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Do satellites have special radioactive hardware in them?

J

janas19

Platinum Member
So, I was watching a re-run of "The Unit" last night, and the team was in a country in Africa to retrieve a component from a fallen Chinese satellite. It was a small electronic piece that appeared to be a controller of some sort. When they opened up the box, there was a small metal tube inside filled with something radioactive.

I Googled this and found nothing. Can anyone explain why a satellite would have radioactive hardware? Thanks.
 
Possibly some kind of energy source? I recall reading something about using Americium as a key ingredient to a very long lasting battery. Whether or not it's actually being used, I don't know though.
 
some satellites use radioactive materials to supply electric power
not a 'nuclear reactor' like is used for commercial power plants, but to provide heat source
 
Red Squirrel said:
Possibly some kind of energy source? I recall reading something about using Americium as a key ingredient to a very long lasting battery. Whether or not it's actually being used, I don't know though.
Click to expand...

Aha. Makes sense. That's cool, I didn't know radioactive stuff was used for energy. But I guess it makes sense in space, because the atmosphere is deadly anyways.





FoBoT said:
some satellites use radioactive materials to supply electric power
not a 'nuclear reactor' like is used for commercial power plants, but to provide heat source
Click to expand...
 
http://en.wikipedia.org/wiki/Radioisotope_thermal_generator

Radioisotope thermoelectric generator


A radioisotope thermoelectric generator (RTG, RITEG) is an electrical generator that obtains its power from radioactive decay. In such a device, the heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect using an array of thermocouples.


RTGs have been used as power sources in satellites, space probes and unmanned remote facilities, such as a series of lighthouses built by the former Soviet Union inside the Arctic Circle. RTGs are usually the most desirable power source for robotic or unmaintained situations needing a few hundred watts (or less) of power for durations too long for fuel cells, batteries, or generators to provide economically, and in places where solar cells are not practical. Safe use of RTGs requires containment of the radioisotopes long after the productive life of the unit.
 
This makes me wish I had been a better student, so that I could understand this stuff. As it is, I feel pretty stupid.
 
Three uses come to mind:
- Radiation source for instrumentation. The Mars Exploration Rovers, and I believe Soujourner also had it: At least one of their instruments had a radiation source, alpha particles I think, which was used to help determine the composition of rocks. I don't think that this is a powerful source of radiation though.
- RTEG: A power source. dmcowen's post covered this. Make plutonium, plutonium decays, decay makes plutonium hot, thermocouples convert heat into electricity. Plenty of radioactive energy present, but they're still not terribly powerful in terms of power output.
- Radioactive heaters. These can be around the "warm electronics box," where the main electronic systems are located. They help keep the stuff from getting terribly frigid, and do so without being a drain on the main power system.


Why is a radioactive thing likely to be in The Unit's satellite? Because TV writers don't know much of anything about reality, and any kind of sciency stuff on many TV shows is automatically going to be radioactive.
 
It doesn't seem sensible to use radioactive substances in Earth orbit satellites, for power/heat anyway. There's so much sunlight around for power.
 
Mr. Pedantic said:
It doesn't seem sensible to use radioactive substances in Earth orbit satellites, for power/heat anyway. There's so much sunlight around for power.
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But solar panels just can't get a plot moving like RADIOACTIVE!!!! can. How many superheroes were ever made because some guy licked a solar cell?

Beware...the Photonic Avenger, sworn enemy of the Silicon Scourge!
 
Mr. Pedantic said:
It doesn't seem sensible to use radioactive substances in Earth orbit satellites, for power/heat anyway. There's so much sunlight around for power.
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That is fine and dandy if the satellite currently has sunlight. Also space is cold, very cold, these help to keep the internals of the satellites warm(er).
 
ussfletcher said:
That is fine and dandy if the satellite currently has sunlight. Also space is cold, very cold, these help to keep the internals of the satellites warm(er).
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Well, insulation goes a long way. And batteries. Not only for night-times, but in case a panel breaks or gets hit. I would have actually thought that overheating would be the bigger problem, because there's very little atmosphere to redistribute heat, which comes not only from hardware, but from the sun as well. For example, the day side of the moon gets to nearly 200C, and that doesn't produce it's own heat, has a huge volume of stuff to redistribute heat energy and a low volume-area ratio.
 
