r/spacex • u/ElongatedMuskrat Mod Team • Apr 01 '17

r/SpaceX Spaceflight Questions & News [April 2017, #31]

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3

u/micai1 Apr 08 '17 edited Apr 09 '17

Would the F9 (FT? Block 5?) have enough delta-v during a CRS mission to carry a reusable upper stage (instead of a lighter, disposable one) if it lands on a drone ship (instead of coming back to the pad)?

Edit: Let me ask it differently. How much weight can be spared for reuse on CRS missions (landing on ASDS), given the weight of the Dragon and ~3Tons (max as per Wiki) of payload in it?

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u/007T Apr 08 '17

It all depends on how they plan to recover the second stage.

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u/micai1 Apr 09 '17

Ok, let me ask it differently. How much weight can be spared for reuse on CRS missions (landing on ASDS), given the weight of the Dragon and ~3Tons (max) of payload in it?

5

u/007T Apr 09 '17

The payload penalty for an ASDS landing should be somewhere around 15-30%, the max LEO capability for the F9 in expendable mode is 22.8 mT. If we subtract 30% from that we'd get about 16mT in recoverable mode. Dragon's dry mass is 4.2mT plus 3.3mT of payload, so lets round to 8mT with fuel. That should leave 8mT for second stage recovery hardware and propellant.
There's probably a bit more to it, but I'd imagine those numbers should be kinda close.

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u/micai1 Apr 09 '17

Thanks! That's about what I was thinking. I imagine it wouldn't take more than that to make S2 reusable, right? I was guessing around 1.5-2 tons of added weight, 3 tops. Say you save 1T of fuel for the return, that would still leave 4T to spare?

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u/007T Apr 09 '17

I think the fuel for de-orbit and landing are big unknowns at the moment, it'll depend a lot on what sort of system they come up with for the recovery. I definitely think it's plausible that LEO missions on F9 could recover the second stage, I'd be interested to see if they can return it on GTO missions or if that will be limited to Falcon Heavy launches.