Defunct satellites could start reaching Earth this month

There are 88 of them, weighing more than half a ton each, and they could start falling toward Earth this month â€“ chunks of them splashing down in oceans and outbacks.<br><br>They're not killer asteroids,

Saturday, September 2nd 2000, 12:00 am

By: News On 6

There are 88 of them, weighing more than half a ton each, and they could start falling toward Earth this month â€“ chunks of them splashing down in oceans and outbacks.

They're not killer asteroids, but $4 billion worth of Iridium global communication satellites launched within the last five years â€“ but for which no one in the world can seem to find a use. Motorola Inc., the system's largest backer, recently gave notice to a U.S. bankruptcy court and to the Clinton administration that it is set to begin the process of controlled "deorbiting" and destruction of the network, which failed to attract many customers to its telephone services.

The system orbiting 485 miles high costs several million dollars a month to maintain, according to the company.

Motorola officials have declined to discuss their deorbiting plan until they complete what spokesman Scott Wyman called "voluntary and courtesy reviews" with government agencies. There are also continuing last-ditch bids to save the network.

If the 53 tons of Iridium castoffs find no savior, they will join a rain of junk that has been peppering Earth throughout much of the space age. Officials say the Iridium hardware is within government guidelines for acceptable risk: less than a one in 10,000 chance of hitting a person on the ground.

But the risk is not zero, experts note. Not all of the Iridium components will burn up during the fiery re-entry through the atmosphere. The largest hardware likely to survive the trauma and make it to Earth's surface is the 2-by-3-foot titanium fuel tank.

Most of the surviving chunks are expected to plunge into one of the oceans that cover two-thirds of the planet. Those that strike land have a good chance of dropping into remote, uninhabited areas. Officials point out that no one in the space age has yet been harmed by a piece of incoming space junk.

"It's still a big world," said a government orbital debris expert. "And even 6 billion people don't cover much of it."

He said the Iridium fuel tanks "are not atypical" in size and mass for spacecraft debris. Delta rocket stages, he added, re-enter regularly with much larger stainless steel tanks, one of which landed outside Austin in January 1997, with no ill effect. In space, astronauts have maneuvered the space shuttle several times to avoid a collision with a piece of junk hardware, and the new international space station was diverted to avoid a head-on crash in October.

Although there are larger satellite constellations aloft than the Iridium system, he said, no one has decommissioned all their craft to re-enter the atmosphere in such numbers.

U.S. policy calls for satellite makers to remove defunct objects from orbit within 25 years to minimize the growing accumulation of old rocket bodies and other detritus. The U.S. Space Command is tracking 9,000 orbiting manufactured objects 4 inches across or larger. By controlling the re-entry and timing the final thruster firings properly, experts say, the ground team can maximize the chances that the hardware will hit empty ocean.

"There are controlled robotic ballistic re-entries that are done with a high degree of accuracy," said one specialist.

Participants in the seven-month government review of Motorola's deorbit plan include the White House science office, the Justice Department, NASA, the Federal Aviation Administration, the Federal Communications Commission and security and economic officials.

The electronically linked network of Iridium satellites, operated by the now-bankrupt Iridium LLC, was designed to permit any type of telephone transmission â€“ voice, paging, fax or data â€“ to reach its destination anywhere on the planet, using either a cell phone or land line.

The system made its commercial debut in 1998 but suffered from marketing mistakes, technical problems, bulky telephones and competition from proliferating land-based cell phone networks.