A Crewed Mission to Mars...


Surface Systems:

How will power be generated?

How will fuel be produced?

What resources will we obtain on Mars?

How will life support work?

 


1) Surface Power

The primary surface power source will be the 160 kW nuclear power modules. These modules will be designed to have a lifetime of 15+ years and they will serve to power the Mars outpost for each of the three crewed missions. While only one of these modules is needed to supply enough power for all of the astronauts' needs, system redundancy provides an added degree of safety. These power plants will be deployed approximately 1 km away from the crew habitat where they will remain during the course of the exploration missions.

Mars receives approximately 44 percent as much solar radiation as Earth, and therefore solar power is feasible as a power source. Secondary surface power will be a solar array capable of producing 120 kW on a clear winter Mars day at the equator. It is not clear whether this will be a tracking (sun following) array or a non-tracking array, but there is one disadvantage in either case. A tracking solar array will cover a larger area and has the potential to require more maintenance than a non-tracking array. A non-tracking array on the other hand, is less efficient and, due to the increased panel area, will need to weigh about 50% more than a tracking solar array. A backup solar array capable of producing 40 kW of power will also be included to provide supplementary power in the event of a sunlight-reducing dust storm.

It is also unclear what power systems will be used for the pressurized long-range surface rover. The two most likely choices for the rover power source are either a methane fuel cell or a Dynamic Isotope Power System utilizing a 238Pu power source. Further investigation into both of these options is necessary. Solar power is not considered as an option for the pressurized rover power source due to the large area that would be required. The unpressurized rovers will be similar to those used on lunar landing missions.

2) Fuel Production: In-Situ Resource Utilization (ISRU)

The martian atmospheric composition will allow the Mars astronauts to take advantage of in-situ resource utilization to provide them with life support reserves as well as the propellant required by the MAV. The martian atmosphere is composed of approximately 95.3% carbon dioxide, 2.7% nitrogen, 1.6% argon, 0.13% oxygen, 0.08% carbon monoxide, and trace amounts of water, nitrogen oxide, neon, krypton and xenon. By utilizing simple reactions between martian carbon dioxide and imported hydrogen, the astronauts will be able to produce methane, water, and oxygen. Direct atmospheric extraction of nitrogen and argon will also be possible.

Hydrogen is the keystone of the ISRU strategy. The Martian atmosphere does not provide a significant source of hydrogen gas, and while it may be possible to acquire hydrogen through electrolysis of melted subsurface Martian water-ice reservoirs, the existence, size, and accessibility of these reservoirs is uncertain. The use of indigenous resources while on the surface of Mars is critical to the success of the mission and the successful implementation of the ISRU strategy will demonstrate the feasibility of long term Mars missions and/or colonization. Fortunately, hydrogen has the lowest molecular weight of any material which we could bring to Mars and it is therefore reasonable to import it on the cargo missions preceding the crew. Water-ice at the poles is known to exist, but a polar landing site is not considered for any of the initial human Mars exploration missions due to the relative hostility of the polar environment when compared with that of a near-equatorial environment.

The Sabatier process involves the reaction of hydrogen with carbon dioxide at elevated temperatures to produce methane and water. The ISRU module will react imported hydrogen with atmospheric carbon dioxide in order to achieve this. For each metric ton (tonne) of imported hydrogen that is reacted, 2 tonnes of methane and 4.5 tonnes of water will be produced. The Sabatier reaction proceeds as follows:

CO2 + 4H2 ------> CH4 + 2H2O

The methane from the Sabatier process will be cryogenically stored in tanks for use by the MAV liquid methane/liquid oxygen rockets which will launch the astronauts from the surface and into Mars orbit where they will rendezvous with an orbiting ERV. The liquid oxygen fuel for the the MAV will need to come from two sources. The first source of oxygen will be the electrolysis of the water produced by the Sabatier reaction. The electrolysis of 4.5 tonnes of water will yield 4 tonnes of oxygen and 0.5 tonnes of hydrogen which can be recycled back into the Sabatier process (this recycling of hydrogen will cut the amount of hydrogen required for methane and oxygen production in half ). The produced oxygen will be cryogenically stored in MAV fuel tanks or in ISRU module tanks as a life support reserve for the astronauts. The water will be decomposed into hydrogen and oxygen in the following reaction:

H2O ------> H2 + 1/2O2

The above two reactions can be combined to produce varying amounts of water and oxygen. The maximum and minimum mass production values of water and oxygen are summarized in the following table (note that methane production is constant):

Water, Oxygen, and Methane Production (per tonne of hydrogen)

Production

Sabatier only

(ie. maximum water production)

Sabatier + Electrolysis of all produced water

(ie. maximum oxygen production)

Methane (tonnes)

2.0

2.0

Oxygen (tonnes)

0

4.0

Water (tonnes)

4.5

0

Hydrogen (tonnes)

0

0.5 (recyclable)

 

At this point it is important to notice that even if all of the water produced by the Sabatier process was decomposed into hydrogen and oxygen, the maximum mass ratio of oxygen to methane would be 2:1. The liquid methane / liquid oxygen engines of the MAV will use oxygen and methane in a mass ratio greater than the 2:1 ratio obtained by the combined Sabatier/Electrolysis processes (the oxygen/methane mass ratio used by the engines will likely be close to 3.5:1). Clearly, another source of liquid oxygen must be found in order to avoid the production of excess methane.