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Mr. Pedantic said:
Well, insulation goes a long way. And batteries. Not only for night-times, but in case a panel breaks or gets hit. I would have actually thought that overheating would be the bigger problem, because there's very little atmosphere to redistribute heat, which comes not only from hardware, but from the sun as well.
Click to expand...

Actually that brings a good point, how do machines in space dissipate heat? From my understanding, heat can't travel in a vacuum, since heat itself is not a substance, it's just the state of a substance, whether it's a liquid, solid, or a gas. For example in a computer, heat will travel through a heat sink, and then through air, and that's how things stay cool. Put a computer in space, and the heat will just stay in the heat sink and not dissipate further. Or am I wrong on this?
 
Red Squirrel said:
Actually that brings a good point, how do machines in space dissipate heat? From my understanding, heat can't travel in a vacuum, since heat itself is not a substance, it's just the state of a substance, whether it's a liquid, solid, or a gas. For example in a computer, heat will travel through a heat sink, and then through air, and that's how things stay cool. Put a computer in space, and the heat will just stay in the heat sink and not dissipate further. Or am I wrong on this?
Click to expand...
There's a certain amount of conduction/convection, since there's still an atmosphere in orbit and to some extent in interplanetary space. But it's not much. Radiation also still occurs at low temperatures, but again, it's not much, and given how much radiation the sun gives out, I don't know if that would even be a net loss - you'd have to play around with materials and orientations to get low absorption on the sun-facing side and high emission on the shaded side.

You could use a vapour chamber thing like in a fridge or a Peltier to concentrate heat into a small, small area in the shade and heat that to glowing, but that requires its own power and would, I imagine, have problems with insulation...

Or, you could have a thermal reservoir like water, to soak up heat during the daytime period and emit it slowly at night.
 
Red Squirrel said:
Actually that brings a good point, how do machines in space dissipate heat? From my understanding, heat can't travel in a vacuum, since heat itself is not a substance, it's just the state of a substance, whether it's a liquid, solid, or a gas. For example in a computer, heat will travel through a heat sink, and then through air, and that's how things stay cool. Put a computer in space, and the heat will just stay in the heat sink and not dissipate further. Or am I wrong on this?
Click to expand...
The same way energy gets here from the Sun: Radiation.

You've got conduction and radiation as the main modes of heat transfer. Convection is stuck in its own category too; it's really just conduction, but the energy is transferring into a fluid, the properties of which can be quite useful too.

Anything above absolute zero (which is everything in the Universe) emits EM radiation all the time. The background radiation from the Big Bang emits in the microwave region of the spectrum, because of its initial temperature and the Universe's expansion. Steel at room temperature is emitting infrared radiation, as are you. As a piece of steel is heated, its peak emissions move along the blackbody curve, until the light it emits begins to enter our narrow visible spectrum, first on the red end, then it keeps going up toward the blue end, until the mix is closer to what we'd see as white light. Heat something up enough, and its frequency spread will keep increasing, past the visible and into UV, at which point you're probably looking at a plasma, but only briefly, as you'll start going blind before too long. 😉


But yes, spacecraft can reject waste heat, and it can only be done either through radiation, or by dumping all the thermal energy into some kind of matter and then dumping that matter overboard. The latter isn't really feasible for long-term missions, like the decades-long trip that the Voyager spacecraft are on.
 
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Mr. Pedantic said:
Well, insulation goes a long way. And batteries. Not only for night-times, but in case a panel breaks or gets hit. I would have actually thought that overheating would be the bigger problem, because there's very little atmosphere to redistribute heat, which comes not only from hardware, but from the sun as well. For example, the day side of the moon gets to nearly 200C, and that doesn't produce it's own heat, has a huge volume of stuff to redistribute heat energy and a low volume-area ratio.
Click to expand...
Insulation does go a long way, partially the reason that many spacecraft are covered in materials that are highly reflective. There is a significant amount of engineering that goes into that department. Additionally these were/are primarily a solution to powering craft when the existing solar technologies would be unable to satisfy power/space requirements. AFAIK most modern uses of this technology are for powering missions to Mars or beyond like the Mars Science Laboratory, where a huge solar panel would be required to get even minimal power.
 
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