For the first time in history, two spacecraft were aligned in formation with millimeter precision. They maintained their mutual position for several hours without any external control. This is stated in the message published on the ESA website.
Artificial Moon
The vehicles under discussion are part of Europe’s Proba-3 mission. Its goal is to study the solar corona, the outer, thinnest and hottest layer of the stellar atmosphere, whose temperature is millions of degrees Celsius. It is the source of solar wind and mass ejections. When the latter reach the Earth, they result in geomagnetic storms and auroras.
The corona becomes visible during total eclipses, when the Moon is completely covered by the solar disk. The Proba-3 mission uses this principle. It consists of two spacecraft. The Occulter satellite plays the role of an artificial Moon — it covers the Sun for the Coronagraph satellite, which can observe its corona.
In order for this to work, Occulter and Coronagraph need to be 150 meters apart and hold position with millimeter accuracy. This task is entrusted to the laser system. It constantly measures the distance between the vehicles, which allows them to keep in line. To change their position, the satellites are equipped with a set of high-precision thrusters capable of making micro-course corrections with thrust comparable to the force of a falling feather.
The Coronagraph is also equipped with a shadow position sensor. An on-board algorithm based on light intensity measurement ensures that it stays within the shadow cast by Occulter.
Perfect accuracy
During the tests held in March, Occulter and Coronagraph managed to build the right formation and held it for several hours. The control and distance measurements occurred autonomously without any external control from the MCC. The operation was conducted at a distance of over 50,000 kilometers from Earth. At this distance, Earth’s gravitational pull is relatively low, so very little propellant is required to hold the formation.
The success of the test was one of the final steps toward beginning observations of the solar corona. In the near future, mission specialists plan to complete the calibration of the spacecraft, after which Proba-3 will begin to carry out its scientific program.
It is worth noting that Proba-3 has the status of a demonstration mission. Its success will open the way for new, more complex and ambitious projects that will allow astronomers to learn even more about the Sun, the processes taking place in its atmosphere and how they affect the Earth.
According to ESA
