essentially means it will more effectly get to its target altitude with less fuel. So you get increased payload per pound of fuel consumed. And yes, with the increased thrust they could reduce the number of rocket engines, but that wouldn’t be practical or efficient. It’s better use of fuel to burn it off quicker and put as much thrust out as the vehicle can take, because as propellant burns the vehicle loses mass, thus increasing efficiency further. So in reality all these upgrades, in simple terms, just means a larger payload to orbit capability; which is the end goal anyhow.

     • You’ve misaligned the dependencies, I think.

       More thrust per engine does NOT improve ISP, the specific thrust figure-of-merit, necessarily. ISP depends almost completely on the accelerated exhaust velocity, at the edge of the rocket motor nacile. Basically, rocket exhaust only thrusts a rocket ‘forward’ if it interacts mechanically with the rocket motor’s chamber and exhaust housing. https:\\en.wikipedia.org\wiki\Rocket_engine_nozzle (repl \ with slash)

       ON THE OTHER HAND, you did get other parts right.

       • Increased payload per kg of fuel used, since the rocket motor mass is less per unit thrust. Yep.

       • Reduced number of rocket engines — certainly possible, though maybe not desired or optimal: perhaps the substantially improved thrust will be marketed into delivering greater payload mass to orbit. Or to higher orbit. Etc.

       The idea of ‘burning off quicker’ is especially good when doing so is also moderateable … which is to say, when thrust can be throttled downrange, to limit the absolute G-load of the payload and rocket housing itself.

       Anyway … just unwanted comment from The GoatGuy

       ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
       ⋅-=≡ GoatGuy ✓ ≡=-⋅

       • Now, I like the idea of wet workshops.

         Instead of covering a whole Starship with TPS, what about having a second stage atop SuperHeavy have a large LOX tank and maybe a denser fuel like kerosene in a tank directly attached to an engine block.

         The front of the LOX tank behind the payload and the aft of the tank have androgynous docking ports.

         Just the engine block with kerosene fuel tank returns.

   • You are missing that more thrust allows less gravitational loss, so even with the same amount of engines, more thrust will allow a larger payload by allowing a larger acceleration. This is what the second picture is getting at.

   • They want to maximize payload to orbit, so more engines, plus higher thrust per engine, and stretched tanks if needed. When fully reusable, the main cost adder per flight is just the added fuel/ox.

   • I think the main benefit here is reusability. I figure if the desired rocket performance is now more further away from its peak, it will be less strained. Maybe it’s more like driving between 2-3×1000 RPM now than 4-5… I know nothing about rockets.

7. Another future SpaceX payload. If nothing else, it will mean more money for SpaceX:

   “A controversial new type of electric propulsion system that physicists say defies Newton’s Laws of Motion, known as the Quantum Drive, has secured a spot on a SpaceX rocket and will launch into low Earth orbit (LEO) this October.”

   See:

   https://thedebrief.org/impossible-quantum-drive-that-defies-known-laws-of-physics-scheduled-for-do-or-die-october-space-flight/

   • SpaceX will happily take money from idiots as well.

     • Even if it works, (Like hell it will…) it wouldn’t be competition for them. Not remotely enough thrust to get off earth, it would only be useful for orbital transfers, not taking off from or landing on a planet.

   • There is no free lunch in Physics. Not at any scale, at all.

     Without nuclear energy (the notable “sort-of-exception” to the free lunch deal), all other processes are bound by the conventional (including both quantum and relativistic) Laws of Physics.

     And to that, nuclear energy (which seems nearly magical in extracting energy from otherwise inert elements!) actualy still conserves energy balance through exchanging bound nucleon mass (energy) for energetic fission or fusion daughter energies. E = mc² … ΔE = Δmc² … and all that.

     Anyway, we can count on Physics not to deceive us mathematically.

     ⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
     ⋅-=≡ GoatGuy ✓ ≡=-⋅

8. Hi Brian, could you put the source for the pics, it looks like some are from Everyday astronaut’s YouTube channel.
   Good article btw. 🙂

9. Musk said that earlier Starships alone could achieve SSTO, but with nearly zero payload. This makes it doable, but worthless. Not sure if this comment was for reusable or expendable variants (if reusable, that means some payload could be possible for an expendable model, by having the payload match the mass savings in fuel, heat tiles, and flaps. I doubt better Raptors would change much. Ultimately the ‘winners’ will have the lowest cost to orbit per kg, and this means one stage rockets will never compete with two stage, except for niche payloads
   where cost is not a concern.

