The tensest moment in spaceflight: Docking with a 100-ton space station while orbiting Earth at five miles per second.
- By Thomas D. Jones
- Air & Space magazine, May 2006
Veteran astronaut Tom Jones gives readers an insider’s look at spaceflight in his book Sky Walking: An Astronaut’s Memoir (Smithsonian Books/Collins). In this adapted excerpt, he recounts his STS-98 space shuttle crew’s February 2001 mission to the International Space Station (here called Alpha). Among the station’s other challenges, it tested the relationship between the United States and its former rival in space, Russia, as they worked together to build the largest and most complex structure ever placed in orbit.
Even 600 feet away, I was getting nervous. The station’s golden solar arrays and silvery white hull seemed motionless against the black sky, but I couldn’t dismiss the fact that both ships were racing around the globe at five miles per second. Each of us concentrated on our cockpit tasks, and there was little superfluous chatter. The quiet was punctuated by the occasional thud of a thruster firing and the clicking shutters and whirring motor drives of our cameras. Alpha was an irresistible target for photography; it was etched so cleanly on the black sky above that my friend and crewmate Marsha Ivins said later, “It was as if someone had squeegeed my eyes.”
I searched the faces of the others for signs of the tension I felt. Taco—Ken Cockrell—peered up through the overhead window in the aft cockpit, fingers curled around the hand controller for the shuttle’s maneuvering thrusters. Taco was Atlantis’ commander, piloting the orbiter through this crucial docking. This was his third space rendezvous as commander, but the most demanding yet, with the critical job of attaching the new Destiny science laboratory to the station. Mark Polansky—“Roman” to his friends—backed up Taco as pilot. As a rookie, this was his first rendezvous, and he was as focused and intense as I’d ever seen him. My spacewalking partner, Bob Curbeam—“Beamer”—babysat the docking system panel to Taco’s right. Stationed in the right front seat, I served as the pilots’ rendezvous assistant, riding herd on the checklist and our network of a half-dozen laptop computers. Marsha, on her fifth mission, would have the critical job after we docked of grappling the Destiny module from the payload bay and berthing it at the station. Now, as the “floater” for our rendezvous, she drifted face-up at the port aft window, rangefinder in one hand, camera in the other.
Marsha, having been to the Russian Mir station four years earlier, was less worried about the docking than tomorrow’s berthing: Could the system—her brain and hands, the computers, the robot arm, the berthing latches and bolts—pull off the task, which required moving the 16-ton lab module around with clearances of only a few inches? The “I’m doomed!” T-shirt she wore during training was a none-too-subtle sign of her worries. Sweating out a session in the arm training rig back in Houston, she had peered up at the mockup of the massive lab hoisted high on the slender arm. “What are they thinking? This is nuts! 1.4 billion dollars!” she groaned inwardly. Later, after we were back on Earth, she would tell me how keenly she had felt the pressure: “The rest of you guys just kind of guffawed around and joked and laughed, but every time I did the lab task I felt nauseous.”
My own feelings about visiting the International Space Station had changed over time. More than once in the early 1990s, I thought NASA might be better off if it cut its losses and canceled the ISS. Was it really required to get us out of low Earth orbit and on the way to the moon, asteroids, or Mars? Or was it a dead-end distraction that would doom NASA to a cash-strapped future endlessly circling Earth?
The five-year-old U.S.-Russian partnership, I felt, had been driven purely by NASA’s need to salvage the space station (and NASA’s bureaucratic prospects) under an indifferent administration that wanted to engage the Russians in some post-Cold War joint technology effort as a foreign policy exercise. But the realities of working with the creaky Russian space establishment had more than once threatened to drag the entire program down.
My cynicism slowly yielded to pragmatism as I recognized some hard facts. The administration would never give NASA the authority to jettison the Russians, no matter how difficult the partnership became. That would be a minor foreign policy disaster for the Clinton-Gore team. So for NASA, the road to the ISS had to go through Moscow. And my responsibility to NASA lay with moving the project forward if I could.
