Ultra-Thin Lightweight Mirrors

Ultra-Thin Lightweight Mirrors

Space Solar Power System: an ambitious project driven by JAXA

All around the world, we are seeing new initiatives to provide stable supplies of clean renewable energy. In Japan, for instance, the Japan Aerospace Exploration Agency (JAXA) is conducting research on the Space Solar Power System (SSPS) in pursuit of a promising future energy source. The concept behind this ambitious project is to put solar panels into stationary orbit that will collect sunlight with great efficiency and beam the generated power down to Earth. We are proud to contribute by developing ultra-thin lightweight mirrors, and the project is slated to come online in the 2030s.
Read on to Related Information about ultra-thin lightweight mirrors and the latest advances.

Thin, light mirrors are the key to making SSPS a reality

SSPS (Image is for illustration purposes.)

Giant mirrors are essential for SSPS

JAXA is currently working on a project called the Space Solar Power System. This energy supply system will have a satellite outfitted with giant mirrors in space to collect sunlight, convert that energy into microwaves or laser light, then send it down to a receiving facility on the ground or at sea.
In addition to offering a stable supply of power without needing to deplete natural resources here on Earth, the SSPS will be the ultimate natural energy system capable of utilizing the unlimited energy of the sun, regardless of weather conditions and during both day and night – because it will generate power in space! Once again, Japan has identified a niche area and is leading the world in its exploration.

Our technology meets needs for ultra-thin glass and thin film

Our ultra-thin lightweight mirrors come from a combination of our ultra-thin glass manufacturing technology, and our thin film technology that keeps reflective coating to a bare minimum thickness – only nanometers! Thus, our mirrors consist of a high-performance reflective coat on glass and it’s still only 100 microns (0.1 mm) thick.
In 2011 we delivered prototype SSPS mirror units to JAXA.

The two types of mirrors delivered to JAXA

Mirrors with all-wavelength reflective film (for microwaves)

These mirrors make maximum use of sunlight, which spans a broad range of the electromagnetic spectrum. They are combined with a protective film, the basis of which is a silver film possessing high reflective efficiency. This design reflects approximately 95% of the total energy from the Sun.

reflective film (for laser light)

These mirrors turn energy into laser light that can be beamed down to Earth.
They let infrared and other unneeded light pass through, while only reflecting the required high-energy light. The glass panels are coated with 50 layers of film on each side to prevent warping.

* The illustrations above were created based on JAXA images.

Glass-resin laminates result in ultra-thin lightweight mirrors

To be feasible, these gigantic mirrors must be lighter, thinner, and stronger than can be built with conventional techniques. With this in mind, we bonded our incredible ultra-thin glass with resin to develop a new, ultra-thin lightweight mirror with the abrasion resistance and glass barrier of glass coupled with the light weight, shock resistance, and crack confinement properties of resin.
We delivered a combination of ultra-thin glass 0.1 mm thick and polyimide resin 0.05 mm thick to JAXA for assessment testing in the hope of achieving increased mirror strength.
Our mission is to help make the SSPS a reality, and we are aiming to do that by bringing three technologies together: ultra-thin glass manufacturing, thin film, and bonding.

Glass+resin technology protects mirrors by confining cracks

What makes a glass-resin combination so effective?
It’s the combination of durability and performance. The SSPS project entails placing a satellite equipped with enormous mirrors in space, but the area is peppered with meteoroids and space junk (e.g. pieces of satellites). Presumably, the mirrors will be hit by the debris, and should a crack in one unit’s mirror spread, that could have an effect on surrounding mirrors as well.
The technology that bonds glass with resin can also prevent this problem. Even if space junk strikes and cracks the mirror, the bonded structure prevents any damage from spreading further to shatter the glass.

Extra-strong mirrors made with polyimide resin

The choice of resin is also important.
We chose polyimide resin for its exceptionally high resistance to heat and radiation. It is suited to long-term use in space, a harsh environment subject to extreme temperature changes and hazardous radiation. For example, the gold color material covering the surface of a satellite contains polyimide resin treated with aluminum foil. A more familiar application of polyimide resin in our everyday lives is in circuit boards—such as those in mobile devices and liquid-crystal displays—due to its durability and electrical resistivity.
By bonding polyimide resin, a material with a proven track record in aerospace, with our ultra-thin glass and forming a film, it is possible to create extra-strong, high-performance mirrors.

Our challenge: thinner, lighter mirrors by first operations in the 2030s

The mirrors are huge—they will stretch 3.5 kilometers across space—so it is impossible to launch them into space with a single rocket.
Lightweight cargo is a very important key to efficient conveyance, and we are currently attempting to get our mirrors down to 100 grams per square meter 40 microns thick. And we are determined to supply JAXA with mirrors that are not only light and thing, but also strong by combining these mirrors with resin. In this way, we are helping to achieve the goal of bringing the SSPS online in the 2030s.
The technologies born in the process of these developments will surely lead to new feats of engineering, such as thin, light and bendable displays and lightings, thus growing next-generation industries.

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