8 ms·

Super cool! I'm still dubious of the benefits of the aerospike but I'm happy to see the pursuit.

rbanffy 5y ago
They'd be most useful in single-stage-to-orbit craft, but, if they can increase efficiency of reusable boosters and orbit-to-ground propulsive landings, that's still great - an aerospike-based Starship wouldn't need both vacuum and sea-level engines and could use the same engines in space as it would use to land.
- gameswithgo 5y ago
  Yeah but saying "This is useful for SSO" is like saying "This is a better way to get to orbit a bad way"
  - rbanffy 5y ago
    SSTO is not great, but when you add full reusability to the mix, it becomes attractive. You spend more in propellant but makes operations so much easier.
- PaulHoule 5y ago
  In principle the SSTO is better for reuse because you can refuel a single vehicle and send it out again, compared to a Starship-class vehicle which has two stages that need to be stacked each time. The trouble is that SSTO is on the margin of the possible and mastering reuse of a 2 stage system is a certain win whereas the SSTO is risky. You have to perfect quite a few technologies such as the aerospike engine, very lightweight tanks and thermal management system and get them to all work together and really be able to reuse them without tearing it down each time like the old STS.
  - rbanffy 5y ago
    For SSTO to be worth for a Starship-Superheavy class vehicle, the aerospike engines would need to be as efficient as the Merlin ones at the same weight and the removal of the Starship engines would need to account for added thermal protection of the lower part. The napkin math seems workable, but rockets require a lot more than napkin math. Having said that, Shuttles were almost SSTOs in the sense that the fuel tank could be placed in orbit (and reused as pressurized habitation space, with some extra work). Maybe some SLS-derived work can add some very large volumes able to dock into a future space station.
    - pbronez 5y ago
      > Shuttles were almost SSTOs in the sense that the fuel tank could be placed in orbit (and reused as pressurized habitation space, with some extra work). That is super cool! I gotta dig into that.. pity they never did that. It would be neat to have an ISS module that was a re-purposed shuttle external fuel tank.
    - PaulHoule 5y ago
      The Shuttle still dropped the two solid rocket boosters. Still it performed better than Tsiolkovsky and everyone else thought a chemical rocket could perform because running rich with extra H2 lets you get a better ISP since it lowers the molecular weight of the exhaust even if it does lower the temperature a little.
      - rbanffy 5y ago
        > The Shuttle still dropped the two solid rocket boosters. Yeah... I kind of cheated. "Almost", but a lot of the kick came from the SRBs.
- Tuna-Fish 5y ago
  > an aerospike-based Starship wouldn't need both vacuum and sea-level engines and could use the same engines in space as it would use to land. In vacuum, an aerospike will not be as efficient as a maximally expanded traditional nozzle. If you could conjure an aerospike raptor from thin air, you'd still probably want the vacuum engines there, but you'd of course want to replace the sea-level ones with the spikes for higher efficiency immediately after stage sep (when all 6 are firing).
  - panick21_ 5y ago
    I agree, but I don't think its worth it. At sea-level you rather have a sea-level optimized engine then a spike as I understand. So you would actually lose landing efficiency, and that is the most important place to save energy. I'm not even sure if Starship will light all 6 engines on separation. Its a question of gravity loses vs lower ISP of sea-level engine. Maybe they turn them on for a initial boost and then turn the center 3 engines off.
  - rbanffy 5y ago
    > immediately after stage sep (when all 6 are firing) And don’t forget the landing. Aerospikes are easier to justify if you are doing a propulsive landing.

They'd be most useful in single-stage-to-orbit craft, but, if they can increase efficiency of reusable boosters and orbit-to-ground propulsive landings, that's still great - an aerospike-based Starship wouldn't need both vacuum and sea-level engines and could use the same engines in space as it would use to land.

gameswithgo 5y ago
Yeah but saying "This is useful for SSO" is like saying "This is a better way to get to orbit a bad way"
- rbanffy 5y ago
  SSTO is not great, but when you add full reusability to the mix, it becomes attractive. You spend more in propellant but makes operations so much easier.
PaulHoule 5y ago
In principle the SSTO is better for reuse because you can refuel a single vehicle and send it out again, compared to a Starship-class vehicle which has two stages that need to be stacked each time. The trouble is that SSTO is on the margin of the possible and mastering reuse of a 2 stage system is a certain win whereas the SSTO is risky. You have to perfect quite a few technologies such as the aerospike engine, very lightweight tanks and thermal management system and get them to all work together and really be able to reuse them without tearing it down each time like the old STS.
- rbanffy 5y ago
  For SSTO to be worth for a Starship-Superheavy class vehicle, the aerospike engines would need to be as efficient as the Merlin ones at the same weight and the removal of the Starship engines would need to account for added thermal protection of the lower part. The napkin math seems workable, but rockets require a lot more than napkin math. Having said that, Shuttles were almost SSTOs in the sense that the fuel tank could be placed in orbit (and reused as pressurized habitation space, with some extra work). Maybe some SLS-derived work can add some very large volumes able to dock into a future space station.
  - pbronez 5y ago
    > Shuttles were almost SSTOs in the sense that the fuel tank could be placed in orbit (and reused as pressurized habitation space, with some extra work). That is super cool! I gotta dig into that.. pity they never did that. It would be neat to have an ISS module that was a re-purposed shuttle external fuel tank.
  - PaulHoule 5y ago
    The Shuttle still dropped the two solid rocket boosters. Still it performed better than Tsiolkovsky and everyone else thought a chemical rocket could perform because running rich with extra H2 lets you get a better ISP since it lowers the molecular weight of the exhaust even if it does lower the temperature a little.
    - rbanffy 5y ago
      > The Shuttle still dropped the two solid rocket boosters. Yeah... I kind of cheated. "Almost", but a lot of the kick came from the SRBs.
Tuna-Fish 5y ago
> an aerospike-based Starship wouldn't need both vacuum and sea-level engines and could use the same engines in space as it would use to land. In vacuum, an aerospike will not be as efficient as a maximally expanded traditional nozzle. If you could conjure an aerospike raptor from thin air, you'd still probably want the vacuum engines there, but you'd of course want to replace the sea-level ones with the spikes for higher efficiency immediately after stage sep (when all 6 are firing).
- panick21_ 5y ago
  I agree, but I don't think its worth it. At sea-level you rather have a sea-level optimized engine then a spike as I understand. So you would actually lose landing efficiency, and that is the most important place to save energy. I'm not even sure if Starship will light all 6 engines on separation. Its a question of gravity loses vs lower ISP of sea-level engine. Maybe they turn them on for a initial boost and then turn the center 3 engines off.
- rbanffy 5y ago
  > immediately after stage sep (when all 6 are firing) And don’t forget the landing. Aerospikes are easier to justify if you are doing a propulsive landing.