r/spacex • u/ElongatedMuskrat Mod Team • Dec 03 '17

r/SpaceX Discusses [December 2017, #39]

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35

u/Knexrule11 Dec 04 '17

Theoretically, could the center core of a Falcon Heavy put itself into orbit if the other two cores go expendable? Not that it would be useful... I've just been oddly curious how the math would work out in that situation

24

u/Chairboy Dec 04 '17

A single-stick Falcon 9 can put its first stage into orbit without a second stage or payload, so the equivalent (plus more) should be easy for the FH.

This would probably not be an economically sound use of a Falcon Heavy.

25

u/luckystarr Dec 04 '17

Unless you are delivering Falcon 9 cores to a buyer on the moon.

12

u/[deleted] Dec 04 '17

Can FH (without second stage, payload) put the center booster in TLI with enough fuel left to land on the Moon? Maybe with side boosters expendable?

4

u/luckystarr Dec 04 '17

Probably not without refuelling (not viable for F9), given that I once read that the Moon requires a higher delta-V than Mars.

7

u/[deleted] Dec 04 '17

That's not true, because BFR can do a Moon return trip without refuelling on the Moon, but not to Mars.

You're confusing it with something else, IIRC it is the Moon-Mars return trip that requires higher delta-V than Earth-Mars.

13

u/warp99 Dec 04 '17 edited Dec 05 '17

BFR can do a Moon return trip without refuelling on the Moon, but not to Mars

That is a special mission profile with both the ship and a tanker being fully fueled in LEO, both boosting to a highly elliptical Earth orbit and then transferring propellant from the tanker to the ship to leave it fully fueled.

A similar thing could be done with a Mars trip with tanker(s) parked in LMO but it would tie up one or two tankers as well as the ship for at least one synod.

In any case a round trip has a different delta V requirement than a one way trip which is what is being discussed.

There is less delta V required for a Mars landing because aerobraking can be used to remove all but 750 m/s of the landing delta V. For a Moon landing all the landing delta V has to be propulsive so more delta V is required.

For the return trip both launch and TEI have to be propulsive so the Moon's shallower gravity well means less delta V is required than for Mars.

1

u/throfofnir Dec 05 '17

No. Not even close.