Yesterday SpaceX launched a pair of astronauts into space. This was a huge deal, for reasons NASA captured on Twitter:
One small part of this effort was automated docking at the International Space Station. As The Verge explains:
“The vehicle is designed to autonomously approach the ISS and latch on to a standardized docking port, without any input from its human passengers…The predecessor to the capsule, SpaceX’s cargo Dragon, did not have this capability when it delivered supplies and food to the ISS. For all of those cargo missions, astronauts on board the ISS had to use the station’s robotic arm to grab hold of an approaching cargo Dragon and bring it onto a docking port. That technique is known as berthing, and it requires a lot of work from the astronauts on board the ISS. The Crew Dragon’s automated capabilities should help free up time for the astronauts to work on other things when new crews arrive.”
The SpaceX video that captures automated docking is a anticlimatic, compared to the rocket launch, but what’s going on behind the scenes is plenty impressive.
State estimation and control must have been huge challenges to make this work. On the ground — in automobiles, for example — gravity and the earth reduce the complexity of motion control from three dimensions down to only two dimensions. In a car you can go left or right, forward or backward, but you can’t go straight up or down.
In space — or in the air — that third dimension makes motion control much harder.
What’s also hard, and less obvious, is state estimation. This is sometimes called just “localization” in self-driving cars, because that’s really all there is to the problem (believe me, localization alone is hard enough). But in three dimensions it becomes a real challenge to keep track of your present state in three dimensions.
Hats off to SpaceX!