OSIRIS-REx team confirms date for sample grab from Bennu

Nightingale landing site on Bennu
Click for full image.

The OSIRIS-REx science team has confirmed October 20, 2020 as the date the spacecraft will attempt a sample grab from the asteroid Bennu.

OSIRIS-REx is charged with collecting at least 2 oz. (60 grams) of Bennu’s rocky material to deliver back to Earth – the largest sample return from space since the Apollo program – and the mission developed two methods to verify that this sample collection occurred. On Oct. 22, OSIRIS-REx’s SamCam camera will capture images of the TAGSAM head to see whether it contains Bennu’s surface material. The spacecraft will also perform a spin maneuver on Oct. 24 to determine the mass of collected material. If these measures show successful collection, the decision will be made to place the sample in the Sample Return Capsule (SRC) for return to Earth. If sufficient sample has not been collected from [the primary landing site] Nightingale, the spacecraft has onboard nitrogen charges for two more attempts. A TAG attempt at the back-up Osprey site would be made no earlier than January 2021.

The press release at the link provides a lot of technical and interesting details about the sample-grab-and-go attempt, expected to put the spacecraft in contact with the asteroid’s surface for no more than sixteen seconds.

The maneuver itself is quite risky, as the available smooth landing area, as shown in the image above, is only half the size the equipment was designed for, and surrounded by large boulders.

Ryugu, like Bennu, appears to have rocks from other asteroids

Japanese scientists today announced that 21 rocks identified by Hayabusa-2 on the asteroid Ryugu have a composition that suggests they were formed on another asteroid.

Although Ryugu’s surface is uniformly dark [because it is a C-type asteroid], the scientists behind the new research found numerous boulders scattered across the asteroid that were 1.5 or more times brighter than their surroundings — that is, they reflected at least 50% more light than most of the rest of Ryugu. This contrast made the researchers suspect these boulders may have come from outside the asteroid.

By analyzing the spectrum of light reflected off 21 of these boulders, the scientists deduced they were made of minerals known as anhydrous silicates. Prior studies have suggested that such water-poor, silicon-rich rocks make up silicaceous or S-type asteroids, the most common kind of asteroid found in the inner main asteroid belt. The brightness of these boulders also matches the brightness of S-type asteroids.

This result compliments the result yesterday from scientists studying Bennu with OSIRIS-REx, and was in fact released at the same time. Both asteroids apparently contain material from other asteroids, suggesting that asteroids in their initial formation (as rubble piles) are routinely a mixture of material from many asteroids, thrown out during impacts and then recaptured.

Rocks from Vesta on Bennu?

Scientists reviewing data of Bennu from OSIRIS-REx have found six very bright boulders that have a make-up similar to that found on Vesta, which suggests they initially came from that asteroid.

The unusual boulders on Bennu first caught the team’s eye in images from the OSIRIS-REx Camera Suite. They appeared extremely bright, with some almost ten times brighter than their surroundings. They analyzed the light from the boulders using the OSIRIS-REx Visible and Infrared Spectrometer instrument to get clues to their composition. … The signature from the boulders was characteristic of the mineral pyroxene, similar to what is seen on Vesta and the vestoids, smaller asteroids that are fragments blasted from Vesta when it sustained significant asteroid impacts.

Of course it’s possible that the boulders actually formed on Bennu’s parent asteroid, but the team thinks this is unlikely based on how pyroxene typically forms. The mineral typically forms when rocky material melts at high-temperature. However, most of Bennu is composed of rocks containing water-bearing minerals, so it (and its parent) couldn’t have experienced very high temperatures. Next, the team considered localized heating, perhaps from an impact. An impact needed to melt enough material to create large pyroxene boulders would be so significant that it would have destroyed Bennu’s parent-body. So, the team ruled out these scenarios, and instead considered other pyroxene-rich asteroids that might have implanted this material to Bennu or its parent.

The make-up of Vesta matches. While these rocks might have been flung from Vesta during an impact there, eventually to settle on the surface of Bennu, Vesta is not the only possibility. We do not have a good census of the asteroids in the solar system. Others whose make-up is not yet determined could be a source, as well as an asteroid that no longer exists, destroyed by a collision long ago.

Regardless, these rocks confirm that in the process of formation in the early days of the solar system, asteroids of all types exchanged material.

Bennu tosses particles from its surface routinely

Objects ejected from Bennu
Tracked particles after August 28, 2019 ejection event.

During OSIRIS-REx’s more than twenty months flying close to the Bennu, scientists have found that the asteroid routinely kicks particles from its surface into space, with these events linked to the asteroid’s day-night cycle.

