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Author
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Topic: SpaceX Falcon 9 landing vs. shuttle RTLS
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Aeropix
Member Posts: 41
From: Houston
Registered: Apr 2010
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posted 02-21-2017 04:40 AM
   
I was watching the SpaceX Falcon 9 LZ-1 landing and it got me to thinking how is it possible that SpaceX can return the booster to the launch site after orbital insertion of the upper stage, while the space shuttle return to launch site (RTLS) abort profile had to be initiated much earlier in the launch phase? The SpaceX system seems to require much less fuel and is being done routinely, while the shuttle performing the same maneuver seems to have required prodigious amounts of fuel, thereby being limited as an option to the earlier phase of flight. Another thought occurred, that while SpaceX is performing what is basically an RTLS as a matter of routine, it was deemed too risky to ever try as an "operational experiment" on shuttle. I understand that the SpaceX system is not returning the payload to the launch facility (unlike shuttle) so somewhat less fuel is required, but it seems to be a truly minimal amount of fuel to reverse the course of that huge mass and return it to the launch site after delivering the payload to orbit, and I'm curious to discover more detail as to how this can be accomplished where it once seemed difficult if not impossible. |
Jim Behling
Member Posts: 1463
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 02-21-2017 06:44 AM
The return of the Falcon 9 booster isn't "after orbital insertion of the upper stage." It is after jettison of the first stage. It is equivalent of the shuttle SRBs returning to the launch site quote:
Originally posted by Aeropix:
...thereby being limited as an option to the earlier phase of flight.
Actually, it is the opposite. The Falcon 9 can do it because it is early in the flight. The Falcon 9 first stage only burns for 140 seconds or so and then it returns. Shuttle RTLS couldn't start until SRB jettison (120 seconds) and it was a viable until around 240 seconds. The shuttle RTLS pitch around was timed to ensure minimal propellant would remain in the external tank when it was jettisoned after boost back. quote:
...it was deemed too risky to ever try as an "operational experiment" on shuttle.
Because the shuttle was a winged vehicle attached to the side of a tank that was still full of propellant versus just a cylinder with minimal propellant. The dynamics are completely different. quote:
I understand that the SpaceX system is not returning the payload to the launch facility...
It is not just payload. Shuttle orbiter mass is seven to eight times more than the Falcon 9 first stage.The Falcon 9 first stage only burns for 140 seconds, unlike other vehicles, in which the first stage burns for four to six minutes. The Falcon 9 has a second stage that has higher thrust than most other vehicles, so that it can take over earlier. That is why the first stage can return. The proper comparison would be SRBs vs. Falcon 9 first stage and orbiter vs. second stage with payload. Even today with the Falcon 9 "routinely" performing first stage RTLS, it would still be too risky for the shuttle to do it in a non abort scenario. | |
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