In situ propellant production (ISPP) was examined in terms of its applicability to a manned Mars mission. Production of oxygen from Martian atmosphere was used as the baseline system for ISPP technology assessment. It was concluded that production of oxygen was an important element in a manned Mars mission which could be developed in terrestrial laboratories. Expert system methodology will be required to enable reliable, autonomous production of oxygen. Furthermore, while no major technical breakthroughs are required, this research requires a long lead time to permit its systematic evolution

Ash, Robert L.

English

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N87-17750
CHEMICAL PRODUCTIOU ON MARS USING
IN SITU PROPRLLANT PRODUCTION TECHNOLOGY
Robert L. Ash
01d Dominion University
Norfolk, VA
ABSTRACT
In situ propellant production (ISPP) has been examined in terms of
its applicability to a manned Mars mission. Production of oxygen from
Martian atmosphere was used as the baseline system for ISPP technology
assessment. It was concluded that production of oxygen was an important
element in a manned Mars mission which could be developed in terrestrial
laboratories. Expert system methodology will be required to enable
reliable, autonomous production of oxygen. Furthermore, while no major
technical breakthroughs are required, this research requlres a long lead
time to permit its systematic evolution.
INTRODUCTION
It sltu propellant production (ISPP) was described initially in 1978
(Ref. 1) as a method for producing rocket fuel for a Mars sample return
mission. Use of ISPP resulted in significantly less Earth launch mass
than by other concepts. The orlglnal concept proposed utilization of
atmospheric carbon dioxide and absorbed water in a simple chemical
processor to produce methane and oxygen. A major constraint in that
study was the avallabillty of water, but an important finding was that
primitive chemical processors could be operated at very low throughputs
and produce very large quantities of chemicals in time intervals of one
year. Subsequently, the technology was investigated for posslble
applications at other planetary bodies (Ref. 2) and recently, a more
comprehensive investigation of the technology required to produce oxygen
from the Martian atmosphere for a low mass sample return was reported
(Ref. 3). In sltu production of chemlcals is a logical element in an
overall manned Mars program. The purpose of this brief report is to
place the technological issues before the manned Mars mission working
group.
The production of oxygen from Martian atmosphere is an important
process both for life support and as an oxidizer source for ascent
vehicle propellant. The processor technology is also an important
element in a variety of other scientific and propulsive systems. Since
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that technology is understood sufficiently to permit specific
identification of future research needs and programmatic emphases, it
will be described in some detail. The broader issue of production of
fuels and other chemicals will be discussed briefly in terms of its
potential for future enhancements in an overall Mars exploration program.
ISPP is an important technology in the evolution of a Manned Mars
Mission because it exploits the following advantages: (1) Substitution
of power generating equipment for chemical mass results in a more
flexible system, (2) Radioisotope sources produce much higher energy
densities (several orders of magnitude) than conventional rocket fuels
when the radioiosotope is used several hundred days, (3) Up to fifty
percent reduction in Earth launch mass is possible by offloading the
return propellant, (4) Autonomous production of oxygen at Mars is an
important element in a manned Mars mission for life support, regardless
of return vehicle or surface stay time, (5) ISPP can enable the return
vehicle to be sent to the Martian surface well in advance of the manned
landing, thereby allowing the Earth return vehicle to be certified prior
to sending people to the surface, and 6) The ISPP system can be
developed and tested in terrestrial laboratories.
Depending upon constraints, ISPP is an enabling technology.
Furthermore, using the oxygen production technology as an example, it is
possible to show that ISPP is not a radical departure from presently
understood terrestrial systems. The idea of depending on the resources
of an unexplored landing site for the ultimate success of a mission is
both logical and consistent with historlcal precedent. Technological
issues do remain and will be outlined subsequently.
OXYGEN PRODUCTION
The composition of the Martian atmosphere is well documented (Ref.
4). While there may be slight variations in composition due to location
and season, the availability of relatively pure carbon dioxide (95.32_)
as a feedstock for oxygen production is insensitive to landing site
selectlon. It is tempting to consider atmospheric water vapor as an
equally available feedstock since the atmosphere is relatively humid
(Ref.
water
volume.
