NationMaster - Encyclopedia: Solar and Heliospheric Observatory

The Solar and Heliospheric Observatory (SOHO) is a spacecraft that was launched on an Atlas IIAS launch vehicle on 2 December 1995 to study the Sun, and began normal operations in May 1996. It is a joint project of international cooperation between the European Space Agency (ESA) and NASA. Originally planned as a two-year mission, SOHO currently continues to operate after over ten years in space. In addition to its scientific mission, it is currently the main source of near-real time solar data for space weather prediction. Along with the Advanced Composition Explorer (ACE), SOHO is one of two spacecraft currently in the vicinity of the Earth-Sun L1 point, a point of gravitational balance located approximately 0.99 astronomical units (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. This article is about the European Space Agency. ... The National Aeronautics and Space Administration (NASA) is an agency of the United States federal government, responsible for the nations public space program. ... The wavelength is the distance between repeating units of a wave pattern. ... See also list of optical topics. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... In physics, magnetism is a phenomenon by which materials exert an attractive or repulsive force on other materials. ... A contour plot of the effective potential (the Hills Surfaces) of a two-body system (the Sun and Earth here), showing the five Lagrange points. ... A heliocentric orbit is an orbit around the sun. ... December 2 is the 336th day (337th in leap years) of the year in the Gregorian calendar. ... 1995 (MCMXCV) was a common year starting on Sunday of the Gregorian calendar. ... Mission Atlas II is a member of the Atlas family of launch vehicles, which evolved from the successful Atlas intercontinental ballistic missile (ICBM) program. ... In cargo transport, the payload is the valuable contents of the vehicle. ... The structure of the Sun The core of the Sun is considered to extend from the center to about 0. ... Oscillation is the variation, typically in time, of some measure as seen, for example, in a swinging pendulum. ... In astronomy, photometry is the measurement of the flux or intensity of an astronomical objects electromagnetic radiation. ... A corona is a type of plasma atmosphere of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... A telescope (from the Greek tele = far and skopein = to look or see; teleskopos = far-seeing) is an instrument designed for the observation of remote objects. ... For Acoustic uses in spectrographs of sound waves, see below. ... The optical spectrum (light or visible spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. ... In optics, a Fabry-Perot interferometer or etalon is typically made of a transparent plate with two reflecting surfaces, or two parallel highly-reflecting mirrors. ... The plasma in the solar wind meeting the heliopause For the British comic, see Solar Wind (comic). ... In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: Ï (rho) is the density of the substance, measured in kgÂ·m-3 m is the mass of the substance, measured in kg V is... ... The Space Shuttle Discovery as seen from the International Space Station. ... Mission Atlas II is a member of the Atlas family of launch vehicles, which evolved from the successful Atlas intercontinental ballistic missile (ICBM) program. ... December 2 is the 336th day (337th in leap years) of the year in the Gregorian calendar. ... 1995 (MCMXCV) was a common year starting on Sunday of the Gregorian calendar. ... The Sun is the star at the center of the Solar System. ... 1996 (MCMXCVI) was a leap year starting on Monday of the Gregorian calendar, and was designated the International Year for the Eradication of Poverty. ... ESA redirects here. ... The National Aeronautics and Space Administration (NASA) is an agency of the United States federal government, responsible for the nations public space program. ... For the Manfred Mann album, see 2006 (album). ... Space has been an interest for philosophers and scientists for much of human history. ... It has been suggested that Real-time computing be merged into this article or section. ... Aurora australis observed by Discovery, May 1991. ... Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition Explorer Advanced Composition... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... The Sun is the star at the center of the Solar System. ... In celestial mechanics, the Lagrangian points, (also Lagrange point, L-point, or libration point) are the five stationary solutions of the circular restricted three-body problem. ... The astronomical unit (AU or au or a. ... A momentum wheel is a type of flywheel used primarily by spacecraft to change their angular momentum without using fuel for rockets or other reaction devices. ... A gyroscope For other uses, see Gyroscope (disambiguation). ... 1998 (MCMXCVIII) was a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean [1]. // Coated in ice, power and telephone lines sag and often break, resulting in power outages. ...

Orbit

The 610 kg SOHO spacecraft is in a halo orbit around the Sun-Earth 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. It is about 1.5 million kilometers from the Earth. Gravity from the Sun is 2% (118 µm/s²) more than at the Earth (5.9 mm/s²), while the reduction of required centripetal force is half of this (59 µm/s²). The sum of both effects is balanced by the gravity of the Earth, which is here also 177 µm/s². m. ... The Sun is the star at the center of the Solar System. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... In celestial mechanics, the Lagrangian points, (also Lagrange point, L-point, or libration point) are the five stationary solutions of the circular restricted three-body problem. ... The Sun is the star at the center of the Solar System. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... A centripetal force is a force pulling an object toward the center of a circular path as the object goes around the circle. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ...

Although sometimes described as being at L1, the SOHO satellite 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 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 at a good position for communication with Earth at all times. An Earth observation satellite, ERS 2 For other uses, see Satellite (disambiguation). ... In celestial mechanics, the Lagrangian points, (also Lagrange point, L-point, or libration point) are the five stationary solutions of the circular restricted three-body problem. ...

