Author Topic: Should SpaceX aim for a 330,000 lbs engine rather than am F1 class engine?  (Read 53339 times)

Offline spectre9

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I think SpaceX is more likely to build something like Briz-M than Centaur.

Super Draco hypergolic stage?

Why even bother with new engines?

Offline Jim

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I think SpaceX is more likely to build something like Briz-M than Centaur.


Huh?  There is no data to suppose that and actually data that says the opposite.

Offline hkultala

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Propulsive landing is not necessary for re-usability. Honestly, I think grasshopper is a pipe dream. Doing everything with engine thrust simply uses too much propellant and too risky in the sense that an engine failure will result in a 30~80 ton object partially fueled with RP-1/LOX crashing down on the launch site.


How does this differ to landing aeroplanes?

That they still maintain some manouverability even without engines?

And it's not doing _everything_ with engine thrust. Atmospheric drag helps a lot also.

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In the end, I believe that if they achieve 1st stage re-usability, they use engine thrust to reduce the re-entry velocity to about Mach 4~5 from about Mach 9~10 only. As long as the stage survives re-entry and slows down to sub-sonic speeds via atmospheric drag, they'll use parachute(s) to slow it down sufficiently for a water landing -- like they originally intended to do. In this model, the engine does not need to be on the centerline. It just has to be gimballed so the thrust goes through the CG (very much like SSMEs). Besides, there is no reason to fire just one engine they can fire two or all four.

Elon wants "rapid reusability". That means not needing to spend lots of time and money to recover and fix/refurbish boosters that have been on salty sea water.

And in other to do propulsive landing, capability to thrust down to T/W of 1 is needed.

Offline FOXP2

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Propulsive landing is not necessary for re-usability. Honestly, I think grasshopper is a pipe dream. Doing everything with engine thrust simply uses too much propellant and too risky in the sense that an engine failure will result in a 30~80 ton object partially fueled with RP-1/LOX crashing down on the launch site.


How does this differ to landing aeroplanes?

That they still maintain some manouverability even without engines?

And it's not doing _everything_ with engine thrust. Atmospheric drag helps a lot also.

Well do wings weigh more than propellent? Also we might give points to propulsive landing for not needing a runway.


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Elon wants "rapid reusability". That means not needing to spend lots of time and money to recover and fix/refurbish boosters that have been on salty sea water.

I have to disagree with his strategy then, parachute landing would be a technologically safer avenue, making the falcon 9 partially reusable even if you have to spend weeks refurbishing would save money for the development of a more radical propulsive landing system later.   


Offline douglas100

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There's another thread for discussing re-usability.
Douglas Clark

Offline Karloss12

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I consider this a disadvantage. 4 engines would mean
* Reusable version could not land with one engine, as the T/W would be too big, and the engine alignment would also be problematic for this
* It would have worse engine-out capability than falcon 9.

(3) Having 4 engine also gives nearly as good a level of practical engine out capability as having nine.

Any basis for this claim?

Propulsive landing is not necessary for re-usability. Honestly, I think grasshopper is a pipe dream. Doing everything with engine thrust simply uses too much propellant and too risky in the sense that an engine failure will result in a 30~80 ton object partially fueled with RP-1/LOX crashing down on the launch site. In the end, I believe that if they achieve 1st stage re-usability, they use engine thrust to reduce the re-entry velocity to about Mach 4~5 from about Mach 9~10 only. As long as the stage survives re-entry and slows down to sub-sonic speeds via atmospheric drag, they'll use parachute(s) to slow it down sufficiently for a water landing -- like they originally intended to do. In this model, the engine does not need to be on the centerline. It just has to be gimballed so the thrust goes through the CG (very much like SSMEs). Besides, there is no reason to fire just one engine they can fire two or all four.

The thing about engine out capability is that with 4 engines you can lose an engine through about 50~70% of the 1st stage flight envelope depending on how close to the limit the payload happens to be. With 9 engines you can lose an engine through about 60~80% of the flight envelope. It is worse with 4 but not horribly worse. Besides, most engine failures happen either during the initial start and throttling to full thrust, or late in the burn. The former is mitigated by the 2 second hold down, the latter is fine with either 4 or 9 engines.

Elon says "It really comes down to what the staging Mach number would be.  For an expendable Falcon 9 rocket, that is around Mach 10. For a reusable Falcon 9, it is around Mach 6, depending on the mission." and goes on to say "The payload penalty for full and fast reusability versus an expendable version is roughly 40 percent,"

Sounds like an attempt at FH side core recovery to me.  A logical first step to recovering other equipment.

I would expect there would be more then one landing pad and the concrete to fill the crater costs about $500 per cubic metre.

Anyway, if the F9 can be recovered then a 9 x 330,000 core could replace the FH.  It all depends on recovery though.

But I see how your pessimism about SpaceX's current plan to achieve rapid recovery produces your idea.

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