X-37B Still Largely Unexplained: "The fourth mission of the X-37B robot spaceplane is well underway. We know much of what is happening with the flight. There's a test of a Hall Effect thruster for the US Air Force and a set of materials samples provided by NASA. Beyond this, little else is known. On previous X-37B missions, there has been plenty of disclosure about the spacecraft itself, but little talk about the payloads concealed under its clamshell doors. This time, it's the reverse. We know a lot about the payloads carried on board, but not much about the X-37B itself!"