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“In the Dental Chair”: Endeavour on Stage for Five EVAs

Laden with tools and equipment, Jeff Hoffman waves from the end of the RMS arm during Hubble repair operations. Photo Credit: NASA

In the small hours of 4 December 1993, Endeavour – the youngest of NASA’s fleet of Space Shuttle orbiters – closed in on the Hubble Space Telescope. In doing so, she prepared for the mission which would make or break not only her own career, but the very future of NASA itself. That year had been a troubled one: Space Station Freedom, already grossly over-budget, had come within a whisker of cancellation and controllers had inexplicably lost contact with Mars Observer in August, a couple of days before it was due to enter orbit around the Red Planet. Added to that was the very real memory of Challenger in the public consciousness and Hubble’s own ‘spherical aberration’, which prevented it from focusing properly, which left NASA in a very bad position for the future. Administrator Dan Goldin had already been told by President Bill Clinton himself that the first Hubble Servicing Mission (SM-1) had to work, with dire consequences for the station project if it failed.

The pressure was well and truly on the seven astronauts of STS-61 – commander Dick Covey, pilot Ken Bowersox, spacewalkers Story Musgrave, Jeff Hoffman, Kathy Thornton and Tom Akers and Swiss-born robot arm operator Claude Nicollier – to execute a perfect retrieval of the showpiece $1.5 billion observatory and perform five intricate EVAs to fit the Goddard Space Flight Center’s Corrective Optics Space Telescope Axial Replacement (COSTAR), together with a new Wide Field Planetary Camera (WFPC, or ‘whiffpick’), a new set of electricity-generating solar arrays, Rate Sensing Units, electronic control units and fuse plugs. Five EVAs had never been attempted before in the Shuttle era and Covey anxiously noted in his NASA oral history that it “really pushed the bounds of what people thought we could do”.

The first major objective was ticked off the list at 3:48 am EST on the 4th, when Nicollier grappled Hubble with the Shuttle’s 50-foot-long Remote Manipulator System (RMS) arm and anchored it onto a Flight Support Structure pallet in the payload bay. Next came the first of the five EVAs, which would be performed daily, in two alternating teams, with Musgrave and Hoffman charged with the first, third and fifth walks and Thornton and Akers assigned to the second and fourth. (Provision was available for sixth and seventh EVAs, if problems arose, but this was ultimately not needed.) Looking back, Covey was filled with pride that his crew accomplished everything they set out to do. “There wasn’t anybody that was chilling down on the middeck,” he said. “Everybody was up top, working. There was concern about whether we could sustain that tempo. We went five straight days doing EVAs and that was the right answer. Everybody felt good about that. Nobody was getting excessively fatigued. The EVA crew members, because they were getting a day off in between were okay with that and so that facilitated us pressing on with five straight days of spacewalks.”

Grappled by the RMS mechanical arm, Hubble displays its glory to the Shuttle crew as it is anchored into the payload bay for five days of repairs and upgrades. Photo Credit: NASA

It was testament to the planning of each of these six-hour-plus excursions that Musgrave and Hoffman were outside in the payload bay, an hour earlier than planned, at 10:46 pm EST on 4 December, to kick off EVA-1. Their main task was the replacement of Hubble’s twin sets of Rate Sensing Units (RSUs), which carried gyroscopes to effect the proper pointing of the telescope. After setting up tools and equipment, Hoffman fitted a foot restraint onto the end of the RMS and was manoeuvred by Nicollier towards Hubble. In the meantime, Musgrave – who, despite being the payload commander, was actually EV2 on the spacewalk, with a pure white suit – installed protective covers over the telescope’s low-gain antenna and exposed voltage-bearing connectors. Next, the two men (whom Dick Covey had lightheartedly nicknamed “the odd couple” during training) opened Hubble’s equipment bay doors and set up another foot restraint inside. Working inside the bowels of the largest space telescope yet placed into orbit, astronomer Hoffman had little time to ponder, and by 12:24 am EST on the 5th, less than two hours into the EVA, the first set of new RSUs were in place. The second set followed, as did the installation of eight fuse plugs to protect the electrical circuits, and another mission success could be recorded: Hubble had a full, healthy set of six crucial gyroscopes.

