One of two STEREO spacecraft
|Major contractors||Johns Hopkins University Applied Physics Laboratory|
|Launch date||2006-10-26, 00:52:00 UTC|
|Carrier rocket||Delta II 7925-10L|
|Launch site||Space Launch Complex 17-B
Cape Canaveral Air Force Station
|Mission duration||>3 years
6 years, 6 months, and 24 days
|Orbital period||STEREO A: 346 days
STEREO B: 388 days
Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI):
STEREO (Solar TErrestrial RElations Observatory) is a solar observation mission. Two nearly identical spacecraft were launched in 2006 into orbits around the sun that cause them to respectively pull farther ahead of and fall gradually behind the Earth. This enables stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections.
Mission profile 
||This section includes a list of references, but its sources remain unclear because it has insufficient inline citations. (February 2011)|
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 itself 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 degree/year. The B spacecraft/sun/earth angle will change −21.999 degrees per year. Their current locations are shown here.
Over time, the STEREO spacecraft will continue to separate from each other at a combined rate of approximately 44 degrees per year. There are no final positions for the spacecraft. They achieved 90 degrees separation on January 24, 2009, a condition known as quadrature. This is of interest because the mass ejections seen from the side on the limb by one spacecraft can potentially be observed by the in situ particle experiments of the other spacecraft. As they passed through Earth's Lagrangian points L4 and L5, in late 2009, they searched for Lagrangian (trojan) asteroids. On February 6, 2011, the two spacecraft were exactly 180 degrees apart from each other, allowing the entire Sun to be seen at once for the first time.
Even as the angle increases, the addition of an Earth-based view, e.g. from the Solar Dynamics Observatory, will still provide full-Sun observations for several years. In 2015, contact will be lost for several months when the STEREO spacecraft pass behind the Sun.
They will then start to approach Earth again, with closest approach sometime in 2023. They will not be recaptured into Earth orbit.
Mission benefits 
The principal benefit of the mission is stereoscopic images of the sun. In other words, because the satellites are at different points along the Earth's orbit from the Earth itself, they can photograph parts of the sun that are not visible from the Earth. This permits NASA scientists to directly monitor the far side of the sun, instead of inferring the activity on the far side from data that can be gleaned from Earth's view of the sun. The STEREO satellites principally monitor the far side for coronal mass ejections—massive bursts of solar wind, solar plasma, and magnetic fields that are sometimes ejected into space.
Since the radiation from coronal mass ejections, or CMEs, can disrupt Earth's communications, airlines, power grids, and satellites, more accurate forecasting of CMEs has the potential to provide greater warning to operators of these services. Before STEREO, the detection of the sunspots that are associated with CMEs on the far side of the sun was only possible using helioseismology, which only provides low-resolution maps of the activity on the far side of the Sun. Since the sun rotates every 25 days, detail on the far side was invisible to Earth for days at a time before STEREO. The period that the sun's far side was previously invisible was a principal reason for the STEREO mission.
STEREO program scientist Lika Guhathakurta expects "great advances" in theoretical solar physics and space weather forecasting with the advent of constant 360-degree views of the sun. STEREO's observations are already being incorporated into forecasts of solar activity for airlines, power companies, satellite operators, and others.
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) has five cameras: an extreme ultraviolet imager (EUVI) and two white-light coronagraphs (COR1 and COR2). These three telescopes are collectively known as the Sun Centered Instrument Package or SCIP, and image the solar disk and the inner and outer corona. Two additional telescopes, heliospheric imagers (called the HI1 and HI2) 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) will study energetic particles, the three-dimensional distribution of solar wind electrons and interplanetary magnetic field.
- PLAsma and SupraThermal Ion Composition (PLASTIC) will study the plasma characteristics of protons, alpha particles and heavy ions.
- STEREO/WAVES (SWAVES) is a radio burst tracker that will study radio disturbances traveling from the Sun to the orbit of Earth.
Spacecraft subsystems 
|This section requires expansion. (June 2008)|
- Launch weight including propellants was 1364 pounds (620 kg).
- Propulsion and attitude control
- 3-axis control
- Attitude determination
- Each STEREO spacecraft has a primary and a backup Miniature Inertial Measurement Unit (MIMU), provided by Honeywell, which measure changes to the spacecraft attitude. Each MIMU is equipped with three ring laser gyroscopes to detect angular changes. Additional attitude information is provided by the Star Tracker and the SECCHI Guide Telescope.
- 475 Watts from solar panels.
- Data downlink: 720 kilobits per second.
- 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 POWER1 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.
Almost the entire surface of the Sun, as seen by the STEREO satellites on 10 February 2011. The image was taken in Extreme Ultraviolet light at 19.5 nm, and the white lines show solar coordinates (0 degrees is directly towards the Earth).
