Why do we rely on solar power sources for robots in space?

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Offline thedoc

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Darren asked the Naked Scientists:
   Why do the Mars rovers and Philae lander use solar panels rather than nuclei power sources as used in satellites. It seems that the Achilles heal for these missions is the intermittent availability of sunlight to power the vehicles. Are there plans to use non-solar reliant power sources to extend the missions and improve reliability.
What do you think?
« Last Edit: 23/02/2016 10:50:01 by _system »


Offline RD

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Why do the Mars rovers and Philae lander use solar panels ...

The Mars Rovers are dual-fuel : they have a nuclear-power ... http://mars.nasa.gov/msl/mission/technology/technologiesofbroadbenefit/power/ , in addition to solar cells.
« Last Edit: 23/02/2016 12:01:48 by RD »


Offline evan_au

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nuclear power sources as used in satellites
It is important to distinguish nuclear power from decay of radioisotopes from a "critical" nuclear reactor (as used on nuclear submarines).

A "critical" nuclear reactor can produce a lot more power, but requires a lot of fissile fuel (almost weapons-grade), more moving parts and can go wrong in more ways. Getting rid of all the heat in space is a real problem, without a cool river nearby. It produces more radiation, and requires more shielding of the electronics. Members of the public are more at risk if one of these falls back to Earth.

A Radioisotope Thermal Generator (RTG) can be made with no moving parts, and can be very compact. But it doesn't produce so much power.

In practice, solar cells work quite well inside the orbit of Mars, while nuclear power is mandatory at Jupiter and beyond.

So Rosetta (with Philae attached) were in the inner solar system for the comet rendezvous, and were powered by solar cells (plus batteries on Philae). But they had to swing way out near Jupiter before comet rendezvous. They hibernated on minimal power for most of the trip, just "waking up" for rocket firing until they approached the comet in the inner solar system.

The preferred orbit for nuclear-powered satellites is where they leave the Earth, go far away, and don't come back. Kosmos 954 came back - the cleanup cost $6M, and only found about 1% of the nuclear fuel; the rest was probably burnt up in the atmosphere, increasing background radiation for everyone.