Successful deployment tests for Rosetta
3 July 2002The hectic schedule of ground tests on ESA's comet chaser has continued in recent weeks as engineers at the European Space Research and Technology Centre (ESTEC) in the Netherlands put the Rosetta spacecraft through its paces.
The latest phase of these critical pre-flight tests has involved checks of the various arrays and booms that will be extended from the cube-shaped body of the Rosetta orbiter during its eight-year trek to Comet Wirtanen.
Most critical of all were the deployment tests on the two giant solar wings that will power Rosetta throughout its 10-year mission to deep space and back. These arrays, each 14 metres in length, are covered with more than 22 000 specially developed silicon cells that are designed to operate in conditions of low sunlight and low temperature up to five times the Earth's distance from the Sun.
The 'minus-y' array, located to the left of the dish-shaped high gain antenna, was the first to be unfolded. This was followed a day later by deployment of the 'plus-y' array on the opposite side of the spacecraft.
Held in place by six Kevlar cables - a necessary means for the hold-down of the arrays during launch - each solar array was released after commands sent via the spacecraft activated the deployment sequence. 'Thermal knives' severed the cables in turn by heating them to a temperature of several hundreds of degrees Celsius.
After the sixth cable was cut, the array began to unfold like a giant accordion. Attached to a huge deployment rig specially developed by Dutch Space (formerly Fokker), the five panels in each array were gradually extended to their full length across the clean room. In order to simulate the zero gravity conditions of outer space, the weight of the arrays was supported by a mass compensation device equipped with dozens of springs.
"Both tests went very well and there was a big round of applause when they were successfully completed," said Walter Pinter-Krainer, Principal AIV Systems Engineer for Rosetta.
Confident that their spacecraft's powerhouse would deploy properly after launch, the engineers went on to check out Rosetta's other movable parts. First came a partial deployment of the 2.2-metre-diameter communications dish, when three explosive charges known as pyros were fired to release the antenna from its stowed launch position.
The engineers also had to retreat to the safety of an observation area in the clean room for the firing of more pyros during the deployment of the upper and lower experiment booms on the orbiter. Each two-metre-long boom carries probes and other equipment that will investigate the magnetic field and particle environment around Comet Wirtanen.
The fifth and final deployment test involved the release of a wire antenna to be used by the CONSERT experiment. After another explosive charge was fired, this unusual, H-shaped aerial was gently unfolded, suspended beneath five helium balloons in order to simulate the weightlessness of space. Once again, the trial was completed without a hitch.
"All of the deployment tests were very successful," commented Walter Pinter-Krainer. "These were crucial moments in our test programme and we were very happy to see everything working so well."
Rosetta will be launched in just over six months' time. The Ariane 5 launch from Kourou in French Guiana is scheduled for the night of 12-13 January 2003.