Wednesday, 30 April 2014

Spaceflight via Russian Trampolines

You can't get off Earth using a trampoline, but you might just be able to escape Mars biggest moon, Phobos. Image: NASA
Since the Space Shuttle was retired in 2011, NASA has had to rely on Russian Soyuz rockets to get its astronauts into space. This hasn't come cheap, costing $70million a seat. But they've had to grin and bear it, as the next American spacecraft capable of carrying humans (probably the SpaceX Dragon) wont be ready until at least 2017.

As you may have noticed in the news, US-Russian relationships are rather strained at the moment, and the Ukraine sanctions are beginning to affect the Russian space industry. Yesterday Dmitry Rogozin, the Russian deputy prime minister, tweeted that:

“After analysing the sanctions against our space industry, I suggest to the USA to bring their astronauts to the International Space Station using a trampoline,”

Now this could have lead to a very interesting long blog post about the politics of space exploration, but there's a far more important question the ask: Could you actually get into space using a trampoline?

The key factor in getting off a planet is the escape velocity, how fast you need to go to escape a given object's gravity. For Earth this value is about 11.2 kilometres per second, which is fairly fast.

How fast can you go using a trampoline?

The Guinness Book of World Records lists the highest height achieved by a team on a trampoline as 6.73 meters, using two people to provide the bounce for a third. With a bit of maths, that means that the speed they were going as they left the trampoline was about 11.5 meters per second.

Not fast enough for Earth, but the Solar System is full of smaller objects. Which is the largest with an escape velocity of less than 11.5 meters per second?

It turns out to be Phobos, one of the moons of Mars, which comes in with an escape velocity of 11.4 metres per second. Its a small world, a lumpy rock with an average diameter of eleven kilometres and a mass nearly two billion times smaller than that of the Earth.

This might be a practical question, as Phobos has been mentioned as a possible destination for Mars-bound astronauts. It takes much less fuel to get there than to land on Mars, and could be used as a base to remotely control Mars rovers without the annoying time delay caused by the signals having to go from Mars to Earth and back.  

So if in 20 years time you're an adventurer stranded on a desolate Martian moon, make sure you've got a trampoline.

Note: Discussions over lunch resulted in the decision that the speed you could jump on the trampoline wouldn't be affected by the lower gravity, as the key factor is the energy you're  producing in your legs. You'd jump higher, but accelerate less slowly down towards the trampoline, affects which would cancel out. If you can do some maths showing this is wrong, please let me know. 

New blogs will be posted on Twitter, as always.


  1. Even I was on the lookout for the same issue and just landed on this classic post. this has made a room in my heart. Rob Stone