NASA tests new asteroid-defense system, DART


NASA tests new asteroid-defense system even as it slashes funding for its mission to spot killer space rocks

Don’t look down. As NASA prepares to test its planetary defense abilities next week by ramming a spacecraft into an asteroid, the agency is quietly shuttering plans for an outer space telescope to detect dangerous space rocks on a collision course with Earth.

On Sept. 26, NASA’s Double Asteroid Redirection Test (DART) spacecraft will ram into the asteroid Dimorphos about 6.8 million miles from Earth at roughly 14,000 miles per hour. The $325 million mission — which will send the 1,325-pound spacecraft into a rock about half the size of a cruise ship — is the first attempt at determining whether humanity could budge a future asteroid headed our way.

But such capabilities are of limited use if no one on Earth knows that such a collision might be imminent.

“This is a trial-and-error experiment in the classic sense. And an important one,” said MIT asteroid expert Richard Binzel about the DART mission. “The ironic thing is that this experiment comes as we are turning a blind eye to what asteroids are out there that we don’t know about.”


NASA in March slashed the $170 million planned budget for a new infrared space telescope, the Near-Earth Object (NEO) Surveyor, meant to find “city-buster” sized asteroids flying near Earth. The decision was a shock to astronomers because the threat of an impact is one Congress has long worried over — concerns that were reinforced by warnings from the National Academy of Sciences in the last few years.

The bottom line is that in 2005, Congress told NASA to find 90 percent of the dangerous space rocks at least 460 feet wide by 2020. Since then, space and terrestrial telescopes have only turned up an estimated 40 percent of them. Without NEO Surveyor, far more capable than current surveyors, that gap will take another three decades to close.

While the movie “Don’t Look Up” satirized politicians ignoring a planet-killing comet, the real worry is space rocks that are smaller, but still big enough to destroy a city or region. Fewer than 1,000 “potentially hazardous asteroids” a kilometer (0.62 miles) or wider — big enough to have continental or planetary consequence on impact — orbit near Earth, and none are on a trajectory for our planet. Instead, unknown mid-sized ones, about the size of Dimorphos, are the real concern. “The odds are that nothing will happen, but luck isn’t a plan,” said Binzel. (Just for perspective, an asteroid like Dimorphos hitting the Earth on a typical 1-in-12,000 year trajectory would leave a crater a mile wide and 1,150 feet deep, according to this fun and scary impact simulator from Purdue University and Imperial College London.)

Next week, soon after DART smacks into Dimorphos, NEO Surveyor will go through a review of its preliminary design at NASA headquarters. It’s a vital last step before a spacecraft moves toward being built. The House and Senate have proposed a $26 billion budget for NASA in 2023, setting aside about $90 million for NEO Surveyor’s funding, — more than the space agency asked for earlier this year, but still only about half the project’s original budget.

That will move NEO Surveyor’s planned launch to 2028 or later, according to NASA. But some observers fear the budget cut this year signals it will never launch.


“Clearly it could have easily been proposed to be canceled, right? Because that’s functionally almost what they’re doing,” said Casey Dreier, senior space policy adviser at the Planetary Society. He called NASA’s initial proposed cut to NEO Surveyor in March “catastrophic” because building, launching and operating a spacecraft is a yearslong endeavor. Seesawing budgets drive away contractors and designers and drive up costs in the long run — a pattern that NASA has repeated for decades in big-ticket projects like the James Web Space Telescope, which launched years behind schedule and billions of dollars over budget.

“You can’t just walk down to the store with the NASA credit card and pick a NEO Surveyor off the shelf. It doesn’t work that way. These take years and years to design and build,” Dreier said.

In the meantime, the dramatically pruned budget is forcing tough choices among the scientists and engineers working on the project.

“We are having to take the steps we have to, to accommodate the budget profile we have been given,” said NEO Surveyor principal investigator Amy Mainzer of the University of Arizona. “We are bath tubbing some large things,” she said, such as big pieces of the spacecraft and its scientific instruments. “We have to make sure we do not run out of money before the end of the year.”

NASA has defended the decision to cut NEO Surveyor’s funding as driven by the need to prioritize other missions headed to Mars and the Solar System’s asteroid belt. Both of those destinations have tight orbital “windows” in which their orientation to Earth makes launches feasible.

“NASA takes planetary defense seriously, and the Planetary Defense Coordination Office was established in 2016 to manage our increasing efforts in this important field,” the agency said in a statement to Grid. “NASA will launch NEO Surveyor as early as possible,” said the statement.

The Chelyabinsk Fireball

On Feb. 15, 2013, astronomers waited calmly for an asteroid about half the size of a football field, called 2012 DA14, to zip 17,200 miles over Antarctica on a close, but harmless, swing past Earth. Which is exactly what happened — but nobody cared.

That’s because on that same day — in a confluence with odds estimated at 1 in 100 million — astronomers also had to hurriedly answer questions about a meteor streaking over Russia, creating panic, breaking windows and injuring hundreds of people (all indirectly) as it exploded with a force of about 440 kilotons of TNT, south of Chelyabinsk, Russia. “The Chelyabinsk event was an extraordinarily large fireball, the most energetic impact event recognized since the 1908 Tunguska blast in Russian Siberia,” concluded a NASA analysis.

