As much as I know of integrated circuits is that military components have lowest temperature working limit - I think -40 deg Celsius. Having in mind that temperatures in open space are less than -200, I come to conclusion that electronics inside spacecraft need heating. Although spacecraft devices spent much time in sleep mode, some electronic circuits must be alive (at least real time clock and few devices that should wake up the rest when needed), by my opinion. I wonder if this way of thinking is OK or maybe there exist some special kind of components regarding severe temperature conditions ? If heating is needed, does it mean that entire interior of spacecraft should be heated (when not sleep) or just few it's separated regions ? In that case I'm really surprised how generator's energy is conserved, having in mind heating and external temperature values, but maybe I missed some important issues.
Space is really cold, that is true. However, how does that temperature get to the spacecraft? There are 3 means of transferring heat, namely:
- Conduction (Direct contact)
- Convection (Contact through air, water, or some other liquid medium)
- Radiation (Radio waves emitted based on the temperature. See Planck's Law)
Of these, in space the only one that matters is the latter. The spacecraft heats up by the rays of the sun, and cools off by large areas that aren't seeing sunlight. Okay, so what does that mean for a spacecraft?
Most spacecraft have electronics that generate heat. Some items do very well with little heat, others are more specialized. For instance, most radios have an Oven Controlled Oscillator (OCXO) that is heated to a precise temperature. Batteries usually have a modest range where they work best. Other electronics might be more forgiving. Propellant is often very sensitive as well.
One of the highest powered devices is usually the radio. These will heat up quite quickly, while other components require heat.
For spacecraft further from the Sun, there is less heating from the sun. A combination of insulation, helps, although the biggest advantage is using the heat from the RTG, which will also help heat the spacecraft, even passively.
The bottom line is, most spacecraft do have a few heaters on specific item, but only heat what needs to be heated, and don't heat what doesn't need to be heated. It's actually quite possible to get a spacecraft that doesn't need any heating around Earth, if it can be maintained in the same environment (Same eclipse periods, for instance) Usually the heat is designed to work best in the hottest environment, and the spacecraft warms itself up otherwise, because it's easier to heat something up than cool it down.