The sampler was initially designed for a sandy area seaside with an space of 165 toes. As we now know, nothing like that exists on Bennu. So as an alternative, the staff has now settled on Nightingale, a 52-foot-diameter website sitting inside a crater that’s regarded as effectively preserved. There are boulders the dimensions of buildings surrounding the positioning, and lots of different giant rocks that would disrupt the pattern assortment or completely wreck the TAGSAM arm. However it nonetheless affords the very best alternative for a secure assortment of significant materials.
A few new capabilities had been additionally developed to attempt to hold the probe secure through the process. One was to nix an imprecise lidar-based navigation and steering system in favor of pure characteristic monitoring (NFT), wherein an optical digital camera repeatedly takes photographs of the floor all through the 4.5-hour TAGSAM process and processes them to replace the estimate of the spacecraft’s trajectory. In line with Billett, that is the primary time NFT is getting used as a part of an area mission. Because it takes greater than 18 minutes for communications to go a method between Earth and OSIRIS-REx, autonomous management will probably be essential for adjusting maneuvers on the fly.
Right here’s how the pattern assortment will work:
The OSIRIS-REx staff has spent weeks inputting all the right command prompts to painstakingly maneuver the spacecraft in order that by October 20, will probably be in precisely the precise spot to start the pattern assortment course of.
2,500 toes above the floor—4.5 hours from landing
The spacecraft begins a maneuver to depart orbit and transit towards Nightingale. Shortly after it leaves orbit, the TAGSAM arm is deployed, the spacecraft rotates into the right orientation, and the navigation digital camera that allows the NFT system is redirected towards Bennu’s floor. From right here, the NFT will probably be working to consistently decide OSIRIS-REx’s place and guarantee its security relative to a map of hazards on the floor.
410 toes—20 minutes from landing
The spacecraft’s photo voltaic arrays are folded right into a “Y-wing” place. OSIRIS-REx fires its thrusters to carry out a “checkpoint burn,” which ensures that the spacecraft is heading towards Nightingale.
177 toes—10 minutes from landing
Thrusters fireplace once more for the “matchpoint burn” to match the spacecraft’s pace with the asteroid’s rotation. This units up the exact contact and velocity for the landing, and the spacecraft is basically in a free-fall descent to the floor.
That is the ultimate benchmark earlier than the precise pattern assortment happens. If the NFT thinks the TAGSAM arm is coming down on one thing harmful flagged by the hazard map, it’ll robotically execute an abort burn that strikes the spacecraft up and away from the floor. Billett says there’s a couple of 5.8% probability this would possibly occur. In any other case, it retains heading down.
TAGSAM will make transient and really mild contact with the floor for 5 to 10 seconds. Throughout that point, the nitrogen gasoline bottle fires, and pattern assortment will get beneath method. As soon as it’s over, the thrusters will fireplace once more and the spacecraft will head out to a secure distance from the asteroid.
The objective is for the TAGSAM head to select up no less than 60 grams of fabric (though it might probably purchase as a lot as two kilograms). The staff will run a sequence of experiments over the following week or so to confirm if this has been achieved. It’ll begin with visible proof of the TAGSAM head from one of many onboard cameras. Then the staff will measure the mass of the pattern contained in the TAGSAM head. You possibly can’t actually weigh issues within the microgravity subject of Bennu (a millionth the gravity at Earth’s floor), so this can deal with observing the spacecraft’s spin (which ought to change with added mass). If the staff thinks a adequate pattern has been collected, will probably be stowed within the pattern return capsule.
However there’s really a 30% probability OSIRIS-REx fails to select up sufficient materials. TAGSAM has two extra nitrogen gasoline bottles for 2 extra assortment makes an attempt. As a result of Nightingale will have already got been disturbed by the primary landing, a second try would most certainly happen in January at a website referred to as Osprey. Which means we might probably get samples from two completely different websites on Bennu—and it will be as much as researchers on Earth to disentangle the whole lot and work out what originated from the place.
That may look like a problem, however it will be a small worth to pay to get some rubble from a rock 200 million miles away. Both method, OSIRIS-REx could be scheduled to go away Bennu later in 2021, and ship the collected samples again house on September 24, 2023.
Correction 10/14: the preliminary model of the story acknowledged that NFT was developed by Lockheed Martin for the US Military. NFT was developed as a part of inner analysis and improvement by the corporate, not for the US army.
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