NASA tried turning lost spacecraft STEREO-B off and on again... but it didn't work. True story

NASA has managed to reestablish a connection with the STEREO-B spacecraft after contact was lost in October 2014.

The spacecraft is part of a pair. STEREO-A flies ahead of Earth’s orbit, whilst STEREO-B trails behind.

Both spacecraft were employed on NASA’s Solar TErrestrial RElations Observatory (STEREO) mission to provide the first-ever stereoscopic measurements of the Sun, allowing scientists to study coronal mass ejections - giant solar flares erupting from the surface of the Sun.

After trying for 22 months, scientists have finally managed to reconnect with STEREO-B by conducting a recovery operation with NASA’s Deep Space Network (DSN).

DSN is the world’s largest and most sensitive scientific telecommunications system with a web of antennas used to track and communicate with spacecraft floating in space.

Ageing spacecraft are more difficult to operate. Both STEREO vessels were launched in 2006 and were designed to last for two years. But scientists decided to keep the mission going as long as the spacecraft were still sending back data.

Since the ships have been working for almost 10 years, their orbit drifted further away to the other side of the Sun from Earth.

Having the Sun wedged in between made communication with Earth nearly impossible as the solar wavelengths make the environment too noisy to pick up signals from Earth.

Scientists would have to wait four months until they were out of the solar interference zone. To keep the chances of communication high during this period, the spacecraft were to be rebooted every 72 hours to correct any underlying issues.

But after the team tested STEREO-B’s reboot on 1 October 2014, it sent a status report via a much weaker signal, after which it faded away. NASA said at the time: "The signal received was so weak and so brief that the team was able to extract only a few packets of data to form a partial status report. From that small amount of information, the STEREO team was able to extrapolate the most likely case for where the Behind spacecraft is and what it’s doing."

All contact was lost, although NASA soon resumed communications with craft A, which resumed its normal science operations after it emerged from the solar interference zone.

The team understood from the telemetry system onboard STEREO-B that incorrect data was causing the vessel to spin in a way that meant its solar panels were receiving less power than normal.

“The telemetry showed that the Inertial Measurement Unit, or IMU—which tells the spacecraft if and how fast it’s rotating—failed in a way we didn’t expect,” said Dan Ossing, mission operations manager for the STEREO mission at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “Rather than cutting out altogether, it was feeding incorrect information into the guidance and control computer.”

Its low battery prevented the transmitter from working and it could not send any signals back to Earth, meaning the team couldn't correct the problem by "instructing STEREO-B’s computer to ignore the information from that particular IMU".

NASA said: "The DSN established a lock on the STEREO-B downlink carrier at 6:27 p.m. EDT. The downlink signal was monitored by the Mission Operations team over several hours to characterize the attitude of the spacecraft and then transmitter high voltage was powered down to save battery power."

The team is now assessing all subsystems and instruments. ®