The experiments that required to operate within a pressurised environment and be tended by the astronauts in a 'hands-on' capacity faced a problem. The two venerable Spacelab modules, which had flown numerous times and supported hundreds of experiments across a variety of disciplines since November 1983, had been officially retired following the 16-day Neurolab mission in April 1998. In its place, NASA had hatched a $47-million deal with a company known as Spacehab Inc., which had, since 1984, been developing its own pressurised research modules for the Shuttle.
In physical appearance, Spacehab was not dissimilar to Spacelab, with the exception that it had a flat roof and thus was not fully cylindrical. Connected to the
Shuttle's crew cabin by a pressurised tunnel, it occupied the forward portion of the payload bay and virtually quadrupled the room available for conducting scientific experiments in the cramped middeck. The original module, which first flew in June 1993, was 3 m long and offered 28.3 m3 of space, much of which was commercially 'sold' by Spacehab Inc. to experimenters who desired relatively easy access to microgravity.
Later adjustments to the company's contract with NASA led to the development of cargo-carrying Spacehab modules - including a 'double' version, in which one module was bolted back-to-back onto a structural-test article for trucking research hardware, equipment and consumables to and from the Mir space station and the International Space Station. In fact, both Rick Husband and Mike Anderson had flown with such cargo modules on their first missions. Inevitably, with the retirement of Spacelab and the need for a similarly large laboratory for standalone flights, the concept of a fully equipped Research Double Module (RDM) was explored in greater depth.
The new module would make its first flight on STS-107, but was much more than 'just' an experiment-carrying canister. ''The [module]'', said Husband before the mission, ''is a double Spacehab that has had some additional equipment added to [its] aft portion. That primarily adds up to some environmental control systems that will remove moisture from the air back in the Spacehab. The other modules - the Logistics Double Modules that deliver supplies to [the] space station - don't have that humidity-removal system in there and so the orbiter is responsible for removing all the humidity. With this additional equipment back there, they figure that it will take some of the load off the orbiter and be able to better control the environment back there for people to work in. They've also added some additional power capability and data-handling so that it can accommodate more experiments and power more experiments as a result . . . and then ship that data to the orbiter to then be sent to the ground or recorded onboard. It's a module that is much more specifically designed to be an on-orbit laboratory in the back of the orbiter['s] payload bay.''
The end product, therefore, was a facility 6.1 m long, 4.3 m wide and 3.4 m high that provided a pressurised volume of 62 m3 for over 4,000 kg of experiments. On its maiden flight, it would carry 3,400 kg of research equipment to support numerous scientific investigations. Its aft portion, said Husband, enabled a new interface with Columbia's uplink-and-downlink system to enable investigators to command their experiments from the ground and receive real-time data from them. For STS-107, Spacehab Inc. marketed 18% of the module's capacity - netting $22 million in revenue - while the remainder was reserved by NASA.
''It's roomy,'' Willie McCool said of the new module, ''and it gives us, the operators, space to operate [and] run the payloads. So that's it in a nutshell. Room. Power. Cooling. Everything you need to make the experiments work.''
Those experiments were both multidisciplinary and roughly divided into life and physical sciences. The former included studies of pulmonary and cardiovascular changes during rest and exercise and investigated bone cell activity. Dave Brown hoped the Canadian-provided bone cell experiments could yield insights into the future treatment of osteoporosis. ''That's something that's a problem for everybody when we get older, particularly women,'' he said before launch. ''It turned out [that] astronauts - when we go to space and no longer have the stress of gravity on our skeletons - lose calcium and so we're going to be studied for that. We're actually a very good model - a very accelerated model - for what happens to people over many years, so it's useful to study us to learn more about how to slow or prevent osteoporosis here on Earth. We also have quite a few [middeck-style] locker experiments that have bone cells in them, again, to study the same metabolism and why bone cells either gain or lose calcium.'' During the flight, the experiments required crew members to gulp down pills and inject fluids containing 'tracer' chemicals to indicate the rate at which calcium was being lost from their bones.
Elsewhere in the Spacehab module was an experiment provided by Michael Delp of Texas A&M University to investigate the impact of microgravity on blood vessels.
On Earth, the pull of gravity causes these vessels to constrict and thus prevent blood from collecting in the lower extremities; however, in space, they become less able to dilate or constrict and, over long periods of time, the circulatory system weakens. Upon returning to Earth, most astronauts feel dizzy when standing upright - a condition known as 'orthostatic intolerance' - and around 60% are unable to pass a 10-minute stand test without losing consciousness.
''Gravity pulls blood down to the feet normally [and] arteries resist that pull,'' explained Delp. ''In microgravity, there's no weight bearing. The body responds to the lack of force by remodelling itself. Look at what happens if a weightlifter stops working out. If a muscle is no longer stressed, it loses mass.'' Delp's study involved a complement of rats, which were being flown on board Columbia to explore the extent to which their hind limbs grew thinner and weaker in response to pressure changes and chemical signals essential to their vascular health.
