NASA Mounts OSIRIS-REx Mission to Asteroid Bennu

Graphic By Alekhya Maram

By Adam Tufts

Ever since the turn of the 18th century, when modern scientific thought started to gain traction, astronomers have puzzled over how Earth, or more generally the Solar System, came to exist. Nothing concrete could be concluded, but several popular hypotheses permeated throughout scientific circles. Currently, the most generally agreed upon theory dictates that 4.5 billion years ago a dense interstellar cloud collapsed upon itself, and the remnants of the phenomenon condensed to form the Sun and all the surrounding astronomical bodies. 

This elegant explanation, however, is inadequate in one key respect: it lacks substantial empirical evidence. Moreover, to the disappointment of many modern-day astronomers, obtaining this evidence, if it were to exist, was, and remains to this this day, an extremely cumbersome process. This can be attributed to the turbulent history of most terrestrial material. 

“It is very hard to find old rocks on Earth, because [Earth] has volcanic eruptions, hurricanes, and plate tectonics. The surface of the Earth is always getting recycled and renewed and reborn,” said astronomy teacher Andrew David. “There are only very few places on Earth where we can go back and see rocks that were formed in the early days of the Earth and Solar System.”

After accepting this reality, many scientists turned their focus to certain extraterrestrial bodies, which they realized, unlike the Earth, could yield incredibly valuable insights on the origins of the Solar System. Following this epiphany, the National Aeronautics and Space Administration (NASA) initiated the OSIRIS-REx mission in September 2016. The core objective of the operation was to send the OSIRIS-REx spacecraft to Bennu, an asteroid whose orbit can run only several million miles from Earth’s, in hopes of gathering a sample. Bennu, in specific, attracted many NASA scientists to the prospect of the OSIRIS-REx mission largely due to its classification as a carbonaceous chondrite, or an asteroid very rich in carbon.  

“[Carbonaceous chondrite] asteroids, which Bennu is one, are important in answering question about the origin… of the solar system because these objects are pretty much unaltered for the past 4.5 billion years…” said Ross Gaunt, member of the Tri-Valley Stargazers Astronomy Club. “The carbon found on Bennu likely came from an exploded star. The star(s) that produced the material contained in our solar system [and, thus, on Bennu] exploded, probably, billions of years earlier.” 

Two years after the launch of the OSIRIS-REx spacecraft, it arrived at Bennu on December 3, 2018. However, while many were excited by the landmark occasion, the NASA research and engineering teams were first greeted with unfortunate news. The engineers of the OSIRIS-REx spacecraft had anticipated a generally smooth surface covered with centimeter-scale particles, but the camera bolted onto the spacecraft revealed a different reality: a surface with an unexpected amount of superficial diversity in the form of boulders, hills, and rocks. In response to the unforeseen developments, the spacecraft orbited and examined the surface of Bennu to find a suitable site from which to extract a sample for a little less than two years. Bennu is a relatively small entity, so extremely precise measurements had to be manipulated to allow the OSIRIS-REx spacecraft to orbit Bennu from the right distance and at the correct speed.

“Bennu is only a couple Empire State Buildings tall, which... compared to the Earth is really tiny, so it has a really small amount of gravity,” said David. “The spacecraft going around Bennu was going at a very specific and precise speed of a couple feet per second. If the spacecraft went any faster, Bennu wouldn’t have enough gravity to keep it in its orbit, but any slower and it would gravitate towards Bennu.” 

Even after the minute calibrations had been administered to the spacecraft, the most intense and stressful leg of the mission had yet to come. On October 20, 2020, after an optimal collection location had been selected, OSIRIS-REx descended towards Bennu. The collection apparatus momentarily came in contact with the asteroid to collect material before boosting off into space. At first glance all appeared to be well, in fact, it was clear that the spacecraft had collected far more than the 60 grams of material they had intended to gather. After close inspection, however, NASA officials reported that the mission had been too successful. During the collection an excess of particles and rocks had been swept into the collection arm, causing several to get caught in the flap of the mechanism. This, in turn, resulted in the precious asteroid material slowly leaking from the OSIRIS-REx spacecraft into space. 

“You’ve got to remember the entire system is in microgravity,” Dr. Lauretta, the principal investigator of the OSIRIS-REx mission, said in a New York Times telephone news conference in October. “The particles are kind of diffusing out.” 

In an effort to mitigate the issue, mission coordinators elected to immediately load the material into the sample return capsule, where it would stay for the remainder of its voyage back to Earth. Previously, they had planned to weigh the rocks—in order to ensure they had enough material—by spinning the collection apparatus around the spacecraft. They quickly noted that such a procedure would likely dispel much of the sample so they opted to contain the rocks before they dissipated, sacrificing an exact measurement of the material’s weight. Gaunt references this decision to emphasize the importance of human control over purely automated commands. 

“Deciding not to weigh the sample… shows the importance of exploration under the control of humans,” said Gaunt. “By having exploration controlled by humans, we enable the missions to overcome problems, to choose landing sites, to select components to sample, etc.” 

Luckily, the process of loading the material into the sample return capsule was successful. Individuals curious about the origins of our Solar System must now sit in anxious anticipation for September 2023, when the spacecraft will supposedly touch down. 

“This achievement by OSIRIS-REx on behalf of NASA and the world has lifted our vision to the higher things we can achieve together, as teams and nations,” said NASA Administrator Jim Bridenstine in an October press release. “Samples like this are going to transform what we know about our universe and ourselves, which is the base of all NASA’s endeavors.”