The next planetary mission in NASA’s New Frontiers program, the Near-Earth Asteroid sample return Origins Spectral Interpretation Resource Identification Security Regolith Explorer, or OSIRIS-REx for short, has passed a major milestone on the road toward its planned launch in September 2016. Earlier this month, the mission successfully completed its Critical Design Review, which signals the transition from the design to the construction stage.
Despite being relatively small in size, asteroids are of high scientific importance. Being composed of the primordial, left-over material from the formation of the Solar System, their study could offer scientists significant insights about the conditions and processes that gave rise to the Sun’s planetary family and possibly even of life on Earth. In addition, a detailed close-up study of asteroids would provide us with a better understanding of the potential threat that these minor Solar System bodies pose to our planet.
Aiming to answer these fundamental questions, NASA selected OSIRIS-REx in 2011 as the next mission in the space agency’s New Frontiers program of medium-class robotic science missions, whose budget doesn’t exceed a cost cap of $800 million, excluding launch costs. OSIRIS-REx is the third mission under the New Frontiers program, following the New Horizons mission, which is currently on its way to Pluto, and Juno, which is scheduled to arrive on Jupiter in 2016. Being selected from a list of such notable mission proposals like the Venus In Situ Explorer and the Lunar South Pole-Aitken Basin Sample Return, OSIRIS-REx will be the first U.S. mission to collect samples from an asteroid and return them to Earth for analysis. Its target, the 546-meter wide 101955 Bennu (formerly known as 1999 RQ36), is a carbonaceous asteroid, which is thought to be rich in primordial organic compounds that were left over from the formation of the Solar System. Scientists believe that these types of asteroids may have played a role in seeding the early Earth with the building blocks of life. “The primary objective of OSIRIS-REx is to return pristine carbonaceous material from the early Solar System,” wrote Dante Lauretta, the mission’s Principal Investigator from the University of Arizona, Tucson, during a recent “Ask Me Anything” session on Reddit. “Spectral analysis of Bennu suggests that it is similar on composition to the very rare CI and CM carbonaceous chondrite meteorites. These rocks are rich in organic compounds and water-bearing minerals like clays. We hope to find organic molecules that may have led to the origin of life on Earth and inform the likelihood that life may have originated elsewhere in our Solar System.”
Although the Japan Aerospace Exploration Agency, or JAXA, was the first to achieve a similar feat with the successful sampling of asteroid 25143 Itokawa with the Hayabusa space probe in 2005, OSIRIS-REx will nevertheless be able to return a sample of hopefully up to 2 kg of asteroid material, compared to the approximately 1,500 microscopic grains, no bigger than 10 micrometers each, that were gathered by Hayabusa. In addition, the asteroid sampled by the Japanese space probe was of an entirely different composition, mostly consisting of iron and magnesium silicates. OSIRIS-REx will be the first mission to offer an insight into the asteroids that most interest astrobiologists, possibly uncovering some of the mysteries of the origin of life on Earth.
The mission, which is a collaborative effort between NASA, the Canadian Space Agency, Lockheed Martin Space Systems, and the University of Arizona, recently ticked off another milestone in its development phase, with the successful completion of its Critical Design Review, or CDR, on April 10. “This is the final step for a NASA mission to go from paper to product,” says Gordon Johnston, the mission’s Program Executive at NASA’s Headquarters, in Washington, D.C. “This confirms that the final design is ready to start the build-up towards launch.” The completion of a mission’s CDR signifies the progression from the design phase toward construction. In the case of OSIRIS-REx, the 10-day review process confirmed that the mission remained on track to meet its targeted launch date in September 2016. “Successfully passing mission CDR is a major accomplishment, but the hard part is still in front of us — building, integrating and testing the flight system in support of a tight planetary launch window,” says Mike Donnelly, OSIRIS-REx Project Manager at NASA’s Goddard Space Flight Center in Greenbelt, Md.
Following a successful launch in 2016 atop an Atlas V 441 rocket, OSIRIS-REx will spend the next two years of its mission cruising through interplanetary space, prior to its rendezvous with Bennu in 2018. Once there, the spacecraft will commence a reconnaissance of the asteroid from a distance of 3 miles (5 km), lasting 505 days. During this time, OSIRIS-REx will acquire high-resolution topography maps and high-definition imaging of the asteroid’s surface, while conducting a series of detailed spectral measurements for determining its mineral and organics composition in the process. Having selected the best sampling site based on the gathered data at the end of the reconnaissance phase of the mission, the spacecraft will then initiate its closest approach to the asteroid, flying as close as 25 meters above its surface, while extending its robotic arm to collect samples and store them into its sampling return system. Having completed its primary science objective, OSIRIS-REx will then begin its journey back toward Earth in May 2021 for a scheduled parachuted landing at Utah’s Test and Training Range in 2023, similar to that of NASA’s Stardust spacecraft, which returned the first ever samples of comet Wild 2 in 2006.
