The Future of Spacecraft Windows: 'We Can't Just Live in a Box'

Space travelers have always wanted to look out the window — but building safe windows for spacecraft is harder than it sounds. From the first tiny portholes on Mercury capsules in the 1960s to the wide dome-shaped windows on today's space stations, spacecraft windows have come a long way. Engineers and astronauts have debated, argued, and worked together for decades to make sure people in space can see the world outside. Now, as NASA plans missions back to the moon, scientists are still finding better ways to design the windows that keep astronauts both safe and connected to the universe around them.

When astronaut Alan Shepard launched into space in 1961, he had only a tiny porthole to see through. Soviet cosmonaut Yuri Gagarin, the first human in space, also had just a small window. Back then, scientists did not even know what floating around in microgravity would do to a person's eyesight. A lot has changed since those early days of space exploration.

Over time, having good windows became more and more important to astronauts. Author Frank White, who wrote a famous book called 'The Overview Effect,' has studied how astronauts feel when they look down at Earth from space. He says that the experience of seeing our planet from far away often changes people in a deep and powerful way. 'Based on my experience of interviewing professional and commercial astronauts, I would say that the windows are key to the Overview Effect experience,' White said.

The International Space Station (ISS) has a special windowed room called the Cupola. The Cupola has six side windows shaped like trapezoids and one round window on top. Astronauts go there during their free time to gaze at Earth and the stars, but they also use it as a work area to control robotic arms. White says this structure made the Overview Effect much more powerful for astronauts living on the station.

Space tourism companies have also paid close attention to windows. Virgin Galactic and Blue Origin, which offer short trips to the edge of space, have made sure their customers get great views. SpaceX also added a special dome window to its Crew Dragon capsule for the Inspiration4 mission in September 2021, giving the four crew members a stunning view of Earth. People who watched videos of the crew seeing that window for the first time could clearly see how emotional the moment was.

Author Samuel Coniglio IV, who wrote a book about making space comfortable for people, says windows are just as important as plants or showers when it comes to feeling good in space. He believes that being able to see the universe outside helps people feel connected to the world. 'We can't just live in a box -- we need to be part of the outside world as well,' Coniglio said. Interestingly, the original Mercury astronauts had to fight hard just to get windows at all, since engineers worried about safety.

Lynda Estes is a spacecraft window expert at NASA's Johnson Space Center in Houston, Texas. She has spent decades figuring out how to safely build windows into spacecraft that carry people. Her work has covered the space shuttles, the ISS, the Orion capsule for the Artemis moon program, and many private spacecraft. She even wrote the official NASA rulebook for how spacecraft windows must be designed.

Estes explains that glass is a tricky material to work with. A big problem is something called static fatigue, which means tiny cracks in the glass slowly grow bigger over time, even without any visible damage. Small flaws in the glass can also make it weaker than it looks. 'Glass is a brittle material. It breaks. That's what it likes to do. But it's also beautifully transparent as well,' she said.

Because of these problems, NASA is working to replace glass with a material called acrylic in future spacecraft windows. Acrylic is a type of clear plastic that is much stronger and more flexible than glass, and it does not break into sharp, dangerous pieces. Estes notes that acrylic can even act like a heat shield during reentry into Earth's atmosphere. This makes it a much safer choice for crew vehicles.

Safety is the top priority for Estes and her team. She points out that cutting a hole in a spacecraft and filling it with glass is a serious risk because broken glass sends sharp shards flying toward whatever is nearby — including people. Even so, NASA has a rule that any spacecraft carrying humans must have at least one window. Estes and her team are now using what they have learned to design windows for future lunar landers as part of the Artemis program, so the next astronauts on the moon will have a view, too.