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Raumfahrt - OSIRIS-REx - ASTEROID SAMPLE RETURN MISSION -Update 18

9.03.2020

First Official Names Given to Features on Asteroid Bennu

Asteroid Bennu’s most prominent boulder, a rock chunk jutting out 71 ft (21.7 m) from the asteroid’s southern hemisphere, finally has a name. The boulder – which is so large that it was initially detected from Earth – is officially designated Benben Saxum after the primordial hill that first arose from the dark waters in an ancient Egyptian creation myth.  

 

Benben Saxum and 11 other features on the asteroid are the first to receive official Bennu feature names approved by the International Astronomical Union (IAU), the internationally recognized authority for naming celestial bodies and their surface features. The accepted names were proposed by NASA’s OSIRIS-REx team members, who have been mapping the asteroid in detail over the last year. The OSIRIS-REx spacecraft, NASA’s first asteroid sample return mission, is currently visiting the asteroid and is scheduled to collect a sample from Bennu’s surface this summer.

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This flat projection mosaic of asteroid Bennu shows the locations of the first 12 surface features to receive official names from the International Astronomical Union. The accepted names were proposed by NASA’s OSIRIS-REx team members, who have been mapping the asteroid in detail over the last year. Bennu’s surface features are named after birds and bird-like creatures in mythology, and the places associated with them.
Credits: NASA/Goddard/University of Arizona

“Since arriving at the asteroid, the OSIRIS-REx team has become incredibly familiar with all of the geological features on Bennu,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “These features are providing us with insight into Bennu’s history, and their new names symbolize the essence of the mission – studying the past to both discover our origins and understand our future,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. 

 

The approved Bennu surface feature names are listed below. Bennu’s diverse terrain types – including regiones (broad geographic regions), craters, dorsa (ridges), fossae (grooves or trenches) and saxa (rocks and boulders) – will be named after birds and bird-like creatures in mythology, and the places associated with them.

 

Tlanuwa Regio is named for the giant birds who scattered the Earth with pieces of a serpent that turned into standing pillars of rocks in Cherokee mythology. Tlanuwa Regio is an area covered by large boulders in Bennu’s southern hemisphere.

 

Benben Saxum is named for an ancient Egyptian mound that arose from the primordial waters Nu. In Egyptian mythology, the god Atum settled upon Benben to create the world after his flight over the waters in the form of the Bennu bird. Benben Saxum is the tallest boulder on Bennu.

 

Roc Saxum is named for the Roc, an enormous bird of prey in Arabian mythology of the Middle East. Roc Saxum is the largest boulder feature on Bennu.

 

Simurgh Saxum is named for the benevolent, mythological bird in Persian mythology. The Simurgh was said to possess all knowledge, and Simurgh Saxum defines the prime meridian on Bennu and is the basis for the asteroid’s coordinate system.

 

Huginn Saxum and Muninn Saxum are adjacent boulders named for the two ravens, Huginn and Muninn, who accompany the god Odin in Norse mythology.

 

Ocypete Saxum is named for one of the Greek harpies, the half-maiden and half-bird personification of storm winds that would snatch and carry things away from Earth. Ocypete Saxum is located near the origin of the Jan. 19, 2019, particle ejection event on Bennu.

 

Strix Saxum is named for the Strix bird of ill-omen from Roman mythology. Strix Saxum is a large boulder flanking the OSIRIS-REx mission’s backup sample collection site.

 

Amihan Saxum is named for the Tagalog (Philippines) mythological deity, who is depicted as a bird and was the first creature to inhabit the universe. This large, flat boulder appears to be partly buried and is located in Tlanuwa Regio, which has an unusually high concentration of large boulders.

 

Pouakai Saxum is named for the monstrous bird who kills and eat humans in Māori (Polynesia) mythology. Pouakai Saxum is a 55 ft (10.6 m)-wide boulder located in Bennu’s southern hemisphere, slightly north of Benben Saxum.

