Hellloooo, Earth! At my current distance -- just under 126 million km (78 million miles) -- it takes 14 minutes round-trip to communicate with the team on the ground. More on my progress #ToBennuAndBack: http://bit.ly/WhereIsOREX
MapCam Images Bennu During Dust Plume Search This MapCam image of the space surrounding asteroid Bennu was taken on Sept. 12, 2018, during the OSIRIS-REx mission’s Dust Plume Search observation campaign. Bennu, circled in green, is approximately 621 thousand miles (1 million km) from the spacecraft. The image was created by coadding 64 ten-second exposures. The mission team conducted the search to determine whether dust and gas plumes could be detected originating from Bennu’s surface. If present, these plumes could present a hazard to the spacecraft during the asteroid proximity operations, as well as provide clues to possible cometary activity on the asteroid. The images from the search did not indicate any dust from Bennu. A second dust plume search will be conducted later in the mission while the spacecraft is operating around Bennu. Date Taken: Sept. 12, 2018 Instrument Used: OCAMS (MapCam) Credit: NASA/Goddard/University of Arizona
Today I'm executing Asteroid Approach Maneuver-1, which is the first in a series of braking maneuvers that will slow my speed as I approach asteroid Bennu. My cruising speed before AAM-1 is about 1,100 miles per hour (490 meters per second). http://bit.ly/WhereIsOREX
NASA’s OSIRIS-REx Executes First Asteroid Approach Maneuver
October 1, 2018 - NASA’s OSIRIS-REx spacecraft executed its first Asteroid Approach Maneuver (AAM-1) today putting it on course for its scheduled arrival at the asteroid Bennu in December.
Artist’s conception of NASA’s OSIRIS-REx spacecraft during a burn of its main engine. Credit: University of Arizona
The spacecraft’s main engine thrusters fired in a braking maneuver designed to slow the spacecraft’s speed relative to Bennu from approximately 1,100 mph (491 m/sec) to 313 mph (140 m/sec). The mission team will continue to examine telemetry and tracking data as they become available and will have more information on the results of the maneuver over the next week.
During the next six weeks, the OSIRIS-REx spacecraft will continue executing the series of asteroid approach maneuvers designed to fly the spacecraft through a precise corridor during its final slow approach to Bennu. The last of these, AAM-4, scheduled for November 12, will adjust the spacecraft’s trajectory to arrive at a position 12 miles (20 km) from Bennu on December 3. After arrival, the spacecraft will initiate asteroid proximity operations by performing a series of fly-bys over Bennu’s poles and equator.
Asteroid Approach Maneuver 1 is a success! It was a 351 m/s burn of 11 min 15 s on the main engines. One more main engine burn remains for @OSIRISREx in its Approach phase, on Oct 15, followed by 2 smaller burns on the TCM thrusters. This was a major mission milestone!
This processed and cropped set of images shows Bennu (in the center of the frame) from the perspective of the OSIRIS-REx spacecraft as it approaches the asteroid. During the period between August 17 and October 1, the spacecraft’s PolyCam imager obtained this series of 20 four-second exposures every Monday, Wednesday, and Friday as part of the mission’s optical navigation campaign.
From the first to the last image, the spacecraft’s range to Bennu decreased from 2.2 million km to 192,000 km, and Bennu brightened from approximately magnitude 13 to magnitude 8.8 from the spacecraft’s perspective.
Almost ready for my second Asteroid Approach Maneuver (AAM-2)! Today is the second time I'll put on the brakes as I approach #asteroid Bennu, slowing my speed from about 313 to about 11.8 miles per hour. #WeBrakeForAsteroids
NASA’s OSIRIS-REx Executes Second Asteroid Approach Maneuver
October 15, 2018 - NASA’s OSIRIS-REx spacecraft executed its second Asteroid Approach Maneuver (AAM-2) today. The spacecraft’s main engine thrusters fired in a braking maneuver designed to slow the spacecraft’s speed relative to Bennu from 315 mph (141 m/sec) to 11.8 mph (5.2 m/sec). Likewise, the spacecraft’s approach speed dropped from nearly 7,580 miles (12,200 km) to 280 miles (450 km) per day.
