Windows have long been an essential part of human spaceflight, giving astronauts a view of the world beyond their spacecraft. But as missions become longer and spacecraft designs evolve, NASA is looking to change the way those windows are made.
NASA engineers are exploring greater use of acrylic materials in future spacecraft to reduce risks associated with the fragile nature of glass.
Experts say windows are more than a way for astronauts to enjoy the view. On future missions that could last months or even years, they may also play an important role in maintaining astronauts’ psychological well-being.
During the first human space missions, astronauts had only limited views of the outside world. The Mercury spacecraft used by one of the first U.S. astronauts, Alan Shepard and the spacecraft that carried the first human in space, Yuri Gagarin, featured relatively small windows.
As spacecraft technology developed, that changed. The Cupola module aboard the International Space Station, with its seven windows, has become one of the main places where astronauts can observe Earth.
SpaceX also installed a large dome window on its Crew Dragon spacecraft for the 2021 Inspiration4 mission. Space tourism companies such as Virgin Galactic and Blue Origin have likewise made wide views of Earth an important feature of their spacecraft.
‘We can’t live inside a box’
According to Samuel Coniglio IV, author of "Creature Comforts in Space,” windows are similarly important to other basic comforts, such as plants and showers, for people living in space for extended periods.
Coniglio said people cannot simply live inside a closed box, adding that being able to see space and the world outside helps astronauts maintain a connection with their surroundings.
The powerful cognitive and emotional changes that can occur when people see Earth from a distance during spaceflight are known as the "Overview Effect.”
Hidden danger of glass
Large windows, however, present significant engineering challenges.
Lynda Estes, a NASA engineer at the Johnson Space Center who works on spacecraft windows, said glass is inherently fragile and can lose structural strength over time.
Microscopic flaws in glass can gradually grow. This process, known as static fatigue, can affect the strength of windows during long-duration missions.
Another risk is that glass can break into sharp fragments. According to Estes, placing glass in a large opening in the pressurized structure of a spacecraft is itself a structural risk.
NASA turns to acrylic windows
For this reason, NASA is working on a fully acrylic window design for the Orion spacecraft, which will be used as part of the Artemis program.
Acrylic is considered structurally more stable than glass. Another potential advantage is its ability to behave similarly to a heat shield when exposed to the high temperatures experienced during atmospheric reentry.
NASA is also working on new safety standards for the windows of lunar landers that will carry people to the Moon under the Artemis program.
Despite these changes, completely removing windows from spacecraft is not being considered. NASA's requirements for human-rated spacecraft explicitly call for vehicles carrying people into space to have windows.
The materials used in future spacecraft may change, but the "window to the outside” will remain, allowing astronauts to look back at Earth and out into deep space.