Twenty years ago this week, the singular space shuttle mission which marked the demarcation between past and future took place. Since the resumption of flights in September 1988, following the horrific loss of Challenger, NASA had steadily rebuilt the nation’s confidence in the capabilities of the reusable spacecraft, but the failure of Mars Observer to reach the Red Planet in August 1993 and the much-publicized problems with the Hubble Space Telescope in the aftermath of its 1990 launch left the space agency in an unenviable position. By the middle of the decade, NASA hoped to begin construction of Space Station Freedom—a project whose future still hung under the axe of possible cancellation—and a spectacularly successful Hubble repair mission was acutely needed to reinvigorate public and political enthusiasm. From 2-13 December 1993, that success was accomplished, when the crew of Endeavour on STS-61 broke virtually every record in the book and restored Hubble to its rightful place as the United States’ dazzling icon of science.
As noted in yesterday’s history article, the spotlight of public and political attention was firmly focused upon this mission from the outset and training for the STS-61 crew—Commander Dick Covey, Pilot Ken Bowersox, Payload Commander Story Musgrave, and Mission Specialists Jeff Hoffman, Kathy Thornton, Tom Akers, and Claude Nicollier—proved difficult at times. “We were invited to come down to NASA Headquarters to meet with Dan Goldin,” remembered Hoffman in his oral history interview. “He told us quite frankly that NASA’s future was in our hands. That was the time when we were waiting for Congress to approve the construction of the space station. Everybody recognized that assembling the space station was going to take a lot of sophisticated EVAs, of the sort that we were getting ready to do for Hubble, so if we went up thinking that we could fix Hubble and then it turned out that we couldn’t, how could people trust NASA to build a space station? That was the attitude.”
Story Musgrave had been assigned to lead the planning of the EVAs, and he had pushed very hard to commit to Endeavour as the orbiter which would carry out the mission. He particularly highlighted the vehicle’s improved capabilities over her sisters, including the capacity for a long mission. He got his way. In NASA’s August 1991 manifest, the SM-1 mission was scheduled for Discovery and by January 1992 had moved to Atlantis and by December 1992 had been shifted to Endeavour. All of the spacewalkers recognised the need to develop physical strength to handle the demands of their space suits and build the necessary stamina for six or seven hours outside. Kathy Thornton worked out in the gym, as did her crewmates, although by Hoffman’s admission most of the servicing tasks did not demand immense physical strength, but placed greater emphasis on “technical co-ordination,” involving them “being very careful in how you moved things around and not messing anything up.”
The delicacy involved in each of the spacewalking tasks was further complicated by the need for sunlight never to enter Hubble’s interior, because it carried the potential to evaporate organic contaminants and potentially ruin the sensitive ultraviolet optics. In normal operation the telescope was never allowed to point anywhere near the Sun. Consequently, the mission was planned with the shuttle’s belly positioned to face the Sun, but this meant that temperatures in the payload bay and upon the astronauts’ suits would fall precipitously. Already, the critical nature of the EVAs had obliged NASA to assign veteran spacewalker Greg Harbaugh in March 1993 to train as a backup crewman and provide “some insurance in the event of the unavailability late in the training cycle of any of the four prime EVA crew members.” Harbaugh would be ready to step in if circumstances dictated.
And they almost did.
On 28 May, Musgrave was performing an eight-hour suited equipment test in one of the thermal vacuum chambers at the Johnson Space Center (JSC) in Houston, Texas, when he complained of intense coldness in his right hand. He persevered and then upon removing his suit at the end of the test, he noticed discolouration and numbness in his fingers. (They were “black and purple,” according to Hoffman.) Flight surgeons quickly identified a case of severe frostbite, and Musgrave was referred to a specialist in Alaska for treatment. At this stage, Hoffman was unsure what would happen. “I don’t know exactly what they did to him,” he told the oral historian, “but they managed to save his fingers, and he flew, but that definitely got management’s attention.”