Earlier rodent experiments had shown that they react more rapidly than humans to space-induced physiological changes and, as a result, a 16-day mission for them was roughly equivalent to a six-month period in microgravity for us. They were housed in special enclosures in the Spacehab module and, it was planned, the blood vessels in their hind limb skeletal muscles would be analysed after Columbia's landing to track structural and genetic changes.
''There are similarities to what happens in microgravity and what happens in old age,'' said Delp. ''When the elderly go to the emergency room, the reason is likely due to orthostatic intolerance, either directly or indirectly. They can't stay upright, and when they do go down, they injure themselves.''
As well as volunteering for blood draws and urine tests in support of the life science experiments, the astronauts also put their names down as test subjects for Charles Czeisler's sleep study. Throughout the mission, they wore watch-sized 'actigraphs', which were essentially tiny accelerometers that measured wrist movements as part of efforts to track disturbances in their sleep-wake cycles. Previous experiments during the Neurolab mission had already highlighted the disruptive effect of 16 sunrises and sunsets during each 24-hour period on astronauts' ability to 'sleep' and 'wake' normally.
Known as 'circadian rhythms', these cycles are essentially daily repeating biological clocks, the disturbance of which can ultimately cause physical or mental impairment, interfere with an individual's concentration and potentially affecting the immune system. According to Laura Barger of Harvard Medical School and Brigham and Women's Hospital in Boston, Massachusetts, astronauts typically are unable to sleep well before a mission due to excitement and shifting their rest times to accommodate launch schedules, and in orbit generally sleep for no more than six hours per night.
Rick Linnehan, who flew on board Neurolab, once commented that, due to his immense workload with the life science experiments, most of his 16 days aloft seemed to roll into one and he slept far less. He was not alone.
''During Shuttle flights, the light-dark cycle is about 90 minutes long,'' said Barger. ''Seeing a sunset and sunrise every 90 minutes can send potentially disruptive signals to the area of the brain that regulates circadian rhythmicity. Additionally, the lighting onboard the Shuttle might not be sufficiently intense to maintain circadian alignment. Consequently, sleep could be disturbed. If the astronaut sleeps one to two hours less per night, over a 16-day mission, that can add up to a 32-hour sleep deficit.'' Undoubtedly, such a deficit could have a detrimental effect on their performance.
Not only did STS-107 combine many scientific disciplines, it brought together many nations, with the European, Canadian, German and Japanese space agencies sponsoring a multitude of different experiments. Students from Australia, China, Israel, Japan, Liechtenstein and the United States also investigated the impact of spaceflight on fish, spiders, ants, silkworms, bees and inorganic crystals. ''It's a humbling experience when you realise how many people work to put together a mission like this,'' Rick Husband said before Columbia's launch, ''and to be able to go to various places and visit the people who have worked very hard on all these experiments.''
Even with more than two weeks aloft, it would have been virtually impossible to complete the crew's overflowing plate of scientific objectives without a dual-shift system operating around-the-clock. The Red Team consisted of Husband, Clark, Ramon and Chawla, while their Blue counterparts were McCool, Anderson and Brown. ''You might say, if we have seven people on one shift, they could just divvy up the experiments and, hence, you should be able to do the same number of things,'' Chawla said before the mission. ''The issue is that, on our orbiter, there are lots of attitude requirements. The orbiter should be in a certain attitude to do the ozone measurements [and] in a different attitude to the dust measurements. In a free-drift attitude - meaning that no jets should be firing and it's just 'drifting' - to do some of our very microgravity-sensitive experiments. One of the [Combustion Module] experiments needs a very quiescent environment . . . so you need to take advantage of the whole day. It really helps to use the crew much more efficiently by doing that.''
Also, the fact that at least three crew members were asleep during most periods of the day or night, made Columbia herself and the Spacehab module - which, eitherway, could only comfortably accommodate four people - considerably more roomy. ''It gives the waking crew members a little more space to work,'' said Mike Anderson, ''[and] a little bit more elbow room to do their job.'' He was perhaps the person most intimately involved with the experiments - having worked on them for two years before STS-107 finally set off - and, as such, was named as its Payload Commander.
''When you have a complex mission like this,'' Anderson said, ''you need a point of contact for answering all the crew questions . . . to help make the decisions about things and try to find the best way to make this mission a success. Who do you train for which payload? How do you take advantage of each crew member's strengths to assign them to a payload that's most appropriate for them? How do you choreograph the operations on-orbit? My job ... was to pull this mission together and that we were going to get the best science we could out of this 16-day flight.''
Like so many previous science missions, therefore, STS-107 had two Commanders: Rick Husband had overall responsibility for the safety of the flight and its crew, while Mike Anderson took care of the experiments crammed into Columbia's payload bay. After launch, the pace was expected to be hectic as both Commanders busied themselves with their respective duties. ''Mike will be the 'post-insertion guru','' Husband said before the flight. ''He's the one who's... in charge of running everything on the middeck and making sure everything gets set up, whereas I'll be running things on the flight deck.''
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