Since arrival the scientists have seen and tracked more than 300 ejection events, with the almost seven hundred objects detected ranging from about an eighth to a half inch in size. Most moved about eight inches per second, comparable to “a beetle scurrying across the ground.”

The image to the right, cropped, reduced, and brightened to post here, comes from the introductory paper of a suite of papers on the subject, published today.

The timing of the events however reveals the most.

As Bennu completes one rotation every 4.3 hours, boulders on its surface are exposed to a constant thermo-cycling as they heat during the day and cool during the night. Over time, the rocks crack and break down, and eventually particles may be thrown from the surface. The fact that particle ejections were observed with greater frequency during late afternoon, when the rocks heat up, suggests thermal cracking is a major driver. The timing of the events is also consistent with the timing of meteoroid impacts, indicating that these small impacts could be throwing material from the surface. Either, or both, of these processes could be driving the particle ejections, and because of the asteroid’s microgravity environment, it doesn’t take much energy to launch an object from Bennu’s surface.

The link includes a cool movie showing the ejections events and the tracked paths of the ejected particles.

What OSIRIS-REx will grab from the asteroid Bennu in October

Closest view of Nightingale taken by OSIRIS-REx

On August 11th the spacecraft OSIRIS-REx did a sample grab-and-go rehearsal that put the spacecraft as close as 135 feet from the asteroid Bennu. During the rehearsal the spacecraft’s mapping camera (MapCam) snapped 22 images of the approach, showing the landing site, dubbed Nightingale, at the highest resolution yet.

From those images the science team created a movie. To the right is the closest image from that movie, lightened slightly and reduced to post here. It gives us the best view of the Nightingale landing site we will have prior to the October sample grab.

In essence, we are looking at the material that OSIRIS-REx will grab, though which particular rocks will be grabbed from this gravel pile are of course unknown. The spacecraft’s equipment is designed to capture pebbles smaller than 0.8 inches across. There are a good number of such rocks here, interspersed with a lot of larger rocks, including the several more than a foot across.

As I have noted previously, this landing site is about half the diameter of the landing sites the spacecraft was designed to touch down on. The rehearsal however gives us strong hope that OSIRIS-REx will be able to hit the bullseye. See this second movie, which shows the approach from two different cameras, with a wider context image provided to show how the spacecraft successfully hones in on its target.

Movie of OSIRIS-REx’s last rehearsal before sample grab

Closest point to Nighingale landing site during OSIRIS-REx's last rehearsal
Click image for full movie.

The OSIRIS-REx science team has released a movie made by the spacecraft’s navigation camera during its August 11th final rehearsal prior to the planned sample grab-and-go now set for October.

The image to the right is a capture of one image when the spacecraft was closest to the asteroid, about 131 feet above the surface. The target landing site, dubbed Nightingale, is the somewhat smooth area near the top half of the frame.

These images were captured over a three-hour period – the imaging sequence begins approximately one hour after the orbit departure maneuver and ends approximately two minutes after the back-away burn. In the middle of the sequence, the spacecraft slews, or rotates, so that NavCam 2 looks away from Bennu, toward space. Shortly after, it performs a final slew to point the camera (and the sampling arm) toward the surface again. Near the end of the sequence, site Nightingale comes into view at the top of the frame. The large, tall boulder situated on the crater’s rim (upper left) is 43 feet (13 meters) on its longest axis. The sequence was created using nearly 300 images taken by the spacecraft’s NavCam 2 camera.

Nightingale might be their best choice, but it remains about half the size they had originally wanted for their grab-and-go site, with far too many objects larger than planned. They designed the grab-and-go equipment to catch objects smaller than 0.8 inches. Little at this location, or on the entire surface of Bennu, is that small. The asteroid is truly a pile of gravel, with no dust.

OSIRIS-REx completes closest sample grab rehearsal

OSIRIS-REx yesterday successfully completed its closest sample grab rehearsal, bringing the spacecraft about 131 feet from the surface of the asteroid Bennu.

The approximately four-hour “Matchpoint” rehearsal took the spacecraft through the first three of the sampling sequence’s four maneuvers: the orbit departure burn, the “Checkpoint” burn and the Matchpoint burn. Checkpoint is the point where the spacecraft autonomously checks its position and velocity before adjusting its trajectory down toward the event’s third maneuver. Matchpoint is the moment when the spacecraft matches Bennu’s rotation in order to fly in tandem with the asteroid surface, directly above the sample site, before touching down on the targeted spot.

