Two decades ago, yesterday, on 11 February 1997, Space Shuttle Discovery roared into the night with a seven-strong crew—Commander Ken Bowersox, Pilot Scott “Doc” Horowitz, Payload Commander Mark Lee and Mission Specialists Greg Harbaugh, Steve Smith, Joe Tanner and Steve Hawley—to perform the second servicing of the $1.5 billion Hubble Space Telescope (HST). During five back-to-back sessions of Extravehicular Activity (EVA), the astronauts installed two new scientific instruments aboard the iconic telescope and provided the tools for an all-new observatory for the 21st century.
Two days after liftoff, Hawley extended the shuttle’s Canadian-built Remote Manipulator System (RMS) mechanical and grappled Hubble, allowing it to be berthed for the servicing operation to commence. Late that evening, Lee and Smith—clad in bulky space suits—became the first astronauts to depart an External Airlock into Discovery’s payload bay. As outlined in yesterday’s AmericaSpace history article, their task for EVA-1 was nothing less than “the Superbowl of EVAs”, for they would remove the aging Goddard High Resolution Spectrograph (GHRS) and Faint Object Spectrograph (FOS) and replace them with the more capable Space Telescope Imaging Spectrograph (STIS) and Near-Infrared Camera and Multi-Object Spectrometer (NICMOS).
However, Lee and Smith’s spacewalk did not begin well. Whilst still inside the airlock, one of Hubble’s solar arrays windmilled through a quarter-turn, reorienting itself from a horizontal to a vertical configuration within a minute, then stabilizing. “That was one of the more memorable things from the flight,” Steve Hawley told the NASA oral historian. “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 Tanner were on Discovery’s aft flight deck when the incident occurred and the two men exchanged anxious glances. Both knew that the array was not supposed to drive so rapidly, but with external cameras focused on the airlock hatch—and not Hubble—there were few people in Mission Control who were aware of the uncommanded motion. Tanner quickly advised them and Hawley was convinced that the EVA would be scrubbed.
It later became clear that the External Airlock—which had been moved from the orbiter’s crew cabin into the payload bay as part of modifications for International Space Station (ISS) operations—had been partly to blame. “They had replumbed the way the air is evacuated from the airlock volume,” said Hawley. “As luck would have it, the way the air exited was through a pipe that came out under the [telescope].” It was this evacuation of air which had impinged on Hubble’s array and caused the uncommanded slew.
Somewhat later than planned, Lee and Smith began EVA-1. 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 and Lee free-floating in the payload bay. They opened Hubble’s aft shroud doors to remove the GHRS and 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 said 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.”
About 2.5 hours into the EVA, the STIS 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 Lee to verbally guide both Smith (who had a face-full of instrument) and Hawley (who was operating the RMS from inside 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 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. After installation, payload controllers verified that the health of the new instruments was good, and after STS-82 they underwent several weeks of calibration.
The following night, it was the turn of Harbaugh and Tanner. Working quickly, the two men replaced a degraded Fine Guidance Sensor (FGS), which would be returned to Earth for refurbishment. 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, “tiny little spider cracks”. Moreover, a small “crater”, caused by a Micrometeoroid Orbital Debris (MMOD) impact, was spotted in one of Hubble’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 and planning began to utilize STS-82 to effect repairs.
With the second spacewalk complete, the crew had fulfilled their minimum requirements for mission success. Lee and Smith were next, departing the airlock for EVA-3 to 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. “It’s is not a piece of cake.” With Lee anchored to the RMS, and Smith free-floating, 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, it was decided to insert an unscheduled fifth EVA to repair Hubble’s damaged thermal insulation. In the meantime, Harbaugh and Tanner floated outside 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 Hubble’s light shield.
From inside the crew cabin, 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 insulation patches to be installed the following night. In total, 35 pages of instructions were transmitted up to the shuttle, employing spare insulation pieces, Kapton tape, parachute cord and alligator clips.
Following a good night’s sleep, Lee and Smith left the airlock for what they expected to be the final time on 17 February. They attached thermal blankets onto three key equipment compartments at the top of the Support Systems Module, at Hubble’s midpoint, where critical data-processing, electronics and instrument telemetry packages were housed. Following this work, the men 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 shuttle’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, success was achieved. A record-setting sixth EVA on a single shuttle mission evaded them and Lee and Smith returned inside Discovery, wrapping up five spacewalks and a total of 33 hours and 11 minutes.
After a job exceptionally well done, Hubble’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 on 19 February. 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 the 21st, 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).
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 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-foot (60-meter) intervals along the centerline. The work undertaken by Discovery’s crew had turned Hubble from a 1970s spacecraft with 1980s optics into an observatory for the 21st century. “Three hundred years from now,” said 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 the 55th anniversary of Friendship 7, when John Glenn became the first American to orbit Earth.