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15-Apr-2014

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N° 50–1993: Hubble gets new ESA-supplied solar arrays

6 December 1993

The Hubble Space Telescope was fitted with a new set of solar arrays after a 6.5-hour spacewalk by Tom Akers and Kathy Thornton. These unique power-generating wings, supplied by the European Space Agency, will power the telescope for at least the remainder of the decade.

Derek Eaton, ESA project manager, was overjoyed with the success of the day's spacewalk.

"To build two such massive arrays some years apart to such tight tolerances and have one replace the other with so few problems is a tribute to the design and manufacturing skills of ESA and British Aerospace, the prime contractor for the arrays", he said. "The skill of Kathy and Tom contributed greatly to this success".

The astronauts began their spacewalk at 09h30 p.m. CST (04h30 a.m. CET, Monday). Their first task was to jettison the troublesome solar array that failed to retract yesterday. Perched on the end of the shuttle's robot arm, 7.5 metres above the cargo bay, Thornton carefully released the array. ESA astronaut Claude Nicollier then pulled the arm away from the free-floating panel and mission commander Dick Covey fired the shuttle's thrusters to back away.
Endeavour and the discarded array are moving apart at a rate of 18.5 kilometres each 90-minute orbit of the Earth. The array is expected to burn up in the Earth's atmosphere harmlessly within a year or so.

The astronauts had no problems installing the new arrays and stowing the left-hand wing in the cargo bay for the return to Earth. The new arrays will remain rolled-up against the side of the telescope until the fifth spacewalk on Wednesday/Thursday. The telescope itself will be deployed on Saturday.

The telescope's first set of arrays flexed in orbit because of the sudden swing in temperature as the craft moved in and out of sunlight. The movement, or "jitter", affected the telescope's pointing system and disrupted observations at times. The Space Telescope Operations Control Centre largely compensated for the problem with special software but this occupied a large amount of computer memory.

The new arrays incorporate three major changes to eliminate the problem. The metal bi-stem booms, which support the solar blankets, is protected from extreme temperature changes by a concertina-style sleeve made up of one thousand laser- welded discs of aluminium coated Teflon. Complicated pulley systems for keeping the blankets under tension are replaced by springs and a brake is added to the drum at the centre of each wing to stop any movement. The addition of large, white hand rails helped the astronauts move the arrays through space.

The new solar arrays measure 12 by 2.8 metres each (in total they cover about the same surface area as a medium sized apartment. The 25,000 solar cells in each array generate a total of 4.5 kW of electricity.

Before returning to the airlock Thorton and Akers had time to install foot restraints in preparation for the replacement of the Wide Field/Planetary Camera tomorrow.


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