Upper Atmosphere Research Satellite

Upper Atmosphere Research Satellite

Type:	Earth observation satellite
Country:	United States United States
Operator:	NASA
COSPAR-ID :	1991-063B
Mission dates
Dimensions:	5,900 kg (13,000 lb)
Size:	10.7 m × 4.6 m
Begin:	September 12, 1991, 11:11:04 p.m. UTC
Starting place:	Kennedy Space Center
Launcher:	Space Shuttle Discovery
Status:	Deactivated: December 14, 2005 Re-entry: September 24, 2011
Orbit data
Rotation time :	96 min
Track height:	575 km
Orbit inclination :	57 °

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

Structure and goals

The NASA began planning for a research satellite for the middle and upper atmosphere in 1979. UARS was from the Astro-Space Division of General Electric built. With a mass of 5900 kilograms, the satellite is 10.7 meters long and 4.6 meters wide. The ten scientific instruments were supposed to measure the concentration and distribution of important gases (such as carbon dioxide , ozone , chlorine , methane , nitrogen oxides , chlorofluorocarbons ) in the upper atmosphere ( stratosphere , mesosphere and thermosphere ) in order to better understand the chemical processes. For example, the researchers wanted to know what influence humans and their technology have on the sensitive ozone layer . In addition, it should be determined what role the upper atmosphere plays in climate change . In addition, the dynamics of the upper atmosphere and the atmospheric water and energy cycles were researched.

The mission was extremely successful and provided valuable data over 14 years, which has been analyzed in several hundred scientific papers.

Instruments

The following measuring instruments were on board UARS:

Improved Stratospheric and Mesospheric Sounder (ISAMS), an infrared radiometer for measuring 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 made it possible to create a vertical height profile of the earth's atmosphere from the ground up to a height of 90 km. The temperature and pressure as well as the concentration of water vapor , sulfur dioxide , chlorine oxide , nitric acid and ozone were recorded.

Halogen Occultation Experiment (HALOE), used four infrared wavelengths to measure the vertical distribution of ozone, hydrogen chloride , hydrogen fluoride , methane, water vapor, nitric oxide and nitrogen dioxide in the atmosphere.

High Resolution Doppler Imager (HRDI), observed the emission and absorption lines of molecular oxygen over the horizon of the earth. The Doppler shift of the lines allowed conclusions to be drawn about the wind speeds.

Wind Imaging Interferometer (WIND II) examined airglow and polar lights . For this purpose, two interferometers were used, which were aligned at an angle of 45 ° and 135 ° to the direction of flight. This made it possible to view the same medium from two different directions in quick succession.

Solar-stellar Irradiance Comparison Experiment (SOLSTICE), to measure the ultraviolet radiation of the sun and stars in the range between 119 and 420 nm. For calibration, the known radiation of certain blue stars was measured regularly.

Solar Ultraviolet Spectral Irradiance Monitor (SUSIM), for measuring the ultraviolet radiation of the sun, comparing direct radiation and radiation attenuated by the atmosphere. The instrument contained two identical spectrometers , one of which was rarely used. This made it possible to check the other's loss of quality.

Particle Environment Monitor (PEM) for measuring X-rays , ions and the magnetic field in the atmosphere.

Active Cavity Radiometer Irradiance Monitor (ACRIM II), the successor to the measuring instrument that was used between 1980 and 1989 on the Solar Maximum Mission . It determined the amount of solar energy reaching the earth and provided data for long-term studies of climate change.

Cryogenic Limb Array Etalon Spectrometer (CLAES), a spectrometer for determining the concentration and distribution of nitrogen and chlorine compounds, ozone, water vapor and methane in the earth's atmosphere.

Mission history

The space shuttle Discovery launched on September 12, 1991 from the Kennedy Space Center for the STS-48 mission. On September 15, the astronauts deploy the satellite with the orbiter's gripper . Most of the instruments started working immediately, only ISAMS was switched on later after the outgassing had subsided.

