4 ms·

What really gets me is that SpaceX's Raptor engines have fuel pump power in that same neighborhood, and there are 33 of them on a Starship.

matrix2003 2y ago
Wikipedia lists it as 37 MW, which does seem to be in the same ballpark (my amateur calculations put an F-16 around 44 MW). Not sure why people are downvoting you, but objectively the Raptor really is a marvel of engineering itself (maybe less than the F-1 that was created with slide rules at the time, but it does seem poised to upend space flight again).
reportingsjr 2y ago
A Raptor engine has about 1/3 to 1/4 of the thrust of an F-1 engine. However, the Raptor is far more efficient and much more impressive technically. They are really a marvel of modern engineering and science.
- JumpCrisscross 2y ago
  > Raptor engine has about 1/3 to 1/4 of the thrust of an F-1 engine Correct for Raptor 2. Raptor 3 is closer to half [1][2]. [1] https://en.m.wikipedia.org/wiki/SpaceX_Raptor https://en.m.wikipedia.org/wiki/SpaceX_Raptor [2] https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
- RoddaWallPro 2y ago
  I have what is probably a dumb question: How can a Raptor turbopump need almost double the HP of a F1 while putting out 1/3 or 1/4th the thrust? (Assuming Elon's 100k HP number was correct, and/or hasn't changed). That just doesn't settle out for me. If it's got double the power, it should be moving double the fuel, so double the power, no?
  - TaylorAlexander 2y ago
    Maybe something to do with pressure. Maybe it is higher chamber pressure and maybe higher pressure even with lower flow rates could require more power.
    - deleted 2y ago
      [deleted]
  - deleted 2y ago
    [deleted]
  - tliltocatl 2y ago
    Raptor has much higher chamber pressure (35 MPa vs 7 MPa of F1) and hence higher Isp (380 vs 304 in vacuum).
    - jcims 2y ago
      35MPa is ~5000psi for anyone wondering lol.
      - tliltocatl 2y ago
        And I took the effort to convert it to metric… Seriously, NASA uses the metric system and so should you.
  - evo 2y ago
    Perhaps it has to do with the relative densities of RP-1 versus methane?
  - dotnet00 2y ago
    Raptor is much smaller, F-1 has a diameter of ~3.7m, Raptor has a diameter of ~1.3m, so it's pumping out 1/4th-1/3rd the thrust in 1/8th the area.
  - _0ffh 2y ago
    Maybe fuel might play a role. The Raptor burns methane, the F-1 refined petroleum. Another possible reason is that the designs may make different efficiency vs power trade-offs.
  - avmich 2y ago
    The formula for Isp - the important measure of efficiency of the rocket engine - says that the speed with which the engine throws away hot gases grows with the difference of pressures - before nozzle and at the exit of the nozzle. The whole idea, by the way, of the full-flow combustion is to extract some more energy from the fuel - before sending that fuel to the chamber, and at the temperature which the turbine of the turbopump can tolerate - so that energy could be used for pumps and more pressure could be created in the chamber. More energy than "more conservative" closed-cycle engines. The pump power is equal to the volume flow (how many cubic meters, or, say, liters of fuel the pump transfers per second) multiplied by the pressure (which pressure is at the exit of the pump). So, it's not the flow - it's the pressure where Raptor has a big advantage over F-1, and that pressure allows to have a better Isp. And of course the better Isp allows to reach bigger characteristic velocity (or just a velocity in a free space, where gravity or atmosphere don't get in the way) using the same amount of fuel. The logic goes roughly like that. Every rocket engine designer wants to reach bigger Isp. For that, using a particular fuel, one need to reach bigger pressure in the chamber, and we move from pressure-fed engines (like the first French orbital rocket, Diamant, which had pressure-fed first stage) to pumps, because high-pressure tanks are too heavy. Pumps initially are open cycle, or gas generator cycle, but we throw away enough gases after the pumps' turbine, so next improvement is we get a closed cycle. With closed cycle we can choose to use all fuel or all oxidizer to move the turbine, but as soon as some component is used fully, we can't get more energy for pumps. Eventually we go to the more complex full-flow cycle, which uses both components and reaches the highest pressure in the chamber. The next step would probably be a detonation engine :) which uses somewhat more efficient process to convert chemical energy into speed, but it's not yet developed enough. We can also talk about more heat-resistant turbines which would allow to extract more energy from the fuel and to increase pressure some more... but there we also have a lot of R&D ahead of us.