 

Aetos Saxum is named for the childhood playmate of the supreme god Zeus, who was turned into an eagle by Hera in Greek mythology. Aetos Saxum is a conspicuously flat boulder, with a general wing-like shape located near Bennu’s equator.

 

Gargoyle Saxum is named for the French dragon-like monster with wings, bird-like neck, and the ability to breathe fire. Gargoyle Saxum is a large prominent boulder near the mission’s backup sample site that is one of the darkest objects on the surface.

 

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.

Quelle: NASA

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OSIRIS-REx Swoops Over Sample Site Nightingale

NASA’s first asteroid-sampling spacecraft just got its best look yet at asteroid Bennu. Yesterday, the Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft executed a very low pass over sample site Nightingale, taking observations from an altitude of 820 feet (250 m), which is the closest that OSIRIS-REx has flown over the asteroid so far. Nightingale, OSIRIS-REx’s primary sample collection site, is located within a crater in Bennu’s northern hemisphere.

 

To perform the 5-hour flyover, the spacecraft left its 0.6-mile (1-km) safe-home orbit and aimed its science instruments toward the 52-ft (16-m) wide sample site. The science observations from this pass are the closest taken of Bennu to date.

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On Mar. 3, the OSIRIS-REx spacecraft performed a low-altitude flyover of site Nightingale. During the pass, science observations of asteroid Bennu took place from a distance of approximately 820 ft (250 m) – the closest the spacecraft has ever been to the asteroid’s surface. The primary goal of this flyover was to collect high-resolution imagery for the team to locate the site’s best areas for collecting a sample.
Credits: University of Arizona

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.

 

This spring, the mission will perform two rehearsals in preparation for the sample collection event. The first rehearsal, scheduled for Apr. 14, navigates the spacecraft down to 410 feet (125 m) over Bennu’s surface. At this altitude, the spacecraft will execute the Checkpoint maneuver, designed to put the spacecraft on a descent trajectory toward the sample collection site on the surface. The spacecraft will stop its descent ten minutes later at an altitude of approximately 164 ft (50 m) by executing a maneuver to back away from the asteroid. The second rehearsal, scheduled for June, follows the same trajectory but takes the spacecraft to a lower altitude of 164 feet (50 m), where it will perform the Matchpoint maneuver, designed to slow the spacecraft’s descent rate. Subsequent to this burn the spacecraft will execute a back away maneuver between 131 ft (40 m) and 82 ft (25 m) from Bennu’s surface. The spacecraft will venture all the way to the asteroid’s surface in late August, for its first attempt to collect a sample. During this event, OSIRIS-REx’s sampling mechanism will touch Bennu’s surface and fire a charge of pressurized nitrogen to disturb the surface and collect its sample before the spacecraft backs away.

 

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.

Quelle: NASA

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Update: 12.04.2020

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Rehearsal Time for NASA’s Asteroid Sampling Spacecraft

In August, a robotic spacecraft will make NASA’s first-ever attempt to descend to the surface of an asteroid, collect a sample, and ultimately bring it safely back to Earth. In order to achieve this challenging feat, the OSIRIS-REx mission team devised new techniques to operate in asteroid Bennu’s microgravity environment – but they still need experience flying the spacecraft in close proximity to the asteroid in order to test them. So, before touching down at sample site Nightingale this summer, OSIRIS-REx will first rehearse the activities leading up to the event.

 

On Apr. 14, the mission will pursue its first practice run – officially known as “Checkpoint” rehearsal – which will also place the spacecraft the closest it’s ever been to Bennu. This rehearsal is a chance for the OSIRIS-REx team and spacecraft to test the first steps of the robotic sample collection event.

