Controlling a single satellite in orbit is difficult enough, but monitoring a pair of satellites as they fly in close formation around each other is likely to be extremely challenging. To simplify monitoring of ESA’s upcoming Proba-3 bi-satellite mission, his team is ensuring that controllers get real-time displays of the satellites’ relative positions.
Scheduled for joint launch in September, the Proba-3 pair will orbit each other with millimeter-scale precision. This will allow one to cast a precisely controlled shadow on the other, in the process eclipsing the Sun’s fiery disk to reveal its faint surrounding corona for sustained observations.
“The Proba-3 satellites will maintain their formation in this way autonomously for a maximum of six hours per orbit,” explains Damien Galano, director of ESA’s Proba-3 mission. “But at other periods during each 19-hour highly elliptical orbit – during which the pair fly from their closest 600 kilometers to Earth to a hundred times further away – active human supervision will indeed be essential.”
“As we developed the initial simulation system, it quickly became clear that we couldn’t simply rely on the numbers we would get from satellite telemetry. Normally what you get is its position expressed in three coordinates that correspond to the X, Y and Z axes, but it is impossible for the human brain to translate that fast enough; We cannot work solely with an incoming stream of numbers.
“What’s even more important to maintain control of the dual satellites is that we need to have an instant idea of exactly how the two platforms are oriented relative to each other; For example, is the shadow cast in the right place or is the laser pointed directly? “Telemetry could eventually give us some graphs showing these variables, but we realized that what we needed was an immediate snapshot that portrayed the dynamics and trajectories of the satellites.”
To make the real-time 2D and 3D visualizations the Proba-3 team realized they needed, they turned to VTS (Spatial Data Visualization Tool), free licensed software owned by the French space agency CNES and developed by space star company in Belgium.
“VTS is not actually a visualization tool as such,” explains Esther Bastida Pertegaz, systems and software engineer at Proba-3. “It is a means to centralize multiple applications perfectly synchronized in time, including visualization software, with the free space simulator. Celestia included as your baseline.”
Updated periodically, the VTS has been used on numerous European space missions in the past, typically to help plan complex maneuvers and acquire images of a given region of the Earth or other planetary bodies.
Esther explains: “What is really new about Proba-3 is that we have developed code that creates a real-time link between the VTS and the incoming telemetry (for now from the simulator, but eventually from the real satellites) so that the operator has an intuitive idea. Feel the two satellites with a single look.”
Having already started using VTS to test the Proba-3 mission simulator, as a next step the team will soon expand its use to begin training Proba-3 operators, who will monitor the pair of satellites from ESA’s Redu centre. in Belgium. Then, once the mission begins flying, the VTS will also be integrated into its control infrastructure.
“The controllers will not monitor the satellites continuously,” adds Esther. “But, for example, when satellites are at perigee, or their closest point to Earth, the VTS will absorb telemetry that estimates their orbital paths 60,530 km away, so controllers will be able to observe at a glance and see if “There are any problems that need to be corrected, for example if the satellites are getting too close or too far away.”
The first version of VTS was released in 2007, but since then it has received regular updates, incorporating packaged applications that include various visualization and plotting tools. It has been used on many major space missions, including ESA’s ATV ‘space trucks’ to the International Space Station, the comet hunter Rosetta and its Philae lander, the European Copernicus Sentinel-3 Earth observation mission and the next Japanese-German Moon exploration mission on Mars. serving to visualize the orbits of Phobos and Deimos around the Red Planet.
Part of the appeal of VTS is that it can be deployed on an operator’s computers completely separately, so it reads data coming from other systems without any risk of altering it if it fails.
“Versatile and easy to use, the VTS has been used in a multitude of contexts, demonstrating its adaptability in different stages and aspects of space missions,” says Thomas Crosnier of CNES. “This ranges from pre-project mission design and simulations to operational mission planning and flight dynamics both around Earth and further into the Solar System. And as space missions become more complex, VTS has kept pace with additional capabilities and features. “We are proud that ESA’s Proba-3 has become the latest space mission to use VTS.”