Mars Express passes milestone with flying colours
10 August 2001As space engineers and scientists met last month for a final review of the Mars Express spacecraft design, the spacecraft itself was taking shape at the premises of Alenia, Torino, Italy. "Normally, we would have the critical design review (CDR) after tests of the spacecraft structural model (SM tests) have been completed. But because of the tight schedule for Mars Express, most of the review had to be completed early. We've done all the reviewing we can. A few items have to wait until after the SM tests," says Rudi Schmidt, Mars Express Project Manager.
The CDR was a lengthy process involving all contributors to the Mars Express spacecraft. After receiving reports from the various industrial teams, a group of 63 engineers met at the offices of Astrium, Toulouse, the prime contractor, for a "co-location" meeting lasting one week at which all reports were scrutinised and awkward questions asked. The co-location report then went before a final board meeting, attended by ESA's Director of Science, the Inspector General and other senior staff outside the Mars Express project team, for final scrutiny. "The CDR went well. The final board made some recommendations, but these were largely what we had expected," says Schmidt.
Meanwhile, in mid-July the Mars Express flight model was delivered to Alenia from Astrium, Stevenage, UK where the propulsion system (engines and fuel tanks) had been fitted (see earlier story). Alenia is installing mass dummies of all instruments and sub-systems into the flight model. Later this month, the Mars Express trailer will transport flight model plus mass dummies to Intespace, Toulouse for four weeks of mechanical tests. These will involve filling the oxidiser and fuel tanks with water and IPA (iso-propyl alcohol), as fuel substitutes, so that the mass of the spacecraft and its centre of gravity can be simulated accurately. The fuel tanks have already been subjected to stringent 'over pressure' tests at Astrium Stevenage, where they were filled with fuel substitute and tested under very high pressure to ensure they could withstand unexpected increases in fuel pressure.
By mid October, all mechanical tests should be completed and the spacecraft will be transported back to Alenia, Torino where the mass dummies will be removed and the flight models installed. "This process is expected to take about six months, but by May next year, the spacecraft that will actually fly to Mars should be ready for the flight model tests," says Schmidt.
In parallel with the spacecraft tests, testing is still continuing on the electrical and functional verification system test bench at Toulouse. "The electrical tests are getting more complex, now that all the sub-systems have to be integrated. These tests are expected to continue at a cracking pace," says Schmidt.