Artist’s conception of NASA’s OSIRIS-REx spacecraft during a burn of its main engine. Credit: University of Arizona
The mission team will continue to examine telemetry and tracking data and will have more information over the next week. This burn marked the last planned use of the spacecraft’s main engines prior to OSIRIS-REx’s departure from Bennu in March 2021.
The OSIRIS-REx spacecraft is in the midst of a six-week series of maneuvers designed to fly the spacecraft through a precise corridor toward Bennu. AAM-1, which executed on Oct. 1, slowed the spacecraft by 785.831 mph (351.298 m/sec) and consumed 532.4 pounds (241.5 kilograms) of fuel. AAM-3 is schedule for October 29. The last of the burns, AAM-4, is scheduled for November 12 and will adjust the spacecraft’s trajectory to arrive at a position 12 miles (20 km) from Bennu on December 3. After arrival, the spacecraft will perform a series of fly-bys over Bennu’s poles and equator.
1, 2, 3, Bennu! Earlier this week, I captured these images of my favorite asteroid growing ever larger -- from about 1 pixel to nearly 4 pixels in PolyCam's field of view -- as I continue to approach Bennu.
This set of PolyCam images shows Bennu getting larger in the camera’s field of view as the OSIRIS-REx spacecraft continues its approach toward the asteroid. The images represent Bennu at 1.09 pixels, 1.71 pixels and 3.75 pixels, and were obtained on Oct. 13, 14 and 15, respectively. From the first to the last image, OSIRIS-REx’s range to Bennu decreased from around 20,720 miles (33,350 km) to around 6,060 miles (9,750 km). The images are cropped and processed.
Image 1: Date and Time: 10/13/2018, 09:23 UTC Range to Target: 33,360 km Phase Angle: 61.5° Bennu’s Distance from the Sun: 1.104 AU Width of Target: 1.093 pixels
Image 2: Date and Time: 10/14/2018, 09:23 UTC Range to Target: 21,347 km Phase Angle: 58.3° Bennu’s Distance from the Sun: 1.101 AU Width of Target: 1.71 pixels
Image 3: Date and Time: 10/15/2018, 09:23 UTC Range to Target: 9,736 km Phase Angle: 45.5° Bennu’s Distance from the Sun: 1.097 AU Width of Target: 3.75 pixels
A simulation showing one of the planned image mosaics that will be captured by OSIRIS-REx's PolyCam camera during the spacecraft's search for natural satellites (small moons) around Bennu in Fall 2018. The asteroid is represented by the green dot in the center. The blue square indicates the camera's field of view, and the large green circle represents the target area to be imaged around the asteroid.
Safety & Science: OSIRIS-REx on the Lookout for Hazards During Approach By Christine Hoekenga
An artist’s concept of OSIRIS-REx searching for dust plumes in the vicinity of asteroid Bennu. Credit: University of Arizona
October 17, 2018 - On Sept. 12, OSIRIS-REx pointed its medium-range science camera, MapCam, toward asteroid Bennu 621,000 miles (one million kilometers) in the distance. Slewing gently side to side and up and down as it captured 64 images, the spacecraft scanned the area around the asteroid in a carefully choreographed pattern. The day before, it had collected a similar mosaic of images with its long-range science camera, PolyCam.
Over the next few days, scientists on the ground pored over the images, looking for any signs of dust in the vicinity of the asteroid, which could present a hazard to the spacecraft as it approaches. Ultimately, they determined that the coast is clear – for now.
But OSIRIS-REx will look for natural satellites (small moons) and conduct another search for dust plumes when the spacecraft is closer to Bennu.
No dust was detected in this MapCam image of the area around Bennu (circled in green) taken Sept. 12, 2018 during OSIRIS-REx’s first Dust Plume Search. Credit: NASA/Goddard/University of Arizona
While comets, with their characteristic tails and comas, are known for releasing plumes of volatile materials like ice, gas, and dust, this behavior has also been observed in some asteroids. If dust had been visible in the images collected in mid-September, it would have suggested that Bennu had comet-like plume activity in the recent past, probably in the weeks or months before OSIRIS-REx conducted its first dust search.
