Baptism of Fire: 25 Years Since the Dramatic Rescue Mission of STS-49 (Part 2)

In the first, and so far only, three-person EVA, astronauts Rick Hieb, Tom Akers and Pierre Thuot manhandle Intelsat 603 into Endeavour’s payload bay for the attachment of a new rocket motor. Photo Credit: NASA

Twenty-five years ago, today, on 7 May 1992, Space Shuttle Endeavour launched into orbit on her maiden voyage, a dramatic nine-day flight to retrieve the errant Intelsat 603 communications satellite and reboost it into geosynchronous orbit. STS-49 Commander Dan Brandenstein led an experienced team, consisting of spacewalkers Pierre Thuot, Rick Hieb, Kathy Thornton and Tom Akers, robotic arm operator Bruce Melnick and Pilot Kevin Chilton. Even before the launch, Endeavour’s flight plan was ambitious. Never before in the shuttle program had as many as three periods of Extravehicular Activity (EVA) been performed, and as circumstances transpired STS-49 would set—and then break—her own record, by providing the platform for four spacewalks, totaling 25 hours and 23 minutes. One of those EVAs also set a record for the longest spacewalk ever conducted; a record which would remain unbroken for almost another decade.

“Happiness on a rendezvous mission,” Kevin Chilton recalled later, was the sight of the tiny “star” of Intelsat 603, appearing in the crosshairs on the morning of 10 May 1992, the fourth day of the mission. Ever since launch, Intelsat controllers had maneuvered their satellite into a “control box”, some six degrees of arc of Endeavour’s orbit. These maneuvers also served to reduce the giant satellite’s rotation rate from 10.5 to 0.65 rpm. Approaching to within 8 miles (13 km), Pierre Thuot and Rick Hieb donned their space suits and were assisted into Endeavour’s airlock by Tom Akers. At 4:25 p.m. EDT, they opened the outer hatch into the payload bay and set to work. Thuot fastened himself into a foot restraint on the end of the Remote Manipulator System (RMS) mechanical arm, deftly operated by Bruce Melnick. Drawing closer toward the satellite, Thuot extended a specially-designed “capture bar” into position, but the latches failed to latch.

He tried again, without success.

A third attempt was similarly fruitless.

Endeavour’s maiden launch on 7 May 1992. Photo Credit: NASA

From his station on Endeavour’s aft flight deck, Brandenstein noticed that Intelsat 603 was beginning to oscillate and drift somewhat, “so I got in my chase-it mode, because I had to keep him aligned”. When Thuot’s third attempt failed, Brandenstein had used a “tremendous” amount of propellant and instinctively knew that the chances of success were now slim. The RMS exacerbated the difficulty, because its joints were being driven into positions which they could not support. “We decided, though consultations with the ground, to get out of there and try another day,” Brandenstein recollected. “That was a pretty low point, because when we left, it had a pretty good rate. We thought we’d lost this $150 million satellite…and Pierre was particularly depressed because, obviously, he thought it was his fault.”

Thuot and Hieb returned inside Endeavour after three hours and 43 minutes, and later that evening Hughes engineers confirmed that they had managed to stabilize Intelsat. Next day, at 4:30 p.m. EDT on 11 May, the spacewalkers were back outside for a second attempt. “Instead of doing it at night, we were going to wait and do it in daylight,” Brandenstein said. “We decided we weren’t going to even make an attempt until everything was just perfect. Pierre went in and the rotation slowed down.” From Hieb’s position, it looked as if Thuot had completed the capture, but, alas, the satellite again began to oscillate.

