Updated Wednesday, 21-Jan-2004 10:06:21 EST
Materials & Biological Research
- Microgravity (micro-g)
- Theoretically, an object in orbit behaves as if it were weightless; however, in a real spacecraft, several phenomena create very small levels of acceleration that mimic gravity. The levels vary from a millionth of a g to several thousandths of a g (i.e., 10-6 to 10-3 g), but the result is still called microgravity.
- What causes it? Motions of astronauts and machinery create vibrations that cause tiny oscillating accelerations. Also, within a relatively large spacecraft such as the Shuttle, any experiment or object that is not at the Shuttle's center of gravity (a single point) will experience a small acceleration that differs from what is needed to maintain the orbit.
- So, objects within the Space Shuttle or any other spacecraft will experience very small pseudo-gravitational effects, but these are a thousand times less than regular gravity on Earth. This is called the micro-g environment.
- Microgravity Benefits (2 major problems that occur in 1 g are significantly diminished in microgravity)
- Stratification -- On Earth, a liquid mixture of materials with different densities will separate into layers (strata) as gravity causes the densest materials to sink to the bottom. Effect is more pronounced if the materials don't naturally mix (example: water and oil can be shaken together but quickly separate and stratify).
- materials production -- many metallic alloys (mixtures of different metals) tend to stratify as the molten metals cool, reducing the strength of the alloy. By mixing the molten components in space (i.e., in microgravity), the stratification is nearly eliminated, giving a superior alloy.
- Convection -- On Earth, if we are trying to separate a mixture into its components, the presence of any heat (that is, anything above the freezing temperature of the liquid) causes part of the liquid to become warmer and expand. It is then less dense than the remaining liquid and so it rises; the cooler, denser liquid sinks. It is impossible to keep all of the liquid at the same temperature, and so the result is convection currents -- continual flow of material from warmer to cooler regions, which results in mixing the components.
- Electrophoresis (one method of separating materials) benefits greatly from near absence of convection currents in microgravity. Electrophoresis uses an electric field between two metal plates to separate a stream of ionized (negatively charged) fluid into its constituent components (see figure below).
- A neutral fluid pushes the material downward, and the positively charged metal plate attracts the materials being separated (A, B & C). A is composed of the least massive molecules, B of the moderately massive molecules and C of the most massive ones. Therefore, molecules of A move farther across the chamber than those of B or C before all reach the bottom of the chamber, where they are collected in special containers.
- On Earth, electrophoresis is complicated by the presence of convection currents and so the separation process is not precise. One cannot exactly separate A from B and C since the convection currents keep everything mixing constantly. In microgravity, the purity of materials in the A, B & C containers is thousands of times greater. This has significant implications for separation of pharmaceutical materials (in particular, human growth hormone and insulin).
- Neurolab experiments
- Neurolab is a set of experiments in the SpaceLab module, which fills about half of the Shuttle's cargo bay. Astronauts can enter the module through the airlock and a tunnel.
- More detailed info on Neurolab can be found at the NeuroLab Web Site. The eight experimental teams are summarized here, with an example experiment from each team.
- Shuttle flight STS-90 (April 1998) -- including Penn State Prof. James Pawelczyk
- Autonomic Nervous System Team
- experiment on orthostatic intolerance (inability to maintain constant blood pressure when standing for long periods of time) -- U.S. experiment
- astronauts experience this sometimes after returning to Earth
- experiment seeks insight into causes and effectiveness of countermeasures
- Neurobiology Team
- insect gravity sensory system -- German experiment
- two groups of grasshoppers, one in rotating cylinder, one in micro-g
- How quickly can each group regenerate severed cerci (gravity sensor)
- Sleep Team
- sleep and respiration in micro-g -- U.S. experiment
- micro-g hypothesized as cause of problems in sleep patterns in space -- motion of chest and abdominal walls altered
- experiment monitors O2 and CO2 levels in blood of crewmembers & motion of chest and abdominal walls
- Vestibular System Team
- separating visual and vestibular cues -- French experiment
- astronaut seated in cylinder spinning at 45 RPM
- watches pattern of moving stripes (visual cue of rotation)
- eye motion (following the stripes) reveals how brain is interpreting rotational effects
- Sensory Motor Performance Team
- measures ability of central nervous system to adapt to stimuli in micro-g -- French experiment
- astronaut catches a ball released by spring mechanism overhead and shot downward
- on Earth, ball accelerates downward, gaining speed, and our brains have learned to anticipate this in order to catch the ball
- in micro-g, the ball will move at constant speed -- how quickly can astronauts re-learn how to catch it?
- Mammalian Development Team
- postnatal development of aortic nerves in space -- Japanese experiment
- baroreflex -- body compensates for tendency of blood to move to lower extremities when we stand suddenly
- rats that spend first 2 weeks of life in space may not develop strong baroreflex
- Aquatic Team
- development of balance sensors in snails and fish -- U.S. experiment
- Adult Neuronal Plasticity Team
- effects of micro-g on gene expression in the brain -- Italian experiment
- circadian rhythms (24-hr cycles) developed in 1 g on Earth -- how are these affected by micro-g environment?
- experiment looks at effects of changing the number of hours of light and dark
Copyright © 1998, Robert G. Melton
Updated Wednesday, 21-Jan-2004 10:06:21 EST