Mir - Station Structure - Microgravity

Microgravity

At Mir's orbital altitude, the force of Earth's gravity was 88% of that at sea level. While the constant free fall of the station offered a perceived sensation of weightlessness, the onboard environment was not one of weightlessness or zero gravity. The environment was, however, often described as microgravity. This state of perceived weightlessness was not perfect, however, being disturbed by five separate effects:

• The drag resulting from the residual atmosphere,
• Vibratory acceleration caused by mechanical systems and the crew on board the station,
• Orbital corrections by the on-board gyroscopes (which spun at 10,000 rpm, producing vibrations of 166.67 Hz) or thrusters,
• Tidal forces. Any parts of Mir not at exactly the same distance from Earth tended to follow separate orbits. However, as each point was physically part of the station, this was impossible, and so each component was subject to small accelerations from tidal forces.
• The differences in orbital plane between different locations aboard the station.