Four hours after departing its 0.6-mile (1-km) safe-home orbit, OSIRIS-REx performed the Checkpoint maneuver at an approximate altitude of 410 feet (125 meters) above Bennu’s surface. From there, the spacecraft continued to descend for another eight minutes to perform the Matchpoint burn. After descending on this new trajectory for another three minutes, the spacecraft reached an altitude of approximately 131 ft (40 m) – the closest the spacecraft has ever been to Bennu – and then performed a back-away burn to complete the rehearsal.

During the rehearsal, the spacecraft successfully deployed its sampling arm, the Touch-And-Go Sample Acquisition Mechanism (TAGSAM), from its folded, parked position out to the sample collection configuration. Additionally, some of the spacecraft’s instruments collected science and navigation images and made spectrometry observations of the sample site, as will occur during the sample collection event. These images and science data were downlinked to Earth after the event’s conclusion.

The actual sample-grab-and-go attempt is scheduled for October 20th.

The short video below the fold shows spacecraft as it makes its closest approach. From the youtube page:
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OSIRIS-REx preps for final rehearsal of sample grab

The OSIRIS-REx science and engineering team is getting ready for its August 11th final rehearsal of the sample grab-and-go at the asteroid Bennu that it plans to do in October.

If the rehearsal goes right, the spacecraft will descend to within 131 feet of the surface of Bennu as it deploys its equipment as if it would continue down to the surface. It will also fly in formation above the Nightingale sample site when it does this, taking the highest resolution images yet of the surface of the asteroid.

It will then back off, returning to its home orbit farther from Bennu. Engineers will then review what happened, and use that data to prepare for the actual sample grab-and-go, set for October 20, 2020.

A gravel pile floating in space that might hit the Earth

flat rock near Osprey
Click for full image.

Come October the probe OSIRIS-REx will attempt a quick touchdown on the asteroid Bennu to grab some tiny particles, all smaller than 0.8 inches across.

Bennu is what scientists have described as a “rubble-pile” asteroid. They use that name because it is simply a conglomeration of a lot of rocks, pebbles, boulders, and stones, all jagged and of all sizes. The overall gravity has never been strong enough to squeeze them together, at least as far as we can see, and so they are piled up loosely across the asteroid’s surface wherever we look.

I think a better name for this asteroid would a floating gravel pile, since the material on it, as clearly shown in the image to the right (reduced and rotated to post here), more resembles the tailings one finds at a mine or quarry. This photo was taken by OSIRIS-REx on May 26, 2020 during its first dress rehearsal over its back-up touch-and-go sample grab site, Osprey. As the release caption notes,

The field of view is 12 ft (3.8 m). For reference, the bright rock [near] the tip of the boulder is 1 ft (0.3 m) across, which is about the size of a loaf of bread.

I have rotated the image 90 degrees so that east is up, because the full mosaic of the entire Osprey landing site, shown below, is oriented that way, and by rotating it to match it is easier to locate this image within it.
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OSIRIS-REx spots sun-caused erosion on Bennu

Rock on Bennu showing exfoliation
Click for full figure.

An analysis of images taken by OSIRIS-REx of the asteroid Bennu has allowed scientists to identify places where the changing temperatures from day to night has caused the surfaces of rocks to flake away, a process geologists label exfoliation.

The image on the right, cropped and reduced to post here, is from figure 1 in the paper. The yellow arrow points to a typical example of exfoliation, which is a process you can see on many rocks here on Earth.

Rocks expand when sunlight heats them during the day and contract as they cool down at night, causing stress that forms cracks that grow slowly over time. Scientists have thought for a while that thermal fracturing could be an important weathering process on airless objects like asteroids because many experience extreme temperature differences between day and night, compounding the stress. For example, daytime highs on Bennu can reach almost 127 degrees Celsius or about 260 degrees Fahrenheit, and nighttime lows plummet to about minus 73 degrees Celsius or nearly minus 100 degrees Fahrenheit. However, many of the telltale features of thermal fracturing are small, and before OSIRIS-REx got close to Bennu, the high-resolution imagery required to confirm thermal fracturing on asteroids didn’t exist.

The mission team found features consistent with thermal fracturing using the spacecraft’s OSIRIS-REx Camera Suite (OCAMS), which can see features on Bennu smaller than one centimeter (almost 0.4 inches). It found evidence of exfoliation, where thermal fracturing likely caused small, thin layers (1 – 10 centimeters) to flake off of boulder surfaces. The spacecraft also produced images of cracks running through boulders in a north-south direction, along the line of stress that would be produced by thermal fracturing on Bennu.