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This artist’s concept shows the trajectory and configuration of NASA’s OSIRIS-REx spacecraft during Checkpoint rehearsal, which is the first time the mission will practice the initial steps for collecting a sample from asteroid Bennu.
Credits: NASA/Goddard/University of Arizona

During the full touchdown sequence, the spacecraft uses three separate thruster firings to make its way to the asteroid’s surface. After an orbit departure burn, the spacecraft executes the Checkpoint maneuver at 410 ft (125 m) above Bennu, which adjusts the spacecraft’s position and speed down toward the point of the third burn. This third maneuver, called “Matchpoint," occurs at approximately 164 ft (50 m) from the asteroid’s surface and places the spacecraft on a trajectory that matches the rotation of Bennu as it further descends toward the targeted touchdown spot.

 

The Checkpoint rehearsal allows the team to practice navigating the spacecraft through both the orbit departure and Checkpoint maneuvers, and ensures that the spacecraft’s imaging, navigation and ranging systems operate as expected during the first part of the descent sequence. Checkpoint rehearsal also gives the team a chance to confirm that OSIRIS-REx’s Natural Feature Tracking (NFT) guidance system accurately updates the spacecraft’s position and velocity relative to Bennu as it descends towards the surface.

 

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.

 

Upon reaching this targeted point, the spacecraft will execute a back-away burn, then return its solar arrays to their original position and reconfigure the TAGSAM arm back to the parked position. Once the mission team determines that the spacecraft successfully completed the entire rehearsal sequence, they will command the spacecraft to return to its safe-home orbit around Bennu.

 

Following the Checkpoint rehearsal, the team will verify the flight system’s performance during the descent, and that the Checkpoint burn accurately adjusted the descent trajectory for the subsequent Matchpoint burn.

 

The mission team has maximized remote work over the last month of preparations for the checkpoint rehearsal, as part of the COVID-19 response. On the day of rehearsal, a limited number of personnel will command the spacecraft from Lockheed Martin Space’s facility, taking appropriate safety precautions, while the rest of the team performs their roles remotely.

 

The mission is scheduled to perform a second rehearsal on Jun. 23, taking the spacecraft through the Matchpoint burn and down to an approximate altitude of 82 ft (25 m). OSIRIS-REx’s first sample collection attempt is scheduled for Aug. 25.

 

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.

Quelle: NASA

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Update: 17.04.2020

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OSIRIS-REx spacecraft carries out first of two rehearsals before sampling asteroid

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This artist’s concept shows the trajectory and configuration of NASA’s OSIRIS-REx spacecraft during the checkpoint rehearsal, which was the first time the mission practiced the initial steps for collecting a sample from asteroid Bennu. Credit: NASA/Goddard/University of Arizona

Operating with on-board autonomy more than 140 million miles from Earth, NASA’s OSIRIS-REx spacecraft succeeded Tuesday in a rehearsal for the sample return mission’s touch-and-go landing on an asteroid later this year.

Tuesday’s practice run lasted around four hours, and the OSIRIS-REx spacecraft moved as close as 213 feet (65 meters) from asteroid Bennu, closer than any point since the mission’s arrival at the asteroid in December 2018.

Mission managers approved the Tuesday’s exercise, called the checkpoint rehearsal, to test the spacecraft’s ability to deploy its sampling arm and autonomously approach asteroid Bennu.

In August, OSIRIS-REx is scheduled to approach the asteroid for a touch-and-go landing to collect at least 60 grams, or 2.1 ounces, of material from Bennu’s gravelly surface. OSIRIS-REx will return the samples to Earth in September 2023 for analysis by scientists inside terrestrial labs far more advanced than the instrumentation that can fit on a spacecraft.

NASA’s Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer, or OSIRIS-REx, spacecraft has been mapping Bennu with cameras, mineral-sniffing spectrometers and a Canadian-built laser to measure its roughness.

Once the samples from Bennu are back on Earth, scientists will examine the specimens to search for signs of organic matter and other chemicals critical to the dawn of life.

Bennu is a 1,614-foot-side (492-meter) asteroid shaped like a spinning top. The asteroid, and OSIRIS-REx, were located some 143 million miles (230 million kilometers) from Earth as of Wednesday.

