Solar and Heliospheric Observatory

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Solar and Heliospheric Observatory (SOHO)
NASA SOHO spacecraft.png
SOHO satellite
NamesSOHO
Mission type Solar observation
Operator ESA  / NASA
COSPAR ID 1995-065A
SATCAT no. 23726
Website sohowww.nascom.nasa.gov
Mission duration2 years (planned)
26 years and 18 days (in progress)
Spacecraft properties
Bus SOHO
Manufacturer Matra Marconi Space
Launch mass1,850 kg (4,080 lb) [1]
Payload mass610 kg (1,340 lb)
Dimensions4.3 × 2.7 × 3.7 m (14.1 × 8.9 × 12.1 ft)
9.5 m (31 ft) with solar arrays deployed
Power1500 watts
Start of mission
Launch date2 December 1995, 08:08:01 UTC
Rocket Atlas IIAS (AC-121)
Launch site Cape Canaveral, LC-36B
Contractor Lockheed Martin
Entered serviceMay 1996
Orbital parameters
Reference system Sun–Earth L1
Regime Halo orbit
Perigee altitude 206,448 km (128,281 mi)
Apogee altitude 668,672 km (415,494 mi)
SOHO insignia.png
SOHO mission patch
Huygens  
 

The Solar and Heliospheric Observatory (SOHO) is a European Space Agency (ESA) spacecraft built by a European industrial consortium led by Matra Marconi Space (now Airbus Defence and Space) that was launched on a Lockheed Martin Atlas IIAS launch vehicle on 2 December 1995, to study the Sun. It has also discovered over 4,000 comets. [2] [3] It began normal operations in May 1996. It is a joint project between the European Space Agency (ESA) and NASA. SOHO was part of the International Solar Terrestrial Physics Program (ISTP). Originally planned as a two-year mission, SOHO continues to operate after over 25 years in space; the mission has been extended until the end of 2025, subject to review and confirmation by ESA's Science Programme Committee. [4]

Contents

In addition to its scientific mission, it is a main source of near-real-time solar data for space weather prediction. Along with Wind, Advanced Composition Explorer (ACE), and Deep Space Climate Observatory (DSCOVR), SOHO is one of four spacecraft in the vicinity of the EarthSun L1 point, a point of gravitational balance located approximately 0.99 astronomical unit (AU) from the Sun and 0.01 AU from the Earth. In addition to its scientific contributions, SOHO is distinguished by being the first three-axis-stabilized spacecraft to use its reaction wheels as a kind of virtual gyroscope; the technique was adopted after an on-board emergency in 1998 that nearly resulted in the loss of the spacecraft.

Scientific objectives

The three main scientific objectives of SOHO are:

Orbit

Animation of SOHO's trajectory
Animation of Solar and Heliospheric Observatory trajectory - Polar view.gif
Polar view
Animation of Solar and Heliospheric Observatory trajectory - Equatorial view.gif
Equatorial view
   Earth ·   SOHO

The SOHO spacecraft is in a halo orbit around the SunEarth L1 point, the point between the Earth and the Sun where the balance of the (larger) Sun's gravity and the (smaller) Earth's gravity is equal to the centripetal force needed for an object to have the same orbital period in its orbit around the Sun as the Earth, with the result that the object will stay in that relative position.

Although sometimes described as being at L1, the SOHO spacecraft is not exactly at L1 as this would make communication difficult due to radio interference generated by the Sun, and because this would not be a stable orbit. Rather it lies in the (constantly moving) plane, which passes through L1 and is perpendicular to the line connecting the Sun and the Earth. It stays in this plane, tracing out an elliptical halo orbit centered about L1. It orbits L1 once every six months, while L1 itself orbits the Sun every 12 months as it is coupled with the motion of the Earth. This keeps SOHO in a good position for communication with Earth at all times.

