Endeavour’s Radar Love: 20 Years Since STS-59 (Part 2)

Endeavour rockets into the dawn on 9 April 1994. Photo Credit: NASA
Endeavour rockets into the dawn on 9 April 1994. Photo Credit: NASA

Twenty years ago this week, the crew of Endeavour on STS-59 demonstrated that the shuttle program was imbued with “Radar Love,” as they operated the first Space Radar Laboratory (SRL-1) to acquire unprecedented views of the Home Planet from orbit. For 11 days, astronauts Sid Gutierrez, Kevin Chilton, Jay Apt, Michael “Rich” Clifford, Linda Godwin, and Tom Jones worked around the clock to ensure that the radar instruments of the SRL-1 payload gathered an enormous quantity of scientific data. Much of that data is still being analyzed to this day and has helped to shape our understanding of Earth’s past, present, and, potentially, its future.

As described in yesterday’s AmericaSpace history article, SRL-1 had its genesis in the Shuttle Imaging Radar (SIR), which flew aboard two missions in the early 1980s. On STS-2 in November 1981, SIR-A’s capabilities were left undemonstrated, because the scheduled five-day mission was cut short by a fuel cell malfunction and Shuttle Columbia returned to Earth after just 54 hours. Three years later, however, it flew again aboard Challenger on STS-41G as “SIR-B,” and its success provoked astonishment. Over an eight-day period in October 1984, it identified ancient caravan trails in Arabia, allowed geologists to construct three-dimensional maps of subtle features on California’s Mount Shasta, permitted contour modeling of parts of eastern and southern Africa, and examined intricate structural features, including fault-lines, folds, fractures, dunes, and rock layers.

A dedicated SRL-1 payload, incorporating both SIR and a German-built X-Band Synthetic Aperture Radar (X-SAR), had been on the cards since before the Challenger disaster and was originally assigned to fly one of the shuttle’s missions from Vandenberg Air Force Base, Calif., into near-polar orbit. The loss of Challenger and the end of operations at Vandenberg, without a single launch, led to a decision to fly SRL-1 from the Kennedy Space Center (KSC) and an orbital inclination no higher than 57 degrees. By 9 April 1994, after two years of training, the six-member crew was ready to go.

The STS-59 crew was tasked with operating a battery of radar instruments around the clock. Left row (front to back) are Tom Jones, Linda Godwin and Kevin Chilton; right row (front to back) are Jay Apt, Michael "Rich" Clifford and Sid Gutierrez. Photo Credit: NASA
The STS-59 crew was tasked with operating a battery of radar instruments around the clock. Left row (front to back) are Tom Jones, Linda Godwin, and Kevin Chilton; right row (front to back) are Jay Apt, Michael “Rich” Clifford, and Sid Gutierrez. Photo Credit: NASA

Writing almost a decade later, in his memoir, Sky Walking, Tom Jones remembered lucidly the adrenaline-charged minutes of his first climb into orbit. A “nasty shaking” was accompanied by a peculiar sensation of the entire cabin whipsawing around him, as the computer-controlled “Roll Program” maneuver, 10 seconds after liftoff, oriented Endeavour for her 57-degree orbit. Jones thought of his father, who had died a little more than a year earlier. Two minutes into the ascent, the twin Solid Rocket Boosters (SRBs) were safely jettisoned and the shuttle continued to power her way into orbit under the thrust of her main engines. At length, Gutierrez and Chilton congratulated Jones as Endeavour crossed the 62-mile (100 km) Kármán line and passed the official boundary between the “sensible” atmosphere and the edge of space.

Suddenly, the G-imposed pressure on his chest was gone, he felt light under his harness straps … and was hit by the instant realization: “This must be weightlessness!” In Skywalking, Jones noted that the sensation of perpetual free-fall was perplexing, but that he encountered no difficulties deciding which way was “up” and which was “down.” Then, as his body adapted to microgravity, fluids normally pulled into his legs and lower abdomen instead migrated toward his chest and his inner-ear balance organs sent confusing messages to his brain … and produced a wave of nausea.

It came, he wrote, as a sudden doubled-over spasm, eyes closed, feeling miserable, and was gone within minutes. A shot of the anti-nausea drug Phenergan from crewmate Rich Clifford provided instant relief, but the malaise would return to haunt Jones a couple of times during the early stages of the flight. Yet the view of Earth was glorious. “As Endeavour rose toward sunrise, I gasped,” he wrote. “Between heaven and Earth was a vision of pure beauty, the robin’s-egg-blue of the atmosphere backlighting the darkened horizon.” For an instant, his eyes filled with tears.

The Space Radar Laboratory (SRL) payload flew twice in 1994, firstly aboard STS-59 in April and later aboard STS-68 in September-October. The large Shuttle Imaging Radar (SIR)-C is clearly visible in the foreground. Photo Credit: NASA
The Space Radar Laboratory (SRL) payload flew twice in 1994, firstly aboard STS-59 in April and later aboard STS-68 in September-October. The large Shuttle Imaging Radar (SIR)-C is clearly visible in the foreground. Photo Credit: NASA

But the clock was forever their enemy. As time ticked down toward the first sleep period for the blue team, Linda Godwin’s red shift led the activation of SRL-1. Despite initial problems with the power-up of the X-SAR amplifier—caused by an overly sensitive protection circuit—the German-built radar entered full operations on 10 April. Although the mission had always been baselined for nine days, it was expected that with appropriate use of consumables, a 10th day could be squeezed out of Endeavour. The decision to extend STS-59 did not drag its heels and came late on Day One, setting the mission on its path of science-gathering discovery in fine fashion.

