NASA is planning an extensive set of robotic and
human exploration missions that will make extensive
use of cryogenic propellants. In-situ-consumable-production
(ISCP) will reduce the mass launched
from Earth by manufacturing propellant gases on the
Mars surface. NASA's Exploration programs will
benefit significantly from ISCP, providing that low
cost, lightweight methods of propellant gas liquefaction
are available to make exploration financially
feasible.
The objective was to demonstrate that the
planned 2003 Mars surface oxygen gas liquefaction
requirement could be met with an existing, off-the-shelf
tactical cryogenic cooler and a simple heat
exchanger. The requirement is that oxygen gas
produced during the daytime on the Mars surface
(typical temperature environment of 240 K) be
liquefied at a rate of 12.6 grams per hour (g/hr) and
stored at a pressure of 0.2 atmospheres (atm)
(0.2 megapascals (MPa)).
Figure 1 shows a schematic of the test setup.
Using nitrogen as a surrogate test gas (for safety
reasons), N2 gas at room temperature was supplied to
a liquefier in an environmental chamber nominally
maintained at 240 K. System pressure was 2 atm
(0.2 MPa). An average liquefaction rate of 9.1 g/hr of
nitrogen was realized over a 3.55-hour period. The
equivalent oxygen liquefaction rate is obtained by
considering both the increase in refrigeration capacity
of the cooler at the higher oxygen liquefaction
temperature and the ratio between the total enthalpy
changes of oxygen and nitrogen when cooled from
room temperature and liquefied. It follows that
liquefying nitrogen at a rate of 9.1 g/hr corresponds
to an oxygen liquefaction rate of 12.9 g/hr. This
exceeds the planned demonstrations for the 2003
Mars mission goal by 2%.
The more formidable challenge remains to
demonstrate that the 2,500 g/hr requirement for the
later human missions can be met with an economically
feasible package.
Point of Contact: L. Salerno
(650) 604-3189
lsalerno@mail.arc.nasa.gov
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