NASA’s surprising reason for an asteroid crashing into the moon

The need to learn how to save the world from an asteroid might seem like a no-brainer, but planetary defense missions have had a hard time attracting government support – deemed too expensive for years.

Planetary scientist Andrew Cheng, who works at the Johns Hopkins Applied Physics Laboratory in Maryland, inserted the D into NASA’s DART mission, key to making the asteroid deflection test much cheaper earlier this week. On September 26, a 1,300-pound spacecraft crashed into a harmless asteroid the size of a soccer stadium about 6.8 million miles away to find out if the collision could nudge the space rock.

The D stands for “double” in the Double Asteroid Redirection Test, and while double everything usually means more money, in this case it had the effect of greatly reducing costs. In fact, by doubling the space rocks involved, NASA has essentially halved their hardware requirements.

“Did a real lightbulb appear over your head?” Tom Statler, a NASA program scientist, joked to Cheng just hours before the spacecraft’s unprecedented impact.

The tweet may have been deleted
(opens in a new tab)

On a winter morning in 2011, Cheng had an epiphany while doing his daily exercises in his basement: target a moon-like asteroid orbiting another asteroid, rather than a rock flying alone through space. Nothing in particular happened to prompt that thought, like a meteor impacting Earth or a new asteroid discovery, he admitted to a handful of reporters Monday. It was just an accidental realization.

“Suddenly you just realize, ‘Hey, I know how to make something,'” he said of the moment the idea came up.

“Suddenly you just realize: Hey, I know how to do something.”

The DART project cost the United States $325 million, including more than $300 million to develop the autonomous spacecraft, which was instantly destroyed on impact.

A European mission proposed in 2004 to deflect an asteroid would have required two spacecraft launched on different trajectories – one to crash into an asteroid and another to orbit and study it for several months . The mission called Don Quixote never got the green light.

Want more science and technology news delivered straight to your inbox? Sign up for Mashable’s Top Stories newsletter today.

The impact of a small spacecraft on a lone asteroid’s journey around the sun is incredibly difficult to track, since the change in its speed would be on the order of millimeters per second, Cheng explained. On the other hand, it’s much easier to measure how the impact changed the asteroid’s orbit around a nearby rock. Another spaceship would not be necessary.

“We can do that with telescopes on the ground,” he said.

Scientists know that Dimorphos and its larger asteroid companion Didymos make an egg-shaped loop around the Sun every two years. But the journey of Dimorphos around Didymos only takes about 11 hours and 55 minutes. If the experiment works as the engineers hope, DART’s nudge should be cut from that time period by about 10 minutes to about 11 hours and 45 minutes, they say.

The DART spacecraft takes its last image of both Didymos and its small moon Dimorphos before colliding with the latter on September 26.
Photo Credit: NASA/Johns Hopkins APL

Pairs of asteroids, known in astronomy as binary asteroid systems, were the stuff of science fiction decades ago. It was necessary to see one such phenomenon up close – a moon-like asteroid orbiting asteroid Ida by NASA’s Galileo probe in 1993 – to prove its existence. Today, experts estimate that about 15 percent of space rocks are binary, or maybe even triple, asteroid systems, according to the European Space Agency.

And throughout their long history, even pairs of asteroids have smashed into the Earth. Researchers know this from double impact craters likely caused by two simultaneous meteorites.

Only recently has public investment in planetary defenses been ramped up. Congress passed legislation requiring NASA to find and track at least 90 percent of all near-Earth objects 500 feet or larger in size by 2020, but lawmakers failed to fund the program and blocked its progress for years, according to the Planetary Society, a non-partisan space political advocacy group. Over the next five years, the survey received less than $4 million a year – “less than the travel budget for NASA headquarters staff.”

Between 2010 and 2020, that all changed with a long-term funding plan to scour the skies for space rocks and fly space missions, with funding levels increasing a whopping 40x. However, momentum could be threatened again as the White House plans a fiscal 2023 budget cut of over $100 million for the NEO Surveyor, a development space-based infrared telescope designed to find potentially dangerous asteroids and comets.

“We’re really looking forward to getting direction from the other branches of government, along with NASA leadership, so we can put this mission on a good schedule for launch in a couple of years,” Statler said.

“Of course,” he added, “we do what we’re told.”

NEO Surveyor is a proposed mission to discover and characterize most of the potentially dangerous asteroids in the vicinity of Earth.
Credit: NASA/JPL-Caltech

Planetary scientists have more work to do on the DART experiment. A European follow-up mission, Hera, will launch in late 2024 and meet with Dimorphos to conduct its own investigation of the accident site. It will measure the mass of the asteroid and examine the crater closely. The data should tie up loose ends of the experiment and perhaps make DART a repeatable planetary defense technique against a real threat in the future.

So far, the team has described the DART mission as a success. The exercise should inspire confidence in humanity’s ability to detect and intervene on potentially problematic space rocks long before they even get close to this planet, said Elena Adams, a mission systems engineer.

“Earthlings should sleep better,” she said. “Definitely, I will.”