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OSIRIS-REx completes New Year’s Eve orbit insertion burn at asteroid
December 31, 2018 Stephen Clark


This mosaic image of asteroid Bennu is composed of 12 PolyCam images collected on Dec. 2 by the OSIRIS-REx spacecraft from a range of 15 miles (24 kilometers). Credits: NASA/Goddard/University of Arizona

After four weeks of navigating in the vicinity of asteroid Bennu, NASA’s OSIRIS-REx spacecraft fired its thrusters for eight seconds Monday to slip into orbit around the carbon-rich object, making Bennu the smallest planetary body ever orbited by a spacecraft.

OSIRIS-REx arrived at Bennu on Dec. 3, ending a journey from Earth that lasted more than two years and spanned 1.2 billion miles (2 billion kilometers). Since then, the robotic spacecraft has surveyed the 1,600-foot-wide (492-meter) asteroid through a series of flybys as close as 4.4 miles (7 kilometers) over Bennu’s north pole, south pole and equator to measure the asteroid’s gravitational tug on OSIRIS-REx, which helped scientists determine the object’s mass.

The mass estimate helped navigators refine the parameters of OSIRIS-REx’s maneuver to enter orbit around Bennu. The craft’s thrusters ignited for 8 seconds at 2:43:55 p.m. EST (1943:55 GMT) Monday to slightly adjust OSIRIS-REx’s velocity, nudging it just enough for Bennu’s tenuous gravity to capture the probe into orbit.

“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.”

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KinetX SNAFD @KinetXSNAFD 7:02 AM - Dec 31, 2018
 Orbit insertion burn design has been finalized: @OSIRISREx will fire its thrusters to enter orbit about Bennu at 19:43:55 UTC (14:43:55 EST) tomorrow, December 31st! The engines will burn for 8 seconds.
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Launched in September 2016, NASA’s $1 billion Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer was built to travel to Bennu and collect samples for return to Earth.

When the solar system formed more than 4.5 billion years ago, chunks of rock and ice collided as they circled the sun like the balls on a billiard table, eventually building up planets. The leftovers became asteroids and comets, and scientists believe Bennu still harbors the basic carbon-bearing organic molecules that were present in the early solar solar system, the stuff that may have helped seed life.

Bennu is in an orbit around the sun that crosses Earth’s orbit, making it a potentially hazardous asteroid that could eventually pose an impact threat with our planet.

The spacecraft carries three cameras — one for long-range viewing, a color camera for mapping, and another imager to take pictures as OSIRIS-REx collects samples from the asteroid’s surface. The rest of OSIRIS-REx’s suite of science instruments includes a thermal emission spectrometer to detect heat coming from the asteroid, a visible infrared spectrometer to locate minerals and organic materials, a laser altimeter provided by the Canadian Space Agency to create topographic maps, and a student-built X-ray spectrometer to identify individual chemical elements present on the asteroid.

Besides revealing Bennu with high-resolution images, OSIRIS-REx has already made discoveries at the asteroid.

Data gathered by thermal emission and visible infrared spectrometer instruments — OTES and OVIRS — indicates clay minerals on the asteroid’s surface contain hydroxyl molecules with oxygen and hydrogen molecules bonded together. This finding suggests Bennu’s surface was once in contact with water, likely when the asteroid was part of a much larger parent body that was smashed to bits in a collision in the chaotic early solar system.


An artist’s concept of OSIRIS-REx at Bennu. Credit: Lockheed Martin

“The presence of hydrated minerals across the asteroid confirms that Bennu, a remnant from early in the formation of the solar system, is an excellent specimen for the OSIRIS-REx mission to study the composition of primitive volatiles and organics,” said Amy Simon, OVIRS deputy instrument scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “When samples of this material are returned by the mission to Earth in 2023, scientists will receive a treasure trove of new information about the history and evolution of our solar system.”

“Our initial data show that the team picked the right asteroid as the target of the OSIRIS-REx mission. We have not discovered any insurmountable issues at Bennu so far,” said Lauretta said. “The spacecraft is healthy and the science instruments are working better than required. It is time now for our adventure to begin.”

