NASA has reestablished contact with its STEREO-B spacecraft, nearly two years after losing communication with the vehicle. The space agency has been trying to get in contact with the spacecraft since October 1st, 2014, when the last signal from STEREO-B was received on Earth. Finally on Sunday, NASA was able to pick up a signal from the vehicle using the Deep Space Network, or DSN — an international network of large radio antennas used for communicating with spacecraft.

The space agency has been trying to get in contact with the spacecraft since October 1st, 2014

STEREO-B is one of two spacecraft that make up NASA’s Solar Terrestrial Relations Observatory (STEREO). The goal of the program is to study the Sun and better understand its behavior. Specifically, STEREO aims to figure out the origins of coronal mass ejections — massive explosions of charged particles that sometimes shoot out from the Sun. These plasma bursts travel all the way to Earth and collide with our planet’s magnetic field, creating powerful geomagnetic storms that can damage communications satellites and mess with our planet’s power grid.

To study these solar outbursts, NASA launched STEREO-A and STEREO-B in 2006. Both spacecraft were inserted into heliocentric orbits; STEREO-A positioned itself "ahead" of Earth, while STEREO-B fell "behind" Earth. These positions allowed the spacecraft to get even more views of the Sun that we can’t get from Earth. The two vehicles have since drifted farther apart on their orbits, though, and will continue to do so while in space.

The current positions of STEREO-A (shown in red) and STEREO-B (shown in blue). (NASA)

But STEREO-B has been offline for the past two years, after NASA reset the spacecraft on purpose in 2014. Prior to the reset, both STEREO-A and STEREO-B had moved to the far side of the Sun, making communication with the vehicles difficult. In order to send signals to Earth, the spacecraft had to point their antennas a lot closer to the Sun, which increased the risk of the antennas getting overheated. So NASA had decided to angle the antennas away from the Sun and put the STEREO spacecraft into a year-long safe mode until they could safely communicate with Earth again. To prepare for this, NASA put the two vehicles through a series of tests and resets to see if they would be ready for the repositioning and hibernation. STEREO-A performed just fine, but STEREO-B failed to send signals back to Earth after one of the planned resets.

STEREO-B failed to send signals back to Earth after a planned reset

NASA has tried establishing communication with STEREO-B ever since. Recently, the space agency has tried using the DSN every month to pick up signals from the spacecraft, and the efforts finally proved fruitful this past weekend when contact with STEREO-B was established at 6:27PM ET on August 21st. The mission team plans to continue communicating with the spacecraft to figure out what kind of shape it's in and regain attitude control.

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