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How to Save a ‘Great Observatory’: Step Two - Launch into Space

The Gamma Ray Observatory (GRO) is positioned for deployment from Atlantis, 21 years ago this week. The observatory's heart-stopping first few hours would ultimately give way to one of the greatest missions ever undertaken in space science. Photo Credit: NASA

With the Gamma Ray Observatory (GRO), NASA hoped to dispel some of the pessimism which had dogged its efforts in the summer and winter of 1990. Hydrogen leaks had grounded two members of the Space Shuttle fleet – Columbia and Atlantis – and eliminated the agency’s plan to stage as eight missions that year, whilst 1991 began with hardly greater promise as more problems associated with the third orbiter, Discovery, came to light. Added to this was the embarrassing debut of the Hubble Space Telescope, whose optics had been improperly ground and which was rendered incapable of focusing correctly on its astronomical targets. Hubble was the first in a series of much-trumpeted ‘Great Observatories’, intended to observe the Universe across the entire electromagnetic spectrum. Hubble would study the visible and ultraviolet cosmos, whilst GRO – whose launch was scheduled for early 1991 – was designed to explore high-energy gamma radiation. Two other missions, an Advanced X-ray Astrophysics Facility (AXAF) and a Space Infrared Telescope Facility (SIRTF), would complete the quartet in the late 1990s. The successful launch of GRO, by the crew of Atlantis on Shuttle mission STS-37, was thus critical to restoring both faith and confidence in NASA.

The crew of STS-37 – Commander Steve Nagel, Pilot Ken Cameron and Mission Specialists Linda Godwin, Jerry Ross and Jay Apt – had other important tasks, too. As part of its drive to prepare for the EVA-heavy workload involved in building Space Station Freedom, in June 1989 NASA began work on an experimental Crew and Equipment Translation Aid (CETA), a kind of hand-propelled ‘cart’, travelling along rails to quickly deliver astronauts and their gear along the station’s exterior. By the time that CETA received approval, the final payload reviews for STS-37 had already taken place, but the interest of the crew in performing the test led to its addition to their mission in March 1990.

By this time, the launch had slipped from April to June and, ultimately, November, giving the astronauts plenty of time to get ready for the CETA trials. Early plans saw CETA as something like an oversized golfing caddy, which engineer Charles ‘Ed’ Whitsett described as “overkill…like taking a bus when all you need to do is go out to the back field on your motorcycle”. At the opposite extreme, astronauts performing a hand-over-hand translation along the station’s external truss would take time and impose unwanted duress on both their space suits and the structure itself, as well as making it difficult to carry large pieces of hardware from place to place. CETA’s beauty was its simplicity – like a railroad handcar of the Old West – and it would run along a set of rails, built into Freedom’s backbone-like truss. For the STS-37 test, Ross and Apt would use a cart mounted on an extendible track in the Shuttle’s payload bay, some 14 m long, and would translate along it in prone positions, hand-over-hand, or angled slightly ‘upwards’, using pedals. Each technique – the manual, mechanical and electrical – incorporated brakes and provisions to move in reverse and the task of the spacewalkers was to assess the amount of energy required to perform each movement, as well as comfort, security, control and visibility.

The GRO is lifted out of the payload bay, preparatory for deployment. The high-gain antenna, which would cause so much trouble in GRO's hours before deployment, is visible at the bottom of this image. Photo Credit: NASA

Not surprisingly, both astronauts were excited, particularly Ross, who had performed the last EVA of the Shuttle programme, just a few weeks before the Challenger accident. However, he stressed that the astronaut office was anxious to build up its pool of EVA experience, since the construction of Freedom would involve a ‘wall’ of EVAs, far more demanding than anything ever attempted in history. In fact, only a handful of astronauts with recent EVA experience remained on active status. That had to change…and quickly. Ross later worked on orbiter-based EVAs, whilst Apt had worked on Freedom-based EVAs, and both men pushed very hard for a series of ‘stand-alone’ EVAs to build up experience. The paucity of experience in the corps actually convinced Ross, at first, that Steve Nagel would assign Apt and Godwin to perform the EVA.

Nagel thought differently. “I understand what you’re saying,” he told Ross, “and I think that’s a good thing to consider, but I’d really look stupid if we had to do some kind of contingency EVA on a primary payload and you weren’t one of the two guys that was outside!”

Ross laughed. “Okay. Sounds good to me.” He was under no illusion that a contingency EVA would realistically be needed to help GRO on its way.

The hydrogen leaks which grounded Columbia and Atlantis during the summer of 1990 conspired to push other missions further downstream and STS-37 was eventually rescheduled for launch early in April 1991. As a direct result of these delays, Jerry Ross had gotten himself an amateur radio licence, courtesy of Ken Cameron. Several earlier missions had carried the Shuttle Amateur Radio Experiment (SAREX) and Cameron, Nagel and Apt were particularly enthusiastic about making contact with ground-based hams during the course of their mission. Every so often, during training, Cameron would pass Ross’ office and dump a pile of application paperwork on his desk. Ross was not particularly enamoured with amateur radio (he was busy enough, with the GRO work, the EVA work, a pair of middeck experiments and his duties as STS-37’s flight engineer), but he finally told Cameron that if the launch was delayed beyond a certain date, he would complete the requirements, including studying Morse code, fill out the application forms and get his licence. As STS-37 moved further back, from April 1990 to June, then to November and finally to April 1991, Ross caved in and finally agreed. Cameron took him to George Bush Intercontinental Airport in Houston to take the exam and, a few months later, in orbit, Ross (with the callsign of N5SCW) became the first amateur radio operator to talk to other hams only from space. “I’ve never used one, physically, on the ground, to talk to anybody else,” he said.

