Back in September 2016, NASA launched the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) spacecraft to orbit the asteroid and subsequently collect samples from its surface.
Asteroid Bennu is among the millions of asteroids found in our solar system. (Image: NASA/Goddard/University of Arizona)
Asteroid Bennu sample collection: NASA successfully completed TAG maneuver on Asteroid Bennu! The US space agency NASA in the early hours of Wednesday added a feather to its cap and successfully completed its first attempt for an asteroid sample collection mission. NASA’s OSIRIS-REx spacecraft, which has been orbiting Asteroid Bennu since the end of December 2018, performed a touch-and-go or TAG maneuver to collect the sample from the surface of the asteroid. The mission went accurately as per the projected timeline, and the sample collection arm of the spacecraft touched the asteroid for a time ranging between five to 15 seconds. While the first attempt to collect samples was successful in safe landing and take off, the team would take a few days to determine whether OSIRIS-REx has been able to collect a sample or not.
Asteroid Bennu sample collection: About the mission
Back in September 2016, NASA launched the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) spacecraft to orbit the asteroid and subsequently collect samples from its surface. The mission had been the brainchild of Dr Michael J Drake, who along with Dante Lauretta, repeatedly proposed to NASA to allow a mission to go to an asteroid for sample collection. After seven years of working on proposals, Dr Drake and Lauretta finally received the proposal from the space agency for the mission. However, in an unfortunate turn of events, Dr Drake passed away a few months after the approval.
Lauretta is now the Principal Investigator of the mission, and he got a little teary eyed remembering Dr Drake when the team at NASA confirmed that OSIRIS-REx’s touch-and-go maneuver had been a success.
Asteroid Bennu is among the millions of asteroids found in our solar system. However, it is not a part of the main asteroid belt found between Mars and Jupiter. Asteroid Bennu is a near-Earth asteroid and scientists believe that it contains clues into the formation of the solar system and the planets.
Lauretta, during the live broadcast of the TAG mission, said that Bennu was selected since the team needed a near-Earth Object with an orbit similar to Earth’s. In fact, Bennu’s orbit passes through the Earth’s orbit. He added that the mission aimed at finding the answers to some fundamental questions like why there is life in the solar system, why Earth has a habitable environment and how did life actually form. He said that Asteroid Bennu is rich in water and carbon, one among many, and it could help in solving clues on how oceans came about on the planet. He added that it is almost certain that the water on Earth was brought by asteroids like Bennu, building a connection between human life and the asteroids.
Lauretta added that it was also important to understand the asteroid because it is a potentially hazardous one that could cause severe damage to Earth if any collision were to occur. In fact, he said that there is a possibility that about 150 years down the line, Bennu might collide with the Earth. Therefore, OSIRIS has been trying to study the orbit of Bennu very closely and understand the impact of the Sun on the orbit, so that any potential alteration that could cause its collision with Earth could be foreseen and acted upon in advance.
How is OSIRIS-REx functioning?
The OSIRIS-REx spacecraft has been deployed about 321 million kilometers from the Earth, which means any data transmitted from the control room on Earth to the spacecraft or vice versa takes over 18.5 minutes to be received. This necessitated the need for a spacecraft that was smart and equipped to make its own decisions while navigating outer space and especially during the sample collection attempt.
Apart from that, the images being transmitted by the spacecraft during the TAG maneuver were low in quality, only enough for the team to know how the maneuver was progressing. OSIRIS is scheduled to send high quality close-up images of the asteroid once it is back on its orbit around Bennu and recharged by the Sunlight.
The OSIRIS also had to be programmed to adjust to certain challenges that were present on Asteroid Bennu. Before the deployment of OSIRIS, the asteroid was pictured based on thermal images, based on which scientists believed that the asteroid had a beach-like surface. However, once the OSIRIS approached the asteroid, the more and more detailed images took scientists by surprise when they saw that its surface was riddled with boulders and rocks.
This came as a challenge for the scientists as they had to then programme OSIRIS to land and take off from Bennu in much more difficult terrain conditions, in addition to the already high rotation speed of the asteroid. Based on the images that the spacecraft transmitted while orbiting the asteroid, scientists narrowed in on Nightingale crater for the sampling TAG maneuver. While the crater is surrounded by huge boulders, there is an 8-metre area which seemed optimal for sample collection.
However, the scientists had earlier hoped for a 50-metre area, and this significant reduction required additional features, which came in the form of Natural Features Tracking (NFT). This marked the first time that the system has been used in outer space, and using this, OSIRIS analysed in real-time while descending whether the sampling site was suitable. The scientists had demarcated hazardous and safe terrains, and using this, the spacecraft was assessing the surface of the asteroid to look for any potential damage. In order to be completely sure that the spacecraft remained safe, it also had the capability of aborting the TAG maneuver if the surface was hazardous, instead backing away into the space from an altitude of 5 metres above the surface.
Fortunately, while undertaking the mission, it did not find the need to abort the mission.
However, an additional challenge on Bennu was its micro-gravitational field. This made sample collection difficult as any force exerted by the spacecraft while collecting samples would result in it bouncing off Bennu. For this, the spacecraft was fitted with a sample arm, called the TAG Sample Acquisition Mechanism or TAGSAM, which had a dish-like head. In order to collect the sample, the TAGSAM has been fitted with three bottles of nitrogen gas.
In a single attempt, a bottle dispels nitrogen at a high rate, creating a kind of vacuum. Moreover, this burst also moves particles on the surface, leading the vacuum and the movement to trap some of the surface material in the TAGSAM sample collection head. Scientists are aiming to bring back 60 grams of matter.
Over the next few days, scientists would confirm whether sample collection has actually taken place or not, by studying the images of Nightingale site before and after the TAG, and by comparing the weight of the TAGSAM after the mission to the weight recorded before. This data is expected to be back by Saturday. If the collection was successful, the scientists will command OSIRIS-REx to begin its return to Earth. Otherwise, it will be prepared for a second landing attempt in January next year.
The OSIRIS is expected to return to Earth by 2023 with the samples.