The first high-resolution images of Bennu taken by OSIRIS-REx revealed a miniature world containing a few relatively smooth regions without many large rocks, interspersed with boulder-filled regions that might be treacherous for the spacecraft’s sample collection touch-and-go maneuver.

One prominent feature of Bennu’s landscape is a large boulder protruding from the surface near the south pole. While ground-based radar images suggested the boulder to be at least 33 feet, or 10 meters, in height, OSIRIS-REx imagery indicates is closer to 164 feet, or 50 meters, tall with a width of approximately 180 feet, or 55 meters, according to NASA.

On approach to Bennu, ground controllers at Lockheed Martin in Denver — where OSIRIS-REx was built — unlatched the probe’s robotic arm from its launch restraint for the first time. Over several days, the ground team commanded the arm to bend its joints and jettison a launch cover over the sample collection mechanism, which will release compressed air during a touch-and-go maneuver to force gravel and surface material into an on-board chamber for the journey back to Earth.


This mosaic compares the size of asteroid Bennu, to scale, with other asteroids and comets visited by spacecraft. Credit: NASA/University of Arizona/ESA/JAXA

Due to the asteroid’s weak gravity, OSIRIS-REx was predicted to move around Bennu at a speed of just one-tenth of a mile per hour, or about 5 centimeters per second, once in orbit. The spacecraft’s first orbital phase will last until mid-February, when OSIRIS-REx will again make a series of flybys of Bennu.

During the mission’s first orbital phase, OSIRIS-REx is orbiting the asteroid at a range of 0.9 miles (1.4 km) to 1.24 miles (2.0 km) from the center of Bennu, setting another record for the closest distance any spacecraft has orbited to a planetary body.

Orbital speeds are determined by the gravitational pull of the parent planet or star. For comparison, objects in low Earth orbit have to travel at around 17,500 mph (7.8 kilometers per second) to avoid falling back into the atmosphere.

“It’s Bennu’s size and small mass that make the navigation challenges on this mission unprecedented, really,” said Michael Moreau, OSIRIS-REx flight dynamics system manager at NASA’s Goddard Space Flight Center, in a conference call with reporters in August.

Comet 67P/Churyumov-Gerasimenko, which was orbited by the European Space Agency’s Rosetta spacecraft from 2014 through 2016, is between five and 10 times larger than Bennu, depending on how you measure. Asteroid Ryugu, where Japan’s Hayabusa 2 spacecraft is currently exploring, is nearly twice the size of Bennu, and Hayabusa 2 will not enter orbit around it.

“Entering orbit around Bennu is an amazing accomplishment that our team has been planning for years,” Lauretta said.

OSIRIS-REx will orbit and explore Bennu for more than a year, allowing scientists and mission planners to examine the asteroid and determine a safe location for the craft’s touch-and-go descent in July 2020 to snag samples from the asteroid. The spacecraft will depart Bennu and head back to Earth, releasing its sample carrier for re-entry and landing in Utah in September 2023.

Scientists will take the samples to an ultra-clean facility at NASA’s Johnson Space Center in Houston for detailed analysis.

Source: OSIRIS-REx completes New Year’s Eve orbit insertion burn at asteroid

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OSIRIS-REx finds rugged terrain on asteroid Bennu
January 31, 2019 Stephen Clark [Spaceflight Now]


NASA’s OSIRIS-REx spacecraft’s navigation camera captured this image of asteroid Bennu on Jan. 17 from a distance of approximately 1 mile (1.6 kilometers). The large boulder in partial shadow at the lower right of the frame is about 165 feet (50 meters) across. Credit: NASA/Goddard/University of Arizona/Lockheed Martin

Some time next year, NASA’s OSIRIS-REx spacecraft will descend to the boulder-strewn surface of asteroid Bennu, reach out with a robotic arm, and fetch a sample for return to Earth, but an initial survey of the space rock millions of miles from Earth suggests the robotic mission may have few suitable targets for the touch-and-go maneuver.

