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  1. X Marks the Spot: NASA Selects Site for Asteroid Sample Collection

    December 12, 2019 -

    After a year scoping out asteroid Bennu’s boulder-scattered surface, the team leading NASA’s first asteroid sample return mission has officially selected a sample collection site.

    This image shows sample site Nightingale, OSIRIS-REx’s primary sample collection site on asteroid Bennu. The image is overlaid with a graphic of the OSIRIS-REx spacecraft to illustrate the scale of the site. Credit: NASA/Goddard/University of Arizona

    The Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-Rex) mission team concluded a site designated “Nightingale” – located in a crater high in Bennu’s northern hemisphere – is the best spot for the OSIRIS-REx spacecraft to snag its sample.

    The OSIRIS-REx team spent the past several months evaluating close-range data from four candidate sites in order to identify the best option for the sample collection. The candidate sites – dubbed Sandpiper, Osprey, Kingfisher, and Nightingale – were chosen for investigation because, of all the potential sampling regions on Bennu, these areas pose the fewest hazards to the spacecraft’s safety while still providing the opportunity for great samples to be gathered.

    “After thoroughly evaluating all four candidate sites, we made our final decision based on which site has the greatest amount of fine-grained material and how easily the spacecraft can access that material while keeping the spacecraft safe,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona in Tucson. “Of the four candidates, site Nightingale best meets these criteria and, ultimately, best ensures mission success.”

    Site Nightingale is located in a northern crater 460 ft (140 m) wide. Nightingale’s regolith – or rocky surface material – is dark, and images show that the crater is relatively smooth. Because it is located so far north, temperatures in the region are lower than elsewhere on the asteroid and the surface material is well-preserved. The crater also is thought to be relatively young, and the regolith is freshly exposed. This means the site would likely allow for a pristine sample of the asteroid, giving the team insight into Bennu’s history.

    Although Nightingale ranks the highest of any location on Bennu, the site still poses challenges for sample collection. The original mission plan envisioned a sample site with a diameter of 164 feet (50 m). While the crater that hosts Nightingale is larger than that, the area safe enough for the spacecraft to touch is much smaller – approximately 52 ft (16 m) in diameter, resulting in a site that is only about one-tenth the size of what was originally envisioned This means the spacecraft has to very accurately target Bennu’s surface. Nightingale also has a building-size boulder situated on the crater’s eastern rim, which could pose a hazard to the spacecraft while backing away after contacting the site.

    This image shows sample site Osprey, OSIRIS-REx’s backup sample collection site on asteroid Bennu. The image is overlaid with a graphic of the OSIRIS-REx spacecraft to illustrate the scale of the site. Credit:

    The mission also selected site Osprey as a backup sample collection site. The spacecraft has the capability to perform multiple sampling attempts, but any significant disturbance to Nightingale’s surface would make it difficult to collect a sample from that area on a later attempt, making a backup site necessary. The spacecraft is designed to autonomously “wave-off” from the site if its predicted position is too close to a hazardous area. During this maneuver, the exhaust plumes from the spacecraft’s thrusters could potentially disturb the surface of the site, due to the asteroid’s microgravity environment. In any situation where a follow-on attempt at Nightingale is not possible, the team will try to collect a sample from site Osprey instead.

    “Bennu has challenged OSIRIS-REx with extraordinarily rugged terrain,” said Rich Burns, OSIRIS-REx project manager at NASA’s Goddard Space Flight Center. “The team has adapted by employing a more accurate, though more complex, optical navigation technique to be able to get into these small areas. We’ll also arm OSIRIS-REx with the capability to recognize if it is on course to touch a hazard within or adjacent to the site and wave-off before that happens.”

    With the selection of final primary and backup sites, the mission team will undertake further reconnaissance flights over Nightingale and Osprey, beginning in January and continuing through the spring. Once these flyovers are complete, the spacecraft will begin rehearsals for its “touch-and-go” sample collection event, which is scheduled for August. The spacecraft will depart Bennu in 2021 and is scheduled to return to Earth in September 2023.

    NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and provides flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

    This flat projection mosaic of asteroid Bennu shows the relative locations of the primary and backup sample collection sites on the asteroid: Nightingale and Osprey. NASA’s OSIRIS-REx spacecraft is scheduled to collect a sample in summer 2020. Credit: NASA/Goddard/University of Arizona

     

  2. NASA’s OSIRIS-REx Mission Explains Bennu’s Mysterious Particle Events

    December 4, 2019 -

    Shortly after NASA’s OSIRIS-REx spacecraft arrived at asteroid Bennu, an unexpected discovery by the mission’s science team revealed that the asteroid could be active, or consistently discharging particles into space. The ongoing examination of Bennu – and its sample that will eventually be returned to Earth – could potentially shed light on why this intriguing phenomenon is occurring.

    This view of asteroid Bennu ejecting particles from its surface on January 6 was created by combining two images taken by the NavCam 1 imager onboard NASA’s OSIRIS-REx spacecraft: a short exposure image (1.4 ms), which shows the asteroid clearly, and a long exposure image (5 sec), which shows the particles clearly. Credit: NASA/Goddard/University of Arizona/Lockheed Martin

    The OSIRIS-REx team first observed a particle ejection event in images captured by the spacecraft’s navigation cameras taken on Jan. 6, just a week after the spacecraft entered its first orbit around Bennu. At first glance, the particles appeared to be stars behind the asteroid, but on closer examination, the team realized that the asteroid was ejecting material from its surface. After concluding that these particles did not compromise the spacecraft’s safety, the mission began dedicated observations in order to fully document the activity.

    “Among Bennu’s many surprises, the particle ejections sparked our curiosity, and we’ve spent the last several months investigating this mystery,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “This is a great opportunity to expand our knowledge of how asteroids behave.”

    After studying the results of the observations, the mission team released their findings in a Science paper published Dec. 6. The team observed the three largest particle ejection events on Jan. 6 and 19, and Feb. 11, and concluded that the events originated from different locations on Bennu’s surface. The first event originated in the southern hemisphere, and the second and third events occurred near the equator. All three events took place in the late afternoon on Bennu.

    The team found that, after ejection from the asteroid’s surface, the particles either briefly orbited Bennu and fell back to its surface or escaped from Bennu into space. The observed particles traveled up to 10 feet (3 meters) per second, and measured from smaller than an inch up to 4 inches (10 cm) in size. Approximately 200 particles were observed during the largest event, which took place on Jan. 6.

    The team investigated a wide variety of possible mechanisms that may have caused the ejection events, and narrowed the list to three candidates: meteoroid impacts, thermal stress fracturing, and released of water vapor.