What’s remarkable about the “Chelyabinsk Fireball” is that the two objects passing by Earth were completely unrelated space rocks, said Binzel. One came from the southern hemisphere and the other came from the north. Their simultaneous visits to Earth on the same day inject a note of unease into the otherwise reassuring odds of asteroid impacts: A city-buster size asteroid is estimated to hit Earth about once every 20,000 years, for example, and a DA14 one about every 1,200 years or so. But the Chelyabinsk blast came only a century after the larger Tunguska one mentioned in the NASA analysis, which flattened hundreds of square miles of cforest.

“It just seemed pretty incredible,” said Binzel, of the asteroid confluence in 2013. “This random thing happened, but that’s the nature of random events. It could be next year, and it could be 300 years.”


Since then, space has delivered a few other unsettling surprises, with the 2017 first sighting of an interstellar comet, ‘Oumuamua which went unseen until it was already past Earth, moving at 196,000 miles per hour. And in 2019, a “sneaky” asteroid zipped from behind the sun’s glare, out of sight of telescopes, to pass within 48,000 miles of Earth, “a surprise to the planetary defense community,” NASA’s Paul Chodas told BuzzFeed News.

More fundamentally, scientific recognition that the age of dinosaurs ended with a tremendous impact about 66 million years and the identification of the Chicxulub crater in the Gulf of Mexico as its site in 1991, changed scientific thinking about asteroids, said geophysicist Mark Boslough of the Los Alamos National Laboratory. The “freight train” impacts of the shattered comet Shoemaker-Levy into Jupiter in 1994 also startled astronomers. “That gave planetary defense a real shot in the arm,” he said.

The 2013 Chelyabinsk airburst is still under analysis. The power of its breakup opened scientists’ eyes to the surprising force of a large meteor passing through the atmosphere. If nothing else, the risks of airbursts might have been underestimated.

“We don’t know how representative Chelyabinsk was. It was one event and from one direction at one angle and one size, and one composition. It doesn’t necessarily represent what would happen the next time,” said Boslough. “We have a lot to learn. We have a heck of a lot to learn.”

A brilliantly conceived experiment

The DART collision is meant to fill in some of those holes. Its target, Dimorphos, was discovered in 2003 circling a larger asteroid called Didymos. Like the Chelyabinsk meteor, both are thought to be porous boulders of clay and sandy minerals that are called “ordinary” chondrites (a chondrite is any kind of stony meteor), because they are the kind most commonly found on Earth.


Just how to deflect one of these stony, sandy piles of rocks away from Earth is the key question for the impact mission. Such objects aren’t like pool balls. They won’t nicely absorb a smack to steer themselves into the corner pocket with mathematical precision, but with a crunchy and loose composition, they might just soak up an impact instead. “We actually don’t know very much, if anything, of how an asteroid acts if we try to push on it,” said Binzel.

That’s where DART comes in. Astronomers will precisely measure the momentum its impact imparts to Dimorphos, as revealed by changes in its orbit around the bigger Didymos. (Because Dimorphos is circling Didymos’ edge, as seen from Earth, that measurement should be easy to make.) The spacecraft will record its death plunge into the asteroid and a small companion, Italy’s LICIACube spacecraft, will record the aftermath, flying past whatever crater is left behind three minutes after impact. NASA expects the impact to change the orbital speed of Dimorphos by less than one percent. That should still be enough to alter its duration by several minutes, an easily observable change.

“It’s actually a brilliantly conceived experiment,” said Boslough. “It’s better to have a prototype or have done this once, than having this suddenly decide you have to do it and never have done it before.”

For planetary scientists, the size and structure of the crater left behind by the impact should reveal the internal structure of the asteroid, and just how well ones like it would respond to deflection attempts. The crater will get an even more thorough inspection in four years from Europe’s follow-up Hera mission.

All that effort makes the decision to delay NEO Surveyor all the more perplexing, said Dreier. In 2019, a National Academy of Sciences panel said the only way that NASA could find most of the city-buster size asteroids left undiscovered within the next decade is with just such a space-based infrared telescope. A more recent decadal survey from the academy reflecting the views of the astronomy community, generally used to guide NASA’s priorities, also endorsed NEO Surveyor. (NASA has even signed a memorandum with the U.S. Space Force that includes collaboration on planetary defense.)


Ground-based telescopes are finding more of these asteroids, Binzel acknowledged, but he estimates they will fall short, spotting only about 70 percent of the city-buster size ones in the next decade. Unlike those, NEO Surveyor will look for asteroids coming from sunward directions 24 hours a day and would likely have picked up a lot of the recent surprises, allowing them to be studied.

“Once NEO Surveyor is in place, we will probably start discovering objects on a collision course with enough advanced warning that we get instruments in place to do some actual careful, scientific observations of something that’s predicted to happen” said Boslough. Those kinds of observation will help fill in a lot of questions about airbursts and impacts in general, he said.

That day looks a few more years off now than it did before, Mainzer acknowledged. In the big picture, an asteroid impact must be weighed against calamities like climate change, she said, where climate change is both certain and severe, a “high” risk. An impact is unlikely but could have severe consequences, making it more of a “medium” one. But that doesn’t mean it should be ignored.

“This is a very hard problem. The objects are dim. They’re faint and far away,” said Mainzer. “NEO Surveyor is optimized to do this job. But we have to launch it. And ideally not spend too much money on it.”

Thanks to Alicia Benjamin for copy editing this article.

  • Dan Vergano
    Dan Vergano

    Science Reporter

    Dan Vergano is a science reporter for Grid.