But at the moment politics was far from my mind. Now it was time to turn the orbiter around for docking. Atlantis, still headed nose-first along our direction of flight with the station above us, would bury her tail in the station’s belly if we docked in this attitude, and we needed the payload bay and lab out in front of the station for berthing. So at 600 feet, Taco initiated a computer-aided yaw maneuver to swing our nose around 180 degrees. Above us, the station pivoted gracefully in our windows, mirroring the orbiter’s actual motion. Three hundred feet now, closing as planned at 0.3 feet per second.
Floating in the overhead window with her laser rangefinder, a modified version of a state trooper’s speed gun, Marsha called out the distance and closing rate. Beamer had the docking system in the green, ready for contact. Roman was now backing up Taco, monitoring the approach and occasionally squeezing off a photo. I called the range rate numbers to Taco every 10 feet or so, the checklist going just like clockwork.
Atlantis glided up the corridor, closing steadily. At 170 feet, Taco fired thrusters and brought us to a temporary halt, a chance for everyone, in orbit and on the ground, to take a deep breath before pressing in for docking. The Expedition One crew on the station called that they were ready, and Moscow confirmed that its systems aboard the ISS were go. Houston agreed: “Atlantis, you’re go for docking.” With two quick pulses, Taco started us upward toward our meeting with the International Space Station.
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.
“Ten feet, zero point nine on the R-dot,” I called out, glancing at the laptop. My voice rose a notch in both volume and pitch.
Up in the commander’s seat, Roman powered up the firing circuit for the automatic thruster sequence to be triggered two inches from contact. “PCT [post-contact thrusting] is armed,” he announced. The computer-controlled shove would bang the shuttle’s and station’s docking rings together with enough force to guarantee capture. The last few feet came in a rush.
“Six feet, point one one.”
From the cockpit, the station seemed to descend on us like a giant industrial press, an enormous mass bent on ramming straight through the cargo bay. I tensed for the impact even as I called out the remaining distance.
“Eighteen inches, R-dot is good.”
“One foot, petal overlap.” The three metal alignment vanes atop each docking ring swept past each other toward impact.
“Six inches…two inches!”
Just before the rings slammed together, Taco mashed the PCT button on the autopilot panel. Atlantis shook with thruster firings as the force of the impact compressed the shock absorbers of the docking rings.
Two blue lights flashed on the docking panel. “Capture!” called Beamer. The two spaceships bobbed gently, held lightly together by the latches on the docking petals. Dampening springs quickly brought the motion to a halt.
“Capture confirmed, Houston,” radioed Taco, satisfaction obvious in his voice.
“Nice job!” Mario replied. “Nice approach.”
In the cockpit, the crew shook hands and smiled in relief. I felt drained but elated—we’d pulled it off; we were safely docked!
Sunrise glowed first a pure blue, then pink, then silver-white across the Russian solar power arrays visible out front. In the harsh sunlight now washing over us, the entire station came into sharp focus. Taco could relax at last. Later he told me, “I was so psyched for the docking, and so trained for it, that I actually felt a little let down when it was over. Things went so smoothly that I felt, somehow, that there should have been more drama, or more angst (Marsha’s influence, maybe?), or more…something.”
The two docking tunnels now formed a slender vestibule between a pair of sealed hatches, one on Atlantis, another above in the station’s Pressurized Mating Adapter. Working with me in the airlock, Beamer quickly equalized the pressure between our cabin and the tunnel vestibule just above. Through the upper hatch window, we could see Shep, Sergei Krikalev, and Yuri Gidzenko opening the station hatch on their side.
We were ready for a reunion. Taco swam up through the airlock and joined us below the hatch. He peered up through the port, giving the Expedition One crew a quick wave.
“Everything ready, Tom?” Taco grinned; I should have seen it coming. “Let’s see how you do opening up this hatch”—a sly reference to the jammed hatch that had thwarted my planned spacewalk on a previous mission (see “No Way Out,” June/July 2002). I cranked the handle smoothly through a full circle. A quick tug and the hatch came off the seals, mingling the atmospheres of the two spaceships. With Beamer’s help on the stiff hinges, we swung the hatch down and flush against the airlock wall. Just like that, the door was open and the five of us floated aboard the space station.