- dotnet00 2y ago
  Raptor is also a lot smaller. F-1s were intentionally designed as large and high thrust because it'd have been simpler to build, test and control a handful of F-1s at the time, compared to say, 30 smaller but more efficient engines. The useful metric on this front would be thrust density, where Raptor 1 is a bit under twice that of F-1A, Raptor 2 is a little over twice of F-1A, and Raptor 3 should be ~2.5x of F-1A.
  - capitainenemo 2y ago
    But with more engines they can tolerate a failure or two (or even more) per launch. If a larger engine fails and you only have 3 of them, you're going to have a bad day. And, they do seem to test the heck out of their engines, even with 30 of them on a ship.
    - sbradford26 2y ago
      Yes those benefits can now be realized now with modern controls. Back when the Saturn V was designed the control systems necessary to manage 30 engines didn't really exist. Digital control was in it infancy and was only really implemented with a backup on the whole Apollo stack. Trying to manage that many engines while technically possible with controls of the era (check out the N1) means your control system would be introducing reliability issues instead of adding fault tolerance through redundancy.
      - capitainenemo 2y ago
        Didn't the soviets give it a try? I'd swear they had a large number of engine design way back when also for fault tolerance. Ok, they didn't get it working but I'm pretty sure it wasn't due to lack of digital control... Surely they wouldn'tve even attempted it if it was impossible :) [edit] ah. That was the N1 you referred to. Ok. So you're saying it was possible, but it introduced more failure points.. So is that why it failed...
        dotnet00 2y ago
hereme888 2y ago
[flagged]
- indoordin0saur 2y ago
  There are many brilliant people at SpaceX, not just the one. Your opinion of him (negative or positive) shouldn't affect the very clear assessment that what the SpaceX team has accomplished is amazing.
JumpCrisscross 2y ago
> have fuel pump power It’s slightly wilder. Raptor uses 100,000 hp per engine [1]. That is two F-1 scale turbo pumps per engine, i.e. 66 pumps altogether. All for the dress rehearsal. [1] https://x.com/elonmusk/status/1076618886932353024 https://x.com/elonmusk/status/1076618886932353024
- trhway 2y ago
  The even more impressive here is the power/weight ratio - about 2000hp/kg (whole Buggati engine in 1 kg). (My speculative estimate - the Raptor turbine in the turbopump can hardly weight more than 500 kg as the whole engine is 1600kg -> whole turbopump less than 1000kg -> the driving turbine is half of it max). So anybody who plans to beat Musk/SpaceX (like i do when i finally get a real garage :) has a very high bar to clear. Additional facet is that Raptor turbopump is full flow and thus runs at very low (relative to other gas turbine machinery out there like for example F-16 at 1200C+) temps like 500-600C which means that the power can still be almost doubled with the same regular materials they use - steel and Inconel (and this is what we're seeing - about 1.5X power increase from Raptor 1 to Raptor 3 in a span of mere few years while the engine weight is even decreasing a bit)
  - reddog 2y ago
    But even MORE impressive is the current raptor engines cost between $1m to $2m each with a target cost of $500k when in full production. The F-1 cost an inflation adjusted $85m-$100m each. And the raptors are reusable.
    - matrix2003 2y ago
      Yep! I understand why people don’t like Musk, but SpaceX is doing some truly amazing work.
  - avmich 2y ago
    > (like i do when i finally get a real garage :) Cool :) > Additional facet is that Raptor turbopump is full flow and thus runs at very low You write it further yourself, but rocket turbopump turbines aren't running with cold gas - the hotter the input gas, the more energy can be provided to pumps, so turbine blades have roughly the same requirements as those in F-16. The design on those blades is pretty complex, with materials, processes and substructures like internal cooling channels - all to reach possibly higher temperature to work with.

matrix2003 2y ago

Wikipedia lists it as 37 MW, which does seem to be in the same ballpark (my amateur calculations put an F-16 around 44 MW). Not sure why people are downvoting you, but objectively the Raptor really is a marvel of engineering itself (maybe less than the F-1 that was created with slide rules at the time, but it does seem poised to upend space flight again).

reportingsjr 2y ago

A Raptor engine has about 1/3 to 1/4 of the thrust of an F-1 engine. However, the Raptor is far more efficient and much more impressive technically. They are really a marvel of modern engineering and science.

