Preserving History at Hypersonic Speeds: A Close-Up Look at the North American X-15

Preserving History at Hypersonic Speeds: A Close-Up Look at the North American X-15

The North American X-15 is a true marvel of aviation history –a pioneering hypersonic research aircraft that pushed the boundaries of aeronautical engineering in the 1960s. This rocket-powered plane set altitude and speed records that still stand today and contributed critical data to the American space program. The Museum’s X-15-1—the first of three in the series—is one of the most iconic of these aircraft, having been piloted by legendary astronaut Neil Armstrong. This aircraft is displayed suspended in a flight pose in the newly redesigned National Mall Building’s Boeing Milestones of Flight Hall opening to the public later this year.

After decades on display, the X-15-1 recently underwent conservation treatment in the Mary Baker Engen Restoration Hangar at the Steven F. Udvar-Hazy Center.  Treatment initially focused on exterior cleaning and corrosion stabilization. The plane’s external shell is made of Inconel X, a specialized alloy designed to withstand the extreme heat of hypersonic flight. Conservator Kate Gabrielli meticulously removed corrosion from the Inconel X panels, using a specialized technique to ensure that the metal remains stable and protected for long-term display.

It was during this treatment that the conservation team had the rare opportunity to open the cockpit and peer inside to examine the historic interior that had not been publicly visible in decades. We not only found a fascinating collection of original instruments and controls, but also a series of unexpected conservation challenges!

Each scratch and abrasion tell a story of the X-15-1’s intense missions. Seeing it up close reveals the tangible traces of how these planes were used, maintained, and modified for different flights. The pilot’s seat still shows signs of wear from multiple missions, and the control panels are marked by subtle traces of use, including a whimsical touch: a pair of tiny eyes drawn on one of the instrument panels. This piece of evidence provides a glimpse into the personality and humor of the test pilots who flew this incredible aircraft. Details like these make the flight deck not only a collection of machinery but a representation of the human spirit of exploration.  Our treatment goal was therefore to preserve the visible evidence of use as a testament to its history while stabilizing these areas to prevent any further deterioration of the artifact. This required a balance of interventive conservation methods and preventive care to mitigate future risk while the plane remains on permanent display.

Conserving the Flight Deck: Stabilizing Delicate Plastics

Conserving plastics can be a major challenge for any museum, as these materials tend to degrade unpredictably.  Plastic polymers are modified with unique additives such as plasticizers, fillers, and stabilizers that aid in their function but complicate how they react to the environment over time. Additionally, the wide range of fabrication processes used to create plastic objects can significantly impact their stability, affecting how these materials break down.

Inside the X-15-1 cockpit, several different types of plastics were found with varying conditions. Many of these materials, like the vinyl-covered armrests and the foam seat cushion, were never designed to last for decades. The seat showed the most severe signs of degradation with torn, discolored vinyl and internal polyurethane foam that had collapsed into a sticky, melted mass. While the vinyl was still somewhat flexible, it had become distorted from shrinking over time as the polymer lost its original plasticizers. Due to time constraints and the extreme deterioration of the material, we were unable to identify the exact polymer used for the vinyl cover, but analysis confirmed that the foam was polyurethane-based.

To address these complex conditions, the treatment focused on stabilizing the seat without further stressing the fragile materials. The sticky foam was gently reshaped and covered with a protective barrier layer of removable silicone-release mylar. Next, a stretchable film commonly used in painting conservation was combined with an archival adhesive to create small “bridges” over the tears, holding the torn vinyl together while allowing for natural movement. This approach will ensure that as the vinyl continues to shrink over time, it won’t detach or fall into the degraded foam, preserving the seat’s structure and appearance for years to come. Since the seat will not be visible on display, the bridges were not toned to match the vinyl. This also allows researchers to easily distinguish the non-original material. Our preservation efforts have prioritized maintaining the severe damage of the seat since the original vinyl and duct tape repairs help tell the stories of the pilots who used flew this aircraft.

Although the seat required significant intervention, the synthetic rubber gaskets and the clear plastic wrapping on the electrical cords were found to be in relatively good condition. This highlights that not all plastics degrade at the same rate; some can remain stable when maintained under optimal conditions. Different types of plastics have varying environmental requirements, but they all benefit from a stable environment with minimal fluctuations in temperature and humidity. The Museum carefully monitors these conditions to keep these vulnerable materials as stable as possible.

Most plastics are also highly susceptible to light-induced deterioration, which can lead to yellowing, cracking, or loss of flexibility over time. To prevent further damage, we designed a custom cover for the cockpit to shield its interior from potential light exposure while on display.

Bringing a Legend to Life

Conserving the cockpit of the X-15-1 is more than just preserving a museum artifact—it’s preserving the spirit of innovation, risk, and exploration that defined an era. Although the flight deck will be closed to visitors, the treatment and documentation ensures that the materials are preserved, and the story of this incredible aircraft continues to be told. You can read more about this incredible aircraft and more about Neil Armstrong’s experience.

Visitors will have the opportunity to view this important artifact, but since it will be displayed hanging with its deck closed, seeing inside this experimental aircraft is a rare and lucky opportunity. The cockpit of the X-15-1 provides a unique glimpse into the past, a preserved time capsule of cutting-edge technology and the experimental spirit of mid-century space exploration.  For those of us who had the opportunity to work on the flight deck's preservation, seeing inside was a privilege.