For a first approximation you can assume a TLI burn has C3=0.
TLI from a parking orbit of 130 x 130 nmi @29 deg inclination; C3 = -0.4 km2/sec2
Quote from: ugordan on 02/28/2012 06:24 pmFor a first approximation you can assume a TLI burn has C3=0.For a second-order approximation TLI from a parking orbit of 130 x 130 nmi @29 deg inclination; C3 = -0.4 km2/sec2Boeing says so.
Quote from: sdsds on 02/28/2012 08:41 pmQuote from: ugordan on 02/28/2012 06:24 pmFor a first approximation you can assume a TLI burn has C3=0.For a second-order approximation TLI from a parking orbit of 130 x 130 nmi @29 deg inclination; C3 = -0.4 km2/sec2Boeing says so.That's even better, considering the payload capacity increases with negative C3 values. Thanks! :-)JR
Entering polar orbit rather than equatorial orbit is principally a matter of arriving in the moon's vicinity above or below the plane of the moon's orbit by somewhat more than a lunar radius. On arrival, the spacecraft will go into an orbit around the moon such that the earth will initially be in view at all times -- it won't loop behind the moon. Thus, I don't think a free-return trajectory is possible, at least not without following a much higher-delta-V trajectory to the moon in the first place.
What's the optimum tank top and bottom profiles? I would guess a catenary, if weight was the pure consideration, hemisphere if pressure. May be parabolic is a solution for an intermediate case? If minimum tank mass was hemispherical, it would require more intertank, so it might not be an optimum solution unless you have common bulkhead.
Is cost a constraint? This determines which propellant. Propellant (all solid, peroxide, some cryo, all cryo) determines which hardware and then which cost. Could minimize GLOW by the choice of propellant, but that wouldn't optimize cost and performance.
Quote from: Antares on 04/22/2012 01:40 amIs cost a constraint? This determines which propellant. Propellant (all solid, peroxide, some cryo, all cryo) determines which hardware and then which cost. Could minimize GLOW by the choice of propellant, but that wouldn't optimize cost and performance. I would say to keep the cost and practicality in the reasonable realm of hobbyists. I'd say no cryo as I'd assume this would make it pretty impractical. Maybe LO2 as an oxidizer but certainly no LH2.
Just trying to get an idea of what the smallest rocket you could make would be to get a small light payload into earth orbit.
Proponent:Thank you for contnuing to look into this, I'll need to take time to read that paper this weekend. I'm guessing that the reason such an approach wasn't used was the extreme distance, even at close approach? On the whole, for full-surface access, how would injecting into polar lunar orbit compare to staging out of L1/L2?