5), but the low atmospheric pressure and temperatures never allow
vapor to represent more than a few hundredths of a percent by
The low density of the atmosphere (on the order of 0.02
378
kg/m 3) means that relatively large volume flow rates of atmosphere are
required to produce useful carbon dioxide flow rates, and the volume flow
rates that would be required for water collection would be staggering--to
say nothing of the refrigeration requirements that would be imposed for
water condensation. Water in small amounts could be collected from the
atmosphere for life support.
A nominal Mars environment was suggested in Ref. 3 for oxygen
processor design considerations. An atmospheric temperature of 200 K, a
barometric pressure of 6.8 mb, an average solar load of 140 W/m 2, a
density of 0.018 kg/m 3, and a wind speed of 1.5 m/s were assumed. Using
those data, rather detailed thermomechanical designs were developed for a
system that could produce 10 kg of oxygen per day. That system was
assumed to have a carbon dioxide conversion efficiency of 25 percent
which meant that for every mole of Martian atmosphere that passed through
the oxygen processor, approximately 0.12 moles of molecular oxygen were
produced.
Oxygen
Essentially,
both sides
collection was accomplished using an electrochemical pump.
a voltage can be applied to porous platinum electrodes on
of a yttrla stabilized zlrconia membrane to selectively
conduct (pump) oxygen ions across the electrolyte. By heating the
collected Martian atmosphere to approximately 1270 K, sufficient carbon
dioxide dissociation can occur to permit the oxygen collection to occur.
That system has been studied extensively by Richter (Ref. 6), and a
schematic cross section of the cell is shown in Figure 1. A schematic
diagram of the oxygen processor system developed in Reference 3, is
shown in Figure 2.
In order to scale up the system described for Mars sample return to
manned mission size, the system mass (less electric power generator) can
be scaled, to a first approximation, by multiplying the ratio of
atmospheric flow rates, raised to the 2/3 power, by the baseline mass.
Baseline mass is affected by trades between ascent vehicle mass and
refrigeration system/electric power generator masses. However, if the
baseline mass was 300 kg for a production rate of 10 kg/day with a
conversion efficiency of 25 percent, a 100 kg/day system with a 20
379
1, INCONEL 600 TUBING 9Smm x 0.9mm WALL
2. INCONEL 600 TUBING 12.7mm x0.9mm WALL
3 BORON NITRIDE SLEEVE (2}
z, HEATER. LINDBERG MODEL 50012 TYPE 74-KS {2)
5. 8% YTTRIA STABILIZED ZIRCONIA TUBE WITH 0.1ram PLATINUM COAT ON BOTH
SIDES 6 6ram x 1.Smm WALL
6. INCONEL 600 TUBING 9.5mm × 1.5ram WALL
7. INCONEL 600 TUBING 4.2mmx0.1mm WALL
Figure 1. Electrolytic Cell Design
MARS
ATMOSPHERE
68mb _6 /..rob 12 mb2oak ---soak73 L,ters/second _ 110 L/s
210 wot_
200 watts(T )
28 bars
z.O0 K
20 watts(TL, Z, 3 cc/s
_ RADI_ATOR
(2 kg) t
2797 bars
230 K
2 5 cc/s
02 TO LIQUEFACTION
AND STORAGE
' 160 wattsiE )
_28 mb
_\ (/.5 kg) J -- 335 K
30 L/s
-- 0gmb _ WASTE
300 K | HEAT100 L/s RECOVERY
t
PURE 02
1rob
1250 K
376 L/s
--I 72% CO 2
201 24% CO
kg: 3% N 21% Ar-
{M=3g 71
EXHAUST
GAS
27.7mb / 20mb
9 50 K _ 1250 K
85 L/s 157 L/s
(70 kg) _
OXYGEN
CELL
(1273 K)
wottslEi
1/.00 wotts(T I
RIG THERMAL
POWER SUPPLY
Figure 2 Schemaltc diagram of 10kg/doy Mars oxygen production system
38O
percent conversion efficiency would have an estimated volume flow rate
which is 12.5 times the baseline and an estimated mass of 1630 kg. The
electric power requirement scales almost linearly with the throughput.
