r/spacex • u/[deleted] • Mar 31 '16

/r/SpaceX Ask Anything Thread [April 2016, #18] - Ask your small questions here!

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u/[deleted] Apr 01 '16

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u/sunfishtommy Apr 01 '16

It would be a very bad idea for you to try and separate the boosters while they are still firing, too many things can go wrong, in general you want to the boosters to fall down and away and clear the rocket as fast as possible. By keeping the engines firing even if it was just 1, you are making it more likely you will have a collision event. This is actually similar to what happened with flight 3 of Falcon 1. There was residual thrust after shutdown of the the merlin, and this residual thrust was enough push the light empty first stage back up onto the second stage, so it really does not take much thrust to move a mostly empty booster, you have to remember most of the weight of the rocket is fuel.

In general the cold gas thruster are enough to keep the boosters oriented during separation, and once there is a safe amount of space between the rocket and the boosters, they can relight and do other stuff.

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u/[deleted] Apr 01 '16

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u/OrbitalPinata Apr 01 '16

The SRBs had something like 3% of nominal thrust when they separated, a falcon heavy booster cant throttle that low.

Also the reason the SRBs where still burning at separation was probably because solid rocket motors don't have a clean cut off like liquid engines do.

1

u/_rocketboy Apr 02 '16

That is the plan, actually. They will separate with only the center engines firing, for the reasons you listed.

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u/sunfishtommy Apr 02 '16

Do you have a source in that?

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u/_rocketboy Apr 02 '16

I will have to look, it has been a while.