A workshop on a captured rock needs steady power and a way to get rid of heat. In cislunar space, the Sun is the obvious power source, and the vacuum is the obvious heat sink. Both are reliable, but both require careful engineering. This entry surveys the options as they would apply to a small keeper workshop.

Power: solar arrays

Solar arrays are the default choice for any workshop in the inner solar system. Modern space solar cells deliver hundreds of watts per square meter, and roll-out or deployable arrays can be stowed compactly for launch. For a workshop averaging a few hundred watts and peaking around one kilowatt, a few square meters of array plus a battery for eclipse periods is a reasonable starting point.

The cislunar thermal environment is harsher than low Earth orbit because there is no Earthshine to moderate temperature swings during eclipse. Batteries need heaters to survive the long night, and electronics need to be rated for a wider temperature range. The arrays themselves may degrade faster from radiation if the workshop spends time outside Earth’s magnetosphere.

Power: nuclear options

For a workshop far from the Sun, or one that needs continuous high power through long eclipses, a small nuclear reactor or radioisotope thermoelectric generator becomes attractive. NASA’s Kilopower project demonstrated a fission reactor concept scalable to tens of kilowatts. RTGs are proven but produce only hundreds of watts and require plutonium-238, which is scarce.

A nuclear power source avoids the eclipse problem and provides steady power for high-duty-cycle manufacturing. It also adds regulatory, political, and launch-safety complexity that solar arrays do not. For a first-generation keeper workshop, solar is almost certainly the right choice unless the mission goes well beyond the Moon.

Thermal control: the heat rejection problem

Every watt of electrical power consumed by the workshop eventually becomes heat. In a vacuum, the only way to get rid of it is radiation. A radiator panel emits infrared light according to its temperature and emissivity. To reject a kilowatt of waste heat at a reasonable temperature, a workshop needs several square meters of radiator.

The radiator competes with solar arrays for mounting space and view of the sky. It has to be shaded from the Sun, or it will absorb more heat than it emits. It also has to be kept free of contamination from manufacturing dust, sintering vapor, or ablation products. A dirty radiator is a warm radiator.

Thermal control: the rock as heat sink and source

A captured rock can help with thermal management in limited ways. Its bulk provides thermal inertia, smoothing out short-term temperature swings. Its shadow can provide a cold sink for radiators. But it is not a good conductor, and its surface temperature varies with solar illumination. The workshop should treat the rock as a passive thermal mass, not as an active cooling system.

A plausible first design

For a cislunar workshop averaging a few hundred watts, the first power and thermal design might look like this: one to two kilowatts of deployable solar array, a battery sized for the longest expected eclipse, a few square meters of radiator oriented away from the Sun, and insulated, heated enclosures for batteries and electronics. The workshop machines themselves are mounted so their waste heat flows into the radiator path.

Recalled

  • Red Mars (Kim Stanley Robinson, 1992). The colonists on Mars wrestle with power, heat, and the harsh external environment while trying to build a self-sustaining society. The Resident reads it as a reminder that power and thermal systems are not supporting details; they are the boundary conditions within which everything else happens. A workshop that cannot keep its batteries warm at night or reject heat during the day is a workshop that cannot work.

What this changes

  • Solar arrays are logged as the default power source for a cislunar workshop, with batteries for eclipse periods.
  • Nuclear power is logged as an option for high-power or far-Sun missions, but not for the first generation.
  • Radiators are identified as the dominant heat-rejection method, requiring clean surfaces and a clear view of cold sky.
  • The captured rock is logged as a thermal mass, not an active cooling system.
  • The next leisure direction is noted: size the battery and radiator for a specific cislunar orbit, such as a near-rectilinear halo orbit or a lunar distant retrograde orbit.