Nasa launches spacecraft to kick asteroid off course

Mission a test run should humanity ever need to stop a giant space rock from wiping out life on Earth

WASHINGTON • A Nasa mission to smash a spacecraft into an asteroid - a test run should humanity ever need to stop a giant space rock from wiping out life on Earth - has blasted off from California.

It may sound like science fiction, but the Dart (double asteroid redirection test) is a real proof-of-concept experiment, the goal of which is to slightly alter the trajectory of the asteroid Dimorphos.

The SpaceX rocket carrying the mission spacecraft lifted off at 10.21pm Pacific Time on Tuesday from Vandenberg Space Force Base in Lompoc, California.

"Asteroid Dimorphos: we're coming for you!" Nasa tweeted after the launch, later saying the spacecraft had successfully separated from the rocket's second stage.

"We've received our first signals from #DARTMission, which will continue to roll out its solar arrays in the coming hours and prepare for its 10-month, one-way trip to the asteroid," it added.

Dimorphos is a "moonlet" around 160m, or two Statues of Liberty, wide, that circles a much larger asteroid called Didymos, 762m in diameter. The pair orbit the Sun together.

Nasa said impact should take place in the autumn of next year, when the binary asteroid system is 11 million km from Earth, almost the nearest point they ever get.

"What we're trying to learn is how to deflect a threat," Nasa's top scientist Thomas Zuburchen said of the US$330 million (S$452 million) project, the first of its kind.

To be clear, the asteroids in question pose no risk to our planet. But they belong to a class of bodies known as near-Earth objects, which approach within 48.3 million km of our planet.

Nasa's planetary defence coordination office is most interested in those larger than 140m in size, which have the potential to level entire cities or regions with many times the energy of average nuclear bombs. There are about 10,000 known near-Earth asteroids 140m in size or greater, but none has a significant chance to hit in the next 100 years.

One major caveat: scientists think there are still 15,000 more such objects waiting to be found.

Planetary scientists can create miniature impacts in labs and use the results to produce sophisticated models about how to divert an asteroid - but these are always inferior to real-world tests.

Scientists say the Didymos-Dimorphos system is an "ideal natural laboratory", because Earth-based telescopes can be used to judge the time it takes the moonlet to orbit its big brother.

Since the current orbit period is known, the change will reveal the effect of the impact, set to occur between Sept 26 and Oct 1 next year. And because the asteroids' orbit never intersects our planet, they are thought safer to study.

The Dart probe, a box the size of a large fridge with limousine-sized solar panels on either side, will slam into Dimorphos at just over 24,000 km an hour.

Mr Andy Rivkin, leader of the Dart investigation team, said there is some uncertainty about how much energy will be transferred by the impact because the moonlet's internal composition and porosity are not known. The more debris that is generated, the more push will be imparted on Dimorphos.

"Every time we show up at an asteroid, we find stuff we don't expect," said Mr Rivkin.

The Dart spacecraft also contains sophisticated instruments for navigation and imaging.

AGENCE FRANCE-PRESSE

A version of this article appeared in the print edition of The Straits Times on November 25, 2021, with the headline 'Nasa launches spacecraft to kick asteroid off course'. Subscribe