stereo image


[ster-ee-oh, steer-]
STEREO (Solar TErrestrial RElations Observatory) is a solar observation mission which was launched on 26 October 2006 at 00:52 GMT. Two nearly identical spacecraft were launched into orbits that cause them to (respectively) pull further ahead of and fall gradually behind the earth. This will enable stereoscopic imaging of the Sun and solar phenomena, such as Coronal Mass Ejections.

Mission profile

The two STEREO spacecraft were launched at 0052 UTC on October 26, 2006 from Launch Pad 17B at the Cape Canaveral Air Force Station in Florida on a Delta II 7925-10L launcher into highly elliptical geocentric orbits. The apogee reached the Moon's orbit. On December 15, 2006, on the fifth orbit, the pair swung by the moon for a gravitational slingshot. Because the two spacecraft were in slightly different orbits, the "ahead" (A) spacecraft was ejected to a heliocentric orbit inside Earth's orbit while the "behind" (B) spacecraft remained temporarily in a high earth orbit. The B spacecraft encountered the Moon again on the same orbital revolution on January 21, 2007, ejecting it from earth orbit in the opposite direction from spacecraft A. Spacecraft B entered a heliocentric orbit outside the Earth's orbit. Spacecraft A will take 347 days to complete one revolution of the sun and Spacecraft B will take 387 days. The A spacecraft/sun/earth angle will increase at 21.650 deg/year. The B spacecraft/sun/earth angle will change -21.999 degrees per year. Because the A spacecraft is going faster than B, they are separating from each other and A is orbiting closer to the sun than B. This means stereoscopic pairs of images will soon be impossible for human eyes to fuse, which is a STEREO paradox. At the end of March 2007, the stereoscopic parallax was 1/50, but in June it is already 1/25. "Ideal" stereoscopic parallax is 1/30 and below 1/10 fusion is difficult even for experts. Already the east and west edges of the sun are becoming difficult, because one eye is seeing further around the sun than the other. Fortunately, the middle of the solar disc and up towards the poles will be fused stereoscopically after the edges become impossible. The A images, from the satellite closer to the sun, are bigger than B. Magnification must be corrected before stereoscopic fusion by human eyes is possible. Of course the mission does not depend on 3D vision to be useful and mathematical reduction of STEREO image data will continue.

Science Instrumentation

Each of the spacecraft carries cameras, particle experiments and radio detectors in four instrument packages:

  • Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) - SECCHI has five cameras: an extreme ultraviolet imager and two white-light coronagraphs (collectively known as the Sun Centered Instrument Package or SCIP), which image the solar disk and the inner and outer corona, plus two heliospheric imagers (called the HI), which image the space between Sun and Earth. The purpose of SECCHI is to study the 3-D evolution of Coronal Mass Ejections through their full journey from the Sun's surface through the corona and interplanetary medium to their impact at Earth.
  • In-situ Measurements of Particles and CME Transients (IMPACT) - IMPACT will study energetic particles, the three-dimensional distribution of solar wind electrons and interplanetary magnetic field.
  • PLAsma and SupraThermal Ion Composition (PLASTIC) - PLASTIC will study the plasma characteristics of protons, alpha particles and heavy ions.
  • STEREO/WAVES (SWAVES) - SWAVES is a radio burst tracker that will study radio disturbances traveling from the Sun to the orbit of Earth.

Spacecraft Subsystems

  • Structure

  • Propulsion and attitude control

  • Power

  • Telecommunications

  • Flight computers

STEREO's onboard computer systems are based on the Integrated Electronics Module (IEM), a device that combines core avionics in a single box. Each single-string spacecraft carries two 25 megahertz RAD6000 CPUs: one for Command/Data-handling, and one for Guidance-and-Control. Both are radiation hardened RAD6000 processors, based on IBM POWER CPUs (predecessor of the PowerPC chip found in older Macintoshes). The computers, slow by current personal computer standards, are typical for the radiation requirements needed on the STEREO mission.

  • Data handling

For data storage, each spacecraft carries a solid state recorder able to store up to one gigabyte each. Its main processor collects and stores on the recorder images and other data from STEREO's instruments, which can then be sent back to Earth.

See also


External links

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