    Meteoroid impacts are common in the deep space neighborhood of Bennu, and it is possible that these small fragments of space rock could be hitting Bennu where OSIRIS-REx is not observing it, shaking loose particles with the momentum of their impact.

    The team also determined that thermal fracturing is another reasonable explanation. Bennu’s surface temperatures vary drastically over its 4.3-hour rotation period.

    This animation illustrates the modeled trajectories of particles that were ejected from Bennu’s surface on January 19. After ejecting from the asteroid’s surface, the particles either briefly orbited Bennu and fell back to its surface or escaped away from Bennu and into space. Credit: NASA/Goddard/University of Arizona/Lauretta & Hergenrother et al., Science 10.1126

    Although it is extremely cold during the night hours, the asteroid’s surface warms significantly in the mid-afternoon, which is when the three major events occurred. As a result of this temperature change, rocks may begin to crack and break down, and eventually particles could be ejected from the surface. This cycle is known as thermal stress fracturing.

    Water release may also explain the asteroid’s activity. When Bennu’s water-locked clays are heated, the water could begin to release and create pressure. It is possible that as pressure builds in cracks and pores in boulders where absorbed water is released, the surface could become agitated, causing particles to erupt.

    But nature does not always allow for simple explanations. “It could be that more than one of these possible mechanisms are at play,” said Steve Chesley, an author on the paper and Senior Research Scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “For example, thermal fracturing could be chopping the surface material into small pieces, making it far easier for meteoroid impacts to launch pebbles into space.”

    If thermal fracturing, meteoroid impacts, or both, are in fact the causes of these ejection events, then this phenomenon is likely happening on all small asteroids, as they all experience these mechanisms. However, if water release is the cause of these ejection events, then this phenomenon would be specific to asteroids that contain water-bearing minerals, like Bennu.

    Bennu’s activity presents larger opportunities once a sample is collected and returned to Earth for study. Many of the ejected particles are small enough to be collected by the spacecraft’s sampling mechanism, meaning that the returned sample may possibly contain some material that was ejected and returned to Bennu’s surface. Determining that a particular particle had been ejected and returned to Bennu might be a scientific feat similar to finding a needle in a haystack. The material returned to Earth from Bennu, however, will almost certainly increase our understanding of asteroids and the ways they are both different and similar, even as the particle ejection phenomenon continues to be a mystery whose clues we’ll also return home with in the form of data and further material for study.

    Sample collection is scheduled for summer 2020, and the sample will be delivered to Earth in September 2023.

    NASA’s Goddard Space Flight Center in Greenbelt, Maryland provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

  3. NASA’s OSIRIS-REx in the Midst of Site Selection

    By Brittany Enos

    December 4, 2019 -

    NASA’s OSIRIS-REx mission is just days away from selecting the site where the spacecraft will snag a sample from asteroid Bennu. After a lengthy and challenging process, the team is finally ready to down-select from the four candidate sites to a primary and backup site.

    OSIRIS-REx is NASA’s first asteroid sample return mission, so this decision of a sample collection site is key for asteroid operations and mission success.

    After selecting the four candidate sample sites – Sandpiper, Osprey, Kingfisher, and Nightingale – in July, the mission completed its Reconnaissance A phase. During Recon A, the OSIRIS-REx spacecraft performed a month-long series of four flyovers – one over each potential sample collection site. This mission phase provided the team with high-resolution imagery in order to thoroughly examine the sampleability (fine-grained material), topography, albedo, and color of each site. The data collected from these high-altitude flyovers is central for determining which site is best-suited for sample collection.

    These are images of the four candidate sample collection sites on asteroid Bennu: Nightingale, Kingfisher, Osprey and Sandpiper. One of these four sites will ultimately be the location on which NASA’s OSIRIS-REx spacecraft will touch down to collect a sample. Credit: NASA/Goddard/University of Arizona

    While the mission is one step closer to collecting a sample, Recon A observations have revealed that even the best candidate sites on Bennu pose significant challenges to sample collection, and the choice before the site selection board is not an easy one.

    “Sample site selection really is a comprehensive activity. It requires that we look at many different types of data in many different ways to ensure the selected site is the best choice in terms of spacecraft safety, presence of sampleable material, and science value,” said Heather Enos, OSIRIS-REx deputy principal investigator at the University of Arizona, Tucson, and chair of the sample site selection board. “Our team is incredibly innovative and integrated, which is what makes the selection process work.”

    The most recent images show that while there is fine-grained material (smaller than 2.5 cm in diameter), much of it may not be easily accessible. The mission was originally designed for a beach-like surface, with “ponds” of sandy material, not for Bennu’s rugged terrain. In reality the potential sample sites are not large, clear areas, but rather small spaces surrounded by large boulders, so navigating the spacecraft in and out of the sites will require a bit more fine-tuning than originally planned.

    Starting in Bennu’s southern hemisphere, site Sandpiper was the first flyover of the Recon A mission phase. Sandpiper is one of the “safer” sites because it is located in a relatively flat area, making it easier for the spacecraft to navigate in and out. The most recent images show that fine-grained material is present, but the sandy regolith is trapped between larger rocks, which makes it difficult for the sampling mechanism to operate.

    Site Osprey was the second site observed during Recon A. This site was originally chosen based on its strong spectral signature of carbon-rich material and because of a dark patch in the center of the crater, which was thought to possibly be fine-grained material. However, the latest high-resolution imagery of Osprey suggests that the site is scattered with material that may be too large to ingest for the sampling mechanism.

    Site Kingfisher was selected because it is located in a small crater – meaning that it may be a relatively young feature compared to Bennu’s larger craters (such as the one in which Sandpiper is located). Younger craters generally hold fresher, minimally-altered material. High-resolution imagery captured during the Recon A flyover revealed that while the original crater may be too rocky, a neighboring crater appears to contain fine-grained material.

    Recon A concluded with a flyover of site Nightingale. Images show that the crater holds a good amount of unobstructed fine-grained material. However, while the sampleability of the site ranks high, Nightingale is located far to the north where the lighting conditions create additional challenges for spacecraft navigation. There is also a building-size boulder situated on the crater’s eastern rim, which could be a hazard to the spacecraft when backing away after contacting the site.

    Bennu has also made it a challenge for the mission to identify a site that won’t trigger the spacecraft’s safety mechanisms. During Recon A, the team began cataloguing Bennu’s surface features to create maps for the Natural Feature Tracking (NFT) autonomous navigation system. During the sample collection event, the spacecraft will use NFT to navigate to the asteroid’s surface by comparing the onboard image catalog to the navigation images it will take during descent. In response to Bennu’s extremely rocky surface, the NFT system has been augmented with a new safety feature, which instructs it to wave-off the sampling attempt and back away if it determines the point of contact is near a potentially hazardous surface feature. With Bennu’s building-sized boulders and small target sites, the team realizes that there is a possibility that the spacecraft will wave-off the first time it descends to collect a sample.

