Seventeen years ago this week, NASA launched its second shuttle Servicing Mission (SM-2) to the Hubble Space Telescope (HST). The $1.5 billion observatory has earned itself a well-deserved reputation as one of the most successful space-based instruments ever launched. Across more than two decades of operations, it has peered deeper into the cosmos than ever before, acquiring images of distant galaxies, making breakthroughs in cosmology and physics by accurately determining the rate of expansion of the Universe, detecting planets around far-off stars, witnessing the impact of Comet Shoemaker-Levy 9 into Jupiter, tracking cloud movements in the atmospheres of Uranus and Neptune, and creating the best currently achievable “map” of the surface of Pluto. It is nothing less than a national and international icon, although its early years were marred by a spherical aberration which the STS-61 SM-1 crew triumphantly resolved in December 1993. Three years later, as described in yesterday’s history article, seven more astronaut set off on STS-82 to turn Hubble from a repaired observatory into essentially a brand-new observatory for the 21st century.
In spite of delays to several shuttle flights in 1996, the mission held firm to its target launch date of February 1997. Originally scheduled to launch on the 13th, it actually flew two days earlier, on the 11th. At first glance, this seemed surprising, in view of numerous minor issues in the weeks preceding the mission. During Discovery’s rollout to the pad in mid-January, whilst on the crawlerway, the stack was halted when a large, Y-shaped crack was identified on the deck plating of the Mobile Launch Platform (MLP). Despite its alarming appearance it was determined that the MLP’s integrity had not been compromised and the rollout continued.
Then, in the hours before liftoff, the loading of propellants into the External Tank met with delay, due to the need to assess the gaseous nitrogen purge system and monitor unusually high concentrations of trapped oxygen in the orbiter’s midbody and payload bay. With the launch window due to open at 3:56 a.m. EST on 11 February, at the opening of a 61-minute “window,” the precise time was adjusted slightly to 3:55:17 a.m. at T-9 minutes, based on a final computation of HST’s orbit. Exactly on time, to the very second, Discovery turned night into day across the Florida coast as she speared into one of the shuttle’s highest ever orbits, with an apogee of 356 miles (574 km) and a perigee of 295 miles (475 km). A few hours later, they were trailing their quarry by 3,560 miles (5,740 km), closing at a rate of about 350 miles (560 km) with each 90-minute orbit.
Following their first night’s sleep, the astronauts began reducing the cabin pressure to prepare the four spacewalkers—Mark Lee, Steve Smith, Greg Harbaugh, and Joe Tanner—for operating in their space suits, as well as serving to clear nitrogen from their bloodstreams and thus avoiding a debilitating attack of the bends. Meanwhile, on Discovery’s flight deck, fellow astronaut Steve Hawley powered up the 50-foot (15-meter) Remote Manipulator System (RMS) mechanical arm and conducted a survey of the servicing equipment, housed on a Flight Support Structure (FSS) in the payload bay. Elsewhere, HST’s controllers remotely closed the telescope’s aperture door and secured its antennas.
Early on 13 February, about two hours before the scheduled retrieval, Discovery had reached a distance of about eight miles (14.8 km) from the telescope, whose shiny surfaces made it literally glow and reflect the blues and whites of Earth. At about 1 a.m. EST, Commander Ken Bowersox and Pilot Scott “Doc” Horowitz executed the Terminal Initiation (TI) maneuver, followed by a number of mid-course correction burns, to guide the orbiter toward its quarry from “below,” thereby minimising the risk of causing contamination from thruster firings. By the time he reached 2,300 feet (730 meters), at about 2:30 a.m., he assumed manual control and gradually brought the shuttle to a position just 35 feet (10 meters) away from the telescope. With the west coast of Mexico just coming into view, Hawley then extended the RMS, grappled HST at 3:34 a.m., and berthed it securely onto the FSS about 30 minutes later.
“You should have seen the expression on Dr Stevie’s face,” Bowersox told Mission Control. “It looked like he just shook hands with an old friend.”
“We watched it from down here, Sox,” replied Capcom Marc Garneau. “It was certainly an absolute thrill for us to see it on television and congratulations to all of you for an outstanding rendezvous and a great capture. We’re looking forward to getting out there and starting work on that telescope.”
Immediately after berthing on the FSS, a remote-controlled umbilical was mated to HST to provide temporary electrical power. With EVA-1 by Mark Lee and Steve Smith scheduled to begin late on 13 February, HST Program Scientist Ed Weiler was under no illusions as to its importance, for it would feature the installation of the Space Telescope Imaging Spectrograph (STIS) and Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). “All EVAs are important,” he told journalists, “but [this] is really the Superbowl of EVAs. If that goes well, I think it will really put Hubble into a position of having world-class scientific capability well into the 21st century.” Preparations proceeded briskly and it seemed likely that Lee and Smith would be outside around an hour earlier than planned. However, whilst in the external airlock, they were suddenly halted when one of the telescope’s 40-foot-long (12.2-meter) solar arrays windmilled through a quarter-turn, reorienting itself within about 60 seconds from a horizontal into a vertical configuration. It then stabilised.
