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'Painted' asteroids: a subtler method of influencing their orbits

26 February 2013

A Texas A&M physics professor is exploring a theory that proposes a novel method of deflecting asteroids - not by blasting them, but by painting them.

Photo: Stock.xchng

Dave Hyland, professor of physics and astronomy and also a faculty member in the aerospace engineering department at Texas A&M, says one possible way to avert an asteroid collision with Earth is by using a process called 'tribocharging powder dispensing' - spreading a thin coating on an approaching asteroid like DA14, which came within 17,000 miles of the earth earlier this month.

What happens is that the paint changes the amount by which the asteroid reflects sunlight, Hyland theorizes, producing a change in what is called the Yarkovski effect (discovered by the Russian engineer in 1902). The force arises because on a spinning asteroid, the dusk side is warmer than the dawn side and emits more thermal photons, each photon carrying a small momentum. The unequal heating of the asteroid results in a net force strong enough to cause the asteroid to shift from its current orbit, Hyland further theorizes.

The kind of paint used is not the kind found at your local hardware store, Hyland explains. “It could not be a water-based or oil-based paint because it would probably explode within seconds of it entering space. But a powdered form of paint could be used to dust on the asteroid and the sun would then do the rest. It cures the paint to give a smooth coating, and would change the unequal heating of the asteroid so that it would be forced off its current path and placed on either a higher or lower orbit, thus missing Earth.

“I have to admit the concept does sound strange, but the odds are very high that such a plan would be successful and would be relatively inexpensive. The science behind the theory is sound. We need to test it in space.”

As for getting the paint on the asteroid, a practical way to do this was discovered by a former student of Hyland’s, Shen Ge, who has since started a new space company. The tribocharging powder dispenser would spray a mixture of inert gas and charged dry-paint powder at the asteroid that would attract the powder to its surface electrostatically. Then solar wind and UV radiation would cure the powder, giving a smooth, thin coat on the surface.

Getting the paint in the asteroid’s path in a timely manner will certainly be a challenge, Hyland observes. “The tribocharged powder process is a widely used method of painting many products,” he says. “It remains only to adapt the technology to space conditions.”

NASA has approached Hyland for developing such a project to test the theory, and the Earth may need it quickly. An asteroid called Apophis is due in 2029 and will come closer than many communications satellites in orbit right now. It will fly by on April 13 (Friday the 13 to be exact) of 2029 and make a return trip in 2036, and it’s estimated to be more than 1,000 feet in length. There is no chance of its hitting Earth in 2029, but a small chance in the next close approach in 2036, Hyland notes.

Meanwhile, ESA’s proposed Asteroid Impact and Deflection Assessment mission now has a target: asteroid Didymos. The recent Russian meteor and, on the same day, our planet’s close encounter with an even larger chunk of celestial debris underline the need for us to learn more about these high-speed space rocks.

For the last two years, ESA has been working with international partners on the mission concept, dubbed AIDA. Last week, research centres each side of the Atlantic agreed the spacecraft would target asteroid Didymos.

Currently under study, the mission would intercept Didymos around the time of the asteroid’s closest approach to within 11 million km of Earth in 2022.

Didymos is a ‘binary’, with two asteroids orbiting each other – one is roughly 800m across, the other about 150m.

AIDA is a low-budget international effort that would send two small craft to intercept a double target. While one probe smashes into the smaller asteroid at around 6.25 km/s, the other records what happens.

ESA’s AIDA mission now has a target: asteroid Didymos (image courtesy of the European Space Agency)

One effect would be a change in the orbital ballet of the two objects. AIDA is not intended to show how we could deflect an asteroid that threatens Earth but it would be a first step.

The craft are conceived to be independent and could achieve most of their goals alone. The collider is the Double Asteroid Redirection Test, or DART, from the Johns Hopkins’ Applied Physics Laboratory in the US. ESA’s Asteroid Impact Monitor, or AIM, would survey Didymos in detail, before and after the collision.

Didymos poses no risk to our planet, but will come close enough to be observable by 1–2m diameter telescopes on Earth before and after the strike. AIM’s close-up view would provide ‘ground truth’ and observe the impact dynamics as well as the resulting crater, allowing ground-based observations and models to be evaluated.

Earlier this month, ESA issued a call for scientists to propose experiments that could be carried on the mission or performed on the ground to increase its return.

“AIDA is not just an asteroid mission, it is also meant as a research platform open to all different mission users,” says Andrés Gálvez, ESA studies manager.

“The project has value in many areas,” agrees Andy Cheng, AIDA lead at Johns Hopkins’ Applied Physics Laboratory, “from applied science and exploration to asteroid resource utilisation.”

Researchers have until 15 March to express their interest. The experiment ideas can be anything that deals with hypervelocity impacts, planetary science, planetary defence, human exploration or innovation in spacecraft operations.

The energy released in the AIDA impact at several kilometres per second is similar to that of a large piece of space junk hitting a satellite. The mission would thus help to model severe spacecraft damage by space debris.

“It is an exciting opportunity to do world-leading research of all kinds on a problem that is out of this world,” says Stephan Ulamec from the DLR German Aerospace Centre. “And it helps us learn how to work together in international missions tackling the asteroid impact hazard.”

“A mission such as this allows us to test technologies before any asteroid is identified as a threat,” explains Patrick Michel, leader of the Planetology team at the Observatoire de la Côte d´Azur (OCA, Lagrange Laboratory) and a member of the Working Group on Near-Earth Objects of the International Astronomical Union.

“Understanding the physics of impacts is also key to planetary science and binary asteroid dynamics.”


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