It’s been 250 years since the United States decided it was no longer interested in being part of Great Britain. To celebrate the momentous anniversary—called a semiquincentennial—the non-profit America250 has numerous events planned including something quite timely.
A roughly 2,000-pound time capsule will be buried at Philadelphia’s Independence National Historical Park on July 4, 2026. The capsule is intended to safeguard a snapshot of America today for another 250 years. While the process of burying random items underground for a few centuries might sound simple, designing and fabricating a storage container to withstand whatever nature might throw at it for the next 25 decades is quite the feat.
The team includes engineers from the National Institute of Standards and Technology (NIST) and preservation experts at the Library of Congress, who are coordinating with the National Park Service for the event in the nation’s first capital. NIST also designed and built the protective display cases that hold an original copy of the Declaration of Independence and America’s other founding documents.
However, NIST engineer and time capsule designer Jay Nanninga tells Popular Science that the original plan didn’t involve burying the time capsule at all. The initial idea was to incorporate the time capsule in a forthcoming monument in Independence National Historical Park called the Join or Die Sculpture, inspired by Benjamin Franklin’s 1754 cartoon of the same name. The sculpture will consist of a giant segmented snake symbolizing the original 13 colonies and is expected to be complete this fall. America250 (the organization leading the anniversary celebrations) wanted to incorporate the time capsule into its granite structure.
The company that carves the granite pulled the plug on that idea, however, because carving out a spot for the capsule would make the granite too weak. The project consequently transitioned to putting the time capsule underground.
Water is not welcome in a time capsule
The team’s granite problem was resolved, but new issues soon arose for Nanninga—particularly, water. Needless to say that the capsule “has to stay dry,” which he says, “has been pretty much driving everything else.”
To keep the time capsule waterfree, the capsule mainly consists of two sections: a tube-shaped container holding the capsule’s precious cargo, and a larger bell jar-like device to seal it with an air pocket. The jar works similarly to pushing an upside-down bucket in a pool of water. Or put in a pop culture way, like Jack Sparrow and Will Turner walking underwater by breathing air trapped in an upside-down rowboat in Pirates of the Caribbean: The Curse of the Black Pearl.
“The amount of force that’s coming back, trying to push that bucket back out of the water, we’re going to exploit that,” he explains. “If the ground becomes saturated with water, the pressure that’s built up in the bell jar will keep the water from filling up the time capsule.”
As such, the time capsule should withstand even heavy flooding. As for other worst-case scenarios, the capsule should be out of reach of wildfires, and Pennsylvania’s earthquake hazard level is extremely low. Even if a seismic event were to occur, Nanninga thinks both the capsule and the contents inside would be fine. Finally, he jokes that “zombies would have a challenge because the stainless steel is not fun to eat.”
Getting into shape
In terms of its shape, Nanninga received vague parameters for the design. He originally came up with a few options: a cylinder, a box, and even a star. “I thought the star was super cool,” he laughed. “I really, really wanted to use my star.”
While that star design would have been symbolic, it turned out to be too complicated, so they decided on the cylinder instead. This shape is the most cost-effective and efficient option from the point of view of fabrication—the team simply needed a standard industrial pipe to create the cylinder instead of having to build the structure from scratch. What’s more, a solid pipe is less likely to leak than a rectangular container whose various sides are welded together.
Critically, Nanninga also needed a plan for how to seal the capsule once all of the objects are stored inside. Welding seemed like the obvious answer, and he planned for the circumference of the seal to be bigger than the actual time capsule, like sealing the brim of a top hat. This way, the heat and potential spatter from the metal or the sealant won’t damage any of the artifacts.
But even with this precaution, the rest of the team was nervous about this sealing process. Instead, the time capsule will be closed with a seal that crushes Indium wire in a groove between the steel lid and the body. Under pressure, Indium wire can self-weld at room temperature, a process called “cold welding.” The wire will fill the groove, its two ends will weld together, and the seal will be a complete circle.
‘We just keep adapting’
Making all of these changes on-the-fly were some of the most challenging aspects for Nanninga, who has been working on the design for at least a year and a half.
“The original idea was something completely different, and that something completely different happened multiple times throughout this,” Michael Berilla, Nanninga’s colleague and head of NIST’s Technology Fabrication Office, tells Popular Science. “You get to a place where you feel comfortable and good, and then someone’s like, ‘oh, wait, that’s not going to work.’ And so I think that’s true resilience in engineering, that we just keep adapting.”
Berilla’s job in all of this is to make sure the people with the right skills are involved in the project, and that they have everything they need. This process is also known as “herding cats,” he jokes. Some other curveballs include changes to the objects that will be stored in the time capsule. Nanninga has had to modify the capsule’s internal design multiple times to account for changes in space. The design is also heavily influenced by how the materials the objects are made from will age and potentially interact with each other. This is where preservation expertise from the Library of Congress comes in handy.
The collection will represent America’s current leadership, institutions, and communities in the form of letters and other artifacts. It will include objects from all 50 states and six territories, each of the three branches of the federal government, and from the America250 commission. For example, Utah, will be represented by coins, pins, and historical building pieces. The complete list will be announced in mid-June.
Paper objects will be sealed into a separate compartment from the non-paper objects, which will be in containers distributed around the paper compartment. None of the objects can be made from plastics, because they release gasses. Electronics are also out of the question, and of course there’s a limit on size.
Once completed, the empty time capsule and bell jar together will weigh 2,000 pounds and stand at 53 inches-tall and will be buried 10 feet underground. The contents won’t be seen again until 2276, when future generations will be celebrating the country’s 500th birthday.
“In most of the endeavors that I do, I search for inspirations or lessons for my three young kids, to show them how to take on a challenge that has never been done before, make sure that it’s done absolutely right, not give up, and have this realization that you can really accomplish anything you set out to do,” Berilla explains. “That is what I strive for, and I found a very warm spot in my heart for this project for that reason.”
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