Last July, an asteroid about the size of a football field careened closer to Earth than any celestial body has in the last century.

Just a hair closer — in the proportions of space, 40,400 miles is a pretty fine hair — and the space rock known as "2019 OK" would have delivered a devastating wake-up call.

What's most disconcerting about our brush with "Armageddon" is that we didn't even have time to throw Bruce Willis and Ben Affleck at the problem.

"This one did sneak up on us," a NASA expert noted in an internal NASA email, obtained by BuzzFeed.

"This object slipped through a whole series of our capture nets," added JPL engineer Paul Chodas.

Okay, so maybe it wouldn't have been the end of the world. The impact of an asteroid the size of 2019 OK would, according to NASA, level a roughly 50-square-mile area. In other words, it was a potential city killer.

But asteroids come in all shapes, sizes and devastations. Just ask the dinosaurs. And, although 2019 OK was considered a rare event, asteroids don't abide by any predictable timeline.

Which is why NASA is taking is stepping up its asteroid-hunting strategy. The space agency is funding a new space-based telescope called the NEO Surveillance Mission designed to sniff out errant celestial bodies.

"This is a priority for us," Thomas Zurbuchen, NASA's associate administrator for science, reportedly told a committee at the agency's Washington, D.C., headquarters.

Currently, NASA relies on ground-based observatories such as Arizona's Catalina Sky Survey and the Pan-STARRS1 telescope in Maui. There's also the NEOWISE space mission, an orbiting telescope that began its survey back in 2010 -- although it was put into hibernation between 2010 and 2013.

It has been an effective tool in NASA's asteroid-hunting arsenal. Last year NEOWISE found 22 near-Earth objects (NEOs) out of 1,837 total NEO discoveries for 2018.

But that hasn't stopped us from getting the occasional jarring reminder that we can't spot them all.

"It should worry us all, quite frankly," Alan Duffy, lead scientist at the Royal Institution of Australia, tells the Washington Post. "It's not a Hollywood movie. It is a clear and present danger."

Time to study up

Enter the NEO Surveillance Mission. The new eye in the sky aims to spot 90 percent of asteroids that are at least 140 meters in diameter — the size that could do real damage to the home world.

At its heart, the NEO Surveillance Mission will employ a 50-centimeter telescope, outfitted with a highly sensitive infrared camera. It won't be ready for launch until at least 2025 and may take another decade to reach that 90 percent goal. And it will cost a cool $650 million. But really, you can't put a price on peace of mind. Besides, the agency has already budgeted for the NEO Surveillance Mission, with the funds coming from its overall planetary defense budget.

Yes, despite the occasional "sneaky" space rock, NASA already has a program in place to track asteroids and determine their threat level.

As you may have guessed, so far, it's been hit or miss.

The thing is, we don't yet have the means to destroy a killer asteroid, and even NASA concedes "no known weapon system could stop the mass because of the velocity at which it travels, an average of 12 miles per second."

The video above maps every known asteroid in our solar system. (It won't make you feel any better, but it does put the agency's urgency into perspective.)

Deflection, on the other hand, may be possible, if a bit dicey.

That strategy would involve "rapid-response NEO reconnaissance missions." Essentially, a spacecraft would be launched toward the potential harbinger of doom in the hopes of persuading it to even slightly alter its course. We're not sure exactly how the craft would make an asteroid flinch, but even the slightest redirection could end up in wide berth for our planet.

Unfortunately, the Trump administration pulled the plug on NASA's plan to test its asteroid-shunting capabilities with the Asteroid Redirect Mission (ARM) in 2021.

But when the NEO Surveillance Mission hits its stride, we will at least be able to plot the trajectory of far more unwelcome visitors. And maybe, if it comes down to it, brace for impact and still have time to cue up a classic Aerosmith song or two.

NASA's new mission will spot killer asteroids before they sneak up on us
The space agency's $650 million Neo Surveillance Mission is designed to spot killer asteroids.