ESA tests microgravity with orbiting pail of water

Jack and Jill on notice for retrieval

After Beagle II went missing on Mars, the European Space Agency could be forgiven for scaling down its ambitions. But, no. For its next trick, the ESA is sending a bucket of water into orbit in the beautifully named Sloshsat-FLEVO mission. (FLEVO stands for Facility for Liquid Experimentation and Verification in Orbit.)

It is a theme Jack and Jill would find familiar, but there are several things that mark it out as a touch more exciting than lugging a bucket of water up or down a hill. For a start, the hill is a teeny bit bigger. It is also a fairly big and very high-tech bucket, and the point of the mission is to find out how fluid dynamics change in microgravity.

Sloshsat itself is a small satellite with a 33.5 litre tank which will be filled with water. The whole thing will weigh just 129kg. The tank has 270 sensors that will measure the distribution of the water, and more for tracking the temperature, pressure and fluid velocity in 17 different parts of the tank. And as if that wasn't enough, six accelerometers and three fibre-optic gyroscopes will measure the motion of the whole craft.

Shuttles and satellites often carry quantities of liquid on board, either some kind of propellant, or water for life support. Scientists want to have a better understanding of how the movement of liquid in micro-G affects the handling and attitude control of the craft carrying it. Although there are some computational models for weightless fluid dynamics, none has ever been verified experimentally.

Jan Vreeburg of the Dutch National Aerospace Laboratory (NLR), the principal investigator for Sloshsat, said: "once the satellite is in orbit, scientists will be able to verify and validate existing models."

He explained that the information will also help pilots to use their liquid cargo to their advantage: "Tests will show us how best to manoeuvre a spacecraft to move the liquid in a [fuel] tank near to the exit hole; this has to be done carefully to avoid ‘ingesting’ bubbles. Once thrust is generated by the engine, its action generally keeps the propellant at the exit hole."

Sloshsat is bound for space aboard the Ariane 5 ECA qualification flight, slated for lift-off in October this year. Once the launcher reaches geo-stationary orbit, Sloshsat will be ejected from the craft and the experiments will begin once it has made contact with the ground crew.

The experiments will run for a total of 24 hours over a minimum period of 14 days. ®

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