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 solar flares, so electrical grids and satellites can be protected from their damaging effects. Deep Space Network (DSN) is an international network of radio antennas that supports interplanetary spacecraft missions, and radio and radar astronomy observations for the exploration of the solar system and the universe. ... A Solar Flare and CME, courtesy NASA A solar flare is a violent explosion in the Suns atmosphere with an energy equivalent to a billion megatons, traveling normally at about 1 million km per hour (about 0. ... Electric power transmission is the second process in the delivery of electricity to consumers. ... An Earth observation satellite, ERS 2 For other uses, see Satellite (disambiguation). ...

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.^[1] However, ESA and NASA engineers managed to use SOHO's low gain antennas together with the larger 34 and 70 meter DSN 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.^[2] Fig. ... The top electromagnet (1) is charged, attracting the topmost four teeth of a sprocket. ... The High Gain Antenna (HGA) is an antenna with a focused, narrow radiowave beam width. ...

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 June 25 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, and the mission interruption had begun. SOHO was no longer pointing at the Sun, spinning, and losing electrical power. June 24 is the 175th day of the year (176th in leap years) in the Gregorian Calendar, with 190 days remaining. ... 1998 (MCMXCVIII) was a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean [1]. // Coated in ice, power and telephone lines sag and often break, resulting in power outages. ... A gyroscope For other uses, see Gyroscope (disambiguation). ... // In the context of spacecraft, attitude control is control of the angular position and rotation of the spacecraft, either relative to the object that it is orbiting, or relative to the celestial sphere. ... June 25 is the 176th day of the year (177th in leap years) in the Gregorian Calendar, with 189 days remaining. ...

Expert ESA personnel were immediately dispatched from Europe to the United States to direct operations. Days passed without contact from SOHO. On July 23, the Arecibo Observatory and DSN antennas were used 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 RPM. Once SOHO was located, plans for contacting SOHO were formed. On 3 August a carrier was detected from SOHO, the first signal since June 25. After days of charging the battery, a successful attempt was made to modulate the carrier and downlink telemetry on August 8. After instrument temperatures were downlinked on August 9, data analysis was performed, and planning for the SOHO recovery began in earnest. This article is about the European Space Agency. ... World map showing the location of Europe. ... July 23 is the 204th day (205th in leap years) of the year in the Gregorian calendar, with 161 days remaining. ... The Arecibo Observatory is located approximately 9 miles south-southwest from Arecibo, Puerto Rico (near the extreme southwestern corner of Arecibo pueblo). ... DSN may stand for: Deep Space Network Defense Switched Network The International Conference on Dependable Systems and Networks Database Source Name Star Trek: Deep Space Nine Delivery Status Notification, especially E-mail bounces This page extends a three-character combination which might be any or all of: an abbreviation, an... This long range radar antenna, known as ALTAIR, is used to detect and track space objects in conjunction with ABM testing at the Ronald Reagan Test Site on the Kwajalein atoll. ... Attitude may refer to: Aircraft attitude Attitude (magazine) Attitude, a song by American pop and jazz singer Suede Attitudes (band) Attitude Adjustment (Hardcore/Crossover/Thrash metal band) Attitude, song from Metallica on their album Reload. ... Revolutions per minute (abbreviated rpm, RPM, r/min, or min-1) is a unit of frequency, commonly used to measure rotational speed, in particular in the case of rotation around a fixed axis. ... August 3 is the 215th day of the year in the Gregorian calendar (216th in leap years), with 150 days remaining. ... This article or section does not adequately cite its references or sources. ... June 25 is the 176th day of the year (177th in leap years) in the Gregorian Calendar, with 189 days remaining. ... Four double-A (AA) rechargeable cells A Duracell AA alkaline cell In science and technology, a galvanic cell is an electrochemical cell that stores chemical energy and makes it available in an electrical form, and a battery is a string of two or more cells in series. ... In telecommunications, modulation is the process of varying a periodic waveform, i. ... Telemetry is a technology that allows the remote measurement and reporting of information of interest to the system designer or operator. ... August 8 is the 220th day of the year in the Gregorian calendar (221st in leap years), with 145 days remaining. ... August 9 is the 221st day of the year in the Gregorian Calendar (222nd in leap years), with 144 days remaining. ... Data analysis is the act of transforming data with the aim of extracting useful information and facilitating conclusions. ...

