On Friday, a spacecraft the size of an SUV will slingshot around Earth’s South Pole, altering its trajectory through space.
The probe is NASA’s OSIRIS-REx, and its upcoming maneuver around our planet is known as a gravity assist — a way to harness Earth’s gravity to alter its orbit.
The move is critical, since it will put OSIRIS-REx on course to meet up with an asteroid in the fall of 2018.
OSIRIS-REx launched last year with a relatively straightforward purpose: grab a sample of rocks from an asteroid and bring them back to Earth.
If all goes well, the vehicle should retrieve the largest sample ever collected from an asteroid, and give scientists the chance to study the space rock components in more detail than ever before.
But first, the probe has to reach its target — a nearby asteroid named Bennu.
NASA picked Bennu partly because the asteroid’s orbit is similar to Earth’s orbit, and that makes it an easier target to reach.
But their paths aren’t the exact same: Bennu’s orbit is tilted by about six degrees compared to Earth’s. In the past year, OSIRIS-REx has been orbiting in the same plane as Earth, traveling slightly ahead of our planet.
And now it’s time for OSIRIS-REx to match Bennu’s orbit in space.
There are two main options to change a spacecraft’s trajectory: one is to use the vehicle’s onboard engines to propel the spacecraft in a certain direction.
The problem with this option is that it uses up the spacecraft’s finite amount of fuel. And OSIRIS-REx would have needed a lot of fuel to alter its course to reach Bennu in time — more than the vehicle is carrying.
So instead, the probe’s navigators opted to use the second option — a gravity assist. “This was the only option to reach Bennu, launching in 2016,” Michael Moreau, a flight engineer at NASA’s Goddard Space Flight Center said.
This maneuver has been used on many previous space missions, to increase or decrease a spacecraft’s speed and course. It’s essentially an exchange of energy, similar to when a roller coaster speeds up while going down a hill.
When OSIRIS-REx swings by Earth, it will steal a little bit of our planet’s momentum in order to change its orbit. Earth is so massive that the maneuver won’t really affect our planet.
But OSIRIS-REx will change its speed and course by more than 8,400 miles per hour. That’s nearly twice the amount the spacecraft would get if it used up all its fuel.
OSIRIS-REx will approach the Earth at a speed of 19,000 miles per hour, flying over Australia first. It will then make its closest approach to Earth at 12:52PM ET, coming within 11,000 miles of Antarctica.
Around that time, the vehicle will lose contact with NASA since it will be out of range with the space agency’s closest tracking stations.
The blackout should last just 50 minutes, though, and NASA expects to regain communications around 1:40PM ET.
The vehicle is also supposed to come into areas dominated by satellites, but NASA says it has taken steps to make sure no collisions happen during the assist.
After Friday’s maneuver, OSIRIS-REx will cruise through space for another year, reaching Bennu in October.
At that point, the vehicle is supposed to fly around the asteroid for two years, surveying the rock’s surface, before actually grabbing the coveted sample and returning to Earth.
The gravity assist is the first step to getting there, and it’ll allow the mission team to meet up with Bennu exactly when they needed to, while saving on fuel.
Please like, share and tweet this article.
Pass it on: Popular Science