Debris from destroyed spy satellite falling back to Earth
BY STEPHEN CLARK
Posted: February 21, 2008
A missile fired from a Navy cruiser struck a wayward U.S. spy satellite late Wednesday, likely obliterating its load of toxic propellant that could have posed a threat to people on Earth, senior military officials said.
"We're very confident that we hit the satellite," said Marine Gen. James Cartwright, vice chairman of the Joint Chiefs of Staff. "We also have a high degree of confidence that we got the tank."
The SM-3 tactical missile, a modified component of the Aegis sea-based missile defense system, was aiming for a fuel tank embedded inside the craft's structure to release an estimated 1,000 pounds of corrosive hydrazine propellant.
Cartwright said he's about 80 to 90 percent sure the missile hit the fuel tank, based on data from a suite of optical, infrared and radar sensors derived from the national missile defense system.
A tracking camera aboard an aircraft flying over the Pacific captured dramatic images of the intercept, showing the moment of impact and a cloud of debris left behind after the collision.
"We have a fireball, and given that there's no fuel, that would indicate that that's the hydrazine fire. We have a vapor cloud that formed. That again would be likely to be the hydrazine. We also have some spectral analysis from airborne platforms that indicate the presence of hydrazine after the intercept. So again that would indicate to us that the hydrazine vented overboard in some quantity and we're starting to see that in space," Cartwright said.
Detailed results of the unprecedented strike must be confirmed through additional analysis before military officials will draw any more conclusions. That analysis is expected to take a day or two to complete.
"We're trying to pull all these pieces together and make sure that we're not stringing facts together erroneously," Cartwright said.
The SM-3 missile launched from the USS Lake Erie stationed northwest of Hawaii at 10:26 p.m. EST Wednesday. High seas in the Pacific Ocean threatened to preclude an attempt early in the day, but Navy ships reported acceptable conditions once they arrived at the launch site.
Based on recommendations from senior military commanders, Defense Secretary Robert Gates ordered the Navy to take advantage of the Wednesday's opportunity. An incoming weather system could have thwarted launch attempts in subsequent days.
A control center at Vandenberg Air Force Base in California confirmed the missile successfully crashed into the orbiting spacecraft at an altitude of 153 miles, Pentagon officials said.
Lacking a warhead, the interceptor relied on hitting the satellite with a combined relative velocity of about 22,000 miles per hour. The energy of the impact was enough to destroy the spacecraft, which was lost almost immediately after its December 2006 launch.
"This was uncharted territory," Cartwright said. "The technical degree of difficulty was significant here."
Initial radar data indicates the dead satellite broke into fragments no larger than a football, Cartwright reported.
"At the point of intercept last night, there were a few cheers from people who have spent many days working on this project," he said.
Infrared sensors detected numerous objects streaking through the atmosphere, but no sizable pieces of debris have reached the ground. Officials expected a large percentage of the debris to re-enter within the first few hours after the satellite's destruction.
A group of amateur astronomers in Prince George, British Columbia, observed more than a dozen visible debris trails crossing the sky less than 15 minutes after the impact, according to message distributed by the Royal Astronomical Society of Canada.
The targeted satellite's orbit would have taken it northeast across the Pacific Ocean and over Canada in the minutes following the strike.
The mission took only a few minutes to complete but more than a month to plan, according to senior military personnel.
The 5,000-pound satellite – called USA 193 in the military's spacecraft naming system – was about the size of a school bus, defense officials say. USA 193 was operated by the National Reconnaissance Office, the federal agency responsible for fielding spy satellites.
Officials don't know why the experimental satellite died because engineers are not able to communicate with it.
"A smoking gun on exactly why (the satellite failed) is something that has eluded us to date, just because we can't get any diagnostics to tell us what's going on," Cartwright said. "It didn't respond to us."
Because the craft failed so soon after launch, nearly all of its hydrazine maneuvering fuel remained on-board. The corrosive propellant had likely frozen during its 14-month stay in space, and military officials say the frozen tank would have survived a fiery uncontrolled entry into the atmosphere and made it to the ground.
