Gentlemen’s Hours: Remembering STS-48, Thirty Years On

Still in the grasp of the RMS, the massive UARS payload is readied for deployment. Photo Credit: NASA

Late in September 2011, the skies above the Pacific Ocean were illuminated by an astonishing fireshow. NASA’s Upper Atmosphere Research Satellite (UARS)—launched 30 years ago today, on 12 September 1991—returned to Earth in a blaze of glowing debris. Originally planned to survive for just two years, UARS spent more than a decade examining gas concentrations and pressures, the effects of solar irradiance and ozone levels in the Earth’s atmosphere. From its vantage point high above the planet, UARS observed 80 degrees in latitude and furnished scientists with near-global coverage of the stratosphere and mesosphere regions.

Video Credit: International Astronautical Federation

Built by General Dynamics, the 13,000-pound (5,900 kg) satellite could take measurements over the full range of time-zones in all major geographical locations, every 36 days. Its ten scientific instruments provided the most complete data on solar energy inputs, terrestrial winds and atmospheric composition for its time. And this data would be used to measure the composition and distribution of nitrogen and chlorine compounds, as well as ozone, water vapor and methane, and study thermal emissions to create vertical abundance profiles and peg the temperatures and pressures of high-level winds.

The five astronauts who deployed UARS from shuttle Discovery were named in December 1990. Commanding STS-48 was John “J.O.” Creighton, joined by pilot Ken Reightler and mission specialists Sam Gemar, Jim Buchli and Mark Brown.

The STS-48 crew comprised (front row, left to right) Mark Brown, John “J.O.” Creighton and Ken Reightler, with Sam Gemar standing at left and Jim Buchli standing at right. Photo Credit: NASA, via

Original plans called for the five-day flight to take place in November 1991, but due to changes in the shuttle manifest STS-48 was brought forward six weeks to September. An early-fall launch for UARS was highly desirable, as its projected minimum lifetime of two years would enable it to observe at least two winters in the northern hemisphere and at least one season studying the much-publicized “ozone hole” above Antarctica.

For the astronauts, it came as a welcome relief to move from low to high priority in the shuttle mission simulator. “All of a sudden, we found out we were going to leapfrog a couple of other flights and be sooner, rather than later,” Creighton remembered. “So then we really had to scramble. That was a tough nine or ten months of very intense training.”

The STS-48 crew patch, bearing the surnames of the five astronauts. Image Credit: NASA

UARS’ orbit demanded one of the highest altitudes ever attained by the shuttle: some 373 miles (600 km), not too much lower than the Hubble Space Telescope (HST). However, unlike Hubble—which had been delivered into a 28.45-degree-inclination orbit in April 1990—the STS-48 astronauts rose to a higher inclination of 57 degrees. “We set a world altitude record for a winged vehicle” at 57 degrees, Creighton proudly recalled of STS-48, and he retains the commemorative plaque to prove it.

Launch of Discovery was set for 12 September 1991 and after a 14-minute delay, due to noisy interference on the air-to-ground communications link, the shuttle roared aloft at 7:11 p.m. EDT, right on the cusp of sunset. The early evening launch meant they did not awaken until early afternoon, which Creighton called “gentlemen’s hours”. It was a totally different experience from his previous mission, STS-36, which launched in the middle of the night. “A lot of shake, rattle and roll going on” was Creighton’s recollection of the launch.

Discovery launches at sunset on 12 September 1991, three decades ago tonight. Photo Credit: NASA

With all but Reightler having flown in space before, the rookie pilot was keen to perform at his peak. One of his concerns was functionality in his bulky partial-pressure suit, which had a tendency to “pull” on his body and impair his ability to reach cockpit switches. “To bolster my confidence, right after liftoff, I started systematically reaching around the cockpit as the G-forces started to build,” Reightler remembered later. His efforts were watched with some consternation by Creighton. At length, the commander politely asked: “Ken, would you please knock that off?”

Reightler complied and the rest of the climb to orbit was a dream come true.

UARS sits in Discovery’s cavernous payload bay, as the RMS mechanical arm (upper right) prepares to grapple it for deployment. Photo Credit: NASA

That dream continued after insertion into space. Reightler unstrapped from his seat and prepared to float downstairs into Discovery’s middeck to remove his suit…when, all at once, his attention was arrested by the continent of Asia, drifting past the windows. “I was looking straight down at Earth,” he told a Smithsonian interviewer, years later. “I was totally unprepared for the colors, textures, detail and vastness of the scene. It literally took my breath away. No amount of training or looking at slides can prepare you for that moment.”

Even the veterans were not immune to awe. Creighton expressed astonishment at how high their orbital altitude was. He had previously flown to lower altitudes on his two prior shuttle missions.

Ken Reightler was making his first shuttle flight on STS-48. Photo Credit: NASA

Yet there was work to do. UARS represented one of the shuttle’s largest payloads and would be deployed by Brown, using the Canadian-built Remote Manipulator System (RMS) mechanical arm. In anticipation of problems, the cabin pressure was lowered to allow Buchli and Gemar to go outside on a contingency spacewalk.

But UARS’ power-up and activation went relatively smoothly, with the exception of a minor communications issue. Deployment of the payload occurred at 12:23 a.m. EDT on 16 September, an orbit later than intended, and within weeks would begin more than a decade of operations.

