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Next Launch CRS-5 on a Falcon 9 rocket from Cape Canaveral AFB, FL
scheduled for:
6 Jan 15 11:18:00 GMT
6 Jan 15 6:18:00 EST

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How to Save a ‘Great Observatory’ - Step One: Pick the Right Team

In an event he never thought would happen on the eve of launch, Jerry Ross grins through the aft flight deck window of Atlantis after he and Jay Apt successfully deployed GRO's jammed high-gain antenna. The enormous observatory hangs in the background, still firmly grasped by the Shuttle's robot arm. Photo Credit: NASA

For a few hours in April 1991, it appeared as if things could not get any worse for NASA. A year earlier, the first of its flagship ‘Great Observatories’, the Hubble Space Telescope, had been launched into orbit and initial tests revealed that its optics had been improperly ground. This meant that the telescope was unable to resolve celestial objects with the kind of precision that NASA had advertised. A Shuttle repair mission had long been on the cards, but the dismal failure provoked many laughs on late-night television and considerable embarrassment for an agency which was struggling to convince Congress to fund a permanent space station. The four Great Observatories were meant to offer fundamental insights into the nature and evolution of the Universe, across the entire electromagnetic spectrum. Hubble would observe at visible and ultraviolet wavelengths, whilst the Gamma Ray Observatory (GRO) would examine high-energy gamma radiation, the Advanced X-ray Astrophysics Facility (AXAF) would study X-rays and the Space Infrared Telescope Facility (SIRTF) would cover the infrared spectral region. With the Hubble difficulties, NASA needed the second Observatory, GRO, to work perfectly and begin delivering the kind of scientific bonanza that it had promised sceptical lawmakers.

The story of GRO begins almost a century ago, when a young scientist named Arthur Holly Compton made a significant discovery in the field of X-ray and gamma ray physics; a discovery whose ramifications would earn him lasting renown and a Nobel Prize. Compton came from an academic family: his father had been a university dean and Arthur and his brothers, Karl and Wilson, all earned PhDs from Princeton. Today, he is best remembered for his identification of the ‘Compton effect’, which would be central to the gamma ray detectors aboard the GRO spacecraft.

Gamma rays represent some of the most energetic events in the Universe and typically arise from astrophysical processes which involve the production of very high-energy electrons. In fact, gamma rays have energies as high as 10 MeV. Life on Earth is protected from them by our planet’s atmosphere and, since the dawn of the Space Age, this has meant that gamma ray research from an astronomical perspective has been undertaken by orbiting satellites. In 1923, Arthur Holly Compton’s work on the interaction of high-energy radiation and matter played a crucial role in the development of modern physics. His subsequent work in the observation of cosmic radiation proved ground-breaking in that it laid the cornerstone to our present understanding of how gamma rays are created. The ‘Compton effect’ and ‘Compton scattering’, named in his honour, won him the Nobel Prize for Physics in 1927.

The sheer size of the GRO is amply illustrated in this view, as it dwarfs spacewalker Jay Apt, working in its shadow. The two large domes are the covers of two of GRO's four instruments, the Energetic Gamma Ray Experiment Telescope (EGRET) and the Compton Telescope (COMPTEL). Both would provide data which fundamentally altered our understanding of the cosmos. Photo Credit: NASA

More than half a century later, in September 1991, the name of Arthur Holly Compton returned to the fore when it was bestowed upon the GRO; a spacecraft whose own contributions to gamma ray astrophysics went on to prove truly monumental. Its launch had been significantly delayed, and changed, too, by the tragic loss of Challenger. Yet its basic premise remained the same: to answer questions relevant to our understanding of the Universe. Four scientific instruments were developed by NASA, the European Space Agency and contributing organisations in Germany, the Netherlands and the United Kingdom and planning for the mission encompassed a 15-month Phase 1, in which an all-sky survey would be conducted, after which two additional phases would offer more observing time to guest astronomers. In total, GRO was expected to remain in orbit for at least five years. As circumstances transpired, it would stay there for almost a full decade.

Physically, it had a gross weight of 15,876 kg, more than a third of which was taken up by its scientific payload. At the time of launch, this made it the heaviest astronomy satellite ever placed into orbit. It reminded astronaut Jerry Ross of a Space Age diesel locomotive. “The thing was huge,” he told the NASA oral historian. “Everything on it was real bulky, real thick, real heavy, and it was just very impressive of the stoutness of the satellite. Most times you go up to a satellite and you’re almost afraid to breathe on it, because it may fall apart on you.” Not so the GRO. Its massive internal beams, which formed the central backbone of the spacecraft, were essential to supporting the large scientific instruments.

