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The trip to Mars

Radiation and the atom · level 6, lesson 4 of 6

A question to start

Curiosity's radiation detector measured the dose inside the spacecraft every day of its flight to Mars. How does a day of that compare with a year at home?

The idea

Inside its spacecraft, Curiosity's detector measured an average of 1.8 mSv a day from galactic cosmic rays during the cruise. That is about the same as a whole year of natural radiation in Canada, every single day.

Dose Per day Per year
Natural radiation in Canada about 0.005 mSv 1.8 mSv
On the International Space Station, average about 0.4 mSv 150 mSv
Between Earth and Mars 1.8 mSv about 660 mSv

The SwRI team worked out that the two trips of a Mars mission, out and back, with today's rockets, would give about 0.66 Sv, or 660 mSv, before counting any time on Mars.

at homespace stationto Mars0.005 mSv, too small to see0.4 mSv1.8 mSv

The bars show the dose in one day, to scale.

Worked examples

1. Curiosity's trip. 253 days at 1.8 mSv a day: \(253 \times 1.8 \approx 455\) mSv.

2. Days to the worker limit. \(50 \div 1.8 \approx 28\) days. In under a month, a crew would get the dose a nuclear worker on Earth may get in a whole year.

3. A faster trip. Suppose new rockets cut each trip to 120 days. \(240 \times 1.8 = 432\) mSv for the two, instead of about 660.

Try it

  1. Roughly how many years of Canadian natural radiation does one day in deep space equal?
  2. Find the dose for a 200-day trip at 1.8 mSv a day.
  3. How much of the dose on the cruise came from solar particles, according to the Curiosity team?
  4. Why does a shorter trip help more than thicker walls?
Answers
  1. About one year.
  2. \(200 \times 1.8 = 360\) mSv.
  3. About 5%.
  4. Walls barely slow galactic cosmic rays, but the dose adds up day by day, so fewer days means less dose.

Common mistake

"The space station is in space, so it gets the same dose." The station orbits inside Earth's magnetic field, and Earth blocks about a third of its sky. Between the planets there is neither.

Where it leads