"Hopefully this is a really straightforward mission," Elon Musk told PM during our recent trip to the headquarters of SpaceX in Hawthorne, Calif. The last mission, he said, was a two-step. "[First we] did a loop around the space station to verify that the systems were functioning well, that we could communicate with the space station, that the docking sensors could lock on and that kind of thing, and then we went in and actually did the docking. So it was a longer mission than ... this one will be. This one, we?re going to go straight up, attempt lock, and go straight in."
As with the first run, the SpaceX Dragon capsule will close to within range of the ISS?s grappling arm, and it will do so on autopilot. "Dragon has quite a bit of onboard intelligence.We?re not steering it with a joystick," Musk says. "As it approaches the space station, it?ll stop at various points and ask for permission to proceed. And then if it encounters something where it can?t proceed with high confidence, it will report that back and pause."
During the first docking, the laser ranging system was thrown off by sunlight glinting from the space station. Musk says the problem has been fixed. "LIDAR is sort of a 3D laser scanner that scans something and then it comes up with a point cloud and tries to figure out what it?s looking at," he says. "The system tries to fit that with what it?s expecting to see, and then, using that, it figures out what the relative position and motion is between Dragon and the space station. And it uses that to plot an approach vector."
During that first approach in May, the Dragon was working from a model of the ISS that wasn?t totally accurate, as pieces have been added to and subtracted from the real-life station. "There was a reflector on the Japanese model that was extremely bright and it was showing up to a far greater degree than we expected," Musk says. SpaceX solved the problem on the fly by uploading some new code to narrow the field of view, similar to putting blinders on a horse so it doesn?t get distracted. That temporary fix has morphed into a permanent reprogramming. "We?ve improved the software on the LIDAR, on the image-recognition software, so if it encounters this again it would not have a problem," Musk says.
When asked what part of the first flight scared him the most, Musk said the deployment of the solar arrays, which continuously move to face the sun. "If they didn?t work then . . . the batteries would run out of energy well before we reached the space station," he says. On the first flight, "Once the Dragon was placed in orbit, separated from the rocket, deployed the solar panels and the panels were producing power better than expected?that?s when I felt really good because I knew that now if something went wrong we had time to fix it," he says.
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