On Sunday, NASA’s Deep Space Network heard from a long lost friend. The global network of radio antenna picked up a signal from one of two spacecraft launched in 2006 as part of the Solar and Terrestrial Relations Observatory: STEREO-B. The craft hasn't been heard from since October 1, 2014.
According to a press release, every week for almost a year after its disappearance the STEREO Missions Operations team used the DSN to attempt to establish contact with the spacecraft. After prolonged silence, however, the recovery efforts had tapered to a monthly endeavor. It wasn't until last Saturday when they finally made contact.
The Solar and Terrestrial Relations Observatory consists of two spacecraft: STEREO-A orbits the sun ahead of the Earth and STEREO-B follows behind. The pair gave two points of view of the sun, allowing researchers to watch solar storms develop and radiate off its surface.
The mission was only scheduled to last for two years, but like the Hubble Telescope and Mars rovers, the STEREOs have lasted much longer. And they've made some exciting discoveries. In 2013, STEREO-A along with the Solar Dynamics Observatory and Japanese research satellite Hinode made a detailed three-view observation of a current sheet on the sun, helping to refine the theories behind solar flare development.
But over time, the pair drifted further along their orbits, taking them to the opposite side of the sun, where communication is nearly impossible.
“The sun emits strongly in nearly every wavelength, making it the biggest source of noise in the sky,” Dan Ossing, operations manager for the STEREO mission at Johns Hopkins University's Applied Physics Laboratory tells Sarah Frazier at NASA. “Most deep space missions only have to deal with sun interference for a day or so, but for each of the STEREO spacecraft, this period lasted nearly four months. We had to take a spacecraft that was meant to talk to Earth every day and get it ready for over three months of radio silence.”
If they do not receive contact from Earth for three days, the STEREO spacecraft are hardwired to reboot. Engineers were testing this reboot function before STEREO-A and -B transited behind the sun when something went wrong, and they lost STEREO-B’s signal. The last bit of data from the spacecraft indicated that its Inertial Measurement Unit malfunctioned, causing it to spin in such a way that its solar panels were not receiving enough sunlight to recharge and reboot the craft.
Now, after years of effort to force it to reboot, DSN has reestablished the link. They are currently assessing the spacecraft’s subsystems and instruments to determine if it’s recoverable.