The astronaut’s alignment was unquestionably correct, but the capture bar refused to seat itself properly and Intelsat wobbled. A few weeks after the mission, Thuot explained to this author that the satellite “was much more dynamic than our training had led us to believe”. As the disappointed spacewalkers returned inside the cabin for the second time—this time after 5.5 hours—they at least knew that the Hughes engineers could regain control of Intelsat 603 for another attempt. However, although propellant reserves allowed for it, three separate rendezvous on a single shuttle mission had never been attempted, and Brandenstein recommended a day off to plan for the third attempt. In an interview for the Smithsonian, Rick Hieb remembered that the evening of the 11th was a somber time. At one point, Chilton joined Hieb on the flight deck and the pair entered an impromptu brainstorming session. It was a session that would mark a significant turnaround in the fortunes of a mission which seemed snake-bitten.

As Hieb and Chilton talked, other members of the crew floated upstairs to join them. The main concern was where to manually grab Intelsat. The top of the satellite, where the delicate antennas were located, was not ideal, and it was Bruce Melnick who suggested an EVA with not two spacewalkers, but three. No excursion in history had ever involved more than two members, partly due to safety concerns and partly because of the sheer practicality of getting three people into the tiny airlock. On the other hand, Endeavour carried four suits for Thuot, Hieb, Thornton and Akers, so in theory it was a possibility.

“When Bruce said that,” recalled Hieb, “a big mental switch flipped over, at least for me. In my mind, having a third set of hands out there meant that we would be successful, although we weren’t yet sure how.”

Mission Control knew that the astronauts were still awake, because Endeavour’s monitors had not been turned off. At length, the crew turned them off and continued talking in the dark, but eventually called the ground with Melnick’s idea. Years later, Brandenstein remembered that it was Chilton who sketched out the practicalities of the three-person EVA and held it in front of the television camera to allow mission controllers to see it. “The big choke point,” Brandenstein said, “was can you put three people in the airlock to get them outside?” In the Weightless Environment Training Facility (WET-F) at the Johnson Space Center (JSC) in Houston, Texas, fellow astronauts Story Musgrave, Jim Voss, and Michael “Rich” Clifford donned suits and demonstrated the techniques and geometries involved in setting themselves up to accomplish the feat.

Their consensus: It was doable.

Armed with the capture bar, Pierre Thuot provides a measure of scale of the enormous size of Intelsat 603. Photo Credit: NASA

Late on 13 May, the third attempt got underway. Truss members belonging to the Assembly of Station by EVA Methods (ASEM)—a Space Station Freedom demonstration payload, to be used during EVA tests later in the mission—were removed and arranged into a triangular structure for Thuot, Hieb and Akers to anchor their feet. Brandenstein positioned the orbiter directly “beneath” Intelsat 603 and controllers verified that its surface temperatures would not exceed the 160 degrees Celsius (320 degrees Fahrenheit) touch limit of the astronauts’ gloves. With Hieb close to the starboard payload bay wall, Akers in the center, attached to an ASEM strut, and Thuot on the end of the RMS on the port side, the astronauts could do little but watch as Endeavour drew closer. They studied its slow rotation for about 15 minutes, until, on Hieb’s call, they moved in for the capture.

All at once, Thuot spotted a slight wobble. He called the attempt off.

Shortly thereafter, they tried again. This time, at last, the three men grabbed the satellite and held it firmly. The time was 7:55 p.m. EDT. “I actually thought the other two guys had stopped it from rotating,” Thuot said later, “so little force had I applied. Very gently, the thing came to a stop.” From the flight deck, Dan Brandenstein asked them if they had a good grasp. On Thuot’s response in the affirmative, the commander was able to advise ground controllers, with more than a hint of relief: “Houston, I think we’ve got a satellite!”

With Intelsat snared, the astronauts removed the steering wheel and installed an extension to the capture bar, which Melnick grappled using the RMS. The satellite was then positioned above its solid-fueled perigee kick motor. After closing four docking clamps to secure the pair, and attaching two electrical umbilicals between Intelsat and the motor itself, the spacewalkers set a pair of deployment timers and retreated to Endeavour’s airlock.

