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Mardi, 03 Janvier 2012 18:00

Risky Rescue for Crippled Air Force Satellite

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Risky Rescue for Crippled Air Force Satellite

It was an epic space rescue that, in audacity and risk, echoed NASA’s campaign to save the astronauts aboard the doomed Apollo 13 moon mission. The biggest difference between the 1970 Apollo operation and the 14-month recovery of AEHF-1, an Air Force communications satellite, is that money was the only thing immediately at stake in the latter.

Granted, it was quite a lot of money: around $2 billion. And the satellite’s loss would also set back the Pentagon’s efforts to revamp its communications infrastructure as battle becomes more bandwidth-intensive.

The details of AEHF-1?s rescue, completed in October this year, are only now becoming clear as members of the Air Force team speak out. Saving the pricey, long-in-development comms satellite — one of a planned six-craft constellation meant to relay data between military forces scattered across the globe — involved some bold decision-making, a lot of creative engineering, not a little bit of luck and, last but not least, a steady supply of pizzas delivered to the Space and Missile Systems Center at Los Angeles Air Force Base, where military and contract space operators worked around the clock to plan the satellite’s recovery.

The brand-new Advanced Extremely High Frequency communications satellite (pictured) was 140 miles over the Earth’s surface before controllers knew anything was wrong. As far as the space operators knew, the Lockheed Martin-built satellite was functioning perfectly. It was Oct. 15, 2010, just one day after the 7-ton AEHF-1 had blasted into orbit atop an Atlas rocket. The controllers planned to activate the satellite’s hydrazine engine in order to alter the spacecraft’s flightpath, gradually transitioning from an oblong elliptical orbit to a circular, geosynchronous one allowing steady coverage of the Earth below.

But when the operators ordered the engine to ignite, nothing happened. They tried again, still nothing. They didn’t know it at the time, but a fuel line had become clogged. The blockage “was most likely caused by a small piece of cloth inadvertently left in the line during the manufacturing process,” according to the Government Accountability Office.

Repeated attempts to fire the engine very nearly caused an explosion. Just in time, David Madden, who oversees comms satellites at the Space and Missile Systems Center, consulted with his engineers and told the operators to stop trying the engine. “We’re very, very fortunate that satellite didn’t blow up,” Gen. William Shelton, head of Air Force Space Command, told Air Force magazine.

AEHF-1 was intact but stranded in a slowly decaying and useless orbit.

Madden told his engineers to figure out some way to salvage AEHF-1 — and not to leave their room at the Space and Missile Systems Center until they did. “We literally were shoving pizza under the door so that these guys could keep working,” Madden recalled.

A week later, they had a plan. Lt. Gen. John Sheridan, then the space center commander, approved it. The basic idea was to use the satellite’s small thrusters, intended for minor course corrections, to shift the orbit thousands of miles. It would take 450 separate maneuvers, carefully managed over a period of 14 months. ”AEHF-1 will be able to get to where it’s supposed to go,” analyst Mark Stout noted. “It’ll just take a year longer than planned.”

It was risky. “There’s no instruction manual for how to do that,” Madden said of the thruster strategy. “It’s basically an art.”

As the controllers inched AEHF-1 towards its correct orbit, Air Force officials began negotiations with Lockheed, seeking financial compensation. “It should not have happened,” Deputy Undersecretary of the Air Force for Space Programs Richard McKinney said of AEHF-1?s fuel-line blockage.

Soon, three new complications arose with the crippled satellite.

First, with each firing of its thrusters, AEHF-1 was held stationary, exposing it to greater amounts of sunlight — and potentially overheating the spacecraft. Madden’s people had to devise new maneuvers, periodically flipping the satellite to allow hot components to cool down.

Second, AEHF-1 risked running out of gas. Engineers wrote new software meant “to save every ounce of fuel,” according to Air Force‘s detailed account of the rescue.

Finally, the orbital shift required crossing paths with scores or even hundreds of other spacecraft. Air Force controllers from a separate unit handled traffic management while Madden and his people focused on the fuel and heat issues.

On Oct. 24, AEHF-1 reached its originally planned orbit. Testing began soon afterward. The Air Force expects to bring the satellite into service in March. Meanwhile, two more AEHFs are slated to launch in 2012.

After an initial bout of very bad fortune, the Air Force got “very lucky” with AEHF-1, service Undersecretary Erin Conaton said.

The space and flying branch might need that luck again very soon. Lacking its own production and launch facilities, the Air Force has no choice to but to trust Lockheed to get AEHF-1?s sister spacecraft right, Stout wrote. “While Lockheed is no doubt embarrassed, I don’t think they’re quaking in their boots as another five AEHFs are in the queue.”

Somewhere in Los Angeles, AEHF-1?s rescuers are no doubt holding their breaths, hoping they won’t have to repeat the yearlong feat of engineering derring-do that saved the Air Force $2 billion and preserved the Pentagon’s space communications systems.

Photo: Lockheed Martin


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