The Long Pole
There are many “long poles” that must be overcome in order to successfully land humans on Mars. To keep the astronauts alive and well, and all of their necessary equipment functioning for the time periods involved in extended stay missions, the generation of sufficient and dependable power on the Martian surface is a critical need. As stated in the critically acclaimed movie, Apollo 13, “Power is everything”. Surface power needs for human Mars missions will require large-scale power generation, far larger than is currently required for robotic missions. Instead of power measured in mere watts, human missions will require supplying tens of kilowatts of power, with power systems that can initially be deployed
robotically and that will remain functional for multiple crew campaigns. Overcoming the Mars surface power “long pole” involves the development and/or scaling up of (1) deployable solar arrays with energy storage, (2) compact fission reactors, and/or (3) radioisotope power systems (RPS).
Statement of Achievability
Current and/or under development solar electric propulsion (SEP) solar array technology may be adaptable for use on the Martian surface (e.g., the Megaflex Solar Array or the Roll-out Solar Array). In addition, there is potential to leverage current terrestrial investments in lightweight batteries (e.g., lithium- ion) that would provide the necessary energy storage capability during periods when the solar arrays are offline entirely or are otherwise operating at less than peak efficiency, such as during nighttime or due to dust storms.
There are also promising prospects for the development of small, affordable fission reactors, using Kilopower technology (see below). Such a system could be used at any location on the Mars surface and provide continuous day/night power at a sufficient scale for human missions. Furthermore, past successes of radioisotope thermoelectric generators (RTGs) on Mars, such as in the Viking missions and in the Mars Science Laboratory’s Curiosity rover, as well as solar power (Pathfinder, Mars Exploration Rover's Spirit and Opportunity, and Phoenix) also speak to the possibility of scaling up these technologies to more robust power levels.
Challenges to Closing the Mars Surface Power Long Pole
There is no current off-the-shelf power solution available at sufficient scale that can operate for long durations in the Martian environment. Current RTGs, for example, are limited to an output of
approximately 100 watts. Solar Photovoltaic (PV) systems are adversely impacted by reduced solar flux, by dust storms, by seasonal changes, and by non-equatorial latitudes. There are also other environmental factors that would have to be taken into consideration, such as Mars’ carbon dioxide atmosphere, 0.38 gravity, dust, wind, diurnal cycle, and surface temperature extremes (-140 C to 35 C). The current lack of availability of Plutonium-238 (Pu-238) would have to be addressed for the use of larger radioisotope power systems (RPS) on Mars.
Closing the Mars Surface Power “Long Pole” Requires Access to the Martian Surface
Because the equipment and machinery that will be needed for surface power is so critical to mission success, and has never been tested under the harsh conditions that exist on the Martian surface, closing this particular long pole will require extensive testing including Mars simulated environmental tests on Earth and under actual conditions, that is, on the Martian surface.
Primary Challenge to Achievability
Accelerated development of Kilopower technology for Mars surface operations is needed. In addition, studies must be undertaken to examine the adaptability of SEP arrays designed to operate in-space to the conditions that exist on the Martian surface. Finally, the potential for scaling up of RPS output to kilowatt-class must also be determined, including the impact on Pu-238 fuel production.
Other Design Considerations
Mars surface power requirements for expanded robotic systems and human habitation are not well- defined at present. For example, power requirements for in-situ production may be significant.
In order to generate the same power on Mars as on the Earth, a solar array would have to be three to four times larger in area. In addition, dust storms are frequent and can develop anywhere on Mars at any time, and landings on the surface will produce dust plumes that may damage nearby solar arrays and radiator surfaces. Dust particles will obscure the Sun for extended periods of time, thus requiring backup power for PV arrays.
Nuclear power systems offer performance advantages, although have unique safety and policy issues including those related to launch. A cold reactor, however, presents minimal risk to the public if the fuel is dispersed during a launch accident. Radioactivity is an issue only after the reactor is turned on, which would not occur until the reactor is safely away from the Earth. Nuclear reactor shielding mass could be
significant and will be dependent on proximity of crew and duration of stay; the use of in-situ materials for shielding may be a possible solution to reduce the delivered mass.
Multiple, distributed landing sites, and multiple, time-phased crew campaigns will complicate the power distribution network: A large, centralized power station may have to be oversized for initial use and require long-distance cabling to connect loads. On the other hand, a distributed power architecture may require the delivery of many, smaller power modules with greater complexity of operations. There is also a theoretical potential for power beaming for surface-to-surface power transmission (instead of cabling) or orbit-to-surface, via laser or microwave.
Time to Close the Mars Surface Power Long Pole
A notional development approach for Mars surface power is shown in Figure 1. Parallel development of solar and nuclear technology options is required for the next ~3-5 years to support informed decisions on a preferred flight system approach, followed by a full-scale engineering unit design/fabrication/test in a Mars simulated environment in the next ~6-8 years. A full-scale power module flight demonstration on a robotic Mars lander in the next ~9-10 years could provide significant risk reduction for later human systems. Following the robotic demonstration, continued development of human-rated flight systems would be required in order to support human missions to Mars in the 2030s.
Figure 1. Mars Surface Power Development Timeline
The time to close this long pole would be approximately 8-10 years for solar and/or RPSs and approximately 10-12 years for nuclear fission.