Built and operated by Lockheed Martin, the OSIRIS-REx spacecraft launched from Cape Canaveral in September 2016. A limited number of personnel managed Tuesday’s checkpoint rehearsal from a Lockheed Martin control center in Colorado, plus sites at the Goddard Space Flight Center in Maryland and the University of Arizona.

Other team members participated remotely due to the coronavirus pandemic.

OSIRIS-REx began Tuesday’s rehearsal by firing thrusters to break out of a 0.6-mile-high (1-kilometer) orbit around Bennu, then extended the robotic sampling arm, or TAGSAM, that will be used to capture rock specimens from the asteroid. OSIRIS-REx flew on autopilot throughout the decent, using a navigation program called natural feature tracking to compare images taken in real-time by the spacecraft with an on-board image catalog of Bennu’s surface.

The comparison yielded precise fixes of the spacecraft’s location relative to the asteroid, guiding OSIRIS-REx through a narrow descent corridor toward Bennu.

OSIRIS-REx later turned to the attitude, or orientation, for the final descent to the asteroid and adjusted its two solar array wings to a “Y-wing” configuration to safely position them away from the asteroid’s surface.

After a final navigation update from the landmark tracking program, OSIRIS-REx pulsed its attitude control rocket thrusters for around three seconds to begin a slow-speed fall from a distance of 410 feet (125 meters). That’s the so-called checkpoint burn during the descent sequence.

OSIRIS-REx’s cameras and some of the craft’s science instruments collected data during the descent, just as they will during the real sampling attempt later this year.

After nine minutes, at a distance of 213 feet (65 meters), the spacecraft fired its thrusters again to back away from the asteroid.

The images below were taken over a 10-minute span between the checkpoint burn and the completion of the back-away maneuver. The spacecraft’s extended Touch-And-Go Sample Acquisition Mechanism, or TAGSAM, arm is visible in the center of the animation.

For scale, scientists say the boulder coming in from the upper right of the image frame is the size of a two-story house.


Credit: NASA/Goddard/University of Arizona

After the end of the back-away burn, the spacecraft’s solar arrays returned to their normal orientation, and the TAGSAM arm was folded back into its parked configuration as OSIRIS-REx climbed back into orbit around Bennu.

“This rehearsal let us verify flight system performance during the descent, particularly the autonomous update and execution of the checkpoint burn,” said Rich Burns, OSIRIS-REx project manager at NASA’s Goddard Space Flight Center. “Executing this monumental milestone during this time of national crisis is a testament to the professionalism and focus of our team. It speaks volumes about their ‘can-do’ attitude and hopefully will serve as a bit of good news in these challenging times.”

On June 23, OSIRIS-REx will perform another rehearsal and descend closer to Bennu. During that exercise, the spacecraft will descend through the so-called “matchpoint” burn and reach a position just 82 feet (25 meters) from the asteroid before again backing away.

If all goes according to plan, the spacecraft will make its first real sampling run Aug. 25.

The primary target site for the touch-and-go landing has been designated Nightingale.

The Nightingale site is located inside a 460-foot (140-meter) crater on Bennu, but the area deemed safe for the spacecraft to touch is 52 feet (16 meters) across. That is about one-tenth the size of the safe sampling area scientists expected before OSIRIS-REx arrived at Bennu.

The asteroid is more rugged than scientists expected. OSIRIS-REx is the first mission to get an up-close view of Bennu.

The Nightingale site appears to have an abundance of fine-grained material within the capability of the OSIRIS-REx sampling mechanism. It appears dark, suggesting it might harbor relatively high concentrations of carbon, the building block of organic molecules, scientists said.

A device mounted on the end of the spacecraft’s TAGSAM arm will contact the asteroid surface and fire compressed nitrogen gas. The gas cartridge will disrupt the rock at the sampling site, and the spacecraft will capture some of the material in a chamber for return to Earth.

If the first sampling attempt turns up empty, scientists have penciled in opportunities for additional tries later this year.

Under OSIRIS-REx’s current flight plan, the spacecraft will depart Bennu next March to begin the return trip to Earth.

