NASA's surprising reason for crashing into an asteroid's moon

The need to learn how to save the world from an asteroid is a no-brainer, but planetary defense missions have had a hard time getting government support.

Andrew Cheng is a planetary scientist who works at the Applied Physics Laboratory in Maryland. A 1,300-pound spaceship crashed into an asteroid the size of a football stadium to see if it could hit it.

Though double of anything usually equates into more money, in this case it had the effect of greatly reducing cost, the D stands for Double Asteroid Redirection Test. NASA halved its hardware requirements because it doubled the space rocks involved.

Tom Statler, a NASA program scientist, asked Cheng if he had a light bulb on.

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Cheng had an idea when he was doing his daily exercises in his basement in the winter of 2011. He admitted to a few reporters on Monday that there was nothing in particular that caused this thought. It wasn't a big deal.

He said that he knew how to do something when the idea came.

The United States spent more than $300 million on the DART project, which was destroyed on impact.

One of the two spaceships needed for the European mission would have to hit the asteroid and the other would have to study it for a long time. The mission didn't get the green light.

Andrew Cheng, a planetary scientist, said he figured out how to accomplish the asteroid impact test with one spacecraft instead of two. Credit: Johns Hopkins APL / Craig Weiman

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Cheng explained that the change in the spacecraft's speed would be on a scale of millimeters per second, making it extremely difficult to track. It's easier to measure how the impact changed the asteroid's trajectory than it is to detect how it happened. There would be no need for another spaceship.

He said that they could do that with telescopes.

Dimorphos and Didymos circle the sun every two years. The journey around Didymos takes about 11 hours. If the experiment was a success, DART's nudging should shave off about 10 minutes from the period.

The DART spacecraft takes its final picture of both Didymos and its moonlet Dimorphos before crashing into the latter on Sept. 26. Credit: NASA / Johns Hopkins APL

A pair of asteroids used to be the stuff of science fiction. It took seeing such a phenomenon up close to prove their existence. The European Space Agency says about 15% of space rocks are double or triple asteroid systems.

Over the course of its history, asteroids have hit Earth. Double impact craters are caused by two meteorites.

Public investment in planetary defense has increased recently. Congress passed a bill requiring NASA to find and track at least 90 percent of all near-Earth objects by 2020, but lawmakers neglected to fund the program, stalling its progress for years, according to the Planetary Society. The survey will receive less than $4 million a year for the next five years.

Funding levels increased 40-fold between 2010 and 2020 as a result of a long-term funding plan to scans the sky for space rocks. The White House wants to cut over $100 million from the budget for the next fiscal year in order to develop a space telescope that can find asteroids and comets.

"We're looking forward to having appropriate direction from the other branches of government, along with NASA leadership, to enable us to put that mission on a good schedule to launch in a few years."

He said that they do what they are told.

NEO Surveyor is a proposed mission to discover and characterize most of the potentially hazardous asteroids that are near Earth. Credit: NASA / JPL-Caltech

There is more work to be done by planetary scientists. A follow-up European mission, Hera, will launch in the late 20th century and rendezvous with Dimorphos to conduct its own crash scene investigation. The asteroid's mass will be measured and it will be able to see the crater. The data should tie up the loose ends of the experiment and possibly make DART a repeatable planetary defense technique in the future.

The DART mission is being called a success so far. Elena Adams, a mission systems engineer, said that the exercise should instill confidence in humanity's ability to spot potential problem space rocks.

She said that earthlings should sleep better. I will definitely.