A lunar transit of the sun captured during calibration of Stereo B's Ultra Violet imaging cameras. The Moon appears much smaller than it does seen from Earth, because the spacecraft-Moon separation was several times greater than the Earth-Moon distance.
The STEREO Space Probes in a Goddard Space Flight Center Cleanroom
A three-dimensional time-for-space wiggle image taken by STEREO
Jupiter as seen by the STEREO-A HI1 on 2008 November 23.
See also 
- Zooniverse – Solar Stormwatch
- Dr. Madhulika Guhathakurta
- Living With a Star
- Advanced Composition Explorer (ACE), launched 1997, still operational.
- Solar Orbiter (SOLO), set to launch in 2015.
- Solar Probe Plus, set to launch in 2015.
- WIND (spacecraft), launched 1994, still operational.
- "NASA Launch Schedule". NASA Missions. September 20, 2006. Retrieved September 20, 2006.
- "First Ever STEREO Images of the Entire Sun". Nasa.gov.
- "Sun bares all for twin space probes". CBC News. February 7, 2011. Retrieved 8 February 2011.
- Lemonick, Michael (February 6, 2011). "NASA Images the Entire Sun, Far Side and All". TIME. Retrieved 8 February 2011.
- Winter, Michael (Feb 07, 2011). "Sun shines in twin probes' first 360-degree images". USA Today. Retrieved 8 February 2011.
- "Stereo satellites move either side of Sun". BBC News. 6 February 2011. Retrieved 8 February 2011.
- Royal Astronomical Society, United Kingdom (April 19, 2011). "STEREO turns its steady gaze on variable stars". Astronomy. Retrieved 2011-04-19.
- "STEREO Spacecraft & Instruments". NASA Missions. March 8, 2006. Retrieved May 30, 2006.
- Howard R. A., Moses J. D., Socker D. G., Dere K. P., Cook J. W. (2002). "Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI)". Solar Variabilit and Solar Physics Missions Advances in Space Research 29 (12): 2017–2026. doi:10.1016/S0273-1177(02)00147-3.
- Luhmann J. G., Curtis D. W., Lin R. P., Larson D, Schroeder P., Cummings A., Mewaldt R. A., Stone E. C., Davis A., von Rosenvinge T., Acuna M. H., Rearnes D., Ng C., Ogilvie K., Mueller-Mellin R., Kunow H., Mason G. M., Wiedenbeck M., Sauvaud A., Aoustin C., Louarn P., Dandouras J., Korth A., Bothmer V., Vasyliunas V., Sanderson T., Marsden R. G., Russell C. T., Gosling J. T., Bougeret J. L., McComas D. J., Linker J. A., Riley P., Odstrcil D., Pizzo V. J., Gombosi T., DeZeeuw D., Gombosi T., DeZeeuw D., Kecskemety K. (2005). "IMPACT: Science goals and firsts with STEREO". Solar Encounter, Solar-B and Stereo Advances in Space Research 36 (8): 1534–1543. doi:10.1016/j.asr.2005.03.033.
- "Honeywell To Provide Miniature Inertial Measurement Units For STEREO Spacecraft". Web. Honeywell International, Inc. Retrieved 2006-10-25.[dead link]
- Driesman, A., Hynes S, and Cancro, G. (2008), The STEREO Observatory, Space Science Reviews, 136, 17–44
- "The Low-Energy Telescope (LET) and SEP Central Electronics for the STEREO Mission"
Further reading 
- "STEREO spacecraft to image solar blasts in glorious 3-D", New Scientist, December 9, 2005
- NASA Orbit simulations
|Wikimedia Commons has media related to: STEREO (spacecraft)|
- STEREO, official site
- STEREO, Applied Physics Laboratory version
- STEREO Mission Profile by NASA's Solar System Exploration
- SECCHI homepage
- U of M, UMNnews
- STEREO, UK version
- STEREO observations of stars and the search for exoplanets (arxiv 1103.0911 : 4 Mar 2011)
- Stereoscopic anaglyphs from STEREO original images
- STEREO Coordinated Observations Calendar
- STEREO Image artifacts (planets, cosmic rays, internal reflections, debris)
- STEREO Planet Finder
- Coronal mass ejection (CME) removing tail of Comet Encke (April 20, 2007)
- Comet 249P (2006 U1) as seen in STEREO HI1A imager (April 2011)
- STEREO/SECCHI Comets: The First 5 Years (Sungrazing Comets : October 26, 2011)
- Davis, Chris. "Solar Scientist". Backstage Science. Brady Haran.
- Procyon and Earth as seen by STEREO HI1-B (2012-12-17)