Hence, if the baseline power requirement was 3000 Watts electric, the
manned system would require approximately 30 kWe. That system could
produce, liquefy and store 10,000 kg of oxygen In 100 days.
The technology issues identified in previous studies will be
discussed briefly, and then other issues which relate to ISPP systems for
production of other chemicals w111 be dtsussed.
Systems
In order to minimize the possibility of a single point design
failure in the system, it will be necessary for ISPP hardware to monitor
itself and anticipate pending system failure. Proper design of system
elements and software should enable these machines to identify pending
problems and take evasive action. The nuclear and chemical industries
are developing such technology at this time, but they are using massive
amounts of historical data and experience to develop these systems. It
will be necessary to develop sufficient long term operating histories on
prototype ISPP machines to enable them to distinguish between normal
degradation and pending failure.
Re__alr vs. Redundancy
When system elements have characteristics masses and/or volumes
which are large, it ls not feasible to carry duplicate or parallel
elements through the system to avoid single point failures. When
considered in the context of the expert system strategy, a system design
that exchanges an increase in power requirements or decreased efficiency
for repairability using computer controlled manipulators and common com-
ponents becomes potentially a more reliable and lower total mass system.
These systems are very desirable for manned missions in order to keep
routine maintenance time to a minimum. Space Station experiments which
are deslgned to develop and test autonomous/repairable chemical processor
systems should be given high priority.
Nobility vs. Fixed Site
If ISPP Is included on a manned mission, the efficiency and risk
related to separating the processor system from the human must be
addressed. It does not make sense to carry a 10,000 kg oxygen processor
381
system over large distances. It may make sense to move these systems for
short distances in the reduced gravitational environment, to reduce the
risk to manned habitat and transportation vehicles.
Filter Systems
A Mars dust filter design has been discussed in Reference 3. Based
upon data returned from Mars, the dust does not appear to be a serious
problem. However, filter designs which minimize inlet pressure drops
and are relatively Insensitive to unusual or unexpected particulate
loading are needed. These systems can be designed and tested In
terrestrial laboratories. The ability to remove the accumulated
particulates periodically should be incorporated Into the design.
Pumps and Compressors
Pumps and compressors operating at Mars will be In an operating
regime which Is similar to roughing pumps in vacuum facilities.
Compressors wlll be required to elevate fluid pressures from a few
millibars to a few bars. Mechanical stresses wlll be low, but tolerances
and efficlencies of these devices will require a systematic research and
development program. Thls program should be started early enough to
permit selection of a set of generic devices which will enable the
evolution of a set of common components amenable to self diagnosis and
repair. The cryogenic refrigeration components wlll be similar.
Fault Tolerant Electrolytic Networks
The electrolytic cell system is likely to be a large matrix of cells
of the type shown in Figure 1. Based on experience to date, one or more
of these cells is likely to fail during an extended operation. It will
be very desirable to design this system in a manner which will permit
either passive tolerance of cell failures or active alteration of the
flow network. This research program could greatly improve system
performance and reliability.
Oxygen Distribution an__ddStorage
It will be desirable to store oxygen and other cryogenic liquids in
more than one tank. Since these liquids will likely be recycled as they
vaporize due to heat exchange with the surroundings, it will be desirable
to develop passive fluid management systems which use Mars gravity and
density gradients to move fluids to desired locations.
382
Propulsion Systems
Methane/Oxygen rockets have been built and tested. However, they
have not been designed for either Mars sample return or a manned nission.
Those engines and a variety of other propellant and propulsion
conbinations should be investigated to optimize opportunities for manned
exploration.
Electric Power
Power generators were not studied here, but the 6all]eo RTG_s are
sufficient for sample relturn. SP-IO0 greatly exceeds anticipated
requlrenents for manned ISPP.
Packaging and De_ent
Depending on the power generation syste_ selected for a manned
mission, the packaging problen can be a serious problea. One advantage
of ISPP is that a large, potentially hazardous power generating system
can be sent in an unnanned mission in advance of the manned ntssion.
