Thursday, April 28, 2011

Surface Power for Human Mars Missions

A human mission to Mars would require a substantial amount of electrical power on the surface. It seems there are two main options for producing a lot of power on Mars: solar and nuclear fission. Both a large array of solar panels and a nuclear reactor would be difficult to deliver to and deploy on the Martian surface.

Solar power has the advantage of being safe and technologically reliable. There is no public resistance to solar power. Since non-tracking solar panels have no moving parts, they do not frequently fail to operate. We can also expect solar panel technology to develop significantly over the next decades because there are a variety of terrestrial applications and initiatives that employ it. Unfortunately the solar flux at Mars is less than half what it is at Earth, and the amount of insolation will decrease at non-equatorial latitudes and during the Martian winter. Accumulation of dust on solar panels, a phenomenon for which Mars is notorious, will further decrease energy outputs. If solar panels are thin and flexible, a stern wind could lift unrestrained panels off the ground. Of course, solar power must be stored during the day with a battery or regenerative fuel cell for nighttime use.

Nuclear fission on the Martian surface can offer much more power per unit mass than solar power. It produces energy at a constant rate and could be used equally at any surface location. These characteristics make the fission reactor an attractive candidate to power a production plant for in-situ resource utilization—machinery that will surely consume loads of power. A nuclear reactor, of course, produces dangerous radiation and therefore must be placed a significant distance from crew members. Typical designs contain numerous moving parts to convert heat into electricity, which introduces complexity and risk of failure. Small-scale nuclear reactors have little application in terrestrial settings, so most development efforts may have to fall on space agencies like NASA. And we are all aware of the political obstacles to developing a nuclear reactor and launching it into space.

9 comments:

  1. Mars often has serious dust storms that last for weeks, which would all but rule out solar.

    Andrew W

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  2. There was an MIT study that compared other studies on Mars surface power. It mentioned the problem of dust storms for solar panels, but said that even during a serious dust storm some scattered light gets to the surface. "The MER rovers experienced at most power drops of 65%." It concluded that solar panels could provide a minimal "stay-alive" power during dust storms if they were intentionally oversized.

    The MIT study is here.

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  3. You might want to Google "TerraPower". It's an outfit planning to build relatively small (truck trailer-sized), easy to transport, nuclear power plants that function without refueling for up to a century. The initial fuel load is mostly U-238. Bill Gates is an investor, which seems to give them a fair degre of plausability.

    Anyhow, "safe" nuclear power systems large enough to provide power to a Martian base but conceivably small enough to be rocket payloads may be attainable within a near-term (10-15 years) time period.

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  4. Well, that's interesting. It seems that it's more important that reactors for space be small and safe than have a high output. If something along these lines could be developed, then many could be clustered together for space applications requiring huge power loads--like a VASIMR interplanetary propulsion module for instance.

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  5. You wouldn't want "many" of these clustered together, since the weight would be high. One perhaps -- the notion is that on earth 2 to 3 semi-trailer sized units would provide power to a medium sized city (several hundred thousand people say), so if we could get one of the suckers to Mars and down to the surface, there'd be enough power for a pretty good sized base.

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  6. Multiple reactors might not be useful at a Mars surface base (except for redundancy), but there could be a benefit for space propulsion. A system like VASIMR can increase the mass flow rate of its exhaust if it has more power available, allowing passengers to reduce their transit times in space. This could broaden the tourism market for Mars if it reduced trip times to a matter of weeks. Or, it could open up destinations in the outer Solar System. A lower-powered VASMIR could still have great specific impulse, but the thrust available is pretty low.

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  7. You need reactors with VERY high power to weight ratios to get VASIMR voyage times for the inner solar system down to what can be achieved with nuclear thermal or solar thermal rockets.

    Andrew W

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  8. If the mass flow rate of VASIMR's exhaust were directly proportional to the power available, then it seems clustering reactors would make sense. Doubling the mass flow rate would mean doubling the thrust produced. But the mass of the whole spacecraft would not quite double, as the original payload mass stays the same. Doubled the thrust with not quite double the total mass would give greater acceleration.

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  9. To get trip times down to less than can be achieved with nuclear thermal proponents of nuclear - VASIMR systems advocate the development of gas core reactors coupled to MHD generators with overall power/wt ratios of 2kw/kg Such reactors are probably not what's called for on the Martian surface for power supply.

    Andrew W

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