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Optical Pulses to Deflect Asteroids

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HUNTSVILLE, Ala., and CAMBRIDGE, Mass., March 27, 2014 — An abundance of rogue asteroids are on a collision course with Earth, more than previously thought, according to recent studies. But don’t panic  the threat is not immediate, and scientists are working on a solution.

Researchers from the University of Alabama in Huntsville and MIT have found that optical energy shaped by quantum phenomena, used in conjunction with the microgravity and vacuum of space, could offer scalable deflection of such asteroids.

Previous solutions have included nuclear detonation, which could alter the course of such asteroids but not prevent collision with the Earth.

Femtosecond pulse trains cause ejecta, slowing an asteroid headed toward Earth. The thin white line represents the orbital path of the asteroid. Images courtesy of SPIE.

Optical quantum energy as femtosecond optical pulses could work, the researchers say, as the pulses can slow down an asteroid long enough to allow Earth to pass unharmed through its orbit and the location where the collision would have occurred.

Although these optical pulses can rapidly lose energy in Earth’s atmosphere, the vacuum of space assures that they are not weakened. The delivery of these pulses can, in turn, be optimized in a microgravity environment to approach “near-unit-efficient application of energy to deflection.”

The researchers noted that the asteroid supplies a large majority of propellant required for deflection. Flat sites on these asteroids have normal surface vectors parallel to the orbital path when the deflection occurs. Ideally, the investigators say, they will “eventually find the means to prepare and optimize such areas in advance of and throughout the deflection event.”

Doing so will allow access and use of a larger number of ablation sites for maximally efficient propulsion.

Using femtosecond pulses emits less heat in the host and produces minimal melting of materials at the ablation site. This, and the delivery of the optical energy before emission of the optically absorbing ejecta, is highly advantageous. The optically absorbing ejecta are emitted with about a 1-ps delay after absorption of the femtosecond pulse.

Challenges do exist in using optical quantum energy, including how to generate a sufficient number of well-synchronized energetic femtosecond pulses per unit time, and applying these pulses optimally to the deflection of the threatening asteroid.

Cross-sectional view of an asteroid. Two femtosecond pulses excite two small locally flat areas (encircled by dotted white lines and enlarged here for illustrative purposes by a factor of 10,000). F: Force exerted by the pulses. r: Radius of the asteroid. T: Torque.
The new technique uses laser systems located within a few kilometers of an asteroid, allowing independent paths for multiple synchronized pulse trains. The researchers say this prevents the difficulty and expense associated with routing high-power laser beams over long distances in space.

The method can be scaled to more massive asteroids as well, using larger numbers of mode-locked lasers, as these can be synchronized with extreme precision. Such femtosecond lasers used in the vacuum and microgravity of space “offer both access to, and precise delivery of, optical energy with close to the minimum uncertainty and maximum efficiency allowed by physical laws,” according to the researchers.

Other systems using such multiplexed synchronized mode-locked lasers to transmit beams over longer distances — such as for spacecraft-to-spacecraft power distribution or for removal of small debris orbiting Earth — have also been identified. However, they could be challenging to implement with adequate precision.

The researchers will continue studying this method and hope to test it in terrestrial lab settings at some point in the future.

The work is published online by SPIE.

For more information, visit
Mar 2014
Any bending of a wave of radiation away from its expected path, as, for example, by diffraction or by a magnetic field.
AlabamaAmericasasteroidsBasic Sciencedeflectionenergyfemtosecond optical pulsesMassachusettsmicrogravityMITorbitpropulsionResearch & TechnologyspaceTest & MeasurementUniversity of Alabama in Huntsvillevacuumquantum phenomenaoptical quantum energyejectalasers

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