“That was one of the more memorable things from the flight,” Steve Hawley told the NASA oral historian, with a hint of understatement. “We coincidentally were trained to recognize an uncommanded slew of the solar arrays. If, for some reason, the solar array drive motor should fail in some manner, and they’ll start to drive, you’re trained to recognize that. You can send a command that will disable the motor so the solar arrays don’t drive into something.” Hawley and Joe Tanner were on Discovery’s aft flight deck when the array moved. The two men exchanged glances. Both of them knew that the arrays were not supposed to drive that rapidly, and it soon became obvious that it was an uncommanded movement. With cameras focused on the airlock hatch, few in Mission Control had any awareness of the motion, and Tanner called the ground to advise them. “I was convinced that we probably wouldn’t be going EVA today,” admitted Hawley. “At the time, we didn’t know what had caused it and they drove [the array] all the way to the stops.”
It subsequently became clear that the new external airlock, which was flying aboard Discovery for the first time on STS-82, was part of the root cause. “There was actually an interior airlock that had been removed,” said Hawley, “and they had replumbed the way the air is evacuated from the airlock volume. As luck would have it, the way the air exited was through a pipe that came out under the [telescope]. We didn’t know it at the time, but what people on the ground figured was that air from the venting of the airlock impinged on the solar arrays and started them moving.” The air had funneled its way through thermal blankets in the payload bay, then vented directly on to the array, causing it to “windmill” from horizontal to vertical. Fortunately, no damage was caused, but Hawley felt that if Mission Control had seen the event on television, they would have cancelled EVA-1. Fortunately no damage was caused, and about 75 minutes later than intended, at 11:34 p.m. EST, Lee and Smith floated out of the airlock to begin the first spacewalk of the mission.
Venturing into open space for the first time in his astronaut career, Smith was electrified. “Oh my gosh … beautiful!” he radioed. “It was worth the wait!”
Quickly, the two men set to work, with Smith riding at the end of the RMS arm and Lee free-floating in the payload bay. They opened HST’s aft shroud doors to remove the Goddard High Resolution Spectrograph (GHRS) and Faint Object Spectrograph (FOS), both of which were stowed for return to Earth. Manipulating a suited crewman on the end of the mechanical arm was entirely new ground for Steve Hawley. “We had enough camera views that I could see what [Smith] was doing,” he remembered, years later. “I knew what his next step was going to be, so it was easy for me to put him where he needed to be.” One of the biggest issues in training had been communication between Hawley and whoever was on the RMS, particularly if communication was also ongoing with the Capcom in Mission Control.
“We developed some hand signals that we could use in the event that somebody else was talking on the radio,” he said. “We didn’t want to sit there and wait for that conversation to end before we could do the next task, because time is pretty critical.” They also devised co-ordination systems, based on the orientations of the shuttle and the EVA crewman, to ensure that movements were crisp and correct. “We spent a lot of time practicing being very disciplined in how we communicated,” added Hawley. For example, in cases where the EVA crewman wanted to move to a different position within the payload bay, he might tell Hawley to move him port, starboard, forward, or aft, relative to the orbiter. In other circumstances (for example, whilst working inside one of the telescope’s bays), the EVA crewman might switch the point of reference from “orbiter co-ordinates” to “body co-ordinates,” with calls to Hawley such as “head-up,” “feet-down,” “left,” or “right.” Although complex at first, months of training and practice turned it into an elegant symphony. Hawley liked its unambiguity, which eliminated errors. “My recollection,” he said, “is that we never made a mistake the whole flight in terms of a bad command or going the wrong direction, because we thought it was very important and we practiced it a lot.”
At about 2 a.m. EST on the 14th, about 2.5 hours into EVA-1, the STIS instrument had been successfully installed. Two hours later, NICMOS was also in place. Tolerances were incredibly tight, with no more than 0.5 inches (1.2 cm) clearance in some cases, requiring the free-floating Lee to verbally guide both Smith (who had a face-full of instrument) and Hawley (who was operating the RMS from the shuttle’s cabin). In fact, the question of who actually fitted the new devices proved a subject of some humor. Since Smith was physically holding the instrument, it might seem initially that he had installed it. Not so, joked Hawley, for it was he who was actually maneuvering the RMS, with Smith and the instrument, into place. “All he can see is a face full of instrument,” Hawley noted, “so my job was to maneuver him around. Steve Smith always said he inserted the instrument in the telescope, but I used to tell him, ‘No, I really did. You were just holding it!'”
