Just a few minutes to 10:00 UTC on December 29th PW-Sat2 deployed its main experiment – 4 m2 deorbit sail.

After 9:00 UTC team of operators, operating two mission ground stations (one on Warsaw University of Technology, Faculty of Electronics and Information Technology, the other one in the headquarters of projects strategic partner – Future Processing in Gliwice) have established a contact with the satellite to perform the health check and make sure that it is ready for its mission’s climax. Everything was fine, which meant that during the next communication session the first attempt to open PW-Sat2 sail will be made.

Jedno z pierwszych zdjęć odebranych po otwarciu żagla. Zdjęcie przedstawia jedną z ćwiartek żagla.
One of the first photos received after the sail deployment. The picture shows on of the sail quarters.

When 1.5 h later satellite have risen above the horizon, there was no time to lose. After telemetry showed once again that satellite is working nominally the main experiment was declared green to go. A command from ground initiated the process which begun with thermal knives getting hot and cutting thin Dyneema wire which held the whole structure stowed. Shorty after the telecommand was sent to the satellite and operators hold their breaths, satellite confirmed telecommand reception and that the process has started. Few more scary minutes later gyroscopes where the first to report the sudden change in rotational speeds – an indication that ‘something’ happened 575 km above operators heads. It took a whole orbit – 96 minutes, however, before the most important information came – on a photo taken by the on-board camera, Earth was no longer visible, this time there was a flat mylar foil taking most of the frame – the sail has deployed perfectly.

Short time lapse showing the opening process of the PW-Sat2 deorbit sail on December 29th, 2018 at ca. 10:00 UTC

Few more communication sessions later the full time-lapse of sail deployment have been received. That wouldn’t be possible so fast (if at all) if not for the outstanding support from the worldwide radio amateurs community. Throughout entire PW-Sat2 mission radio amateurs uploaded to our web app more than 100.000 frames received from PW-Sat2. The video below presents sail’s behavior shortly after deployment, frames are 5 sec. apart.

All of the PW-Sat2 experiments have been performed according to the plan. The whole team feels both proud and relieved, the PW-Sat2 mission is over and the satellite will now take a dozen months to deorbit. Successful sail deployment gives hope that sail designed by young Polish engineers may be used on other satellites yet to be launched into orbit and help to fight the space debris threat.

Change in Plans

Initial mission plan was to open the sail after 40 days of the launch. However, already half way through the mission, after 20 days, we have completed all of the activities planned before sail opening. Secondary experiments – Sun Sensor, camera, and RadFET radiation experiment were conducted and gathered data a few times more than expected. On the other hand, a satellite on orbit is subject to a lot of radiation exposure and its electronic systems performance may deteriorate very quickly, each day increases the probability of unexpected, sometimes irreversible, failures.

What’s ahead?

In the coming days operators will do they best to keep the satellite alive and monitor its health. Large sail structure occults the Sun and makes the amount of solar power gathered by the satellite much smaller than before. However, the most important activity in this phase is to monitor the orbit decay and compare it with simulations. Like any other object on Low Earth Orbit, PW-Sat2 is tracked by NORAD (North American Aerospace Defense Command) and its orbital parameters are published 2-3 times per day in the catalogue in the form of Two-Line-Elements (TLE), the same data was used in ground stations to able to find the satellite on the sky and communicate with it. After 1-1.5 years PW-Sat2 will be removed from the satellite catalogue indicating that it has finally deorbit. The orbital lifetime will be compared with previous simulations and used to asses the final sail effectiveness.

PW-Sat2 was a great success for the whole team. Sail technology may help with the increasingly pressing problem of space debris. PW-Sat2 team experienced the space debris threat on their own when we have received a conjunction message informing us that there is a risk of PW-Sat2 colliding with a piece of space debris. Finally we were lucky, but it passed our spacecraft only 79 meters away with relative speed of more than 3 km/s. This shows perfectly why solutions, such as PW-Sat2 sail are necessary for long-term human utilization of Low Earth Orbit and why space debris are a real threat.

Translated by Artur Łukasik, thanks a lot!