NASA twin STEREO spacecraft prepare to eyeball the Sun

William Atkins
Tuesday, 13 February 2007 20:37

Science - Space

STEREO was launched on October 25, 2006, 8:52 eastern daylight time (EDT), aboard a single Boeing Delta II rocket at Launch Complex 17 of Cape Canaveral Air Force Station, Florida.

The near-twin pair of probes from the spacecraft was launched into highly elliptical geocentric orbits with an apogee (furthest distance away from the Earth) about equal to that of the Moon (about 384,400 kilometers, or 238,900 miles).
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On December 15, 2006, both probes were slung around the Moon in a gravitational slingshot boost that caused Probe “A” to pull further ahead of the Earth and Probe B to fall gradually behind the Earth. The slingshot maneuver placed Probe A on a heliocentric orbit around the Sun that was inside the Earth’s orbit about the Sun. Another gravitational slingshot boost on January 21, 2007 placed Probe B on a heliocentric orbit about the Sun and outside the Earth’s orbit around the Sun.

Thus, Probe A will drift further in front of the Earth at a rate of +1.650 degrees per year (taking 347 days to go once around the Sun) while Probe B will drift further behind of the Earth at a rate of -21.999 degrees per year (taking 387 days to make one complete orbit around the Sun). (The Earth takes about 365 days to go around the Sun.) This positioning will allow them to take stereoscopic images of the Sun and its activities.

Beginning April 2007, the two-year mission of STEREO will begin to provide scientists with the first three-dimensional (3D, or "stereo") images of the Sun. STEREO is already providing non-3D images of the Sun. During the mission, STEREO will study many activities that occur on the Sun, such as solar storms called coronal mass ejections (CMEs). CMEs consists of a plasma mixture of protons and electrons, along with smaller amounts of helium, iron, oxygen, and other heavier elements) that are aggressively thrust out from the Sun’s corona.

Along with other spacecraft and ground-based observatories studying solar activities, STEREO will learn more about CMEs to understand how they affect life on the Earth. CMEs can cause large problems in global climate, satellite operations, communications, power systems, and have the potential to cause health problems to astronauts orbiting the Earth. In particular, the CMEs can make the Northern Lights (aurora borealis) and the Southern Lights (aurora australis) much stronger in intensity.

The Applied Physics Laboratory (APL) at Johns Hopkins University (JHU), in Laurel, Maryland, designed, built, and tested STEREO, and will operate the observatories during their missions. The NASA Goddard Space Flight Center’s Solar Terrestrial Probes Program Office, in Greenbelt, Maryland, will manage the mission, instruments, and science center. The Science Mission Directorate at NASA Headquarters in Washington, D.C. sponsored the solar mission.

STEREO is the third mission of NASA’s Solar Terrestrial Probes Program. Its JPU/APL home Web site is: http://stereo.jhuapl.edu/.

The NASA Solar Terrestrial Probes Program is located at: http://stp.gsfc.nasa.gov/.