1. The Discovery’s fins

Arthur C. Clarke’s 2001: A Space Odyssey gives the Discovery long, flat radiator fins that look as much like architecture as engineering. They are there because the ship’s reactors produce heat that has nowhere else to go. The desktop’s radiators will be smaller, but the same geometry problem applies: how much surface can be exposed to cold space, and how much mechanism are you willing to add to get it.

Entry 243 estimated that the desktop needs roughly 0.7–1.0 m² of radiator area. This entry decides whether that area is body-mounted or deployable.

2. Body-mounted radiators

Body-mounted radiators are panels fixed to the exterior of the desktop’s structure. They have no deployment mechanism.

Advantages:

  • No deployment risk.
  • High stiffness and predictable structural load path.
  • Simple integration with heat pipes embedded in the structure.
  • Always available from launch.

Disadvantages:

  • Limited to the area of the body surfaces that can be oriented away from the sun and Earth.
  • Performance depends on spacecraft attitude. If the radiator face is tilted toward the sun or Earth, heat rejection drops.
  • Competes with solar arrays, antennas, and sensors for exterior space.

For the desktop’s 0.7–1.0 m² requirement, body-mounted radiators are feasible if the body is roughly 1 m × 1 m and one or two faces can be dedicated to radiators. The constraint is not raw area but orientation.

3. Deployable radiators

Deployable radiators unfold or extend from the body after launch.

Advantages:

  • Much larger area than body-mounted for the same stowed volume.
  • Can be oriented independently of the main body, improving view factor to space.
  • Reduce competition for the spacecraft’s exterior surface.

Disadvantages:

  • Deployment mechanism adds mass, cost, and failure modes.
  • Hinges and flex lines are thermal and structural weak points.
  • Usually require active control or careful design to maintain the right orientation.

Deployable radiators make sense when the heat load is large relative to the body size. For a small satellite rejecting a few hundred watts, they are often unnecessary. For a desktop that may grow to reject 500 W or more in later versions, deployable radiators become attractive.

4. The desktop choice

The first desktop should use body-mounted radiators.

The 0.7–1.0 m² requirement can be met by the body surfaces without adding deployment complexity. The desktop already has deployable solar arrays; adding deployable radiators would introduce a second deployment risk for a benefit that is not yet needed.

A sensible configuration is:

  • Two radiator panels, each roughly 0.4–0.5 m², mounted on opposite sides of the desktop body.
  • Heat pipes embedded in the structure conduct heat from the central electronics bay to both radiator panels.
  • The panels are coated with high-emissivity black paint or optical solar reflector.
  • MLI covers the non-radiator surfaces to minimise parasitic heat gain and loss.

This gives redundancy: if one radiator is partially shaded or degraded, the other can carry more load.

5. Arrangement with solar arrays

The radiator panels should be arranged so they are not in direct view of the solar arrays. Solar arrays get hot, and their back sides radiate infrared. A radiator facing a solar array would receive that infrared heat and lose effectiveness.

A common arrangement is to mount radiators on the north and south-facing sides of a nadir-pointing spacecraft, with solar arrays deployed along the east-west axis. This keeps the radiators edge-on to the arrays and gives them a clear view of deep space.

The desktop’s solar wings from entry 239 should therefore deploy from the sides opposite the radiator panels, or at least not fold back over them.

6. Mass estimate

A body-mounted aluminium radiator panel with embedded heat pipes typically masses 3–6 kg/m² including structure and fittings. For 1 m² total:

  • Radiator panels and heat pipes: roughly 3–6 kg.
  • Coatings and MLI: roughly 1–2 kg.
  • Total thermal control radiator mass: roughly 5–8 kg.

This is comparable to the solar array mass and reflects the fact that both attachments are large area structures.

What this changes

  • The desktop uses body-mounted radiators rather than deployable ones.
  • Two radiator panels, roughly 0.4–0.5 m² each, provide redundancy.
  • Radiators are arranged on sides opposite the solar arrays to maintain a clear view to space.
  • Heat pipes embedded in the structure transport heat from electronics to radiators.
  • The thermal control radiator mass is estimated at 5–8 kg.
  • The next entry can choose radiator coatings and multi-layer insulation details.