Nasa examines 'tractor beams' for sample gathering

Research laser The "tractor beam" approaches depend on precise shaping of the intensities of laser beams

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US space agency Nasa has funded a study of "tractor beams" to gather samples for analysis in future missions.

The $100,000 (£63,000) award will be used to examine three laser-based approaches to do what has until now been the stuff of science fiction.

Several tractor-beam ideas have been published in the scientific literature but none has yet been put to use.

Nasa scientist Paul Stysley says the approach could "enhance science goals and reduce mission risk".

"Though a mainstay in science fiction, and Star Trek in particular, laser-based trapping isn't fanciful or beyond current technological know-how," said Dr Stysley of Nasa's Goddard Space Flight Center, whose group was awarded the research funding.

High-beam profile

The team has identified three possible options to capture and gather up sample material either in future orbiting spacecraft or on planetary rovers.

Mars rover image with "tractor beams" The approach could be put to use in space and on planetary surfaces

One is an adaptation of a well-known effect called "optical tweezers" in which objects can be trapped in the focus of one or two laser beams. However, this version of the approach would require an atmosphere in which to operate.

The other two methods rely on specially shaped laser beams - instead of a beam whose intensity peaks at its centre and tails off gradually, the team is investigating two alternatives: solenoid beams and Bessel beams.

The intensity peaks within a solenoid beam are found in a spiral around the line of the beam itself, while a Bessel beam's intensity rises and falls in peaks and troughs at higher distances from the beam's line.

Solenoid beams have already proven their "tractor beam" abilities in laboratory tests published in the journal Optics Express, but the pulling power of Bessel beams, presented on the preprint server Arxiv in February, remains to be proved experimentally.

In all three cases, explained Dr Stysley, the effect is a small one - but it could in some instances outperform existing methods of sample gathering.

"[Current] techniques have proven to be largely successful, but they are limited by high costs and limited range and sample rate," he said.

"An optical-trapping system, on the other hand, could grab desired molecules from the upper atmosphere on an orbiting spacecraft or trap them from the ground or lower atmosphere from a lander.

"In other words, they could continuously and remotely capture particles over a longer period of time, which would enhance science goals and reduce mission risk."

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