The typical erosion processes that can cause exfoliation (weather, gravity) are not possible on tiny Bennu, so the solution appears to rest with sunlight and sunlight alone.

This is not really a surprising result, but it is the first time it has been documented by data.

Bennu’s forbidding gravelly surface

Gravelly Osprey landing site on Bennu
Click for a higher resolution version.

On May 26 the OSIRIS-REx science team completed their first rehearsal and close approach to their back-up sample-grab-and-go site on Bennu, dubbed Osprey, getting as close as 820 feet. The image to the right, cropped and reduced to post here, shows that sample site within the white box. According to the image caption, the “long, light-colored boulder to the left of the dark patch, named Strix Saxum, is 17 ft (5.2 m) in length.” Note also that they have rotated the image so that east is at the top in order to make it more easily viewed.

This particular spot in this crater is actually a revision from their first choice from early in 2019, which originally was to the right and below the dark patch in the center of the crater. After six months of study, they decided instead on the present target area above the dark patch, because it seemed safer with the most sampleable material.

So how safe is this new location? Let’s take a closer look.
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OSIRIS-REx rehearsal and landing rescheduled

The OSIRIS-REx science team today announced that, in order to give them more preparation time needed because of the coronavirus protocols, they have rescheduled their second rehearsal of the spacecraft’s touch-and-go sample grab from the asteroid Bennu from June to August, and delayed the actual touch-and-go sample grab from August to October.

The mission had originally planned to perform the first Touch-and-Go (TAG) sample collection event on Aug. 25 after completing a second rehearsal in June. This rehearsal, now scheduled for Aug. 11, will bring the spacecraft through the first three maneuvers of the sample collection sequence to an approximate altitude of 131 ft (40 m) over the surface of Bennu. The first sample collection attempt is now scheduled for Oct. 20, during which the spacecraft will descend to Bennu’s surface and collect material from sample site Nightingale.

Previously they had said that the rehearsal would get as close as 82 feet. Nothing has changed. That distance was the closest they expected the spacecraft to get. The new number, 131 feet, is in the middle of possible ranges. As explained to me by Erin Morton, head of communications for OSIRIS-REx in the Principal Investigator’s Office, “I originally chose the lowest altitude in that range to include in our public outreach materials, but later realized that it made more sense to use the mid-point altitude number, since that’s the average of the high and low possibilities.”

Though they have the ability to do two more sample grabs if the first in October is unsuccessful, they won’t bother if it succeeds. They must leave Bennu regardless in mid-2021 to return the sample to Earth on September 24, 2023.

OSIRIS-REx’s landing spot on the asteroid Bennu

Bennu, annotated
Click for full resolution unlabeled image.

The OSIRIS-REx science team today released another image of the asteroid Bennu, this time showing the planned Nightingale touch-and-go sample grab landing site.

The image to the right, reduced, cropped, and annotated by me, is that image. From the caption:

The crater where sample site Nightingale is located can be seen near the top, center of the image – it is a small region containing dark, fine-grained material. Bennu’s prime meridian boulder, Simurgh Saxum , is also visible in the lower left of the image, near the asteroid’s limb. Directly east of Simurgh is Roc Saxum . The field of view is 0.3 miles (0.5 km). For reference, Simurgh is 125 ft (38 m) across, which is about the size of a commercial airliner.

Nightingale is only about 50 feet across, which is about a third the size of the kind of smooth areas they had designed their grab-and-go equipment around. This global image illustrates the difficulties they face with that sample grab. Though there appear to be larger areas in this photo that seem smooth, they really are not. The asteroid has no dust, and the sample grab equipment is designed to suck up particles smaller than 0.8 inches in diameter. Most of the surface is covered with pebbles and gravel larger than this.

Thus they needed to find a spot where the bulk of the material is “fine-grained.” Nightingale fits that bill, though it has a small footprint and also has larger particles that pose a risk to the sample grab because they could damage the spacecraft, or clog the sample grab equipment.

Either way, for the spacecraft to autonomously guide itself accurately down to this small spot, surrounded as it is by much larger boulders, will be challenging, and is why they have done one dress rehearsal already, getting as close as 213 feet, and will do a second in June, getting down to 82 feet.

Bennu’s equatorial craters

Bennu's craters
Click for full image.

