STEREO

"STEREO satellite" redirects here. For the musical ensemble, seeStereo Satellite.

This article is about the NASA spacecraft. For other uses of "Stereo", seeStereo (disambiguation).

STEREO

Illustration of a STEREO spacecraft during solar array deployment
Mission type	Solar observation
Operator	NASA
COSPAR ID	STEREO-A:2006-047A STEREO-B:2006-047Bn
SATCATno.	STEREO-A: 29510 STEREO-B: 29511
Website	http://stereo.gsfc.nasa.gov/ http://stereo.jhuapl.edu/
Mission duration	Planned: 2 years STEREO-A elapsed: 17 years, 8 months, 20 days STEREO-B final: 9 years, 10 months, 30 days
Spacecraft properties
Manufacturer	Johns Hopkins UniversityApplied Physics Laboratory
Launch mass	STEREO-A: 620 kg STEREO-B: 620 kg
Dry mass	547 kg (1,206 lb)
Dimensions	1.14 × 2.03 × 6.47 m 3.75 × 6.67 × 21.24 ft
Power	475 W
Start of mission
Launch date	October 26, 2006, 00:52(2006-10-26UTC00:52)UTC
Rocket	Delta II 7925-10L
Launch site	Cape CanaveralSLC-17B
Contractor	United Launch Alliance
End of mission
Last contact	STEREO-B: September 23, 2016
Orbital parameters
Reference system	Heliocentric
Period	STEREO-A: 346 days STEREO-B: 388 days
Instruments SECCHI Sun Earth Connection Coronal and Heliospheric Investigation IMPACT In-situ Measurements of Particles and CME Transients PLASTIC Plasma and Suprathermal Ion Composition S/WAVES STEREO/WAVES
Solar Terrestrial Probes program

STEREO(Solar TErrestrial RElations Observatory) is asolarobservation mission.Two nearly identical spacecraft (STEREO-A,STEREO-B) 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 enabledstereoscopicimaging of theSunand solar phenomena, such ascoronal mass ejections.

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

This introductory video demonstrates STEREO's locations and shows a simultaneous image of the entire Sun.

Animation of STEREO's trajectory

Around the Sun

Relative to the Sun and the Earth

STEREO-A

STEREO-B Earth

Sun

The two STEREO spacecraft were launched at 00:52 UTC on October 26, 2006, from Launch Pad 17B at theCape Canaveral Air Force Stationin Florida on aDelta II7925-10L launcher into highlyellipticalgeocentric orbits.Theapogeereached the Moon's orbit. On December 15, 2006, on the fifth orbit, the pair swung by the Moon for agravity assist.Because the two spacecraft were in slightly different orbits, the "ahead" (A) spacecraft was ejected to aheliocentric orbitinside 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 took 347 days to complete one revolution of the Sun and Spacecraft B took 387 days. The A spacecraft/Sun/Earth angle will increase at 21.650° per year. The B spacecraft/Sun/Earth angle will change −21.999° per year. Given that the length of Earth's orbit is around 940 million kilometres, both craft have an average speed, in a rotating geocentric frame of reference in which the Sun is always in the same direction, of about 1.8 km/s, but the speed varies considerably depending on how close they are to their respective aphelion or perihelion (as well as on the position of Earth). Their current locations are shownhere.

Over time, the STEREO spacecraft continued to separate from each other at a combined rate of approximately 44° per year. There were nofinalpositions for the spacecraft. They achieved 90° separation on January 24, 2009, a condition known asquadrature.This was of interest because the mass ejections seen from the side on the limb by one spacecraft can potentially be observed by thein situparticle experiments of the other spacecraft. As they passed through Earth'sLagrangian pointsL₄andL₅,in late 2009, they searched forLagrangian (trojan) asteroids.On February 6, 2011, the two spacecraft were exactly 180° 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 theSolar Dynamics Observatory,still provided full-Sun observations for several years. In 2015, contact was lost for several months when the STEREO spacecraft passed behind the Sun. They then started to approach Earth again, with closest approach in August 2023. They will not be recaptured into Earth orbit.

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 3° per second; this was too rapid to be immediately corrected using itsreaction wheels,which would become oversaturated.

NASA used itsDeep Space Network,first weekly and later monthly, to try to re-establish communications.

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 hours.

Engineers planned to work and develop software to fix the spacecraft, but once its computer was powered up, there would only have been about 2 minutes to upload the fix before STEREO-B entered failure mode again.Further, while the spacecraft was power-positive at the time of contact, its orientation would drift, and power levels fall. Two-way communication was achieved, and commands to begin recovering the spacecraft were sent through the rest of August and September.

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.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.

Mission benefits

STEREO spacecraft in Delta II fairing

The principal benefit of the mission wasstereoscopicimages of the Sun. Because the satellites are at different points along the Earth's orbit, but distant from the Earth, 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 forcoronal mass ejections— massive bursts ofsolar wind,solarplasma,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 thesunspotsthat are associated with CMEs on the far side of the Sun was only possible usinghelioseismology,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 scientistMadhulika Guhathakurtaexpected "great advances" in theoreticalsolar physicsand space weather forecasting with the advent of constant 360° views of the Sun.STEREO's observations are incorporated into forecasts of solar activity for airlines, power companies, satellite operators, and others.

STEREO has also been used to discover 122eclipsing binariesand study hundreds morevariable stars.STEREO can look at the same star for up to 20 days.