    This flat projection mosaic of asteroid Bennu shows the relative locations of the four candidate sample collection sites on the asteroid: Nightingale, Kingfisher, Osprey and Sandpiper. NASA’s OSIRIS-REx spacecraft is scheduled to touch down on one of these four sites to collect a sample in summer 2020. Credit: NASA/Goddard/University of Arizona

    “Bennu’s challenges are an inherent part of this mission, and the OSIRIS-REx team has responded by developing robust measures to overcome them,” said Mike Moreau, OSIRIS-REx deputy project manager at Goddard. “If the spacecraft executes a wave-off while attempting to collect a sample, that simply means that both the team and the spacecraft have done their jobs to ensure the spacecraft can fly another day. The success of the mission is our first priority.”

    Whichever site wins the race, the OSIRIS-REx mission team is ready for whatever new challenges Bennu may bring. Next spring, the team will undertake further reconnaissance flights over the primary and backup sample sites, and will then start spacecraft rehearsals for touchdown. Sample collection is scheduled for summer 2020, and the sample will return to Earth in September 2023.

    NASA’s Goddard Space Flight Center in Greenbelt, Maryland provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

  4. Flyover of the Candidate Sample Sites

    August 29, 2019 -

    This animated flyover of each of the four candidate sample collection sites on asteroid Bennu, selected by NASA’s OSIRIS-REx asteroid sample return mission, was produced using close-range data from the OSIRIS-REx Laser Altimeter (OLA), an instrument contributed by the Canadian Space Agency. It illustrates the location of each site on Bennu, the topography of each site, and the potential sampling regions that the spacecraft will target, which are 10 meters in diameter.

    The laser altimeter on NASA’s OSIRIS-REx spacecraft has produced the highest resolution topographic maps ever of any planetary body. These maps of asteroid Bennu provide three-dimensional, detailed views of the OSIRIS-REx mission’s final four candidate sample collection sites, which are designated Nightingale, Kingfisher, Osprey and Sandpiper.

    OLAis equipped with two lasers and uses a steerable mirror to rapidly scan the asteroid’s surface to produce detailed images of boulders, craters and other geological features. OLA collected scans using its low-energy laser transmitter (LELT) during the spacecraft’s low altitude orbit– approximately 700 meters above Bennu’s surface. The LELT is designed to fire 10,000 light pulses per second at the asteroid, and three-dimensional terrain models of the four sites were produced using these light pulses.

    High-resolution maps of the four potential sample sites will allow the OSIRIS-REx team to assess the safety and accessibility of each region, locate landmarks that will help the spacecraft navigate during sample collection and identify areas of fine-grained material compatible with OSIRIS-REx’s sampling mechanism. These maps will be crucial for selecting the final two sample collection sites in December.

    OLA’s LELT will continue to gather Bennu data in tandem with the other instruments on the OSIRIS-REx spacecraft. The final selection of a primary and backup sample collection site will be announced in December 2019, and sample collection is scheduled for the latter half of 2020.

    Credit: NASA/Goddard/University of Arizona/CSA/York University/MDA

  5. NASA Mission Selects Final Four Site Candidates for Asteroid Sample Return

    August 12, 2019 -

    After months grappling with the rugged reality of asteroid Bennu’s surface, the team leading NASA’s first asteroid sample return mission has selected four potential sites for the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft to “tag” its cosmic dance partner.

    Since its arrival in December 2018, the OSIRIS-REx spacecraft has mapped the entire asteroid in order to identify the safest and most accessible spots for the spacecraft to collect a sample. These four sites now will be studied in further detail in order to select the final two sites – a primary and backup – in December.

    The final four candidate sample collection sites on asteroid Bennu are designated Nightingale, Kingfisher, Osprey and Sandpiper. The final site will be selected in December 2019. Credit: NASA/Goddard/University of Arizona/CSA/York/MDA

    The team originally had planned to choose the final two sites by this point in the mission. Initial analysis of Earth-based observations suggested the asteroid’s surface likely contains large “ponds” of fine-grain material. The spacecraft’s earliest images, however, revealed Bennu has an especially rocky terrain. Since then, the asteroid’s boulder-filled topography has created a challenge for the team to identify safe areas containing sampleable material, which must be fine enough – less than 1 inch (2.5 cm) in diameter – for the spacecraft’s sampling mechanism to ingest it.

    “We knew that Bennu would surprise us, so we came prepared for whatever we might find,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “As with any mission of exploration, dealing with the unknown requires flexibility, resources and ingenuity. The OSIRIS-REx team has demonstrated these essential traits for overcoming the unexpected throughout the Bennu encounter.”

    The original mission schedule intentionally included more than 300 days of extra time during asteroid operations to address such unexpected challenges. In a demonstration of its flexibility and ingenuity in response to Bennu’s surprises, the mission team is adapting its site selection process. Instead of down-selecting to the final two sites this summer, the mission will spend an additional four months studying the four candidate sites in detail, with a particular focus on identifying regions of fine-grain, sampleable material from upcoming, high-resolution observations of each site. The boulder maps that citizen science counters helped create through observations earlier this year were used as one of many pieces of data considered when assessing each site’s safety. The data collected will be key to selecting the final two sites best suited for sample collection.

    In order to further adapt to Bennu’s ruggedness, the OSIRIS-REx team has made other adjustments to its sample site identification process. The original mission plan envisioned a sample site with a radius of 82 feet (25 m). Boulder-free sites of that size don’t exist on Bennu, so the team has instead identified sites ranging from 16 to 33 feet (5 to 10 m) in radius. In order for the spacecraft to accurately target a smaller site, the team reassessed the spacecraft’s operational capabilities to maximize its performance. The mission also has tightened its navigation requirements to guide the spacecraft to the asteroid’s surface, and developed a new sampling technique called “Bullseye TAG,” which uses images of the asteroid surface to navigate the spacecraft all the way to the actual surface with high accuracy. The mission’s performance so far has demonstrated the new standards are within its capabilities.

    “Although OSIRIS-REx was designed to collect a sample from an asteroid with a beach-like area, the extraordinary in-flight performance to date demonstrates that we will be able to meet the challenge that the rugged surface of Bennu presents,” said Rich Burns, OSIRIS-REx project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “That extraordinary performance encompasses not only the spacecraft and instruments, but also the team who continues to meet every challenge that Bennu throws at us.”