Meanwhile, Kathy Thornton prepared to activate the springs to deploy the payload. At first, it did not move. “They had made a change in the wiring of the deploy system,” recalled Brandenstein, “and the change never made it through the process [and] never got into the checklist. Fortunately, somebody in Mission Control apparently knew about it.” Deployment occurred at 12:53 a.m. EDT on 14 May and the satellite vacated the payload bay.

Speaking a decade after the flight, Dan Brandenstein regarded those few days of STS-49 as “one of those missions from hell” and for newly-appointed NASA Administrator Dan Goldin it was truly “a baptism of fire”. Nevertheless, at 1:25 p.m. EDT on 15 May, Intelsat 603’s new motor ignited perfectly, and it was on-station in geosynchronous orbit by the 21st. As well as becoming the first shuttle crew to accomplish as many as three EVAs in a single mission—a record which they would break with a fourth excursion—the triumphant three-man spacewalk established itself as the longest in history.

Their eight hours and 29 minutes outside would remain unbroken until March 2001. By now, the difficulties had prompted the Mission Management Team (MMT) to extend STS-49 by 48 hours from its planned seven-day duration. On 14 May, a record-breaking fourth EVA got underway when Akers and Thornton ventured outside for the ASEM station tests. Originally scheduled to involve two EVAs—one by Thornton and Akers and the second by Thuot and Hieb—the Intelsat 603 retrieval forced the cancelation of one spacewalk.

The shuttle’s first drag chute blossoms from Endeavour during rollout on 16 May 1992. Photo Credit: NASA

Activities included the construction of a pyramid-shaped truss, the unberthing of a Mission-Peculiar Equipment Support Structure (MPESS)—maneuvered by the RMS—and efforts to evaluate the ability of spacewalkers to work at positions “above” and “forward” of the payload bay, including “over the nose” of the shuttle. The MPESS contained two node boxes for the pyramid, a releasable grapple fixture and interface plate, and a truss leg and strut dispenser. Five crew rescue techniques were to be trialed, including a lasso-like “astro-rope,” a seven-section telescoping pole and a hand-held propulsive device.

During their seven hours and 43 minutes in the payload bay, Thornton and Akers completed the construction and disassembly of the ASEM attachment fixture, tested the propulsive device, affixed six of eight legs onto the MPESS, and, unexpectedly, were called upon to manually stow Endeavour’s Ku-band antenna, which had experienced a positioning motor failure. According to NASA’s post-mission report, this EVA was planned to be RMS-intensive, although the mechanical arm was used to accomplish only a single ASEM task and the spacewalkers’ timeline was further impacted by the Ku-band activity.

Endeavour’s return to Earth on 16 May 1992 brought with it a number of test objectives, the most visible of which was the deployment of the shuttle’s long-awaited drag chute on the runway. Measuring 39 feet (11.8 meters) in diameter when fully unfurled, the chute was designed to reduce steering problems and relieve stress on the shuttle’s brakes and tires, which had suffered particularly significant damage on Mission 51D in April 1985. It trailed the orbiter by 89 feet (27 meters) on a 41-foot (12.4-meter) riser.

Following the successful operational of the reefing line cutter, the chute blossomed to its fully inflated condition. Photographic analysis of the landing illustrated that the reefed chute rode at a higher angle than anticipated and the door trajectory differed slightly from ground tests; additionally, its behavior and closeness to the centerline were attributed to the effect of the aerodynamic flow for the fully-open speed brake.

Endeavour’s first mission produced only 36 anomalies, none of which were of sufficient concern to impact the success of STS-49. “They built a beautiful vehicle,” Brandenstein recalled later, “because it’s based on all the other things that diverted our attention on that flight. It was really nice that Endeavour performed like an old pro.” She would continue to do so for the remainder of her 25-mission career.

 

This is part of a series of history articles, which will appear each weekend, barring any major news stories. Next week’s article will focus on the 20th anniversary of STS-84, a Space Shuttle voyage to Russia’s Mir space station in May 1997.

 

 

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