I'll take a crack at the thermo:Let's take our operating altitude as 40 kft (12 km). The air at this temperature is about 220 K. To liquefy O2 from this temperature requires that we first remove sufficient heat to bring it down to its boiling point:Q_cool = 29.378 [J/mol*K] * (220 K - 90 K) = 3.819 kJ/molThen we must liquefy it:Q_condense = 6.82 [kJ/mol]Assuming we separate the O2 post liquefaction, we must also cool 3.76 moles of N2 down to 90 K per mole of O2. Q_coolN = 3.76 * 29.124 [J/mol*K] * (220 K - 90 K) = 14.24 kJ/molThus the total heat removal requirement is: Q_tot = Q_cool + Q_condense + Q_coolN = 24.8 kJ/mol
Quote from: blazotron on 12/07/2009 02:24 amI'll take a crack at the thermo:Let's take our operating altitude as 40 kft (12 km). The air at this temperature is about 220 K. To liquefy O2 from this temperature requires that we first remove sufficient heat to bring it down to its boiling point:Q_cool = 29.378 [J/mol*K] * (220 K - 90 K) = 3.819 kJ/molThen we must liquefy it:Q_condense = 6.82 [kJ/mol]Assuming we separate the O2 post liquefaction, we must also cool 3.76 moles of N2 down to 90 K per mole of O2. Q_coolN = 3.76 * 29.124 [J/mol*K] * (220 K - 90 K) = 14.24 kJ/molThus the total heat removal requirement is: Q_tot = Q_cool + Q_condense + Q_coolN = 24.8 kJ/molI think you're missing one of the tricks often used in O2 liquification. You don't need the chilled nitrogen after it's been separated off, so you can use that to prechill the incoming LOX, which cuts back quite a bit on the required mass. I don't know if it's necessarily enough to pay for itself, but with N2 being 70% of the atmosphere, I wouldn't be surprised if it cut the required energy by at least half.~Jon
Another approach is to use some sort of strap-on jets, which would operate for the first 60 seconds or so. I would imagine that jet engines are cheap enough to be disposable. I believe that most small SRBs have a marginal cost in the 7 figures, so they are not cheap.
mlorrey wrote:Disposable turbine jet engines? You have to be kidding me... According to my calculations, the F100 engines in the US military inventory are valued at over $3.5 million a piece.