Comments about technological history, system fractures, and human resilience from James R. Chiles, the author of Inviting Disaster: Lessons from the Edge of Technology (HarperBusiness 2001; paperback 2002) and The God Machine: From Boomerangs to Black Hawks, the Story of the Helicopter (Random House, 2007, paperback 2008)

Wednesday, April 27, 2011

Atlantis on STS-46: An alert crew saves the day

In honor of Endeavour's upcoming launch, here's a link to a fine time-lapse video of launch preparations for STS-131: raising the orbiter Discovery, mating it to the external tank and solid rockets, and rolling it out for launch.

While researching a piece on the redesigned solid rocket motor for Air&Space Magazine, I visited the Vertical Assembly Building during operations and had the chance to watch an overhead crane hoist a segment for stacking into a full solid rocket motor. Slow was the word.

Normally visitors aren't allowed into the VAB when the solid rocket booster sections are being moved. The reason is that solid fuel propellant acts like an explosive if dropped -- see this 1990 account of a fatality when a Titan 4 solid fuel booster hit the ground during a crane lift at Edwards AFB. Because my article was specifically about the booster, I got permission to watch the lift in the company of an escort. Movements of the booster segment were most amazingly slow ... much less than walking speed.

The Shuttle program has reached its 30th year and the last flight will be Atlantis, numbered STS-135, a cargo flight to the International Space Station. After that, it's off to the museums

The plans for Atlantis reminds me of one of that ship's earlier missions, STS-46. Within that mission, is a story of how an alert crew caught a potentially dangerous situation from causing damage. Disasters hardly ever come like a bolt from the blue: they develop from a combination of weak spots that join up over days, months, and even years.

The close call involved EURECA, short for European Retrievable Carrier satellite. It was like a truck for long-duration orbital experiments, to be retrieved by another shuttle later. Here's a photo of the Canada Arm lifting EURECA out of the payload bay.

So far, so good. The satellite took up a position 300 meters away while controllers at a command center in Germany ran through a series of checks. The crew waited several hours, then broke for dinner, except astronaut Andy Allen. He stood guard on the flight deck, the crew members all aware that having a powered satellite so close was a factor that needed watching.

It was a good thing that this guard was kept, as Atlantis passed into the night side of the Earth and the shuttle went into a communications blackout zone -- an area between relay stations.

Next, the shuttle's proximity radar set off a "range rate" alarm, indicating that EURECA was heading for the shuttle, later determined to be a closing speed of four to five feet per second. Unable to reach the satellite controllers in Germany, Allen fired the reaction control thrusters to get out of the way, though there was a risk the exhaust could damage the satellite's solar panels. The booms of these thrusters roused the other astronauts, who hustled up from dinner. "Where's the satellite?" they wanted to know. Allen couldn't say, other than it was so close the radar couldn't pick it up. The astronauts looked out the windows with flashlights.

The prompt action had avoided a collision. After conversation with Earth was possible, the crew learned that a glitch in Germany had fired the satellite's thrusters in such a way to send it hustling toward Atlantis.

Afterward, an astronaut took this wonderful photo of EURECA, now safely back in its station-keeping position, seemingly scooting among the clouds east of Cape Canaveral (the coastline visible at bottom).

This photo shows vividly how clouds come in many flavors, and at many altitudes.

 For more such photos, see JSC's image archive. Great stuff!

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