Shuttle Stop

The tensest moment in spaceflight: Docking with a 100-ton space station while orbiting Earth at five miles per second.

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At two feet every 10 seconds, it would take us nearly 15 minutes before our docking ring contacted Alpha’s. At 100 feet the radar echoes grew too noisy for accurate ranging, so we switched solely to laser data.

In the darkness of orbital night, the station hovered in the wan glow of our payload bay floodlights, its feathery solar arrays fading into the inky gloom. Earth was forgotten. All eyes were focused on the station as its bulk slowly hove into the light, like a shipwreck emerging from the gloom of the deep ocean. Atlantis weighed about 120 tons, the ISS about 100, and the two vehicles seemed to squeeze the vacuum between them as they closed the remaining distance.

Inside 100 feet, Taco let the closing rate slow to 0.1 foot per second. We were within one shuttle length of Alpha. Houston was quiet; responsibility for the docking was now in our hands. Our lights clearly illuminated the target mounted on the station’s tightly sealed hatch: The docking ring above seemed close enough to touch. Roman and I crowded up to the TV monitors and stared hard at the zoomed-in target image. The alignment cross was neatly centered in the bull’s-eye; we told Taco that the approach errors were insignificant.

“Houston,” he called. “We don’t see a fly-out required. We’re pressing in.” Mario Runco, the astronaut capcom in mission control, answered promptly: “We concur.”

Across 30 feet of emptiness, Taco made a final call to Shep [Bill Shepherd] and his station crew: “Alpha, Atlantis, here we come.”

With a barely perceptible pulse from the thrusters, Taco nudged us upward, and Marsha started the range calls again. On her Mir mission, she said, the approach was “much less excruciating” because the shuttle docking ring was farther aft; this time the controlled collision would happen just outside our windows.

At 15 feet, she began reading ranges directly off the template on the TV monitor. At the closing rate of 0.1 foot per second, Taco’s margin for error was just 0.03 foot. Too fast and he might bounce the orbiter’s docking ring off the station. Too slow and the capture latches might not snap firmly home.

“Fourteen feet, point one two.”

“Twelve feet, point one one.”

Taco’s eyes were fixed on the target above. Drifting just three inches off-center would put us outside the docking envelope and force an abort.

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