Communication with Earth

In normal operation, the spacecraft transmits a continuous 200 kbit/s data stream of photographs and other measurements via the NASA Deep Space Network of ground stations. SOHO's data about solar activity are used to predict coronal mass ejection (CME) arrival times at Earth, so electrical grids and satellites can be protected from their damaging effects. CMEs directed toward the earth may produce geomagnetic storms, which in turn produce geomagnetically induced currents, in the most extreme cases creating black-outs, etc.

In 2003, ESA reported the failure of the antenna Y-axis stepper motor, necessary for pointing the high-gain antenna and allowing the downlink of high-rate data. At the time, it was thought that the antenna anomaly might cause two- to three-week data-blackouts every three months. [5] However, ESA and NASA engineers managed to use SOHO's low-gain antennas together with the larger 34 m (112 ft) and 70 m (230 ft) NASA Deep Space Network ground stations and judicious use of SOHO's Solid State Recorder (SSR) to prevent total data loss, with only a slightly reduced data flow every three months. [6]

Near loss of SOHO

The SOHO Mission Interruption sequence of events began on 24 June 1998, while the SOHO Team was conducting a series of spacecraft gyroscope calibrations and maneuvers. Operations proceeded until 23:16 UTC when SOHO lost lock on the Sun and entered an emergency attitude control mode called Emergency Sun Reacquisition (ESR). The SOHO Team attempted to recover the observatory, but SOHO entered the emergency mode again on 25 June 1998, at 02:35 UTC. Recovery efforts continued, but SoHO entered the emergency mode for the last time at 04:38 UTC. All contact with SOHO was lost at 04:43 UTC, and the mission interruption had begun. SOHO was spinning, losing electrical power, and no longer pointing at the Sun. [7]

Expert European Space Agency (ESA) personnel were immediately dispatched from Europe to the United States to direct operations[ citation needed ]. Days passed without contact from SOHO. On 23 July 1998, the Arecibo Observatory and Goldstone Solar System Radar combined to locate SOHO with radar and to determine its location and attitude. SOHO was close to its predicted position, oriented with its side versus the usual front Optical Surface Reflector panel pointing toward the Sun, and was rotating at one revolution every 53 seconds. Once SOHO was located, plans for contacting SOHO were formed. On 3 August, a carrier was detected from SOHO, the first signal since 25 June 1998. After days of charging the battery, a successful attempt was made to modulate the carrier and downlink telemetry on 8 August. After instrument temperatures were downlinked on 9 August 1998, data analysis was performed, and planning for the SOHO recovery began in earnest. [8]

The Recovery Team began by allocating the limited electrical power. After this, SOHO's anomalous orientation in space was determined. Thawing the frozen hydrazine fuel tank using SOHO's thermal control heaters began on 12 August 1998. Thawing pipes and the thrusters was next, and SOHO was re-oriented towards the Sun on 16 September 1998. After nearly a week of spacecraft bus recovery activities and an orbital correction maneuver, the SOHO spacecraft bus returned to normal mode on 25 September 1998 at 19:52 UTC. Recovery of the instruments began on 5 October 1998 with SUMER, and ended on 24 October 1998, with CELIAS. [9]

Only one gyroscope remained operational after this recovery, and on 21 December 1998, that gyroscope failed. Attitude control was accomplished with manual thruster firings that consumed 7 kg (15 lb) of fuel weekly, while the ESA developed a new gyroless operations mode that was successfully implemented on 1 February 1999. [9]

Instrument

Scale model of the Solar and Heliospheric Observatory (SOHO) spacecraft at the Euro Space Center in Belgium Solar and Heliospheric Observatory.jpg
Scale model of the Solar and Heliospheric Observatory (SOHO) spacecraft at the Euro Space Center in Belgium

The SOHO Payload Module (PLM) consists of twelve instruments, each capable of independent or coordinated observation of the Sun or parts of the Sun, and some spacecraft components. The instruments are: [10] [11]

Public availability of images

Observations from some of the instruments can be formatted as images, most of which are readily available on the internet for either public or research use (see the official website). Others, such as spectra and measurements of particles in the solar wind, do not lend themselves so readily to this. These images range in wavelength or frequency from optical () to Extreme ultraviolet (EUV). Images taken partly or exclusively with non-visible wavelengths are shown on the SOHO page and elsewhere in false color.

