January 27, 2009 NASA predicts that its two STEREO spacecraft, launched on October 25, 2006, will align on either side of the sun on February 6, 2011, allowing scientists to view the entire sun simultaneously for the first time in history. The Solar TErrestrial RElations Observatory is currently providing scientists with a view of 75% of the sun, allowing them to calculate three days in advance when sunspots and coronal holes will face Earth.
The STEREO program consists of two nearly identical spacecraft, which used the gravitational field of the moon to launch in opposite directions. In two years, this trajectory will afford the satellites a 360 degree vista of the sun. In addition to providing scientists with advance knowledge of solar phenomena, the total perspective of the sun will allow scientists to study the phenomena in far greater detail – tracing the evolution of sunspots, coronal holes, and magnetic filaments.
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Data is beamed to Earth via an X-band radio beacon, though NASA’s Deep Space Network only downloads three hours worth from STEREO per day. In order to make the most of STEREO’s lifespan, a “mini-Deep Space Network” of amateur enthusiasts in the UK, France and Japan has formed, with NASA’s blessing. Anyone with a ten meter dish antenna and suitable receiver can download data, with a complete image being transferred in three to five minutes, at 500 bits per second. NASA is still looking to recruit from the ham radio circuit, though the willingness of people to assist on what will be Super Bowl day remains an X-factor.
Each STEREO craft contains cameras, particle experiments, and four instrument packages. The Sun Earth Connection Coronal and Heliospheric Investigation has an extreme ultraviolet imager, two coronagraphs, and two heliospheric imagers, and is designed to examine the 3-D evolution of Coronal Mass Ejections. The In-situ Measurements of Particles and CME Transients package is designed to study energetic particles, solar wind electrons, and interplanetary magnetic fields. The PLAsma and SupraThermal Ion Composition is designed to study the plasma characteristics of protons, alpha particles, and heavy ions. And the STEREO/WAVES package is designed to study radio disturbances from the sun to Earth orbit.
STEREO is the third mission in NASA's Solar Terrestrial Probes program.