Author Topic: Orion to the moon using F9 and F9H  (Read 4840 times)

Offline sevenperforce

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Re: Orion to the moon using F9 and F9H
« Reply #20 on: 03/07/2018 11:47 am »
I doubt those Falcon Heavy on-orbit delivery figures. The official figure is 63,800 kg to orbit - the mass of the stage combined with it's residual propellant should get to be a little more than that; since it would not be pushing against payload gravity losses, still...
It's not a difference in gravity drag (though the enhanced TWR helps), but a difference in mass fraction. The key is to look at Falcon Heavy's performance for very small payloads rather than looking at the largest possible payloads.

FH is advertised at being able to send 3.5 tonnes to Pluto. A Hohmann transfer to Pluto requires an 8.2 km/s burn from low Earth parking orbit. 8.2 km/s at the MVac's 345 s of specific impulse requires a propellant mass fraction of 91.14%. 4 tonnes for the upper stage and 3.5 tonnes of payload means 77.19 tonnes of propellant to perform that 8.2 km/s injection burn toward Pluto.

The Falcon family upper stage carries 107.5 tonnes of propellant, so this means it must burn 30.31 tonnes of propellant to get from staging to LEO with a payload of 3.5 tonnes. That's 1.035 km/s of dV, suggesting a staging velocity of around 6.765 km/s. Now, if the upper stage is not carrying 3.5 tonnes of payload at staging, it will burn slightly less propellant (29.39 tonnes) to achieve the same 1.035 km/s from staging to LEO, leaving it with 78.11 tonnes of propellant in LEO.

And that's without factoring in lower gravity losses (3% higher TWR at staging) and a higher staging velocity (the "payload" of the core booster is 3% lower).

Yes - figure should be closer to, but still less than 70 metric tons all up.
Try at least 80 tonnes. 90+ might be pushing it but a lot depends on the ascent and booster separation profile for Falcon Heavy: how and when it throttles will really change a lot of things.

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Re: Orion to the moon using F9 and F9H
« Reply #21 on: 03/07/2018 09:24 pm »
Yes - things would certainly look good for lunar missions, doing 'distributed launch' of the spacecraft and the Earth Departure Stage (EDS). A Falcon 9 could place a 20 ton Lander or Command Module type vehicle into orbit first. A Falcon Heavy places it's upper stage as an EDS into orbit next, where it's only payload is propellant (65-70 tons?) and a docking mechanism. The spacecraft docks with this and the EDS burns for TLI. With a 'long duration kit' modification to the EDS; it could also insert the payload into lunar orbit with another burn. Any residuals could put the stage on lunar escape later or de-orbit it to the lunar surface.
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Offline sevenperforce

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Re: Orion to the moon using F9 and F9H
« Reply #22 on: 03/07/2018 09:33 pm »
Yes - things would certainly look good for lunar missions, doing 'distributed launch' of the spacecraft and the Earth Departure Stage (EDS). A Falcon 9 could place a 20 ton Lander or Command Module type vehicle into orbit first. A Falcon Heavy places it's upper stage as an EDS into orbit next, where it's only payload is propellant (65-70 tons?) and a docking mechanism. The spacecraft docks with this and the EDS burns for TLI. With a 'long duration kit' modification to the EDS; it could also insert the payload into lunar orbit with another burn. Any residuals could put the stage on lunar escape later or de-orbit it to the lunar surface.
Yeah, this is quite a good approach.

Propellant on the EDS is 70-80 tonnes with FH expendable, 60-70 tonnes with side booster recovery, and 30 tonnes with three-core recovery.

Offline redliox

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Re: Orion to the moon using F9 and F9H
« Reply #23 on: 03/08/2018 04:07 am »
Probably doable, at least between two FH launches.  The real showstoppers however would be a mix of Orion's low dv, safety concerns (since FH isn't crew rated), and NASA bureaucratic pride.  A better investment would be to develop a one-way lander that could use FH.  The Orion needs some overhauling, or at least its service module, if you wish it to be invested.

Also, I don't think SpaceX would be interested since it will be creating ITS/BFR which will make both FH obsolete and be capable of moon landings itself.
« Last Edit: 03/08/2018 04:09 am by redliox »
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