Two years later, NASA re-established communication with the STEREO-B spacecraft.

Photo of the Sun in extreme ultraviolet, obtained from the board STEREO-A. The photo was taken at a wavelength of 171 Angrstrom (17.1 nm), which is usually painted in blue. Photo: NASA

On August 21, 2016, NASA engineers managed to reestablish communication with the STEREO-B spacecraft, one of the two Solar Energy Resource Observatory ( STEREO) observatories for studying solar activity.

The STEREO-B Observatory last contacted us on October 1, 2014, after which the contact was lost. For 22 months, NASA experts tried to save the device - and they still succeeded!

Another attempt to establish communication with the lost device was made through NASA's Deep Space Network (DSN), an international network of radio telescopes, which is used for radio astronomy research and for controlling interplanetary spacecraft. This time the attempt was successful.


Solar Observatory STEREO-B. Illustration: NASA

on August 21, 2016 at 6:27 pm EDT DSN set the focus on the downlink beam from STEREO-B. A few hours the signal was analyzed by Mission Operations specialists to establish the coordinates of the spacecraft. After that, they remotely disconnected the high voltage transmitter to save battery power.

Now that the STEREO-B coordinates are known, engineers can remotely turn on the transmitter again at any time. They plan to do this in the near future, in order to continue the process of restoring the satellite’s working capacity, regain control over its movement, assess the working capacity, and check the functional readiness of all subsystems and scientific tools.


The illustration shows the positions of the observatories and their orbits relative to the Earth, Venus, Mercury and the Sun. Illustration: NASA

The STEREO-A and STEREO-B solar observatories should shoot the sun from unusual angles. For example, on the opposite side of the Earth. Thus, for the first time, scientists were able to photograph the sun from all sides simultaneously. One of the vehicles gradually lags behind the Earth (Behind - B), and the other, on the contrary, overtakes it (Ahead - A). Due to this, you can simultaneously observe the Sun from two different points and create three-dimensional images.


It was the specific orbit of the STEREO devices that caused interference in the communication. Due to the slow drift relative to the Earth at some point in time, each of the vehicles went beyond the Sun, that is, to the point of orbit opposite to the Earth. At this time, radio contact with him was interrupted for three months due to interference.

Two STEREO spacecraft launched in October 2006, counting on their two-year operation. As often happens with NASA spacecraft, they were able to work much longer than planned. When scientists realized that the devices could go to the zone of interference for the Sun, and then go out and continue to work longer than planned, they began to plan this operation .

Each of the devices was equipped with a hardware loss of communication timer programmed to automatically reboot the systems if no commands were received from Earth within 72 hours. Such a timer was implemented to automatically fix problems that could cause a loss of communication. This means that after going behind the Sun, the device rebooted every 72 hours, after that it corrected its orbit in the stars, sent an antenna to the Earth - and continued attempts to get in touch. Having gone for the Sun, the device had to do such reboots for three months. Therefore, NASA engineers had previously tested the performance of both devices after a reboot, specifically silencing the connection with them for 72 hours.

STEREO-A successfully passed the test, but for some reason, its twin STEREO-B, after silencing the connection and forcing a reboot on October 1, 2014, failed to reach the connection after 72 hours 20 minutes. He could not properly direct the antenna to Earth. On a weak and fragmentary signal, the engineers determined that an unexpected failure had occurred in the Inertial Measurement Unit, which determines the rotational speed. This module gave out incorrect information to the computer guidance system and control of the device — and reported rotation even when the device was in a static position. Because of this, the antenna could not aim at Earth. Worse, due to incorrect information about the rotation, the device could turn the solar panels on the wrong side and partially lose energy. And even worse the control computer could decide to use the engines to eliminate the rotation of the apparatus. Since in fact there was no rotation, then after such a correction it could really begin.

The specialists tried to send a command to the STEREO-B control computer to ignore the readings from the failed IMU module, but the connection with the device was already lost.

STEREO-A continued to work normally , coming out from behind the Sun, but it was no longer possible to get stereo pairs of photos from two observatories.

Engineers have yet to figure out the exact cause of the malfunction, but the main thing is that now the connection with STEREO-B has been restored. Solar observatories for almost ten years. Scientists expect that they will still send valuable scientific information about solar activity. In addition to photographs of the Sun itself, the STEREO observatories took pictures of interesting events in the near-solar space. For example, in April 2007, they took great photos of Comet Encke.that flew past the sun. The photographs were able to detect signs of turbulence in the tail of a comet from bunches of ionized gas.


If the connection with STEREO-B is lost again, then the engineers have a backup plan. In 2019, the device will be at a sufficiently close distance to establish direct visual contact, examine it in the lens of the Hubble Space Telescope - and determine the degree of rotation. Around 2023, the Earth should catch up with STEREO-B - and then it will be possible to contact him at close range, or even deliver to Earth for study, if it is economically feasible.