Your mission to Mars: the data (part two)

• 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. You need to calculate the values for 220 days.

You therefore need to extrapolate the numbers through to 220 days. Every 10 mission days equates to a 2.15% reduction in body mass, 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.

Alternatively you could work out what the percentage reduction would be for one day and then multiply this up to 220 days. You can only do this with data that are linear.

For example, for body mass, 2.15 % in 10 days would be 0.215 % in one day (2.15/10) and then 0.215 % x 220 days gives 47.3 % in 220 days. You then do this for the other columns.

1. Each of these negative effects are reduced by 30% by daily exercise. So what & reduction would you expect after 220 days?

Hint: If you are happy to do these calculations with a spreadsheet, use the spreadsheet to reduce the losses by 30%. You could create a new column in your spreadsheet that multiplies the relevant three columns of your existing table by 70%.

Or you could take the values you calculated and find 70% of these values. For example, 70/100 x 47.3 = 33.11 %. This is the % reduction in body mass after 220 days, taking into account daily exercise.

1. 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 mass, as cardiac output is unaffected by gravity. Assume a benefit of 10% for body mass and 30% for leg strength.

Hint: If you are using a spreadsheet, 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.

If manually calculating, you would add 10% onto the reduction of 33.11 %. So 10 % of 3311 is: 10/100 x 33.11 = 3.11. This is taken away from 33.11%.

Next Step

What do these data mean? What conclusions can you draw from these results? Do any of the fitness reductions prohibit useful activity on the surface of Mars? Which measurement is least affected by the journey?

Now, after 220 days of diminishing fitness, the astronauts have just arrived on Mars. They now have a six-month mission on the planet’s surface (at 4 m s-2 gravity (40 % of the gravity on Earth) followed by a 220 day return journey. When they arrive back on Earth they will be subjected to Earth’s gravitational pull of 10 m s-2 again. Do you think that this mission is likely to succeed?

Next Step

Change the table column headings to % reduction in body mass, % reduction in leg strength, % reduction in cardiac output Then remove the % from the end of each number in the table.

The basic message from the data is that the astronauts will be severely affected by the lack of gravity. They may well be able to function, but imagine such a loss of mass and fitness in your own body. And then think about the demands of moving and working on a new planet in all the gear you would have to wear and jobs you would be expected to do.

As in the first week of this MOOC, talking about asking questions, you need to question the data. Is there anything you think might not be right about the data, or perhaps unrealistic about any of the calculations?

What about problems with other body functions such as brain activity?

The data are taken from some research done way back in the 1970s. Many more studies need to be done to better understand the problems with long-term space flight.