Carbon dioxide electrolysis is a possible solution to the oxygen deficit problem. While still under development, this process uses zirconia cells at high temperatures to decompose carbon dioxide. This process could be performed on Martian atmospheric carbon dioxide, producing oxygen and carbon monoxide. The carbon monoxide would be vented into the atmosphere and the oxygen would be cryogenically stored for use as MAV propellant and/or life support reserves for the crew. The overall reaction for carbon dioxide electrolysis is as follows:

2CO2 ------> 2CO + O2

Direct extraction of atmospheric nitrogen and argon will provide life support buffer gas reserves. This will likely be achieved by passing compressed Martian atmosphere over a material which will absorb the available nitrogen and argon. Each time the absorbing material became saturated, the nitrogen and argon would be released through heating. The nitrogen and argon would then be cryogenically stored as life support reserves.

For all atmospheric collection, it will surely be necessary to filter dust particles out of incoming Martian "air".

The importance of the ISRU strategy cannot be understated. Further research and development of ISRU processes is needed and these processes must be demonstrated before a full scale human Mars exploration program can be launched. Current plans call for methane/oxygen propellant ISRU strategies to be implemented on an unmanned Mars sample return mission in the near future (ie. 2003 or 2005 opportunity). Supplementary oxygen production processes (ie. carbon dioxide electrolysis) and nitrogen/argon buffer gas extraction processes should also be demonstrated to be both feasible and reliable as soon as possible.

3) Surface Life Support

Due to the critical nature of the system, crew life support will have threefold system redundancy. The crew transit/habitation module will provide the primary life support system while the joined surface laboratory will play the role of the first backup. Should it become necessary, both the crew module and the laboratory module will have life support systems able to support the entire crew for the duration of the mission. The third level of life support system redundancy will come from the ISRU module stored life support reserves. The ISRU plant will be produce and store adequate reserves of oxygen, buffer gases, and water for use by the astronauts.

The life support systems in the crew habitat and laboratory modules will both utilize current physical/chemical purification technology in use aboard the space shuttle. This technology uses a combination of physical and chemical processes to remove impurities from air (ie. convert CO2 to O2 , regulate humidity) and water (ie. waste water purification).

Methods of transfer of cryogenically stored reserves from the ISRU plant will need to be defined prior to the astronauts' departure. Also, auxiliary systems which will allow direct "injection" of raw life support reserves will need to exist in the crew and laboratory modules.

While the bioregenerative life support experiment will provide valuable experience in bioregenerative life support system technology, it will not be depended upon as a life support backup. It is possible that "greenhouse" methods will be used to grow fresh produce and cleanse air and water, but the scale and reliability of such an undertaking remains unclear. Further development of closed loop bioregenerative technology such as that used in the Biosphere experiments is needed before we can place any level of dependence upon the bioregenerative life support system.

A possible strategy for the bioregenerative system is a hybridization of bioregenerative greenhouse components and existing life support systems (ie. chemical/physical, stored reserves). This hybridization would provide the benefits of in-situ foodstuff production and, by maintaining dependence upon the robust primary life support systems, it would allow for the flexibility needed in bioregenerative systems. In a Mars-based greenhouse, it must remain possible for the astronauts to use existing life support systems to compensate for the dynamic nature of biological systems.


Why Go to Mars? - motivations behind a human Mars exploration program

Mission Objectives and Profiles - objectives, risk evaluation, trajectories, travel/stay times, split mission strategy

Launching the Mission - propulsion, launch schedule, launch payloads

Landing on the Martian Surface - entry & landing, surface equipment, surface operations

Return to Earth - ascent from the Mars surface, Earth Return Vehicle


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Author/Curator:
Dr. David R. Williams, dave.williams@nasa.gov
NSSDCA, Mail Code 690.1
NASA Goddard Space Flight Center
Greenbelt, MD 20771
+1-301-286-1258


NASA Official: Ed Grayzeck, edwin.j.grayzeck@nasa.gov
Original Page Author: Malcolm J. Shaw, Malcolm_Shaw@pcp.ca
Last Updated: 06 January 2005, DRW