After installation, payload controllers verified that the health of the new instruments was good, and after STS-82 they underwent several weeks of calibration. In the meantime, EVA-1 concluded at 6:16 a.m. EST, after six hours and 42 minutes. The following night, it was the turn of Greg Harbaugh and Joe Tanner, who ventured into Discovery’s payload bay almost an hour ahead of schedule at 10:25 p.m. EST. Working quickly, the two men replaced a degraded Fine Guidance Sensor (FGS), which would be returned to Earth for refurbishment and re-installation during the SM-3 mission, then planned for November 1999. Late in the spacewalk, they noticed cracks and wear in the Teflon outer coat of the telescope’s 17-layered thermal blanketing on the side facing toward the Sun and into the direction of travel. Some of the cracks were as long as eight inches (20 cm) and were not, said Harbaugh, simply “tiny little spider cracks.” Moreover, a small “crater,” caused by an orbital debris impact, was spotted in one of HST’s antennas.
“In several places, it’s cracked,” said Tanner. “It’s just gotten old, it looks like.” Although there was no obvious evidence of crumbling, he recommended that care should be taken when touching the insulation. It was clear that although a more comprehensive fix would be necessary on SM-3, planning began to utilise some of the servicing time on STS-82 to effect repairs. In the meantime, at the end of EVA-2, Discovery’s thrusters were fired for 22 minutes to gently raise HST’s altitude by about two miles (3.3 km). Executing such a maneuver required Bowersox and Horowitz to fire the thrusters in a rocking, side-to-side motion to gradually ascend along the velocity vector. Discovery’s tail-mounted thrusters were fired continuously throughout the reboost, with those on either side of the nose firing sequentially at 60-second intervals. Two more reboosts were planned at the end of EVA-3 and EVA-4 to raise the telescope’s orbit by a total of about 5.7 miles (9.2 km). “If we were to have a camera outside actually looking at it, you would hardly notice this,” said STS-82 Lead Flight Director Jeff Bantle before launch. “Using the venier jets is going to be like normal attitude control. In fact, all of our reboost is planned while the [EVA] crew is outside doing the clean-up in the bay.”
With the second spacewalk officially concluded at 5:52 a.m. EST on 15 February, after seven hours and 27 minutes, the STS-82 crew fulfilled their minimum requirements for mission success. Lee and Smith were next, departing the airlock at 9:53 p.m. that same night to firstly change the Data Interface Unit (DIU), which was never intended for orbital replacement. “The DIU is really a tough nut, because you have got a whole bunch of connectors you have to unfasten and reconnect and any one of them could be balky and create problems,” said Harbaugh before launch. “It’s is not a piece of cake.” With Lee anchored to the RMS arm, and Smith free-floating in the payload bay, the DIU was replaced successfully. The spacewalkers then exchanged one of the telescope’s engineering science tape recorders for a new solid-state recorder and concluded EVA-3 by replacing one of the Reaction Wheel Assemblies (RWA), which had failed a year earlier. Shortly after Lee and Smith returned inside Discovery at 5:04 a.m. EST on 16 February, it was decided to insert an unscheduled fifth EVA to repair HST’s damaged thermal insulation. A conversation between Bowersox and Jeff Bantle prompted the lead flight director to approve the “short” EVA-5, lasting around four hours, to effect a fix.
In the meantime, Harbaugh and Tanner floated outside at 10:45 p.m. on the 16th to begin the fourth spacewalk, whose primary objectives included the replacement of one set of Solar Array Drive Electronics (SADE) for the solar arrays and the installation of covers over magnetometers. This latter task required them to ascend about 60 feet (18 meters) “above” the payload bay and attach thermal blankets over two areas of degraded insulation around HST’s light shield. From inside the crew cabin, Mark Lee compared Tanner’s ascent to “riding your Harley,” whilst the spacewalker admired the view and remarked that it was fortunate he did not suffer from a fear of heights. During the course of the EVA, Horowitz and Lee worked on Discovery’s middeck to fabricate four new insulation patches to be installed the following night. In total, 35 pages of instructions were transmitted up to the shuttle, employing spare micrometeroid insulation pieces, Kapton tape, parachute cord, and alligator clips. By the time Harbaugh and Tanner returned inside the orbiter at 5:19 a.m. EST on 17 February, after six hours and 34 minutes, the grand finale of EVA-5 had taken shape and was ready to go.
