Rolling Robot Moon Explorer

This is an idea for a light-weight spherical robot, which I propose to send.... to the Moon!

The robot consists of a small, weighty sphere within a larger, inflatable sphere. The small sphere contains all the robot's hardware - it's radio transceiver, power-pack, camera, and so on. The large sphere is simply a transparent beach-ball. I envision it being about six feet in diameter.

The small sphere is connected to the large sphere, and suspended within it, by six strings. These strings form three axes at right angles to each other, so that the small sphere is sitting at a sort of three dimensional cross-roads, with up and down in addition to left, right, front and back. Please feel free to take a moment to visualise this in your mind. Draw a picture if it helps.

Now, it should be obvious that by altering the length of some of the strings, we can move the small sphere around within the big sphere. If we shorten the up string, and lengthen the down string, the small sphere will just move a little closer to the top of the big sphere. If we move the small sphere to the left, the large sphere will be unbalanced, and will roll until the centre of gravity is once again directly over the point where it touches the ground. If we keep on moving the small sphere, by devious manipulation of the strings, the large sphere will keep on rolling. By this means it can be moved in any direction.

How is the length of the string altered? There are certain materials, commonly called artificial muscles, that contract when an electric current is passed through them. and expand again when the current is switched off.

I think that a robot like this would be very useful for lunar or martian exploration because, being inflatable, it would be quite light; it would also be rugged,and would bounce rather than break if it went over small drops; it cannot fall over, since it's sperical; and it's large diameter would allow it to roll easily and quickly over rough terrain. Keeping the camera pointing where you want it is the main problem; I have a suggestion for that if anyone's interested, but this idea is already quite long enough.