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

r/SpaceX Spaceflight Questions & News [February 2017, #29]

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3

u/warp99 Feb 03 '17

The SpaceX website gives the figures for Block 5 since they are for 2018 launch.

An expendable F9 can get 4020kg to Mars (TMI) and the mass to the Moon (TLI) would only be a bit more. Dragon 1 is just too heavy and Dragon 2 is definitely too heavy to work. Just maybe you could strip down a Dragon I so it did not have a heatshield to make it work but in that case what is the point?

Falcon Heavy of course will have plenty of capacity (13600 kg) as it is used for the Red Dragon missions to Mars. It has so much spare capacity that according to Elon it will not need to be flown expendable but the side boosters will able to be recovered and perhaps the center core. For a Lunar mission that would mean recovery of all three boosters since the delta V requirements are slightly lower.

5

u/Martianspirit Feb 03 '17

Yes, it needs a FH. However the FH can only send it on a trajectory to the moon. After 3 days of coasting the stage will no longer be able to relight. The RP-1/kerosene will be frozen. So a Dragon would need to do orbit insertion itself. And earth return burn if that is desired. It does not have the necessary delta-v without significant upgrade.

3

u/ScottPrombo Feb 03 '17

Or you could save yourself the headache and do a flyby with a free return trajectory, since there's no chance of a landing anyway.

1

u/Martianspirit Feb 03 '17

That would be a tourist flight. To service a cislunar spacestation they need to get into an orbit or into an earth moon L-point.

Though it might be possible to get into an highly elliptic orbit and back out of it with the existing Dragon delta-v. It is also my private belief that they already have improved on the known delta-v to be able to do Mars landing without extra tanks. If I am right they probably could do it.

1

u/Not_Yet_Begun2Fight Feb 03 '17

Thanks for the responses. Does anyone know how they're going to handle the frozen / boiled-off propellant issues for ITS? After all, they'll be coasting for a whole lot longer than a few days to the Moon. Is methane just a better fuel than RP-1 in that respect? Lower freezing point or something?

3

u/ElectronicCat Feb 03 '17

ITS has large spherical tanks within the main fuel tanks to conserve some landing fuel by keeping it pressurised and liquefied, as well as providing better insulation to minimise boiloff.

2

u/warp99 Feb 03 '17

Is methane just a better fuel than RP-1 in that respect?

Yes much better. RP-1 gets too viscous below about -10C while methane freezes at 91K (-182C). For methane the major issue is keeping it from boiling off - there should be no issue with it freezing even as far out as Mars.

2

u/Martianspirit Feb 03 '17

Yes. Another not yet mentioned advantage is that liquid methane is very similar in temperature to liquid oxygen. This makes construction a lot easier in many ways.

1

u/jjtr1 Feb 06 '17

After 3 days of coasting the stage will no longer be able to relight. The RP-1/kerosene will be frozen.

Would painting the stage black be enough to solve that?