OSIRIS-REx's Spacecraft, Up Close and Personal
The UA's Dante Lauretta has been on a lengthy mission to design, build and launch a spacecraft to a near-Earth asteroid to collect a sample and return that sample to Earth.
LITTLETON, Colo. — For a dozen years, Dante Lauretta has flown to and from his home in Tucson to Littleton, Colorado. Now, on a snowy spring morning at Lockheed Martin’s sprawling Colorado compound, Lauretta is talking with a group of visitors about the impetus behind his frequent trips here.
He and his colleagues from around the world have been on a years-long mission to design, build and send a spacecraft to a near-Earth asteroid to collect a sample of that asteroid and return it to Earth for analysis. The mission’s aim would be to better understand asteroids — and the origins of the solar system.
And so was born OSIRIS-REx. The final opportunity for outsiders to see and photograph the mission's 9-square-meter spacecraft before its scheduled Sept. 8 launch came Friday in a six-hour media gathering hosted by NASA and Lockheed Martin. During a tour of Lockheed's facilities, reporters and social-media representatives were able to observe the spacecraft receiving its finishing touches. It will be transported by an Air Force C-17 cargo plane to Cape Canaveral, Florida, on May 20.
In addition to Lauretta, the group heard from Jason Dworkin, a NASA scientist; Richard Kuhns, Lockheed program manager for OSIRIS-REx; and Scott Messer, a program manager for United Launch Alliance.
The spacecraft for OSIRIS-REx — the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer — must pick up a pristine sample of an asteroid’s regolith, the loose soil and rocky material found on its surface.
"I’m really interested in the role these bodies have played or potentially play in the origin of life on Earth and the establishment of the habitability of our planet," says Lauretta, professor of planetary science and cosmochemistry at the University of Arizona Lunar and Planetary Laboratory and principal investigator for OSIRIS-REx.
"We’re really going back 4.5 billion years in history," he says. "We’re getting rocks that record the processes that were taking place right at the dawn of our solar system, when the planets were being born and the materials that would go into those planets were being formed.”
The spacecraft was designed and built at Lockheed Martin in Littleton, and within days scientists and technicians will be wrapping up the testing phase there.
To capture a sample of the regolith, the spacecraft will hover over a carefully chosen area on the asteroid’s surface and then "will be sent down at a very slow and gentle" 10 centimeters per second to make five seconds of contact with the asteroid’s surface to vacuum up the regolith, Lauretta says.
The precise maneuvering of the spaceship around the asteroid — or proximity operations capabilities, as it is known — was one of the greatest challenges involved in developing OSIRIS-REx.
"That’s a real important capability for any mission that’s going to interact with asteroids in the future," Lauretta says.
The asteroid involved in the mission is not just any old asteroid.
This one is known as Bennu, one of more than 700,000 in our solar system. It was chosen for many reasons, but chiefly because it’s one of the most accessible carbonaceous asteroids in our solar system and one of the most well-characterized ones. Scientists have a good read on the radar data and telescopic data that tell about its orbit and composition.
"When you know a lot about an object, it really helps you plan the mission," Lauretta says.
Data show that Bennu, provisionally known as 1999 RQ36, has a polar diameter of 508 meters and mean diameter of 492 meters. It also has a spinning-top shape; that is, it sports a bulge along its equator, a common feature among near-Earth asteroids.
"What we think this means is that this is a rubble-pile object," Lauretta says.
That means Bennu is probably made out of many boulders tens to hundreds of meters across.
"(The boulders) are loose, and they’re responding to the forces of the asteroid spinning, and material is migrating from the pole of the asteroid and accumulating at the equator and building up a ridge," Lauretta says. "That’s the theory. The good news is that we’re going to get out there and take a good look at the asteroid, and we’re going to test that theory, and we’re going to try and figure out why so many asteroids have that spinning-top shape."
No matter the reason, Bennu is in an unstable orbit, which means it probably won’t last more than 10 million years before it collides with Earth or another planet, or falls into the sun, Lauretta says.
Which is of concern to Lauretta and other scientists. In fact, Bennu is considered a potentially hazardous object and has a relatively high probability of impacting the Earth. So scientists are interested in understanding how asteroids’ orbits evolve.
Key to that evolution is something known as the Yarkovsky effect.
"Which is simply that an asteroid receives energy from the sun, turns that energy into heat, and as it rotates into the afternoon throws that energy back into space as thermal energy, and that acts like a thruster and changes the orbit of the asteroid slowly but surely over time," Lauretta says. "If you want to know where an asteroid is going to be in the future, particularly in our future, then you want to know about the Yarkovsky effect."
Likewise, if you want to know what an asteroid is made of, take a look at its spectroscopic data.
"With spectroscopy, we look at how asteroids reflect light and how they emit light," Lauretta says. "That tells us something about the temperature on the surface and something about the composition, especially the minerals that make up the surface of the asteroids.
"We have samples of (asteroids) on Earth in the form of meteorites. But we have a really hard time linking the spectral properties of the meteorite with those of an asteroid so that we can say what the distribution of compounds in our solar system is.”
That's why getting a pristine sample of the regolith is imperative.
In addition to a touch-and-go sample acquisition mechanism and a sample return capsule, the spacecraft will carry a laser altimeter; a suite of cameras to which the UA contributed; spectrometers; and lidar, which is similar to radar, using light instead of radio waves to measure distance.
"I never dreamed I’d be in charge of a program of this magnitude and this significance and this much fun," Lauretta says. "I’m anxious to get through the launch phase and into space and change our mode of operation, because we’ve been building this thing and designing it for so long.
"Getting to fly it is going to be a new and exciting challenge."
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