The course of the mission
On May 7, 2013, the first Estonian satellite ESTCube-1 was launched aboard the European Space Agency’s Vega launcher to a 670 km sun-synchronous low Earth orbit.
During the first year in orbit, the satellite was actively used for taking images and downloading data, while students rapidly continued improving software for all subsystems. Year 2014 for ESTCube-1 comprised overcoming various challenges in orbit and working towards the execution of the E-sail experiment.
In March 2014, the attitude determination and control system software reached its full functionality. Shortly after this, a strong magnetic disturbance within the satellite was discovered, which did not allow spinning up the satellite around the axis predetermined for the E-sail experiment.
In the following months, engineers worked towards overcoming the disturbance by developing a coil output correction function that would take into account the disturbance measured in the lab and try to cancel the negative effects. However, the internal magnetic moment was so strong that its effects could not be reduced. According to simulations, it would also be possible to carry out the experiment with the satellite spinning around a different axis. Despite the magnetic disturbance and the resulting attitude control problems, the first full images of Estonia were taken in April.
In May 2014, spin-up and detumbling tests in preparation for the E-sail experiment were started. In the beginning of September ESTCube-1 was spun up to 250 deg/s, which was the spin rate required for reeling out 3 m of the tether – the first step towards reeling out the planned 10 m.
The experiment began on September 16 with burning the reel and end-mass locks, followed by an attempt to unreel a small amount of the E-sail tether. According to telemetry, all commands had been successful, however the downloaded images did not confirm deployment of the tether. Unreeling the tether was attempted several more times and it was decided to spin up the satellite even further to increase centrifugal force in hope of loosening any stuck components.
On October 13, ESTCube-1 was spun up to 841 deg/s, which is the fastest spin rate known to be deliberately reached by any spacecraft. After spinning down to lower angular velocities, further investigation and tests led to the conclusion that the tether reel motor is not rotating, the reason being the failure of either the motor or the reel lock.
From there, the solar panels produced less energy than the satellite needed while the rest was taken from batteries which started to empty. On May 19, 2015, the batteries got empty for good and we heard the satellite for the last time.
Results in numbers
About 200 students from 10 countries participated in the project. Over 30 Bachelor thesis and over 20 Master thesis were defended. 14 scientific articles were published, 50 presentations made and 4 spin-off companies created. ESTCube-1 captured 300 photographs from space.