Either way, thernal and radiation problens will require careful
exanlnation.
Radiators
While the Mars atmosphere is thin, the wind appears to blow nearly
all of the time (Ref. 7). The increased energy exchange is very
Important for radiator surfaces with temperatures approaching Nars
aobient conditions.
Trace Contaninants
A research program which identifies potential contaninants that can
danage elements in the ISPP system should be undertaken. Simultaneously,
realistic probabilities of contaminant existence should be developed
based on current knowledge of the solar system. Study of samples
collected on a precursor or early aission will be essential.
ConplenentarySystem Elements
The machinery required for in sttu propellant production can be used
intermittently for a variety of manned or scientific systens. This
opportunity has been given little attention by the scientific community.
However, the electric power and cryogenic cooling capabilities of the
ISPP system can enhance nany activities ranging fron water collection to
sophisticated chemical analyses.
383
Acceptance
While ISPP technology requires a different perspective for manned
missions to Mars, it does not require major scientific break throughs.
In fact, the research required to place ISPP on equal footing with other
options can be accomplished at modest total costs If the program Is
spread over a long enough period of time. Not only does ISPP become an
accepted option with increasing time, but the historical data required to
develop expert system-based machinery becomes economical. However,
compressing a decade of machine history Into less than a year can be very
expensive.
OTHER ISPP OPTIONS
I have attempted to use the oxygen production system as a base from
which to identify technology Issues related to In sltu propellant
production. It is important to realize that the simplest system Is the
oxygen production system, since It uses a simple chemical processor
operating on an abundant raw material. If a manned station were
established In the north polar region of Mars, where there Is known water
ice, use of water and carbon dioxide to produce methane and oxygen
becomes very attractive. In addition, carbon monoxide can be recovered
from the oxygen processor system and used as a fuel. Both of these
systems Involve more than one chemical process. The methanation process
was described in Reference 1, but the extraction of carbon monoxide was
not. Commercial recovery of carbon monoxide is common, but the systems
require thermal energy and relatively complex flow networks (Ref. 8),
Ultimately, all manned extraterrestrial stations wlll likely require
autonomous production of fuels and oxidizers for continued operation.
Production of methane and carbon monoxide are both important resource
options that should be studied in greater detail.
REFERENCES
1. Ash, R. L., Dowler, W. L. and Varsl0 G. (1978)
"Feasibility of rocket propellant production on Mars."
Acta Astronautlca, Vol. 5, pp. 705-724.
2. Ash. R.L., Cuda, V. 0 Stancatl, N. L. and Nlehoff, J.
C., (1981) "Outer planet satellite return missions
using In sltu propellant production." Acta
Astronautlca, Vol. 8, pp. 511-526.
384
,4.
,
.
7,
8.
Ash, R. L., Richter, R., Dowler, W. L., Hanson J. A.,
and Uphoff, C. W. (1982) "Autonomous oxygen production
for a Mars return vehicle" presented at the 33rd
Congress of the International Astronautical Federation,
Paris. Paper IAF-82-210.
Owen, T., 81emann, K.,k Rushneck, D. R., Hiller, J. E.,
Howarch, D. W., and Lafleur, A. L. (1977) "The
composition of the atmosphere at the surface of Mars."
J. Geophys. Res., Vol. 82, pp. 4635-4639.
Davies, D. W. (1977) "The vertical distribution of Mars
water vapor." J. Geophy. Res., Vol. 82, pp 2875-2879.
Richter, R. (1982) "Basic investigation into the
electrical performance of solld electrolyte membranes."
Jet Propulsion Laboratory Publication 82-75.
Ryan, J. A., Sharman, R. D. and Luchich, R. D., (1981)
"Mars meterology: Three seasons at the surface." J.
Geophys. Res., Vol. 86, pp_3247-3254.
Anonymous (1977) "Carbon monoxide from lean gases."
Chemical Engineering, Dec. 5, 1977, pp.122-123.
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Chemical production on Mars using in situ propellant production technology

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