Unlike many space-based and ground telescopes, there is no time formally allocated by the SOHO program for observing proposals on individual instruments; interested parties can contact the instrument teams via e-mail and the SOHO website to request time via that instrument team's internal processes (some of which are quite informal, provided that the ongoing reference observations are not disturbed). A formal process (the "JOP" program) does exist for using multiple SOHO instruments collaboratively on a single observation. JOP proposals are reviewed at the quarterly Science Working Team (SWT) meetings, and JOP time is allocated at monthly meetings of the Science Planning Working Group. First results were presented in Solar Physics, volumes 170 and 175 (1997), edited by B. Fleck and Z. Švestka.

Comet discovery

This visualization presents a small sample of the 9 years of comets seen by SOHO from the perspective an observer at a fixed point above the ecliptic plane with the Sun at the center.
Comet discoveries [13] [14]
Year#
2013213
2012222
2011216
2010209

As a consequence of its observing the Sun, SOHO (specifically the LASCO instrument) has inadvertently allowed the discovery of comets by blocking out the Sun's glare. Approximately one-half of all known comets have been spotted by SOHO, discovered over the last 15 years by over 70 people representing 18 different countries searching through the publicly available SOHO images online. SOHO had discovered over 2700 comets by April 2014, [2] [15] with an average discovery rate of one every 2.59 days. [16] In September 2015, SOHO discovered its 3000th comet. [17]

Instrument contributors

The Max Planck Institute for Solar System Research contributed to SUMER, Large Angle and Spectrometric Coronagraph (LASCO), and CELIAS instruments. The Smithsonian Astrophysical Observatory (SAO) built the UVCS instrument. The Lockheed Martin Solar and Astrophysics Laboratory (LMSAL) built the MDI instrument in collaboration with the solar group at Stanford University. The Institut d'Astrophysique Spatiale is the principal investigator of GOLF and Extreme ultraviolet Imaging Telescope (EIT), with a strong contribution to SUMER. A complete list of all the instruments, with links to their home institutions, is available at the SOHO Website.

See also

Related Research Articles

Solar flare Sudden flash of increased brightness on the Sun

A solar flare is an intense eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections and solar particle events.

<i>Ulysses</i> (spacecraft) 1990 robotic space probe; studied the Sun from a near-polar orbit

Ulysses was a robotic space probe whose primary mission was to orbit the Sun and study it at all latitudes. It was launched in 1990 and made three "fast latitude scans" of the Sun in 1994/1995, 2000/2001, and 2007/2008. In addition, the probe studied several comets. Ulysses was a joint venture of the European Space Agency (ESA) and the United States' National Aeronautics and Space Administration, under leadership of ESA with participation from Canada's National Research Council. The last day for mission operations on Ulysses was 30 June 2009.

Coronal mass ejection Significant release of plasma and magnetic field from the solar corona

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TRACE NASA satellite of the Explorer program

Transition Region and Coronal Explorer was a NASA heliophysics and solar observatory designed to investigate the connections between fine-scale magnetic fields and the associated plasma structures on the Sun by providing high resolution images and observation of the solar photosphere, the transition region, and the solar corona. A main focus of the TRACE instrument is the fine structure of coronal loops low in the solar atmosphere. TRACE is the third spacecraft in the Small Explorer program, launched on 2 April 1998, and obtained its last science image on 21 June 2010, at 23:56 UTC.

Solar Orbiter European solar observatory studying the Suns heliosphere; medium-class mission in the ESA Science Programme

The Solar Orbiter (SolO) is a Sun-observing satellite, developed by the European Space Agency (ESA). SolO is intended to perform detailed measurements of the inner heliosphere and nascent solar wind, and perform close observations of the polar regions of the Sun, which is difficult to do from Earth, both serving to answer the question "How does the Sun create and control the heliosphere?"

