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The 610 kg ''SOHO'' spacecraft is in a halo Orbit around the L1 Lagrange 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 kilometres from the Earth. Gravity from the Sun is 2% (118 µm/s&2) more than at the Earth (5.9 mm/s&2), while the reduction of required centripetal force is half of this (59 µm/s&2). The sum of both effects is balanced by the gravity of the Earth, which is here also 177 µm/s&2. 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, describing on the plane an elliptical orbit centered about L1. It orbits L1 once every six months, while L1 itself orbits the sun every 12 months as a direct consequence of 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 Solar Flare s, so Electrical Grid s and Satellite s can be protected from their damaging effects. 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'' SCIENTIFIC OBJECTIVES The three main scientific objectives of ''SOHO'' are:
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 , there is no need for such a process. As a consequence of its observing the Sun, ''SOHO'' (specifically the LASCO instrument) has inadverdently 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 . REFERENCES | ||||||||||||||||||||||||||||||||||||||||||||
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