JumpCrisscross 2y ago
> Raptor engine has about 1/3 to 1/4 of the thrust of an F-1 engine Correct for Raptor 2. Raptor 3 is closer to half [1][2]. [1] https://en.m.wikipedia.org/wiki/SpaceX_Raptor https://en.m.wikipedia.org/wiki/SpaceX_Raptor [2] https://everydayastronaut.com/raptor-engine/ https://everydayastronaut.com/raptor-engine/
RoddaWallPro 2y ago
I have what is probably a dumb question: How can a Raptor turbopump need almost double the HP of a F1 while putting out 1/3 or 1/4th the thrust? (Assuming Elon's 100k HP number was correct, and/or hasn't changed). That just doesn't settle out for me. If it's got double the power, it should be moving double the fuel, so double the power, no?
- TaylorAlexander 2y ago
  Maybe something to do with pressure. Maybe it is higher chamber pressure and maybe higher pressure even with lower flow rates could require more power.
  - deleted 2y ago
    [deleted]
- deleted 2y ago
  [deleted]
- tliltocatl 2y ago
  Raptor has much higher chamber pressure (35 MPa vs 7 MPa of F1) and hence higher Isp (380 vs 304 in vacuum).
  - jcims 2y ago
    35MPa is ~5000psi for anyone wondering lol.
    - tliltocatl 2y ago
      And I took the effort to convert it to metric… Seriously, NASA uses the metric system and so should you.
- evo 2y ago
  Perhaps it has to do with the relative densities of RP-1 versus methane?
- dotnet00 2y ago
  Raptor is much smaller, F-1 has a diameter of ~3.7m, Raptor has a diameter of ~1.3m, so it's pumping out 1/4th-1/3rd the thrust in 1/8th the area.
- _0ffh 2y ago
  Maybe fuel might play a role. The Raptor burns methane, the F-1 refined petroleum. Another possible reason is that the designs may make different efficiency vs power trade-offs.
- avmich 2y ago
  The formula for Isp - the important measure of efficiency of the rocket engine - says that the speed with which the engine throws away hot gases grows with the difference of pressures - before nozzle and at the exit of the nozzle. The whole idea, by the way, of the full-flow combustion is to extract some more energy from the fuel - before sending that fuel to the chamber, and at the temperature which the turbine of the turbopump can tolerate - so that energy could be used for pumps and more pressure could be created in the chamber. More energy than "more conservative" closed-cycle engines. The pump power is equal to the volume flow (how many cubic meters, or, say, liters of fuel the pump transfers per second) multiplied by the pressure (which pressure is at the exit of the pump). So, it's not the flow - it's the pressure where Raptor has a big advantage over F-1, and that pressure allows to have a better Isp. And of course the better Isp allows to reach bigger characteristic velocity (or just a velocity in a free space, where gravity or atmosphere don't get in the way) using the same amount of fuel. The logic goes roughly like that. Every rocket engine designer wants to reach bigger Isp. For that, using a particular fuel, one need to reach bigger pressure in the chamber, and we move from pressure-fed engines (like the first French orbital rocket, Diamant, which had pressure-fed first stage) to pumps, because high-pressure tanks are too heavy. Pumps initially are open cycle, or gas generator cycle, but we throw away enough gases after the pumps' turbine, so next improvement is we get a closed cycle. With closed cycle we can choose to use all fuel or all oxidizer to move the turbine, but as soon as some component is used fully, we can't get more energy for pumps. Eventually we go to the more complex full-flow cycle, which uses both components and reaches the highest pressure in the chamber. The next step would probably be a detonation engine :) which uses somewhat more efficient process to convert chemical energy into speed, but it's not yet developed enough. We can also talk about more heat-resistant turbines which would allow to extract more energy from the fuel and to increase pressure some more... but there we also have a lot of R&D ahead of us.
dotnet00 2y ago
Raptor is also a lot smaller. F-1s were intentionally designed as large and high thrust because it'd have been simpler to build, test and control a handful of F-1s at the time, compared to say, 30 smaller but more efficient engines. The useful metric on this front would be thrust density, where Raptor 1 is a bit under twice that of F-1A, Raptor 2 is a little over twice of F-1A, and Raptor 3 should be ~2.5x of F-1A.
- capitainenemo 2y ago
  But with more engines they can tolerate a failure or two (or even more) per launch. If a larger engine fails and you only have 3 of them, you're going to have a bad day. And, they do seem to test the heck out of their engines, even with 30 of them on a ship.
  - sbradford26 2y ago
    Yes those benefits can now be realized now with modern controls. Back when the Saturn V was designed the control systems necessary to manage 30 engines didn't really exist. Digital control was in it infancy and was only really implemented with a backup on the whole Apollo stack. Trying to manage that many engines while technically possible with controls of the era (check out the N1) means your control system would be introducing reliability issues instead of adding fault tolerance through redundancy.
    - capitainenemo 2y ago
      Didn't the soviets give it a try? I'd swear they had a large number of engine design way back when also for fault tolerance. Ok, they didn't get it working but I'm pretty sure it wasn't due to lack of digital control... Surely they wouldn'tve even attempted it if it was impossible :) [edit] ah. That was the N1 you referred to. Ok. So you're saying it was possible, but it introduced more failure points.. So is that why it failed...
      - dotnet00 2y ago