The astonishing experience of 16 sunrises and sunsets in each 24-hour period was best illustrated through one of Tom Jones’ written recollections. Orbiting at twice the average shuttle inclination, and a much lower altitude of just 136 miles (220 km), he and his crewmates were provided with an astonishing vista of the Home Planet. “Now the eggshell-blue light of the sunrise is coating the horizon,” he wrote at one point, late in the mission. “The payload bay is now going bluish-white as we come up out of the darkness. Across Nova Scotia now, and Labrador, and still no sunshine visible. I can still see the stars. No, not for long. Here comes the orange of the Sun. Boom! Sunrise! Now the payload bay is pink-orange, yellow, going to white, and it will soon be brilliant. Fantastic!”

Amidst all the high technology and intensive science workload, it was a profoundly spiritual experience. On the second Sunday after Easter, Jones, Chilton, and Gutierrez—all Catholics, and Chilton a Eucharistic minister—gathered on the flight deck for a short service of Communion. They also had the opportunity, on 16 April, to speak via the Shuttle Amateur Radio Experiment with fellow astronauts Norm Thagard, Bonnie Dunbar, and Ken Cameron, who had recently moved to Russia to support the early Shuttle-Mir effort.

Overall, SRL-1 was a remarkable scientific triumph. In its post-flight mission report, NASA announced that the SIR-C/X-SAR observations had accomplished 97 percent of their required data takes from 400 primary science targets and 99 percent from the 19 critical super-sites. The crew also handled additional requests, including imaging Germany’s Rugen Island, in the Baltic Sea, and examining Japanese rice fields. Ninety-four hours of radar data, taken over 44 discrete nations and covering an area in excess of 27 million miles2 (70 million km2), were stored on 165 of the digital tapes. Elsewhere, the Measurement of Air Pollution by Satellite (MAPS) experiment performed flawlessly, acquiring data on the regrowth of forests in a fire-scarred area of China. On one occasion, Jones verbally report on thunderstorms over Taiwan, the Philippines, and New Guinea to augment the MAPS data.

Jay Apt performs Earth resources photography through Endeavour's flight deck windows. Photo Credit: NASA
Jay Apt performs Earth resources photography through Endeavour’s flight deck windows. Photo Credit: NASA

On 19 April, the payload bay doors were closed and sealed on time, but cloud conditions at the Shuttle Landing Facility (SLF) at KSC caused the first scheduled landing attempt of the day to be waved off, just half an hour before the anticipated de-orbit burn. “Unfavourable and dynamic” weather later that afternoon also put paid to a second attempt to bring STS-59 home. This forced mission managers to reschedule the landing for the following day, the 20th. However, weather at KSC remained “No-Go,” and Gutierrez and his crew were diverted to Edwards Air Force Base, Calif., touching down without incident at 9:54 a.m. PDT on concrete Runway 22, after a mission lasting a little more than 11 days. STS-59 had proven a spectacular success, gathering sufficient data to fill an estimated 20,000 encyclopedias, taking more than 15,000 photographs, and requiring in excess of 400 maneuvers to position the shuttle for the radar observations.

Two weeks later, with the ink barely dry on their crew flight report, Tom Jones returned to his office at the Johnson Space Center (JSC) in Houston, Texas, to begin his next assignment. More than two years of his professional life at NASA had been devoted to the Space Radar Laboratory, and in August 1993 he had been assigned to serve as payload commander for the second flight, SRL-2. The Jet Propulsion Laboratory (JPL) of Pasadena, Calif., which developed the radar, wanted two of its own experts to serve as payload specialists, but had been told that NASA career mission specialists could handle the tasks. Next, JPL insisted that at least one crew member should fly both missions.

This followed typical NASA practice of “carrying over” an experienced crew member from one payload to the next on important science flights … but Jones’ transition from SRL-1 to SRL-2 offered something a little different. Originally, the two radar flights were supposed to fly at least a year apart, as shown by NASA’s February 1991 and January 1992 manifests, which anticipated a 15-month gap between them. However, when the decision was taken, in mid-1992, to advance Endeavour’s Hubble repair flight ahead of SRL-1, the two missions drew much closer—within four months of each other—on the manifest.

Twenty years ago, today, on 20 April 1994, Endeavour made landfall at Edwards Air Force Base, Calif., at the end of STS-59. Photo Credit: NASA
Twenty years ago today, on 20 April 1994, Endeavour made landfall at Edwards Air Force Base, Calif., at the end of STS-59. Photo Credit: NASA

By the time Jones was named as the SRL-2 payload commander, he was still almost eight months away from flying SRL-1. “I recalled my surprise,” he wrote in Skywalking, “when I met with chief astronaut Robert “Hoot” Gibson … He had just invited me to fly again.” By then, the manifest envisaged SRL-2—aboard STS-68—flying aboard Endeavour in mid-August 1994, a mere four months after SRL-1. “Hoot laughed at my startled reaction,” Jones continued, “but he wasn’t kidding. What else could I say but yes?” Two months later, in October 1993, NASA announced the names of the remainder of the STS-68 crew: Mike Baker in command, joined by pilot Terry Wilcutt and mission specialists Steve Smith, Dan Bursch, and Jeff Wisoff. The five men had pestered Jones mercilessly during his SRL-1 training and even whilst he was in orbit.

“Don’t forget you start sims with us next week,” read one note, authored by Baker. It was signed off with simplicity: “Your STS-68 Associates.”

Little did any of them realize that SRL-2 would only get off the ground after a particularly hair-raising on-the-pad engine abort, less than two seconds ahead of liftoff.


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-31, an April 1990 shuttle mission which placed the Hubble Space Telescope—one of the most important satellites ever built—into orbit to begin a journey which would change the way we looked at our world, our cosmos, and ourselves.


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