Tim Furniss/LONDON

NASA says that the partially unfurled solar panel on the Mars Global Surveyor (MSG) spacecraft, launched on 7 November, will "-not significantly impair" the craft's ability to aerobrake into its orbit around the planet or "-affect its performance" during the cruise and science elements of the mission.

The optimism surrounding the MSG comes as the exploration of the Red Planet received another boost with the successful launch of the Mars Pathfinder, which is planned to explore the planet's surface. Despite earlier delays, caused by bad weather and a technical fault, the launch finally took place on 4 December.

The MSG's onboard engine was fired for 43s on 22 November to place it en route for Mars, which it will reach in September 1997. One of the Surveyor's two 3.5m-long gallium-arsenide/silicon solar-cell arrays has been successfully deployed, but the other is tilted 20.5¹ away from the intended position.

It appears that the "damper arm", which is part of the panel's deployment mechanism, may have broken during the panel's initial rotation. It is believed that a piece of metal has become trapped. Engineers consider that the obstruction may be cleared by gently rotating the panel.

Concerns focus on how the errant solar panel will be affected by aero-braking manoeuvres, to be conducted after the MSG enters its initial orbit - the first time that such a manoeuvre will have been tried operationally. Aerobraking will use atmospheric drag against the craft, especially its extended wing-like solar panels, to reduce speed and gradually alter the orbit.

The aerobraking could, however, fold the errant panel up, as well as expose the solar cell-face to the atmospheric drag. NASA hopes to be able to control the tilt of the array in such a way that it will not be adversely affected, or show its cell-face to the path of travel, but will be effective to aid the aerobrake manoeuvres.

The other concern centres on the panel's ability to function properly to provide the electricity required for the operational science phase of the mission - which is flying six of the eight instruments flown on the ill-fated Mars Observer, lost in 1993.

The MSG problem was also followed by the total loss of the Russian Mars '96 spacecraft on 16 November. This means that the launch of the latest Mars Pathfinder is critical. The spacecraft is due to reach Mars on 4 July.

Source: Flight International