OSIRIS-REx will release a return capsule protected by a heat shield to plunge into Earth’s atmosphere and parachute to a landing in Utah on Sept. 24, 2023.

OSIRIS-REx Asteroid Sample Collection Set for Oct. 20

The new date allows the team more time to assess Bennu's unexpectedly rugged terrain. The event will mark NASA's first-ever asteroid sample collection.

After more than a decade of work and much anticipation, the University of Arizona-led OSIRIS-REx mission will swipe a sample from the asteroid Bennu's rocky surface on Oct. 20 from the Nightingale sample site.

The mission team successfully completed a first rehearsal last month, and on Tuesday, NASA approved a second rehearsal date of Aug. 11 and the Touch-and-Go, or TAG, sample collection event in October.

The original target date for sample collection was planned for late August, but the new Oct. 20 date will allow the team more time to prepare, in the wake of the COVID-19 pandemic.

"From the project's inception, and from experience on previous missions, the principal investigator, Dante Lauretta, myself and the team laid out a methodical schedule with strategically placed schedule margin with the knowledge that we need to accommodate unexpected events along the way," said Heather Enos, deputy principal investigator for the OSIRIS-REx mission. "The fact that this is such a long mission means there's more opportunity to experience the unexpected. We knew that and planned for it. I'm in awe of how adaptable this team is."

OSIRIS-REx has three major partners: Lockheed Martin, NASA's Goddard Space Flight Center and the University of Arizona. They're currently using remote communications, Enos said, but for big operations, such as rehearsal and sample collection, there is a lot of value in having your team in one location.

After the first rehearsal on April 14, the team decided to schedule more time between the second rehearsal and sample collection.

"We want to provide the team more time to see if there's anything we can to do improve the mission's probability of success," Enos said. "We gave them two more weeks between rehearsal and sample collection. We were expecting a 25-meter (about 80-foot) target radius, but we quickly learned that Bennu's rocky surface would only allow for two to four meters (less than 14 feet) to work with."

The OSIRIS-REx spacecraft arrived at the asteroid Bennu in December 2018 and has since been surveying and studying the asteroid from orbit. The mission is scheduled to leave Bennu in March 2021 and return to Earth on Sept. 24, 2023.

Quelle: University of Arizona

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Update: 16.04.2020

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NASA’s OSIRIS-REx Finds Heat, Cold Fracturing Rocks on Asteroid Bennu

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Exfoliation features on a cliff face (a) and on boulders (b-f) with varying size and location. The bright dome on the horizon of panel (a) is a boulder behind the exfoliating cliff.

Credit: NASA/Goddard/University of Arizona

June 9, 2020, Tucson, Ariz. -- Close-up observations of asteroid Bennu by NASA’s OSIRIS-REx spacecraft contain the first evidence of thermal fracturing of rocks on an airless body, a Nature Communications paper by Planetary Science Institute Research Scientist Jamie Molaro says. 

Thermal fracturing or thermal stress weathering occurs as rocks heat and cool each day, and mechanical stresses build up that can cause cracks to develop and grow. Over time the cracks grow larger and cause the rock to disaggregate or split into multiple pieces. For example, daytime highs on Bennu can reach  about  400 degrees Kelvin (260 degrees Fahrenheit), and nighttime lows plummet to 200 degrees Kelvin (-100 degrees Fahrenheit). 

“This is the first time evidence for thermal fracturing has been definitively observed on an object without an atmosphere,” said Molaro, lead author of the paper “In situ evidence of thermally induced rock breakdown widespread on Bennu’s surface“ (http://dx.doi.org/10.1038/s41467-020-16528-7) published June 9, 2020. “It is one piece of a puzzle that tells us what the surface used to be like, and what it will be like millions of years from now.” 

“This thermally induced breakdown has long been known on Earth. The OSIRIS-REx Camera Suite (OCAMS) orbiting as close as 0.6 km (0.4 mi) has obtained images of the surface of Bennu at pixel scales down to about 1 centimeter per pixel, providing an opportunity to search over a wide range of scales for evidence of thermal breakdown occurring in situ,” Molaro said. 