Following a good night’s sleep, Lee and Smith left the airlock for what they expected to be the final time at 10:15 p.m. on the 17th. They attached thermal blankets onto three key equipment compartments at the top of the Support Systems Module, at HST’s midpoint, where critical data-processing, electronics, and instrument telemetry packages were housed. Specifically, Bay 7 carried mechanisms to control the solar arrays, Bay 8 held pointing electronics and a retrieval mode gyro assembly, and Bay 10 accommodated the science instrument control and data-handling subsystems. All three required protection to prevent problems in the future.
Following this work, Lee and Smith began cleaning up their work site and returned to the airlock, when flight controllers noticed a potential problem with one of the four RWAs. Although the RWA fitted on EVA-3 was operating without problems, one of its older siblings had begun to exhibit discrepancies. “They would like to perform some testing on it that may take 15-30 minutes, just to assure themselves that nothing is wrong with it,” Capcom Marc Garneau told the spacewalkers. “In the meantime, because we want to keep open the possibility of changing it out today, we’d like to hold off doing anything further.” Lee and Smith entered the airlock and connected their suits’ utilities to the orbiter’s Servicing and Cooling Umbilical (SCU).
Had the call come from the ground to replace the RWA, it would be have been necessary to repressurize the airlock, open the internal hatch, and retrieve a spare unit from Discovery’s middeck. Fortunately, engineers ran a series of tests and powered up the three “old” RWAs to assess them for problems. Engineers worked to modify software originally written to test the newly-installed RWA so that it could test the troublesome unit, which required a couple of hours. At length, when the software commanded the RWA to put high torque on the wheel, “the thing just took off,” in Weiler’s words, “and we knew it was just fine.” A record-breaking sixth EVA on a single mission evaded the STS-82 crew. Lee and Smith concluded EVA-5 after five hours and 17 minutes, bringing the SM-2 spacewalking total to 33 hours and 11 minutes. A final burn of the maneuvering thrusters increased their orbit to a final deployment altitude of 368 miles (593 km) x 383 miles (617 km). “We did 82 minutes of reboost,” Steve Hawley recalled years later, “and got Hubble, I guess, as high as it had been.” Ed Weiler was ecstatic, describing the observatory as no longer the “original” Hubble Space Telescope … but as a brand-new instrument: “You can call it Hubble-2.”
After a job exceptionally well done, HST’s solar arrays were oriented toward the Sun to provide electrical power and recharge its batteries. As Steve Hawley grappled the telescope with the RMS, payload controllers commanded its aperture door to open and HST and Discovery parted company at 1:41 a.m. EST on 19 February. Shortly afterward, the telescope resumed standard operations and began processing commands to the ground through the Tracking and Data Relay Satellite (TDRS) system. Two days later, it was time for the final curtain to fall on STS-82. Originally, Discovery was scheduled to land at the Kennedy Space Center (KSC) in Florida at 1:50 a.m. EST on 21 February, but Entry Flight Director Wayne Hale called off the first attempt, due to the presence of off-shore showers and low cloud cover over the Shuttle Landing Facility (SLF) runway.
The next opportunity to land was at 3:32 a.m., requiring the irreversible deorbit burn to occur at 2:21 a.m. At length, Bowersox was given the “Go” to begin the 3.5-minute burn, committing Discovery to a 71-minute-long descent. Re-entering the upper atmosphere over the Pacific Ocean, the shuttle swept across the entire continental United States and appeared as a bright streak as it passed over Texas.
“I think we just flew over Houston,” Bowersox radioed at one stage.
“You certainly did,” replied Capcom Kevin Kregel, “and you lit up the entire sky with the orbiter and its trail. It was pretty impressive.”
“It was a pretty good view from here, too,” said Bowersox. “We almost saw the Astrodome.”
Touching down on Runway 33 at 3:32 am, the STS-82 landing was aided for the first time by the presence of 52 halogen lights, positioned at 200 feet (60 meter) intervals along the centreline. Although overshadowed by the success of its predecessor, SM-1, the second HST servicing mission had proven equally as challeging for the crew and the thousands of ground personnel who put it together. Yet the work undertaken by Discovery’s crew had turned the telescope from a 1970s spacecraft with 1980s optical technology into an observatory for the 21st century, with more modern instruments. “Three hundred years from now,” explained project scientist David Leckrone, “none of us in all likelihood will be remembered as individuals, but certainly the Hubble Space Telescope will be remembered … as a high point in human civilization. That’s an awe-inspiring thought and something that motivates us to do our very best for Hubble and for science.”
The astronauts themselves were also pleased and relieved that their mission was complete. After almost two years of training, Mark Lee declared that he was ready to buy his crewmates a drink. “Up here,” he said whilst in orbit, “we’ve got some orange mango and some lemonade, but that’s as stiff as it gets. So I’m ready for a margarita!”
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 STS-75, a February 1996 shuttle mission which re-flew Italy’s Tethered Satellite System with mixed results.