OSIRIS-REx is still in the early weeks of its stay at asteroid Bennu, a roughly 1,640-foot-wide (500-meter) object that oscillates inside and outside of Earth’s orbit on each trip around the sun. Bennu’s proximity to Earth, which makes it an impact risk to the planet in the distant future, allowed ground-based radars to scan the asteroid in detail, revealing its size and shape before OSIRIS-REx’s launch in 2016.

The radar observations made by stations at Arecibo, Puerto Rico, and Goldstone, California, did a “phenomenal job of predicting the shape and topography of the asteroid for us,” said Dante Lauretta, principal investigator for the $1 billion Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer mission at the University of Arizona, Tucson.

On its approach to the asteroid last year, OSIRIS-REx showed Bennu is shaped like diamond, or a spinning top, just as the radar observations suggested.

“It’s really good news that we got it so right, and that all our mission design plans are valid as we move forward,” Lauretta said Wednesday at a meeting of NASA’s Small Bodies Assessment Group, a community of scientists with research interests in asteroids, comets and other small objects in the solar system.

“We do have the expected, so-called ‘spinning top’ shape, which seems to be characteristic of a subset of the near-Earth asteroid population,” Lauretta said.

“One of the reasons we think it’s top-shaped is because it’s been accelerated by thermal pressures to sort of spin up,” said Olivier Barnouin, a co-investigator on the OSIRIS-REx mission from the Johns Hopkins University Applied Physics Laboratory. “You can imagine if you take a top and start spinning up, if you have little rocks on it, things might go flying off.”

OSIRIS-REx’s cameras searched for evidence of moons or debris around Bennu late last year.

“We can confirm, to this point, that we have not identified any rocks that are flying around, and that there’s no risk to the spacecraft, which actually I think is kind of remarkable because this place is very dynamic,” Barnouin said in a Dec. 31 presentation of the mission’s preliminary findings at Bennu.

But Bennu did present some surprises to scientists, such as its jagged, craggy terrain covered with a collection of boulders, rock piles, craters and ridges.

“Some of the things that jump out at us right away from the asteroid’s surface are the large boulders,” Lauretta said Wednesday. “We are a looking at a pretty rough and rugged surface, more so than we expected.”

The first detailed images from OSIRIS-REx suggest Bennu exhibits the scars from collisions with other objects in the solar system, perhaps when Bennu orbited in the main asteroid belt between the orbits of Mars and Jupiter. The basins include up to a dozen large impact craters that measure up to 500 feet (150 meters) in diameter, according to Lauretta.

“We’re thinking that the asteroid surface’s cratering age may be older than we expected, and may record its collisional history in the main asteroid belt,” he said.

Scientists believe the asteroid’s visible surface may be between 100 million and 1 billion years old, and Lauretta says Bennu is likely a “rubble pile” asteroid, made by the merging of several distinct objects. With the data already returned by OSIRIS-REx, scientists have calculated Bennu has a bulk density just 20 percent higher than that of water, and a bit less than that of Jupiter.

Officials marked OSIRIS-REx’s arrival at Bennu on Dec. 3, when the spacecraft flew over the asteroid’s north pole. Subsequent passes over both poles and the equator allowed scientists to calculate the asteroid’s mass, a crucial parameter for planning the probe’s future trajectories.


OSIRIS-REx is currently in the mission’s “Orbital A” phase, following a maneuver Dec. 31 that directed the spacecraft into a slow-speed loop around Bennu that ranges between 1 mile and 1.3 miles (1.6 to 2.1 kilometers) from the asteroid. Due to Bennu’s weak gravity field, thousands of times weaker than that of Earth, OSIRIS-REx travels at a speed of just one-tenth of a mile per hour, or 5 centimeters per second, relative to the asteroid.

The orbital velocity of satellites circling the Earth can be as high as 17,500 mph (7.8 kilometers per second).

OSIRIS-REx has set records, becoming the first mission to orbit an object as small as Bennu, and as the closest any spacecraft has orbited to any planetary body.

