NASA: Satellite odds of hitting someone 250-1
WASHINGTON (Reuters) -- U.S. space scientists put
the odds at nearly 1 in 250 that debris from the proposed burn-up of the world's first global satellite telephone mesh would hit someone on Earth.
The prospects of a casualty from the now-averted mass "de-orbiting" of the system known as Iridium were spelled out in a previously secret study by the National Aeronautics and Space Administration.
Last week, the Pentagon, citing its own needs, stepped in to rescue the necklace of 66 cross-linked, low Earth orbiting satellites plus its spares from the ashes of bankruptcy court.
The analysis was done in April as a government task force weighed fears that a hurry-up,
14-month schedule for bringing back cast-off hardware might trigger "widespread anxiety."
"With the information currently available, the probability of someone being struck by surviving Iridium debris is assessed to be 1 in 18,405 per re-entry and 1 in 249 for all 74 spacecraft combined," NASA calculated.
The study was made available to Reuters by the Federal Communications Commission under the Freedom of Information Act. It found four types of Iridium components were likely to survive a flaming reentry into the atmosphere -- 10-kg titanium fuel tanks, 30-kg batteries, 6.3-kg structural brackets and 116-kg electronic control panels.
Motorola Corp., which built, bankrolled and operated the $5.5 billion system, had said it would begin nudging the 560-kg satellites into decaying orbits this month in the absence of a buyer.
In staving off a fiery end for now, the Pentagon signed a $3-million-a-month deal for unlimited air time for up to 20,000 U.S. government users of wireless satellite telephones, including military forces worldwide.
The deal could be worth as much as $252 million if the Defense Department picks up options for service through 2007. It was a condition for court approval of the purchase of Iridium, for $25 million, by an investors group led by Dan Colussy, president of Pan American World Airways from 1978 to 1980.
The Pentagon already owned about 1,600 Iridium satellite phones. The State Department has another 2,000. They have been used by Navy ships at sea, polar teams, special operations forces and combat search-and-rescue missions in areas without U.S. military satellite coverage or when military channels are full.
Iridium "will provide a commercial alternative to our purely military systems," said Dave Oliver, principal deputy under secretary of defense for acquisitions, technology and logistics. The Navy, for example, needed more than twice as much such point-to-point secure communications capability as was available, the Pentagon said.
But a Defense Department briefing paper prepared last month also cited a "strong government desire to avoid having more than 70 satellites de-orbit within 14 months," as had been planned by Motorola.
A U.S. interagency group led by the Justice Department feared that this "might create widespread anxiety and lead to a public outcry for ill-considered government action," the Pentagon paper said.
In its study, NASA said a total mass equal to 300 Iridiums, or more than 168,000 kilos, fell to Earth last year alone in "natural," or untargeted, re-entries from decaying orbits.
Since the Soviets launched the basketball-sized Sputnik I on October 4, 1957, no one has ever been reported hurt by falling debris, though there have been 4,100 natural re-entries, said Nicholas Johnson, NASA program manager for orbital debris and author of the report.
The bottom line, he added in an interview, is that the Iridium satellites would plunge back to Earth if not now, then in about 108 years given their current orbits.
The risk to life and limb, while statistically small, would increase "somewhat" due to projected world population growth in the next 100 years, Johnson concluded.
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