The Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space, launched on a Lockheed Martin Atlas II AS launch vehicle on December 2, 1995 to study the Sun. SOHO has discovered over 3,000 comets, it began normal operations in May 1996. It is a joint project of international cooperation between the European Space Agency and NASA. Planned as a two-year mission, SOHO continues to operate after over 25 years in space: the mission is extended until the end of 2020 with a extension until 2022. In addition to its scientific mission, it is a main source of near-real-time solar data for space weather prediction. Along with Wind, ACE and DSCOVR, SOHO is one of four spacecraft in the vicinity of the Earth–Sun L1 point, a point of gravitational balance located 0.99 astronomical unit s 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 spacecraft is noted for enabling the discovery of many comets. The three main scientific objectives of SOHO are: Investigation of the outer layer of the Sun, which consists of the chromosphere, transition region, the corona. CDS, EIT, LASCO, SUMER, SWAN, UVCS are used for this solar atmosphere remote sensing. Making observations of solar wind and associated phenomena in the vicinity of L1. CELIAS and COSTEP are used for "in situ" solar wind observations. Probing the interior structure of the Sun. GOLF, MDI, VIRGO are used for helioseismology; the 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 Sun's gravity and the 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 at L1 as this would make communication difficult due to radio interference generated by the Sun, because this would not be a stable orbit.
Rather it lies in the 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 lissajous 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. 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 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. 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 to prevent total data loss, with only a reduced data flow every three months; the SOHO Mission Interruption sequence of events began on June 24, 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, entered an emergency attitude control mode called Emergency Sun Reacquisition; 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 at 4:43 UTC, the mission interruption had begun. SOHO was spinning, losing electrical power, no longer pointing at the Sun.
Expert ESA personnel were dispatched from Europe to the United States to direct operations. Days passed without contact from SOHO. On July 23, the Arecibo Observatory and Goldstone Solar System Radar combined to locate SOHO with radar, 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, was rotating at one revolutions every 53 seconds. Once SOHO was located, plans for contacting SOHO were formed. On August 3 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, planning for the SOHO recovery began in earnest; 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 August 12.
Thawing pipes and the thrusters was next, 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 space
Dhrangadhra Junction railway station is a major railway station in Dhrangadhra town of Surendranagar district, Gujarat. It serves Dhrangadhra town, its code is'DHG'. DEMU, passenger and superfast trains halt here. Two trains start from here. Dhrangadhra Junction is well connected by rail to Bandra Terminus, Dadar Western, Visakhapatnam Junction, Shri Mata Vaishno Devi Katra, Bareilly Junction, Bangalore City, Pune Junction, Gandhidham Junction, Howrah Junction and Shalimar. 22955/56 Bandra Terminus - Bhuj Kutch Superfast Express 12993/94 Gandhidham - Puri Weekly Superfast Express 18501/02 Gandhidham - Visakhapatnam Express 19115/16 Dadar - Bhuj Sayajinagari Express 14311/12 Ala Hazrat Express 16505/06 Gandhidham - KSR Bengaluru City Express 16335/36 Gandhidham − Nagercoil Express 11091/92 Bhuj - Pune Express 22829/30 Shalimar - Bhuj Weekly Superfast Express 12937/38 Gandhidham - Hawrah Garbha Superfast Express 12473/74 Gandhidham - Shri Mata Vaishno Devi Katra Sarvodaya Express Dhrangadhra Railway was owned by Princely state of Dhrangadhra.
It was opened to traffic in 1898. Dhrangadhra Railway
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