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Planning a sol of commands

Space and time · level 6, lesson 3 of 6

A question to start

The round trip to Mars is at most about 45 minutes. So why can a rover team usually make only one big decision a sol?

The idea

The delay is only part of it. The other part is the rhythm of the two planets' days.

  • The rover works in Mars daylight, when it has sunlight and warmth.
  • Its pictures and data come home through orbiters, several times through the day and night.
  • On Earth, the team studies the latest data, decides what to do, builds the commands and checks them.
  • The finished plan is sent up once, in the Mars morning, and the rover carries it out through the sol.

So the loop is: rover works → data comes down → team plans → plan goes up. That loop takes about one sol. A rover that needs a decision cannot wait for the next phone call; it gets the answer the next sol.

That is why each plan has to be complete and safe on its own, and why the rover's own software, such as AutoNav, makes the small decisions in between.

rover worksdata comes downteam plansplan goes upone sol

Worked examples

1. A real morning. On sol 345, Perseverance woke at 02:07 Mars time for a short task, and saw sunrise at 05:16. Its plan for the sol arrived from Earth around 11:00, and the science began soon after.

2. Many questions, one answer. Suppose a team would like to try three ways of drilling and choose the best. On Earth that takes an afternoon. With one plan a sol, trying, checking and choosing takes at least three sols.

3. Why not more uplinks? Even with a 10-minute one-way time, a second plan the same sol would need fresh data, a new plan and checks, all within Mars daylight.

Try it

  1. How often does a rover normally receive a new plan?
  2. When in the Mars day is it sent?
  3. Why does the plan have to be complete and safe on its own?
  4. What makes the small decisions between plans?
Answers
  1. Once a sol.
  2. In the Mars morning.
  3. Nobody can step in quickly if something goes wrong.
  4. The rover's own software, such as AutoNav for driving.

Common mistake

"The delay is the only reason rovers are slow." The bigger reason is the one-plan-a-sol loop, set by the rover's working day, the data relays and the time the team needs to plan safely.

Where it leads