“On Earth there are chemical weathering processes that help make thermal fracturing more efficient. The presence of air and moisture within cracks makes them easier to grow, and so on Earth this effect really cannot be decoupled from the effect of the thermal stresses themselves. We’ve observed evidence of thermal fracturing on Earth and on Mars, both environments where chemical weathering may play a role. Therefore, while it was theoretically possible for thermal fracturing on an airless body to occur alone, it was not clear whether or not the stresses would be strong enough to cause crack growth in absence of the chemical effects,” Molaro said. 

“Like any weathering process, thermal fracturing can cause the evolution of boulders and planetary surfaces over time; from changing the shape and size of individual boulders, to producing pebbles or fine-grained regolith, to breaking down crater walls,” Molaro said. “How quickly this occurs relative to other weathering processes tells us how quickly the surface has changed. It is one piece of a puzzle that tells us what the planetary surface used to be like, and what it will be like millions of years from now. We don’t have good constraints yet on breakdown rates from thermal fracturing, but we can get them now that we can actually observe evidence for it for the first time in-situ. 

“We show observations of boulder morphologies and fractures on Bennu that are consistent with models of thermally induced rock breakdown, and not easily explained by other weathering mechanisms. Boulders on Bennu exhibit many possible signs of thermal fracturing, but the clearest is images showing exfoliation, where thin layers of material flake off boulder surfaces,” Molaro said. “These findings provide substantive and compelling evidence that thermal fracturing plays an important role on airless body surfaces, which has major implications for understanding the evolution of asteroid surfaces, orbits, and populations.” 

Molaro’s research was funded by a grant to PSI from NASA’s Participating Scientist program.

bennu thermal fracturing

Examples of disaggregation (top) and linear fractures (bottom) in boulders of varying sizes on Bennu.

Credit: NASA/Goddard/University of Arizona 

Quelle: Planetary Science Institute

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Update: 9.08.2020

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NASA's OSIRIS-REx spacecraft prepares for final asteroid-sampling rehearsal

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OSIRIS-REx is expected to collect a sample from asteroid Bennu on Oct. 20. This artist's concept shows the trajectory and configuration of the spacecraft during its matchpoint rehearsal.
(Image: © NASA/Goddard/University of Arizona)

NASA's OSIRIS-Rex spacecraft is preparing for its final rehearsal before touching down on asteroid Bennu this fall to snag a piece of space rock. 

OSIRIS-REx, which has been orbiting Bennu since 2018, is NASA's first asteroid-sampling spacecraft. The probe is scheduled to practice its touchdown sequence for a second time on Tuesday, Aug. 11. 

 

During the practice session, the spacecraft will rehearse the touch-and-go sample-collection event, similar to the mission's April 14 checkpoint rehearsal, which practiced the first two maneuvers of the descent. But this time, the spacecraft will add a third maneuver, called the matchpoint burn, and fly closer to the sample site, known as Nightingale, than it has before. 

As part of the matchpoint burn, OSIRIS-REx will fly in tandem with Bennu's rotation for the first time. This rehearsal provides the team with another opportunity to practice navigating the spacecraft through the descent maneuvers, as well as to test the spacecraft's imaging, navigation and ranging systems, according to a statement from NASA

 

During the Aug. 11 rehearsal, the $800 million OSIRIS-REx (Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer) mission will perform several different activities. Traveling at an average speed of 0.2 mph (0.3 kph), the spacecraft will fire its thrusters three separate times during its decent to the asteroid's surface. The first will pull the spacecraft out of its 0.6-mile-high (1 kilometer) orbit around Bennu. 

 

Other milestones in the rehearsal include extending the spacecraft's robotic sampling arm, collecting images for its autonomous navigation system, and moving its solar panels into position away from the asteroid's surface.

