Today is National Asteroid Day, and to celebrate, we’re going to fast forward to 2018, when the OSIRIS-REx spacecraft is slated to vacuum up the first asteroid sample ever collected and return the rock dust to Earth. And if all goes as planned, the spacecraft will return that sample in 2023. Why the seven-year journey?
Searching for the perfect asteroid to visit is no easy task. And Bennu, the chosen asteroid, had to satisfy a lot of requirements, including what scientists at NASA call low eccentricity and inclination.
If a planet or asteroid like Bennu moves in a circular orbit, remaining an equal distance from the sun at all times, it has zero eccentricity. But if an asteroid’s orbit is more of an ellipse – meaning its distance from the sun varies during a single orbit – that’s known as high eccentricity.
Video courtesy of NASA
And high eccentricity can be a tricky thing. Since the OSIRIS-REx spacecraft relies in part on solar power, it can never stray too far from the sun. But too close to the sun, and it can’t stand the heat. Just like Earth, Bennu has very low eccentricity which makes it a perfect ‘not too hot, not too cold’ destination.
Our solar system exists on a flat plane. The spacecraft’s trajectory must bend toward Bennu when it jets off the Earth, angling it’s path slightly off the Earth’s plane. Because bending the trajectory requires a lot of energy, “we will do what is called an Earth-gravity assist,” said University of Arizona planetary scientist Dante Lauretta, NASA’s lead scientist on the mission. The spacecraft will first fly under Antarctica and use Earth’s gravity to make a six-degree change before pushing off toward Bennu. “It would take a lot more energy to bend farther away,” Lauretta said.
Bennu orbits the sun at 63,000 mph. To intercept the rock, OSIRIS-REx will race toward it at a pace of 12,000 mph, but then slow down to a crawl, approaching Bennu at less than half a mile per hour. After its 2016 launch, it will take two years to reach the asteroid.
Once OSIRIS-REx is within three miles of Bennu, it will collect a detailed map of the asteroid’s surface, which extends roughly the size of four football fields. NASA’s scientist will then determine where it is safe for OSIRIS-REx to extend its 10 foot robotic arm and vacuum up a two ounce sample, without landing and risking damage to the spacecraft.
When dreaming up a way to collect a sample from Bennu, scientists brainstormed the use of many tools – shovels, drills, claws and scoops. But each had its downside. “In the microgravity environment, it is really hard for those tools to work. We thought wouldn’t it be great if we just had a vacuum cleaner?” Lauretta said.
But Bennu already exists in a vacuum – there is no gravity or atmosphere. So the team designed a space vacuum called TAGSAM or “touch and go acquisition mechanism.” TAGSAM works by generating a brief and tiny atmosphere on Bennu. First, It puffs nitrogen outward, causing particles to fly off the asteroid. Then a screen inside TAGSAM acts as a vacuum bag, catching the dust particles as they leave the asteroid’s surface.
Scientists test the robotic vacuum arm called TAGSAM or “touch and go acquisition mechanism” from the OSIRIS-REx spacecraft. Video courtesy of NASA
After collecting a sample, OSIRIS-REx must wait years before it can depart for Earth. Because Bennu’s trajectory is an ellipse, the distance between Bennu and Earth varies from about 62,000 to 1.8 million miles. Once the Earth gets close to Bennu again, OSIRIS-REx will use its engines to kick off the asteroid’s orbit and head home.
What is on Bennu?
Scientists don’t expect to find life on Bennu. But Bennu’s sample could tell us more about what resources are available in space and help us understand the origins of our solar system.
Astronomers believe that Bennu originated from a cloud of hydrogen, helium and dust – the same components that led to the creation of our solar system.
“The way the asteroid’s surface absorbs sunlight and re-emits energy as heat plays a substantial role in its orbital evolution,” Lauretta said. In other words, analyzing how much heat Bennu’s sample gives off can shed light on the birth of our solar system.
Since all meteorite samples become contaminated the moment they encounter the Earth, Bennu’s sample will be kept pristine in a
“If you were able to actually mine an asteroid the size of Bennu, you would become the first trillionaire on Earth,” Lauretta said.