That attention was both positive and negative for Musgrave. On the positive side, it led to the elimination of the belly-to-Sun attitude, in favor of an attitude whereby Covey and Bowersox would execute attitude maneuvers during each orbit to ensure that sunlight did not enter the telescope. In Dick Covey’s recollections, the single-mindedness of Musgrave toward training caused some anger and demands for his removal from the crew. “Story had been around for a long time,” said Covey. “There was this concerted effort to use Story’s injury as a reason to get him thrown off the crew by some people with the agency and [JSC] and I had to go fight that … The reasons were political and personality-based, rather than technically based on his capabilities and whether he was going to recover from his injuries. That was hard to deal with.” Harbaugh was also recovering from recent knee surgery and, for a while, struggled to even don a space suit, but both he and Musgrave were declared ready to support the mission. In fact, Harbaugh went on to serve as EVA Capcom for STS-61 and also flew aboard the second Hubble servicing mission in February 1997.
A windstorm on 30 October 1993 prompted the movement of Endeavour from Pad 39A to Pad 39B, following sand-blasting grit contamination of the payload changeout room, with much anticipation of a successful launch in the small hours of 1 December. The attempt was scrubbed due to high winds at the Shuttle Landing Facility, together with excessive cloud cover and the presence of a ship in restricted waters, but, after a 24-hour delay, STS-61 blazed into the darkened Florida skies at 4:27 a.m. EST on the 2nd.
Several burns of Endeavour’s thrusters over the following two days closed their separation distance from Hubble by around 59 miles (95 km) per orbit, until, early on the 4th, Hoffman spotted the telescope through his binoculars … and noted that one of its solar arrays—due to be replaced by Thornton and Akers during the second EVA—appeared to be bent in a 90-degree angle. “It was a beautiful sight when we finally could really see the Hubble,” Dick Covey remembered in his NASA oral history, “and it is as bright as anything you can imagine, because of the silver-colored insulation, and the gold of the solar arrays just made it spectacular when it first came into visual range and tracked on in.” Two hours ahead of retrieval, at a distance of 7.4 miles (12 km), Covey executed the Terminal Initiation burn, then performed several small mid-course correction firings to bring Endeavour to a position some 1,180 feet (360 meters) “below” and 500 feet (150 meters) “behind” Hubble. By this time, the telescope’s twin high-gain antennas had been stowed against its main body.
Closing in on their quarry just after orbital sunset, this approach was designed to minimize contamination from the shuttle’s thruster pulses. As the orbiter drew closer, a ground-commanded maneuver of the telescope aligned its grapple fixture convenient for the RMS. Finally, at 3:48 a.m. EST, Covey brought the orbiter to a position just 35 feet (10 meters) from Hubble and Nicollier gingerly extended the Remote Manipulator System (RMS) mechanical arm and grappled the target. Endeavour was high above the South Pacific, to the east of Australia, at the moment of capture.
“Houston,” radioed Covey, triumphantly, “Endeavour has a firm handshake with Mr Hubble’s telescope.”
“Roger, Covey,” replied Capcom Susan Helms. “There’s smiles galore down here.”
The first major objective of the mission had been accomplished. Yet the real challenge of the five back-to-back EVAs and the uncertainty about whether the efforts of the astronauts would succeed remained to be seen.
With the enormous bulk of Hubble safely anchored to the Flight Support Structure—a rotatable and “tiltable” turntable, a little like an oversized Lazy Susan—in Endeavour’s payload bay, the next step was EVA-1. The spacewalks would be performed daily, with Musgrave and Hoffman charged with the first, third, and fifth and Thornton and Akers assigned to the second and fourth. Encased within their pressurized suits, the astronauts were identified by the presence (or absence) of markings on their legs: Hoffman (EV1) would have red stripes, Musgrave (EV2) would have no stripes, Thornton (EV3) would have dashed red stripes, and Akers (EV4) would have diagonal broken red stripes. All four spacewalkers were extensively “cross-trained” to allow them to perform any one of the mission’s given EVA tasks, and around 200 tools—from power ratchets and sockets to safety bars and articulating foot restraints and from portable work lights and locking connectors to instrument covers, handles, and umbilical connectors—and a total of 15,800 pounds (7,200 kg) of equipment would be transported into orbit for the repair.
Looking back on those adrenaline-charged days, 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.”
