First Cluster spacecraft is the ultimate 'Clean Machine'
2 August 1999What happens to a spacecraft when it has been assembled and tested, and its launch date is still almost a year away? For Cluster II engineers and technicians, pushing the spacecraft into a dusty cupboard and forgetting about it is not an option.The satellite has to be continually monitored and looked after with tender, loving care.
Now that the first Cluster II spacecraft, flight model (FM) 6, has been completed and finished its exhaustive environmental tests at IABG in Ottobrunn, Germany, it has to be protected from contamination until the time comes for it to be placed on the launch vehicle. Cocooned in its protective transport container, FM6 has been moved into an airlock where it will await shipment back to the Dornier Satellitensysteme site in Friedrichshafen next November.
Cleanliness is vital at all times when handling spacecraft with their sensitive electronics and scientific instruments. Anyone entering the spacecraft integration (assembly) room and test chambers has to enter a large airlock - a middle room which separates the spacecraft chamber from the outside world. There, they put on laboratory coats, elasticated hats and shoe covers before entering the clean room. In the case of the Cluster II spacecraft, they are handled in what are known as Class 100 000 clean rooms. This means that the air they contain has been passed through giant filters so that it is virtually dust free - each cubic foot of air contains up to 100 000 dust particles no larger than 5 thousandths of a millimetre across.
Now that FM6 has been safely installed in its temporary home - a white metal casing 5.4 m long, 3.5 m wide and 3 m high - this remarkable level of cleanliness and environmental control has to be maintained. The first requirement is to keep its temperature at 20 °C, plus or minus two degrees. Condensation and dust must also be prevented from settling on the sensitive surfaces. This is achieved by bathing the spacecraft in a continuous stream of nitrogen gas which is fed into the container. As they empty, the two gas bottles are replaced every four to five days.
This careful treatment will continue over the coming months as FM6 waits to be joined by the other members of the Cluster quartet.