July 4, 2014
NASA’s STEREO Mission Being Prepped For Upcoming Orbital Phase
[ Watch the Video: STEREO Solar Conjunction ]
Gerard LeBlond for redOrbit.com - Your Universe Online
NASA’s STEREO mission began in 2006 and has been providing scientists with images from the far side of the sun since February 2011. The spacecraft duo that were placed in orbit around the sun are now about to embark on the next phase of their mission.
The two STEREO (Solar Transfer Relations Observatory) probes orbit the sun at different speeds and different locations.
“Both STEREO spacecraft orbit the sun like Earth does, but one is slightly inside Earth's orbit, the other slightly outside. As a result, one circles the sun slightly faster than Earth, and one slightly slower,” Joe Gurman, project scientist for STEREO at NASA’s Goddard Space Flight Center in Greenbelt, MD, said in a statement.
Because of the different orbits and speeds of the spacecraft, Earth is able to receive for the first time a 360-degree view of the sun, made possible by STEREO and near-Earth telescopes like NASA’s Solar Dynamics Observatory.
Both STEREO spacecraft will become close to each other on the far side of the sun. While they are in this position, the Earth is blocked from their view and communication will cease for a period of time and the probes will not collect any data. STEREO-Ahead will be silent from March 24 to July 7, 2015; STEREO-Behind from January 22 to March 23, 2015; at least one will be collecting data while the other remains out of sight.
However, both before and after this happens, communication from the craft will still be affected by the sun. The STEREO probes aim their dish antennas continually toward the Earth to send data. While they are orbiting on the far side of the sun, the extreme heat can damage the electronics. Because the antennas will be repositioned slightly, the signal will become fainter and less data will be transmitted. STEREO-Ahead will be adjusted on August 20, 2014 and STEREO-Behind on December 1, 2014.
While in this orbital phase, the instruments aboard the crafts still collect data, but it is a lower resolution so a portion of it will be stored and down-linked to an Earth receiver when the spacecraft are in a better orbital position sometime in early 2016.
“We might not know what's happening in real time. But in early 2016, we will receive a message in a bottle. There will be a complete record of the radiation, the solar wind, and the magnetic field changes during any events on the sun. That kind of information helps us protect future NASA assets throughout the solar system,” Gurman said.
The STEREO probes will undergo tests to prepare for this, and during these tests, the crafts will not collect any data. STEREO-Ahead will be tested from July 6-12, 2014; and STEREO-Behind from September 29 to October 6, 2014.
This is an important phase of the STEREO mission. However, at least one craft will be collecting data at any one time until 2016, allowing scientists to have an uninterrupted record of events on the far side of the sun that will be coordinated with observations from Earth's solar telescopes.
Image 2 (below): Graphic showing the approximate positions for the two STEREO spacecraft for July 2014. Credit: NASA/Goddard Space Flight Center