The European Space Agency's (ESA) Automated Transfer Vehicle (ATV) Georges Lemaitre captured the International Space Station (ISS) in a new light in August, as it fired up a set of experimental sensors that may form the basis of the next generation of automated docking systems. Such tech will be vital for the increasingly-ambitious missions planned by NASA and its partners to explore the Red Planet and beyond.
Using the contemporary system, ESA's ATVs have successfully completed five automated dockings, with each attempt safely affixing the resupply vessels to the Russian Zvesda module of the ISS. With the tested system, an ATV is required to set up a communications link with the station to allow the resupply vessel to undertake precision maneuvers relative to the station using advanced GPS technology.
During this phase, the station repositions its solar panels edge-on with the ATV, in order to minimize interference with the GPS signal. At a distance of 249 m (817 ft) from the station, the spacecraft uses videometer and telegoniometer data in addition to a set of "eye-like sensors" to automatically dock with the outpost at a gentle 7 cm/s.
August's docking of the Georges Lemaitre represented the first field test of a system that could replace the current navigational sensors. The experimental Laser Infrared Imaging Sensors (LIRIS) switched on while the ATV was positioned 7 km (4.3 mi) below the station. By utilizing the device so far from the station, ESA could test the experimental equipment's long-range target acquisition capabilities. As the ATV approached the ISS, it tracked and imaged the station using its lidar component – an apparatus that is like a radar that uses light instead of radio waves and operates by pulsing laser beams over a mirror in order to collect high-resolution 3D data.
Using this technique, the sensors can track the station in both sunlight and darkness, with a high degree of accuracy. Furthermore, lidar has the ability to register the amount of light reflected from the surface of the object it scans, gaining an insight into the composition of the reflecting material in the process. As LIRIS does not require a direct link to, or hardware installed aboard its target, the system is potentially capable of tracking and docking with an inert object, such as another spacecraft beyond low-Earth orbit.
Data collected during the experiment was stored on hard-disk in the ATV's cargo hold and has since been returned to Earth aboard Soyuz TMA-12M, the capsule that ferried astronauts Steve Swanson and cosmonauts Alexander Skvortsov and Oleg Artemyev back to the planet's surface in September.
Following a preliminary assessment of the data returned by LIRIS, it is clear that the sensors succeeded in tracking the station perfectly while creating a detailed 3D map of it. The system also managed to maintain the track during several 30-minute intervals of darkness, displaying high levels of reliability both at distance, and close up with the station. The potential applications of the technology, especially its ability to enable docking with an inert object, could allow spacecraft to de-orbit space junk or even dock around a distant planet.