Controlling a single satellite in orbit is very difficult, but tracking a pair of satellites in close orbit can be more challenging. To facilitate oversight of ESA's upcoming dual-satellite Proba-3 mission, its team ensures controllers receive visualizations of the satellites' relative positions in real time.
Scheduled to launch together this September, the Proba-3 pair will fly in orbits relative to each other to the nearest millimeter. This would allow one precisely controlled shadow to be cast over another, in the process eclipsing the Sun's fiery disk and exposing its faint surrounding corona for extended observations.
„The Proba-3 satellites will maintain formation in this way on an autonomous basis for up to six hours per orbit,” explains Damian Gallano, ESA's Proba-3 mission manager. „But during other periods during each highly elliptical 19-hour orbit — when the pair fly a hundred times farther than 600 km from Earth — active human supervision is really necessary.”
„When we built the initial simulator system, it soon became clear that we couldn't just rely on the numbers we were getting back from the satellites' telemetry. Usually what you get is their position in three coordinates along the X, Y and Z axes, but that's impossible for the human brain to translate that fast; with an incoming stream of numbers We cannot work alone.
„More importantly, to maintain dual-satellite control, we need to instantly sense how the two platforms are looking at each other—for example, is the shadow cast in the right place, is the laser pointed directly? Telemetry can eventually give us some maps showing these variables, but what we need is an instant snapshot depicting the dynamics and trajectories of the satellites. We realized that.
Realizing they needed the Proba-3 team to perform real-time 2D and 3D visualizations, they turned to it. VTS (Visualization Tool for Space Data) Free Software Licensed Software owned by the French Space Agency CNES and created by Spacebell Company in Belgium.
„VTS is not really a visualization tool,” explains Proba-3 system and software engineer Esther Bastida Bertegas. „It is a means of centralizing multiple applications on a seamless time-synchronized basis, including visualization software such as the freeware Space Simulator. Celestia included as its basis.”
Regularly updated, the VTS has been used by several European space missions in the past, usually to help plan complex maneuvers and acquire images for a specific region of Earth or other planetary bodies.
Esther explains: „What's really new for Proba-3 is that we've developed a code that creates a real-time link between the VTS and incoming telemetry – now from the simulator but eventually from real satellites – so the operator gets an intuitive. Sense of two satellites at a glance.”
After starting to use VTS to test Proba-3's mission simulator, the team will soon expand its use to train Proba-3 operators who will oversee the satellite pair from ESA's Red Center in Belgium as a next step. Then, once the mission flight begins, the VTS will be integrated into their control infrastructure.
„Controllers don't constantly monitor the satellites,” says Esther. „For example, when satellites are at perigee or closest to Earth, VTS injects telemetry that estimates their orbital tracks at a distance of 60 530 km, so controllers can see at a glance. For example, whether satellites are coming too close to each other or moving too far apart. There is a problem that needs to be done.
The first version of VTS was released in 2007, but since then has received regular updates, including bundled applications including various visualization and planning tools. It has been used on several major space missions, including ESA's ATV 'space trucks' to the International Space Station, the Rosetta comet chase and its Philae lander, Europe's Copernicus Sentinel-3 Earth observation mission and the upcoming Japanese-German Mars probe mission. Helps visualize the orbits of Phobos and Deimos around the red planet.
Part of the appeal of VTS is that it can be used on an operator's computers on a completely stand-alone basis, so it can read data from other computers without any risk if it goes wrong.
„Versatile and user-friendly, VTS has been used in a variety of environments, demonstrating its applicability in various stages and aspects of space missions,” notes Thomas Krasnier of CNES. „This ranges from pre-project mission design and simulations to operational mission planning and flight dynamics around Earth and further out into the solar system. And as space missions become more complex, VTS keeps pace with additional capabilities and features. ESA's Proba-3 is the latest space mission to use VTS. We are proud to have changed.
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