The SOHO 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 August 12. Thawing pipes and the thrusters was next, and SOHO was re-oriented towards the Sun on September 16. After nearly a week of spacecraft bus recovery activities and an orbital correction maneuver, the SOHO spacecraft (bus) returned to normal mode on September 25 at 19:52 UTC. Recovery of the instruments began on October 5 with SUMER, and ended on October 24, 1998 with CELIAS. Hydrazine is the chemical compound with formula N2H4. ... August 12 is the 224th day of the year (225th in leap years) in the Gregorian calendar. ... A thruster is a small propulsive device used by spacecraft and watercraft for station keeping, attitude control, or long duration low thrust acceleration. ... // 1400 - Owain GlyndÅµr declared Prince of Wales by his followers. ... September 25 is the 268th day of the year (269th in leap years) in the Gregorian calendar. ... October 5 is the 278th day of the year in the Gregorian calendar (279th in leap years). ... October 24 is the 297th day of the year (298th in leap years) in the Gregorian calendar, with 68 days remaining. ... 1998 (MCMXCVIII) was a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean [1]. // Coated in ice, power and telephone lines sag and often break, resulting in power outages. ...

Only one gyro remained operational after this recovery, and on December 21 that gyro failed. Attitude control was accomplished with manual thruster firings that consumed 7kg of fuel weekly, while ESA developed a new gyroless operations mode that was successfully implemented on February 1, 1999. A gyroscope For other uses, see Gyroscope (disambiguation). ... December 21 is the 355th day of the year (356th in leap years) in the Gregorian calendar. ... This article is about the European Space Agency. ... February 1 is the 32nd day of the year in the Gregorian calendar. ... 1999 (MCMXCIX) was a common year starting on Friday, and was designated the International Year of Older Persons by the United Nations. ...

Additional References

March 11 is the 70th day of the year in the Gregorian calendar (71st in leap years). ... For the Manfred Mann album, see 2006 (album). ... March 11 is the 70th day of the year in the Gregorian calendar (71st in leap years). ... For the Manfred Mann album, see 2006 (album). ... March 11 is the 70th day of the year in the Gregorian calendar (71st in leap years). ... For the Manfred Mann album, see 2006 (album). ... March 11 is the 70th day of the year in the Gregorian calendar (71st in leap years). ... For the Manfred Mann album, see 2006 (album). ... For the Manfred Mann album, see 2006 (album). ... January 9 is the 9th day of the year in the Gregorian calendar. ...

Scientific Objectives

The chromosphere (literally, color sphere) is a thin layer of the Suns atmosphere just above the photosphere, roughly 10,000 kilometers deep (approximating to, if a little less than, the diameter of the Earth). ... TRACE 19. ... A corona is a type of plasma atmosphere of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... The Sun is the star at the center of the Solar System. ... The plasma in the solar wind meeting the heliopause For the British comic, see Solar Wind (comic). ... In situ is a Latin phrase meaning in the place. ... A computer generated image showing the pattern of a p-mode solar acoustic oscillation both in the interior and on the surface of the sun. ...

Instruments

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:

Observations from some of the instruments can be formatted as images, most of which are also 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 (Hα) to extreme ultraviolet (UV). 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 directly via e-mail and the SOHO web site 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. The photosphere of an astronomical object is the region at which the optical depth becomes one for a photon of wavelength equal to 5000 angstroms. ... The convection zone is the outermost layer of the suns interior. ... The Sun is the star at the center of the Solar System. ... A corona is a type of plasma atmosphere of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... In telecommunications, a virtual channel is a channel designation which differs from the actual radio channel or frequency which the signal travels. ... A magnetogram is a pictorial representation of the variations in strength of a magnetic field. ... A computer generated image showing the pattern of a p-mode solar acoustic oscillation both in the interior and on the surface of the sun. ... Download high resolution version (2192x1658, 83 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (2192x1658, 83 KB) Wikipedia does not have an article with this exact name. ... This article needs to be cleaned up to conform to a higher standard of quality. ... The plasma in the solar wind meeting the heliopause For the British comic, see Solar Wind (comic). ... The wavelength is the distance between repeating units of a wave pattern. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ... See also list of optical topics. ... In physics and astronomy, H-alpha, also written Hα, is a particular emission line created by hydrogen. ... UV redirects here. ... A false color image showing the Chesapeake Bay and the city of Baltimore. ... Betrothal is a formal state of engagement to be married. ...

As a consequence of its observing the Sun, SOHO (specifically the LASCO instrument) has inadvertently discovered comets by blocking out the Sun's glare. Approximately one-half of all known comets have been discovered by SOHO. Recently, it discovered its 1000th comet.^[3] Comet Hale-Bopp Comet McNaught as seen from Swifts Creek, Victoria, Australia on 23 January 2007 For other uses, see Comet (disambiguation). ...

Instrument contributors

The Max Planck Institute for Solar System Research contributed to SUMMER, LASCO and CELIAS instruments. The Smithsonian Astrophysical Observatory built the UVCS instrument. Max Planck Institute for Solarsystem Research April 2006 The Max Planck Institute for Solar System Research (MPS) is part of the Max Planck Society which operates 80 research facilities in Germany. ... The Smithsonian Astrophysical Observatory (SAO) is a research institute of the Smithsonian Institution headquartered in Cambridge, Massachusetts, where it is joined with the Harvard College Observatory (HCO) to form the Harvard-Smithsonian Center for Astrophysics (CfA). ...

Contents

Orbit

Communication with Earth

Near Loss of SOHO

Additional References

Scientific Objectives

Instruments

Instrument contributors

See also

References

External links