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{{Short description|Solar observation mission (2006–present)}}
{{redirect|STEREO satellite|the musical ensemble|Stereo Satellite}}
{{About|the NASA spacecraft|other uses of "Stereo"|Stereo (disambiguation)}}
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| mission_type = Solar observation
| operator = [[NASA]]
| COSPAR_ID = STEREO-A: {{cospar|2006-047A}} <br /> STEREO-B: {{cospar|2006-047B}}n
| SATCAT = STEREO-A: 29510 <br /> STEREO-B: 29511
| website = http://stereo.gsfc.nasa.gov/ <br /> http://stereo.jhuapl.edu/
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* Planned: 2 years
* STEREO-A elapsed: {{time interval|26 October 2006 00:52|show=ymd|sep=,}}
* STEREO-B final: {{time interval|26 October 2006 00:52|
| manufacturer = [[Johns Hopkins University]] [[Applied Physics Laboratory]]
| dry_mass = {{convert|547|kg|lb|0|abbr=on}}
| launch_mass = STEREO-A: 620 kg<br />STEREO-B: 620 kg<ref name="STEREO">{{cite web|url=https://stereo.gsfc.nasa.gov/spacecraft.shtml |title=STEREO |publisher=NASA |access-date=December 2, 2022}}</ref>
| dimensions = {{convert|3.75|xx|6.67|xx|21.24|ft|m|abbr=on|order=flip|disp=br}}
| power = 475 W
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| next_mission = [[Magnetospheric Multiscale Mission|MMS]]
}}
'''STEREO''' ('''Solar Terrestrial Relations Observatory''') is a [[Sun|solar]] observation mission.<ref>{{cite web |url=http://www.nasa.gov/missions/highlights/schedule.html |title=NASA Launch Schedule |publisher=NASA |date=September 20, 2006 |accessdate=September 20, 2006}}</ref> 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 ejection]]s.▼
▲'''STEREO''' ('''Solar
Contact with STEREO-B was lost in 2014, but STEREO-A is still operational.▼
▲Contact with STEREO-B was lost in 2014 after it entered an uncontrolled spin preventing its solar panels from generating enough power, but STEREO-A is still operational.
==Mission profile==
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| direction = vertical
| width = 220
| header = Animation of STEREO
| image1 = Animation of STEREO trajectory.gif
| caption1 = Around the Sun
| image2 = Animation of STEREO trajectory relative to Sun and Earth.gif
| caption2 = Relative to the Sun and the Earth
| footer =
{{legend2|OrangeRed|STEREO-A}}
{{legend2|Magenta|STEREO-B}}
{{legend2|RoyalBlue|Earth}}
{{legend2|Yellow|Sun}}
}}
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 [[ellipse|elliptical]] [[geocentric orbit]]s. The [[Apsis|apogee]] reached the Moon's orbit. On December 15, 2006, on the fifth orbit, the pair swung by the Moon for a [[gravity assist]]. 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, being ejected from Earth orbit in the opposite direction from spacecraft A. Spacecraft B entered a heliocentric orbit outside the Earth's orbit. Spacecraft A
Over time, the STEREO spacecraft
Even as the angle increases, the addition of an Earth-based view,
===Loss of contact with STEREO-B===
On October 1, 2014, contact was lost with STEREO-B during a planned reset to test the craft's automation, in anticipation of the aforementioned solar "conjunction" period. The team originally thought that the spacecraft had begun to spin, decreasing the amount of power that could be generated by the solar panels. Later analysis of the received telemetry concluded that the spacecraft was in an uncontrolled spin of about
NASA used its [[NASA Deep Space Network|Deep Space Network]], first weekly and later monthly, to try to re-establish communications.<ref name="nasa20151211" />
After a silence of 22 months, contact was regained at 22:27 UTC on August 21, 2016, when the Deep Space Network established a lock on STEREO-B for 2.4
Engineers planned to work and develop software to fix the spacecraft, but once its computer was powered up, there would only have been about
Six attempts at communication between September 27 and October 9, 2016, failed, and a carrier wave was not detected after September 23. Engineers determined that during an attempt to despin the spacecraft, a frozen thruster fuel valve probably led to the spin increasing rather than decreasing.<ref name="stereonews20161023" /> As STEREO-B moved along its orbit, it was hoped that its solar panels may again generate enough power to charge the battery.