Solar physics is the branch of astrophysics that specializes in the study of the Sun. It deals with detailed measurements that are possible only for our closest star. It intersects with many disciplines of pure physics, astrophysics, and computer science, including fluid dynamics, plasma physics including magnetohydrodynamics, seismology, particle physics, atomic physics, nuclear physics, stellar evolution, space physics, spectroscopy, radiative transfer, applied optics, signal processing, computer vision, computational physics, stellar physics and solar astronomy.

The Lockheed Martin Solar and Astrophysics Laboratory (LMSAL) is part of the Lockheed Martin Advanced Technology Center (ATC) that is known primarily for its scientific work in the field of solar physics, astronomy and space weather. The LMSAL team is part of Lockheed Martin Space Systems and has close affiliations with NASA and the solar physics group at Stanford University.

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Solar Dynamics Observatory NASA mission

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THEMIS NASA satellite of the Explorer program

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96P/Machholz Periodic comet with 5 year orbit

Comet 96P/Machholz or 96P/Machholz 1 is a short-period sungrazing comet discovered on May 12, 1986, by amateur astronomer Donald Machholz on Loma Prieta peak, in central California using 130 millimetres (5.1 in) binoculars. On June 6, 1986, 96P/Machholz passed 0.40373 AU from the Earth. 96P/Machholz last came to perihelion on October 27, 2017, and will next come to perihelion on January 31, 2023. The comet has an estimated diameter of around 6.4 km (4.0 mi).

Coronal loop Structure in the lower corona and transition region of the Sun

Coronal loops are huge loops of magnetic field beginning and ending on the Sun's visible surface (photosphere) projecting into the solar atmosphere (corona). Hot glowing ionized gas (plasma) trapped in the loops makes them visible. Coronal loops range widely in size up to several thousand kilometers long. They are transient features of the solar surface, forming and dissipating over periods of seconds to days. They form the basic structure of the lower corona and transition region of the Sun. These highly structured loops are a direct consequence of the twisted solar magnetic flux within the solar body. Coronal loops are associated with sunspots; the two "footpoints" where the loop passes through the sun's surface are often sunspots. This is because sunspots occur at regions of high magnetic field. The high magnetic field where the loop passes through the surface forms a barrier to convection currents, which bring hot plasma from the interior to the sun's surface, so the plasma in these high field regions is cooler than the rest of the sun's surface, appearing as a dark spot when viewed against the rest of the photosphere. The population of coronal loops varies with the 11 year solar cycle, which also influences the number of sunspots.

C/2011 W3 (Lovejoy) Kreutz Sungrazer comet discovered in November 2011 by Terry Lovejoy

Comet Lovejoy, formally designated C/2011 W3 (Lovejoy), is a long-period comet and Kreutz sungrazer. It was discovered in November 2011 by Australian amateur astronomer Terry Lovejoy. The comet's perihelion took it through the Sun's corona on 16 December 2011, after which it emerged intact, though greatly impacted by the event.

Comet C/2012 E2 (SWAN) was a Kreutz group sungrazing comet discovered by Vladimir Bezugly in publicly available images taken by the SWAN instrument on board the SOHO spacecraft. It is recognized for being the first Kreutz sungrazer observed in SWAN imagery.

Heliophysics Science Division

The Heliophysics Science Division of the Goddard Space Flight Center (NASA) conducts research on the Sun, its extended Solar System environment, and interactions of Earth, other planets, small bodies, and interstellar gas with the heliosphere. Division research also encompasses geospace—Earth's uppermost atmosphere, the ionosphere, and the magnetosphere—and the changing environmental conditions throughout the coupled heliosphere.

Lagrange is a 2018 concept study for a solar weather mission by the European Space Agency (ESA). This is a British-led concept that envisions two spacecraft to be positioned at Lagrangian points L1 and L5.