Taco, a body length above me, rose into the burly embrace of a grinning Shep and two exuberant Russians. Drifting after him with Beamer, Roman, and Marsha, I entered the roomy world of the International Space Station. Shep, Yuri, and Sergei met us in their “foyer”; for a few minutes the Node, its trim a cheerful salmon color, was a scene of friendly chaos as we traded hugs, handshakes, and huge grins with our colleagues. The Expedition One crew had been on their own since Endeavour’s astronauts had departed nearly two months before, and they were delighted to see visitors, especially visitors bearing a lab-size housewarming gift.
Marsha later recalled her first impression: “Cleaner, compared to Mir. Cleaner and smelled a whole lot better.” The ISS surprised me too: It wasn’t some austere outpost, clinging to the very edge of human existence. It was a home port in space. The Node’s roomy interior, warmer temperature, and softer lighting made it cozy, compared with the shuttle’s cramped, sterile cabin.
Shep formally welcomed us aboard with a brief speech over the radio to both control centers, and a ceremonial ringing of the ship’s bell he had installed above the port hatch (he’d been a Navy SEAL). For the next week, the eight of us would work together as one crew. I looked forward to it, although the three space station astronauts were only casual friends of mine. I didn’t know Shep well, and he’d been scarce at NASA during the past few years, with most of his time spent in Russia. During Sergei’s shuttle training in Houston, I had enjoyed collaborating with him on a scientific paper. Yuri I knew only through his reputation as a well-regarded cosmonaut.
Marsha was closest to Shep. Both members of the 1984 astronaut class, they had a lot of catching up to do. “Shep wanted to know what was going on in the world…what was going on in the [Astronaut] Office,” she said. “I thought, playing with my crew is fine, but playing, talking, hanging out with these guys is a short moment in time, and I ought to take advantage of it.”
We moved on to the Russian-built Service Module for a quick safety briefing and tour; then our hosts returned with us to Atlantis. Over the next few hours we inventoried and turned over to Shep’s crew a half-dozen suitcase-size bags of priority cargo. Included was a locker full of fresh foods and snacks, a welcome break from the freeze-dried, canned, and thermo-stabilized fare they had been eating for more than three months. Four hours after boarding the ISS we were back in Atlantis, closing the hatch to prepare for our spacewalk the next day.
Taco and Roman sent air whistling overboard through the airlock depress valve, lowering the cabin pressure to 10.2 pounds per square inch. The reduction from sea-level pressure would bring down the nitrogen content of our blood, reducing our chances of getting the bends and shortening the time we’d spend the next morning in our spacesuits, preparing for our first spacewalk, or extravehicular activity (EVA). To further lower our blood nitrogen levels, Beamer and I donned portable breathing masks to begin flushing that unwanted gas from our lungs. Looking like a couple of wayward scuba divers, we breathed pure oxygen while readying the EVA tools. We quickly located nearly every item on the checklist, but three critical electrical components, called loopbacks, were missing.
For months we had trained underwater to install these soda-can-size plugs on the lab’s hull, where they would shunt electrical power or data to the proper circuits. These had to be in place for lab activation after EVA 1. We searched our lockers again for the loopbacks, and Marsha checked her inventory sheets. No loopbacks, but she did find several listed items called “1553 bus terminators.”
No doubt at some point in our training we had been exposed to the proper technical name for the loopbacks, but none of us had ever used that term. We quickly realized that “1553 bus terminators” probably referred to the missing parts. A call to Houston confirmed our fears: The lost components had been packed in one of the cargo bags we had just transferred to the station. They were now on the wrong side of a sealed hatch.
The pressure differential between the two vehicles prevented us from simply opening hatches and grabbing the parts. My first thought was that we would have to repressurize either our cabin or the station’s docking tunnel, wasting precious breathing gas in the process. I had just made the call to Houston admitting our mistake when Sergei made a suggestion. Because the loopbacks were only the size of a six-pack, he could place them in the foot-wide vestibule between the orbiter and station hatches; it would take just a few liters of air to equalize the pressure there, making it safe for us to retrieve them.
Sergei’s solution soon had us back in business. As I grabbed the loopbacks from the vestibule, I met his gaze through the porthole in the Russian-built station hatch. He returned my nod and wave of thanks with an easy smile. The irony of having a former Communist rescue our first spacewalk from an embarrassing foul-up wasn’t lost on me, a former Cold Warrior who’d spent my Air Force days flying B-52 bombers. This partnership might yet work.