One of the science goals of the mission will be to accurately measure the Yarkovsky effect acting on Bennu. This effect, in essence, constitutes a gentle “push” on the body of the asteroid, resulting from the Sun’s light hitting its surface. Although the kinetic energy of every single photon hitting the asteroid is miniscule, the effect nevertheless builds up over time, helping to disrupt and ultimately alter the asteroid’s orbit. In Bennu’s case this is of great importance, since calculations of its orbit have shown that the 546-meter asteroid has a one in 2,700 chance of hitting the Earth, during a series of eight close passages to our planet in the late 2100s. “We now know where Bennu has been and where she is headed between 1654 and 2135,” writes Lauretta in his blog. “In 2135 Bennu will pass 300,000 km (186,000 miles) over the surface of the Earth and be closer than the Moon. We don’t know enough about Bennu to accurately predict what will happen to her orbit as a result of this encounter. Beyond 2135, our calculations are statistical in nature. We do know that Bennu has a high probability (~1 in 3,000 chance) of impacting the Earth soon after this, sometime in the 2175 – 2196 time frame.” Bennu is a member of the potentially hazardous Apollo family of Near-Earth Objects, whose orbits intersect that of Earth’s. It completes one orbit around the Sun every 437 days, at a distance ranging between 0.8 and 1.3 Astronomical Units (1 AU is the mean distance between the Earth and the Sun, approximately 150 million km). The detailed observations that OSIRIS-REx will help to gather will allow scientists to better refine Bennu’s orbit and more accurately assess future impact probabilities. “The Yarkovsky force [on Bennu] at its peak, when the asteroid is nearest the Sun, is only about a half ounce – about the weight of three grapes on Earth,” says Michael C. Nolan, a staff scientist at the Arecibo Observatory in Puerto Rico, who has made detailed radar observations of Bennu, studying its orbit. “Meanwhile, the mass of the asteroid is estimated to be about 68 million tons. You need extremely precise measurements over a fairly long time span to see something so slight acting on something so huge.”
The spacecraft will meet its mission objectives with the help of a science payload suite consisting of six instruments:
- The OSIRIS-REx Laser Altimeter, or OLA, a remote-sensing instrument for creating high-resolution topographical maps of the asteroid’s surface.
- The OSIRIS-REx Visible and IR Spectrometer, or OVIRS, for determining the asteroid’s mineral and organics composition.
- The OSIRIS-REx Thermal Emission Spectrometer, or OTES, for determining the asteroid’s mineral and organics composition in conjuction with OVIRS and for determining the asteroid’s thermal emission profile.
- The OSIRIS-REx Camera Suite, or OCAMS, consisting of a set of three cameras for providing high-definition imaging.
- The Regolith X-ray Imaging Spectrometer, or REXIS, an X-ray telescope sensitive at soft X-ray wavelengths between 0.3 and 7.5 keV, for studying the effect of the solar wind and solar x-ray radiation on the asteroid’s surface.
- The Touch-And-Go Sample Acquisition Mechanism, or TAGSAM, the sample return system responsible for collecting and storing up to 2 kg of asteroid samples.
Video Credit: NASA/Goddard Space Flight Center
With the CDR now successfully behind it, the spacecraft’s various components will start taking shape at Lockheed Martin Space Systems in Denver, Colo., with final assembly not scheduled to occur before May 2015, pending a successful System Integration Review. “There is a lot of work to do before our spacecraft begins its journey, and we have to be very disciplined to get everything done in time,” says Mike Donnelly, OSIRIS-REx Project Manager at NASA’s Goddard Space Flight Center.
“Osiris was formed from pieces scattered across ancient Egypt, where he awoke as the bringer of life and ruler of the underworld,” says Lauretta. “Our spacecraft has a similar story — it will be consisted of components fabricated in locations around the world, that once together, will allow us to connect with a Near-Earth Object that is an accessible remnant from the formation of our Solar System.”
Taking a cue from its mythological namesake, one of the central themes of OSIRIS-REx’s story will be the study of 101955 Bennu as a potential bringer of both life and death. That might ultimately prove to be one of the most important scientific studies of our time.
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