All seemed well…until they hit their first glitch: the doors to the gyro compartment refused to close and seal properly. “The doors in the telescope gyro compartment are the biggest doors in the whole telescope,” Hoffman explained. “In fact, they’re asymmetrical; one of the doors is bigger than the other. We had opened and closed those doors a hundred times in the water. We knew how they worked. There were several latches, but there was one big handle. You turned that handle and that basically closed the latches; then you just had to throw a couple of bolts and tighten up the bolts and the door is secured.” Upon closer inspection, it appeared that two door bolts did not reset correctly and Hoffman suspected that the doors had somehow become ‘warped’, perhaps by the effect of uneven heating. If the doors did not close, Hubble would be lost, for its thermal control capability would be gone and light leaking into the telescope’s innards would ruin its delicate instruments.

Whenever he tried to close the top of the door, the bottom would refuse to close, and its height precluded Hoffman from holding both ends at once. He called Musgrave to help. Unfortunately, Musgrave was tethered and floating freely and could only push the door with one hand, since he needed to steady himself with the other hand. “It was basically a five-handed job,” said Hoffman, “and we only had four hands. We tried a few times.” On one occasion, Musgrave even tried pushing with his helmeted head, to no avail. At length, the spacewalkers recommended to Mission Control the use of the payload restraint device – “kind of a webbing tool, with a ratchet” – to help bring the doors into closure. Lead Flight Director Milt Heflin agreed that the crew were in the best position to make the decision and gave them the go-ahead. It worked and the doors were successfully closed and latched…but at the expense of EVA-1 turning into the second-longest Shuttle spacewalk to date: seven hours and 54 minutes.

Kathy Thornton is dwarfed by Hubble’s 16-foot-long solar array as she prepares to release it into space, during EVA-2. Photo Credit: NASA

With Kathy Thornton and Tom Akers slated to replace Hubble’s twin solar arrays on the next day’s EVA-2, the complexity of the back-to-back spacewalks became evident. “All four of us worked together,” said Hoffman, “because when you get a space suit ready, you try to be each other’s personal valet. There’s just a lot of work to be done. When you’re doing a spacewalk, it really takes over the entire Shuttle. You can’t really be doing anything else while the EVAs are planned.”

Thornton and Akers ventured into the payload bay at 10:35 pm on 5 December to the sight of a slightly different Hubble, for the roller-blind-like solar arrays had been commanded to fold up. One of them folded up perfectly and could be stowed for return to Earth, but a bent strut prevented the other one from following suit, leaving the spacewalkers with little alternative but to dump it overboard. An hour into the EVA, they dismounted the damaged array – which measured 16 feet long when folded up and weighed 350 pounds – during orbital darkness, to minimise electrical activity, and Thornton held it until the next daylight pass. This would allow mission controllers to track its position and relative velocity. She threw it overboard at 11:52 pm, as Endeavour sailed high above Somalia, describing its departure as “like a bird”.

“Then we had to fire our manoeuvring jets to get away from it,” remembered Hoffman. “The solar array was just inert. That was really spectacular, because when the exhaust plume from the reaction control jets hit this solar array…and it started to oscillate, up and down, it looked like the wings of a giant prehistoric bird, just flapping out in space.” The array somersaulted a few times in the vacuum. Watching from Endeavour, the crew of STS-61 was mesmerised by the spectacle. Those moments of silent awe were suddenly broken by a voice over the radio. It was Tom Akers. “Hey,” he said, “isn’t somebody supposed to be reading me the procedures? We have work to do!”

Story Musgrave had worked on the development of the Shuttle space suit from its conception in the 1970s and always described EVA as being akin to a ballet. On STS-61, he led a series of EVAs which were ballet-like in their perfection, in their excellence and in their accomplishment. Photo Credit: NASA

That broke the spell, recalled Hoffman, and they went back to work. EVA-2 ended after six hours and 36 minutes. It came as something of a relief, for the astronauts were at least able to enjoy dinner together and a proper night’s sleep after the comparatively short spacewalk. In Hoffman’s mind, if EVA-2 had lasted as long as EVA-1, it might have thrown them seriously behind on the timeline. He also had the fright of his life when he helped Thornton to remove her space suit; as he pulled off one of her gloves, Hoffman noticed that her fingertips were bright red. His first thought was that it was blood. As it turned out, a chunk of Thornton’s red-coloured food bar had floated away from her mouth and somehow made its way down through her suit, into one of the arms and into the glove…

“Not nearly as serious as it looked,” Hoffman acquiesced, “but I got quite a shock when I pulled her glove off.”

It was Musgrave and Hoffman’s turn the following night, 6-7 December, with the primary task of installing the new Wide Field Planetary Camera (WFPC-2). An hour into the spacewalk, Hoffman crisply removed the old whiffpick from its housing in Hubble’s bowels and placed it into a storage container in the payload bay. A protective hood was then removed from the new device and it was installed perfectly at 1:05 am EST. Ground controllers ran a so-called ‘Aliveness’ test and verified that the 620-pound WFPC-2 was working correctly. The astronauts then turned their attention to the replacement of a pair of magnetometers, before returning aboard Endeavour after six hours and 47 minutes.

