The United States Air Force’s X-37B space plane and the Planetary Society’s LightSail spacecraft both launched today aboard a United Launch Alliance Atlas V rocket. The launch took place at 11:05am EDT from Florida’s Cape Canaveral Air Force Station. As we reported yesterday, details about the X-37B’s highly classified mission are hard to come by, although we do know that part of the mission is to test a new Hall thruster, an electric propulsion device that ionizes and accelerates a gas such as Xenon in order to increase fuel economy and payload capacity, if not outright thrust.

You can watch a replay of the OTV-4 mission takeoff and the first few minutes of the rocket’s launch above the Earth’s surface below.

The X-37B will also carry aboard a NASA payload called the Materials Exposure and Technology Innovation in Space (METIS) investigation, which will help researchers figure out how being in space affects over 100 different kinds of materials. “By exposing materials to space and returning the samples to Earth, we gain valuable data about how the materials hold up in the environment in which they will have to operate,” said Miria Finckenor, the co-investigator on the MISSE experiment and principal investigator for METIS at NASA’s Marshall Space Flight Center in Huntsville, Alabama, in a statement. “Spacecraft designers can use this information to choose the best material for specific applications, such as thermal protection or antennas or any other space hardware.”

Investigations like this have helped engineers decide on materials for missions like the Mars Curiosity rover, the James Webb Space Telescope, and SpaceX’s Dragon spacecraft. Beyond that and the Hall thruster test, the rest of X-37B’s mission remains a mystery.

We know a lot more about the LightSail (pictured above). Originally conceived by the famous late astronomer Carl Sagan, the LightSail employs its namesake for propulsion, and will now be tested in the Earth’s upper atmosphere to ensure the sails deploy correctly. Solar sail technology works because light has just a little bit momentum that you can transfer to a spacecraft — enough to guide it and push it along. The LightSail is a tiny craft with 32 square meters of mylar material, as well as a comm system, solar panels, a computer, batteries, and some other flight-related parts.

If the current test goes well, the Planetary Society plans to begin preparation for a real mission in April 2016 in low Earth orbit. As for the X-37B, aside from the NASA experiments, we’ll just have to wait for whatever the military deems we’re allowed to know.