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 p.m. EST on 4 December, to kick off EVA-1. Their main task was the replacement of Hubble’s twin sets of Rate Sensing Units (RSU), which carried gyroscopes to effect tracking of the telescope. Three of a total complement of six gyroscopes had failed between December 1990 and November 1992 … and at least three were required to maintain proper pointing. After setting up tools, safety tethers, and equipment, Hoffman fitted a foot restraint onto the end of the RMS and was manoeuvred by Nicollier toward Hubble. In the meantime, Musgrave 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 because they were assigned the odd-numbered EVAs) opened Hubble’s equipment bay doors and emplaced 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 a.m. 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. By now, Hubble had a full, healthy set of gyroscopes.
Then the spacewalkers hit their first major problem: 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 the doors had somehow become warped, perhaps by 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 asked Musgrave to help him. 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 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.
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.”
Pre-flight training indicated that changing both arrays would require around five hours, thereby necessitating an entire EVA to be devoted to this objective. Although the arrays were designed to accommodate expansion and contraction caused by heating and cooling during orbital daytime and nighttime, actual experience demonstrated that this did not occur as smoothly as hoped. A temporary fix had been effected, whereby Hubble’s pointing system compensated automatically for the jitter induced by the solar panels, but the European Space Agency (ESA) was assigned the responsibility to produce a new set and reduce the effect to an acceptable level. The new arrays included thermal insulation sleeves on their bi-stem supports to minimise heating and cooling and springs worked like shock absorbers to take up tension at the ends.
Thornton and Akers (“the even couple,” according to Dick Covey) ventured into the payload bay at 10:35 p.m. EST on 5 December to the sight of a slightly different Hubble, for the roller-blind-like solar arrays had been commanded to fold up. The plan was to replace the arrays with new ones, carried aboard a Solar Array Carrier (SAC) in the payload bay, then load the old arrays onto the SAC for the return to Earth. One of them (the port-side array) folded up perfectly and could be stowed for return to Earth, but a bent bi-stem strut prevented the other one from doing likewise. It could only be moved to a position about 30-percent-closed, because any attempt to fold it further risked breaking the bi-stem and creating a risk to the spacewalkers. This left Thornton and Akers with little alternative but to dump it overboard. Interestingly, Thornton lost voice communications with Endeavour or the ground until around three hours into the EVA, requiring Akers to serve as a relay. (Earlier, she had also experienced lower-than-normal pressure in her vent garment, due to a temporary ice plug in the suit’s plumbing system.) An hour into the EVA, they dismounted the damaged array—which was 15.7 feet (4.8 meters) long when folded up and weighed 350 pounds (160 kg)—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 p.m., as Endeavour sailed high above Somalia, describing its departure as resembling a bird in flight.
“Then we had to fire our maneuvering 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.” Watching from Endeavour, the crew of STS-61 was mesmerised by the spectacle, as the array somersaulted a few times in the vacuum. 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!”
That broke the spell, recalled Hoffman, and they went back to work. EVA-2 ended after six hours and 36 minutes. Its relative brevity came as a relief, for the astronauts were at least able to enjoy dinner together and a proper night’s sleep. 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 into the telescope. This had been developed by the Jet Propulsion Laboratory (JPL) in 1985 as a “spare,” and after the discovery of the spherical aberration NASA and the WFPC team had installed an optical corrector. “The new design incorporates an optical correction by the refiguring of relay mirrors already in the optical train of the cameras,” read NASA’s pre-flight press kit for STS-61. “Each relay mirror is polished to a new specification that will compensate for the incorrect figure on [Hubble’s] primary mirror. Small actuators will fine-tune the positioning of these mirrors on-orbit, ensuring the very precise alignment that is required.” The WFPC team also upgraded the instrument, by reducing the number of cameras from eight to four, in order to develop an alignment system, and adding improved charge-coupled devices to aid its ultraviolet sensitivity.
An hour into the spacewalk, Hoffman crisply removed the old “whiffpick” from its housing in Hubble’s bowels and inserted 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 a.m. EST. Ground controllers ran an “aliveness” test and verified that the pie-wedge-shaped WFPC-2 was working correctly. The spacewalkers then replaced a pair of magnetometers, before returning inside Endeavour after six hours and 47 minutes. This proved exceptionally good time, when one considers that training for the whiffpick replacement alone had typically taken four and a half hours in the water tank.
