Spacecraft in space.

Artist's concept of SOHO spacecraft.

SOHO is the longest-lived Sun-watching satellite to date. Numerous mission extensions enabled the spacecraft to observe two 11-year solar cycles and discover thousands of comets.

  • During its pioneering career it has returned a wealth of new information on the Sun's deep core through to the hot and dynamic outer atmosphere, the solar wind and solar energetic particles.
  • SOHO monitors the effects of space weather on our planet, and it plays a vital role in forecasting potentially dangerous solar storms.
  • SOHO also is the most prolific discoverer of comets in astronomical history, with with more than 3,000 tracked during encounters with the Sun.

SOHO is a cooperative international project between ESA and NASA. NASA contributed three instruments and launch services. ESA leads the mission.

Mission Elapsed Time
Launch Date Dec. 2, 1995 | 08:08:01 UT
Launch Site Cape Canaveral Air Force Station, Fla., USA | Launch Complex 36B
Launch Vehicle Atlas Centaur IIAS (AC-121 / Atlas IIAS no. 8206 / Centaur II)
Destination Observing the Sun from the Sun-Earth L1 Point
Type Orbiter
Status Successful—Extended Mission in Progress
Nation Europe and United States
Alternate Names Solar and Heliospheric Observatory, 23726, 1995-065A

Key Dates

Dec. 2, 1995 | 08:08:01 UT: Launch

Feb. 14, 1996: Sun-Earth L1 Orbit Insertion

Sep. 13, 2015: 3,000 Comet Discovered

In Depth

Nation: ESA and USA
Objective(s): Sun–Earth L1 Lagrange Point
Spacecraft: SOHO
Spacecraft Mass: 4,109 pounds (1,864 kilograms)
Mission Design and Management: ESA / NASA

Scientific Instruments:

  1. solar-ultraviolet measurements of emitted radiation experiment (SUMER)
  2. coronal diagnostic spectrometer (CDS)
  3. extreme ultraviolet imaging telescope (EIT)
  4. ultraviolet coronograph spectrometer (UVCS)
  5. large angle and spectrometric coronograph (LASCO)
  6. solar wind anisotropies experiment (SWAN)
  7. charge, element, and isotope analysis experiment (CELIAS)
  8. comprehensive suprathermal and energetic particle analyzer (COSTEP)
  9. energetic and relativistic nuclei and elec- tron experiment (ERNE)
  10. global oscillations at low frequencies experiment (GOLF)
  11. variability of solar irradiance and gravity oscillations experiment (VIRGO)
  12. Michelson Doppler imager/solar oscilla- tions investigation (MDI/SOI)

The ESA-sponsored Solar and Heliospheric Observatory (SOHO) carries 12 scientific instruments to study the solar atmosphere, helioseismology, and the solar wind.

Information from the mission has allowed scientists to learn more about the Sun’s internal structure and dynamics, the chromosphere, the corona, and solar particles.

The SOHO and Cluster missions, part of ESA’s Solar Terrestrial Science Programme (STSP), are ESA’s contributions to the International Solar Terrestrial Physics (ISTP) program, which has involved the work of other spacecraft such as Wind and ACE, which, like SOHO, operate in the vicinity of the Sun–Earth L1 point.

NASA contributed three instruments on SOHO as well as launch and flight operations support.

About two months after launch, on Feb. 14, 1996, SOHO was placed at a distance of about 93,000 miles (1.5 million kilometers) from Earth in an elliptical Lissajous orbit around the L1 libration point where it takes approximately six months to orbit L1 (while the L1 itself orbits the Sun every 12 months).

The spacecraft returned its first image on Dec. 19, 1995 and was fully commissioned for operations by April 16, 1996. SOHO finished its planned two-year study of the Sun’s atmosphere, surface, and interior in April 1998.

Communications with the spacecraft were interrupted for four months beginning June 24,1998, after which the spacecraft was apparently spinning, losing electrical power, and not pointing at the Sun. After intensive search efforts, by September 25, controllers managed to regain control and return SOHO to “normal mode.” Because of the failure of onboard gyros, ESA developed a special gyroless method of orientation (which used reaction wheels) that was successfully implemented beginning Feb. 1, 1999. Barring three instruments, the spacecraft was functional and was declared operational once again by mid-October 1998.

SOHO’s original life- time was three years (to 1998), but in 1997, ESA and NASA jointly decided to prolong the mission to 2003, thus enabling the spacecraft to compare the Sun’s behavior during low dark sunspot activity (1996) to the peak (around 2000).

One of SOHO’s most important discoveries has been locating the origin of the fast solar wind at the corners of honey- comb-shaped magnetic fields surrounding the edges of large bubbling cells located near the Sun’s poles. Another has been its discovery, as of September 2015, of over 3,000 comets (more than half of all known comets), by over 70 people representing 18 different nations. These discoveries were made possible because of the LASCO instrument that while observing the Sun, blocked out the Sun’s glare, rendering comets visible.

SOHO’s mission at L1 has now been extended multiple times.

In December 2015, SOHO marked 20 years of continuous operation, having fundamentally changed our conception of the Sun “from a picture of a static, unchanging object in the sky to the dynamic beast it is,” in the words of Bernhard Fleck, the ESA project scientist for SOHO. The longevity of the mission has allowed SOHO to cover an entire 11-year solar cycle and the beginning of a new one.

One of the recent highpoints of the mission was SOHO’s observation of a bright comet plunging toward the Sun on August 3–4 2016 at a velocity of nearly 1.3 milliom mph (2.1 million kilometers/hour.)

Additional Resources

European Space Agency: SOHO

NASA: SOHO Portal

NASA: SOHO Project Site

National Space Science Data Center Master Catalog: SOHO

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