Most miss the point that with an on orbit (in flight) refueling with a SC and tanker set architecture there is not actually a limit on the delta V possible with this system. It is only a matter of costs since for each 6.3km/s of delta V is an equation of 6.3*N where number of launches is = 5^N + 5^(N-1) +...+5(N-N)N DV (km/s) Launches1 6.3 62 12.6 313 18.9 156The problem comes in how to get the tankers back in some reasonable amount of time or if there is enough funds to expend them.
The problem comes in how to get the tankers back in some reasonable amount of time or if there is enough funds to expend them.
Quote from: oldAtlas_Eguy on 11/17/2017 11:15 pmThe problem comes in how to get the tankers back in some reasonable amount of time or if there is enough funds to expend them.If you're expending them, you can also in principle remove most engines, for some tons of weight saving.Tankers that don't need to launch full, and never need to land can get by with many fewer. At that point you might also consider how much an absolutely minimal tanker that had one raptor, and was carried to orbit mostly empty on cargo could cost.Fuel is cheap, but at some point the exponentials of trying to recover tankers going quite fast away from you means that the logistics get expensive.I do wonder on the cost of a simple aluminium one-raptor tanker, with very little else. (it would of course have a compatible base-frame for propellant transfer)Expendable looks somewhat different if the margins required to launch to orbit don't need to be there, and you have a rapidly reusable (though expensive in terms of capital) propellant transfer for those expendables.
This mentions doing a "solar fry by" that could also be useful for a fast HSF mission within the solar system.https://www.centauri-dreams.org/?p=38728Im thinking perhaps you could use this just to accelerate some fuel depots. The crew BFS could catch the depots as they fly past the earth, leapfrogging from the slowest up to the fastest.
Coming from so close to the Sun means the orbits are nearly radially outwards, thus significantly different to an orbit that launches cotangentially to Earth's orbit, which is needed to minimise delta-vee.Plus the "Solar Fryby" (a phrase I coined BTW) needs a Jupiter Gravity Assist to get so close to the Sun.Quote from: KelvinZero on 11/30/2017 03:02 pmThis mentions doing a "solar fry by" that could also be useful for a fast HSF mission within the solar system.https://www.centauri-dreams.org/?p=38728Im thinking perhaps you could use this just to accelerate some fuel depots. The crew BFS could catch the depots as they fly past the earth, leapfrogging from the slowest up to the fastest.
There's a Russian propellant combination which I think is really interesting in a Titan context - acetam / atsetam.A 30/70 mix of acetylene/ammonia, with O2 oxidiser. Titan has acetylene deposits on the surface and very likely has ammonia. Of course, there's lots of methane and it's possibly the easiest for initial ISRU - but acetam seems to get an Isp in the low 400s. If the ice on Titan is a eutectic of water/ammonia, then there'll be ammonia produced by water-mining for oxygen. Of course we might need to use dry ice for oxygen, so really ground-truthing local resources will decide.