Thornton and Akers were next, on 7-8 December, with the long-awaited installation of the COSTAR optics package to restore Hubble’s blurred vision. Before launch, Hoffman remembered being told not to worry if they did not accomplish everything on the manifest; as long as either the new whiffpick or COSTAR was successfully installed, the scientists on the ground would be “deliriously happy”. But they were not fully appreciative of NASA’s collective mindset of having a one-hundred-percent-successful mission. In the months prior to the mission, there was talk that STS-61 was too complex and that all of the tasks could not be fitted into even five EVAs and a mammoth 11-day flight. Some managers considered splitting the mission into two halves. “But from a technical point of view,” said Hoffman, “if you removed half the tasks from a mission, how do you know that you’ve not left the ones that you’re going to fail at? At least if you have more things for us to do, we have a better chance of at least getting some of them done.” To Hoffman and his crewmates, it made little sense splitting SM-1 into two halves.

The intensity of the mission – an intensity which had impacted Story Musgrave for almost two years, to such an extent that he remarked, with the merest hint of jest, that the only peace he could find from the mission was whilst sat in the dentist’s chair – began to lessen somewhat when Thornton and Akers successfully removed Hubble’s High Speed Photometer and installed COSTAR in its place. By the end of their six hour and 50 minute EVA, both the new whiffpick and the corrective optics had been triumphantly fitted. Whilst still critical, Musgrave and Hoffman’s final EVA, lasting seven hours and 21 minutes on the night of 8-9 December, replaced the solar array drive electronics on the telescope, installed magnetometer covers and an electrical connection box on the Goddard High Resolution Spectrograph. By the time the two men returned inside the Shuttle, STS-61 had accomplished five remarkably complex EVAs and a tally of more than 35 hours of spacewalking…in a single flight. Whilst this would be duplicated several times over the years, it must be borne in mind that STS-61 was the first Shuttle flight in which the bounds of accomplishment in terms of mission duration, complexity and the intricately linked EVA-RMS-orbiter operations were pushed to their absolute limits.

And it was Endeavour – on only the fifth voyage of her 25-mission career – which had proven, once again, that she was a trailblazer for the remarkable achievements which would follow. Her crew’s demonstration that intricate spacewalks and RMS activities and manoeuvring could be done, back to back and simultaneously, within a single mission, laid an important cornerstone for NASA’s bold plans to build the space station.

Backdropped by the Hubble Space Telescope through Endeavour’s aft flight deck and overhead windows, the STS-61 crew celebrates their success. On the front row are Claude Nicollier and Kathy Thornton, with Story Musgrave, Dick Covey, Jeff Hoffman, Ken Bowersox and Tom Akers behind. Photo Credit: NASA

That night, the night of the final EVA, the crew of STS-61 celebrated their success. They did not yet know if the corrective optics would work, of course, but they had completed their share of the mission. Claude Nicollier successfully deployed Hubble back into space and on 13 December, in the nighttime darkness, Endeavour swooped like a bird of prey onto the Kennedy Space Center’s Shuttle Landing Facility to conclude a voyage which had done nothing less than save NASA itself. Few other human space missions since Apollo 11 had exerted such a positive influence on the agency’s subsequent fortunes. Of course, we know today that fixing Hubble’s optics was triumphantly successful and the telescope repair team received the prestigious Robert J. Collier Trophy in March 1994 to their work.

Acapulco, it seemed, would prove to be a vacation destination – and not a place for out-of-work engineers from NASA to wait tables – once more.

But perhaps the best testimony to the personal success invested in the Hubble repair is told by Jeff Hoffman himself. As the only professional astronomer amongst the seven STS-61 astronauts, he had devoted more than a year of his life to bringing the greatest telescope in history back from the brink of despair. In the early hours of New Year’s Day 1994, he and his English-born wife, Barbara, had hosted friends at their house. Everybody had left and Hoffman was cleaning up in the kitchen.

Suddenly, the telephone rang. It was one of Hoffman’s astronomer friends.

“Jeff, hi,” came the greeting. “Do you have any champagne left?”

“Yeah. I still have a half bottle in the refrigerator. Why?”

“Well, crack it open, because we’ve just gotten the first pictures back from Hubble. It works!

 

The next two-part article in this Endeavour series will focus on STS-88, the first mission to deliver US-built hardware into orbit for the construction of the International Space Station in December 1998.

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