Shortly after the OMS burn, Thornton and MS 1 Dale Gardner left their seats and began setting up the medical measurement apparatus. The experiments had to be conducted shortly after ascent to ensure accurate measurements of the body's initial adaptation to weightlessness. Both crewmen moved slowly while adapting to the new environment but still managed to accomplish the task prior to OMS 2, with measurements being taken shortly afterwards some forty-five minutes after leaving the ground. With Gardner having to assist Thornton during the post-insertion period, this took MS 1 away from support duties with MS 2 Bluford, who performed not only his own post-insertion tasks but also most of those assigned to Gardner. The crew reported that, although the post-insertion period was normally kept as free of payload activities as possible, having the three MS aboard meant that the timeline could be more lenient, especially if this involved the movement or the manipulation and set-up of payloads.25
Thornton's new treadmill was available for STS-8 having been tested on earlier flights from STS-4, but Thornton was the only crew member to use the treadmill on a regular basis, evaluating his own design in orbit. His fellow crew members tried it only once during the mission. What surprised them was the amount of noise and vibration produced in the crew cabin when a user began a slow run or jog. More positively, however, they found that the treadmill gave some relief to back discomfort. After standing in the harness for a few minutes, the bungee recompressed the spine slightly, relieving the minor lower back discomfort that had been reported during previous space flights.
On the mission, both Gardner and Thornton became sick, ''which was just great timing,'' according to Thornton. Collecting data on the other crew members was more difficult, with Thornton having to ''grab them when he could,'' although some of the crew became interested in the physician's work. Truly, for example, came down from the flight deck during the mission and seemed almost pleased to let Thornton ''have at him'' with his box of medical delights. However, Thornton would not dream of asking
the rest of the crew to give blood. This was still a restricted procedure during space flight, so all the blood drawn on STS-8 was Thornton's own.
The in-flight investigations of human adaptation to space featured over fifty different studies, some of which were conducted several times on each crewman. The hardware was stored in five of the mid-deck lockers and was set up as required. Thornton also used both a removable seat and associated gear (which was fixed almost permanently in place during the mission) and the airlock to support his research. Most of the experiments were non-invasive and non-provocative, with each crew member taking part during pre-flight, in-flight and post-flight tests to provide three sets of data for comparison. Some investigations were performed only by Thornton, who spent virtually all of his time on these studies, while other crew members participated whenever their primary assignments allowed.
It was not the number of investigations that was important, but rather the significance of direct clinical observations while in orbit. The experiments helped to determine that at least one of the primary causes of SAS was an intra-vestibular conflict between the semicircular ear canals and the otolith mechanisms, though this was not the complete answer. Temporary - and painful - obstruction of the intestine (ileus) was observed to be the cause of vomiting (first observed by Thagard on STS-7) and its reversal by the use of a drug was also an important finding. Thornton determined that negative findings or results were as important as the positive ones. For example, the documentation of a rapid (one hour or less) and large fluid shift from the legs followed by slight puffiness of tissue and blood vessels in the head helped to confirm that neither the vestibular apparatus nor the central nervous system was affected by any excess of pressure or fluids. It was also found that despite constant and significant (up to 4-5 cm in some cases) increases in the length of the spinal column and changes in the body's size, posture and shape, there were no adverse affects on the central nervous system. Thornton also observed that while changes in heart rate, blood pressure and other parameters were documented during SAS, he could not find any abnormal physical functions. Both blood pressure and heart rate during re-entry and post-flight activities were normal and the anti-g bladder suit was found to be an adequate method of alleviating pressure during the return to Earth.26
During FD 5 Thornton, normally out of the frame during TV broadcasts, participated in a twenty-minute televised news conference to demonstrate what he had been doing on orbit, using each of his colleagues as "volunteers" to model some of his experiments as he explained the theory to the audience on the ground. More akin to an educational presentation than a PAO telecast, it was nevertheless a fascinating glimpse into the world of space medicine and space flight adaptation. Thornton began by explaining that instant changes occur to the human body when it enters orbit. As much as 1.5 litres of fluid shifts from the legs towards the head during the first day on orbit, which, as Thornton observed, "makes our faces rather broad and puffy.'' Thornton also explained that the shift of body fluids puts added pressure on the brain and can be a factor in the headaches some astronauts have reported. Fluid shift may also be connected to how the eye perceives motion and light while in space, which could in turn help to trigger the nausea and malaise that also affects some, but not all astronauts. Holding up Gardner's leg, Thornton showed his colleague wearing a stocking device that extended from the ankle to the hip, secured by several straps and designed to limit the movement of fluids.
While Guion Bluford demonstrated Thornton's treadmill, wearing a harness and bungee cords to create the force to work the treadmill and stop him floating off into the mid-deck, Thornton pointed out a small video recorder used to record eye and hand motions and a second device (also designed by Thornton) to record blood pressure and heart rate. Thornton then called upon his commander, Dick Truly, to model instruments that measured brain reactions to light stimuli: "We all know commanders have large brains, which is why I'm demonstrating this equipment with our commander,'' Thornton joked. At the end of the telecast, the joke was turned on the good doctor. Referring to Thornton's working habits in space, Truly acknowledged his hard work, but then quipped that he and his colleagues were fed up of what they called "Thornton's chamber of horrors,'' whereupon he picked up a hammer and floated across the mid-deck to reveal Thornton being securely restrained against the bulkhead with grey tape. His three colleagues each wielded knives, wrenches, pliers and hammers and as the screen faded, a muffled scream from the good doctor was heard to close the telecast.
After a highly successful mission, Challenger came home to the programme's first night landing on 5 September 1983, landing on Runway 22 at Edwards AFB after a flight of 6 days 1 hour 8 minutes 43 seconds and 98 orbits. Following the landing,
The crew of STS-8 participate in a post-flight news broadcast in which they discussed their mission.
Thornton commented, ''I learned more in the first hour-and-a-half of the flight than I did in all the previous years that I put into this study on Earth. Space sickness is a transient problem and not the dreaded monster it's made out to be. I'm convinced the problem is solvable.'' To Thornton, this was a confirmation of what he had assumed and with the added ''bonus'' of Gardner and himself becoming sick as a result of their movements on orbit, he had immediately discovered what a huge role the otoliths played in SAS.
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