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Hundreds of scientists and engineers have labored for the better part of two decades to reach this point. Now, their passenger-van-sized spacecraft is finally ready for its big moment, hovering near an asteroid about as long as the Empire State Building is tall.
Later today, this space drama will play out 333 million kilometers from Earth. NASA’s OSIRIS-REx spacecraft will approach an asteroid named Bennu and extend its sampling arm. The circular head at the end of this arm will essentially bump into the asteroid for about five seconds.
During this critical juncture, the spacecraft will expel nitrogen gas onto the surface of Bennu, aiming to drive small particles on the asteroid’s surface—with a width of 2cm or less—into a device akin to a catcher’s mitt.
So how are the scientists and engineers who worked on this mission for NASA, at universities, and at the mission’s primary contractor, Lockheed Martin, feeling? Excited, and perhaps a little anxious, said Beth Buck, the OSIRIS-REx mission operations program manager for Lockheed Martin Space.
Asked on Monday how the mission’s delicate approach compares to the landing of the Curiosity rover on Mars in 2012, Buck said there would probably be fewer white knuckles. “I’m not thinking of this as seven minutes of terror,” she said. “This is much more like four-and-a-half hours of mild anxiousness.”
The OSIRIS-REx spacecraft launched toward the near-Earth asteroid Bennu on an Atlas V rocket in 2016. It spent about two years catching up to the asteroid and then began a preliminary survey before getting into a stable orbit around Bennu. As the spacecraft got closer, scientists were surprised to discover Bennu’s surface was not like a sandy beach.
Rocks and boulders
Rather, it was strewn with large boulders and small rocks, and this created a problem. Because Bennu is now so far from Earth, there is an 18.5-minute time delay between here and there. This means the spacecraft will be flying on its own, with automated navigation. Originally, mission planners had hoped to set the vehicle down within a smooth square about 25 meters by 25 meters. But because of the asteroid’s rough surface, no such areas existed.
So now OSIRIS-REx will target a smaller area, just seven meters on a side, adding to the challenge today. The spacecraft will depart its orbit, a little more than 1km from Bennu, at 1:50pm ET Tuesday (17:50 UTC). It will slowly approach the asteroid and have the ability to abort the “touch-and-go” maneuver up until a distance of five meters from the asteroid.
Factoring in the time delay, the spacecraft arm will touch Bennu at 6:12pm ET (22:12 UTC), and scientists should know pretty quickly whether the maneuver happened. (NASA will provide live coverage.) However, they won’t have an indication of whether the effort to grab a sample was successful until they start getting high-resolution data Tuesday night. The researchers will perform tests on Saturday to try to measure precisely how much asteroid material OSIRIS-REx gathered before determining whether a second attempt is necessary.
To declare the mission a success, scientists say they need to grab 60g of asteroid dust. But Heather Enos, a University of Arizona, Tucson, scientist and an OSIRIS-REx deputy principal investigator, said the team is hoping for more. “We have the capability of collecting up to two kilograms, and I would love for that capsule to be completely full,” she said. “And I can tell you I have had some wild dreams.”
After scientists determine that OSIRIS-REx has grabbed enough pebbles and dust grains from Bennu, it will be time for the spacecraft to return to Earth. A capsule carrying the material is due to land in a Utah desert on September 24, 2023. There may be a few more white knuckles at that time.
Original Source From : https://arstechnica.com/science/2020/10/todays-the-big-day-for-nasas-mission-that-seeks-to-pluck-asteroid-dust/ , Edited By coronaupdatestoday.com