The craft’s navigation team on Earth is plotting the location of landmarks and other prominent features on the asteroid’s surface. Beginning next month, OSIRIS-REx will fly on station-to-station trajectories around the asteroid, pulsing its thrusters to cover Bennu globally and periodically move to closer and farther distances.

“The orbit phase is not really a science campaign phase,” Lauretta said. “It’s primarily there for the navigation team to transition from using star fields to landmarks on the asteroid surface. That transition is going very well, and are achieving navigation accuracies that are required for us to depart orbit in about four weeks and begin the detailed survey campaign of the mission.”

When the solar system formed more than 4.5 billion years ago, chunks of rock and ice collided as they circled the sun like the balls on a billiard table, eventually building up planets. The leftovers became asteroids and comets, and scientists believe Bennu still harbors the basic carbon-bearing organic molecules that were present in the early solar solar system, the stuff that may have helped seed life.

The spacecraft carries three cameras — one for long-range viewing, a color camera for mapping, and another imager to take pictures as OSIRIS-REx collects samples from the asteroid’s surface. The rest of OSIRIS-REx’s suite of science instruments includes a thermal emission spectrometer to detect heat coming from the asteroid, a visible infrared spectrometer to locate minerals and organic materials, a laser altimeter provided by the Canadian Space Agency to create topographic maps, and a student-built X-ray spectrometer to identify individual chemical elements present on the asteroid.

Data gathered by thermal emission and visible infrared spectrometer instruments — OTES and OVIRS — indicates clay minerals on the asteroid’s surface contain hydroxyl molecules with oxygen and hydrogen molecules bonded together. This finding suggests Bennu’s surface was once in contact with water, likely when the asteroid was part of a much larger parent body that was smashed to bits in a collision in the chaotic early solar system.

One prominent feature of Bennu’s landscape is a large boulder protruding from the surface near the south pole. While ground-based radar images suggested the boulder to be at least 33 feet, or 10 meters, in height, OSIRIS-REx imagery indicates is closer to 164 feet, or 50 meters, tall with a width of approximately 180 feet, or 55 meters, according to NASA.

On approach to Bennu, ground controllers at Lockheed Martin in Denver — where OSIRIS-REx was built — unlatched the probe’s robotic arm from its launch restraint for the first time. Over several days, the ground team commanded the arm to bend its joints and jettison a launch cover over the sample collection mechanism, which will release compressed air during a touch-and-go maneuver to force gravel and surface material into an on-board chamber for the journey back to Earth.


One of the darkest features spotted so far on Bennu appears to be rich in magnetite and iron oxide, Lauretta said, based on early spectral measurements from OSIRIS-REx’s instruments. Scientists are intrigued by the darker regions of the asteroid because they are expected to contain more carbon, the scientific pay dirt for the sample return mission.

But officials will evaluate where OSIRIS-REx can safely reach the surface in the coming months, with the tough-and-go descent currently scheduled for July 4, 2020. That can be pushed back a few months, if necessary, before the spacecraft must depart Bennu in March 2021 to reach Earth in September 2023.

“The OSIRIS-REx mission’s sample site selection campaign starts next month, which is when we will start receiving science data at the resolution needed to make informed assessments about the safety of various regions on Bennu,” Lauretta said in a written response Thursday to questions from Spaceflight Now.

“We’re thinking about sampling the surface … and the craters are starting to look as possibly good candidates because they’re fairly smooth in structure, as far as we can tell at this point in the mission,” Barnouin said.


Source: https://spaceflightnow.com/2019/01/31/osiris-rex-finds-rugged-terrain-on-asteroid-bennu/

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OSIRIS-REx Finds Plumes and Other Surprises on Asteroid Bennu
By Paul Scott Anderson, on March 19th, 2019 [AmericaSpace]


View of a particle plume erupting from the surface of Bennu, as seen by OSIRIS-REx on Jan. 19, 2019. This is the first time that such plumes have ever been observed on an asteroid. Photo Credit: NASA/Goddard/University of Arizona/Lockheed Martin

Close-up observations of the near-Earth asteroid Bennu have revealed many surprises, NASA announced today during the 50th Lunar and Planetary Conference in Houston. These include particle plumes and a much more rugged surface than had been anticipated.

