ISS - Purpose - Scientific Research - Microgravity

Microgravity

Contrary to popular belief, the earth's gravity is only slightly less at the altitude of the ISS as at the surface. According to the equivalence principle, gravity only seems absent because, like any orbiting object, it is in continuous freefall. This state of perceived weightlessness is not perfect however, being disturbed by five separate effects:

• Drag from the residual atmosphere; when the ISS enters the Earth's shadow, the main solar panels are rotated to minimise this aerodynamic drag, helping reduce orbital decay.
• Vibration from movements of mechanical systems and the crew.
• Actuation of the on-board altitude control moment gyroscopes.
• Thruster firings for altitude or orbital changes.
• Gravity-gradient effects, also known as tidal effects. Items not at the exact ISS center of mass would, if not attached to the station, follow slightly different orbits than that of the ISS as a whole. Those closer to the earth would tend to follow faster, shorter orbits and move forward along the velocity vector. Those farther away would have slower, longer orbits and move rearward against the velocity vector. Those to the left or right of the ISS center of mass would be in different orbital planes. Being attached to the rigid ISS, however, these items experience small forces that keep them moving along with the ISS center of mass.

Researchers are investigating the effect of the station's near-weightless environment on the evolution, development, growth and internal processes of plants and animals. In response to some of this data, NASA wants to investigate microgravity's effects on the growth of three-dimensional, human-like tissues, and the unusual protein crystals that can be formed in space.

The investigation of the physics of fluids in microgravity will allow researchers to model the behaviour of fluids better. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. In addition, an examination of reactions that are slowed by low gravity and temperatures will give scientists a deeper understanding of superconductivity.

The study of materials science is an important ISS research activity, with the objective of reaping economic benefits through the improvement of techniques used on the ground. Other areas of interest include the effect of the low gravity environment on combustion, through the study of the efficiency of burning and control of emissions and pollutants. These findings may improve current knowledge about energy production, and lead to economic and environmental benefits. Future plans are for the researchers aboard the ISS to examine aerosols, ozone, water vapour, and oxides in Earth's atmosphere, as well as cosmic rays, cosmic dust, antimatter, and dark matter in the universe.