    The four candidate sample sites on Bennu are designated Nightingale, Kingfisher, Osprey, and Sandpiper – all birds native to Egypt. The naming theme complements the mission’s two other naming conventions – Egyptian deities (the asteroid and spacecraft) and mythological birds (surface features on Bennu).

    The final four candidate sample collection sites on asteroid Bennu are designated Nightingale, Kingfisher, Osprey and Sandpiper. Each circle has a 16.4 ft (5 m) radius. Credit: NASA/Goddard/University of Arizona

    The four sites are diverse in both geographic location and geological features. While the amount of sampleable material in each site has yet to be determined, all four sites have been evaluated thoroughly to ensure the spacecraft’s safety as it descends to, touches and collects a sample from the asteroid’s surface.

    Nightingale is the northern-most site, situated at 56 degrees north latitude on Bennu. There are multiple possible sampling regions in this site, which is set in a small crater encompassed by a larger crater 459 feet (140 m) in diameter. The site contains mostly fine-grain, dark material and has the lowest albedo, or reflection, and surface temperature of the four sites.

    Kingfisher is located in a small crater near Bennu’s equator at 11 degrees north latitude. The crater has a diameter of 26 feet (8 m) and is surrounded by boulders, although the site itself is free of large rocks. Among the four sites, Kingfisher has the strongest spectral signature for hydrated minerals.

    Osprey is set in a small crater, 66 feet (20 m) in diameter, which is also located in Bennu’s equatorial region at 11 degrees north latitude. There are several possible sampling regions within the site. The diversity of rock types in the surrounding area suggests that the regolith within Osprey may also be diverse. Osprey has the strongest spectral signature of carbon-rich material among the four sites.

    Sandpiper is located in Bennu’s southern hemisphere, at 47 degrees south latitude. The site is in a relatively flat area on the wall of a large crater 207 ft (63 m) in diameter. Hydrated minerals are also present, which indicates that Sandpiper may contain unmodified water-rich material.

    This fall, OSIRIS-REx will begin detailed analyses of the four candidate sites during the mission’s reconnaissance phase. During the first stage of this phase, the spacecraft will execute high passes over each of the four sites from a distance of 0.8 miles (1.29 km) to confirm they are safe and contain sampleable material. Closeup imaging also will map the features and landmarks required for the spacecraft’s autonomous navigation to the asteroid’s surface. The team will use the data from these passes to select the final primary and backup sample collection sites in December.

    The final four candidate sample collection sites shown on a map of asteroid Bennu. They are designated Nightingale, Kingfisher, Osprey and Sandpiper. Credit: NASA/Goddard/University of Arizona

    The second and third stages of reconnaissance will begin in early 2020 when the spacecraft will perform passes over the final two sites at lower altitudes and take even higher resolution observations of the surface to identify features, such as groupings of rocks that will be used to navigate to the surface for sample collection. OSIRIS-REx sample collection is scheduled for the latter half of 2020, and the spacecraft will return the asteroid samples to Earth on Sept. 24, 2023.

    Goddard provides overall mission management, systems engineering, and safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

    To explore the final four candidate sites in detail, click here.

  6. Asteroid Bennu’s Features To Be Named After Mythical Birds

    August 8, 2019 -

    Working with NASA’s OSIRIS-REx team, the International Astronomical Union’s Working Group for Planetary System Nomenclature (WGPSN) approved the theme “birds and bird-like creatures in mythology” for naming surface features on asteroid (101955) Bennu.

    This image shows boulder formations on asteroid Bennu’s surface. It was taken by the PolyCam camera on NASA’s OSIRIS-REx spacecraft on April 11, 2019 from a distance of 2.8 miles (4.5 km). Credit: NASA/Goddard/University of Arizona

    OSIRIS-REx is NASA’s first mission to bring a sample from an asteroid back to Earth. The OSIRIS-REx spacecraft has been mapping Bennu’s surface since its arrival on December 3rd, 2018, looking for a site from which to take a sample. Bennu is the smallest body in the Solar System to be orbited and surveyed by a spacecraft at close range.

    The named features on Bennu will include several terrain classification types that the IAU also approved for asteroid (162173) Ryugu’s surface features (currently being explored by the Japanese Space Agency’s Hayabusa2 spacecraft). These include craters, dorsa (peaks or ridges), fossae (grooves or trenches) and saxa (rocks and boulders). The last of these types – saxum – is a new feature classification that the IAU introduced earlier this year for small, rocky asteroids like Ryugu and Bennu. These surface features on Bennu will be named after mythological birds and bird-like creatures, complementing the mission’s existing naming theme, which is rooted in Egyptian mythology.

    The name OSIRIS-REx is an acronym for the mission’s major concepts and goals, which stands for Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer. The name also finds inspiration in the Egyptian myth of the god Osiris. In ancient Egyptian mythology, Osiris is associated with the afterlife, the underworld and rebirth. He granted all life, including sprouting vegetation and the fertile flooding of the Nile River. Similarly, the OSIRIS-REx mission seeks to understand the origin and process of life on Earth by studying Bennu’s carbon-rich regolith.

    Bennu was named in 2013 by a 9-year-old boy from North Carolina who won the Name that Asteroid! Competition, a collaboration between the mission, the Planetary Society, and the LINEAR asteroid survey that discovered Bennu. Michael Puzio won the contest by suggesting that the spacecraft’s Touch-and-Go Sample Mechanism (TAGSAM) arm and solar panels resemble the neck and wings in illustrations of Bennu, whom ancient Egyptians usually depicted as a gray heron. Bennu is the ancient Egyptian deity linked with the Sun, creation and rebirth — Puzio also noted that Bennu is the living symbol of Osiris. The myth of Bennu suits the asteroid itself, given that it is a primitive object that dates back to the creation of the Solar System. Themes of origins, rebirth and duality are all part of this asteroid’s story. Birds and bird-like creatures are also symbolic of rebirth, creation and origins in various ancient myths.

    The process of naming of Bennu’s surface and features will begin this summer. The OSIRIS-REx team is scheduled to begin detailed reconnaissance on candidate sample sites this fall. Sample collection is scheduled for summer 2020, and the sample will return to Earth in September 2023.

    NASA’s Goddard Space Flight Center in Greenbelt, Maryland provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

  7. NASA’s OSIRIS-REx Mission Breaks Another Orbit Record

    June 13, 2019 -

    On June 12, NASA’s OSIRIS-REx spacecraft performed another significant navigation maneuver—breaking its own world record for the closest orbit of a planetary body by a spacecraft.

