Structural Thermal Model (STM) of the Rosetta spacecraft in the ESA/ESTEC test centre. Photo: ESA

The test programme of the Rosetta Structural Thermal Model (STM) continues to go with a bang. At the end of last week, the STM underwent a series of shocking experiences in order to check its ability to survive the rough treatment that will be meted out during launch. This was followed Monday by a deployment test of a giant solar array.

The first of the STM's trials to be carried out last week was the so-called 'shogun' test. This was a joint operation by technicians from CNES, Arianespace, and ESA's European Space Research and Technology Centre (ESTEC) in The Netherlands. (Arianespace operates the Ariane 5 launch vehicle that will send Rosetta on its way to Comet Wirtanen in 2003.)

The shogun test was a simulation of the shock transmitted to the spacecraft when its protective fairing separates from the rocket's upper stage. Using a copy of the actual spacecraft adapter which will attach Rosetta to the upper stage, a set of pyrotechnic devices was attached around the underside of the adapter. With all staff withdrawn to safe positions behind protective glass, these explosive charges were set off instantaneously to rupture the aluminium plate on the adapter.

"It only lasted a millisecond, but it went off with quite a loud crack," commented Rosetta Assembly and Integration Verification Engineer Alan Moseley.

The next day, the STM was subjected to a 'clamp band separation test'. The clamp band is a metal strip that attaches the launch adapter to the spacecraft. After checking that the clamp band fitted properly, technicians once again had to discover whether its explosive separation would damage Rosetta. This time, two pyrotechnic charges were set off. As the band was split in two, both sections were pushed away from the spacecraft interface by springs and caught by special 'catcher' brackets.

"Although the tests themselves were extremely short, the shocks imparted to the STM were quite severe. The detailed analysis of the impact on the spacecraft's units will data take several days, to come to a realistic conclusion," said J. C. Salvignol, Rosetta mechanical systems engineer.

An artist's concept of the Rosetta comet probe. Photo: ESA

"I'm pleased to say that the STM passed both tests without any damage," added his colleague, Jacques Candé.

Monday saw the deployment test for one of Rosetta's 16 metre-long solar arrays. These enormous arrays are needed because Rosetta will be operating at five times the Earth's distance from the Sun, where levels of sunlight are only 4 percent those on our planet. Rosetta will be making history as the first spacecraft ever to use solar arrays to generate electrical power during a deep space mission beyond the asteroid belt.

The check-out began when six 'thermal knives' were used to melt through the attachments which held the array to the side of the spacecraft. Using a special jig, springs on the giant panel caused it to slowly open out to its full, impressive length. After 3 minutes 47 seconds, the array was fully extended, allowing engineers to check its alignment and condition.

Later in the day, yet another shock test took place. This time, the dish-shaped high-gain antenna was shaken by three pyrotechnic devices which exploded one after another. During a subsequent performance check of the antenna motor, the dish was successfully moved more than 40 degrees from its fixed position.

"Once again, everything was nominal," declared a highly satisfied Alan Moseley.