Solar v. Nuclear Power…on Mars

By | September 3, 2007
7 Comments

For the last six weeks the Spirit and Opportunity rovers on Mars have been out of commission due to a huge planet-wide dust storm. The dust probably is not the best thing for electronics, but the real problem was the lack of sunlight. Both Spirit and Opportunity are solar powered.

But we got good news earlier this week – as the storm has slacked off both rovers have checked out as okay.

When the severity of the storms became clear, mission managers elected to have the craft hibernate to ride it out. Then, earlier this week, NASA said the craft could resume their exploration.

Although the skies are now clearer, it will also take some time for the skies to clear properly, as project scientist Bruce Banerdt explains: “The clearing could take months. There is a lot of very fine material suspended high in the atmosphere.”

…

Both rovers are now generating around 300 watt hours from their panels. This is more than twice as much as five weeks ago, but less than half the output prior to the storm.

Both the Spirit and the Opportunity were built with a three month active lifetime in mind. I guess NASA was being cautious because both rovers just surpassed the milestone of 1281 Sols – the service life of Viking 2. Only Viking 1 has operated on Mars longer – 2245 Sols.

Both Viking 1 and 2 were nuclear powered – and expensive. The combined cost of both the Spirit and the Opportunity is $820 million – less than a fourth of the inflation adjusted cost of the two Viking missions.

The Viking probes weren’t subject to power failure in sand storms, but they were immobile.

On Mars… advantage solar.

spirit small.JPG

  • http://www.kirigin.com ivankirigin

    Just to be clear: you’re suggesting solar is advantageous because a mobile mission from today beats a stationary mission from decades past?

    That isn’t a fair comparison.

    RTGs will win in the end
    http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

    That is, they will work well until we use fuel from the site. We could have a hydrogen cycle that used local water and stationary solar arrays to convert water to hydrogen.

    That kind of system engineering will win in the end.

  • https://www.blog.speculist.com Stephen Gordon

    Ivan:

    It’s probably not a fair comparison, but its the only comparison available. At this moment solar appears to win easily for dollars:science.

    Fuel from the site – well, that includes solar.

    Don’t get me wrong, I’m not down on nuclear power. Part of the problem is the weight of a nuclear system v. solar.

    Also, I’m not suggesting that nuclear is out of the race forever. If we had, for example, a space elevator weight would matter less and we could put nuclear powered craft almost as cheap as solar.

  • Karl Hallowell

    The two rovers are still alive only because of light-weight radioisotope heater units (or LWRHU). This is a bit of plutonium oxide (Pu 238 isotope, half life 87.7 years), I think, that generates heat in a vital piece of equipment. Each rover supposedly has eight of them. I get the impression that the LWRHUs generate collectively several watts of heat and have been doing so since launched from Earth.

    Casting this as a straight win for solar power is a mistake.

  • Karl Hallowell

    Hmmm, “mistake” is a harsh characterization, I just mean the Spirit and Opportunity missions aren’t pure solar.

    Second, I understand solar power will be better for small power needs while fission will be better for large power needs. Supposedly the breakpoint is somewhere around 100 kilowatts. Once you start building stuff from local resources, this might swing things in favor of solar power since that strikes me as being easier to make.

  • https://www.blog.speculist.com Stephen Gordon

    Karl:

    Yeah, these two rovers do have that nuclear component to help keep critical circuits warm enough to operate.

    But they are exclusively solar powered. No onboard nuclear reactor for these machines.

  • Karl Hallowell

    But they are exclusively solar powered. No onboard nuclear reactor for these machines.

    The Vikings didn’t have a nuclear reactor either. They were fission powered, but the RTGs don’t qualify as nuclear reactors. Namely, one doesn’t induce chain reactions in the radioactive material, but instead generates electrical power from the passive heat generation from a radioactive substance.

    In a similar fashion, the two rovers are partly fission powered, though that power isn’t exploited for electricity generation, but they don’t have a fission reactor on board.

    My point here is that it is incorrect to claim these rovers are solely solar powered when a small but nontrivial share of their energy needs comes from fission power.

  • http://www.myspace.com/neutrino78x Brian

    I do not agree with Karl. The phrase “solar power” is understood to mean electricity. Hence these are solar powered rovers. It would only be a nuclear powered rover if the RTGs were used for electricity.