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A NASA spacecraft is within the means of choosing up asteroid particles

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The sampler was originally designed for a sandy beach measuring 165 feet. As we now know, there is nothing like it on Bennu. Instead, the team has now chosen Nightingale, a site 52 feet in diameter that sits in a crater that is believed to be well preserved. There are boulders the size of buildings surrounding the site and many other large rocks that could disrupt sample collection or destroy the TAGSAM arm entirely. But it still offers the best opportunity for a safe collection of meaningful material.

Some new features have also been developed to keep the probe safe during the procedure. One was to use an inaccurate lidar-based navigation and guidance system in favor of natural feature tracking (NFT), in which an optical camera continuously takes images of the surface during the 4.5 hour TAGSAM process and processes them to determine the Estimate the spacecraft trajectory to be updated. According to Billett, this is the first time that NFT has been used as part of a space mission. Since the communication between the earth and OSIRIS-REx takes more than 18 minutes, the autonomous control for the adaptation of maneuvers during operation is of crucial importance.

This is how the sample collection works:

In preparation

The OSIRIS-REx team has spent weeks entering all of the correct prompts to carefully maneuver the spacecraft so that it will be in exactly the right place by October 20th to begin sampling.

2,500 feet above the surface – 4.5 hours after touchdown

The spaceship begins a maneuver to leave orbit and head towards the nightingale. Shortly after it leaves orbit, the TAGSAM arm is triggered, the spaceship rotates into the correct orientation, and the navigation camera that enables the NFT system is redirected to Bennu's surface. From here, the NFT will work to continually locate OSIRIS-REx and ensure its safety in relation to a map of the surface hazards.

410 feet – 20 minutes after touchdown

The spacecraft's solar panels are folded into a Y-wing position. OSIRIS-REx fires its engines in order to carry out a "checkpoint burn", which ensures that the spaceship is heading towards the nightingale.

177 feet – 10 minutes after touchdown

The engines fire again so that the "Matchpoint Burn" adjusts the speed of the spacecraft to the rotation of the asteroid. This establishes the exact contact and speed for touchdown, and the spaceship is essentially in free fall to the surface.

16 feet

This is the final benchmark before the actual sampling takes place. If the NFT believes the TAGSAM arm falls on something dangerous as marked by the hazard map, it automatically performs a demolition burn that moves the spacecraft up and away from the surface. According to the ticket, there is a 5.8% chance that this could happen. Otherwise it goes further down.

landing

TAGSAM will make brief, very gentle contact with the surface for five to 10 seconds. During this time, the nitrogen gas bottle burns and sampling begins. Once it's over, the engines fire again and the spaceship moves a safe distance from the asteroid.

An animation of TAGSAM's sample collection in Bennu's low-gravity environment.

The consequences

The goal is for the TAGSAM head to hold at least 60 grams of material (although it can potentially hold up to two kilograms). The team will run a series of experiments over the next week to see if this has been achieved. It begins with the visual detection of the TAGSAM head from one of the on-board cameras. The team then measures the mass of the sample in the TAGSAM head. You can't really weigh things up in Bennu's microgravity field (one millionth of gravity at the Earth's surface), so this focuses on observing the spacecraft's spin (which should change with the added mass). When the team believes that a sufficient sample has been taken, it is placed in the sample return capsule.

However, there is a 30% chance that OSIRIS-REx is not picking up enough material. TAGSAM has two further nitrogen gas cylinders for two further collection experiments. With Nightingale already disrupted by the first touchdown, a second attempt would most likely take place in January at a place called Osprey. That said, we could potentially get samples from two different locations on Bennu – and it would be up to researchers on Earth to untangle everything and find out what came from where.

This may seem like a hassle, but it would be a small price to pay to get debris off a rock 200 million miles away. In any case, OSIRIS-REx is to leave Bennu later in 2021 and deliver the collected samples home on September 24, 2023.

Correction 10/14: The first version of the story stated that NFT was developed by Lockheed Martin for the US Army. NFT was developed as part of the company's in-house research and development, not for the U.S. military.

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Steven Gregory