    On Jun. 12, 2019, NASA’s OSIRIS-REx spacecraft went into orbit around asteroid Bennu for a second time — breaking its own record for the closest orbit of a planetary body by any spacecraft.

    The maneuver began the mission’s new phase, known as Orbital B, and placed the spacecraft in an orbit 680 meters (2,231 feet) above the surface of asteroid Bennu. The previous record—also set by the OSIRIS-REx spacecraft—was approximately 1.3 kilometers (0.8 miles) above the surface.

    Upon arrival at Bennu, the team observed particles ejecting into space from the asteroid’s surface. To better understand why this is occurring, the first two weeks of Orbital B will be devoted to observing these events by taking frequent images of the asteroid’s horizon. For the remaining five weeks, the spacecraft will map the entire asteroid using most of its onboard science instruments: the OSIRIS-REx Laser Altimeter (OLA) will produce a full terrain map; PolyCam will form a high-resolution, global image mosaic; and the OSIRIS-REx Thermal Emission Spectrometer (OTES) and the REgolith X-ray Imaging Spectrometer (REXIS) will produce global maps in the infrared and X-ray bands. All of these measurements are essential for selecting the best sample collection site on Bennu’s surface.

    OSIRIS-REx will remain in Orbital B until the second week of August, when it will transition to the slightly higher Orbital C for additional particle observations. During Orbital C, the spacecraft will be approximately 1.3 kilometers (0.8 miles) above the asteroid’s surface.

    The OSIRIS-REx team will also use data collected from Orbital B phase to assess the safety and sample-ability (the likelihood that a sample can be collected) of each potential sample collection site. The team will then choose four possible sample sites to be thoroughly evaluated this fall during the Reconnaissance phase of the mission. Data from the Reconnaissance phase will be used to evaluate the candidate sites for further down-selection, as well as provide the closeup imaging required to map the features and landmarks necessary for the spacecraft’s autonomous navigation to the asteroid’s surface.

    On June 12, 2019, NASA’s OSIRIS-REx spacecraft entered its second orbital phase around asteroid Bennu, called Orbital B, and broke its own world record for the closest orbit of a planetary body. The spacecraft moved into a circular orbit 0.4 miles (680 meters) above Bennu’s surface. The previous record was set by OSIRIS-REx on Dec. 31, 2018, when the spacecraft flew 0.8 miles (1.33 km) above the asteroid’s surface during Orbital A phase.

    Several safety requirements must be considered before sample collection. For instance, any candidate site must be clear enough of large rocks or boulders so that the spacecraft can navigate to the surface without encountering dangerous terrain. Additionally, to keep OSIRIS-REx upright during sample collection, the chosen site can’t be tilted too much compared to the sampling arm. Bennu’s unexpectedly rocky surface has made it more challenging than originally predicted to identify sites that meet both of these safety requirements. In response, the team is evaluating both spacecraft and navigation performance capabilities, which will likely enable greater precision guidance to target more confined sites.

    The OSIRIS-REx spacecraft is on a seven-year journey to study the asteroid Bennu and return a sample from its surface to Earth. This sample of a primitive asteroid will help scientists understand the formation of the Solar System over 4.5 billion years ago. Sample collection is scheduled for summer of 2020, and the spacecraft will deliver the sample to Earth in September 2023.

    NASA Goddard provides overall mission management, systems engineering, and safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

  8. NASA Invites Public to Help Asteroid Mission Choose Sample Site

    May 22, 2019 -

    Citizen scientists assemble! NASA’s OSIRIS-REx mission to the asteroid Bennu needs extra pairs of eyes to help choose its sample collection site on the asteroid – and to look for anything else that might be scientifically interesting.

    This image shows the wide variety of boulder shapes, sizes and compositions found on asteroid Bennu. It was taken by the PolyCam camera on NASA’s OSIRIS-REx spacecraft on March 28 from a distance of 2.1 miles (3.4 km). Credit: NASA/Goddard/University of Arizona

    The OSIRIS-REx spacecraft has been at Bennu since Dec. 3, 2018, mapping the asteroid in detail, while the mission team searches for a sample collection site that is safe, conducive to sample collection and worthy of closer study. One of the biggest challenges of this effort, which the team discovered after arriving at the asteroid five months ago, is that Bennu has an extremely rocky surface and each boulder presents a danger to the spacecraft’s safety. To expedite the sample selection process, the team is asking citizen scientist volunteers to develop a hazard map by counting boulders.

    “For the safety of the spacecraft, the mission team needs a comprehensive catalog of all the boulders near the potential sample collection sites, and I invite members of the public to assist the OSIRIS-REx mission team in accomplishing this essential task,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson.

    For this effort, NASA is partnering with CosmoQuest, a project run out of the Planetary Science Institute that supports citizen science initiatives. Volunteers will perform the same tasks that planetary scientists do – measuring Bennu’s boulders and mapping its rocks and craters – through the use of a simple web interface. They will also mark other scientifically interesting features on the asteroid for further investigation.

    The boulder mapping work involves a high degree of precision, but it is not difficult. The CosmoQuest mapping app requires a computer with a larger screen and a mouse or trackpad capable of making precise marks. To help volunteers get started, the CosmoQuest team provides an interactive tutorial, as well as additional user assistance through a Discord community and livestreaming sessions on Twitch.

    “We are very pleased and excited to make OSIRIS-REx images available for this important citizen science endeavor,” said Rich Burns, OSIRIS-REx project manager at NASA Goddard Space Flight Center. “Bennu has surprised us with an abundance of boulders. We ask for citizen scientists’ help to evaluate this rugged terrain so that we can keep our spacecraft safe during sample collection operations.”

    This image shows a view of asteroid Bennu’s surface in a region near the equator. It was taken by the PolyCam camera on NASA’s OSIRIS-REx spacecraft on March 21 from a distance of 2.2 miles (3.5 km). Credit: NASA/Goddard/University of Arizona

    Sample return isn’t new for NASA – this year, the agency is celebrating the 50th anniversary of the Apollo missions to the Moon, which allowed astronauts to bring back 842 pounds (382 kilograms) of rocks and lunar soil. Those samples helped scientists discover that the Moon has water locked in its rocks and even permanently frozen in craters. These findings and others inspired the agency to create the Artemis program to return humans to the Moon by 2024 and start preparing for human exploration on Mars.

    “The OSIRIS-REx mission will continue the Apollo legacy by giving scientists precious samples of an asteroid,” said Lori Glaze, director of the Planetary Science Division at NASA Headquarters in Washington. “These samples will help scientists discover the secrets of planetary formation and the origins of our planet Earth.”

