Nasa gears up to practise saving Earth from killer asteroids with new mission

An artist’s illustration of Nasa’s Double Asteroid Redirection Test (DART) mission as it closes in on the asteroid Dimorphos (Nasa)
An artist’s illustration of Nasa’s Double Asteroid Redirection Test (DART) mission as it closes in on the asteroid Dimorphos (Nasa)

The dinosaurs could only watch helplessly as an asteroid or comet brought their reign on Earth to an end, as have countless fictional humans in space rock doomsday Hollywood fare such as “Don’t Look Up” or “Seeking a Friend for the End of the World.”

But accepting the inevitability of a planet scouring asteroid impact doesn’t sit well with Nasa, and on Monday, the space agency is doing something about it — testing a technique to deflect hazardous asteroids away from Earth by hitting them with a fast moving spacecraft.

“The ground systems are ready, and the spacecraft is healthy and on track for an impact on Monday,” Edward Reynolds, of the Johns Hopkins Applied Physics Laboratory, APL, told reporters during a Thursday press conference on the test. “We have plenty of propellant, and we have plenty of power.”

APL handles the operations of the Dart — Double Asteroid Redirection Test — spacecraft for Nasa, and Mr Reynolds is the mission program manager. He’ll be in the APL Mission Operations Center in Laurel Maryland at 7.14pm EDT Monday evening when the 1,200 pound spacecraft slams into the small asteroid Dimorphos in a bid to slightly change its orbit — the asteroid does not pose a threat to Earth.

It’s a first of its kind mission, and an ambitious one.

“Dimorphos is just barely over 100 meters in diameter; it’s not very big. We’re at 14,000 miles per hour, we’re approaching something that we’ve never seen before,” Mr Reynolds said. “That’s why the ‘T’ in Dart is ‘test.’”

Dart is a proof of concept mission that could help scientists understand if a scaled up version of this “kinetic impactor” technique could deflect a larger asteroid or comet threatening Earth, Nasa’s Dart program scientist, Tom Statler, told reporters Thursday.

“There are two tests in Dart. The first test is the test of our ability to build an autonomously guided spacecraft that will actually achieve the kinetic impact on the asteroid,” he said. “The second test is the test of how the actual asteroid responds to the kinetic impact. Because at the end of the day, the real question is, how effectively did we move the asteroid?”

Dimorphos is a small asteroid about 525 feet across that also orbits a larger asteroid, Didymos. This creates a perfect natural laboratory for Dart, according to Dr Statler, as Dimorphos currently takes 11 hours and 55 minutes to complete an orbit of Didymos. Scientists expect Darts impact could slow that orbit time anywhere from 73 seconds to 10 minutes, assuming the mission is a success.

A successful mission would confirm scientists’ models of how asteroids like Dimorphos behave, Dr Statler added, and which would give Nasa confidence in its design of any future mission to deflect an actual threatening asteroid.

“On the other hand, if the asteroid responds to the dart impact in a way that’s totally unexpected,” he said, “that might actually send us back to reconsider whether, to what extent kinetic impact is really generally usable.”

It won’t be long now till Nasa and APL get an answer to that question, as Dart is closing in on the Didymos and Dimorphos system fast.

“At about 24 hours prior to impact, it will be all hands on deck,” at APL, APL Dart mission systems engineer Elena Adams told reporters Thursday. Although Dart will transition to fully autonomous flight four hours prior to impact, APL operators will be standing by to step in if anything goes wrong, up to and including a miss of the tiny asteroid.

“We have 12 contingencies, and number 21 Is ‘Missed impact,’” Dr Adams said. “We’ll start conserving propellant and we’ll start looking for the objects to come back to. So that’s the plan.”

Dart took its first image of the two asteroids in July, and what were tiny points of light will rapidly grow in the field of view of the spacecraft’s Didymos Reconnaissance and Asteroid Camera for Optical navigation, or Draco instrument, as Dart closes in. Dimorphos is so small, and Dart traveling so fast, Dr Adams said, that the asteroid will remain relatively small up until the last few moments before impact, providing scientists their first real look at the shape and texture of the asteroid.

“Our last image is probably going to be from about two and a half seconds prior to impact,” she said. “So Draco field of view is actually going to be completely filled with this beautiful image of Dimorphos.”

Nasa will carry the Dart impact live in two different feeds. A silent stream of images from Dart’s Draco camera, about one image a second, will be available on Nasa’s media channel beginning at 5.30pm EDT, while a broadcast with commentary and the Draco images can be viewed on Nasa TV beginning at 6pm EDT.

Success in the first part of the test will be marked by loss of radio contact with Dart following its last pictures and its impact with Dimorphos, and there will be celebrations among the engineers at APL, but that just marks the beginning of the next half of the mission, Dr Statler said.

“The engineering team will be celebrating and the astronomers at that moment will be saying, ‘OK, time to get to work,’” he said.

That’s because a wide array of telescopes on the ground and in space will be watching Dimorphos for signs of Dart’s impact, and then keep checking the asteroid for signs that its orbit has in fact changed.

First and foremost will be the Light Italian CubeSat for Imaging of Asteroids, or LiciaCube, a small satellite produced and operated by the Italian Space Agency that hitched a ride on Dart until parting ways on 11 September. It will be in a position to record the impact and any resulting material that is ejected from Dimorphos.

“LiciaCube, will follow Dart about three minutes behind,” Dr Statler said, and “pass by Dimorphos at a safe distance of about 55 kilometers.”

Also focusing on Dimorphos will be The Hubble Space Telescope, James Webb Space Telescope, and even Nasa’s Lucy mission, which is on its way to study the Trojan asteroids in the orbit of Jupiter.

“In the first few hours after the impact, what we’re looking for there is an overall brightening of the whole system indicating how much dust and other debris got kicked up,” Dr Statler said.

Those eyes in the sky combined with ground-based telescopes and radar measurements will help Nasa determine how much, if any, Dart changes the orbit of Dimorphos, but it won’t happen overnight.

“I think the optical observers and the radar observers have a friendly rivalry to see who’s gonna get it first,” Dr Statler said. “I don’t want to get into the middle of that debate. But I think I would be surprised if we had a firm measurement of the period change in less than a few days., and I would be really surprised if it took more than three weeks.”

Whether it’s a handful of days or much longer to get the results, and whether Dart moves Dimorphos’s orbit a lot or a little, Dr. Statler pointed out that the mission remains historic and groundbreaking, the first time people on Earth have attempted — with a chance of success — to change the conduct of the heavens.

“We are moving an asteroid, we are changing the motion of a natural celestial body in space —  humanity has never done that before,” Dr Statler said. “This is the stuff of science fiction books and really corny episodes of Star Trek from when I was a kid. And now it’s for real.”