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Important notice about STEREO Behind
about STEREO-A close approach to Earth, August 2023
STEREO-B Status Update
Communications with Solar Terrestrial Relations Observatory-B (STEREO-B) were
lost on Oct. 1, 2014, due to multiple hardware anomalies affecting control of
the spacecraft orientation. Communications with STEREO-B were re-established on
Aug. 21, 2016, during a monthly attempt to reach the spacecraft using NASA's
Deep Space Network. During the next weeks, the NASA and the Johns Hopkins APL
STEREO teams worked tirelessly to discover the spacecraft's current conditions
and to recover the spacecraft fully. The attempt to recover the spacecraft was
not successful. STEREO-B has now been out of contact since Sept. 23, 2016.
Four years after the initial loss of communications anomaly with the Behind
observatory, NASA directed that periodic recovery operations cease with the
last support on October 17, 2018.
- LOSS HISTORY:
Communications with STEREO-B were lost on Oct. 1, 2014, during a test of
the spacecraft's command loss timer, a hard reset that is triggered after the
spacecraft goes without communications from Earth for 72 hours. This test was
in preparation for STEREO to be out of contact with Earth as it passed behind
the sun. This event is known as solar conjunction and disrupts the DSN's
ability to communicate with the spacecraft; as conjunction occurred beyond
STEREO's two-year design mission lifetime, STEREO had no design requirements
anticipating periods of weeks without communications. During this two to three
week period, STEREO's command loss timer would have expired multiple times.
- RECOVERY ATTEMPTS:
After a persistent search and utilizing a special command sequence designed
to interrupt a cycle of collapsing battery voltage, communications with
STEREO-B were re-established on Aug. 21, 2016. During the next weeks, the
STEREO team worked to learn more about the state of the spacecraft and to
recover it. However, data was very limited; the large distance to the
spacecraft (~2 AU) and the uncontrolled orientation meant that while the DSN
could detect that STEREO-B was transmitting, very few packets of telemetry --
containing the on-board measurements of temperatures, voltages, etc. - were, in
With the limited data available, the team formulated a plan to attempt a
recovery and stabilize the spacecraft pointing. The attempt was not
successful. The limited data available during the recovery attempt revealed
that STEREO-B came close to achieving a stable orientation, but one set of
thrusters on-board may have performed abnormally, possibly due to frozen
propellant and ultimately spun the spacecraft back up into an uncontrolled
state. STEREO-B has now been out of contact since September 23. The information
during those few weeks has provided guidance for plans forward, however, and
the team will continue to try to reestablish communication.
- INFORMATION LEARNED:
The 2016 contact with STEREO-B revealed new information about the
spacecraft's rate of spin and precise location in space - which is particularly
important since, when contact was lost, it wasn't clear if STEREO-B had fired
its thrusters in such a way as to affect its expected orbit. Data from STEREO-B
also shows that the spacecraft battery is operating with very low charge, a
challenge made more difficult to overcome by the fact that STEREO-B's solar
panels are no longer pointed directly at the sun, meaning that the battery
charges only a fraction of the time. Mission operators also have new
information about how STEREO-B responds to extreme conditions including both
very high and low temperatures. STEREO-B has proved to be a resilient
spacecraft capable of surviving under an array of circumstances that is was not
designed to accommodate. Consequently, the hope of recovery persists.
- STEREO BACKGROUND:
The Solar Terrestrial Relations Observatory is part of the Heliophysics Systems
Observatory, a collection of missions that observes the sun and our space
environment, providing research that contributes to the safety of spacecraft
both in near-Earth space and as they travel further from home.
STEREO consists of two nearly identical spacecraft put into slightly different
orbits around the sun - one moving faster than Earth, one moving more slowly -
so they each have a different vantage point of the star.
Launched in October 2006, the STEREO mission design lifetime was two
years. Having delivered far beyond expectations, the mission is now poised to
enter its second decade of operations.
The STEREO mission was designed to provide the first-ever stereoscopic
measurements of the sun, providing 3-dimensional views of the structure and
evolution of eruptions on the sun - eruptions such as coronal mass ejections
that can disrupt the space environment near Earth and interfere with radio
communications and satellite electronics.
STEREO-A continues to operate normally. STEREO's current mission extension was
based on using just one spacecraft, so, regardless of what happens with
STEREO-B, the STEREO mission will provide robust solar research in the coming
Planned research is to characterize space weather throughout the inner
heliosphere, support 360 degree coverage of the sun (along with SDO and SOHO)
and improve our understanding of phenomena from the sun's atmosphere, all the
way to the edges of the heliosphere.
STEREO is the third mission in NASA's Solar Terrestrial Probes program, which
is managed by NASA Goddard for NASA's Heliophysics Division of the Science
Mission Directorate, in Washington. The Johns Hopkins University Applied
Physics Laboratory, in Laurel, Maryland, designed, built and operates the twin
Detailed updates about the recovery operations between August 21 and October 9,
2016, can be found on our What's New page.
The original message about the loss of contact with STEREO Behind can be found
Last Revised: Friday, 04-Aug-2023 18:43:00 UTC
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