Robustness of household battery saves XMM
9 October 1998The managers of XMM, the European Space Agency's X-ray spaceobservatory due to be launched in January 2000, are thanking their luckystars! The robustness of an alkaline household battery has saved themfrom a serious setback.
One of the three mirror-modules of the large 10 metre-tall telescope, whose development has meant overcoming formidable engineering challenges, was this Spring being submitted to a prolonged vacuum test at the ESA-coordinated test facility Centre Spatiale de Lihge (CSL) in Lihge, Belgium.
The modules, at the heart of XMM, are made up of 58 wafer-thin circular mirrors, between 30 and 70cm in diameter and 60 cm long. Delicately nested one inside the other, their manufacture and processing has been undertaken in spotlessly clean conditions. The mirrors will be able to capture an unprecedented quantity of X-rays - more in one hour than on any previous x-ray satellite mission.
During the test-installation for one of the flight-model modules, a torchlight was inadvertently left inside the vacuum chamber. The depressurization (10-6 millibars) lasted an entire week, all measurements on the mirror confirming its extremely high characteristics. Only when the chamber was reopened, was the torch discovered.
All involved in XMM could not believe their good fortune. The torch and the alkaline 4.5 volt battery made by Duracell, which is used in everyday applications, had resisted. No alkaline battery can normally resist such depressurisation. In these extreme conditions, the battery could have released some gas or possibly exploded, deteriorating the mirror-module, rendering it useless.
Both the torch and the battery were examined to evaluate any possible consequences to the mirror module. The plastic torch casing was found to have released some gaseous products, but these had been trapped by a special device in the chamber and did not reach the module. The battery in its plain plastic cover was found to be absolutely intact.
Says Robert Laine, XMM Project Manager: "Considerable effort throughout Europe has enabled us so far to keep this difficult XMM project on track. We strenuously try to avoid such nasty mishaps. But here good luck has also intervened. There9s no doubt losing a mirror module at that stage would have created difficulties, even if we did have a backup. It really was a close one, thank heavens for this robust battery."
Duracell, which manufactures batteries mainly for everyday consumer usage (also in a variety of industrial applications) has expressed its own satisfaction. "Although this type of battery is not designed or tested for such extreme conditions, this further reinforces the top quality of our products", said a company spokesman. "Today this model is widely used in household torches and alarm systems".
Final assembly of the XMM X-ray observatory, the largest scientific satellite ever to be built by Europe, has begun in Immenstaad at the Bodensee in Germany. The different sections of the spacecraft are due to arrive this Autumn at ESTEC, ESA's technical centre in Noordwijk, The Netherlands. After extensive testing, the satellite is due to be shipped in November 1999 to French Guiana for a launch aboard Ariane-5, scheduled for 21 January 2000.
XMM is expected to help astronomers unveil even more mysteries of our universe during its 10 years in orbit. For this duration, the satellite has its own special power supplies, large solar arrays and accumulators, together with on-board propellants. But those on the project will remember that week this Spring when a small alkaline cell saved the day.