Resolved: Can We Store Cryogenic Propellant at L4/L5 Without Losing It?

Cryogenic propellant (liquid hydrogen at 20K, liquid oxygen at 90K) offers the highest performance for in-space transportation, but it boils off continuously. If we can't store it, we're stuck with storable propellants that carry a devastating 30-40% specific impulse penalty. This question blocks three downstream research questions.

The deliberation reached unanimous consensus in a single round.

The Answer: Sunshield + Modest Active Cooling = Zero Boil-Off

The L4/L5 Lagrange points have a critical advantage: the sun direction is essentially fixed (with slow libration). This makes a large sunshield incredibly effective.

The numbers:

• Unshielded solar input: ~204 kW on a 50-tonne LH2 tank
• After 30m x 30m sunshield: ~40-135 W residual (3-4 orders of magnitude reduction)
• Active cooling power needed: ~700 W per 100-tonne LH2 tank
• Total for full tank farm (100t LH2 + 600t LOX): 10-20 kW
• That's less than 1% of the station's 2.5-3.25 MW power budget

Why Storable Propellants Are Off the Table

The 30-40% Isp reduction from switching to storable propellants would fundamentally undermine the economic rationale for in-situ production. The entire ISRU business case depends on high-performance cryogenic propulsion. With ZBO demonstrated at 10-20 kW, there's no reason to accept that penalty.

Subcooled Storage as Insurance

Cooling LH2 below its boiling point to ~15K during production provides approximately 190 days of thermal margin against cryocooler failure. Even if active cooling goes down, you have over six months before you start losing propellant.

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