From: Andy Soos, ENN
Published April 19, 2013 07:39 AM

Shooting Asteroids

Asteroids is a video arcade game. The object of the game is to shoot and destroy asteroids and saucers while not colliding with either. Real asteroids are minor planets (small Solar System bodies and dwarf planets) that are not comets, especially those of the inner Solar System. They have also been called planetoids, especially the larger ones. Shyam Bhaskaran of NASA is working a lot with asteroids these days. And also like many of his colleagues, the deep space navigator devotes a great deal of time to crafting, and contemplating, computer-generated 3-D models of these intriguing nomads of the solar system. But while many of his coworkers are calculating asteroids' past, present and future locations in the cosmos, zapping them with the world's most massive radar dishes, or considering how to rendezvous and perhaps even gently nudge an asteroid into lunar orbit, Bhaskaran thinks about how to collide with one.

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"If you want to see below the surface of an asteroid, there's no better way than smacking it hard," said Bhaskaran. "But it's not that easy. Hitting an asteroid with a spacecraft traveling at hypervelocity is like shooting an arrow at a target on a speeding race car."

The term hypervelocity usually refers to something traveling at very high speed -- two miles per second (6,700 mph / 11,000 kilometers per hour) or above. Bhaskaran's hypothetical impacts tend to be well above. It also refers to velocities so high that the strength of materials upon impact is very small compared to inertial stresses and both objects simply vaporize.

"Most of the hypervelocity impact scenarios that I simulate have spacecraft/asteroid closure rates of around eight miles a second, 30,000 miles per hour [about 48,000 kilometers per hour]," said Bhaskaran.

In the majority of our solar system, where yield signs and "right of way" statutes have yet to find widespread support, hypervelocity impacts between objects happen all the time. But all that primordial violence usually goes unnoticed here on Earth, and almost never receives scientific scrutiny.

"High-speed impacts on asteroids can tell you so many things that we want to know about asteroids," said Steve Chesley, a near-Earth object scientist at JPL. "They can tell you about their composition and their structural integrity -- which is how they hold themselves together. These are things that are not only vital for scientific research on the origins of the solar system, but also for mission designers working on ways to potentially move asteroids, either for exploitation purposes or because they may be hazardous to Earth."

Hypervelocity impacts by spacecraft are not just a hypothetical exercise. Scientists have taken the opportunity to analyze data from used spacecraft and rocket stages that have impacted the moon and other celestial bodies since the Apollo program. On July 4, 2005, NASA's Deep Impact spacecraft successfully collided its dynamic impactor with comet 9P/Tempel 1 -- it was the first hypervelocity impact of a primitive solar system body.

"Impacting an asteroid presents slightly different challenges than impacting a comet," said Bhaskaran. "Comets can have jets firing material into space, which can upset your imaging and guidance systems, while potential asteroid targets can be as small as 50 meters [164 feet] and have their own mini-moons orbiting them. Since they're small and dim, they can be harder to spot."

"Asteroids hardly ever resemble perfect spheroids," said Bhaskaran. "What you've got floating around out there are a bunch of massive objects that look like peanuts, potatoes, diamonds, boomerangs and even dog bones -- and if the spacecraft's guidance system can't figure out where it needs to go, you can hit the wrong part of the asteroid, or much worse, miss it entirely."

"So, instead, we have AutoNav do the job for us. It is essentially a cyber-astronaut that takes in all the pertinent information, makes its own decisions and performs the actions necessary to make sure we go splat where we want to go splat."

"AutoNav's imaging system and its orbit determination algorithms will detect the asteroid and compute its location in space relative to the impactor," said Bhaskaran.

"We expect the crater excavated by the impact of ISIS could be around 100 feet across," said Chesley. "From its catbird seat in orbit around the asteroid, OSIRIS-REx, at its leisure, would not only be able to determine how big a hole there is, but also analyze the material thrown out during the impact."

The data would not only provide information on what makes up the asteroid, but how its orbit reacts to being hit by a NASA spacecraft.

"While the effect of ISIS (The name of a mission to impact an asteroid) on the orbit of asteroid 1999 RQ36 will be miniscule, it will be measurable," said Chesley. "Once we know how its orbit changes, no matter how small, we can make better assessments and plans to change some future asteroid's orbit if we ever need to do so. Of course, to get all these great leaps forward in understanding, we have to hit it in the first place."

NASA detects, tracks and characterizes asteroids and comets passing relatively close to Earth using both ground- and space-based telescopes. The Near-Earth Object Observations Program, commonly called "Spaceguard," discovers these objects, characterizes a subset of them, and predicts their paths to determine if any could be potentially hazardous to our planet.

With all of this there may be one day an exact way to deter an asteroid impact on Earth. Just abetter game of Asteroids...

For further information see Smashing Asteroids.

Asteroid image via NASA.

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