Space Weather Follow On-Lagrange 1

Space Weather Follow On-Lagrange 1 (SWFO-L1) is a future spacecraft mission planned to monitor signs of solar storms, which may pose harm to Earth's telecommunication network. The spacecraft will be operated by the National Oceanic and Atmospheric Administration (NOAA), with launch scheduled for February 2025. It is planned to be placed at the Sun–Earth L1 Lagrange point, a location between the Earth and the Sun. This will allow SWFO-L1 to continuously watch the solar wind and energetic particles heading for Earth. SWFO-L1 is an ESPA Class Spacecraft, sized for launch on an Evolved Expendable Launch Vehicle Secondary Payload Adapter (ESPA) Grande ring in addition to the rocket's primary payload. The spacecraft's Solar Wind Instrument Suite (SWIS) which includes three instruments will monitor solar wind, and the Compact Coronagraph (CCOR) will monitor the Sun's surroundings to image coronal mass ejection (CME). A CME is a large outburst of plasma sent from the Sun towards interplanetary space.

References

  1. "SOHO (Solar and Heliospheric Observatory)". ESA eoPortal. Retrieved 12 April 2016.
  2. 1 2 "3000th Comet Spotted by Solar and Heliospheric Observatory (SOHO)". NASA. Retrieved 15 September 2015. (2,703 discoveries as of 21 April 2014) PD-icon.svgThis article incorporates text from this source, which is in the public domain .
  3. Frazier, Sarah (16 June 2020). "4,000th Comet Discovered by ESA and NASA Solar Observatory". NASA. Retrieved 12 February 2021.
  4. Colangeli, Luigi (13 October 2020). "ESA Science & Technology - Extended operations confirmed for science missions". sci.esa.int. European Space Agency. Retrieved 15 December 2021.
  5. "Antenna anomaly may affect SOHO scientific data transmission". ESA. 24 June 2003. Retrieved 14 March 2005.
  6. "SOHO's antenna anomaly: things are much better than expected". ESA. 2 July 2003. Retrieved 14 March 2005.
  7. "SOHO "Mission Interruption Joint NASA/ESA Investigation Board Final Report"". NASA. Retrieved 12 March 2018.PD-icon.svgThis article incorporates text from this source, which is in the public domain .
  8. David, Leonard (May 1999). "Saving SOHO" (PDF). Aerospace America.PD-icon.svgThis article incorporates text from this source, which is in the public domain .
  9. 1 2 "SOHO's Recovery: An Unprecedented Success Story" (PDF). European Space Agency. Retrieved 12 March 2018.
  10. Domingo, V.; Fleck, B.; Poland, A. I.; Solar Physics 162, 1--37 (1995)
  11. Fleck B. (1997). "First Results from SOHO". Rev Modern Astron. 10: 273–296. Bibcode:1997RvMA...10..273F.
  12. "MDI Web Page". soi.stanford.edu. Retrieved 16 January 2019.
  13. Karl Battams [@SungrazerComets] (16 April 2014). "These are SOHO discovery counts in the past few years: 2013: 213, 2012: 222, 2011: 216, 2010: 209 ... consistent!" (Tweet) via Twitter.
  14. Karl Battams [@SungrazerComets] (2 January 2013). "The SOHO comet discovery rate has been remarkably consistent over past 3yrs: 2010: 222 comets, 2011: 213, 2012: 219" (Tweet) via Twitter.
  15. Karl Battams [@SungrazerComets] (21 April 2014). "As of April 21, 2014, the @ESA/@NASA SOHO satellite comet discovery count stands at 2,703! #Sungrazers" (Tweet) via Twitter.
  16. Karl Battams [@SungrazerComets] (19 October 2012). "Since the @ESA/@NASA SOHO mission launched in 1995, it has discovered a new comet every 2.59-days on average!" (Tweet) via Twitter.
  17. Mike well, space.com (16 September 2015). "Whoa! Sun-Watching Spacecraft Finds 3,000th Comet" . Retrieved 16 September 2015.