Video Credit: NASA

Deployment of the giant satellite required all five astronauts, working in tight harmony. Brown and Reightler handled the RMS controls, whilst Buchli monitored Discovery’s systems and Gemar kept track of the shuttle-to-UARS interface. Meanwhile, in Brown’s words, Creighton, “with his rubber hose, kept an eye on all of us”. By Brown’s recollection, it took about nine or ten minutes to move UARS from its berthed position in the payload bay to its deployment position, high above Discovery’s windows. “It is not a sleek spacecraft, by any means,” Brown said later, “but is extremely functional.”

After release, Creighton issued a separation “burn” of the forward-facing Reaction Control System (RCS) thrusters, which carried the shuttle away from the payload at a rate of a couple feet per second. As UARS drifted away into the inky blackness, the astronauts began snapping photographs. “It’s gonna take me an hour to review all these pictures,” one of them muttered.

Mark Brown was primarily responsible for the UARS deployment. Photo Credit: NASA

“One of the things they saw is that the chloroflurocarbons that come from the industrialized northern hemisphere were migrating down over the Antarctic,” said Creighton in a NASA oral history interview, “and that’s what was a direct correlation to what was causing the destruction of the ozone layer in the Antarctic spring. It would release all of these things that were trapped in the lower atmosphere and then it would spiral up, because of the circular wind patterns, up into the ozone and then create the hole. That was kind of exciting to see that what people had long suspected was proven.”

STS-48 remained in orbit for five days and the astronauts were fully occupied by a battery of scientific, medical and technical experiments. Investigations in protein crystal growth, muscular atrophy in rats and polymer membranes were conducted, measurements of cosmic and gamma radiation were taken and an intriguing demonstration of a model truss structure for Space Station Freedom was assembled in the middeck.

Video Credit: NASA

This MIT-funded study, known as the Middeck Zero-Gravity Dynamics Experiment (MODE), incorporated accelerometers and strain gauges to examine the behavior of truss members and the sloshing of fluids (represented in the test by water and silicon oil) and assess the performance of “rotary joints” to steer the station’s massive solar arrays.

For the first time, an Electronic Still Camera (ESC)—a modified Nikon F-4 35 mm camera, fitted with a charge-coupled device for digital image storage—was carried into space aboard the shuttle. Today, it is easy to take the real-time downlink capabilities of electronic still cameras for granted, but on STS-48 this was demonstrated for the first time.

Mark Brown (left) and Jim Buchli work to assemble the Middeck Zero-Gravity Dynamics Experiment (MODE) on Discovery’s middeck. Photo Credit: NASA

For Creighton, the MODE tests were particularly memorable. “It was almost being a kid with a Tinker Toy set,” he recalled, “putting all those things back together again. We had a little shaker with a bunch of strain gauges on it to vibrate this structure to see how it would react in space. What they were trying to do is verify the computer models down on the ground to make sure that the vibration and the characteristics of this truss would react in space the way they thought they were predicting they would in computers…and that was successful.”

NASA had been flying spacecraft for several decades, of course, but the behaviour of fluids in partially-empty propellant tanks under microgravity conditions was still imperfectly understood. MODE’s clear Plexiglas vials of water and silicon oil enabled the first detailed analyses to take place.

Video Credit: Kennedy Space Center Visitor Complex (KSCVC)

The mission briefly entered the news on 17 September, when it became the first shuttle flight to take evasive action to avoid a piece of space junk. Four days after launch, Mission Control advised the astronauts that their trajectory would carry them uncomfortably close to the Soviet Union’s car-sized Cosmos 955 satellite—perhaps as close as just 0.7 miles (1.2 km). “With the planned space station,” Brown told journalists after the flight, “which will be less maneuverable than a shuttle, NASA will need to study the potential problem of collisions with debris much more carefully.”

A short “burn” of Discovery’s Reaction Control System (RCS) thrusters established a 10-mile (16 km) berth between the crew and the long-since-defunct Cosmos 955, which had been in orbit for 14 years. “We were all busy conducting experiments,” Reightler recalled, “so no one gave this operation much time or attention. I didn’t even take a look out the window to see if I could see the intruder go by. I just wanted to make sure we didn’t make the news back home!”

Discovery alights at Edwards Air Force Base, Calif., on 18 September 1991. Photo Credit: NASA

For Reightler, his big event at the end of STS-48 was lowering the shuttle’s landing gear, a few seconds prior to touchdown. It was the pilot’s crucial task and one that Reightler’s wife, Maureen, had constantly reminded him about during training. Discovery’s 13th return from space was unusual in two ways: Firstly, it was only the second post-Challenger mission to have the Kennedy Space Center (KSC) as its scheduled landing site, and secondly, it would touch down, for the first time in Florida, in darkness.

As a result, much of the astronauts’ re-entry training had been in darkness, crossing the darkened United States and alighting on the swamp-fringed runway on the Space Coast. The actual event turned out to be somewhat different, when rain clouds in Florida forced a one-orbit extension and an eventual decision to land at Edwards Air Force Base, Calif. Creighton and Reightler brought Discovery perfectly onto concrete Runway 22, in darkness, at 12:38 a.m. PDT (3:38 a.m. EDT) on 18 September.


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