Minimizing Telescopes with Irregular Mirrors
Erin Green posted on November 09, 2015 |
Using freeform optics in space may be the key to miniaturizing telescopes and other optical equipmen...

Optical engineers at NASA have been working on new ways to look into space – and one of those ways happens to be a mirror that look like a potato chip.

A traditional, rotationally symmetrical mirror shape (left) is the current choice for telescopes, but freeform mirrors such as the one on the right are an emerging technology. (Image courtesy of NASA.)
A traditional, rotationally symmetrical mirror shape (left) is the current choice for telescopes, but freeform mirrors such as the one on the right are an emerging technology. (Image courtesy of NASA.)

The new structure is an asymmetrical mirror designed for use in telescopes. Its design hails from the up-and-coming field of freeform optics, where engineers are working to reduce packaging for telescopes and other optical devices.

Traditionally, the mirrors and lenses used in telescopes come in a standard rotationally symmetric form. They need to be aligned along the telescope’s axis to direct light properly and to avoid blurring photos with optical aberrations.

However, this approach can require a large number of mirrors and can result in bulky telescopes. In this day and age, that just won’t do.

A Better Optical Design?

As can be inferred from the name, freeform mirrors can assume any shape. So why did the team at the Goddard Space Flight Center decide on this shape?

“If you want to put these telescopes into a smaller box, you need to let the mirrors bend like a potato chip,” said Goddard optical engineer Joseph Howard.

The asymmetrical mirror design offers the potential for reducing the packaging size required for telescopes. The irregular shape provides a wider usable range of view and can correct for common optical aberrations exhibited by symmetrical mirrors.

Howard also explained that the team’s studies suggest that the volume of optical instrumentation can be reduced by a factor of five or more using freeform surfaces.

One particular experiment conducted by the team demonstrated that a coastal measurement instrument could be reduced from nine symmetrical mirrors to six asymmetrical ones, reducing the overall packaging tenfold and improving image quality.

Manufacturing Asymmetrical Mirrors

Asymmetrical mirrors haven’t been prevalent in telescopes and other optical devices in the past due to the complexity of manufacturing them. However, their popularity is growing with the advent of 3D printing.

Currently, the team is working to conduct simulation tests. It is waiting for two asymmetrical mirrors to build the first prototype instrument.

The team hopes to use asymmetrical mirrors to produce telescopes and optical equipment small enough to ride a CubeSat like this one. (Image courtesy of NASA.)

The team hopes to use asymmetrical mirrors to produce telescopes and optical equipment small enough to ride a CubeSat like this one. (Image courtesy of NASA.)

By next year, the team hopes to create its own freeform mirror with 3D printing. A computer-controlled laser will be able to melt material in precise locations according to a 3D CAD model to create any mirror shape layer by layer.

Outfitting Smaller Satellites

Asymmetrical mirrors present a viable option for researchers looking to build compact telescopes for small satellites.

Freeform optical technology will provide larger fields of view on smaller vessels such as CubeSats.  It is also well-suited to situations with restricted space allocations on larger missions.

For more information on the project, check out the NASA website.

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