page_title: International Space Station
section_title: Freefall
hierarchical_section_title: International Space Station / Purpose / Scientific research / Freefall
caption_attribution_description: English: A comparison between a flame on Earth and a flame in a microgravity environment. This occurs because the flame on Earth is hot and since heat rises it makes that nice slender shape but since there isn't gravity in the second picture it just expands in a sphere. Українська: Порівняння полум'я свічки на Землі (зліва) та полум'я у середовищі мікрогравітації. На Землі на нього діє тяжіння планети, полум'я підіймається, видовжується; оскільки друге зображення зроблене в умовах майже відсутньої гравітації, полум'я просто поширюється в усі сторони, формуючи сферу.
context_page_description: The International Space Station is a modular space station in low Earth orbit. It is a multinational collaborative project between five participating space agencies: NASA, Roscosmos, JAXA, ESA, and CSA. The ownership and use of the space station is established by intergovernmental treaties and agreements. The ISS program evolved from the Space Station Freedom, an American proposal in the 1980s to construct a permanently crewed Earth-orbiting station.
  The ISS serves as a microgravity and space environment research laboratory in which scientific experiments are conducted in astrobiology, astronomy, meteorology, physics, and other fields. The station is suited for testing the spacecraft systems and equipment required for possible future long-duration missions to the Moon and Mars. It is the largest artificial object in space and the largest satellite in low Earth orbit, regularly visible to the naked eye from Earth's surface. It maintains an orbit with an average altitude of 400 kilometres by means of reboost manoeuvres using the engines of the Zvezda Service Module or visiting spacecraft. The ISS circles the Earth in roughly 93 minutes, completing 15.5 orbits per day.
context_section_description: Gravity at the altitude of the ISS is approximately 90% as strong as at Earth's surface, but objects in orbit are in a continuous state of freefall, resulting in an apparent state of weightlessness. This perceived weightlessness is disturbed by five separate effects:
  Drag from the residual atmosphere.
  Vibration from the movements of mechanical systems and the crew.
  Actuation of the on-board attitude control moment gyroscopes.
  Thruster firings for attitude or orbital changes.
  Gravity-gradient effects, also known as tidal effects. Items at different locations within the ISS would, if not attached to the station, follow slightly different orbits. Being mechanically interconnected these items experience small forces that keep the station moving as a rigid body.
  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.
  Investigating the physics of fluids in microgravity will provide better models of the behaviour of fluids. Because fluids can be almost completely combined in microgravity, physicists investigate fluids that do not mix well on Earth. In addition, examining reactions that are slowed by low gravity and low temperatures will improve our 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.
caption: A comparison between the combustion of a candle on Earth (left) and in a free fall environment, such as that found on the ISS (right)
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