Without control of the satellite, military leaders watched as drag from the thin outer reaches of the atmosphere gradually lowered the craft's orbit. The satellite's orbit fell by an average of more than 60 miles between its launch and this month, a rate that would have led to its natural decay by sometime next month, according to analysis by international hobbyists that observe spacecraft orbiting the planet.
Aerospace industry analysts predicted the hydrazine could be dispersed in an area about the size of two football fields, although the tank would have most likely landed in the ocean or an unpopulated area.
But hydrazine could be deadly to humans if they are exposed to heavy concentrations of the rocket fuel.
"You have to treat this as if it's going to hurt someone," Cartwright said. "If you can mitigate the threat, then you should take action if you have the opportunity."
Engineers estimated up to 2,800 pounds of debris could have made it to Earth if left intact. The satellite also carried sensitive experimental reconnaissance equipment, according to reports.
Some experts said the Pentagon's actions could be driven by the potential of classified technology falling into the wrong hands should the spacecraft come down on land.
"The hydrazine was unique here, not the size of the mass, not the reentry, not the classified nature," Cartwright said. "It was the hydrazine that drove this."
Officials began planning a possible strike in January, and President Bush gave the go-ahead to shoot down the satellite earlier this month.
"You want to reach out to each one of those people that probably gave up their weekends and nights to get this done in 30 days and put it together," Cartwright said.
The Missile Defense Agency added special instrumentation to beam telemetry from the missile to control centers, giving engineers additional insight into the mission. Other changes included tweaking software to allow the interceptor, originally designed to fend off short- and medium-range missiles, to reach a satellite in orbit.
"It's not something that we would be entering into the service in some standard way," Cartwright said. "This is a one-time type of event."
The launch also used a network of sensors used by the missile defense system to detect incoming ballistic missiles. The sensors included airborne detectors, ground radars and telescopes in Hawaii, tracking stations on ships, and satellite-based infrared instruments on the military's early warning satellites, a senior military official said on background.
The use of multiple tiers of the missile defense system in Wednesday's space shot proves it works, Secretary Gates said.
"Completely a side benefit of yesterday's action was to underscore the money that the Congress has been voting for this has resulted in a very real capability," Gates said.
Wednesday's intercept was the first time the U.S. military destroyed an orbiting satellite since 1985, when an air-launched missile struck a beleaguered solar observatory. China garnered international criticism last year when it conducted an unannounced test of an anti-satellite, or ASAT, weapon against one of its own weather satellites.
Military leaders drew distinctions between that test and Wednesday's mission. The concern that compelled the Pentagon's decision was public safety, Cartwright said.
"We did that in the 1980s. We understand ASAT. There's no reason to go back and reprove what we've already done," he said.
Government officials also informed foreign governments a week before the test. The Pentagon worked closely with the State Department to begin diplomatic efforts, according to Ambassador James Jeffrey, President Bush's deputy national security advisor.
Agencies are following a U.N. treaty that calls for member states to inform other countries about space activities of potential concern, Jeffrey said.
"What we've tried to do from the beginning was be as open as possible about the intention," said Navy Adm. Mike Mullen, chairman of the Joint Chiefs of Staff.
Senior military leaders say the strike can serve as a model of openness to China and other countries conducting similar operations.
"The Chinese did not do that when they launched their anti-satellite test," said Navy Adm. Timothy Keating, commander of U.S. Pacific Command. "We hope there are some lessons that become apparent to them."
China's test last year created more than 2,000 pieces of space junk, most of which is still in orbit and could pose a risk to other spacecraft.
"The Chinese ASAT test was conducted against a satellite in a circular orbit at around 850 kilometers of altitude," said Mike Griffin, NASA administrator, during a press conference last week. "So the debris that was generated could go (through) a very large swath of Earth orbital space and will be up for decades."
Most of the chunks generated from Wednesday's intercept were expected to be down within hours and days.
"That's an enormous difference to spacefaring nations," Griffin said.