It could point itself at celestial targets for periods of days or weeks at a time, with an accuracy of just 0.5 degrees, and its hydrazine fuel supply was to be used not only for station-keeping, but also to execute a controlled re-entry at the end of the mission. (This would prove critical when the time came for that re-entry in June 2000.) Built by TRW, it carried a pair of accordion-like solar arrays and a set of nickel-cadmium batteries to provide electrical power. Moreover, it was designed to operate from an orbit of 450 km, high enough to avoid excessive atmospheric drag and low enough to avoid the effects of the Earth’s Van Allen radiation belts, which might compromise its observations.

As the heaviest satellite ever launched by the Shuttle, the GRO is lifted from Atlantis' payload bay for deployment. Photo Credit: NASA

In the bulletproof days before Challenger, GRO was scheduled to be launched in May 1988, loaded with 1,800 kg of hydrazine and plans were advanced to use a subsequent Shuttle mission to refuel it. This would have marked the first time that a fully operational satellite had ever been refilled with propellant in space…and hydrazine was known to be extremely toxic and volatile. Contracts to develop a coupling mechanism for a hydrazine transfer unit were awarded by NASA in December 1984, for completion and delivery just 15 months later. There were safety mechanisms in place – with triple redundancy – but it was with a great sigh of relief that the destruction of Challenger ended all such plans. Six months after the Shuttle returned to flight operations, in April 1989, NASA announced the names of five astronauts to deploy GRO on STS-37. They were scheduled to fly in April 1990, although hardware and other delays pushed their launch considerably to the right…and contributed to the addition of both a planned and an unplanned spacewalk.

In command was Steve Nagel, who saw his role as getting himself and his crew ready to fly, although a tremendous weight of responsibility also lay on his shoulders, for the $630 million GRO was a major scientific payload. “If it goes well, you take the pats on the back,” he told the NASA oral historian, “but if it goes poorly, you take the blame.” Nagel had no input in the selection of his crew, but he was intimately involved in dividing up their duties. When it came to the issue of contingency EVAs, the one man who stood out was the only other veteran member, Jerry Ross, who already had two prior spacewalks under his belt. STS-37 was not supposed to include an EVA – it was to spend five days in orbit, deploy GRO on the third day and return home – but this situation changed in 1989-1990. “Everybody wants to do an EVA,” said Steve Nagel, “and I just used my own best judgement on that and try to give people what they want or have an aptitude for.” One crew member with limitless reserves of ‘aptitude’ was Jay Apt, a civilian physicist who had worked on GRO in his pre-astronaut days as a NASA payload controller. The final members of the crew were a crew-cutted Marine named Ken Cameron as the pilot and another civilian physicist, Linda Godwin, who would be responsible for deploying GRO, using the Shuttle’s robot arm.

As for GRO itself, the massive craft was delivered from Redondo Beach to Los Angeles International Airport, atop a flatbed truck, in February 1990, and airlifted to Cape Canaveral a few days later. During launch, it would be unpowered, save for provisions to keep its star tracker shutters closed, and it was to be electrically activated within 90 minutes of reaching orbit. Twenty-one hours into the mission, an in-bay checkout of GRO would begin, running through everything, from command and telemetry to control systems and communications, and this would serve as a partial rehearsal for the actual deployment. At length, on the third day of the mission, Godwin would lift GRO out of the bay with the robot arm and the observatory’s twin solar panels and high-gain antenna would unfold. She would then release the payload and Nagel and Cameron would manoeuvre the Shuttle away. Alone now, GRO’s systems would be powered up within a strict six-hour time limit and, within five days, it would be ready to begin scientific operations.

Whilst on the end of the RMS, the potential for anything to go wrong was vast; the solar arrays might not unfold correctly or the high-gain antenna might not open and it was the responsibility of Ross and Apt to be in a position to perform a contingency EVA if necessary. In fact, Apt had worked extensively on GRO and one of his achievements was helping to implement contingency EVA capabilities – including astronaut-friendly handholds – onto the spacecraft. For much of 1989, the two men trained extensively in the Weightless Environment Training Facility (WET-F), a huge water tank in Houston, but did not anticipate that a real spacewalk would come their way.

That changed early in the spring of 1990.

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