Ken Tapping, November 23, 2011

Earlier this month, six volunteer astronauts stepped out of a spacecraft mock-up in which they had been living for 18 months. The idea was to see how they would stand up to the rigors of a real trip, which involves living in a confined space mostly out of contact with the outside world for a long period of time. You have to be special to handle something like that.

The time it takes to reach even the nearest of planets is a major problem, not only for technology, but also for the crew. In addition to the psychological challenges, a long time in interplanetary space, outside the protection of the Earth’s magnetic field, increases the risk of radiation from solar flares. It would be nice to be able to cut that time back to something more reasonable, like a week. If we had a rocket engine that could produce enough thrust to provide an acceleration equivalent to the Earth’s gravity, running that engine for five days would get us to Mars in about a week. However, currently we do not have rocket engines that can do that. We can either use conventional rocket engines to produce huge thrusts for minutes, burning tons of fuel per second, or use ion engines to produce tiny thrusts almost indefinitely, using small quantities of fuel. Improved ion engines will probably be the solution that opens up the Solar System to exploration, but we have a long way to go before that becomes viable.

Using chemical rockets, which provide big shoves for short periods, is rather like throwing a ball at another ball that a friend has thrown into the air. The aim, timing and the velocity of the throw are all critical. The ball then essentially “falls” to the target. In the case of a spacecraft heading for Mars, there would be additional fuel on board for minor course corrections, but nothing more than that, so getting the timing, velocity and direction right at the beginning of the trip is even more critical.

When we arrive at Mars, we would prefer to orbit round it or land on it rather than smash into it, or perhaps hurtle past it. This means that we will need the means to decelerate, which in turn requires more fuel, more weight, a bigger launcher, higher costs and so on. Therefore we would like to arrive at Mars with a speed not too different from Mars’ speed. We can then use small retrorockets or even Mars’ atmosphere to slow us down. By the time we have designed the space mission to do all of these things, we are back to spending months in transit.

This leads to the argument that we should hold off with manned exploration of the Solar System until we have developed marvelous new propulsion technologies, however they are decades away. Imagine being back in the 17th or 18th Century, sitting in France or Britain, and planning a mission to Canada. You look at those fragile, uncomfortable, sailing ships and decide to hold off until new technologies, like the jet airliner, are developed. How would that have changed history? Consider the scientific discoveries and technical innovations that have come about because of things we are doing in space, which could not have come about by waiting until there are better ways to get there. Imagine finding alien life on Mars!