 

When OSIRIS-REx reaches an altitude of 410 feet (125 meters), it will perform the checkpoint burn and descend quickly toward Bennu's surface for about eight minutes. When the spacecraft is 164 feet (50 m) above the asteroid, it will fire its thrusters a third time to execute the matchpoint burn, slowing its rate of descent and aligning with Bennu's rotation. 

 

OSIRIS-REx will reach an altitude of only 131 feet (40 m) above the sample site — its closest approach yet — before heading back to orbit with a back-away burn, according to the statement.

 

Assuming the rehearsal goes smoothly, OSIRIS-REx will remain in its orbit around Bennu until it travels all the way to the asteroid's surface during its first sample collection attempt on Oct. 20. The samples are expected to be returned to Earth on Sept. 24, 2023.

Quelle: SC

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Update: 11.08.2020

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One Rehearsal Away from Touching Asteroid Bennu

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NASA's OSIRIS-REx is ready for touchdown on asteroid Bennu. On Aug. 11, the mission will perform its “Matchpoint” rehearsal – the second practice run of the Touch-and-Go (TAG) sample collection event. The rehearsal will be similar to the Apr. 14 “Checkpoint” rehearsal, which practiced the first two maneuvers of the descent, but this time the spacecraft will add a third maneuver, called the Matchpoint burn, and fly even closer to sample site Nightingale – reaching an altitude of approximately 131 ft (40 m) – before backing away from the asteroid.

This artist's rendering shows OSIRIS-REx spacecraft descending towards asteroid Bennu to collect a sample of the asteroid’s surface.

A Successful Second Rehearsal Puts NASA’s OSIRIS-REx on a Path to Sample Collection

Yesterday, the OSIRIS-REx spacecraft performed its final practice run of the sampling sequence, reaching an approximate altitude of 131 feet (40 meters) over sample site Nightingale before executing a back-away burn. Nightingale, OSIRIS-REx’s primary sample collection site, is located within a crater in Bennu’s northern hemisphere.

 

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.

 

These images were captured over a 13.5-minute period. The imaging sequence begins at approximately 420 feet (128 meters) above the surface – before the spacecraft executes the “Checkpoint” maneuver – and runs through to the “Matchpoint” maneuver, with the last image taken approximately 144 feet (44 meters) above the surface of Bennu. The spacecraft’s sampling arm – called the Touch-And-Go Sample Acquisition Mechanism (TAGSAM) – is visible in the lower part of the frame.
Credits: NASA/Goddard/University of Arizona

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.

 

Because the spacecraft and Bennu are currently about 179 million miles (288 million km) from Earth, it takes approximately 16 minutes for the spacecraft to receive the radio signals used to command it. This time lag prevented live commanding of flight activities from the ground during the rehearsal. As a result, the spacecraft performed the entire rehearsal sequence autonomously. Prior to the rehearsal's start, the OSIRIS-REx team uplinked all of the event's commands to the spacecraft and then provided the “Go” command to begin the event. The actual sample collection event in October will be conducted the same way.

 

This second rehearsal provided the mission team with practice navigating the spacecraft through the first three maneuvers of the sampling event and with an opportunity to verify that the spacecraft’s imaging, navigation and ranging systems operated as expected during the first part of the descent sequence.

 

Matchpoint rehearsal also confirmed that OSIRIS-REx’s Natural Feature Tracking (NFT) guidance system accurately estimated the spacecraft’s trajectory after the Matchpoint burn, which is the final maneuver before the sample collection head contacts Bennu’s surface. This rehearsal was also the first time that the spacecraft’s on-board hazard map was employed. The hazard map delineates areas that could potentially harm the spacecraft. If the spacecraft detects that it is on course to touch a hazardous area, it will autonomously back-away once it reaches an altitude of 16 ft (5 m). While OSIRIS-REx did not fly that low during the rehearsal, it did employ the hazard map to assess whether its predicted touchdown trajectory would have avoided surface hazards, and found that the spacecraft’s path during the rehearsal would have allowed for a safe touchdown on sample site Nightingale.

