The European Space Agency’s Rosetta space probe has been travelling in the solar system since 2004, but is still far from its destination. Not until 2014 will it reach the comet 67P/Churyumov-Gerasimenko and be the first probe to study a comet at close quarters. On its way, Rosetta is studying some of the asteroids it passes on its journey of roughly seven billion kilometres.
In 2008 Rosetta flew past the asteroid Stein and in July this year encountered the asteroid Lutetia. As asteroids are only very rarely as densely packed as Star Wars films would have us believe, the flybys have to be planned precisely to the minute. This would not be possible without the reliable engines from Lampoldshausen; these function perfectly in the freezing cold temperature of -130°C and keep the spacecraft – designed and built by Airbus Defence and Space in Friedrichshafen – on course.
Rosetta – twelve hi-tech cubic metres
24 small engines have the job of accelerating, decelerating and stabilising Rosetta’s position in space. They each generate ten newtons (10N) of thrust. This is equivalent to the force required here on Earth to hold a bag containing ten apples. At launch, Rosetta carried 1,650 kilogrammes of fuel in its two tanks – representing about half of the launch weight – to supply the engines with enough fuel on the long journey through space.
10N engines have been built in small series production at Lampoldshausen for more than 20 years. They have been deployed successfully not only on numerous communication satellites, but also several times on interplanetary missions – including Mars Express and Venus Express – as well as on Galileo. Although more than 2,000 of these small engines have been built at Lampoldshausen, this work still represents a major production engineering challenge – one ably tackled by the highly motivated group led by Joachim Barthelmä, who together make up a production team that, time after time, succeeds in constructing these dependable, high-precision engines.
On completion, all rocket engines have to undergo ‘hot run’ vacuum acceptance tests, in the test area on site, because it is vitally important to precision test their functionality before they are installed on the spacecraft. The demands placed on these small engines are extreme – not only must they be able to deliver very short bursts lasting just a few milliseconds, but they also have to prove themselves reliable in continuous operation over several hours. This is certainly reflected in the costs involved: even though the weight of one of these engines only amounts to 500g, its price is almost equivalent to that of a high-power sports car. However, the crucial difference is that a sports car can be taken to a garage at anytime, but the Rosetta engines have to get through the journey in space without any maintenance or repairs.
On 10 July at 15:44:57 hrs Universal Time (UT), the probe sped past Lutetia at a distance of 3,160 kilometres, travelling at the tremendous speed of 15 kilometres per second. As it did so, the probe had to be turned to the right position for the cameras to get a good view. The small engines from Lampoldshausen did their work as precisely as ever and the entire manoeuvre went perfectly.
Rosetta: specialist in flyby mass determination
Scientists will receive reliable data on the shape and therefore the volume of the asteroid by means of the probe’s onboard camera. Mass and volume enable the mean density to be calculated and therefore to distinguish between a C-type asteroid made of porous rock and an M-type of solid rock containing metal. The data is currently being downloaded and analysed, which can take a few weeks. And while we anxiously await the final analysis of the data we wish Rosetta all the best on her continuing journey to comet 67P/Churyumov-Gerasimenko.