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STEREO (Solar Terrestrial Relations Observatory) is a solar observation mission.[1] 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.
The two STEREO spacecraft were launched at 00:52 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.[2]
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. On October 1, 2014, contact was lost with STEREO-B during a planned reset to test the craft's automation, in anticipation of this Solar 'conjunction' period. As of May 2015, contact had not been re-established, but efforts were still underway to regain communication and control.[3]
They will then start to approach Earth again, with closest approach sometime in 2023. They will not be recaptured into Earth orbit.
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.[4]
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.[4] 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.[5]
STEREO program scientist Madhulika Guhathakurta expects "great advances" in theoretical solar physics and space weather forecasting with the advent of constant 360-degree views of the Sun.[6] STEREO's observations are already being incorporated into forecasts of solar activity for airlines, power companies, satellite operators, and others.[7]
STEREO has also been used to discover 122 eclipsing binaries and study hundreds more variable stars.[8] STEREO can look at the same star for up to 20 days.[8]
On July 23, 2012, STEREO-A was in the path of the Solar storm of 2012 which was similar in strength to the Carrington Event.[9] Its instrumentation was able to collect and relay a significant amount of data about the event. STEREO-A was not harmed by the solar storm.
Each of the spacecraft carries cameras, particle experiments and radio detectors in four instrument packages:
STEREO also carries Actel FPGAs that use triple modular redundancy for radiation hardening. The FPGAs hold the P24 MISC and CPU24 soft microprocessors.[15]
Launch of the STEREO spacecraft atop a Delta II (7925-10L) rocket, 00:52 GMT on October 26, 2006.
Almost the entire surface of the Sun, as seen by the STEREO satellites on February 10, 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 probes in a Goddard Space Flight Center cleanroom.
One of the first images of the Sun taken by STEREO.
The Moon passing in front of the Sun from STEREO-B, February 25, 2007 (See the movie of the transit)
The Sun's South Pole. Material can be seen erupting off the Sun in the lower right side of the image.
A three-dimensional anaglyph taken by STEREO, released by NASA on April 23, 2007. 3D red cyan glasses are recommended to view this image correctly.
A three-dimensional time-for-space wiggle image taken by STEREO
An image of nearly the entire far side of the Sun taken on February 2, 2011. The entire far side became visible on February 6, 2011 when the satellites closed the gap represented by the black line in this image.
A full day of Sun data from the STEREO satellites.
Jupiter as seen by the STEREO-A HI1 on 2008 November 23.
Jupiter, Venus, Earth, Cassini–Huygens, Amalthea (moon)
Charon (moon), Pluto, Jupiter, WebCite, Nasa
Solar System, Saturn, Venus, Earth, Mass
Solar cycle, Star, Trace, Solar and Heliospheric Observatory, Solar System
YouTube, Stereo, Coronal mass ejection, Solar storm of 1859, List of solar storms
Sun, Galileo (spacecraft), New Horizons, Mars Science Laboratory, Jupiter