In June 1992 problems arose with the tracking of the solar cells. While the problem was being analyzed and resolved, the instruments were shut down for two weeks. From July 1992, ISAMS no longer provided any data. Originally, the satellite was only supposed to remain operational until spring 1993, but the mission exceeded expectations and was extended while the instruments were still working, with CLAES ceasing to operate in April 1993 as planned. In March 1995 the tracking of the solar cells finally failed, so that the instruments had less electrical power available. Further losses had to be accepted from June 1997, when one of the three batteries was defective. The instruments were operated alternately or only in direct sunlight when sufficient energy was available. From October 1999 the tape drive could no longer be used and the data transfer had to be handled by relay satellites without intermediate storage. As a result, two thirds of the recorded data could still be transmitted to earth.

Originally designed for a lifetime of only 18 months, UARS worked for over 14 years and was deactivated on December 14, 2005 for cost reasons. At this point in time, six of the ten experiments on board were still functional. NASA lowered the satellite's orbit to speed re-entry and reduce the risk of collision with another satellite.

Re-entry

The re-entry into the atmosphere happened on September 24, 2011 and was accompanied by great media interest. As early as 2002, NASA had simulated reentry with the ORSAT (Object Reentry Survival Analysis Tool) software and calculated that the satellite would break but not burn up completely. According to the calculations, 26 parts with a total mass of 532 kg would reach the surface of the earth. The debris would spread over a distance of about 800 km along the satellite orbit.

On September 7, 2011, NASA announced that the satellite would crash to Earth in late September or early October. The probability of a death in the UARS crash was given by NASA as 1: 3200. According to current standards, NASA and other space agencies are trying to keep the risk of death when a satellite re-enters to 1: 10,000. For the Space Debris Committee IADC , UARS was not a risk object, but the re-entry was used for the annual exercise in which 12 space agencies worldwide work together.

The prediction for the time of the crash became more precise in the following days, but the exact time and therefore also no exact place of the crash could be given because the deceleration in the high atmosphere was also influenced by the fluctuating solar activity and later by the position and rotation of the satellite.

According to NASA's final report, the re-entry into the atmosphere took place on September 24, 2011 at 04:00 UTC at 14.1 ° South latitude and 170.2 ° West longitude over the South Pacific near American Samoa . The stray field of the satellite debris is 500 to 1300 km northeast of the reentry point, far from any major land mass. NASA has no knowledge of debris sightings from this area. Nothing has been known about personal injury or property damage either. -14.1 -170.2

Web links

Wikinews: NASA research satellite crashes to Earth - news

NASA Science Missions: UARS (English)
Official UARS page (English)

Individual evidence

↑ ^a ^b UARS Re-Entry Overview. NASA, September 27, 2011, accessed September 27, 2011 .
^ Re-entry and Risk Assessment for the NASA Upper Atmosphere Research Satellite (UARS). (PDF; 510 kB) NASA Orbital Debris Program Office, September 9, 2011, accessed on September 22, 2011 (English, the simulation is from 2002, the assessment from 2011).
^ Leonard David: Huge Defunct Satellite to Plunge to Earth Soon, NASA Says. space.com, September 7, 2011, accessed September 25, 2011 .
↑ UARS Mission Updates. NASA, September 2011, accessed on September 27, 2011 (English, 16 reports).
^ Phil Chamberlin, Karen C. Fox, Tony Phillips: Solar Activity Can Affect Re-Entry of UARS Satellite. NASA, September 22, 2011, accessed September 23, 2011 .

[nasa_uars-1] UARS Re-Entry Overview. NASA, September 27, 2011, accessed September 27, 2011 .

[2] Re-entry and Risk Assessment for the NASA Upper Atmosphere Research Satellite (UARS). (PDF; 510 kB) NASA Orbital Debris Program Office, September 9, 2011, accessed on September 22, 2011 (English, the simulation is from 2002, the assessment from 2011).

[3] Leonard David: Huge Defunct Satellite to Plunge to Earth Soon, NASA Says. space.com, September 7, 2011, accessed September 25, 2011 .

[4] UARS Mission Updates. NASA, September 2011, accessed on September 27, 2011 (English, 16 reports).

[5] Phil Chamberlin, Karen C. Fox, Tony Phillips: Solar Activity Can Affect Re-Entry of UARS Satellite. NASA, September 22, 2011, accessed September 23, 2011 .