Wired.com has a good article about yesterday’s tests and today’s rendezvous and capture of the SpaceX Dragon spacecraft. There were some nervous moments concerning the LIDAR (LIght Detection And Ranging) getting false signals off the Kibo module on the International Space Station.
ISS has these “bulls eye” targets of black and white over much of the station. Most of them are black centers with white background, but there are some reverse ones, as you can see here on the right.
The docking system is supposed to recognize the pattern of these targets and know where it’s at.
Kibo was one of the last pieces in place on ISS, so it doesn’t have any docking targets except for the “back porch”. (This is a platform for space environment effects experiments. Might have something there someday.)
Perhaps the LIDAR was picking up reflections off the meteoroid/space debris shields, but the ground controllers narrowed down the field-of-view to just the module for docking and were able to complete the mission.
Trivia of the day: the black and white of the docking targets would look the same in infrared light. The coatings might have a 2% difference in infrared on a good day, whereas the black coating is roughly 5% reflective and the white coating is over 90% reflective in visible light. Your ordinary house paint in white is maybe 80% reflective and wouldn’t last very long in space. If you did have an infrared docking system, it would still see a difference between the docking target and the anodized aluminum around it.
Very glad that SpaceX was successful, especially because I still remember the Progress vehicle crashing into the Mir space station. This is why they had some maneuvers and holds at 250, 235, 150, 78, 30, and 10 meters. The success also hopefully means I will get one of my experiments back in 2013 or 2014. The astronauts will unload the supplies and fill it up for the return trip to Earth. Splashdown in the Pacific is scheduled for May 31.