The crew of STS-37. These five astronauts saved GRO from the jaws of defeat. Spacewalkers Jay Apt (back left) and Jerry Ross (back right) were right on the coal face of the contingency repair, but their comrades - left to right, Ken Cameron, Steve Nagel and Linda Godwin, seated - provided invaluable support from inside Atlantis' cabin. Photo Credit: NASA

In the spring of 1991, STS-37 was to come hard on the heels of another flight, STS-39, during which Discovery’s crew would operate a complex payload for the Department of Defense. Unfortunately, in late February, shortly before the STS-39 launch, cracks were found in four hinges associated with the two umbilical door drive mechanisms between the External Tank and the orbiter. “The cracks are not in the door hinges,” explained a NASA Headquarters news release on 28 February, “but rather in metal that supports the mounts for electric mechanisms that open and close the doors.” It all boiled down to the fact that the doors were critical to the success of a flight; they had to close properly following the jettison of the External Tank in order to protect Discovery from the extreme heat of re-entry into the atmosphere. Although documented events were suspected of overly stressing the doors and possibly initiating the cracks, no conclusive evidence could be found to pin down their origin and NASA management opted, conservatively, to investigate further.  

The decision was made as Discovery underwent final preparations at Pad 39A and the scheduled 9 March launch was cancelled and rescheduled for late April or early May. In the meantime, STS-39 was returned to the Vehicle Assembly Building (VAB) and the Shuttle destacked and rolled into the Orbiter Processing Facility (OPF) for repairs. Hinges from Columbia – themselves exhibiting minor cracks – were removed, reinforced and installed onto Discovery. With STS-37 now scheduled to begin on 5 April, NASA decided that the GRO mission would fly first and STS-39 would follow a few weeks later. On 1 April, Discovery returned to Pad 39A, tracking a new launch attempt on the 23rd. By now, Atlantis had sat patiently on Pad 39B for several weeks and Steve Nagel and his crew arrived at KSC in their fleet of T-38 jets.

Liftoff of STS-37 was delayed only slightly, by about five minutes, due to low cloud cover. This carried the potential to threaten the maximum allowable cloud ceiling if Nagel and Cameron were forced to perform a Return to Launch Site abort in the first few minutes of ascent, as well as having implications fo wind effects on blast propagation. Both conditions were found to be acceptable and the final seconds of the countdown ticked away, almost symphonic in their perfection:

“T-31 seconds…we have the handoff to Atlantis’ onboard computers…Atlantis now controlling…T-16 seconds, sound suppression water system operating…T-10, nine, eight, seven, six, five…main engine start…three good engines, up and burning…two, one…zero…and liftoff of the Space Shuttle Atlantis, with the Gamma Ray Observatory, seeking out the explosive forces in the Universe…”

Twenty-one years ago today, Atlantis roared into orbit on a mission which would prove historic. As well as staging the first post-Challenger EVAs, the astronauts of STS-37 would save a Great Observatory and demonstrate that the capabilities of men and women in space can never be underestimated. Photo Credit: NASA

With a crackling roar, Atlantis speared for orbit at 9:22 am EST on the 5th. After insertion into orbit – at 450 km, one of the highest yet attained by the Shuttle – the process to prepare GRO for deployment ran like a well-oiled machine. Early on 7 April, GRO hung above Atlantis’ payload bay, backdropped by the blue and white Earth, still in the firm grasp of the Canadian-built robot arm. To preserve the opportunity for Ross and Apt to go outside on a contingency EVA, the entire cabin had already been depressurised from its normal 101.3 kPal to around 70.3 kPal. This would prepare them for operating inside the 29.6 kPal pure oxygen atmosphere of the space suits, as well as clearing nitrogen from their blood to avoid an attack of the bends.  

Ross had earlier checked out the two suits in Atlantis’ airlock, as Apt worked upstairs with Godwin on the flight deck on GRO pre-deployment tasks. They had also donned their biomedical body sensors and gotten into their liquid-cooled long underwear to enable a rapid response if an EVA was deemed necessary. The underwear contained a threaded network of plastic tubes and took the form of a single-piece, zip-up suit, officially known as the Liquid Cooling and Ventilation Garment. During an EVA, it would pump cooling water through the tubes to control the astronauts’ body heat, exhaled gases and perspiration. Anti-fog compound was applied to the insides of their helmet visors. With Ken Cameron on hand to assist them with donning the space suits, Ross and Apt were ready to go.

So was GRO itself…or so it seemed. The gigantic electricity-generating solar arrays unfolded perfectly and without incident. Apt looked over at Ross and offered a word of encouragement: “Well, I guess everything’s downhill from here!” Nagel also felt that they were out of the woods. After all, the two arrays were very mechanically complicated, unfurling one at a time, like a pair of giant accordions, to reach a total wingspan of more than 20 m. The false sense of confidence would quickly overtake them. The next step was the deployment of the observatory’s critical high-gain antenna – needed for high-rate communications, this was indispensable to the mission - and commands were transmitted from the ground to extend it out on its 3 m boom.

It did not move.

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