There are two main reasons why scientists study meteors: the potential threat they pose to Earth-orbiting satellites, and the clues they hold about the formation of the planets.

Although they are very small, the tremendous speed of the Leonids means they pack a mighty punch. Apart from knocking a spacecraft off alignment or causing physical damage in the form of an impact crater, such collisions can also generate a cloud of plasma (gas composed of neutral and electrically charged particles) which may cause electrostatic discharges or damage a spacecraft's sensitive electronics.

This threat is not simply theoretical. In 1993, a European Space Agency satellite called Olympus spun out of control, possibly as the result of an electrical disturbance caused by the impact of a particle from the Perseid meteor shower.

The situation back in 1999 was further complicated by the fact that there were more satellites in orbit around the Earth than ever before, all of which posed a tempting target for one of nature's miniature missiles. Despite this spacecraft population explosion, few, if any, satellites were likely to suffer significant problems from meteors, even during a storm. Researchers estimate that the chance of one getting hit by a Leonid meteor was only about 0.1 percent.

This low hit rate was born out by an absence of damage during the 1998 Leonids event. Nevertheless, driven by uncertainty over the future of their high-tech hardware, satellite operators were once again taking precautions to protect their multi-million dollar charges.

"There could be a lot of activity, but we just don't know for sure," commented Walter Flury. "It's better to take precautions now than be sorry later."

The ESA Space Science Department was to provide information on meteor numbers every 15 minutes for the European Space Operations Centre (ESOC) at Darmstadt in Germany. Using this data and radar counts from other sources, ESOC would have been able to issue a security alert, warning spacecraft operators to power down their spacecraft or turn them away from the storm.

One of the largest targets, the NASA-ESA Hubble Space Telescope was to be manoeuvred so that its mirrors faced away from the incoming meteors and its solar arrays are aligned edge on to them. These precautions would continue for several Earth orbits, a duration of seven hours, during the Leonids' predicted peak.

Apart from reducing the exposed area of giant solar arrays, operators could have shut off power to vulnerable electrical components of satellites. In the case of ESA's two European Remote Sensing (ERS) satellites, all of the science instruments were to be switched off during the peak of the Leonid activity. At the same time, their power levels were to be monitored and measures were to be taken to reduce the possibility of electrical discharges and unexpected changes in attitude.

Even spacecraft located some distance from the Earth were at risk. ESA's Solar and Heliospheric Observatory (SOHO) studied the Sun from a vantage point 1.5 million kilometres away, but it, too, was rolling so that its main navigational aid, the star tracker, was pointing out of harm's way.

	ESA scientists seek to study the Leonids
	Meteors, comets and the Rosetta Mission