Thornton and Akers were next, on 7-8 December, with the long-awaited installation of the critical Corrective Optics Space Telescope Axial Replacement (COSTAR) 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 the COSTAR was successfully installed, the scientists on the ground would be “deliriously happy.” However, they were not fully appreciative of NASA’s collective mindset of having a 100-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 demanded far more than could be achieved by even five EVAs and an 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 to split Servicing Mission (SM)-1 into two halves. They were in it for the long haul.
Exchanging Hubble’s High Speed Photometer (HSP) for COSTAR involved Thornton and Akers opening the telescope’s bay doors and loosening latches and removing electrical connectors in order to slide out the instrument. The new corrective optics package was then fitted. In training on Earth, the operation had taken around three and a half hours. 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 and solace he could find from the mission was sitting in the dentist’s chair—began to lessen somewhat when Thornton and Akers successfully removed the 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.
Musgrave and Hoffman’s final EVA, lasting seven hours and 21 minutes on the night of 8-9 December, replaced the overheating solar array drive electronics on the telescope and installed magnetometer covers and an electrical connection box on the Goddard High Resolution Spectrograph (GHRS). All were listed as critical tasks. 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 integrated EVA-RMS-orbiter operations were pushed to their limits.
That night, the night after the final EVA, the crew of STS-61 celebrated their success above the roof of the world. “Of all of the programs that I have been associated with,” Dick Covey remembered, years later, “it’s the one that was best planned and has been best executed, in terms of using astronauts and crewed vehicles to be able to support, enable and enhance the scientific mission of space.” They did not yet know if the corrective optics would work, of course, but they had carried out their share of the repair. Prior to deploying Hubble back into space, its orbit was slightly boosted to around 370 miles (600 km) in order to overcome the drag experienced since its initial deployment in 1990.
Late on the evening of 12 December, preparations for STS-61’s triumphant return to Earth got underway. Re-entering from almost twice the average altitude for a shuttle mission, the de-orbit burn of Endeavour’s OMS engines lasted almost five minutes, but was completed by 11:19 p.m. EST, committing the shuttle to a 70-minute descent. Passing over Mexico City during their period of peak heating, Covey was convinced that Endeavour gave ground-based observers a great view. “The orbiter was fully enveloped in the ionization plume,” he said later, “and as we banked up into a left bank coming over Mexico City and the windows were white because of the plume, I could look out and still see all the lights. It was not washed out at all; it was very bright through that, so we had to be giving them a great show.” Eventually, the crew of STS-61 returned to Florida airspace. At 12:25 a.m. on the morning of the 13th, trailing double sonic booms in her wake, she swept into Florida and alighted perfectly onto the concrete surface of the Kennedy Space Center’s Runway 33.
STS-61 did nothing less than save NASA. Few other missions since Apollo 11 had exerted such a positive influence on its 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 for their work. The citation praised their “outstanding leadership, intrepidity and the renewal of public faith in America’s space program by the successful orbital recovery and repair of the Hubble Space Telescope.”
Over the following weeks, the Servicing Mission Orbital Verification (SMOV) got underway, encompassing the checkout of Hubble and a resumption of scientific activities as soon as possible. This included the optical alignment and focusing of WFPC-2 and the deployment of COSTAR, as well as test observations. The announcement came on 13 January 1994, when NASA Administrator Dan Goldin revealed the first new images at a press conference at the Goddard Space Flight Center in Greenbelt, Md. Accompanied by Dr John Gibbons, Assistant to the President for Science and Technology, and Senator Barbara Mikulski of Maryland, Goldin told the gathered media that Hubble was “a true international treasure.” Mikulski, who had earlier poured scorn upon the telescope after the discovery of its spherical aberration in mid-1990, now lauded the successful repair as “a wonderful victory for the Hubble team.”
The astronauts, of course, knew of the success well ahead of the press conference.
And for Jeff Hoffman, a professional astronomer, it came as a particularly sweet gift. In the early hours of New Year’s Day 1994, he and his English-born wife, Barbara, hosted friends to their Houston house. By the end of the evening, everybody had left and Hoffman was cleaning up in the kitchen.
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!”
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 Gemini VI-A and VII, the first rendezvous in space between two piloted space vehicles, back in December 1965, which rose from the ashes of disappointment … and ended to the sound of “Jingle Bells.”