   • I wonder if a custom made SS made of titanium instead of stainless steel -20 tons lighter?- may be an useful SSTO. A SS for military?

     • Stainless steel is an excellent choice for developing the Starship, once the design stabilizes they *might* find it worthwhile to switch materials. SS has decent properties for rocketry, and is easy to work with, but it’s not necessarily the best material for mass production of an established rocket design, when the rocket is reusable. Spending extra money and trouble to get a slightly better mass ratio starts to make sense.

       They started out trying 301 stainless, which on paper looked good, but has a difficult learning curve and issues with halogen induced delayed stress cracking. (A big deal when you’re welding it in a sea breeze!) Then they moved to 304 stainless, which is easier to work with, and doesn’t have the delayed stress cracking issue. At this point they’re using their own proprietary SS alloy, IIRC. They’ll stick with that until the design stops changing, then they might try something else. Or maybe prefer investing the money in further engineering, instead.

       However, with reusable boosters that return to the launch point, and have quick turn around, most of the point of SSTO goes away. It’s only brought up to point out how high the performance of the rocket is.

     • That would be quite a bit of Titanium and would cost quite a bit. They would probably go with Aluminum first.

       But the default choice is to go with what is easy and cheap and reliable which is some variant on steel. There are plenty of other optimizations in other places (for example this article on Rapty 3 vs Raptor 1).

       • No, Titanium is very expensive, and not good for very high temperatures like SS is. They don’t want tiles on the entire Starship, and they chose SS (currently SS304L I think) to handle the high (but not extreme) temperatures it will encounter returning from orbit or landing on Mars. Theoretically though, the Booster could be made out of Aluminum.

         • I think that Al is the best bet for an alternate material for both booster and Starship. Musk likes low cost because he wants to mass manufacture these.

           That being said I strongly suspect that they will optimize mass to LEO via other mechanisms. Hot staging, Raptor 3 do more than swapping your structural metal and dealing with all the headaches that come from replacing a working design with a slightly better optimized design.

         • Titanium is expensive, yes, but not so expensive that it wouldn’t be worth it if it increased their payload by 10%. And it’s not that bad at high temperatures, if it were, they wouldn’t have used it for the SR-71, or originally meant to build the Space Shuttle out of it. It’s no Inconel, but the right alloy will get you up to temperatures where aluminum turns to mush.

           I also have it on good authority that it welds like a dream once you know how to do it.

           But as I said above, there’s no point in their exploring more expensive but potentially lighter materials until the design has stabilized.

       • Aluminium wouldn’t work, because part of the mass savings is letting the steel skin of the Starship reach temperatures which would compromise the structural integrity of an aluminium rocket.

     • One big issue is that the SS chosen gets even stronger at cryogenic temperatures and does not transition to a brittle phase. Not sure of Ti properties at these temperatures. Welding Ti would be a nightmare at this scale.

       SpaceX is working on their own SS alloy, dubbed SS30x, but we have not heard much about that. They may also try to go thinner (4mm to 3.5mm or 3.0mm) to save weight if their safety margins allow that. A stronger SS alloy would make this easier.

       • Depends on the alloy, some have good cryogenic properties, some get brittle.

         It does have to be inert gas welded, though. Otherwise it catches fire, and take it from me, you do NOT want to have to try putting out a titanium fire. Had the swarf catch fire from a spark while turning some on a lathe once, and hoo, boy.

         It’s not as bad as magnesium for catching, though, you can cut the sheet with a plasma cutter safely enough if you’re quick about it. A lot easier than sawing, it work hardens something fierce.

10. Beware the VelociRaptor engine upgrade ! Smaller and more powerful. BO’s BE-4 is
    already obsolete due to its size and cost.

11. So doesn’t this make the Starship by itself an SSTO with the possibility to safe land?

    • Not necessarily. Without an increase in Isp the total theoretical delta-V is the same. Higher thrust and velocities means less gravity drag, but also higher atmospheric drag. So it’s a complicated balancing act to find the change in actual delta-V, especially without the launch profile being public.

      • Higher thrust for the same weight engine implies a better mass ratio for the rocket, even with an unchanged ISP, because less of the rocket can be rocket engine. It also implies a better capacity to deal with a lost engine, because you have more ability to throttle up the good engines. And your booster can carry more fuel with the same number of engines, give the 2nd stage more boost before separation.

        So, even if they kept exactly the same acceleration profile, it’s all gain.

        • Now that is common sense American engineering ingenuity

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