4.20

Your mission to Mars: the data

The following bar chart illustrates the rate of muscle loss experienced by SkyLab crews during their various missions.

Reference for this bar chart

Below, however, is a dummy data set created solely for the purposes of this exercise. It describes the reduction in three health indicators with increasing mission length.

Things you need to know:

• Journey times vary considerably according to the relative positions of Earth and Mars at the time of launch. For your mission use a figure of 220 days each way.

• Gravity on Mars is about 0.38 of that on Earth. A 100kg astronaut would weigh 38kg on Mars. The effort required to walk is reduced accordingly.

• Astronauts will undertake treadmill exercise for a minimum of five hours per day to reduce loss of fitness. With exercise the loss figures in the table will be reduced.

• When any of the three fitness measurements reaches 65% of the initial value, then normal activity becomes impossible (so a reduction of >35% is unacceptable).

We want to establish whether, with existing exercise regimes, it will be possible to land an astronaut on Mars and perform useful tasks whilst on the planet’s surface.

Firstly we need to look at the effects of the flight:

1. The data provided for each of the three measurements show a linear reduction in fitness. But they only run up to 60 days. We therefore need to extrapolate the numbers through to 220 days. This is simple to do: Every 10 mission days equates to a 2.15% reduction in body weight, a 2.5% reduction in leg strength and a 1.5% reduction in cardiac output.
Hint: one of many ways to do this is to enter the first two rows of the table into a spreadsheet, select those two rows, then click and drag the bottom-right corner of your selection downwards until you have 22 rows.

2. However, each of these negative effects are reduced by 30% by daily exercise. You’ll have, no doubt, realized that the best way to do these calculations is with a spreadsheet. Now, use the spreadsheet to reduce the losses by 30%.
Hint: you could create a new table in your spreadsheet that multiplies the relevant three columns of your existing table by 70%.

3. There is a benefit to be gained from the low gravity on Mars but the astronauts will be wearing spacesuits and carrying equipment so we’ll combine all these positive and negative effects into one factor. However this will only apply to leg strength and body weight as cardiac output is unaffected by gravity. Assume a benefit of 10% for body weight and 30% for leg strength.

At this point you should now have a spreadsheet that provides the overall reduction in fitness for each of the three health measurements after 220 days of space flight.