Final Mars Express science working team meeting before building starts
5 October 1999The scientists who are building instruments for Mars Express met in ESTEC last week for the final science working team meeting before the spacecraft and instrument designs are frozen at the end of the year. Over the next few weeks, each instrument and the spacecraft itself will undergo a "preliminary design review" (PDR), which marks the end of the design phase (Phase B) before construction (Phase C) begins early next year. The meeting was an opportunity for the science team to discuss progress on resolving the few remaining hardware design issues and to move on to the difficult task of planning the mission and science operations in detail.
Rudi Schmidt, Mars Express Project Manager, told the meeting that progress on qualifying the new Fregat upper stage of the Soyuz launcher is going well. Mars Express will be launched by a Fregat/Soyuz in June 2003.
Discussions with the Jet Propulsion Laboratory in Pasadena, California over collaboration between Mars Express and NASA's sample return mission are also underway, he said. The plan is for Mars Express to help retrieve from orbit around the red planet the canister containing Martian rock samples for return to Earth.
Most of the outstanding design issues are a consequence of the very strict limit imposed on payload weight. Some of the scientific teams hoped that a few extra grams could be found for refinements to their instruments. But the "mass margin has further deteriorated," warned Schmidt.
The discussion then turned to orbit planning. At issue is how to divide up the observing time between the instruments throughout the mission's lifetime. This is a complex task because each instrument has its own specific requirements, which may be incompatible with other instruments. For example, some instruments need to take measurements in broad daylight when the spacecraft is at its closest to Mars and can point directly at the surface (nadir pointing); others prefer dusk or dawn for their measurements; and others still need to take measurements at a glancing angle through the Martian atmosphere and not directly at the surface. There is also seasonal variation to be taken into account, with some instruments needing to record data during each season and others being indifferent to seasonal variation. Each of the orbits Mars Express will make during its operation - that's up to 4,500 orbits - will need to be planned individually.
Data retrieval and handling was another topic for lively debate. At issue were how to get data to the PIs (Principal Investigators) as quickly as possible, and how to make it compatible with data being generated by the other Mars missions that will be heading for the red planet at a similar time. "The PIs need to present their precise requirements by January," summed up Schmidt. "It's the software (for mission and science operations) that takes the time and 3 years before launch in 2003 is on the critical side," he said.