yesterday, OSIRIS-Rex the spacecraft performed its final sampling sequence practice, reaching an approximate height of 131 meters (40 meters) above the Nightingale sampling site before executing a back burn. Nightingale, the main sampling site of OSIRIS-REx, is located inside a crater in the northern hemisphere of Bennu.
The approximately four-hour “Matchpoint” effort took the spacecraft through three sampling sequence maneuvers: orbital launch combustion, “Checkpoint” combustion, and Matchpoint combustion. The checkpoint is the point when the spacecraft autonomously controls its position and speed before adjusting its trajectory down in the third event maneuver. The Match Point is the moment when the spacecraft matches Bennu’s rotation so that it flies at the same time as the asteroid surface, directly above the sample site, before tapping down on the target site.
Four hours after leaving its safe orbit at home of 0.6 miles (1 km), OSIRIS-REx performed the checkpoint maneuver at an approximate height of 410 feet (125 meters) above the Bennu surface. From there, the spacecraft continued to descend for another eight minutes to perform Matchpoint burning. After landing on this new trajectory for another three minutes, the spacecraft reached an altitude of approximately 131 ft (40 m) – the closest spacecraft has ever been to Bennu – and then performed a back burn to complete test.
These images were captured over a 13.5-minute period. The image sequence begins at approximately 420 feet (128 meters) above the surface – before the spacecraft executes the Checkpoint maneuver – and goes all the way to the Matchpoint maneuver, with the final view taken approximately 144 meters (44 meters) above the surface of Bennu. The vessel sampling arm – called the Touch-and-Go Sample Purchase Mechanism (TAGSAM) – is visible at the bottom of the frame. credits: NASA/ Goddard / University of Arizona
During the test, the spacecraft successfully deployed its sampling arm, the Touch-and-Go Example Purchase Mechanism (TAGSAM), from the folded, parked position, to the sample collection configuration. Furthermore, some of the spacecraft instruments collect science and navigation images and make spectrometric observations of the sample site, as will happen during the sample collection event. These images and scientific data were left down to Earth after the event.
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 delay has prevented direct command of ground-based flight activities during the test. As a result, the spacecraft conducted the entire test sequence autonomously. Prior to the start of the test, the OSIRIS-REx team linked all event commands to the spacecraft and then gave the “Go” command to start the event. The current sampling event in October will take place in the same way.
This second test provided the ship’s practical navigation mission team with the first three maneuvers of the sampling event and with an opportunity to verify that the spacecraft’s imaging, navigation and ranking systems operated as expected during the part first of the subtraction sequence.
The Matchpoint test also confirmed that the OSIRIS-REx Natural Feature (NFT) guidance system accurately assessed the trajectory of the aircraft ship after the Matchpoint burned, which is the final maneuver before the sampling head contacts the Bennu surface. This test was also the first time the hazard map on board the ship was used. The hazard map identifies areas that could potentially damage the ship. If the ship detects that it is in the right course to touch a dangerous area, it will return autonomously once it reaches an altitude of 16 ft (5 m). While OSIRIS-REx did not fly so low during the test, it used the hazard map to assess whether its predicted trajectory would have avoided surface hazards, and found that the spacecraft path during the test would allow safe contact in night page sample.
During the final minutes of the spacecraft landing, OSIRIS-REx also compiled new high-resolution navigation images for the NFT navigation system. These detailed images of Bennu monuments 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 test – from communications, space intruders, and most importantly, the on-board Natural Impact Impact guidance system and hazard mapping,” said OSIRIS-REx lead investigator Dante Lauretta of the University. of Arizona, Tucson. “Now that we have completed this milestone, we have confidence in the completion of procedures for the TAG event. This test confirmed that the crew and all spacecraft systems are ready to collect a sample in October.”
The mission team has spent the last few months preparing for the Matchpoint test while maximizing remote work as part of Covida-19 answer. On test day, a limited number of personnel monitored the ship’s telemetry from the Lockheed Martin Space facility, NASA’s Goddard Space Flight Center and the University of Arizona, taking precautions while the rest of the team performed the roles of them from a distance.
The spacecraft will travel all the way to the asteroid surface during its first sampling attempt, scheduled for October 20th. During this event, the OSIRIS-REx sampling mechanism will touch the Bennu surface for a few seconds, igniting a load of nitrogen under pressure to disturb the surface, and collect a sample before the side vessel turns away. The spacecraft is scheduled to return the sample to Earth on September 24, 2023.
NASA’s Godaard Space Flight Center in Greenbelt, Maryland, provides general mission management, systems engineering, and mission security and safety for OSIRIS-REx. Dante Lauretta from the University of Arizona, Tucson, is the lead investigator, and the University of Arizona also leads the science and mission team planning scientific observation 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, to the Agency’s Science Mission Directorate in Washington.