NASA's twin STEREO spacecraft, built and operated by
the Johns Hopkins Applied
Physics Laboratory, completed a series of complex
maneuvers on Jan. 21 to position the spacecraft in their
mission orbits. The spacecraft, whose acronym comes from Solar TErrestrial RElations
Observatory, will be in position to produce the first
3-D images of the sun by April.
Spacecraft trajectories and lunar swingby maneuvers
were created by mission design engineers at APL. "STEREO is
the first mission to use the moon's gravity to redirect
multiple spacecraft, launched aboard a single rocket, to
their respective orbits," said Ron Denissen, APL STEREO
project manager.
During the initial weeks following launch, mission
operations personnel at APL guided both spacecraft through
a series of four highly elliptical phasing orbits around
Earth to position them for their lunar gravitational
assists that propelled them into their respective mission
orbits.
On Dec. 15, STEREO's "A" observatory flew past the
moon at a distance of approximately 4,550 miles above its
surface, using lunar gravity to redirect the spacecraft
away from Earth and into its orbit "ahead" of Earth.
The "B" observatory passed approximately 7,300 miles
above the lunar surface, where gravity is slightly weaker.
Although the "B" observatory's orbit was slightly boosted,
the spacecraft didn't undergo its full lunar gravitational
assist until Jan. 21, when it re-encountered the moon. The
spacecraft then came within approximately 5,468 miles of
the surface, swinging past the lunar body in the opposite
direction of the "A" spacecraft and into an orbit "behind"
Earth.
The two observatories will orbit the sun from this
perspective, separating from each other by approximately 45
degrees per year. Just as the slight offset between your
eyes provides you with depth perception, this
mirror-image-like positioning of the spacecraft will allow
them to take 3-D images and particle measurements of the
sun.
During post-launch instrument checkouts, scientists
got a close-up view of some intense solar activity from our
nearest star, the sun, when the "A" observatory sent back
its first images in early December.
When the cover to the "A" observatory's SECCHI Extreme
Ultraviolet Imager telescope was removed on Dec. 4, it
captured images of a very powerful active region on the sun
known as AR903, which produced a series of intense flares
last month. SECCHI, for Sun-Earth Connection Coronal and
Heliospheric Investigation, was built by the Naval Research
Laboratory in Washington, D.C., and is the imaging
instrument suite aboard both observatories.
A few days later, during an unusually active solar
period, the "A" observatory captured images of a coronal
mass ejection with one of SECCHI's two white-light
coronagraphs.
Coronal mass ejections, among the largest explosions
in the solar system, are giant clouds of plasma shot into
space from the sun's atmosphere and can equal the force of
a billion megaton nuclear bombs. When they collide with
Earth at speeds approaching 1 million mph, CMEs can produce
spectacular auroras and trigger severe magnetic storms. The
energetic particles associated with these storms can cause
electrical power outages, disrupt and/or damage
communications satellites and be hazardous to
astronauts.
Each STEREO observatory is carrying more than a dozen
instruments, which are housed in a platform designed and
built by APL. STEREO's data, when combined with that from
observatories on the ground or in space, will allow
scientists to track in 3-D the buildup and liftoff of
magnetic energy from the sun and the trajectory of
Earth-bound coronal mass ejections.
STEREO, the third mission in NASA's Solar Terrestrial
Probes Program, is sponsored by NASA's Science Mission
Directorate, Washington, D.C. NASA Goddard's Solar
Terrestrial Probes Program Office, in Greenbelt, Md.,
manages the mission, instruments and science center. APL
designed and built the spacecraft and is operating them for
NASA during the mission.
For more about the mission, go to
stereo.jhuapl.edu.
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