    The Bennu mapping campaign continues through July 10, when the mission begins the sample site selection process. Once primary and secondary sites are selected, the spacecraft will begin closer reconnaissance to map the two sites to sub-centimeter resolution. The mission’s Touch-and-Go (TAG) sampling maneuver is scheduled for July 2020, and the spacecraft will return to Earth with its cargo in September 2023.

    Goddard provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

    To volunteer as a Bennu mapper, visit:

    Bennu.cosmoquest.org

  9. OSIRIS-REx Special Collection in Nature

    March 26, 2019 -

    When NASA’s OSIRIS-REx spacecraft arrived at asteroid Bennu on Dec. 3, 2018, it found a tiny world that in many respects was as the mission team had expected based on ground-based observations — but the team also found that Bennu held quite a few surprises, too. On March 19, 2019, Nature­ published a special collection of eight papers from the OSIRIS-REx mission team providing a first look at asteroid Bennu. The following provides the key findings published in those scientific papers. The full Nature collection may be accessed directly here.

    Global elevation map of asteroid Bennu. Credit: NASA/Goddard/University of Arizona

    Lauretta and DellaGiustina et al. “The unexpected surface of asteroid (101955) Bennu.” Nature.

    NASA’s OSIRIS-REx spacecraft recently arrived at Bennu, a primitive body that represents the objects that may have brought prebiotic molecules and volatiles such as water to Earth. Bennu is a low-albedo B-type asteroid that has been linked to organic-rich hydrated carbonaceous chondrites. Such meteorites are altered by ejection from their parent body and contaminated by atmospheric entry and terrestrial microbes. Therefore, the primary mission objective is to return a sample of Bennu to Earth that is pristine—that is, not affected by these processes. The OSIRIS-REx spacecraft carries a sophisticated suite of instruments to characterize Bennu’s global properties, support the selection of a sampling site and document that site at a sub-centimeter scale. Here we consider early OSIRIS-REx observations of Bennu to understand how the asteroid’s properties compare to pre-encounter expectations and to assess the prospects for sample return. The bulk composition of Bennu appears to be hydrated and volatile-rich, as expected. However, in contrast to pre-encounter modelling of Bennu’s thermal inertia and radar polarization ratios—which indicated a generally smooth surface covered by centimeter-scale particles—resolved imaging reveals an unexpected surficial diversity. The albedo, texture, particle size and roughness are beyond the spacecraft design specifications. On the basis of our pre-encounter knowledge, we developed a sampling strategy to target 50-meter-diameter patches of loose regolith with grain sizes smaller than two centimeters. We observe only a small number of apparently hazard-free regions, of the order of 5 to 20 meters in extent, the sampling of which poses a substantial challenge to mission success.

     

    Barnouin et al. “Shape of (101955) Bennu indicative of a rubble pile with internal stiffness.” Nature Geoscience.

    The shapes of asteroids reflect interplay between their interior properties and the processes responsible for their formation and evolution as they journey through the Solar System. Prior to the OSIRIS-REx mission, Earth-based radar imaging gave an overview of Bennu’s shape. Here we construct a high-resolution shape model from OSIRIS-REx images. We find that Bennu’s top-like shape, considerable macroporosity and prominent surface boulders suggest that it is a rubble pile. High-standing, north–south ridges that extend from pole to pole, many long grooves and surface mass wasting indicate some low levels of internal friction and/or cohesion. Our shape model indicates that, similar to other top-shaped asteroids, Bennu formed by reaccumulation and underwent past periods of fast spin, which led to its current shape. Today, Bennu might follow a different evolutionary pathway, with an interior stiffness that permits surface cracking and mass wasting.

     

    DellaGiustina and Emery et al. “Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis.” Nature Astronomy.

    Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASA’s OSIRIS-REx spacecraft, we show that asteroid Bennu’s surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennu’s moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. Our findings imply that ages of Bennu’s surface particles span from the disruption of the asteroid’s parent body (boulders) to recent in situ production (micrometer-scale particles).

     

    Hamilton et al. “Evidence for widespread hydrated minerals on asteroid (101955) Bennu.” Nature Astronomy.

    Early spectral data from the OSIRIS-REx mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid Bennu in the form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic chemistry to Earth.

     

    Hergenrother et al. “Operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations.” Nature Communications [open access].

    During its approach to asteroid Bennu, NASA’s OSIRIS-REx spacecraft surveyed Bennu’s immediate environment, photometric properties, and rotation state. Discovery of a dusty environment, a natural satellite, or unexpected asteroid characteristics would have had consequences for the mission’s safety and observation strategy. Here we show that spacecraft observations during this period were highly sensitive to satellites (sub-meter scale) but reveal none, although later navigational images indicate that further investigation is needed. We constrain average dust production in September 2018 from Bennu’s surface to an upper limit of 150 g s–1 averaged over 34 min. Bennu’s disk-integrated photometric phase function validates measurements from the pre-encounter astronomical campaign. We demonstrate that Bennu’s rotation rate is accelerating continuously at 3.63 ± 0.52 × 10–6 degrees day–2, likely due to the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, with evolutionary implications.

     

    Scheeres et al. “The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements.” Nature Astronomy.

    The top-shaped morphology characteristic of asteroid Bennu, often found among fast-spinning asteroids and binary asteroid primaries, may have contributed substantially to binary asteroid formation. Yet a detailed geophysical analysis of this morphology for a fast-spinning asteroid has not been possible prior to the OSIRIS-REx mission. Combining the measured Bennu mass and shape obtained during the Preliminary Survey phase of the OSIRIS-REx mission, we find a notable transition in Bennu’s surface slopes within its rotational Roche lobe, defined as the region where material is energetically trapped to the surface. As the intersection of the rotational Roche lobe with Bennu’s surface has been most recently migrating towards its equator (given Bennu’s increasing spin rate), we infer that Bennu’s surface slopes have been changing across its surface within the last million years. We also find evidence for substantial density heterogeneity within this body, suggesting that its interior is a mixture of voids and boulders. The presence of such heterogeneity and Bennu’s top shape are consistent with spin-induced failure at some point in its past, although the manner of its failure cannot yet be determined. Future measurements by the OSIRIS-REx spacecraft will provide insight into and may resolve questions regarding the formation and evolution of Bennu’s top-shape morphology and its link to the formation of binary asteroids.

     

    Walsh et al. “Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface.” Nature Geoscience.

