page_title: Mir
section_title: Radiation and orbital debris
hierarchical_section_title: Mir / Station operations / Safety aspects / Radiation and orbital debris
caption_attribution_description: English: Image made from models used to track debris in Earth orbit. Of the approximately 19,000 man-made objects larger than 10 centimetres in Earth orbit as of July 2009, most orbit close to the Earth.
context_page_description: Mir was a space station that operated in low Earth orbit from 1986 to 2001, operated by the Soviet Union and later by Russia. Mir was the first modular space station and was assembled in orbit from 1986 to 1996. It had a greater mass than any previous spacecraft. At the time it was the largest artificial satellite in orbit, succeeded by the International Space Station after Mir's orbit decayed. The station served as a microgravity research laboratory in which crews conducted experiments in biology, human biology, physics, astronomy, meteorology, and spacecraft systems with a goal of developing technologies required for permanent occupation of space.
  Mir was the first continuously inhabited long-term research station in orbit and held the record for the longest continuous human presence in space at 3,644 days, until it was surpassed by the ISS on 23 October 2010. It holds the record for the longest single human spaceflight, with Valeri Polyakov spending 437 days and 18 hours on the station between 1994 and 1995.
context_section_description: Without the protection of the Earth's atmosphere, cosmonauts were exposed to higher levels of radiation from a steady flux of cosmic rays and trapped protons from the South Atlantic Anomaly. The station's crews were exposed to an absorbed dose of about 5.2 cGy over the course of a 115-day expedition, producing an equivalent dose of 14.75 cSv, or 1133 µSv per day. This daily dose is approximately that received from natural background radiation on Earth in two years. The radiation environment of the station was not uniform; closer proximity to the station's hull led to an increased radiation dose, and the strength of radiation shielding varied between modules; Kvant-2's being better than the core module, for instance.
  The increased radiation levels pose a higher risk of crews developing cancer, and can cause damage to the chromosomes of lymphocytes. These cells are central to the immune system and so any damage to them could contribute to the lowered immunity experienced by cosmonauts. Over time, lowered immunity results in the spread of infection between crew members, especially in such confined areas. Radiation has also been linked to a higher incidence of cataracts in cosmonauts. Protective shielding and protective drugs may lower the risks to an acceptable level, but data is scarce and longer-term exposure will result in greater risks.
  At the low altitudes at which Mir orbited there is a variety of space debris, consisting of everything from entire spent rocket stages and defunct satellites, to explosion fragments, paint flakes, slag from solid rocket motors, coolant released by RORSAT nuclear powered satellites, small needles, and many other objects. These objects, in addition to natural micrometeoroids, posed a threat to the station as they could puncture pressurised modules and cause damage to other parts of the station, such as the solar arrays. Micrometeoroids also posed a risk to spacewalking cosmonauts, as such objects could puncture their spacesuits, causing them to depressurise. Meteor showers in particular posed a risk, and, during such storms, the crews slept in their Soyuz ferries to facilitate an emergency evacuation should Mir be damaged.
caption: Space debris in low Earth orbit
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