TIMED
TIMED in low Earth orbit
NamesThermosphere • Ionosphere • Mesosphere • Energetics and Dynamics
Mission typeIonosphere
Atmospheric science
Space weather research
OperatorNASA
COSPAR ID2001-055B
SATCAT no.26998
WebsiteTIMED at APL
Mission durationPlanned: 2 years
Elapsed: 22 years, 21 days
Spacecraft properties
ManufacturerApplied Physics Laboratory
Launch mass660 kg (1,460 lb)
Dimensions2.72 meters high
11.73 meters wide
1.2 meters deep
Power406 watts
Start of mission
Launch date7 December 2001, 15:07:35 UTC
RocketDelta II 7920-10
(Delta D289)
Launch siteVandenberg, SLC-2W
Entered service22 January 2002
Orbital parameters
Reference systemGeocentric orbit[1]
RegimeLow Earth orbit
Altitude625 km (388 mi)
Inclination74.1°
Period97.3 minutes
 

The TIMED (Thermosphere • Ionosphere • Mesosphere • Energetics and Dynamics) mission is dedicated to study the influences energetics and dynamics of the Sun and humans on the least explored and understood region of Earth's atmosphere – the Mesosphere and Lower Thermosphere / Ionosphere (MLTI). The mission was launched from Vandenberg Air Force Base in California on 7 December 2001 aboard a Delta II rocket launch vehicle. The project is sponsored and managed by NASA, while the spacecraft was designed and assembled by the Applied Physics Laboratory at Johns Hopkins University. The mission has been extended several times, and has now collected data over an entire solar cycle, which helps in its goal to differentiate the Sun's effects on the atmosphere from other effects.[2] It shared its Delta II launch vehicle with the Jason-1 oceanography mission.

Atmospheric region under study

TIMED Mission diagram (NASA)

The Mesosphere, Lower Thermosphere and Ionosphere (MLTI) region of the atmosphere to be studied by TIMED is located between 60 and 180 kilometres (37 and 112 mi) above the Earth's surface, where energy from solar radiation is first deposited into the atmosphere. This can have profound effects on Earth's upper atmospheric regions, particularly during the peak of the Sun's 11-year solar cycle when the greatest amounts of its energy are being released. Understanding these interactions is also important for our understanding of various subjects in geophysics, meteorology, aeronomy, and atmospheric science, as solar radiation is one of the primary driving forces behind atmospheric tides. Changes in the MLT can also affect modern satellite and radio telecommunications.

Scientific instruments

The spacecraft payload consists of the following four main instruments:

  • Global Ultraviolet Imager (GUVI), which scans cross track from horizon to horizon to measure the spatial and temporal variations of temperature and constituent densities in the lower thermosphere, and to determine the importance of auroral energy sources and solar extreme ultraviolet sources to the energy balance in that region.
  • Solar Extreme ultraviolet Experiment (SEE), a spectrometer and a suite of photometers designed to measure the solar soft X-rays, extreme-ultraviolet and far-ultraviolet radiation that is deposited into the MLT region.
  • TIMED Doppler Interferometer (TIDI), designed to globally measure the wind and temperature profiles of the MLT region.
  • Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), multichannel radiometer designed to measure heat emitted by the atmosphere over a broad altitude and spectral range, as well as global temperature profiles and sources of atmospheric cooling.

The data collected by the satellite's instruments are made freely available to the public.[3]

Specifications

  • Mass: 660 kilograms
  • Dimensions:
    • 2.72 meters high
    • 1.61 meters wide (launch configuration)
    • 11.73 meters wide (solar arrays deployed)
    • 1.2 meters deep
  • Power consumption: 406 watts
  • Data downlink: 4 megabits per second
  • Memory: 5 gigabits
  • Control and data handling processor: Mongoose-V
  • Attitude:
    • Control - Within 0.50°
    • Knowledge - Within 0.03°
    • Processor: RTX2010
  • Total mission cost:
    • Spacecraft: US$195 million
    • Ground operations: US$42 million

Satellite operations

TIMED experienced minor problems with attitude control when, after launch, the magnetorquers failed to slow the spacecraft's spin as intended. An engineer installing the magnetorquers had mistakenly recorded the reverse of their actual polarities, which generated a sign error in the flight software. The problem was fixed by temporarily disabling the orbiter's magnetic field sensor and uploading a software patch to fix the sign error.[4] In a separate incident, another software update fixed a problem caused by faulty testing of the Sun sensors. After these corrections, the attitude control system functioned as intended.[4]

Scientific results

TIMED has improved scientific understanding of long-term trends in the upper atmosphere. The SABER instrument has collected a continuous record of water vapor and carbon dioxide levels in the stratosphere and mesosphere.[5][6]

SABER is able to collect 1,500 water vapor measurements per day, a vast improvement from previous satellites and ground-based observations.[7] SABER had a flaw in its optical filter that caused it to overestimate water vapor levels; this error was discovered and the data were corrected.[8] Based on the corrected data, SABER found that between 2002 and 2018, water vapor levels in the lower stratosphere were increasing at an average rate of 0.25 ppmv (around 5%) per decade, and in the upper stratosphere and mesosphere, water vapor levels were increasing at an average rate of 0.1-0.2 ppmv (around 2-3%) per decade.[9] Growth in methane levels is thought to be partially responsible for the growth in water vapor levels, as methane decomposes into carbon dioxide and water vapor, but changes driven by the solar cycle may also be responsible.[10]

SABER has also monitored carbon dioxide levels in the upper atmosphere. The instrument found that carbon dioxide levels in the upper atmosphere are increasing: at an altitude of 110 kilometres (68 mi), CO2 levels were rising at an average rate of 12% per decade.[11] This rate is faster than what has been predicted by climate models, and suggests that there is more vertical mixing of CO2 than previously thought.[12]

By collecting upper atmosphere data, TIMED assists the modeling of environmental impacts. Water vapor and carbon dioxide are greenhouse gases and their growth in the upper atmosphere must be factored into climate models. Additionally, upper atmosphere water vapor contributes to ozone depletion.[13]


Instrument teams

United States

International

See also

References

  1. ↑ "Trajectory: TIMED 2001-055B". NASA. 14 May 2020. Retrieved 23 November 2020. Public Domain This article incorporates text from this source, which is in the public domain.
  2. ↑ Fox, Karen. "Ten Successful Years of Mapping the Middle Atmosphere". NASA. Public Domain This article incorporates text from this source, which is in the public domain.
  3. ↑ "TIMED SDS Data Product Downloads". Johns Hopkins University Applied Physics Laboratory. Retrieved 15 September 2020.
  4. 1 2 Harland, David M.; Lorenz, Ralph D. (2006). Space Systems Failures: Disasters and Rescues of Satellites, Rockets, and Space Probes. Berlin: Springer. pp. 214–215.
  5. ↑ Yue 2019, p. 13452.
  6. ↑ Yue 2015, p. 7195.
  7. ↑ Yue 2019, p. 13458.
  8. ↑ Rong 2019, p. 3-4.
  9. ↑ Yue 2019, p. 13456.
  10. ↑ Yue 2019, pp. 13456, 13458.
  11. ↑ Yue 2015, p. 7197.
  12. ↑ Yue 2015, p. 7198.
  13. ↑ Yue 2019, p. 13459.

Further reading

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