In just a few days, a NASA spacecraft is going to perform a gravitational slingshot around the Earth to rendezvous with the asteroid Bennu … and Australia is being awarded one of the closest views.
Since its launch more than a year ago, NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer) spacecraft has been racing around the sun at an average speed of 100,800km/h, but on 23 September, that trajectory is going to change. Making a close approach to Earth, the OSIRIS-REx is going to undergo a gravitational slingshot to rendezvous with Near-Earth Asteroid 101955 Bennu and complete its primary mission of mapping the asteroid and retrieving a sample of the surface.
This isn’t the first time a spacecraft has used a gravity assist manoeuvre – far from it – the first was the Mariner 10, a US space probe launched in 1973. But what makes this unique is just how close the OSIRIS-REx is going to be to the Earth when it does its flyby – a minimum distance of 17,000km, about 22 times closer than the moon – with Australia being awarded one of the closest views.
The apparent pathway of the OSIRIS-REx spacecraft over Australian skies will take an hour, beginning over Rockhampton at 00.22am local time and exiting over Adelaide at 00.53am local time on 23 September (click to view interactive map) (credit: Desert Fireball Network).
“The purpose of the slingshot is change the spacecraft’s trajectory and velocity in the most efficient way possible,” explains Curtin Professor Phil Bland, team leader of the Desert Fireball Network and a member of the OSIRIS-REx science team.
“If you use the Earth, you don’t have to use as much fuel to get to the asteroid and saving that extra mass will allow you to put on more scientific instruments.”
Triangulating the spacecraft’s position over the Earth
The Desert Fireball Network is a series of 52 autonomous stations across the continent, designed to track meteorites as they enter the atmosphere and pinpoint their fall positions, but the system will be ideal for tracking the spacecraft as it hurtles over the country.
The team has three separate goals for tracking the spacecraft: providing a baseline so NASA can compare its telemetry from the spacecraft with the team’s ground observations, testing the team’s equipment and orbital analysis calculations, and engaging Australian astronomers and the broader community.
The members of the Desert Fireball Network, who have become minor internet celebrities and made headlines in their success at recovering meteorites in the remote Outback, are working with NASA to track the spacecraft as it hurtles over the Australian mainland. Pictured here is team leader Professor Phil Bland (credit: Desert Fireball Network).
“We’re flying out about eight to nine groups of designated scientists,” says Trent Jansen-Sturgeon, a Curtin PhD candidate responsible for the data analysis of OSIRIS-REx, who goes on to explain that each team will have a high-end DSLR camera with custom-built geotagging equipment to create a 3D map of the spacecraft’s flight path.
“We’ll be stationed around Australia so we can get more accurate triangulations and determine more precise orbits of the spacecraft.”
Once the OSIRIS-REx has left the Earth’s gravitational pull and approaches Bennu, it will use a series of final rocket thrusting and braking manoeuvres to match the asteroid’s velocity. After a year of surveying, the spacecraft will then move into position to collect a sample of the asteroid and begin the long voyage back home, scheduled for arrival in 2023.
As part of the OSISIR-REx science team, Bland and his group of planetary scientists will be amongst the first researchers in the world to analyse this unique material, which is expected to reveal insights into the early history of the solar system and molecular precursors to the origin of life.
“It looks like an asteroid that very little has happened to since it came together. It’s probably got water and clay minerals on it, and all of that means we can see further back in time then if we were looking at an igneous rock,” says Bland.
“Hopefully when it’s recovered, it won’t be contaminated, which means it’ll be the most pristine rock that’s ever arrived at the Earth’s surface.”
Members of the Desert Fireball Network (left to right): Ben Hartig, Morgan Cox holding a scale model of Bennu, Renae Sayers, Trent Jansen-Sturgeon, team leader Professor Phil Bland, Hadrien Devillepoix, Martin Towner and Ellie Sansom with a cut-out of OSIRIS-REx.
Expanding the Desert Fireball Network’s sphere of operations
Because of the immense success of the Desert Fireball Network and the increased recognition it’s receiving thanks to NASA’s SSERVI (Solar System Exploration Research Virtual Institute) initiative, the team are hoping to share their practices and equipment internationally when they expand to create a new body, the Global Fireball Observatory.
“There are other fireball networks around the world, but they’re not like ours,” says Ben Hartig, the mechatronic engineer responsible for developing the team’s high-end custom camera equipment.
“They tend to only use video, which has a lot lower resolution, and they don’t save their data, whereas we take photos and keep all the data we collect so we can go back and look at things that happened for new insights; it gives us a far better data set.
“Right now, we’re building cameras that we can send to colleagues and partner organisations all over the world so we can help set up their own networks.”