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SOHO Launch AC-121

NASA Glenn managed the launch of the European Space Agency's Solar and Heliospheric Observatory (SOHO) aboard an Atlas IIAS rocket. A successful launch was achieved on December 2, 1995 at 03:08 EST from complex 36 B of the Cape Canaveral Air Force Station. The launch was scheduled for 02:34 EST, but 70 seconds before liftoff an electrical anomaly was discovered in the Centaur. The problem was solved and the countdown was re-started at 02:53 EST at the L-15 minute mark.

The sunThe sun as seen by SOHO. Credit: NASA

The first burn of the Centaur upper stage placed the SOHO/Centaur vehicle in a circular parking orbit about the Earth. A second Centaur engine firing successfully sent SOHO into a transfer trajectory towards its final orbit. Its mission complete, the Centaur stage separated.

In this time frame, the Initial Sun Acquisition and the Solar Array Deployment had been achieved and the SOHO Flight Operations Team, based at NASA Goddard, had used the uplink channel to send commands to the spacecraft for the first time.

After a four-month journey, the spacecraft reached its vantage point in orbit 1.5 million km nearer to the Sun than the Earth's own orbit. There at L1, or Lagrange Point No. 1, the gravitational pull of the Sun is balanced by the pull of the Earth and the centrifugal force acting on a spacecraft orbiting in step with the Earth. SOHO can therefore remain hovering around that relative position, in a halo orbit, while it accompanies the Earth in its annual march around the Sun.

SOHO is providing scientists with a comprehensive study of the Sun, the nuclear powerhouse in the center of our solar system. Its twelve experiments, developed by scientists from Europe and the United States, are investigating the Sun from its core outwards - from the very inner workings of the star, to the solar wind which blows through the solar system. It will provide a better understanding of the Sun and its importance to life on Earth.

SOHO is a cooperative, international mission between the European Space Agency (ESA) and NASA. The Glenn Research Center in Cleveland, OH, was responsible for the NASA launch services management. Lockheed Martin of Denver, Co., was under contract to Glenn to provide launch services.

The Kennedy Space Center was responsible for government oversight of the Atlas IIAS rocket processing activities for AC-121 as it does for all NASA Expendable Launch Vehicle missions. KSC also integrated the SOHO spacecraft with the launch vehicle and conducted launch countdown activities.

NASA's Goddard Space Flight Center in Greenbelt, Md., supplied some of the equipment including a tape recorder, power amplifiers, and a sun-pointing sensor. Goddard is controlling the spacecraft and handling the scientific data via the Deep Space Network of ground stations managed by NASA's Jet Propulsion Laboratory. The European Space Agency retains overall charge of the spacecraft and its operations.

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