NASA plans to use clouds of reflective glitter-like particles rather than mirrors to help it find stars and planets beyond our solar system. This could enable high-resolution imaging at a fraction of the cost involved in setting up expensive and cumbersome mirrors, say researchers at the Jet Propulsion Laboratory (JPL) in Pasadena, California.
Telescopes typically use solid mirrors to image distant objects. However, the large, complex mirrors required for stargazing are very expensive and difficult to build. Their enormous size and heavy weight add to the challenges of launching a space telescope in the first place.
JPL scientists wondered whether Orbiting Rainbows might help solve many of these problems. They propose using clouds of reflective glitter-like particles instead of mirrors to help telescopes view exoplanets (planets beyond our solar system), stars and galaxies.
White light regleted off a glitter mirror onto a camera sensor. (Credit: G. Swartzlander/Rochester Institute of Technology)
Orbiting Rainbows would enable high-resolution images at considerably lower costs, they say.
Orbiting Rainbow’s lead researchers at JPL, Marco Quadrelli, said:
“It’s a floating cloud that acts as a mirror. There is no backing structure, no steel around it, no hinges; just a cloud.”
Glitter could be manipulated by laser beams
The scientists propose that multiple laser beams would trap and manipulate the glitter-like grains in a small cloud. The laser light would trap the particles with the momentum of photons (tiny particles of light) in two directions: one that pushes them away, and another that pushes them toward the axis of the light beam.
The laser light would come from different directions, applying pressure from various points and shaping the cloud, pushing the small grains to align in the same direction.
In a space telescope, the cloud would consist of millions of grains, each one just a fraction of a millimeter in diameter.
A suitable telescope would need to have a wide adjustable aperture, the space through which light passes during a photographic or optical measurement. In fact, if the idea takes off, it would lead to larger apertures in future telescopes than those of existing ones.
Scientists made a mirror surface out of glitter to test the idea of using a cloud of reflective particles as a space telescope mirror. (Credit: G. Swartzlander/Rochester Institute of Technology)
Orbiting telescopes would be easier to deploy
A telescope made for an Orbiting Rainbows system would be much simpler to package, transport and send into space compared to conventional ones.
“You deploy the cloud, trap it and shape it.”
There is an abundance of structures in nature that have light-scattering and focusing features, such as rainbows or comet trails.
Observing these phenomena, as well as recent, successful laboratory experiments in optical trapping and manipulation have contributed to the Orbiting Rainbows idea.
French astronomer Antoine Émile Henry Labeyrie, from the College de France in Paris, first proposed using a telescope based on a laser-trapped mirror in a 1979 paper.
Orbiting Rainbow scientists are currently trying to identify ways to manipulate and maintain the shape of an orbiting cloud of dust-like particles using laser pressure so it can function as an adaptive surface with useful electromagnetic characteristics, for example, in the optical or radar bands.
There would be more distortions
The surface of a cloud made up of glitter particles is not smooth, so the image produced from those specks in a telescope will be ‘noisier’ – there will be more speckled distortion – than what would be generated from a regular mirror.
To get over the possible distortions, the scientists are creating algorithms to take multiple images and remove the speckle effect from the glitter with computers.
To test the idea, co-researcher Gover Swartzlander, an associate professor at the Rochester Institute of Technology, New York, and some of his students spread glitter on a concave lens in the lab.
They used lasers to represent light from a binary star system. The speckled mirror was pointed at the simulated stars, and a camera was used to take pictures. After several exposures and lots of processing, an image of the two ‘stars’ appeared using the glitter mirror.
“This is a major achievement. This demonstrates a highly controlled experiment in which we were able to do imaging in the visible light spectrum.”
Radio-band versus visible light signals
The technology could more easily be used for radio-band signals. Radio-band signals are one centimeter in length, compared to just nanometers in visible light, so the mirror grains would not need to be as precisely controlled or aligned.
This opens up applications for several Earth science possibilities, including earthquake detection and remote sensing of water, as well as other phenomena. Darmindra Arumugam, who works at JPL, is researching potential mechanisms for remote sensing with Orbiting Rainbows.
JPL’s optical design team has been working on the adaptive optics techniques that would be required by an Orbiting Rainbows telescope. So far, the scientists have been exploring diffractive and reflective versions of a telescope based on Orbiting Rainbows, with maximum sensitivity at one specific frequency.
In order to demonstrate Orbiting Rainbows in low-Earth orbit, the scientists will need to deploy a telescope with a small patch of particles, no bigger than a bottle cap, to show that it can be trapped and shaped to reflect light.
“The next step would be to make many of these patches and synthesize an aperture with which to do imaging.”
NASA Video – Orbiting Rainbows
This is a laboratory demonstration of the Orbiting Rainbows concept.