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Green light for deployment of
ESA’s Mars Express radar
The European Space Agency has given the green light for
the MARSIS radar on board its Mars Express spacecraft to be deployed during
the first week of May. Assuming that this operation is successful, the
radar will finally start the search for subsurface water reservoirs and
studies of the Martian ionosphere.
ESA's decision to deploy MARSIS follows eight months of intensive computer
simulations and technical investigations on both sides of the Atlantic.
These were to assess possible harmful boom configurations during deployment
and to determine any effects on the spacecraft and its scientific instruments.
The three radar booms of MARSIS were initially to have been deployed
in April 2004, towards the end of the Mars Express instrument commissioning
phase. They consist of a pair of 20-metre hollow cylinders, each 2.5 centimetres
in diameter, and a 7-metre boom. No satisfactory ground test of deployment
in flight conditions was possible, so that verification of the booms'
performance had to rely on computer simulation. Just prior to their scheduled
release, improved computer simulations carried out by the manufacturer,
Astro Aerospace (California), revealed the possibility of a whiplash effect
before they locked in their final outstretched positions, so that they
might hit the spacecraft.
Following advice from NASA’s Jet Propulsion Laboratory (JPL), which
contributed the boom system to the Italian-led MARSIS radar instrument,
and the Mars Express science team, ESA put an immediate hold on deployment
until a complete understanding of the dynamics was obtained. JPL led a
comprehensive investigation, including simulations, theoretical studies
and tests on representative booms, the latter to assess potential aging
of the boom material. European experts, from ESA and the former spacecraft
prime contractor, Astrium SAS, France, worked closely with JPL throughout
the entire investigation. An independent engineering review board, composed
of ESA and industry experts, met in January to evaluate the findings and
advise on ‘if and when’ to proceed with deployment.
The ESA review board, at its final meeting on 25 January, recommended
deployment of the MARSIS booms. The rationale for the decision was based
on the results of the analyses, which showed the possible impact scenarios,
the amount of energy involved, the nature of the materials, and the physical
conditions in space. The board concluded that the risk of an impact on
the spacecraft could not be ruled out, but that the impact energy would
be low and the probability of a severe failure was very small.
One credible failure case is that an antenna boom could become blocked
during deployment, either by itself or by the spacecraft. Although means
are available to unblock a deployment, in the worst case MARSIS would
have to be considered partially or completely lost. However, the analyses
have shown that the Mars Express control systems would be able to cope
with such a configuration and minimise the consequences for the other
scientific instruments.
The ESA board recommended planning the deployment for the week beginning
2 May. However, should the remaining preparations proceed faster than
planned, it might be feasible to start deployment during the week beginning
25 April. An early deployment is scientifically desirable, as the evolution
of the Mars Express orbit will allow radar measurements of the most interesting
scientific regions on Mars to start in May 2005.
If, as expected, the deployment is successful, MARSIS will probe the
secrets of Mars’s subsurface at least until 30 November 2005, the
nominal end date of Mars Express operations, and beyond if the mission
is further extended.
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