The hunt for water on Mars is going underground with the long-awaited deployment of a “divining rod” antenna on Europe’s Mars Express spacecraft. A 10-day deployment sequence began on Monday after more than a year of delays.

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument consists of three long fibreglass tubes strung with wires that will bounce radio waves off the planet. Some waves will penetrate the surface – potentially revealing oases of water, in liquid or ice form – lurking a few kilometres underground.

The antenna is stored folded on Mars Express and was scheduled to be deployed in April 2004. But European Space Agency officials postponed the date over concerns the antenna could endanger the mission by smacking into, or getting snagged on, the spacecraft during deployment.

But further Earth-based reconstructions showed the antenna material has a small chance of damaging the craft in the event of a strike. And mission officials say they expect to be able to operate the spacecraft even if a tube gets caught on it.
Whiplash effect

Initial reports of the “whiplash” effect did cause concern, says Fred Jansen, Mars Express’s mission manager. “But we’ve spent a year analysing all this and convincing ourselves any risks that may exist are not relevant to the spacecraft. By now we can be pretty relaxed about it.”

Engineers began the deployment process on Monday with initial checks of the spacecraft and plan to deploy each of the three antenna tubes – or “booms” – in turn. The first, one of two 20 metre-long booms, is scheduled to pop out on 4 May, followed by the second long boom a few days later and the 7-m boom a few days after that.

Each is expected to spring out in just seconds, then settle into a stable position within a few minutes. Engineers will then take about a day to analyse about 11 tests of the spacecraft’s movement to determine whether the boom deployed successfully. And the results of that first boom deployment could make or break the experiment. “If the first antenna is not deployed fully we will never have MARSIS working,” Jacques Louet, head of science projects at ESA, told New Scientist.
Surface topography

But ESA officials say determining the success of the deployment can be tricky, so they may wait until all three booms appear to be operating properly before making any announcements about the experiment. “We will not make the mistake of touting the trumpets when we are not sure,” Jansen told New Scientist.

But if all goes well, the instrument will be tested for three weeks in a commissioning phase before starting to take scientific data in June 2005. At that time, it will be positioned to observe the Red Planet’s north pole. The plains in that region are especially flat which makes it an ideal location to calibrate the radar, which is expected to experience noise from surface topography.

Then, in the first few months of the experiment, the craft will pass over an equatorial region that some scientists suggest harbours a frozen sea just beneath the surface.

by Maggie McKee

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