For the first time, the 'videometer' (VDM), a new technology device to ensure very precise automatic rendezvous operations between the 20.7 tonne Jules Verne Automated Transfer Vehicle and the ISS, has been successfully tested this month.
State of the art
"For the first time, the ATV rendezvous sensors were used successfully in real conditions. And, within their operational domain, they worked exceptionally well," said ESA ATV engineer Stein E. Strandmoe, who supervised a critical 10-day test campaign.
These built-in automatic capabilities of the ATV must be compatible with the demanding requirements of human spaceflight safety, necessary for the permanently crewed ISS.
During the last 200 metres of the orbital final approach manoeuvre, the videometer must automatically recognize the retroreflectors target patterns and then calculate the distance and direction to the docking port.
This precise tracking of the relative motion between the two spacecraft as they get closer – starting at a speed of up to 3.6 km/h – provides indispensable information to the on-board Guidance, Navigation and Control (GNC) system, which automatically pilots the bus-sized cylindrical ESA cargo ship towards the ISS.
Inside an exceptional building, 600 metres in length, a 120 000 kg mobile platform, able to ride on 550 metre long rails, enabled the simulation of a continuous approach between the two space vehicles from a range of several hundred metres to within almost docking distance. On the platform, a set of passive rendezvous targets (retroreflectors), identical to the ones to be installed on ISS, were facing the videometer which was mounted on an articulated robotic arm (with six degrees of freedom) representing the ATV motion.
This seven metre high mobile arm was used to simulate the angular movements of the ATV to check if the videometer was still able to target the ISS retroreflectors and provide the information to the ATV control system necessary to adjust its trajectory accordingly.
First time success
"The most surprising thing was that the sensors were almost undisturbed when we tried to fool them with other reflecting surfaces or other lights that could interfere with rendezvous targets in the ISS background," said Strandmoe. "It's amazing how the videometer, as a totally new development, proved to be such a robust system. I was quite surprised that it worked so well the first time it was tested!"
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Docking With Precision
Houston TX - Mar 26, 2004
The skills astronauts need to dock the Space Shuttle with the International Space Station (ISS) may be more familiar to school students than adults. The training simulator astronauts use to learn docking skills is found in many American homes; a video game console. However, the program used by astronauts is more sophisticated and complex than a game you might play at home, but the skills it requires are quite similar.
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