Satellites prepare for meteor storm
- — 06 November, 1998 21:49
A mid-November meteor storm at its strongest since 1966 probably will not short-circuit telecommunications satellites, but many satellites will be reoriented just in case.
On November 17 and 18, the Earth's orbit around the Sun will carry us through the Leonid meteor shower, so named because it appears to come from the constellation Leo. Most years we pass through a lightly populated part of the 16-million-kilometre-wide shower which trails Comet Tempel-Tuttle, but this year we will plow through a dense section of particles, which sloughed off from the comet when it passed close to the Sun in February.
Meteors are sand-grain-sized particles, but because they travel so fast (up to 71 kilometres per second), when they collide with something an electrically charged plasma cloud is formed which could cripple a satellite by short circuiting it.
"That is the biggest concern for these missions, that a plasma cloud will be generated and that will cause some electrical disturbance," said Phil Liebrecht, associate director for networks and mission services at Goddard Space Flight Center, a NASA facility.
But the risk is small. In 1966, when Leonid last peaked, there were still several miles in between the sand-sized particles of the storm, according to Geoff Chester, public affairs officer at the US Naval Observatory.
Within an area of a couple of miles wide, the odds of a satellite being hit are the same as "the odds of a pea hitting something the size of the house," Chester said.
Those odds were good enough for PanAmSat, which this week launched a Pacific Ocean Region satellite from Kazakhstan, bringing its spacecraft fleet up to 18.
Not all satellites face the same risk, and PanAmSat apparently thought the risk did not warrant waiting. Low-earth-orbit (LEO) satellites, which rotate the earth in 90 or 100-minute cycles close to the earth, will be shielded by the earth for around half of the time, according to the Naval Observatory's Chester. Geo-stationary (GEO) satellites are too far from earth to use it as a shield and will be at risk the whole time, as will the handful of L1 heavy duty scientific satellites, which are farthest out of all, he said.
Risk models vary, but LEOs and GEOs probably face a risk on the order of a hundredth of a percent, according to NASA's Liebrecht. The risk to L1 satellites is estimated at between 1 and 5 per cent, he said.
In fact, LEOs are much more at risk, around the clock, of being hit by one of 8000 human-made objects larger than a soccer ball in orbit around them, including spent rocket boosters and trashbags from the Mir spacecraft, according to Chester.
"The probability is greater that a LEO will be incapacitated by a piece of space junk," Chester said.
Still, many commercial and scientific satellites will be rotated so that their vulnerable parts, including antennas and solar panels, are turned away from Leonid.
At NASA's Goddard Space Flight Center, 60 per cent of the 22 satellites will be reoriented so that the solar panels which power the satellite's batteries are on edge, minimising the surface that is exposed to the storm, Liebrecht said.
Loral Space & Communications Ltd., which has a fleet of 14 broadcast and communications satellites, will also turn solar panels on many of its satellites, according to a Loral spokesman. Loral has also reviewed its contingency plans for reestablishing service for its customers in case anything happens, he said.
"Typically I don't think anything is done annually on Leonid (but) the number of meteorites that's going to hit (this year) is roughly equivalent to that from a whole year," the spokesman said.
Realigning the satellites will not interrupt service for commercial customers. For scientists, however, realignment can extract a heavy toll. Science satellites gather data, and in most cases realignment will interrupt that function, Liebrecht of NASA said. Gaps in data are especially problematic when measurements are cumulative, and one NASA scientist decided that maintaining continuity of data was worth the risk. His satellite is a LEO and is therefore at the least risk of colliding with a meteor, but the majority of scientists chose to reorient, he said.
"Most of the missions, the scientists obviously want to maintain the instrument for the long term ... and so they definitely (opt) to lose the data for a few hours," Liebrecht said.
Though Leonid is unlikely to affect service for telecommunications customers, it may afford quite a show, especially for people in Asia/Pacific.
Users of radio and television may experience a boosting of these appliance's capabilities, according to Chester of the Naval Observatory. There may be enough meteors to affect radio waves and let people tune in TV and radio stations which are ordinarily outside of their range, he said.
More information about Leonid, including personal viewing strategies, can be found at http://www.serve.com/meteors, http://medicine.wustl.edu/~kronkg/meteor_shower.html, or http://www.skypub.com/