The future of spacecraft windows: 'We can't just live in a box'

No need for a quick spray of Windex to get a clear view of this situation.

There's a growing need for windows for rubbernecking space travelers, whether they're making suborbital hops, staying in Earth orbit or conducting far-flung sojourns to the moon and beyond.

Retrofire back decades ago when the first Mercury space capsule offered a tiny porthole for its single seat occupant, Alan Shepard. Similarly, the first human in space, cosmonaut Yuri Gagarin, had but a small window to take in the view.

Oddly, in those early years of pioneering space treks, nobody knew what microgravity would do to the human eye and a person's vision. Talk about floaters!

That aside, sightseeing in space has meant an evolution of safe and sound windows and tackling the engineering challenges to produce them. But what's the outlook ahead for space voyagers?

Earthgazing

"Based on my experience of interviewing professional and commercial astronauts, I would say that the windows are key to the 'Overview Effect' experience," said Frank White, who coined the phrase and is author of "The Overview Effect: Space Exploration and Human Evolution" (Houghton Mifflin Harcourt, 1987).

White called attention to the deep shift in cognitive awareness that most space travelers undergo in viewing our planet from Earth orbit and beyond.

It's clear that, for NASA astronauts, transitioning from space shuttle missions to the International Space Station (ISS) was critical to a more meaningful opportunity to view Earth from a distance, White said.

"This shift intensified with the advent of the ISS Cupola, where astronauts spend a great deal of time ‘Earthgazing,'" he told Space.com.

Customer experience

White said that, because Virgin Galactic and Blue Origin have focused on having their suborbital space tourism customers experience the Overview Effect, "both companies have ensured great views from the windows of their spacecraft. As a result, commercial astronauts have had profound experiences, even though they are weightless and looking at the Earth only briefly."

It is no accident that SpaceX installed a special "cupola" on its Crew Dragon capsule for the Inspiration4 astronaut mission in September 2021, and it paid off, White observed. Anyone who doubts this fact, he said, should watch the video of the unveiling of that window by the Inspiration4 crew.

"The story goes that the engineers for the Mercury flights did not want the spacecraft to have windows," White said. "The astronauts insisted and eventually prevailed. Fortunately, their precedent continues to this day, to the benefit of the astronauts and the people of Earth. The Overview Effect is one of the most important 'spinoffs' of space exploration."

Human comfort

Similar in view is Samuel Coniglio IV, author of "Creature Comforts in Space: Designing Enjoyment and Sustainability for Off-World Living" (BookBaby, 2024).

Coniglio also points to that scene from the 1983 film "The Right Stuff," in which the original Mercury astronauts were arguing with the engineers for a need to see outside their capsule. After all, they were an elite set of pilots and may have needed to take manual control of their craft at some point.

"Just as plants and taking a shower play a critical role in human comfort, so do windows," said Coniglio. "Being able to see the vast heavens allows you to become one with the universe, and to see all the cool stuff going on outside. We can't just live in a box — we need to be part of the outside world as well."

Structural reliability

Lynda Estes is the spacecraft transparencies discipline lead at NASA's Johnson Space Center in Houston. She's an engineering expert who has been integrating windows into crew-carrying spacecraft for decades.

Estes has worked with many vehicles during her NASA career — the space shuttles, the International Space Station, the Artemis program's Orion capsule and every private human-rated spacecraft developed by companies partnering with the agency's Commercial Crew Program.

Estes is an internationally sought-after resource for design, development, engineering, testing and operations for high-risk, human-rated pressure cabins in both aviation and spaceflight. She's the author of the governing NASA requirements document that ensures high structural reliability in spacecraft glass window designs.

Starting as a stress analyst for mechanisms, "windows are a whole new PhD," Estes told Space.com. "Glass is a brittle material. It breaks. That's what it likes to do. But it's also beautifully transparent as well."

Room with a view

In earlier NASA programs, windows were made of multiple panes of different types of glass. For example, the European-built Cupola on the ISS — offering the "best room with a view" — consists of six trapezoidal side windows and a circular top window. Each window consists of four panes for protection from astronaut-induced scratches, as well as outside dings from space debris.

The entire window, or the individual scratched or debris-pocked panes, can be replaced. Reinstating an entire window requires a "big, fancy ballet," said Estes — one that is well-choreographed, with an astronaut first fitting an external pressure cover over the window during a spacewalk.

Overall, the ISS Cupola serves as an observation and work area when the crew operates the station's robotic arms or observes visiting vehicles. But it's a lure during leisure time as well, as it affords astronauts extraordinary views of Earth and celestial objects.

Static fatigue

But there are troubling features of glass, too. For one, tiny flaws affect its strength. And glass actually loses structural capability over time, according to Estes.

"We call that static fatigue," she said, referring to cracks that grow microscopically under a load.

"We're working hard to remove glass because of those two features," Estes said, explaining that NASA wants to move to an all acrylic window design for the Orion spacecraft. "Acrylic, when seeing reentry temperatures, acts like a heat shield."

As a structural engineer, Estes advises that windows are worrisome.

"We come at it from, How do we keep everybody alive? Cutting a hole in the side of your pressure vessel and installing something like glass to replace that hole is a really poor choice," said Estes. "That's why we are trying to move contractors and our partners to acrylic. That is a much more structurally stable material."

Buying risk

One of the challenges with glass is that it produces shards when it breaks. "And the first place those shards want to go is to that human body that just went over to the window to see what happened," Estes pointed out.

With glass you are buying risk, said Estes. On the other hand, NASA has a written requirement, she said: "If you are going to put humans inside and send it to space, it must have a window."

Estes and her team are now providing guidance for spacecraft windows to be utilized for future moon operations, including the human landing systems for the Artemis program.

Back down here on Earth, does she clean windows at home?

"I do not," Estes responded.