The OSIRIS-REx science team today released a neat image of Bennu, highlighting the string of impact craters along the rubble-pile asteroid’s equatorial ridge. The image to the right, cropped and reduced to post here, shows that image. From the release:

Bennu’s darkest boulder, Gargoyle Saxum , is visible on the equator, near the left limb. On the asteroid’s southern hemisphere, Bennu’s largest boulder, Benben Saxum , casts a long shadow over the surface. The field of view is 0.4 miles (0.7 km). For reference, the largest crater in the center of the image is 257 ft (78 m) wide, which is almost the size of a football field.

The photo was taken from a distance of six miles on April 28. The craters illustrate well the rubble pile/sandbox nature of this asteroid. They all look like what you’d expect if the impact was able to easily drive itself deep into the a pile of sand and loose rocks. The resulting crater thus has a very indistinct rim and a sloping floor down to a central point.

Movie of OSIRIS-REx’s 1st landing rehearsal

Closest NavCam-2 image during rehearsal
Click for full movie.

The OSIRIS-REx science team has released a short movie taken by one of the spacecraft’s navigation camera (NavCam-2) during its first landing rehearsal on April 14. The image to the right, cropped to post here, is the closest image in the sequence, and shows the relatively smooth Nightingale target landing site near the bottom of the image, approximately 50 feet in diameter.

According to the release,

NavCam 2 captures images for the spacecraft’s Natural Feature Tracking (NFT) navigation system. The NFT system allows the spacecraft to autonomously guide itself to Bennu’s surface by comparing real-time images with an onboard image catalog. As the spacecraft descends to the surface, the NFT system updates the spacecraft’s predicted point of contact depending on OSIRIS-REx’s position in relation to Bennu’s landmarks. During the sample collection event, scheduled for August, the NavCam 2 camera will continuously image Bennu’s surface so that the NFT system can update the spacecraft’s position and velocity relative to Bennu as it descends towards the targeted touchdown point.

When the image above was taken the spacecraft was at its closest point, about 213 feet above the surface. Based on this movie, it looks like the system was working, and the spacecraft was refining its aim to head towards Nightingale.

Still, the landing site is not in the center of the image, which I would think is a concern, especially because Nightingale is only one-third the size of the kind of smooth target areas they had designed the system for. (When launched they expected to see smooth areas at least 160 feet across, and designed the system for this.)

The second rehearsal is presently scheduled for June 23, and will drop OSIRIS-REx to within 82 feet of the surface.

Movie of OSIRIS-REx touch-and-go rehearsal

Checkpoint rehearsal: last image
Click for movie.

The OSIRIS-REx science team yesterday released a short movie, compiled from thirty images taken during the April 14, 2020 rehearsal of the spacecraft’s planned August touch-and-go sample grab from the asteroid Bennu.

The rehearsal brought the spacecraft through the first two maneuvers of the sampling event to a point approximately 213 feet (65 meters) above the surface, before backing the spacecraft away. These images were recorded over a ten-minute span between the execution of the rehearsal’s “Checkpoint” burn, approximately 394 feet (120 meters) above the surface, and the completion of the back-away burn, which occurred approximately 213 feet (65 meters) above the surface. The spacecraft’s sampling arm – called the Touch-And-Go Sample Acquisition Mechanism (TAGSAM) – is visible in the central part of the frame, and the relatively clear, dark patch of Bennu’s sample site Nightingale is visible in the later images, at the top. The large, dark boulder that the spacecraft approaches during the sequence is 43 feet (13 meters) on its longest axis.

The image to the right is the last frame of the movie, as the spacecraft has begun its retreat. The smoother area of Nightingale is at the top.

Based on the video, it appears as if the spacecraft would have missed the Nightingale target site had the rehearsal continued to touchdown. This might not be so, however. And even if it is, the reason for the rehearsal is to allow engineers to refine the process to make it more accurate. We shall see what changes in the second rehearsal in about a month or so.

OSIRIS-REx successfully completes touch-and-go rehearsal

OSIRIS-REx yesterday successfully completed its first dress rehearsal of the maneuver that will allow it in August to touch the surface of the asteroid Bennu and grab a sample.

Four hours after departing its 0.6-mile (1-km) safe-home orbit, the spacecraft performed the Checkpoint maneuver at an approximate altitude of 410 feet (125 meters) above Bennu’s surface. From there, the spacecraft continued to descend for another nine minutes on a trajectory toward – but not reaching – the location of the sampling event’s third maneuver, the “Matchpoint” burn. Upon reaching an altitude of approximately 246 ft (75 m) – the closest the spacecraft has ever been to Bennu – OSIRIS-REx performed a back-away burn to complete the rehearsal.

