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Keeping a rover warm

Heat and matter · level 3, lesson 6 of 6

A question to start

At the Viking 1 landing site, nights fell to about −89 °C. A rover's batteries and computer must stay far warmer than that. How do engineers keep them warm?

The idea

A rover fights all three ways of losing heat, and adds heat of its own.

warm electronics boxinsulationheater cold Mars nightbrainsbattery
  • Against conduction and convection: the electronics sit in an insulated warm electronics box, the rover's body. Perseverance's body has this name.
  • Against radiation: surfaces are chosen to give out little infrared.
  • Adding heat: electric heaters switch on when it gets too cold. Spirit and Opportunity each also carried eight small radioisotope heater units, each giving about 1 W of heat from a pellet of plutonium the size of a pencil rubber, with no electricity needed. Perseverance pipes spare heat from its nuclear power source around its body.
Keeping warm Mars Earth
Average temperature about −60 °C about 15 °C
Mass of 1 m³ of air at the ground about 0.016 kg about 1.2 kg

Worked examples

1. Why so many methods? Each slows a different kind of heat loss. Leave one out and the heat leaks that way.

2. Electric heaters cost power. A solar rover in a dust storm has little power to spare, which makes heaters that need no electricity very useful.

3. Eight heater units. \(8 \times 1 = 8\) W, day and night, for as long as the plutonium lasts: tiny, but always there.

Try it

  1. How does a rover's warm electronics box slow conduction and convection?
  2. Name two ways a rover adds heat.
  3. How much heat did Spirit's eight heater units give in total?
  4. Why is a heater that needs no electricity useful in a dust storm?
Answers
  1. It is insulated, so heat passes through its walls slowly and warm air stays inside.
  2. Electric heaters, and radioisotope heater units (or spare heat from a nuclear power source).
  3. About 8 W.
  4. In a storm, solar panels give little power, and electric heaters would drain the batteries.

Common mistake

"A heater alone is enough." Without insulation, heat would leak out as fast as the heaters made it, and the batteries would soon run flat. The box and the heaters work together.

Where it leads