The findings come from the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft, which entered orbit around Bennu on December. 31, 2018.

One of the most interesting discoveries has been the plumes – the first-ever observation of such plumes – also called “ejection events” – erupting from the surface of an asteroid. They were seen in images taken by the spacecraft when it was about one mile (1.61 kilometers) from the asteroid. Plumes are, of course, well-known on comets, and even icy moons like Enceladus and possibly Europa, but until now had not been seen on an asteroid. Scientists don’t know the cause yet for the plumes on such a small body – Bennu is only about 0.306 miles (492 meters) across.

“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.”



Incredible view of the boulder-covered surface of Bennu in the southern hemisphere, taken by OSIRIS-REx on March 7, 2019. Photo Credit: NASA/Goddard/University of Arizona

“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.”

The particle plumes were discovered on Jan. 6, 2019, and observed multiple times during the next couple months. Some of the particles even orbited Bennu as tiny “satellites” before settling back on the surface again.

Fortunately, none of the particles pose a danger to the spacecraft.

The other primary discovery was that Bennu’s surface is much more rugged than expected, literally covered with boulders. Scientists had thought the surface would be smoother, with fewer boulders, based on telescopic and radar observations from Earth. But as often happens in planetary missions, the truth turned out to be rather different.

OSIRIS-REx is scheduled to return a sample of Bennu to Earth in 2023, with the sample collection done in the summer of 2020. The high density of boulders, however, will make the sample collection – Touch-and-Go (TAG) – a bit more tricky. It can still be done, but the sample site will need to be much smaller than first calculated. The anticipated sample site had an 82-foot (25-meter) radius, but will now have to be significantly reduced in order to avoid large boulders. The new sample collection process will now be called Bullseye Touch-and-Go.



Another view of the boulder-strewn surface of Bennu. Photo Credit: NASA/Goddard/University of Arizona

“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.”

There is also now evidence for thermal fracturing on Bennu, where the boulders forms cracks and break into smaller pieces.

“Based on what we’re seeing in these images, we believe rock breakdown due to thermal fracturing is happening on Bennu. What is really exciting is that this is the first time we’re observing direct evidence for this process on a planetary surface,” said Planetary Science Institute Research Scientist Jamie Molaro.

Another key finding is that of water-bearing minerals on Bennu, similar to those on carbonaceous chondrites.

“Scientists are interested in the composition of Bennu because similar objects may have seeded the Earth with water and organic materials,” said SwRI’s Dr. Victoria Hamilton, a mission co-investigator and lead author of a paper outlining the discovery published March 19 in Nature Astronomy. “OSIRIS-REx data confirm previous ground-based observations pointing to aqueously altered, hydrated minerals on the surface of the asteroid.”



Mosaic image of Bennu. Photo Credit: NASA/GSFC/University of Arizona

“During planetary formation, scientists believe that water was one of many chemical components that accreted to form Earth; however, most scientists think additional water was delivered in part by comets and pieces of asteroids, including water-bearing carbonaceous meteorites,” Hamilton said. “Many of these meteorites also contain prebiotic organic chemicals and amino acids, which are precursors to the origin of life. The details of water delivery to Earth as well as the larger issue of the different inventories of water ice in the early solar system affect how we view solar system formation.”

OSIRIS-REx also found that Bennu’s rotation is slowly increasing in speed, due to uneven heating and cooling as it rotates in sunlight – the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect. As a result, Bennu’s rotation period is decreasing by about one second every 100 years.

The study of Bennu by OSIRIS-Rex is not only providing fascinating details about the asteroid itself, but also valuable clues as to how asteroids in general formed billions of years ago.

More information about OSIRIS-REx is available on the mission website.


Source: https://www.americaspace.com/2019/03/19/osiris-rex-finds-plumes-and-other-surprises-on-asteroid-bennu/