During the rehearsal, the spacecraft successfully deployed its sampling arm, the Touch-And-Go Sample Acquisition Mechanism (TAGSAM), from its folded, parked position out to the sample collection configuration. Additionally, some of the spacecraft’s instruments collected science and navigation images and made spectrometry observations of the sample site, as will occur during the sample collection event.

They plan one more rehearsal, getting even closer to the asteroid, before the August 25 sample grab.

OSIRIS-REx’s sample grab location on Bennu

Nightingale site on Bennu
Click for full image.

On April 14th engineers for the probe OSIRIS-REx will do the first of two dress rehearsals of their planned touch-and-go sample grab from the asteroid Bennu, presently planned for August 25.

The image to the right was taken on March 3, 2020 from about 1,000 feet away during the spacecraft’s third reconnaissance phase, and is centered on that touch-and-go site, dubbed Nightingale by the science team. It illustrates why that sample grab carries risks that were unexpected. As they point out on the image’s release page, “the rock in the [upper right] of the image is 2 ft (70 cm) long, which is about the length of a small ice chest.” Moreover, across the entire touchdown site are numerous other rocks ranging in size from fists to laptops.

When they designed the mission, they had assumed there would be places on Bennu’s surface made up mostly of dust. areas where such dust would have gathered into ponds, as seen in other asteroids. The expectation also assumed these areas would be larger than any of the smooth areas found on Bennu. As they have noted:
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OSIRIS-REx to do sample-grab rehearsal at Bennu

The OSIRIS-REx science team today released a step-by-step description of the first touch-and-go sample grab rehearsal, planned for April 14, 2020.

During the rehearsal, dubbed “Checkpoint,” they expect the spacecraft to get less than 250 feet from the surface of the asteroid Bennu before pulling away.

Checkpoint rehearsal, a four-hour event, begins with the spacecraft leaving its safe-home orbit, 0.6 miles (1 km) above the asteroid. The spacecraft then extends its robotic sampling arm – the Touch-And-Go Sample Acquisition Mechanism (TAGSAM) – from its folded, parked position out to the sample collection configuration. Immediately following, the spacecraft slews, or rotates, into position to begin collecting navigation images for NFT guidance. NFT allows the spacecraft to autonomously guide itself to Bennu’s surface by comparing an onboard image catalog with the real-time navigation images taken during descent. As the spacecraft descends to the surface, the NFT system updates the spacecraft’s predicted point of contact depending on OSIRIS-REx’s position in relation to Bennu’s landmarks.

Before reaching the 410-ft (125-m) Checkpoint altitude, the spacecraft’s solar arrays move into a “Y-wing” configuration that safely positions them away from the asteroid’s surface. This configuration also places the spacecraft’s center of gravity directly over the TAGSAM collector head, which is the only part of the spacecraft that will contact Bennu’s surface during the sample collection event.

In the midst of these activities, the spacecraft continues capturing images of Bennu’s surface for the NFT navigation system. The spacecraft will then perform the Checkpoint burn and descend toward Bennu’s surface for another nine minutes, placing the spacecraft around 243 ft (75 m) from the asteroid – the closest it has ever been.

They will do a second rehearsal on June 23, getting within 100 feet of the surface. The actual touch-and-go sample grab is now scheduled for August 25.

OSIRIS-REx makes closest reconnaissance of Bennu yet

The spacecraft OSIRIS-REx yesterday made its closest reconnaissance yet of the asteroid Bennu, sweeping past its primary touch-and-go landing site Nightingale by a distance of only 820 feet.

The main goal of yesterday’s low flyover was to collect high-resolution imagery of the site’s surface material. The spacecraft’s sample collection mechanism is designed to pick up small rocks less than 0.8 inches (2 cm) in size, and the PolyCam images from this low pass are very detailed, allowing the team to identify and locate rocks of this size. Several of the spacecraft’s other instruments also took observations of the Nightingale site during the flyover event, including the OSIRIS-REx Thermal Emissions Spectrometer (OTES), the OSIRIS-REx Visual and InfraRed Spectrometer (OVIRS), the OSIRIS-REx Laser Altimeter (OLA), and the MapCam color imager.

After completing the flyover, the spacecraft returned to orbit – but for the first time, OSIRIS-REx reversed the direction of its safe-home orbit and is now circling Bennu clockwise (as viewed from the Sun). This shift in orbital direction positioned the spacecraft for its next close encounter with the asteroid – its first rehearsal for the sample collection event.

The touch-and-go sample grab is targeted to take place in August.

