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In response to
"4 minutes til deorbit sequence starts for Dragon -- (link)"
by
prayformojo
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I had to go look up previous spacecraft as the deorbit burn time of 11 minutes seemed really long to me -- (edited)
Posted by
JD (aka Jason Dean)
Aug 2 '20, 11:16
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Turns out it is. Previious US spacecraft have used burn times of under a minute to 4-5 minutes
Which is kind of a cool demonstration of total force applied. Previous craft had dedicated retro systems which applied a relatively large amount of thrust in a short amount of time.
The Dragon capsules are using the same Draco thrusters that are used for manuevering as well as the deorbit burn. They're relatively small in thrust so they fire for a longer time to achieve the same change in velocity.
It's also a design consideration that went into Crew Dragon that previous US capsule spacecraft didn't use, didn't have to think about
If you're only going to use it once as well as you were designing as fast as you could, it makes all the sense to have dedicated systems. Separate maneuvering vs retro rockets. Also could be an evolution of engine technology as Mercury and Gemini used solid rockets which makes sense to me as no pumps, fuel tanks etc
But Crew Dragon, if one can use the same Draco thrusters for multiple purposes then why not? Economies of scale in building them and all that. As well should make for easier refurbishment.
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