One of two STEREO spacecraft |
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| Operator | NASA |
|---|---|
| Major contractors | Johns Hopkins University Applied Physics Laboratory |
| Mission type | Orbiter |
| Satellite of | Sun |
| 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 5 years, 3 months and 30 days |
| COSPAR ID | 2006-047 |
| Homepage | http://stereo.jhuapl.edu/ |
| Mass | 620 kg |
| Power | 475.0 W |
| Orbital elements | |
| Orbital period | STEREO A: 346 days STEREO B: 388 days |
| Instruments | |
| Main instruments |
Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI):
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STEREO (Solar TErrestrial RElations Observatory) is a solar observation mission.[1] Two nearly identical spacecraft were launched into orbits that cause them to respectively pull farther ahead of and fall gradually behind the Earth. This will enable stereoscopic imaging of the Sun and solar phenomena, such as coronal mass ejections.
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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.[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.
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.[3]
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.[3] Before STEREO, the development 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.[4]
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.[5] STEREO's observations are already being incorporated into forecasts of solar activity for airlines, power companies, satellite operators, and others.[6]
STEREO has also been used to discover 122 eclipsing binaries and study hundreds more variable stars.[7] STEREO can look at the same star for up to 20 days.[7]
Each of the spacecraft carries cameras, particle experiments and radio detectors in four instrument packages:
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