NASA’s OSIRIS-REx probe is about to land on asteroids and sample
▲ After 4.5 hours of slow landing, the OSIRIS-REx probe will land on the asteroid Bennu and take samples within a few seconds (imagine)
Beijing time on September 28, the National Aeronautics and Space Administration (NASA) recently announced that the OSIRIS-REx probe, which aims to sample and return asteroids, will land on the asteroid Bennu on October 20. 101955). By then, the probe will carefully land for up to 4.5 hours, and then touch and leave the asteroid within a few seconds.
The full name of the OSIRIS-REx detector is “Origin of the Solar System, Spectral Interpretation, Resource Identification, Security, Regolith Explorer” (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer). NASA has selected its landing site, the “Nightingale”, located in a 16-meter-diameter rocky area in the northern hemisphere of Bennu. This candidate site is considered to have the finest soil.
This truck-sized probe is equipped with a robotic arm to collect samples from the asteroid’s surface. Scientists hope that this mission can deepen our understanding of planet formation and the origin of life, and further explore asteroids that may affect the Earth. The landing site was chosen “Nightingale” because this is one of the clearest areas on Bennu’s surface, and it is the easiest to come into contact with fine particles.
However, there are some huge stones the size of a building around the landing site, and there is only a place about the size of a few parking spaces for landing. On the other hand, if the landing is slightly off, the situation of the OSIRIS-REx detector may also be very bad.
Bennu is located between the Earth and Mars, about 334 million kilometers from Earth. At such a long distance, the signal transmission from the OSIRIS-REx probe to NASA headquarters takes approximately 18.5 minutes. This means that manual landing is impossible, and all hopes of successful landing rest on the airborne autonomous system.
According to the plan, the OSIRIS-REx probe should collect at least 57 grams of asteroid rock material and bring it back to Earth. This will be the largest sample collection mission since the Apollo mission, and the Apollo mission has received more funding and more help on the ground in collecting samples. If the material on the surface of Bennu is successfully collected, the OSIRIS-REx probe will return to Earth on September 24, 2023.
NASA also revealed some details about how the OSIRIS-REx probe will land on the surface of the asteroid. This four and a half hour test will be divided into three steps. The first step is to ignite the thruster on the OSIRIS-REx probe to get it out of orbit about 770 meters from the surface.
The reason why the height of the orbit is so low is that Bennu’s average radius is only 246 meters, and the overall gravity is very small. At this time, the sampling arm of the detector, called the “Touch-And-Go Sample Acquisition Mechanism” (TAGSAM), will unfold and point downwards towards Bennu. The fragile solar panels will be spread out in a Y-shaped wing above the detector to safely avoid any danger.
The sampling head of TAGSAM will be the only part of the detector that will touch the surface of Bennu. Mike Morrow, deputy director of the OSIRIS-REx project, said that after years of planning and hard work for this mission, TAGSAM will basically only contact the asteroid surface for 5 to 10 seconds during the landing process.
NASA staff will authorize the OSIRIS-REx probe to land autonomously, and it will use a navigation system called “Natural Feature Tracking” (NFT) to control its landing. The system uses all the detailed images of the asteroid’s surface taken by the OSIRIS-REx mission and transforms it into a map that points out all potential hazards. If the landing deviates from various predefined limits, which may put the detector in danger, the system will perform a pre-programmed abort mission.
If this happens, NASA will reorganize the mission team and try again at a later date. The slow and steady descent process of the detector takes about 4 hours, and then the so-called “checkpoint” maneuver is carried out at an altitude of about 125 meters.
As the propeller fires again, the slow descent will become steeper and faster, and the probe will get closer and closer to the surface of the asteroid. Approximately 11 minutes later, the third and final maneuver will take place, the “Matchpoint”. At this time, the computer system will use thrusters to stabilize the probe at a height of 54 meters from the landing site. The OSIRIS-REx probe will slow down again and try to match its rotation before approaching the asteroid.
NASA predicts that the time for the OSIRIS-REx probe to land on the asteroid’s surface will not exceed 16 seconds. After that, the detector’s nitrogen bottle will spray gas, blowing debris from Bennu’s surface. The detector will try to collect some debris before igniting again, and then withdraw to a safe track. One week after this landmark landing, NASA will know whether it can successfully obtain about 60 grams of asteroid material.
On October 22, an onboard camera will take pictures of the retractable sampling arm to see if any material has been collected. On October 24, the OSIRIS-REx detector will try to determine the quality of these substances. If the sample volume is sufficient, these substances will be safely packaged and placed in the “Sample Return Capsule” (SRC) to begin the journey back to Earth.
If the sampling volume is not satisfactory to NASA, the OSIRIS-REx probe will return to the top of the asteroid and try again, because the probe carries enough nitrogen for three attempts. If this happens, NASA will abandon the “Nightingale” and change the landing point to the alternate “Osprey” (Osprey), and it will not land again until January 2021 at the earliest.
Vesta fragment on Bennu’s surface
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Images of the asteroid “Bennu” taken by NASA show that there is another asteroid fragment on its surface and it is “extremely bright.” These fragments are from Vesta, ranging in size from 1.5 meters to 4.3 meters, scattered around Bennu’s southern hemisphere and its center.
The researchers detected these boulders in images from the OSIRIS-REx detector, and they looked much brighter than the surrounding dark carbon-rich areas. The probe analyzed the fragments using an onboard spectrometer and found signs of pyroxene minerals-a known compound on Vesta.
NASA researchers believe that the material came from Bennu’s mother asteroid, which was hit by Vesta debris. Hannah Kaplan of NASA’s Goddard Space Flight Center said: “Our main hypothesis is that a piece of Vesta fragment hit Bennu’s mother asteroid, and then Bennu inherited these from the mother asteroid. Matter. Later, when this mother asteroid broke catastrophically, some of its fragments gathered under its own gravity to form Bennu, including some pyroxene from Vesta.”
The asteroid “Benu” was photographed by the OSIRIS-REx probe on December 2, 2018.
How will the OSIRIS-REx probe mission obtain samples from asteroids?
Scientists say that this ancient asteroid may contain clues to the origin of life. It is believed that it was formed 4.5 billion years ago and carries remnants from the birth of the solar system.
The OSIRIS-REx probe was launched on the Atlas 5 rocket at 19:05 Eastern Time on September 8, 2016. After carefully investigating the characteristics of the Bennu asteroid and determining the most suitable sampling location, the OSIRIS-REx probe will use a robotic arm to collect about 60 to 2000 grams of asteroid surface material and pass through a detachable space in 2023 The cabin sends the samples back to earth.
In order to collect samples on the surface of the asteroid, the OSIRIS-REx probe will hover over a specific area and then land slowly and gently at a speed of 10 centimeters per second. The detector also carries a laser altimeter and a set of cameras provided by the University of Arizona, as well as a spectrometer and lidar.