    Small, kilometer-sized near-Earth asteroids are expected to have young and frequently refreshed surfaces for two reasons: collisional disruptions are frequent in the main asteroid belt where they originate, and thermal or tidal processes act on them once they become near-Earth asteroids. Here we present early measurements of numerous large candidate impact craters on near-Earth asteroid Bennu by the OSIRIS-REx mission, which indicate a surface that is between 100 million and 1 billion years old, predating Bennu’s expected duration as a near-Earth asteroid. We also observe many fractured boulders, the morphology of which suggests an influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface. However, the surface also shows signs of more recent mass movement: clusters of boulders at topographic lows, a deficiency of small craters and infill of large craters. The oldest features likely record events from Bennu’s time in the main asteroid belt.

     

     Enos and Lauretta. “A rendezvous with asteroid Bennu.” Nature Astronomy.

    The OSIRIS-REx mission has reached its target, asteroid Bennu, and is engaging in reconnaissance and early science observations in preparation for sample collection. Principal investigator team Heather Enos and Dante Lauretta provide an overview.

  10. NASA Mission Reveals Asteroid Has Big Surprises

    March 19, 2019 -

    A NASA spacecraft that will return a sample of a near-Earth asteroid named Bennu to Earth in 2023 made the first-ever close-up observations of particle plumes erupting from an asteroid’s surface. Bennu also revealed itself to be more rugged than expected, challenging the mission team to alter its flight and sample collection plans, due to the rough terrain.

    This view of asteroid Bennu ejecting particles from its surface on January 19 was created by combining two images taken by the NavCam 1 imager onboard NASA’s OSIRIS-REx spacecraft: a short exposure image (1.4 ms), which shows the asteroid clearly, and a long exposure image (5 sec), which shows the particles clearly. Other image processing techniques were also applied, such as cropping and adjusting the brightness and contrast of each layer. Credit: NASA/Goddard/University of Arizona/Lockheed Martin

    Bennu is the target of NASA’s Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) mission, which began orbiting the asteroid on Dec. 31. Bennu, which is only slightly wider than the height of the Empire State Building, may contain unaltered material from the very beginning of our solar system.

    “The discovery of plumes is one of the biggest surprises of my scientific career,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “And the rugged terrain went against all of our predictions. Bennu is already surprising us, and our exciting journey there is just getting started.”

    Shortly after the discovery of the particle plumes on Jan. 6, the mission science team increased the frequency of observations, and subsequently detected additional particle plumes — also known as “ejection events” — during the following two months. Although many of the particles were ejected clear of Bennu, the team tracked some particles that orbited Bennu as satellites before returning to the asteroid’s surface.

    The OSIRIS-REx team initially spotted the particle ejection events in images while the spacecraft was orbiting Bennu at a distance of about one mile (1.61 kilometers). Following a safety assessment, the mission team concluded the particles did not pose a risk to the spacecraft. The team continues to analyze the particle ejection eventsand their possible causes.

    “The first three months of OSIRIS-REx’s up-close investigation of Bennu have reminded us what discovery is all about — surprises, quick thinking, and flexibility,” said Lori Glaze, acting director of the Planetary Science Division at NASA Headquarters in Washington. “We study asteroids like Bennu to learn about the origin of the solar system. OSIRIS-REx’s sample will help us answer some of the biggest questions about where we come from.”

    OSIRIS-REx launched in 2016 to explore Bennu, which is the smallest body ever orbited by spacecraft. Studying Bennu will allow researchers to learn more about the origins of our solar system, the sources of water and organic molecules on Earth, the resources in near-Earth space, as well as improve our understanding of asteroids that could impact Earth.

    This image shows a view across asteroid Bennu’s southern hemisphere and into space, and it demonstrates the number and distribution of boulders across Bennu’s surface. The image was obtained on Mar. 7 by the PolyCam camera on NASA’s OSIRIS-REx spacecraft from a distance of about 3 miles (5 km). The large, light-colored boulder just below the center of the image is about 24 feet (7.4 meters) wide, which is roughly half the width of a basketball court. Credit: NASA/Goddard/University of Arizona

    The OSIRIS-REx team also didn’t anticipate the number and size of boulders on Bennu’s surface. From Earth-based observations, the team expected a generally smooth surface with a few large boulders. Instead, it discovered Bennu’s entire surface is rough and dense with boulders.

    The higher-than-expected density of boulders means that the mission’s plans for sample collection, also known as Touch-and-Go (TAG), need to be adjusted. The original mission design was based on a sample site that is hazard-free, with an 82-foot (25-meter) radius. However, because of the unexpectedly rugged terrain, the team hasn’t been able to identify a site of that size on Bennu. Instead, it has begun to identify candidate sites that are much smaller in radius.

    The smaller sample site footprint and the greater number of boulders will demand more accurate performance from the spacecraft during its descent to the surface than originally planned. The mission team is developing an updated approach, called Bullseye TAG, to accurately target smaller sample sites.

    “Throughout OSIRIS-REx’s operations near Bennu, our spacecraft and operations team have demonstrated that we can achieve system performance that beats design requirements,” said Rich Burns, the project manager of OSIRIS-REx at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Bennu has issued us a challenge to deal with its rugged terrain, and we are confident that OSIRIS-REx is up to the task.”

    The original, low-boulder estimate was derived both from Earth-based observations of Bennu’s thermal inertia — or its ability to conduct and store heat — and from radar measurements of its surface roughness. Now that OSIRIS-REx has revealed Bennu’s surface up close, those expectations of a smoother surface have been proven wrong. This suggests the computer models used to interpret previous data do not adequately predict the nature of small, rocky, asteroid surfaces. The team is revising these models with the data from Bennu.

    The OSIRIS-REx science team has made many other discoveries about Bennu in the three months since the spacecraft arrived at the asteroid, some of which were presented Tuesday at the 50th Lunar and Planetary Conference in Houston and in a special collection of papers issued by the journal Nature.

    The team has directly observed a change in the spin rate of Bennu as a result of what is known as the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect. The uneven heating and cooling of Bennu as it rotates in sunlight is causing the asteroid to increase its rotation speed. As a result, Bennu’s rotation period is decreasing by about one second every 100 years. Separately, two of the spacecraft’s instruments, the MapCam color imager and the OSIRIS-REx Thermal Emission Spectrometer (OTES), have made detections of magnetite on Bennu’s surface, which bolsters earlier findings indicating the interaction of rock with liquid water on Bennu’s parent body.

    Goddard provides overall mission management, systems engineering, and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

  11. NASA’s OSIRIS-REx Spacecraft Enters Orbit Around Bennu, Breaking Record

    By Lonnie Shekhtman

    January 2, 2019 -

    On Dec. 31, 2018, NASA’s OSIRIS-REx spacecraft went into orbit around asteroid Bennu for the first time – — setting new records for the smallest body ever orbited by a spacecraft and the closest orbit of a planetary body by any spacecraft.

