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The Solar-Terrestrial Relations Observatory (STEREO) mission includes two spacecraft respectively lagging (STEREO A) and leading (STEREO B) the Earth in heliocentric orbit around the Sun for remote 3-D imaging and radio observations of coronal mass ejections (CMEs). These events are responsible for large solar energetic particle events in interplanetary space and are the primary cause of major geomagnetic storms at Earth. The two spacecraft are launched to drift slowly away from the Earth in opposite directions at about 10 degrees per year for the lagging spacecraft and 20 degrees per year for the leading one. Optimal longitudinal separation of about sixty degrees is achieved after two years. Afterwards the separation gradually increases beyond the design lifetime of two years with the possibility of extended mission observations at larger angles. Science instruments selected for STEREO include the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) for extreme ultraviolet (EUV), white-light coronographic, and heliospheric imaging, the STEREO/WAVES (SWAVES) interplanetary radio burst tracker, the In situ Measurements of Particles and CME Transients (IMPACT) investigation for in-situ sampling the 3-D distribution and plasma characteristics of solar energetic particles and the interplanetary magnetic field, and the PLAsma and SupraThermal Ion and Composition (PLASTIC) experiment to measure elemental and charge composition of ambient and CME plasma ions. STEREO data recorded and stored onboard each spacecraft will be downlinked through the NASA Deep Space Network on a daily schedule. Real-time space weather data will be continuously transmitted through a separate beacon system to NASA and non-NASA receiving stations.

On 06 February 2011, STEREO A and B achieved 180 degrees of separation. This enabled, for the first time, the simultaneous observation of the entire Sun.

Due to multiple hardware anomalies affecting control of the spacecraft orientation, communication with STEREO-B was lost on 01 October 2014. Communication with the spacecraft was re-established on 21 August 2016 during a monthly attempt to reach the spacecraft using NASA's Deep Space Network. Following this the STEREO team worked to discover the spacecraft's condition and to fully recover it, but the attempt was not successful. On 17 October 2018 periodic attempts to recover it ceased .

Alternate Names

  • 29511
  • STEREO Lead
  • STEREO West
  • Solar Terrestrial Relations Observatory B

Facts in Brief

Launch Date: 2006-10-26
Launch Vehicle: Delta II
Launch Site: Cape Canaveral, United States
Mass: 620 kg
Nominal Power: 475 W

Funding Agency

  • National Aeronautics and Space Administration (United States)


  • Space Physics
  • Solar Physics

Additional Information

Questions and comments about this spacecraft can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Dr. Joseph B. GurmanProject ScientistNASA Goddard Space Flight
Mr. Michael DelmontDeputy Project ManagerNASA Goddard Space Flight
Dr. Therese A. KuceraDeputy Project ScientistNASA Goddard Space Flight
Mr. Nicholas G. ChrissotimosProject ManagerNASA Goddard Space Flight
Mr. Stephen K. OdendahlMission DirectorNASA Goddard Space Flight

Other STEREO Data/Information at NSSDCA


Other Sources of STEREO Data/Information

STEREO Project page

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