Upper Atmosphere Research Satellite

The Upper Atmosphere Research Satellite ( UARS ) was an American earth observation satellite. It was launched on 12 September 1991 with the Space Shuttle Discovery (STS- 48) and exposed on September 15. The satellite cost 750 million U.S. dollars. The re-entry into the Earth's atmosphere on 24 September 2011.

Structure and objectives

NASA began planning for a research satellite for the middle and upper atmosphere in 1979. UARS was built by the Astro- Space Division of General Electric. With a mass of 5900 kg, the satellite is 10.7 meters long and 4.6 meters wide. The ten scientific instruments should measure the concentration and distribution of important gases ( such as carbon dioxide, ozone, chlorine, methane, nitrous oxide, chlorofluorocarbons, hydrochlorofluorocarbons ) in the upper atmosphere ( stratosphere, mesosphere and thermosphere ), to better understand the chemical processes. For example, the researchers wanted to know what impact the man and his art on the delicate ozone layer. In addition, it should be noted that the role of the upper atmosphere in climate change. In addition, the dynamics of the upper atmosphere and the atmospheric water and energy cycles was investigated.

The mission was extremely successful and provided over 14 years of valuable data that have been evaluated in several hundred scientific papers.

Instruments

On board of UARS following measuring instruments were:

  • Improved Stratospheric and mesospheric sounder ( ISAM ), an infrared radiometer to measure the thermal emission of the earth on the horizon on both sides of the satellite.
  • Microwave Limb sounder (MLS) for determining the natural microwave emission of the earth. This allowed a vertical height profile of the Earth's atmosphere to be created from the ground up to 90 km altitude. The temperature and pressure were recorded and the concentration of water vapor, sulfur dioxide, Chloroxid, nitric acid and ozone.
  • Halogen Occultation Experiment ( HALOE ), took advantage of four infrared wavelengths to measure the vertical distribution of ozone, hydrogen chloride, hydrogen fluoride, methane, water vapor, nitrogen monoxide and nitrogen dioxide in the atmosphere.
  • High Resolution Doppler Imager ( HRDI ), observed the emission and absorption lines of molecular oxygen on the earth's horizon. The Doppler shift of the lines left to draw conclusions on the wind speeds.
  • Wind Imaging Interferometer ( WIND II ) examined airglow and auroras. For this purpose, two interferometers were used, which were oriented at an angle of 45 ° and 135 ° to the direction of flight. Thus, it was possible to view the same medium in rapid succession, from two different directions.
  • Solar -stellar irradiance Comparison Experiment ( SOLSTICE ), to measure the ultraviolet radiation of the sun and stars in the range 119-420 nm For calibration, the known radiation of certain blue stars was measured regularly.
  • Solar Spectral Irradiance Ultraviolet Monitor ( Susim ), to measure the ultraviolet radiation of the sun, with direct and attenuated by the atmosphere irradiation were compared. The instrument contained two identical spectrometer, one of which is seldom used. So that the loss of quality of the other could be checked.
  • Particle environment monitor (PEM ) for measurement of X-rays, ions, and the magnetic field in the atmosphere.
  • Active Cavity Radiometer Irradiance Monitor ( ACRIM II), the successor of the measuring instrument, which was 1980-1989 in the Solar Maximum Mission in use. It determined the amount of solar energy that reaches the earth and this provided data for long-term studies on climate change.
  • Cryogenic Limb array etalon spectrometer ( Claes ), a spectrometer to determine the concentration and distribution of nitrogen and chlorine compounds, ozone, water vapor and methane in the atmosphere.

Mission History

The Space Shuttle Discovery launched on 12 September 1991 from the Kennedy Space Center on mission STS - 48th On September 15, the astronauts put the satellite with the gripper arm of the orbiter. Most of the instruments took the job immediately, only Isam was only later on, after the gassing had subsided.

In June 1992, problems occurred with the tracking of the solar cells. While the problem was analyzed and corrected, the instruments were turned off two weeks. As of July 1992 ISAMs returned no more. Originally, the satellite should only until the spring of 1993 remain in operation, but the mission exceeded expectations and was extended as long as the instruments were still working, with CLAES as planned in April 1993 stopped the work. In March 1995, the tracking of the solar cells failed permanently, so that the instruments was less electrical power. Other losses had to be accepted from June 1997, as one of the three batteries was defective. The instruments were alternately or only when sunlight when sufficient energy was available, operated. As of October 1999, the tape drive could no longer be used, and the data transfer had to be handled without caching via relay satellites. This allowed two thirds of the recorded data are transmitted to the earth.

Originally designed for a lifetime of only 18 months, UARS has worked for over 14 years and was deactivated on 14 December 2005 for cost reasons. At that time, six of the ten experiments aboard functional. NASA lowered from the orbit of the satellite, in order to speed up the re-entry and to reduce the risk of collision with other satellites.

Reentry

The re-entry into the atmosphere occurred on 24 September 2011 and was accompanied by a large media interest. Back in 2002, NASA had with the software ORSAT (Object Reentry Survival Analysis Tool ) simulates the re-entry and calculates that the satellite break, but would not completely burn up. According to the calculations 26 parts would reach the earth's surface with a total mass of 532 kg. The debris would be spread over a distance of about 800 km along the satellite orbit.

On September 7, 2011, NASA announced that the satellite in late September or early October would fall on the ground. The probability of a fatality in the crash of UARS was specified by NASA with 1:3200. According to current standards, NASA and other space agencies are trying to keep the risk of a death during re-entry of a satellite at 1:10.000. For the IADC Space Debris Committee UARS was no risk object, the re-entry but was used for the annual exercise in which to work together 12 space agencies around the world.

The forecast for the crash time was more precise in the following days, but could not specify exact time and therefore no exact crash site because the braking was affected in the upper atmosphere by the fluctuating solar activity and later on the position and rotation of the satellite.

According to the final report of the NASA re-entry into the atmosphere on September 24, 2011 have been clock at 04:00 UTC at 14.1 ° south latitude and 170.2 degrees west longitude -14.1 - 170.2 over the South Pacific near American Samoa. The stray field of the satellite debris is 500-1300 km northeast of the re-entry location, far from any major land mass. NASA has no knowledge of Trümmersichtungen from this area. About personal injury or damage has been also not known.

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