 

During the last minutes of the spacecraft’s descent, OSIRIS-REx also collected new, high-resolution navigation images for the NFT guidance system. These detailed images of Bennu’s landmarks will be used for the sampling event, and will allow the spacecraft to accurately target a very small area.

 

 “Many important systems were exercised during this rehearsal – from communications, spacecraft thrusters, and most importantly, the onboard Natural Feature Tracking guidance system and hazard map,” said OSIRIS-REx principal investigator Dante Lauretta of the University of Arizona, Tucson. “Now that we’ve completed this milestone, we are confident in finalizing the procedures for the TAG event. This rehearsal confirmed that the team and all of the spacecraft’s systems are ready to collect a sample in October.”

 

The mission team has spent the last several months preparing for Matchpoint rehearsal while maximizing remote work as part of the COVID-19 response. On the day of rehearsal, a limited number of personnel monitored the spacecraft’s telemetry from Lockheed Martin Space’s facility, NASA’s Goddard Space Flight Center and the University of Arizona, taking appropriate safety precautions, while the rest of the team performed their roles remotely.

 

The spacecraft will travel all the way to the asteroid’s surface during its first sample collection attempt, scheduled for Oct. 20. During this event, OSIRIS-REx’s sampling mechanism will touch Bennu’s surface for several seconds, fire a charge of pressurized nitrogen to disturb the surface and collect a sample before the spacecraft backs away. The spacecraft is scheduled to return the sample to Earth on Sept. 24, 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.

Quelle: NASA 

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NASA spacecraft completes final test before collecting samples from asteroid Bennu

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This imade shows particles ejecting from asteroid Bennu’s surface on Jan. 19, 2019. Of the 8,000 asteroids discovered, only 12 have ever been observed releasing their material into space. (NASA/Goddard/University of Arizona/Lockheed Martin via The New York Times)

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This artist's rendering made available by NASA in July 2016 shows the mapping of the near-Earth asteroid Bennu by the OSIRIS-REx spacecraft. (NASA/Goddard/University of Arizona via AP)

A NASA spacecraft has completed its final test and is preparing to touch the surface of asteroid Bennu to return samples to Earth.

On Tuesday, the OSIRIS-REx spacecraft got within 131 feet of the asteroid to practice its navigation and verify that its imaging, navigation and ranging systems are working.

The spacecraft moved very slowly, 0.2 mph, during the four-hour test. And because it took 16 minutes one way for signals to travel between Earth and the spacecraft, the OSIRIS-REx team sent commands to the spacecraft prior to its test. The spacecraft operated autonomously after the "Go" command was given.

Preliminary data show that the test went as planned, and the next step will be on Oct. 20 when the OSIRIS-REx spacecraft will touch Bennu’s surface for five seconds, fire a charge of pressurized nitrogen to disturb the surface and collect a sample. The spacecraft is scheduled to return the sample to Earth on Sept. 24, 2023.

 

The OSIRIS-REx (Origins Spectral Interpretation Resource Identification Security – Regolith Explorer) spacecraft launched on Sept. 8, 2016 and orbited the sun for a year. Using the Earth's gravitational field to match the trajectory of Bennu, OSIRIS-REx began its approach to Bennu in August 2018. It reached the asteroid Dec. 3, 2018.

Bennu holds a lot of promise: Its surface may record the earliest history of our solar system, and the asteroid may contain the molecular precursors to the origin of life and Earth's oceans.

It's also a threat. Bennu, about one-third of a mile wide at its equator, orbits the sun every 1.2 years and makes a relatively close approach to Earth about every six years. It’s expected to pass the Earth within the moon’s orbit in 2135. This will change the asteroid’s orbit by a small amount and may lead to a potential impact with Earth between 2175 and 2199, though the cumulative risk during this 24-year period is a 1 in 2,700 chance.

Knowing Bennu's composition, thanks to this sample return mission, could help determine a deterrence technique should the asteroid be on a collision course with Earth.

Quelle: Houston Chronicle

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