Satellites braced for space 'hurricane'

DETAILS EMERGED yesterday of safety measures being taken to protect hundreds of orbiting satellites from the fiercest meteor storm in three decades.

The Leonid meteor storm on 17 November - the space equivalent of a hurricane - will send thousands of tiny particles hurtling towards the atmosphere at 50 miles per second, threatening to sandblast any spacecraft in their way.

There is a small but real possibility of physical damage, electrical short-circuits and computer malfunctions severe enough to knock out a satellite.

Nasa scientists at the Goddard Space Flight Centre inMaryland, USA, are taking special precautions to protect a fleet of 22 highly sensitive scientific satellites.

They include the Hubble Space Telescope, which will be manoeuvred so that its mirrors face away from the storm and its solar panels meet the meteors edge-on.

It will stay in this position for 10 hours, but remain operational, observing distant galaxies from its new viewpoint.

Other satellites will also be manoeuvred so their most sensitive instruments are not in the direct line of fire.

Some will have instruments switched off to protect them from short-circuits or be shut down.

They include the Solar Heliospheric Observatory and another satellite called the American Advanced Composition Explorer, which are both in a distant location, a million miles away between the Sun and the Earth. This places them nearer the main stream of meteors and in greater danger than other Earth- orbiting satellites.

Similar safety measures are being taken by the European Space Agency's (ESA) operations centre.

Damage to satellites by meteors is very rare. In the past 40 years, only one spacecraft, the ESA's Olympus communication satellite, is known to have been disabled by a meteor strike, this time from the Perseid shower.

However, there are now more than 500 spacecraft orbiting the Earth, more than 10 times as many as there were in the mid-1960s.

The veteran astronaut John Glenn's shuttle mission was deliberately timed to avoid the Leonid meteors, and there are plans for the two crewmen of the Mir space station to move into a Soyuz lifeboat, if necessary, at the peak of the storm.

Meteors are mostly no bigger than small grains of sand, but can nevertheless erode sensitive outer surfaces such as thermal blankets, mirrors and solar cells.

One of the biggest hazards is the particles vaporising on impact to create a cloud of electrically charged gas. This can produce a chain reaction culminating in a massive short-circuit.

Professor Tony McDonnell, of the Unit for Space Sciences and Astrophysics at the University of Kent at Canterbury, said: "These microparticles could penetrate a fairly weak spacecraft skin. However, the most likely form of damage is to vulnerable power systems. Perhaps a handful of satellites could have unusual electrical anomalies."

The biggest uncertainty was the hourly rate at which the meteors arrived, said Professor McDonnell. "If this reaches 150,000 per hour, there will be all sorts of damage, but there may only be 1,800 an hour."

Philip Liebrecht, associate director for Networks and Mission Services at the Goddard Space Flight Centre, said: "Each spacecraft has an operating plan that balances the risk of taking specific defensive measures against the risk of taking no action. We've had independent review teams assess our plans, and I think we are doing everything prudent and practicable to ensure the safety of our spacecraft."

The Leonid meteors, debris shed by the comet Tempel-Tuttle, visit every year, but once every 33 years they mark their arrival with a storm. This is when the comet makes its closest approach to the Sun.

Material boiling off the comet, a dirty ball of rock and ice, litters its path in the form of meteors.