Rosetta Lander springs into action
09 May 2000A major landmark in the Rosetta development programme will be reached this week when the final tests on the Structural Thermal Model (STM) are completed.
Since last year, the 3 tonne STM has been subjected to an extensive series of tests at the European Space Research and Technology Centre (ESTEC) in The Netherlands, in order to ensure that the spacecraft can survive the rigours of interplanetary space travel. The final sequence of checks began on 2 May when an emergency separation test was conducted on the Rosetta Lander.
Under normal flight conditions, the lander will be deployed from the orbiter by a motor-driven release system. This sophisticated piece of equipment allows mission planners to select the appropriate release speed (between 5 and 50 cm/sec), in order to ensure that the lander touches down in the chosen spot on the surface of the Comet Wirtanen's solid nucleus.
However, spacecraft designers always prefer to have a back-up in case something goes wrong. In this case, the Rosetta orbiter carries a simple spring mechanism which is capable of pushing the lander away from the orbiter. During the recent test at ESTEC, engineers successfully activated a small pyro (explosive) cable cutter which activated this spring release. In order to prevent the lander crashing to the ground, and to simulate the microgravity conditions of outer space, the released lander was counterbalanced by using weights attached to a pulley.
The following day, engineers deployed the one-metre-long antenna to be used by the orbiter's CONSERT radar sounding experiment. The main objective of this test was to ensure that the antenna unfolds freely without damaging the multi-layer insulation on the spacecraft. When in its operational position, the CONSERT antenna resembles a rod which is bent at a 90 degree angle as it protrudes from the side of the spacecraft. While Rosetta is orbiting the comet, this antenna will emit pulses of radio waves in order to probe the interior of the icy nucleus.
The final stage of the STM test sequence is to verify that none of the sensors on the orbiter have shifted from their correct positions during the prolonged programme of thermal and mechanical checks. Once this is completed, the STM will be transported to the Turin plant of Alenia Aerospazio, where it will be stripped down and refurbished for use as the Rosetta Electrical Qualification Model (EQM).