Glass: The Final Frontier

In the quest to explore space, glass has played a key role in astronomy, on Moon missions, and beyond. Glass-ceramics are found in monolithic and segmented telescopes, helping to advance our knowledge of the solar system and the universe. These telescopes, both ground-based and space-based, rely on mirror substrate materials with low thermal expansion in order to see into space in such fine detail. This is important because even the tiniest expansion can severely affect the image focus, as well as rendering any instrument readings unusable.

Developed in 1968 for the Max Planck Institute for Astronomy telescope in southern Spain, Schott’s ZERODUR® glass-ceramic is the industry standard in astronomy, found in many of the world’s most powerful observatories. Its near-zero thermal expansion coefficient can be tailored to the application temperature and is extremely homogeneous throughout. The nonporous lithium aluminium silicon oxide material exhibits remarkably low levels of inclusions, striae, and bulk stress. Soon, ZERODUR® will be used for the mirrors of what is to be the world’s largest optical telescope, the European Southern Observatory’s Extremely Large Telescope, scheduled for first light in 2027.

For decades, ZERODUR® has also been part of long-term missions in space: It has flown on more than 40 successful missions that required high-precision optics for Earth observation and astronomy. These include the secondary mirror substrate for the Hubble Space Telescope and the Walter mirrors of the Chandra X-ray Observatory, as well as several weather-forecast satellites.

Beyond astronomy, glass and glass-ceramics have played a central role in space exploration, from the Apollo 11 mission that put a human on the Moon to the Juno space probe currently orbiting Jupiter. The key to these materials’ success is that they maintain their strength and tightly controlled range of physical properties throughout their operational lifetime. The harsh environment of space demands materials that can withstand large temperature changes, high radiation, and the extreme mechanical challenges present during launch.

Spacecraft and satellites use a range of specialty glass and glass-ceramic materials, as well as hermetic glass-sealed components. One such example is the ultrathin glass that provides protection for photovoltaic cells by blocking harmful ultraviolet (UV) radiation while maintaining high light transmission over the lifetime of a space mission. Glass cylinders provide transparent hermetic packaging for sensors, while custom-made hermetic light-weight packages with glass-to-metal sealed feedthroughs protect sensitive components effectively against harsh environmental conditions and support efficient transmission of optical signals.

What is more, a broad range of optical glass, filters, and aspheres can perform increasingly complex roles in spacecraft and satellites. The sheer breadth of transmission, reflectance, and absorption properties available—plus high-quality surface processing and stability—not only results in highly precise instrument readings, but also in images that provide valuable insights into the cosmos. For example, onboard the asteroid probe OSIRIS-REx are three cameras, each equipped with cerium-doped optical glass able to withstand cosmic radiation and protect against solarization to produce stunning images. The mission will gather samples from the asteroid Bennu and return them to Earth to enable scientists to learn more about the formation and evolution of our solar system.

Another example of a glass application is the flexible and rigid optical fiber bundles used in rockets for monitoring propulsion and fuel systems as well as for calibration. By guiding light optically without direct electricity, glass optical fibers offer a safe way for constant operational surveillance over distance, even in tight spaces and without short-circuit risk.

The success of these glass solutions in space comes down to a combination of consistently stable transmission, from the UV into the near infrared; a high absorption of UV radiation; protection against particle radiation; and a low coefficient of thermal expansion as well as lightweight materials. This results in components that are able to function in the harshest environments known to humankind—and some that we have yet to experience.

Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE). Credit: NASA

The planet Mars has long held a deep fascination for astronomers and science-fiction writers, particularly because of its potential to sustain life. NASA’s Mars 2020 mission, which touched down on 18 February 2021, carries onboard the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE), developed to investigate the possibility of extracting oxygen from the Red Planet’s carbon-dioxide-rich atmosphere. Here, too, glass plays an important role. MOXIE’s ground-breaking technology relies on a solid oxide electrolysis (SOXE) stack made up of layers of metal and ceramic plates separated and sealed by glass, applied in the form of powder. This ensures a tight seal able to withstand extreme temperature changes not only on Mars, but also during rocket launch and operation. That is, it needs to remain functional in temperatures ranging from –55 degrees C to more than 800 degrees C and to withstand the huge amount of vibration involved in take-off and landing.

On 20 April 2021, MOXIE produced its first oxygen from carbon dioxide on Mars. As the first extraction of a natural resource from another planet for human use, the implications of this achievement are huge. If scaled up, this oxygen could not only sustain human life, but also generate the oxidizer required for a spacecraft to return to Earth. Because oxygen could also possibly be used to produce water on Mars, it’s no wonder scientists are excited about this development. Because electrolysis has strong potential for space exploration and human ability to survive on another planet, glass will likely play a major part in the development of the technologies that have the potential to change all of our lives.

Boris Eichhorn is Senior Manager New Venture, SCHOTT. He can be reached at boris.eichhorn@schott.com
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