When NASA’s Orion spacecraft takes to the sky atop the 322-foot Space Launch System Rocket for the uncrewed Artemis I mission, the capsule will do so with lighter, cheaper and more structurally sound windows compared to previous spacecraft.

Orion’s windows include interior lites of an acrylic plastic material that improves the windows’ integrity.

“Glass windowpanes have historically been part of the pressure shell on spacecraft that holds cabin pressure to keep the astronauts alive, and they also provided thermal protection from entry through Earth’s atmosphere,” says Lynda Estes, Orion window subsystem manager at NASA’s Johnson Space Center in Houston. “But the insidious thing about glass is that it’s a poor structural material. If you put loads on it, it will lose strength over time, and if you get a ding on it, the strength is dramatically decreased. The spaceflight environment is one that unfortunately exploits these vulnerabilities.”

According to NASA, Orion’s development phase included searching for transparent materials that perform better than glass. Developers chose the acrylic material because it provides a clear view and is extremely durable.

Each window on Orion has three lites: a fused silica thermal pane, an acrylic pressure lite and a redundant lite. The move to acrylic helps keep the capsule lighter while retaining its structural integrity. The acrylic material is half as dense as glass and doesn’t weigh as much.

Estes says that the use of acrylic pressure lites reduced the windowing subsystem’s weight by more than 200 pounds. The lower weight reduces the cost of going to space since decreasing weight means less propulsion.

Orion consists of a gumdrop-shaped capsule and service module, which together are about 26 feet long with a diameter of 16.5 feet. The spacecraft’s habitable volume is 316 cubic feet, which is about 1.5 times larger than the Apollo spacecraft.

Artemis I is the first flight test of NASA’s Space Launch System rocket and uncrewed Orion spacecraft as an integrated system. The flight is also the first of a series of missions that will eventually land astronauts on the moon by 2024 to establish a sustainable presence and enable human exploration of Mars. Artemis II will follow as the first crewed mission to the moon.

The design, development, test and evaluation phase will end after Artemis II. Although no structural changes on the vehicle are expected to come from Artemis I and II, the mission outcomes could drive minor changes or upgrades into subsequent builds.