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Last Updated: Tuesday, 8 February, 2005, 13:45 GMT
Mars probe radar to deploy in May
Mars Express, Esa
How the spacecraft should look if Marsis deploys successfully
A radar on Europe's Mars Express probe to look for water on the Red Planet is set to deploy during the first week of May after a delay of over a year.

The Marsis instrument was due to open out of the spacecraft in April 2004.

But last-minute concerns that its antenna booms could swing back and hit the probe kept the instrument in its box while the issue was investigated.

The radar altimeter will search for water up to 5km (3 miles) beneath the surface of the Red Planet.

Marsis' three booms are folded up onboard Mars Express and spring out when a pyrotechnic mechanism is fired.

Two 20m-long (65ft) hollow fibreglass booms comprise the instrument's primary antenna, while a 7m-long (23ft) boom acts as a receive-only antenna.

Damage fears

Data from mathematical models carried out by the antenna's manufacturer, Californian-based Astro Aerospace early in 2004, suggested the booms might swing back with a greater range of motion than expected after opening.

Fears that they could hit delicate components on the spacecraft prompted mission controllers to call a halt to the deployment, while the Marsis instrument team carried out a comprehensive investigation of the dynamics of the instrument.

Marsis main antenna, Esa
Marsis' main antenna is folded up like a concertina in a box

The investigation concluded there was a likelihood that one of the components could whip back and strike the spacecraft.

A European Space Agency review board met in January to discuss the findings and finally recommended deployment of the booms.

The board concluded that if an impact were to occur, the impact energy would be low and the probability of a severe failure was very small.

However, the board said it was possible an antenna boom could become blocked during deployment, either by itself or by the spacecraft.

The Esa board recommended deployment for the week beginning 2 May. However, should the remaining preparations proceed faster than planned, the agency said, it might be feasible to start deployment the week beginning 25 April.

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (Marsis) will seek evidence of underground water, either frozen or liquid. It is thought the greatest reservoir of retained water on the Red Planet could be found beneath the planet's surface.

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