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STEREO (Solar TErrestrial RElations Observatory) is the third mission in NASA's Solar Terrestrial Probes program, scheduled to launch in November 2005 aboard a single Delta-7925-10L launch vehicle. This two-year mission will employ two nearly identical space-based observatories to provide the first-ever, 3-D stereoscopic images to study the nature of coronal mass ejections, or CMEs.

The STEREO mission will provide a totally new perspective on solar eruptions by imaging CMEs and background events from two observatories simultaneously. To obtain unique views of the sun, the twin observatories must be placed into a rather challenging orbit where they will be offset from one another. One observatory will be placed “ahead” of the Earth in its orbit and the other, “behind” using a series of lunar swingbys. Just as the slight offset between your eyes provides you with depth perception, this placement will allow the STEREO observatories to obtain 3-D images of the sun.

APL mission designers determined that the most efficient and cost-effective method to place the twin observatories, launched aboard a single rocket, into their respective orbits is to use lunar swingbys. This is the first time this technique has been used to manipulate orbits of more than one spacecraft. Mission designers will use the moon's gravity to redirect the observatories to their appropriate orbits – something the launch vehicle alone can't do.

For the first three months after launch, the observatories will fly in an orbit from a point close to Earth to one that extends just beyond the moon. STEREO Mission Operations personnel at The Johns Hopkins University Applied Physics Laboratory, in Laurel, Md., will synchronize spacecraft orbits so that about two months after launch they encounter the moon, at which time one of them is close enough to use the moon's gravity to redirect it to a position “behind” the Earth. Approximately one month later, the second observatory will encounter the moon again and be redirected to its orbit “ahead” of Earth. When combined with data from observatories on the ground or in low-Earth orbit, STEREO's data will allow scientists to track the buildup and lift-off of magnetic energy from the sun and the trajectory of Earth-bound CMEs in 3-D.

The two STEREO observatories will be nearly identical with selective redundancy. The spacecraft bus will be built by The Johns Hopkins University Applied Physics Laboratory (APL), in Laurel, Md., with NASA Goddard Space Flight Center procuring the instruments. Each observatory and its instruments will be integrated at APL.

The STEREO mission consists of two solar-powered, 3-axis-stabilized spacecraft, each with a launch mass – including propellant – of approximately 620 kg. The spacecraft will communicate with the APL-based Mission Operations Center via NASA's Deep Space Network.

The significant challenge in spacecraft design is the large number and extent of the instrument fields-of-view, coupled with the various instruments' competing design requirements to ensure successful science observations.

The major design drivers to support the science instrument performance are a conductive outer surface for the energetic particle experiments, stringent electromagnetic compatibility and interference requirements for the radio burst tracker, and contamination control of both volatiles and particulates for the imager experiment.

The spacecraft bus consists of six operational subsystems supporting two instruments and two instrument suites. This combination provides a total of 16 instruments per observatory. The subsystems include: command and data handling; radio frequency communications; guidance and control; propulsion; power; and thermal.

Following Instruments are on board of each of the two probes:

  • The Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) is a suite of remote-sensing instruments consisting of an extreme ultraviolet imager, two white-light coronagraphs, and a heliospheric imager. These instruments will study the 3-D evolution of coronal mass ejections–the most energetic eruptions on the sun and primary cause of major geomagnetic storms – from their origin at the sun's surface through the corona and interplanetary medium to their eventual impact at Earth.
  • The In situ Measurements of PArticles and CME Transients (IMPACT) investigation provides measurements of the solar wind electrons, interplanetary magnetic fields, and solar energetic particles. IMPACT comprises seven instruments including a solar wind electron analyzer, a magnetometer, and an array of particle detectors measuring the energetic ions and electrons accelerated in coronal mass ejection (CME) shocks and in solar flares.
  • The PLAsma and SupraThermal Ion Composition (PLASTIC) instrument is slated to study coronal-solar wind and solar wind-heliospheric processes. PLASTIC will provide in situ plasma characteristics of protons, alpha particles and heavy ions. It will supply key diagnostic measurements of mass and charge state composition of heavy ions and will characterize the coronal mass ejection plasma from ambient solar wind plasma.
  • STEREO/WAVES (S/WAVES) is an interplanetary radio burst tracker that will trace the generation and evolution of traveling radio disturbances from the sun to Earth's orbit. A radio and plasma wave receiver, S/WAVES is both a remote-sensing and an in-situ instrument.

The STEREO probes were launched 26 October 2006. Observation began in early 2007. On 6 February 2011, the two spacecraft were exactly 180 apart from each other, allowing a view of the entire Sun for the first time.

Contact with STEREO B was interrupted on 1 October 2014, immediately after a planned reset of the spacecraft. In August 2016 signals of STEREO B were received again.

Nation: USA
Type / Application: Science, Solar
Operator: NASA
Contractors: Johns Hopkins University Applied Physics Laboratory (APL)
Power: 2 deployable fixed solar arrays, batteries
Lifetime: 2 years (primary mission); still active
Mass: 620 kg
Orbit: Earth leading (#A) or trailing (#B) solar orbit
Satellite COSPAR Date LS Launch Vehicle Remarks
STEREO A (STEREO Ahead, STP 3A) 2006-047A 26.10.2006 CC SLC-17B Delta-7925-10L with STEREO B
STEREO B (STEREO Behind, STP 3A) 2006-047B 26.10.2006 CC SLC-17B Delta-7925-10L with STEREO A


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