HAND - THE THROWAWAY SATELLITE

Dr Roger Moses, University of Bristol, on 1 November 2002

The Human Activated Nanosatellite Demonstration (HAND) can be launched by hand by Space Shuttle astronauts during a space walk.

Eleven avionics and aeronautics students undertook the design in 1999/2000 and it has since been refined and a prototype built.

It is like a stick, 1.25 m long, weighing 6.5 kg. It is hinged so that it can be folded into a box, which can be carried on to the Space Shuttle as `hand luggage' and stored in a locker.

It could be used, for example, to measure the contamination of the local atmosphere around the International Space Station. Its payload is 0.5 kg. It is stabilised in space by the Earth's gravitational field and has detectors that sense the sun's position and the Earth's horizon, but no thrusters.

It radios its measurements via a circularly-polarised aerial in the `ham' radio frequency of 437.2 MHz as 432 bytes every 4 seconds at 1200 Baud using AFSK coding (Bell 202T). The signal may be picked up by radio amateurs, downloaded into a PC and decoded via software accessible from the Web.

Fourteen lithium batteries in the tube provided power for a six-day life - 150 orbits of the Earth. The boxes containing the electronics are mounted outside the lower tube; on the upper tube is the

propulsion unit, which consists of a carbon dioxide cylinder providing about 15 minutes thrust to push the satellite away from the launch vehicle.

To launch this satellite the astronaut takes it from its storage box, pushes on the antenna, and carries it through the airlock. He unfolds the tube, which automatically turns on the power (with a 20 minutes delay before radio transmission begins) and turns the tap on the propulsion unit to release the carbon dioxide through tiny nozzles 0.1 mm diameter. He then holds the satellite horizontally with the antenna at the `back' and pushes it gently away from him.

It is thrust into a separate orbit from the Space Shuttle and will not collide with it. On the first half of each Earth orbit it moves further away for about 46 minutes and then stays at that distance for the next half orbit. In 6 orbits, approximately 10 hours, it is about 20 km away.

During these manoeuvres it collects data, so some is taken during the `pauses' at about every 4 km. giving a useful collection of information

The batteries run out after six days and the satellite burns up in the atmosphere after a few months.

The satellite has been designed using commercial components that adequately resist the radiation environment for the duration of its life, and the vibration of launch. This kept the cost low and with a `free' launch from the Space Shuttle, which its small size and weight make feasible, it is hoped to get a demonstration in space of the value of such a device within the next year or so.

Dr Moses made acknowledgements to his colleague Mark Hempsell who originated the idea, and to all their students who worked so hard on its realisation.

Donald Lovell