NASA’s Plan to Save the World: Let’s Slam a Spacecraft Into an Asteroid
In a plan fit for Michael Bay, NASA is going to ram a spacecraft into an asteroid. Why? To see how much force is necessary to stop one from destroying Earth.
Let’s face it: the biggest threat to civilization (besides civilization) is asteroids. Ever since the summer of 1998, America and filmgoers the world over have realized the risks associated with large, unstoppable blocks of rock headed on a collision course for society.
Sure, we’ve seen them dealt with heroically by teams of astronauts and president Morgan Freeman, but the real world question still remains: how will we stop world destruction from occurring?
That’s the question NASA is trying to answer with an upcoming series of experiments. What they’ve got planned right now: battering ram.
The Asteroid Impact and Deflection Assessment (AIDA) will essentially be a two stage effort. First, the European Space Agency will put a satellite into orbit around an asteroid, allowing it to collect data. After that, a NASA spacecraft will slam into it head first, and we’ll see what happens. 2022: get excited.
It all seemed simpler back in the ‘90s, when you could just load a bunch of oil rig experts on a shuttle with nuclear weapons, but these days the science is actually trying to take the drilling out of the equation. Blasting the world-destroying asteroid to smithereens isn’t really even necessary, according to Near-Earth Objects Program executive Lindley Johnson at NASA. “To deflect an asteroid that may be on an impact path with the Earth,” says Johnson, “we simply must either speed up its orbital velocity a small amount or slow it down a small amount.”
And that’s the true purpose of NASA’s new joint program: seeing how much force is necessary. Think of the future of asteroid defense less like a Terminator film, and more like a mega cut of goalie saves in soccer: a simple tip can save the day. According to Johnson, asteroids orbit the Sun with velocities relative to Earth that average about 12 miles per second. “But if you were add or subtract just an inch per second of velocity to the asteroid, that will over time change the position of the asteroid in its orbit enough that in a couple of years the asteroid will miss the Earth rather than hit.”
That means that, in the future, NASA could fix next year’s asteroid problems on this year’s passer-by.
Johnson says once you discover a problem asteroid, “you need to determine how much force is required to impart that inch per second of velocity change, which of course depends on the mass of the asteroid. We estimate the mass of the asteroid by determining its composition, which provides us some estimate of its density, and combined with an estimate of size we can arrive at an estimate for its mass.”
That’s where the current program might help, says Johnson. He explains that spacecraft of several tons “simply running into an asteroid on the right trajectory, a so-called kinetic impactor, could impart enough force to change the velocity of an average few hundred meter sized asteroid by an inch or two per second.” That’s the plain behind DART.
And yes, action movie fans, there’s the “Armageddon” theory, too. While we may not want to send Michael Bay’s chosen band of brothers into orbit with half a dozen nuclear weapons, NASA doesn’t necessarily think it’s out of the question. “Use of a nuclear device to deflect an asteroid is not preposterous,” says Johnson, “but it wouldn’t be used in the way depicted in the movies. The most effective way we think to use a nuclear device is to detonate it at a standoff distance from the asteroid’s surface. The irradiation will cause a layer of that surface to heat up and blow-off, which in turn imparts a shove of force on the rest of the asteroid in the opposite direction.”
Think of it as a hair-dryer on the side of an ice block—or a quick chemical peel to the side of Mount Rushmore.
The biggest questions in how to deal with an asteroid aren’t empirical, they’re results of individual circumstances. “One of the concerns that must be better understood is the coherent strength of the hazardous asteroid,” says Johnson. “Is it strong enough to absorb the force of the kinetic impactor, or will it simply break up into smaller pieces still headed on pretty much the same impacting trajectory?”
Johnson says a creative solution to moving a fragile asteroid might be to use the force of gravity to effect the change in velocity. “The attractive force of gravity between a heavy spacecraft and the asteroid might be enough to affect the velocity change by having the spacecraft “hover” using ion thrusters on the appropriate side of the asteroid long enough that the gravitational attraction gradually slows it down or speeds it up.”
Johnson says this is a technique NASA plans to demonstrate during the Asteroid Redirect Mission (ARM), which will take place in the next decade.
Which technique will be most effective of course remains to be seen. Asteroids as explained earlier can’t be dealt with exactly the same way, and since one well-placed rock to end civilization, it’s for the best that they try as many options out as possible.
After all, what would we do without Bruce Willis?