Although OSIRIS-REx is designed to withstand the rigors of spaceflight and the occasional collision with stray particles, flying through a dust plume would pose a risk to the spacecraft’s instruments and solar panels. If the mission team had identified plume activity in the images, they had contingency plans to execute a braking maneuver, placing the spacecraft at a safe distance so that the dust activity could be studied further.
The existence of dust plumes would suggest that Bennu has active deposits of ice or other volatiles. Finding frozen water on the asteroid would be an exciting result for mission scientists who are in part studying Bennu to understand whether asteroids could have been the delivery mechanism for the water and organic materials needed to seed life on Earth billions of years ago. Plumes would also have implications for where OSIRIS-REx could safely collect a sample of material fr om Bennu’s surface in 2020 – and what types of material would likely be in that sample.
A view of Comet 67P backlit by the Sun makes plumes coming off the comet’s surface highly visible. Credit: ESA/Rosetta/NAVCAM
“We probably wouldn’t want to sample too near a vent for safety reasons,” says Carl Hergenrother, the OSIRIS-REx Astronomy Working Group Lead, who helped plan the hazard searches. “But it would be interesting since plumes mean that there could be subsurface volatile material nearby.”
OSIRIS-REx’s second dust plume search, scheduled for two days in Spring 2019 when the spacecraft will be about 3.1 miles (five kilometers) from Bennu, will look for active dust plumes coming off Bennu’s surface. For those observations, the spacecraft will be positioned between the Sun and the asteroid (at a high phase angle) so that Bennu is backlit and any dust plumes are more visible. Some of the 13 mosaics that the spacecraft captures will include offset images of the asteroid so that any jets coming from the surface are easier to see against the dark backdrop of space.
Dust isn’t the only potential hazard that OSIRIS-REx is looking out for. Later this fall, the spacecraft will use PolyCam and MapCam to search for natural satellites – any chunk of rock orbiting Bennu that is larger than 10 centimeters and bright enough to be seen (which requires an albedo of at least 0.03). While most asteroids exert a weak gravitational pull due to their relatively small sizes (Bennu has a diameter of roughly 500 meters), they are capable of holding small moons in orbit around themselves. In fact, asteroid 243 Ida, the second asteroid ever visited by a spacecraft, surprised scientists when images from the Galileo mission revealed it had a small moon, now called Dactyl.
243 Ida is the second asteroid visited by a spacecraft (Galileo) and the first found to have its own moon. Credit: NASA/JPL
To look for moons, two of OSIRIS-REx’s cameras will again capture a series of carefully planned mosaics covering the area around Bennu. First, PolyCam will map the asteroid’s entire Hill Sphere (the area wh ere a satellite could theoretically exist), looking for objects that are one meter or larger. Then, as the spacecraft gets closer, MapCam will conduct a search pattern for smaller satellites (down to 10 centimeters), which could only exist in a stable orbit closer to Bennu.
Similar to a dust plume discovery, if OSIRIS-REx were to detect a natural satellite orbiting Bennu, it would trigger a contingency plan. The spacecraft would conduct a braking burn and stop its approach to the asteroid about 40 or 50 kilometers out. The team would then take a few weeks to closely map the moon’s orbit around Bennu and decide whether any changes need to be made to the mission plan for the spacecraft to safely avoid the satellite. Later on, the team would study the moon in more depth, collecting images and other data about its color, reflectivity, shape, size, and other features.
Also similar to a dust plume detection, a moon would be an interesting scientific discovery. “If we did find a satellite, mapping its orbit would allow us to refine the mass of Bennu before going into orbit around the asteroid or even doing close approaches,” says Hergenrother. “It would also tell us more about Bennu’s history.”
While potential hazards like dust and natural satellites present navigation, safety and other challenges, they are part of the inherent adventure of exploring a never-before-visited world. Although Bennu has been thoroughly studied from Earth, the asteroid may have many surprises in store for the mission team. Careful planning and thorough observation strategies will ensure that these surprises are transformed from potential hazards into new scientific knowledge.