Author Topic: If ACES launched a Dream Chaser to the ISS, how much fuel would it bank?  (Read 4039 times)

Offline su27k

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Slightly OT shower thought: Centaur/ACES is being designed to be an upper stage, a propellant depot, a space tug, a lunar lander, and a spacestation module. It seems to me it is just as multi-use as BFS, something to think about when you feel the urge to make a swiss army knife/F-35 comparison.

The difference is that it's being designed for one primary use, with the idea of making variants/derivatives for the others. They're not trying to make every ACES stage have the full equipment for lunar landing, space habitats, orbital tugs, and propellant depots. There's a big difference, IMO.

Not every BFS has full equipment for everything it plans to do. Satellite launcher has a big cargo bay door and doesn't have all the crew related equipment. We don't know the details about Mars cargo version and the point-to-point version, but it wouldn't be surprising that they would have differences from the crew version as well. The only double duty BFS maybe the satellite launcher and the tanker, but Elon Musk already mentioned they may build a more optimized tanker in the future, right now it's using satellite launcher for tanker just to save money.

So I'm not sure I see the big difference. The variants of Centaur/ACES also share some common elements like structure and propulsion, BFS shares more in the form of re-entry and landing equipment, it's a difference in degree, the basic idea of a multi-use upper stage is the same.

Offline edzieba

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Vulcan ACES 504 probably won't lift much more than ~18 tonnes to ISS, which is pretty much what a fully loaded Dream Chaser cargo will be. So the fuel excess is probably minimal.

The 564 can likely lift about twice that. How much is ~18 tonnes of propellant in 51.6 degree LEO worth?

At ~$6M per solid (am I remembering that right?) it would be ~$36M cost, so you could breakeven at $2k/kg, which is actually competitive with Falcon 9 if I'm doing my math right.

Similar exercise for Vulcan/ACES with a Cygnus instead of a Dreamchaser (though you'd likely need to chip in a little to subsidize the Cygnus launch in order to make it worth their while vs flying on Antares.

~Jon

Sure, but why? Who is willing to pay for propellant in 51.6 degrees LEO? Most other Vulcan/ACES customers will want to go to SSO or GTO/GEO, and that's pretty much impossible from ISS orbit.
ULA themselves have expressed that they are willing to pay $3k/kg for propellant in LEO, so if they can accumulate excess at $2k/kg that's nothing to sniff at. Any excess propellant they can loft along with other launches (even if some of that needs to be expended in slow-but-efficient plane-changes or phasing to get it in position) means propellant already available to use in Distributed Lift launches independent of any future supplier(s).

Offline jongoff

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FWIW, I posted a pair of blog posts yesterday and today over in the In-Space Hardware/Propellant Depots thread about such an ISS-coorbital depot and how it could be used for interplanetary missions using leftover prop from commercial crew/cargo vehicles...

~Jon

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