OSIRIS-REx, One of humanity’s finest

OSIRIS-REx, One of humanity’s finest
Captured on Oct. 20, during the OSIRIS-REx mission’s Touch-And-Go (TAG) sample collection event, this series of 82 images shows the SamCam imager’s field of view as the NASA spacecraft approaches and touches down on asteroid Bennu’s surface. Credit: NASA/Goddard/University of Arizona

In my last post I had mentioned that NASA’s OSIRIS-REx, one-of-its-kind mission to collect samples from an asteroid and return to Earth, and the mission that forms the crux of my project. Personally, it is surreal to imagine such a feat being accomplished in our time. With forays such as these, space exploration surely seems to be on an exciting trajectory once again. I am writing this post to provide some context.

Asteroids offer a fascinating insight into early-universe. They are thought to contain substances from the formation of our solar system, possibly providing additional bit of information than one hopes to obtain from planets. Bennu, one of the primitive and carbon-rich asteroids, is thought to contain organic materials that could very well provide new insight into origin of life. Situated around 200 million miles away from Earth, it is classified as a Near-Earth Object (NEO). Interestingly, it is also thought to have a 1/2700 chance of colliding with Earth in 22nd Century. A combination of such factors led to it being the focus of OSIRIS-REx mission.

In our project, we focus on the material that makes up the surface of such asteroids. Assumed to be a loose, grainy material, it is thought to preserve information regarding a celestial body’s geophysical history. Chunks of such a surface could be likened to randomly packed spheres. A study of thermal properties in such a model could be related to the physical properties of the regolith, which in turn provides a better understanding of the celestial body in focus — Bennu in OSIRIS-REx mission’s case. This crux of our project is the finite element method, which is a numerical technique to solve governing differential equations of a physical model. Using this, we can predict the thermal properties such as temperature distribution, or conductivities and so on.

This mosaic of Bennu, created using observations made by NASA’s OSIRIS-REx spacecraft. Credit: NASA/Goddard/University of Arizona

Launched in 2016 by NASA’s New Frontiers program, OSIRIS-REx first reached Bennu in 2018. Initially, the probe mapped the asteroid extensively, while the team analyzed these observations to choose an appropriate site to collect samples from. The team shortlisted at least four such sites. One such sites, termed Nightingale, was earmarked to grab material (Regolith) from the asteroid. In October 2020 the probe performed a sample Touch-and-Go (TAG) event, which meant that the probe collected debris after impacting it for 5 seconds.

The TAG event consisted of a series of maneuvers, and was specified to take 4.5 hours. After descending from an altitude of 770m from Bennu’s surface, the probe fired one of its pressurized Nitrogen bottles to agitate the asteroid’s surface. The resultant dust is then collected using probe’s collector head. Once this sequence was complete, the probe fired its thrusters to reach a safe altitude again. It was expected to collect 60 grams of sample, and the extra pressurized nitrogen containers were provided in case the sample collected was insufficient. However, this isn’t the case. The sampler is thought to have impacted the asteroid too hard, leaving particles wedged around the rim of its container. The mission later reported that some of the material may have flown off into space, and that the quantity of sample collected is now unknown, as they had to abort a scheduled spin maneuver that would’ve determined the mass of collected material. The sample collected remains safely sealed now, and the probe had departed from the asteroid.

OSIRIS-REx in the clean room at Lockheed Martin in April 2016 after the completion of testing. Credit: University of Arizona/Christine Hoekenga

One of the more recent updates from the mission places the spacecraft at a distance of 528,000km from Earth. It had fired its engines on May 10 that initiated the return trip, and is expected to be on-course for a scheduled arrival on 24th September, 2023. Additionally, it had been recently revealed that the data collected by this spacecraft helped refine orbital models. Before OSIRIS-REx, scientists had expressed uncertainty owing to an unclear assessment of influence of Earth’s gravity on the asteroid. The study suggested that Bennu could make a close approach with Earth in 2135, and identified Sept. 24, 2182, as a significant date in terms of potential impact. Nevertheless, it must be stressed that there exists no apparent threat of collision.

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