Rosetta STM on the Multishaker at ESTEC. Photo: ESA

Environmental tests on the Structural Thermal Model (STM) of the Rosetta spacecraft are back in full swing after the long break for Christmas and Millennium celebrations. The latest endurance trial, known as a Sine (or Sinusoidal) Test, was successfully completed on January 31 in the giant check-out room at the European Space Research and Technology Centre (ESTEC) in the Netherlands.

"We are delighted with the progress made so far," said Rosetta Project manager, Bruno Gardini. "We have a very tight launch schedule to meet, so every successful test is a bonus."

The completed Sine Test is the latest in a series of vibration tests designed to search for potential problems that could be encountered during an Ariane 5 launch. The STM has already passed its Acoustic Tests, which reproduce the spacecraft vibrations caused by the tremendous noise generated during lift-off. Now, the STM has been subjected to another session on the Multishaker platform in order to simulate the effects of sudden acceleration as the rocket leaves the launch pad.

The Multishaker allows technicians to move the 3 tonne spacecraft at different speeds in three directions. At its fastest, the platform can reproduce acceleration forces equal to three times normal gravity. For a few minutes, this motion can cause the STM to weigh three times as much as it would prior to lift-off. Sensors measure these forces at different places on the body of the spacecraft.

By shaking the STM in this way, engineers can find out if the spacecraft is behaving in line with their predictions. If the design specifications are exceeded, they know that something is wrong and further checks will have to be made.

The next major step will be the Thermal - Balance tests at the end of February.