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A sand blaster in space

M D Riti

Particles to the right of them, particles to the left of them, particles in front of them. This is what the 10 Indian satellites up in space can expect to experience at about 0210 hours on Wednesday, November 18.

This is approximately when the earth and the 500 operational satellites in orbit around it will plough through the swarm of dust particles precipitated by the meteoroid shower Comet-55P, also known as Temple-Tuttle.

This year and the next, we are passing close to the comet's orbital path at a time when the comet has recently passed by. As a result, the earth, and our orbiting satellites, are likely to experience a meteoroid shower as we pass through the cloud of debris following closely behind the comet.

This meteoroid storm will be the largest such threat ever yet experienced by the satellites.

A comet is a solid body composed primarily of a combination of ice and cosmic dust. It is usually formed quite far out in the solar system, but sometimes these orbits are disturbed so that the comets swing into the inner solar system. The Tuttle comet debris always causes a meteor shower because its dust enters the orbit of the earth, tumbles down and burns up in the atmosphere.

As the debris seems to be coming from the direction of the constellation Leo, the meteor shower is called a Leonid shower. The word meteor comes from the Greek metéoron, a thing in the air. The flash of light one sees in the sky when a meteoroid enters the atmosphere at high speed and burns up is termed a meteor. A meteorite is any piece of a meteor that survives the trip through the atmosphere and gets to the earth's surface.

According to astrophysicist Rajesh Kochhar, of the Indian Institute of Astrophysics, through the naked eye, constituents of this meteor shower will look like a shooting star or a speck of descending light. If you miss the spectacle this time, it is expected at the same time, same place, same date, next year.

Space scientists T Parimala Rangan, P Kesava Rao, K Nageswara Rao and P Soma of the Indian Space Research Organisation said they hoped that the shower did not affect Indian satellites.

Even before the first satellite, Sputnik, was launched in 1957, it was clear that meteors could hit satellites and precautions were taken. The threat depended on the combined effect of several factors like the relative velocity of the meteoroids, the vulnerability of satellite subsystems and the sensitivity of instruments on board.

Communication satellites like the five INSAT communication satellites in geo-stationary orbit have several microprocessors on board. The surface area of these satellites exposed to the storm is small.

Available data indicates that these five satellites, as well as the four remote sensing satellites, in polar orbit and one scientific SROSS in orbit will endure the Leonid storm despite the particle speed of 70 km/sec.

So the satellites will be "sand blasted" by very small particles travelling at 100 times the speed of a bullet. At these speeds, even a tiny particle can cause damage. While major holes and physical damage to solar panels and structures are unlikely since the meteor storm is coming in parallel to the solar panels, impact of small particles can induce shorting and failure in sensitive electronic components.

Optical surfaces and mirrors may be pitted, degrading the performance of critical sensors.

Senior spacecraft controllers and sub-system specialists will all be at hand at the spacecraft control centre during the storm to take measures to minimise damage.

According to ex-chairman U R Rao, ISRO is likely to put its satellites into the 'safe mode,' which involves shutting down high voltage instruments and tilting the solar panels so that optical surfaces are less likely to be hit.

During the last major meteoroid storm, in the mid-sixties, there were no operational Indian satellites. This year, though, there are operational satellites performing critical functions like providing uplinks for communication and research.

In 1993, the weaker Perseid meteoroid shower put the European Space Agency's Olympus satellite out of commission. And the crucial nature of satellite function can be gauged by the fact that when the Galaxy IV satellite ran into trouble, up to 90 per cent of the 45 million pagers used in the United States went out of service.

Indian scientists, of course, provide balmy assurance that the storm will benignly go its way, leaving the satellites unharmed. But that doesn't stop them from crossing their scientific fingers.

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