UA's OSIRIS-REx slingshots past Earth

NASA asteroid hunter takes snapshots of home planet on the way to asteroid Bennu

The University of Arizona behind OSIRIS-REx talk about the space robot like it's their baby, because it is: They built it, they raised it (it takes a village, you know), and when the time came last September—as it does for all parents—they launched it into space at thousands of miles per hour.

Last Friday, though, Tucson's favorite space bot swung by the earth to say hello, take some pictures and borrow some of the planet's gravity in order to launch off toward the asteroid Bennu, the spacecraft's destination site.

"We made the decision to use nature to help us to get us to our destination," said Heather Enos, deputy principal investigator of the OSIRIX REx mission. "What that means is we actually used the earth's gravity in order to propel us onto our destination into the orbital plane necessary to match our target, Bennu."

OSIRIS-REx's mission is to travel to and survey the asteroid Bennu (it should arrive in the vicinity around August 2018), spend a few months surveying Bennu to determine a good site to grab a sample, and then move up close to the asteroid, blast it with nitrogen gas and knock loose a sample of regolith (asteroid dust, more or less) in order to capture it in a special capsule. The spacecraft is scheduled to start the journey back to earth in 2021, and to touch down back home in September 2023, where scientists can study the regolith to learn about its chemical and physical makeup—and possibly the makeup of some of the solar system's very beginnings.

OSIRIS-REx spent the last year orbiting the sun, and came back home briefly to do a little gravity freeloading in the earth gravity assist (EGA). While it was nearby, the OSIRIS REx team used the opportunity to recalibrate the spacecraft's instruments, including the multiple cameras on board.

Carl Hergenrother, astronomy lead and a science planner for the project, explained that all of the shaking during take-off shifted—ever so slightly—many of the instruments on board OSIRIS-REx, so having a common reference point helped get them realigned. "Observing something big and bright like the earth and the moon was a way for all the instruments, almost all the instruments—the spectrometers, the OTES [OSIRIS-REx Thermal Emission Spectrometer] mirrors, and all the cameras—to be looking at the same thing at the same time."

John Kidd, another science planner, added that taking glamour shots of good ol' earth made excellent practice for OSIRIS-REx's upcoming photoshoot with Bennu.

NavCam 1 captured the spacecraft's first image—a black and white one—from 69,000 miles away on Friday, Sept. 22. NavCam 1 acts as a part of OSIRIS-REx's guidance, navigation and control system; it will be used to determine the spacecraft's position by tracking landmarks on Bennu in the future.

Like any parents waiting to hear from their grown up children, the team of scientists spent Friday evening huddled around their monitors, eagerly waiting for images from the spacecraft to arrive. After a downlink process that seemed to take forever, one team member finally pulled it up on her laptop.

"We all dove across the room, and were fumbling for the HDMI cable and trying to jam it into the USB port, because it's dark in the room," said Dante Lauretta, principal investigator of the UA-led NASA mission. "And we're all so excited, and we can't get the thing plugged in, and we finally get it plugged in, and there we see our beautiful world, exactly as we planned it."

In that first image, cloud coverage obscures much of the Pacific Ocean, but Hurricanes Maria and Jose were clearly visible (in the upper-right area of the image), and the team was struck with the impact of the moment.

MapCam captured a color composite a few hours after the EGA from 170,000 kilometers (or 106,000 miles) away from the earth. It's largely of the Pacific Ocean, but you can see Australia in the lower left and Baja California in the upper right.

Lauretta said the photo represents one of his favorite new angles of the earth.

"What if we were an alien species and we sent a flyby spacecraft to the earth and they took this picture?" he asked "It really looks like it is an ocean world... It is a nice reminder of how beautiful and important the oceans are, and our planet is."

The black marks at the top of the photo—the OSIRIS REx team calls them "icicles"—are the result of a camera designed to take pictures of a very dark (darker than coal) asteroid trying to take pictures of a very bright earth. So OSIRIS-REx had to take the images as quickly as possible, which led to a few minor readout issues.

While, as any mom or dad will tell you, parenting can be an anxiety-inducing experience, it's also fun. In a Reddit AMA conducted by some of the team members it was confirmed by Joshua Nelson. Osiris-REx senior research scientist, that, in honor of the "rex" part of the spacecraft's name, "some dinosaur-related content did make its way onboard the spacecraft in an official capacity."

In the coming year, the team will be busy with a deep space maneuver to get the spacecraft on track for the rendezvous with Bennu, potential trajectory correction maneuvers (or TCMS) and two checkout and calibration activities to make sure everything's up to snuff. For now, they seem pretty confident.

"The spacecraft and the scientific instruments are performing in an outstanding fashion," Lauretta said. "In fact, the performance of the scientific instruments are exceeding our expectations, so this is getting us very, very excited for the encounter with Bennu."

Lauretta described Friday and Saturday as the second most exciting days of the mission so far—besides, of course, the day of the launch. After all, team members agreed, there's nothing like watching your baby grow up and do everything it was meant to do.

"It felt like I was actually in space and I was looking at that image," Lauretta said. "Because OSIRIS REx is us. We built it, and we own it and we really feel like it's a projection of ourselves that's out there exploring the solar system."

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