Still more investigations focused on changes in the muscles and bones of 74 male rats (Rattus norvegicus), 28 of which actually flew on Columbia, while another 45 served as ground-based 'control' specimens. Originally, 29 rats were supposed to fly, but a clogged water line in one of the cages failed early on 5 June, just a few hours before launch, and so it was flown 'empty'. ''I assume he's having a happy life now,'' Test Director Mike Leinbach said of the sole rat dropped from the mission.
The rats weighed around 275 g and were about nine weeks old at the time of launch; the 20 (soon to become 19) specimens were loaded into the RAHF a few days before STS-40 lifted off. This facility had been greatly improved since its first flight on Spacelab-3 in April 1985, when escaped monkey faeces left the Spacelab module, entered Challenger's flight deck and floated under Commander Bob Overmyer's nose . . .
The new RAHF flown on SLS-1 required an entire Spacelab rack and contained cages that provided the rats with food, water and waste-management functions, as well as controlling temperature and humidity, lighting and ventilation. The rats' movements were monitored and recorded by infrared light sources and sensors mounted inside each cage. During the mission, the facility was extensively tested by the science crew, who demonstrated its ability to capture escaped food crumbs, rodent hair and simulated faeces (black-eyed peas) and avoid contaminating the cabin. General results were favourable and showed that it maintained high levels of containment.
The facility's containment was so good, in fact, that it was possible for the astronauts to move several rats from the RAHF to a workbench called the General Purpose Workstation (GPWS), using a special transfer unit. This marked the first time that rats had been allowed to float freely in space and also provided scientists with an opportunity to assess their behaviour and performance outside their cages. Scientists would use the GPWS on SLS-2 to conduct rat dissections in space. The only problems with the facility were failures of the activity sensors and a fault in the drinking-water pressure transducer.
Nine other rats were flown in two Animal Enclosure Modules (AEMs) in one of Columbia's middeck lockers. Like the RAHF cages, these also provided food, water, waste-management, air and lighting for the rodents. Although the AEMs did not allow the astronauts to actually handle the rats, they were able to view them through a clear plastic window on the front of each unit. These nine rats rode in the middeck because they were loaded on board the Shuttle so late in the countdown - just 15 hours before launch - which was too late for technicians to easily access the Spacelab module.
A focal point of the rat research on SLS-1 were studies of the effect of microgravity on their muscles and bones, particularly by measuring changes in circulating levels of calcium-metabolising hormones and the uptake and release of calcium in their bodies. These changes were a cause for concern, because they appeared to be similar to those observed in human patients with osteoporosis - a condition in which bone mass decreases and bones become porous and brittle - and understanding the mechanisms responsible for them was deemed vital when planning future long-duration space station missions.
Bone growth in the rats' legs, spines and jaws was closely monitored and the loss of calcium and phosphorus was measured, revealing decreased skeletal growth and reduced leg-bone breaking strengths and spinal masses. Other experiments investigated decreases in the strength and endurance of their muscles. In general, the rats returned from space much more lethargic than when they left Earth, with reduced muscle tone, and were found to use their tails much less frequently as a balancing aid. Their red and white blood cell quantities decreased during the mission, although overall they were in much better shape than expected.
The crew participated in the calcium experiments, too, by carefully measuring their daily intakes of food, fluid and medication and weighing themselves frequently. The science team also took blood samples to better determine the role of calcium-regulating hormones on the observed changes in their calcium balance.
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