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NASA spacecraft will slam into an asteroid Monday — if all goes right

This illustration depicts NASA's DART probe, foreground right, and the Italian Space Agency's LICIACube, bottom right, at the Didymos system before impact with the asteroid Dimorphos, left. DART is expected to zero in on the asteroid on Monday and is intended to slam it head-on. (Steve Gribben/Johns Hopkins APL/NASA)

Heart rates are spiking in the Washington suburbs, where scientists and engineers on Monday evening hope to witness a vending-machine-sized spacecraft that is 7 million miles from Earth crash into an asteroid.

If everything goes as planned, and the laws of gravity and motion don’t change at the last minute, this will happen at 7:14 p.m. Eastern time — or, to be precise: 7:14:23.

There’s nothing major at stake here, other than demonstrating a technology that someday might save civilization.

It’s important to note that the targeted asteroid isn’t a threat to Earth and has done nothing wrong to deserve this attention. But the space collision is a critical moment for the Double Asteroid Redirection Test (DART), NASA’s first test of “planetary defense.”

This mission is designed to show how a “kinetic impactor” could deflect a dangerous asteroid that might strike the Earth. There are a lot of space rocks out there that could interrupt our typically peaceful journey around the sun. The general strategy in planetary defense is to alter the orbits of asteroids so that, even if they come close to Earth, they’ll pass by harmlessly.

The DART team members are confident they’ll succeed, but they admit this is not a slam dunk. The spacecraft could miss. There will be no consolation for the scientists and engineers if they almost hit the target. This isn’t horseshoes or hand grenades: Close doesn’t count when you’re trying to change the course of an asteroid.

“Mission success is pretty clear: You need to hit that asteroid,” said Elena Adams, an engineer at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., which is conducting the mission under contract with NASA.

The asteroid is called Dimorphos. It is roughly 500 feet in diameter. No one knows precisely what it looks like. It’s just a fuzzy blob in telescopes. The first time Earthlings will get a good look at it will be less than an hour before impact.

Dimorphos orbits another, larger asteroid, named Didymos (Greek for “twin”), as both hurtle around the sun. Such “binary” asteroids are common.

The spacecraft was launched last November from California. The bigger asteroid serves essentially as the guide star of the mission. But only the smaller asteroid is being targeted. When the spacecraft gets close to big Didymos, it should see little Dimorphos swinging around from behind its companion. It’ll be a head-on collision.

Things will surely be tense in the Mission Operations room in Laurel. The Applied Physics Laboratory handles a lot of classified government research but sometimes does nifty space missions. Seven years ago it successfully flew NASA’s New Horizons spacecraft by Pluto and got the first close-up images of the dwarf planet.

How it works: NASA hopes to hit an asteroid now in case we really need to knock one away later

This mission is similar in that it’s fraught with difficulties and uncertainties. The spacecraft must make crucial last-second navigational decisions autonomously. Flying a spacecraft at high speed — about 14,000 miles per hour — into a relatively small asteroid is something no one has ever done before.

If the DART spacecraft misses the target, it will theoretically have a second chance for a smashup encounter with Dimorphos in another two years — but the engineers aren’t even thinking about taking a mulligan.

Previous space science missions by NASA and the Japanese space agency took samples of asteroids, but those were carefully choreographed rendezvous involving gradual approaches. DART envisions a high-speed crash. The scientists and engineers behind the mission say they won’t know if they’ll hit the asteroid until about 20 seconds before impact.

“The asteroids are extremely dark,” Adams said. “We have to hit something that’s the size of two stadiums. You can’t see them until about an hour before hitting them …. Even then it’s just a pixel in our camera.”

Mission engineers are making their last adjustments to the spacecraft’s trajectory, but the final approach, in the hours before the anticipated collision, will be automated. A camera on board the spacecraft will capture images of the smaller asteroid while simultaneously helping the vehicle zero in on the target.

The final images transmitted by the spacecraft’s camera will show a tiny white dot growing into something brighter, bigger and more asteroidal. Then, if all goes as hoped, Dimorphos will loom so large it fills the field of view.

And that will be the last thing anyone will see as the spacecraft makes the ultimate sacrifice.

Telescopes on Earth as well as the Webb and Hubble out in space will also be observing the impact.

The most worrisome asteroids with potentially global climate repercussions are the ones larger than 1 kilometer in diameter. They’re the easiest to spot. More than 95 percent of the estimated population of such killer rocks has been identified, said planetary scientist Nancy Chabot, DART’s coordination lead.

Fewer than half of the asteroids between 140 meters and 1 kilometer have been identified. That’s an ongoing effort. Rocks in that size range — and Dimorphos is one of them — could wipe out a major city with a direct hit. Chabot said early detection is key to planetary defense.

“This is something that you don’t do last-minute. This is something that you do years in advance,” she said.

NASA and its partners have a catalogue of 30,000 objects at this point, said the agency’s planetary defense officer, Lindley Johnson. Scientists can calculate their orbits for some decades into the future, but as the timeline gets longer, the orbital uncertainties increase.

No dangerous asteroid at the moment appears to be on track to slam into Earth, to the extent that these things can be calculated, Johnson said. But he’ll be watching Monday night’s asteroid redirection test closely.

“We’ve got to have such technology,” he said. “It would be prudent upon us to test that all out ahead of time, so we’re not trying to do it for the first time when we really need it to work.”

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