How do you keep your space agency interesting, when younger, sexier outfits are blowing up headlines (and launch pads) seemingly every other week? Send a rocket-fueled spacecraft to track down a spinning, unstable asteroid, sync up with its wonky orbit, gently caress it with a vacuum on a selfie stick, and bring the dusty contents of the vacuum bag back to Earth for scientists to study. That’s exactly what NASA is doing today, with the launch of OSIRIS-REx. As if rocket science weren’t tough enough as it is.
OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) is the latest in a string of sample return attempts, and space exploration’s best shot at bringing home some serious dirt after previous efforts by the Stardust and Hayabusa missions returned with only a disappointing sprinkling of dust. If it succeeds, it will be the US’s first mission to sample an asteroid, and the largest sample returned to Earth since the Apollo era.
This evening, OSIRIS-REx will blast off from Cape Canaveral to begin its seven year-long mission. The launch is scheduled for 7:05 p.m. ET, with live coverage beginning at 5:30 p.m. ET, all of which you can watch right up top.
It will take two years and one Earth-gravity slingshot maneuver to get OSIRIS-REx to Bennu by September of 2019. Upon reaching its target, the spacecraft will then brake its way down to a crawl (relatively speaking, both the asteroid and the spacecraft are still hurtling around the sun at a speed of 63,000 mph). After some initial surveys, OSIRIS-REx will then go into a one-mile orbit around Bennu. The asteroid, which is 1,614 feet across at its widest point---about the height of the Empire State Building---is the smallest thing that NASA has ever tried to orbit around.
Because the asteroid is so small, it doesn’t have much gravity for the spacecraft to work with. So OSIRIS-REx’s movements have to be very gentle. To accomplish that, it is equipped with the smallest thrusters of any mission flight in history. The pair of extra small engines give NASA’s navigators a fine-grained level of control, and completes a suite of 28 different engines on board. The navigation team intends to only use them for pinpoint maneuvers later in the mission, but they've got 'em if they need 'em.
Low gravity also means that OSIRIS-REx has to contend with other forces like solar wind and pressure from solar and re-emitted infrared radiation, all of which affect the orbit. To deal with these navigational uncertainties, NASA will use landmarks from Bennu’s surface to understand OSIRIS-REx’s position and make adjustments to its orbit. Every two hours, the spacecraft will take pictures of the asteroid, which will get strung together and transmitted to mission headquarters, where navigators will do the math to keep it on course. “Kind of like photographic breadcrumbs,” says mission design lead, Brian Sutter, of Lockheed Martin.
OSIRIS-REx will do this for more than a year, using that time and its bevy of high-powered cameras, spectrometers, Lidar and other instruments to create detailed 3-D maps of every crack, canyon and space-wind-swept plain on Bennu’s surface. In addition to providing unprecedented detail about the asteroid’s topography and interior geology, these maps will also help engineers identify a site from which to collect the mission’s real payload: four tablespoons of bonafide Bennu dust.
OSIRIS-REx won’t be landing on the asteroid to make the grab; the low gravity situation and the fact that Bennu is basically a loosely-held pile of rubble makes that next to impossible, and very dangerous. (I think we all remember when Ben Affleck jumped the armadillo...over the asteroid canyon in one of the more scientifically debatable scenes from Armageddon). Instead, NASA’s craft will swoop to within spitting distance (if spitting worked in low gravity) and then extend a 10-foot long articulated arm equipped with a sampling head that looks not unlike a large, circular air filter.
Moving at a painful 4 in/s (cue the extra-tiny thrusters!), the arm will slowly reach for Bennu’s surface, and once the head makes contact, a nitrogen bottle on the arm will expel its contents downward, kicking up dust and other loose sediments into a collecting chamber that can accommodate small rocks up to a half inch across. Because of the brief seal with the asteroid’s surface, the only exit for the blast of gas and dust is through the filter on the outside, where it gets captured. Contact pads along the base plate of the filter also act like steel velcro, grabbing additional material as the arm pulls away. The whole move lasts just five seconds. NASA's calling it a Touch-and-Go Collection, or the "high-five."
The team has enough nitrogen for three attempts at collecting the necessary minimum sample size of a 2.1 ounces, presuming they find a site with adequate loose material. Once collected, the samples will be stowed in a capsule, modeled after the successful Stardust comet mission. After the long return journey, the capsule will re-enter Earth’s atmosphere at 27,000 mph, where if the heat shield holds and the parachute deploys, it will land softly in the sands of the Utah desert in September 2023.
Opening up OSIRIS-REx’s cargo hold will be like opening a window into the earliest days of our little corner of the universe. Bennu is a carbonaceous regolith---a very primitive kind of asteroid that has barely changed since the formation of our solar system 4.5 billion years ago. Materials gathered on its surface will contain new chemical and physical information about the environment that formed Earth and its neighboring planets. “Why we are here, how the solar system evolved, these are all questions this sample will help answer,” says Philipp Heck, who curates the largest private collection of meteorites in the world, held at the Field Museum in Chicago. “Of course we will never have a complete picture, but this will provide an important new puzzle piece.”
Of Earth’s 60,000 known meteorites, only a tiny fraction of them come from carbonaceous asteroids. And Earth changes them: Volatile gases evaporate, minerals dissolve in our water-rich world. The Bennu sample will provide a missing link---and open up new realms of discovery for people not yet born, using technology not yet invented. Seventy-five percent of the sample will be archived at NASA’s Johnson Space Center for future generations of scientists. Hopefully one of them figures out how to stop Bennu from nicking Earth late in the 22nd century, because that might happen. Even worse, it might inspire an Armageddon sequel.