Four years after the initial loss of contact, NASA terminated periodic recovery operations effective October 17, 2018.<ref name="stereo20181023">{{cite web |url=https://stereo-ssc.nascom.nasa.gov/behind_status.shtml |title=STEREO-B Status Update |publisher=NASA/STEREO Science Center |editor-first=Therese A. |editor-last=Kucera |date=October 23, 2018 |
{{clear left}}
==Mission benefits==
[[File:Delta II 10L fairing installation around STEREO spacecraft.jpg|thumb|STEREO spacecraft in Delta II fairing]]
The principal benefit of the mission
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.<ref name=CBC /> Before STEREO, the detection of the [[sunspot]]s 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
STEREO program scientist [[Madhulika Guhathakurta]]
STEREO has also been used to discover 122 [[eclipsing binaries]] and study hundreds more [[variable star]]s.<ref name="variable">{{cite news |url=http://www.astronomy.com/news-observing/news/2011/04/stereo%20turns%20its%20steady%20gaze%20on%20variable%20stars |title=STEREO turns its steady gaze on variable stars |work=[[Astronomy (magazine)|Astronomy]] |agency=Royal Astronomical Society |date=April 19, 2011 |
On July 23, 2012, STEREO-A was in the path of the CME of the [[solar storm of 2012]].
==Science instrumentation==
[[File:Stereo mission.jpg|thumb|upright=1.2|Instrument locations on STEREO]]
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 [[coronagraph]]s (COR1 and COR2).
* '''In-situ Measurements of Particles and CME Transients (IMPACT)''',
* '''PLAsma and SupraThermal Ion Composition (PLASTIC)''', led by [[Antoinette Galvin]],
* '''STEREO/WAVES (SWAVES)''' is a radio
==Spacecraft subsystems==
Each STEREO spacecraft had a [[dry mass]] of {{convert|547|kg|lb|abbr=on}} and a launch mass of {{convert|1364|lb|kg|abbr=on|order=flip}}. In their stowed configuration, each had a length, width and height of {{convert|6.67|xx|4.00|xx|3.75|ft|m|1|abbr=on|order=flip}}. Upon solar
The STEREO spacecraft are 3-axis
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 CPUs, one for command
STEREO also carries Actel [[FPGA]]s that use [[triple modular redundancy]] for radiation hardening. The FPGAs hold the [[minimal instruction set computer|P24 MISC]] and CPU24 [[soft microprocessor]]s.<ref name="Mewaldt2008">{{cite journal |url=ftp://mussel.srl.caltech.edu/pub/stereo/docs/LET-paper-full.pdf |title=The Low-Energy Telescope (LET) and SEP Central Electronics for the STEREO Mission |journal=Space Science Reviews |first1=R. A. |last1=Mewaldt |first2=C. M. S. |last2=Cohen |first3=W. R. |last3=Cook |first4=A. C. |last4=Cummings |first5=A. J. |last5=Davis |display-authors=etal |volume=136 |issue=1 |pages=285–362 |date=April 2008 |doi=10.1007/s11214-007-9288-x |bibcode=2008SSRv..136..285M |citeseerx=10.1.1.459.4982|s2cid=21286304 }}</ref>
For data storage, each spacecraft carries a [[solid-state drive|solid
==Gallery==
<gallery widths="160" heights="160">
File:The two STEREO observatories.jpg|STEREO probes stacked at Astrotech in Florida <br /> August 11, 2006
File:STEREO launch Delta7925-10L 261006.jpg|Launch of the STEREO probes on a [[Delta II]] rocket <br /> October 26, 2006