New OSIRIS-REx close-up image of secondary asteroid landing site

Osprey landing site on Bennu
Click for full image.

The OSIRIS-REx science team today released one of the images taken during the spacecraft’s recent close reconnaissance of its secondary touch-and-go landing site on the asteroid Bennu.

I have cropped their oblique image to focus, in full resolution, on that landing site, dubbed Osprey, which is the crater on the left side of the photo. The boulder in that crater “is 17 ft (5.2 m) long, which is about the length of a box truck.”

After the fly-by, the science team had announced that the spacecraft’s laser altimeter had failed to operate, and the images taken by its highest resolution camera (not the camera that took today’s image) “are likely out of focus.”

Based on this image, what look like tiny pebbles inside the crater are actually boulders ranging in size from mere inches to as much as five feet across. If their high resolution images are soft, it will thus be hard to map out the terrain sufficiently to safely make a touch-and-go landing here.

More important, there is still no word on whether they have fixed the laser altimeter. Without it I suspect a landing will be very difficult, if not impossible.

Anomaly during OSIRIS-REx flyover of secondary landing site

During its close fly-over of its secondary candidate touch-and-go landing site on the asteroid Bennu, OSIRIS-REx’s laser altimeter failed to work as planned.

On Feb. 11, NASA’s OSIRIS-REx spacecraft safely executed a 0.4-mile (620-m) flyover of the backup sample collection site Osprey as part of the mission’s Reconnaissance B phase activities. Preliminary telemetry, however, indicates that the OSIRIS-REx Laser Altimeter (OLA) did not operate as expected during the 11-hour event. The OLA instrument was scheduled to provide ranging data to the spacecraft’s PolyCam imager, which would allow the camera to focus while imaging the area around the sample collection site. Consequently, the PolyCam images from the flyover are likely out of focus.

They are analyzing their data to figure out what went wrong and whether it can be fixed. The press release implies that this loss will not impact the touch-and-go at the primary landing site, but does not say so directly. Without the laser altimeter I wonder, how they will know their exact distance as they approach?

Then again, they have not yet downloaded the full dataset from the fly-over, so they might be able to get the instrument working again.

OSIRIS-REx completes close fly-over of Bennu touchdown site

OSIRIS-REx has successfully completed the first of a series of increasingly closer fly-overs of its primary sample grab sites on the asteroid Bennu.

The spacecraft got as close as about 2,000 feet in order to take more high resolution images of the Nightingale landing site where they hope in August to do a touch-and-go sample grab.

A similar flyover of the backup sample collection site, Osprey, is scheduled for Feb. 11. Even lower flybys will be performed later this spring – Mar. 3 for Nightingale and May 26 for Osprey – as part of the mission’s Reconnaissance C phase activities. The spacecraft will perform these two flyovers at an altitude of 820 feet (250 m), which will be the closest it has ever flown over asteroid Bennu’s surface.

OSIRIS-REx team picks primary sample site

Four candidate landing sites
Click for full image.

The OSIRIS-REx science team has picked the site they have dubbed Nightingale as the primary landing site where they will attempt to obtain a sample from the asteroid Bennu in the summer of 2020. The back-up site is Osprey at the equator.

I have embedded the replay of the NASA live stream of the press event below the fold. The first 21 minutes of the video are an overview of the mission, leading up to the announcement by Dante Lauretta, OSIRIS-REx’s principal investigator. He notes then that the site “does have some hazards” but they chose it for its “scientific value.” While its higher latitude location has some advantages, it also makes it more difficult for landing. The one large boulder there, which Lauretta calls “Mt Doom,” also carries risk for the touch-and-go operations.

The back-up site, Osprey, is on the equator with less hazards, but will present more problems obtaining the tiny-sized particles the sample grab equipment was designed to get.

Not that this matters, but if I have been in a betting pool I would have won, since Nightingale has been my guess for which site they’d pick since early November.
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OSIRIS-REx completes reconnaissance of four candidate sample sites

Four candidate landing sites
Click for full image.

OSIRIS-REx has completed its high resolution reconnaissance of the four candidate sites on the asteroid Bennu, chosen for possible sample capture during touch-and-go operations planned for the summer of 2020.

In the next few days the science team will decide which of these four sites, shown above, will be the primary and back-up landing locations. The decision however appears challenging, based on the information gathered.

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.

Based on the information at the link, plus the presentation by Dante Lauretta, OSIRIS-REx’s principal investigator, given at the asteroid conference I attended in November, I suspect that Nightingale will be primary landing site.

