Back in 1988, Bill Thornton believed that crew assignments were based on need rather than politics and, fortunately, so did those assigned to selecting astronauts for Shuttle missions. Thornton felt that he flew his two space missions exactly when he should have flown and, after the loss of Challenger, was philosophical about the need to "return the Shuttle to routine flight operations and solving all the engineering problems" before flying himself, even if this meant his chances of a third mission would be slimmer. "When we get a bit of breathing space, then yes, once again I could make some real contributions towards long-duration flight ... I have no idea if and when this might occur and I am certainly not getting any younger, but as long as I can perform, it is a possibility."15
His Astronaut Office (CB) assignment at this point was on long-duration space flight issues, and over the next few years he worked on exercise and Space Adaptation Syndrome countermeasure equipment for the extended duration Shuttle programme and space station. According to his 1994 official NASA biography, he "continued his work in space medicine while awaiting his next flight opportunity. Thornton has worked on problems relating to extending mission durations in the Space Shuttle, the space station, and in space exploration, and designed the necessary exercise and other hardware to support such missions. He continued his analysis and the publication of results from studies of neurological adaptation, and the study of neuromuscular inhibition following flight, osteoporosis in space and on Earth, and post-flight ortho-statics. He has completed designs for exercise and other countermeasure equipment for the Extended Duration Orbiter (EDO), and for Space Station Freedom, including improved treadmills, rowing machines, isotonic exercise devices, and a bicycle. Much of this is currently scheduled for flight."
What was not included in this account was mention of his work in designing an affordable (and more importantly, reliable) waste management system for long-
duration Shuttle flights. The Shuttle system, while much improved over the Apollo "toilet-bag" and Skylab toilet procedures, was still temperamental and prone to breaking down. For a long-duration mission on Shuttle in which five to seven members of a mixed crew could be confined for over two weeks, having a reliable toilet system helps not only with hygiene but also with the well-being of the crew. On a space station, months of orbital life could be either a great experience or a nightmare depending on whether the toilet system functioned properly. Thornton's work - certainly appreciated by the other astronauts - was every bit as important as more "attractive" areas of extended duration space flight.
Thornton also helped to design and develop a new type of waste management system.13 Designed under a joint Detailed Test Objective, the Improved Waste
Collection System (IWCS) was developed as a cooperative effort between ILC Space Systems, SSPSG Systems Division and Whitmore Enterprises Inc. It was designed and developed between 1983 and 1986 and was certified ready for flight in 1986, but was put on hold due to the Challenger accident. In 1989, it was manifested as DTO-0329 and assigned to STS-35 (Astro-1). The unit was flown on that mission in December 1990, installed next to the Shuttle WCS on the mid-deck. It was tested during Flight Days 7, 8 and 9 and performed flawlessly, receiving favourable comments from grateful crew members.
The main difference between the IWCS and the Shuttle commode was that instead of a slinger and vacuum/airflow suction device, it had a compactor device - hand-cranked by the user - that used pistons to move the waste to the end of a chamber. The piston was wiped clean by a highly absorbent wiper pad (added prior to use) which also wiped the chamber clean during operation and absorbed all waste moisture. A series of filters cleaned any odours from the chamber. Despite some minor difficulties, the unit was given a good report by the crew. Although this one flight proved the system, it was not developed further, much to Thornton's frustration, with NASA deciding to proceed with a more expensive commercially developed unit. Though developed at a fraction of the cost, Thornton's system never flew again. NASA once again wasted money and time flying a unit that was more corporate gloss than engineering practicality.
Thornton's frustrations over the increasing bureaucracy of the space programme and space industry while trying to develop cost-effective, workable and, more importantly, useful items for space flight continued. Not having the opportunity to fly a third mission was a great loss both to the astronaut and the programme. He was selected initially to participate in long-duration Apollo Applications Program missions, but never got the opportunity to fly such a mission on Skylab or any long-duration Shuttle mission. He was also never assigned to Spacelab life science or to any of the EDO Shuttle missions. On 27 May 1994, NASA announced Thornton's resignation, effective at the end of the month, but did not reveal what his next position would be. At least he would have more time to devote to writing about his work in the space programme over the previous thirty years. As Thornton himself indicated in the official press release. "Due to my work, I haven't really had the opportunity or the time to do any writing about my technical work, other than a few reports, and none at all about other matters.''
In 1995, Thornton became a clinical professor of medicine (cardiology) at the University of Texas Medical Branch in Galveston. After four years on the teaching staff, he developed a computer-based self-teaching system that provided hands-on training in seeing, hearing, and feeling a patient's symptoms. This was subsequently developed for more extensive and broader use. When Thornton began work at UTMB, there was minimal equipment for the students to use, and the extra work involved in developing support material for students took up much of his time. In addition, in the late 1990s the Thorntons moved from their residence in Friendswood near JSC to a new property on the outskirts of San Antonio. This meant commuting about 500 km each week.
On 11 October 2002, Thornton's system was dedicated in the Lucile Matthews
Wallace Memorial Thornton Self-Teaching Laboratory at UTMB. The Physical Diagnosis Self-Teaching System (PDSTS) integrates three of the traditional elements of cardiac examination - inspection (observing carefully), palpitation (feeling) and auscultation (listening) into a complete interactive teaching/learning experience. Thornton explained: "This lab will be an essential resource at UTMB for the establishment of basic physical diagnostic training consistent with the realities of twenty-first century medical education, in which practicing on patients is replaced by high fidelity simulations."16 The system was greatly appreciated by faculty members and students alike, and the School of Medicine Class of 2000 recorded a personal message of thanks at the end of their graduation year: "Your excellent and innovative efforts in teaching cardiovascular physical diagnosis will make us and future UTMB students better physicians, no matter what our speciality choices."17
Thornton left UTMB in 2003 with a desire to complete interrupted work on his publications in space medicine and to devote time to the development of a new clinical system for the University of North Carolina. He was also awarded the 2003 North Carolina Award for Science for his life's work dedicated to the betterment of medicine - on Earth and in space.
Thornton was always hopeful of another space flight, but several things happened that prevented him from getting that coveted third trip. In 2006, Thornton reflected on an observation that Karol Bobko had made during the 1972 SMEAT ground test for Skylab. Bobko said, "Bill, they may forgive you for telling them they are wrong, but they'll never forgive you for proving it.'' When Thornton came back after STS 51-B and expressed his strong concerns that the animal cages would not work as designed and that some of his space motion sickness studies were wasted, he had a strong feeling that he had sealed his fate with regard to a third mission.
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