    At 2:43 p.m. EST on December 31, while many on Earth prepared to welcome the New Year, NASA’s OSIRIS-REx spacecraft, 70 million miles (110 million kilometers) away, carried out a single, eight-second burn of its thrusters – and broke a space exploration record. The spacecraft entered into orbit around the asteroid Bennu, and made Bennu the smallest object ever to be orbited by a spacecraft.

    “The team continued our long string of successes by executing the orbit-insertion maneuver perfectly,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “With the navigation campaign coming to an end, we are looking forward to the scientific mapping and sample site selection phase of the mission.”

    Lauretta, along with his team, spent the last day of 2018 with his feet planted on Earth, but his mind focused on space. “Entering orbit around Bennu is an amazing accomplishment that our team has been planning for years,” Lauretta said.

    Inching around the asteroid at a snail’s pace, OSIRIS-REx’s first orbit marks a leap for humankind. Never before has a spacecraft from Earth circled so close to such a small space object – one with barely enough gravity to keep a vehicle in a stable orbit.

    Now, the spacecraft will circle Bennu about a mile (1.75 kilometers) from its center, closer than any other spacecraft has come to its celestial object of study. (Previously the closest orbit of a planetary body was in May 2016, when the Rosetta spacecraft orbited about four miles (seven kilometers) from the center of the comet 67P/Churyumov-Gerasimenko.) The comfortable distance is necessary to keep the spacecraft locked to Bennu, which has a gravity force only 5-millionths as strong as Earth’s. The spacecraft is scheduled to orbit Bennu through mid-February at a leisurely 62 hours per orbit.

    Now that the OSIRIS-REx spacecraft is closer to Bennu, physical details about the asteroid will leap into sharper focus, and the spacecraft’s tour of this rubble pile of primordial debris will become increasingly detailed and focused.

    “Our orbit design is highly dependent on Bennu’s physical properties, such as its mass and gravity field, which we didn’t know before we arrived,” said OSIRIS-REx’s flight dynamics system manager Mike Moreau, who is based at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

    “Up until now, we had to account for a wide variety of possible scenarios in our computer simulations to make sure we could safely navigate the spacecraft so close to Bennu. As the team learned more about the asteroid, we incorporated new information to hone in on the final orbit design,” he said.

    The simulations have played a critical role. The OSIRIS-REx mission, after all, was designed based on complex computer programs that predicted — quite accurately, as it turns out — the properties of Bennu and how the spacecraft’s trajectory would behave. This diligent preparation allowed the team to navigate the vehicle safely to Bennu in December and put some questions to rest (there are, indeed, signs of ancient water preserved in Bennu’s rocks) and to fly over its poles and equator in a preliminary survey that led to some surprises (Bennu has many large boulders).

    Having completed the preliminary survey of Bennu with a flyby of its south pole on December 16, the spacecraft moved to a safe 31 miles (50 kilometers) away from the asteroid to give the navigation team a chance to regroup and prepare for orbit insertion. Next, Lockheed Martin engineers programmed the spacecraft to begin moving back to a position about nine miles (15 kilometers) over Bennu’s north pole to prepare for three burns of its thrusters over the course of 10 days that would place the spacecraft into orbit.

    Even though OSIRIS-REx is in the most stable orbit possible, Bennu’s gravitational pull is so tenuous that keeping the spacecraft safe will require occasional adjustments, said Dan Wibben, OSIRIS-REx maneuver and trajectory design lead at KinetX Aerospace in Simi Valley, California.

    “The gravity of Bennu is so small, forces like solar radiation and thermal pressure from Bennu’s surface become much more relevant and can push the spacecraft around in its orbit much more than if it were orbiting around Earth or Mars, where gravity is by far the most dominant force,” he said.

    The OSIRIS-REx navigation team will use “trim” maneuvers to slightly thrust the spacecraft in one direction or another to correct its orbit and counter these small forces. If the spacecraft drifts away from Bennu, or some other problem forces it into safe mode, it has been programmed to fly away from the asteroid to stay safe from impact.

    “It’s simple logic: always burn toward the Sun if something goes wrong,” said Coralie Adam, OSIRIS-REx lead optical navigation engineer at KinetX. Engineers can navigate the spacecraft back into orbit if it drifts away, Adam said, though that’s unlikely to happen.

    The navigation and spacecraft operations teams are focused on the first orbital phase. Their primary goal is to transition away from star-based navigation, which allowed the team to locate the spacecraft based on pictures of the star formations around it taken by the cameras onboard. Navigators use methods like this since there is no GPS in deep space and we can’t see the spacecraft from Earth-based telescopes. From this point forward, though, the OSIRIS-REx team will rely on landmarks on Bennu’s surface to track OSIRIS-REx, a more precise technique that will ultimately guide them to a sample-collection site clear of boulders and large rocks, said Adam.

    “After conducting a global imaging and mapping campaign during our recent preliminary survey phase, the science team has created 3-D models of Bennu’s terrain that we’re going to begin using for navigation around the asteroid,” she said.

    Another critical objective of this orbital phase, Adam said, is to get a better handle on Bennu’s mass and gravity, features that will influence the planning of the rest of the mission, notably the short touchdown on the surface for sample collection in 2020. In the case of Bennu, scientists can only measure these features by getting OSIRIS-REx very close to the surface to see how its trajectory bends from Bennu’s gravitational pull.

    “The Orbital A phase will help improve our detailed models for Bennu’s gravity field, thermal properties, orientation, and spin rate,” said Wibben. “This, in turn, will allow us to refine our trajectory designs for the even more challenging flight activities we will perform in 2019.”

    The December 31 maneuver to place the spacecraft into orbit about Bennu is the first of many exciting navigation activities planned for the mission. The OSIRIS-REx team will resume science operations in late February. At that point, the spacecraft will perform a series of close flybys of Bennu for several months to take high-resolution images of every square inch of the asteroid to help select a sampling site. During the summer of 2020, the spacecraft will briefly touch the surface of Bennu to retrieve a sample. The OSIRIS-REx mission is scheduled to deliver the sample to Earth in September 2023.

    Goddard provides overall mission management, systems engineering and the safety and mission assurance for OSIRIS-REx. Dante Lauretta of the University of Arizona, Tucson, is the principal investigator, and the University of Arizona also leads the science team and the mission’s science observation planning and data processing. Lockheed Martin Space in Denver built the spacecraft and is providing flight operations. Goddard and KinetX Aerospace are responsible for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama for the agency’s Science Mission Directorate in Washington.