Regardless, it appears the science team has recognized that the landing will difficult, and will likely require multiple attempts before the spacecraft’s navigation system lets it happen.

Bennu & Ryugu: Two very old and strange asteroids

Bennu as seen by OSIRIS-REx
Bennu’s equatorial ridge. Click for full image.

This week the science team operating the OSIRIS-REx spacecraft at the asteroid Bennu hosted a joint conference in Tucson, Arizona, with the scientists operating the Hayabusa-2 spacecraft at the asteroid Ryugu. Both gave up-to-date reports on the science so far obtained, as well as outlined upcoming events. I was fortunate enough to attend.

First an overview. Both Bennu and Ryugu are near earth asteroids, with Bennu having an orbit that might even have it hit the Earth in the last quarter of 2100s. Both are very dark, and are rubble piles. Both were thought to be of the carbonaceous chondrite family of asteroids, sometimes referred to as C-type asteroids. This family, making up about 75% of all asteroids, includes a bewildering collection of subtypes (B-types, F-types, G-types, CI, CM, CV, CH, CB, etc), all of which were initially thought to hold a lot of carbon. We now know that only a few of these categories, the CI and CM for example, are carbon rich.

Even so, we actually know very little about these types of asteroids. They are very fragile, so that any that reach the Earth’s surface are not a good selection of what exists. About 90% of the material gets destroyed in the atmosphere, with the remnant generally coming from the innermost core or more robust nodules. We therefore have a biased and limited sample.

It is therefore not surprising that the scientists are finding that neither Bennu nor Ryugu resembles anything else they have ever seen. Both have aspects that resemble certain types of carbonaceous chondrite asteroids, but neither provides a very good fit for anything.
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OSIRIS-REx’s four candidate landing sites

The OSIRIS-REx engineering team has released a short video that flies over in close-up, showing the spacecraft’s four candidate sites on the asteroid Bennu, one of which will be where they will do a touch-and-go sample grab.

They continue to accumulate data on the four sites, all of which pose issues and risks because of nearby boulders and the looseness of Bennu’s rubble pile make-up.

Though all the sites are being considered, my sources in the industry suggest that the two dubbed Sandpiper and Nightingale are being favored. I like Osprey, because it is inside a crater and looks clear, but then, what do I know?

OSIRIS-REx team picks four finalist sample return sites on Bennu

After months of photographing and analyzing the very rocky-shrewn surface of the rubble-pile asteroid Bennu, the OSIRIS-REx team has chosen four finalist sites, one of which they will do a touch-and-go sample grab.

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 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.

They given the four sites the names Nightingale, Kingfisher, Osprey and Sandpiper.

IAU approves 2nd set of Pluto names chosen by New Horizons team

My heart be still! The International Astronomical Union (IAU) has now officially given its glorious stamp of approval to a second set of fourteen names given by the New Horizons’ team to features on Pluto.

Several people and missions who paved the way for the historic exploration of Pluto and the Kuiper Belt – the farthest worlds ever explored – are honored in the second set of official Pluto feature names approved by the International Astronomical Union (IAU), the international authority for naming celestial bodies and their surface features.

The new names were proposed by NASA’s New Horizons team, which carried out the first reconnaissance of Pluto and its moons with the New Horizons spacecraft in 2015. Along with a short list of official names the IAU had already approved, the mission science team had been using these and other place names informally to describe the many regions, mountain ranges, plains, valleys and craters discovered during the first close-up look at Pluto’s surface. [emphasis mine]

In case you don’t get it, I am being very sarcastic above. I consider the IAU to be incredibly arrogant in its claim that it, and it alone, can approve the names given to surface features on other worlds. Initially the IAU was given the task by the astronomical community of organizing the naming of celestial bodies seen in telescopes, to reduce confusion. Somehow the IAU has expanded that responsibility to include the naming of every rock and pebble on every world in the universe.

To this I say bunk. I also know that future spacefarers in space will say the same thing, and tell the IAU to go jump in a lake. In a sense, the New Horizons team did exactly that when they made their name choices very public from the beginning, essentially telling the IAU that the New Horizons’ team is picking the names, not the IAU.

In related news, the IAU has now approved the naming convention the OSIRIS-REx team intends to use to name features on Bennu. However, in this case the IAU is doing its real job, helping to organize the naming conventions to reduce confusion.

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 actual names the OSIRIS-REx team will chose for each unique feature will however be their choice, not the IAU’s. Though the IAU will eventually announce it has “approved” those choices, it will never really have the right to have a say in those decisions.

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