On July 23, 2012, STEREO-A was in the path of the CME of thesolar storm of 2012.This CME, if it were to collide with Earth's magnetosphere, is estimated to have caused a geomagnetic storm of similar strength to theCarrington Event,the most intense geomagnetic storm in recorded history.STEREO-A's instrumentation was able to collect and relay a significant amount of data about the event without being harmed.

Science instrumentation

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-lightcoronagraphs(COR1 and COR2). These three telescopes are collectively known as the Sun Centered Instrument Package or SCIP. They image the solar disk and the inner and outercorona.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 ofcoronal mass ejectionsthrough their full journey from the Sun's surface through the corona and interplanetary medium to their impact at Earth.The principal investigator for SECCHI was Russell Howard.
• In-situ Measurements of Particles and CME Transients (IMPACT),to studyenergetic particles,the three-dimensional distribution of solar-wind electrons and interplanetary magnetic field.Janet Luhmannwas the principal investigator for IMPACT.
• PLAsma and SupraThermal Ion Composition (PLASTIC),led byAntoinette Galvin,to study the plasma characteristics ofprotons,Alpha particlesandheavy ions.
• STEREO/WAVES (SWAVES)is a radio-burst tracker to study radio disturbances traveling from the Sun to the orbit of Earth.Jean Louis Bougeret was principal investigator for SWAVES, with co-investigator Michael Kaiser.

Spacecraft subsystems

Each STEREO spacecraft had adry massof 547 kg (1,206 lb) and a launch mass of 619 kg (1,364 lb). In their stowed configuration, each had a length, width and height of 2.0 × 1.2 × 1.1 m (6.67 × 4.00 × 3.75 ft). Upon solar-array deployment, its width increased to 6.5 m (21.24 ft).With all of its instrument booms and antennae deployed, its dimensions are 7.5 × 8.7 × 5.9 m (24.5 × 28.6 × 19.2 ft).The solar panels can produce an average of 596 watts of power, and the spacecraft consumes an average of 475 watts.

The STEREO spacecraft are 3-axis-stabilized, and each has a primary and backupminiature inertial measurement unit(MIMU) provided byHoneywell.These measure changes to a spacecraft's attitude, and each MIMU contains threering laser gyroscopesto detect angular changes. Additional attitude information is provided by thestar trackerand the SECCHI Guide Telescope.

STEREO's onboard computer systems are based on the Integrated Electronics Module (IEM), a device that combines coreavionicsin a single box. Each single-string spacecraft carries two CPUs, one for command and data handling and one for guidance and control. Both areradiation-hardened25-megahertzIBM RAD6000processors, based onPOWER1CPUs (predecessor of the PowerPC chip found in olderMacintoshes). The computers, slow by currentpersonal computerstandards, are typical for the radiation requirements needed on the STEREO mission.

STEREO also carries ActelFPGAsthat usetriple modular redundancyfor radiation hardening. The FPGAs hold theP24 MISCand CPU24soft microprocessors.

For data storage, each spacecraft carries asolid-staterecorder able to store up to 1gigabyteeach. 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. The spacecraft have anX-banddownlink capacity of between 427 and 750kbit/s.

Gallery

• 
  STEREO probes stacked at Astrotech in Florida
  August 11, 2006
• 
  Launch of the STEREO probes on aDelta IIrocket
  October 26, 2006
• 
  One of the first images of the Sun taken by STEREO
  December 4, 2006
• Alunar transitof the Sun captured during calibration of STEREO-B's ultraviolet imaging cameras. The Moon appears much smaller than it does from Earth, because the spacecraft–Moon separation was several times greater than the Earth–Moon distance.
  February 25, 2007
• 
  The Sun's South Pole. Material can be seen erupting from the Sun in the lower right side of the image.
  March 2007
• 
  A three-dimensionalanaglyphtaken by STEREO
  March 2007
  3D red cyanglasses are recommended to view this image correctly.
• 
  A three-dimensionaltime-for-space wiggleimage taken by STEREO
  March 2007
• 
  Jupiteras seen by STEREO-A HI1
  November 23, 2008
• 
  Nearly the entire far side of the Sun
  February 2, 2011
• 
  Nearly the entire surface of the Sun, taken inextreme ultravioletat 19.5 nm, with white lines showing solar coordinates (0° is directly towards Earth)
  February 10, 2011
• A full day of Sun data from the STEREO satellites
  February 13–14, 2011
• For STEREO's 10th anniversary, Deputy Project Scientist Terry Kucera gives an overview of the mission's top 5 success stories.

See also

• Advanced Composition Explorer(ACE), launched 1997, still operational as of 2023.
• Heliophysics
• Living With a Star(NASA program), still ongoing as of February 2020
  • Solar Dynamics Observatory(SDO), launched 2010.
  • Parker Solar Probe,launched August 2018.
• Solar and Heliospheric Observatory(SOHO), launched 1995, still observational as of February 2020.
• Solar Orbiter(SolO), launched February 2020.
• TRACE,launched 1998.
• Ulysses,spacecraft launched in 1990.
• Wind,spacecraft launched 1994, still operational as of February 2020.
• Zooniverse – Solar Stormwatch

External links

• STEREO websitebyGoddard Space Flight Center
• STEREO websitebyApplied Physics Laboratory
• STEREO Science Centerby NASA
• Instrument sites
  • SECCHI websiteArchivedFebruary 17, 2011, at theWayback Machineby theNaval Research Laboratory
  • Heliospheric ImagerbyRutherford Appleton Laboratory
• Comets
  • Tail of Comet Encke removed by CMEby Science@NASA
  • STEREO/SECCHI Comets: The First 5 Yearsby the Sungrazer Project