Phase II Final Report - NASA's Institute for Advanced Concepts

Planetary Exploration Using Biomimetics
An Entomopter for Flight on Mars
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25
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kg H2 / kg system *100
kg H2 / m^3
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6.89 13.79 20.68 27.58 34.47 41.37 48.26 55.16 62.05 68.95
Storage Pressure (MPa)
Figure 3-151: Glass Microsphere Hydrogen Storage: Mass Fraction and Density for
Various Storage Pressures
3.5.3.1.2 Cryogenic Hydrogen Storage
To reduce tank mass and volume over high-pressure gas storage, cryogenic storage of hydrogen
can be used. The properties of liquid hydrogen enable significant increases in density over highpressure
gas storage, as well as reduced tank mass due to lower pressure operation. Liquid
hydrogen is around -260° C (-425° F) and has a density (ρLH) of 71 kg/m 3 (4.43 lb/ft 3 ). To get a
further increase in density above that of liquid hydrogen, a mixture of solid and liquid hydrogen
can be produced. This mixture is called slush hydrogen. For a 50% solid/50% liquid mixture, the
hydrogen density is 80.9 kg/m 3 .
Cryogenic storage maximizes the density of hydrogen but imposes some significant operational
constraints on the fuel system:
1. It requires an airtight insulation system to reduce the boil-off of the liquid hydrogen and
maintain it at cryogenic temperatures.
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Phase II Final Report