hereme888 2y ago

[flagged]

indoordin0saur 2y ago
There are many brilliant people at SpaceX, not just the one. Your opinion of him (negative or positive) shouldn't affect the very clear assessment that what the SpaceX team has accomplished is amazing.

JumpCrisscross 2y ago

> have fuel pump power It’s slightly wilder. Raptor uses 100,000 hp per engine [1]. That is two F-1 scale turbo pumps per engine, i.e. 66 pumps altogether. All for the dress rehearsal. [1] https://x.com/elonmusk/status/1076618886932353024 https://x.com/elonmusk/status/1076618886932353024

trhway 2y ago
The even more impressive here is the power/weight ratio - about 2000hp/kg (whole Buggati engine in 1 kg). (My speculative estimate - the Raptor turbine in the turbopump can hardly weight more than 500 kg as the whole engine is 1600kg -> whole turbopump less than 1000kg -> the driving turbine is half of it max). So anybody who plans to beat Musk/SpaceX (like i do when i finally get a real garage :) has a very high bar to clear. Additional facet is that Raptor turbopump is full flow and thus runs at very low (relative to other gas turbine machinery out there like for example F-16 at 1200C+) temps like 500-600C which means that the power can still be almost doubled with the same regular materials they use - steel and Inconel (and this is what we're seeing - about 1.5X power increase from Raptor 1 to Raptor 3 in a span of mere few years while the engine weight is even decreasing a bit)
- reddog 2y ago
  But even MORE impressive is the current raptor engines cost between $1m to $2m each with a target cost of $500k when in full production. The F-1 cost an inflation adjusted $85m-$100m each. And the raptors are reusable.
  - matrix2003 2y ago
    Yep! I understand why people don’t like Musk, but SpaceX is doing some truly amazing work.
- avmich 2y ago
  > (like i do when i finally get a real garage :) Cool :) > Additional facet is that Raptor turbopump is full flow and thus runs at very low You write it further yourself, but rocket turbopump turbines aren't running with cold gas - the hotter the input gas, the more energy can be provided to pumps, so turbine blades have roughly the same requirements as those in F-16. The design on those blades is pretty complex, with materials, processes and substructures like internal cooling channels - all to reach possibly higher temperature to work with.