A lot of people don’t think of it this way, but the International Space Station is really a huge orbiting science laboratory.   And after 188 days, more than 3,000 orbits, and nearly 130 million kilometers traveled, the three crew members of the space station’s Expedition 39 are back on Earth -- and they have a lot of science to share.   Expedition 39 accelerated the ISS mission of improving our knowledge of how space affects humans -- and not just by trying it out for themselves, but by continuing research while they were up there.   For example, among the cargo that returned to Earth with the astronauts last weekend were samples of specialized human immune cells: T-cells.   These are the white blood cells that first recognize an infection and start your body’s defensive response.    But previous research has found that the activity of T-cells slows down a lot in microgravity -- much as it does in old age -- and astronauts themselves have proven to be more vulnerable to infections during and after their missions.     So, the crew of ISS-39 conducted an experiment using 10 samples of T-cells. They put some in a centrifuge, to simulate Earth-like gravity, and left others to basically float in an incubator. Now they’re back on Earth, where they’ll be studied to see how these different environments affected their structure.     The Dragon cargo capsule also returned with hundreds of samples of bacteria, whose growth will be analyzed. Because some bacteria -- like Salmonella -- have returned from space more virulent than when they went up, which is kinda scary. And if we’re going to understand and prevent diseases both in space and on Earth, we need to figure out why.   Expedition 39 also studied how protein crystals grow in space, how mixtures of liquids known as emulsions behave in low gravity, and how future missions might make the best use of robots, like the experimental humanoid robot, R2.     So, the excitement of the International Space Station is not limited to David Bowie covers and real life Angry Birds, as awesome as those things are. ISS equals science!     Looking ahead, NASA is about to test a new technology that’s probably going to help us land on Mars one day.     On June 2nd, the Hawaiian island of Kauai will hopefully host the first landing of the Low-Density Supersonic Decelerator, or LDSD, which is basically a big flying saucer tricked out with inflatable rings.     Ever since the Viking landers of the 1970s, NASA’s pretty much been using the same unchanged technology for landing spacecraft: parachutes.   And parachutes have served really well. But we’ve gotten to the point that we want to start building larger, heavier spacecraft -- including ones carrying people -- and landing them more gently.    And landing on Mars is tricky, because its atmosphere is less dense than Earth’s, so simple friction and parachutes aren’t going to be enough. While we’ve managed to land heavy craft on the moon, which has almost no atmosphere, it also has very little gravitation to work against.    So, NASA engineers think that the LDSD -- whose design was inspired by a Hawaiian puffer fish -- might be the right shape to meet the challenges of landing on Mars.    In about a week, the LDSD will be carried to an altitude of 55 kilometers, and then dropped. When its speed reaches around three and a half times the speed of sound, its ring-shaped decelerator will inflate, slowing it down enough that THEN, a parachute will deploy to carry it to the ocean's surface.     Finally, I’m glad to tell you that reports of Kepler’s death are exaggerated!   The Kepler Space Telescope has been the single most important tool in the study of exoplanets, and, since some of you have been asking, an exoplanet is a planet outside of our solar system.   Since its launch in 2009 it’s found more than 960 confirmed alien worlds.   But last spring, Kepler lost the second of its four reaction wheels, the devices that allowed its sensors to be re-positioned. This made the telescope pretty much unusable, even though the rest of the equipment works perfectly fine.    Thankfully, last week, NASA approved a new, adapted mission for Kepler, called K2, which will put the telescope back in service by using the power of the sun.   The constant bombardment of photons from the sun exerts pressure on Kepler. And NASA has calculated the exact position needed to keep Kepler balanced against that pressure.   By reorienting the whole craft so that it’s parallel to the plane of its orbit, it’ll stay steady enough to study patches of space for 83 days at a stretch, until it has to be re-balanced against the pressure of the sun’s radiation.   Kepler should be up and running again by May 30, with at least another 2 years of planet-hunting ahead of it.   Space, guys! It’s amazing!     Thanks for joining me for this update of this week’s space news!   If you want to keep exploring the universe with us, check out subbable.com/scishow to learn how you can help support SciShow Space. And don’t forget to go to youtube.com/scishowspace and subscribe!