They're streaks of lights in the sky which make for a pleasant sight. But meteor showers are known to damage manmade satellites in their orbits. Bearing this in mind, Indian space agency Isro has braced itself for the Leonid meteor showers expected to peak on Sunday, 18 November, during their ongoing passage through Earth's orbit.

The government agency has taken steps to ensure its satellites' wellbeing when the showers reach their zenith between 2.30 PM and 3.30 PM and again between 10.30 PM and 11.30 PM on the weekend. Isro will temporarily suspend camera operations and the camera steering mechanism for its remote sensing satellites (IRS) which help meteorologists predict weather through satellite images. Solid state recorders will be off for about 10 hours.

It is taking precautions for its communications and broadcast satellites as well. The solar arrays of the Insat series of satellites will be positioned so that they present minimum surface area to the showers. The Gyros on board these birds will be kept continuously on to detect any disturbances due to impact. In case of any disturbances, the satellites will be brought back to their proper orientation using reaction control thrusters on board. ISRO has also kept designers of the various satellite subsystems on alert to help in taking contingency measures in case of any incident.

Leonid meteor showers are a result of the dust and debris left behind by the comet Tempel-Tuttle, which passes through the inner solar system every 33.25 years. The debris is burned off the comet's nucleus by a wind of charged particles that stream outward from the Sun. Most meteoroids are no larger than a grain of sand, that vaporize when they zoom through Earth's atmosphere at 260 times the speed of sound.

While the visual spectacle is a treat, in the form of 'shooting stars' lit brilliantly by the constellation Leo, they also have the potential to create havoc to satellites by pitting solar cells, optical surfaces and mirrors. Equipment could get damaged and thus send satellites spinning out of their geostationary orbits. The satellite's microprocessors are sensitive to the meteoroids. The plasma cloud can cause elcetrical circuits and short fuses or even ruptures. Even the momentum of the impact can throw a satellite off course.

IRS satellites are in the near earth polar orbits. According to the Isro, the probability of meteors hitting the IRS satellites is about 0.013 per cent and for INSATs, it is around 0.035 per cent. ISRO currently has five satellites in operation (IRS-1C, IRS-1D, IRS-P3, IRS-P4 and TES) in the Polar sun-synchronous orbits and five satellites (INSAT-2C, INSAT-2DT, INSAT-2E, INSAT-3B and GSAT-1) in the geo-stationary orbit.

The last time Leonids produced what astronomers call a storm was in 1966 when only a handful of satellites orbited Earth. This time round, hundreds of satellites are at risk, providing services ranging from pagers and television to weather forecasts. Predictions for the number of meteors per hour during this year's peak on 18 November range from 1,400 to 15,000, with Asia slated to see around 8000 per hour.

In 1999, the last year that a strong Leonids meteor shower was predicted, satellite operators effectively put many of their spacecraft into hibernation (turning off or minimizing data collecting and sending operations) while still maintaining critical services here on Earth.

NASA Space Flight Center's Bill Cooke has told media that the odds of a satellite being damaged during the peak hours of the Leonid meteor shower are between 1 in 10,000 and 1 in 1,000. Cooke has indicated that at least one satellite could be significantly damaged during the entire storm which spans several days. The risk this year is five to 10 times greater than in 1999, Cooke said.