File:Sun STEREO 4dec2006 lrg.jpg|One of the first images of the Sun taken by STEREO <br /> December 4, 2006
File:Moon transit of sun large.ogg|A [[Astronomical transit|lunar transit]] of the Sun captured during calibration of STEREO-B's ultraviolet imaging cameras. The Moon appears much smaller than it does from Earth, because the
File:174719main LEFTREDSouthPole304.jpg|The Sun's South Pole. Material can be seen erupting
File:Sun 3D anaglyph STEREO crop bright.jpg|A three-dimensional [[anaglyph image|anaglyph]] taken by STEREO <br /> March 2007 <br /> {{3D glasses}}
File:BLUE STEREO 3D Time for Space Wiggle.gif|A three-dimensional [[time-for-space wiggle]] image taken by STEREO <br /> March 2007
File:Jup20081123 000901 s4h1A 1024.jpg|[[Jupiter]] as seen by STEREO-A HI1 <br /> November 23, 2008
File:Far side of the Sun 3D STEREO crop.jpg|Nearly the entire far side of the Sun <br /> February 2, 2011
File:STEREO EUV Feb10 rotating.gif|Nearly the entire surface of the Sun, taken in [[extreme ultraviolet]] at 19.5 nm, with white lines showing solar coordinates (0
File:STEREO Far Side of the Sun.OGG|A full day of Sun data from the STEREO satellites <br /> February 13–14, 2011
File:STEREO Mission Turns 10.webm|For STEREO's 10th anniversary, Deputy Project Scientist Terry Kucera gives an overview of the mission's top 5 success stories.
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==See also==
{{Portal|Spaceflight}}
* [[Advanced Composition Explorer]] (ACE), launched 1997, still operational
* [[Heliophysics]]
* [[Living With a Star]] (NASA program), still ongoing {{as of|2020|2|lc=y}}
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** [[Parker Solar Probe]], launched August 2018.
* [[Solar and Heliospheric Observatory]] (SOHO), launched 1995, still observational {{as of|2020|2|lc=y}}.
* [[Solar Orbiter]] (
* [[TRACE]], launched 1998.
* ''[[Ulysses (spacecraft)|Ulysses]]'', spacecraft launched in 1990.
* ''[[Wind (spacecraft)|Wind]]'', spacecraft launched 1994, still operational {{as of|2020|2|lc=y}}.
* [[Zooniverse#Solar Stormwatch|Zooniverse – Solar Stormwatch]]
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* [http://stereo-ssc.nascom.nasa.gov/ STEREO Science Center] by NASA
* Instrument sites
** [http://secchi.nrl.navy.mil/ SECCHI website] {{Webarchive|url=https://web.archive.org/web/20110217101119/http://secchi.nrl.navy.mil/ |date=February 17, 2011 }} by the [[Naval Research Laboratory]]
** [http://www.stereo.rl.ac.uk/ Heliospheric Imager] by [[Rutherford Appleton Laboratory]]
* Comets
** [https://science.nasa.gov/science-news/science-at-nasa/2007/01oct_encke/ Tail of Comet Encke removed by CME] by Science@NASA
** [http://sungrazer.nrl.navy.mil/index.php?p=news/secchi_5yrs STEREO/SECCHI Comets: The First 5 Years] {{Webarchive|url=https://web.archive.org/web/20120401090124/http://sungrazer.nrl.navy.mil/index.php?p=news/secchi_5yrs |date=April 1, 2012 }} by the Sungrazer Project
{{Sun spacecraft}}
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[[Category:Solar space observatories]]
[[Category:Space weather]]
[[Category:Discoveries by STEREO|*]]
[[Category:Articles containing video clips]]
[[Category:Twin satellites]]
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