Science

1225 Articles

Site Of Secret 1950s Cold War Iceworm Project Rediscovered

October 17, 2025 by 9 Comments

The overall theme of the early part of the Cold War was that of subterfuge — with scientific missions often providing excellent cover for placing missiles right on the USSR’s doorstep. Recently NASA rediscovered Camp Century, while testing a airplane-based synthetic aperture radar instrument (UAVSAR) over Greenland. Although established on the surface in 1959 as a polar research site, and actually producing good science from e.g. ice core samples, beneath this benign surface was the secretive Project Iceworm.

By 1967 the base was forced to be abandoned due to shifting ice caps, which would eventually bury the site under over 30 meters of ice. Before that, the scientists would test out the PM-2A small modular reactor. It not only provided 2 MW of electrical power and heat to the base, but was itself subjected to various experiments. Alongside this public face, Project Iceworm sought to set up a network of mobile nuclear missile launch sites for Minuteman missiles. These would be located below the ice sheet, capable of surviving a first strike scenario by the USSR. A lack of Danish permission, among other complications, led to the project eventually being abandoned.

It was this base that popped up during the NASA scan of the ice bed. Although it was thought that the crushed remains would be safely entombed, it’s estimated that by the year 2100 global warming will have led to the site being exposed again, including the thousands of liters of diesel and tons of hazardous waste that were left behind back in 1967. The positive news here is probably that with this SAR instrument we can keep much better tabs on the condition of the site as the ice cap continues to grind it into a fine paste.

Top image: Camp Century in happier times. (Source: US Army, Wikimedia)

A Deep Dive Into Molten Bismuth

October 16, 2025 by 2 Comments

Bismuth is known for a few things: its low melting point, high density, and psychedelic hopper crystals. A literal deep-dive into any molten metal would be a terrible idea, regardless of low melting point, but [Electron Impressions]’s video on “Why Do Bismuth Crystals Look Like That” may be the most educational eight minutes posted to YouTube in the past week.

The whole video is worth a watch, but since spoilers are the point of these articles, we’ll let you in on the secret: it all comes down to Free Energy. No, not the perpetual motion scam sort of free energy, but the potential that is minimized in any chemical reaction. There’s potential energy to be had in crystal formation, after all, and nature is always (to the extent possible) going to minimize the amount left on the table.

In bismuth crystals– at least when you have a pot slowly cooling at standard temperature and pressure–that means instead of a large version of the rhombahedral crystal you might naively expect if you’ve tried growing salt or sugar crystals in beakers, you get the madman’s maze that actually emerges. The reason for this is that atoms are preferentially deposited onto the vertexes and edges of the growing crystal rather than the face. That tends to lead to more vertexes and edges until you get the fractal spirals that a good bismuth crystal is known for. (It’s not unlike the mechanism by which the dreaded tin whiskers grow, as a matter of fact.)

Bismuth isn’t actually special in this respect; indeed, nothing in this video would not apply to other metals, in the right conditions. It just so happens that “the right conditions” in terms of crystal growth and the cooling of the melt are trivial to achieve when melting Bismuth in a way that they aren’t when melting, say, Aluminum in the back yard. [Electron Impressions] doesn’t mention because he is laser-focused on Bismuth here, but hopper crystals of everything from table salt to gold have been produced in the lab. When cooling goes to quick, it’s “any port in a storm” and atoms slam into solid phase without a care for the crystal structure, and you get fine-grained, polycrystaline solids; when it goes slowly enough, the underlying crystal geometry can dominate. Hopper crystals exist in a weird and delightful middle ground that’s totally worth eight minutes to learn about.

Aside from being easy to grow into delightful crystals, bismuth can also be useful when desoldering, and, oddly enough, making the world’s fastest transistor.

Continue reading “A Deep Dive Into Molten Bismuth” →

A vertically-mounted black disk with a concentric pattern of reflective disks is illuminated under a red light. A large number of copper wires run away from the the disk to a breadboard.

Deforming A Mirror For Adaptive Optics

October 13, 2025 by 16 Comments

As frustrating as having an atmosphere can be for physicists, it’s just as bad for astronomers, who have to deal with clouds, atmospheric absorption of certain wavelengths, and other irritations. One of the less obvious effects is the distortion caused by air at different temperatures turbulently mixing. To correct for this, some larger observatories use a laser to create an artificial star in the upper atmosphere, observe how this appears distorted, then use shape-changing mirrors to correct the aberration. The physical heart of such a system is a deformable mirror, the component which [Huygens Optics] made in his latest video.

The deformable mirror is made out of a rigid backplate with an array of linear actuators between it and the thin sheet of quartz glass, which forms the mirror’s face. Glass might seem too rigid to flex under the tenth of a Newton that the actuators could apply, but everything is flexible when you can measure precisely enough. Under an interferometer, the glass visibly flexed when squeezed by hand, and the actuators created enough deformation for optical purposes. The actuators are made out of copper wire coils beneath magnets glued to the glass face, so that by varying the polarity and strength of current through the coils, they can push and pull the mirror with adjustable force. Flexible silicone pillars run through the centers of the coils and hold each magnet to the backplate.

A square wave driven across one of the actuators made the mirror act like a speaker and produce an audible tone, so they were clearly capable of deforming the mirror, but a Fizeau interferometer gave more quantitative measurements. The first iteration clearly worked, and could alter the concavity, tilt, and coma of an incoming light wavefront, but adjacent actuators would cancel each other out if they acted in opposite directions. To give him more control, [Huygens Optics] replaced the glass frontplate with a thinner sheet of glass-ceramic, such as he’s used before, which let actuators oppose their neighbors and shape the mirror in more complex ways. For example, the center of the mirror could have a convex shape, while the rest was concave.

This isn’t [Huygens Optics]’s first time building a deformable mirror, but this is a significant step forward in precision. If you don’t need such high precision, you can also use controlled thermal expansion to shape a mirror. If, on the other hand, you take it to the higher-performance extreme, you can take very high-resolution pictures of the sun.

Tubeless X-Ray Runs On Patience

October 12, 2025 by 9 Comments

Every time we check in on [Project326], he’s doing something different with X-rays. This week, he has a passive X-ray imager. On paper, it looks great. No special tube is required and no high voltage needed. Actually, no voltage is needed at all. Of course, there’s no free lunch. What it does take is a long time to produce an image.

While working on the “easy peasy X-ray machine,” dental X-ray film worked well for imaging with a weak X-ray source. He found that the film would also detect exposure to americium 241. So technically, not an X-ray in the strictest sense, but a radioactive image that uses gamma rays to expose the film. But to normal people, a picture of the inside of something is an X-ray even when it isn’t.

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A magnifying glass is seen behind a small tea candle. The magnifying image is projecting the shadow of a column of heated air.

Finding Simpler Schlieren Imaging Systems

October 6, 2025 by 3 Comments

Perhaps the most surprising thing about shadowgraphs is how simple they are: you simply take a point source of light, pass the light through a the volume of air to be imaged, and record the pattern projected on a screen; as light passes through the transition between areas with different refractive indices, it gets bent in a different direction, creating shadows on the viewing screen. [Degree of Freedom] started with these simple shadowgraphs, moved on to the more advanced schlieren photography, and eventually came up with a technique sensitive enough to register the body heat from his hand.

The most basic component in a shadowgraph is a point light source, such as the sun, which in experiments was enough to project the image of an escaping stream of butane onto a sheet of white paper. Better point sources make the imaging work over a wider range of distances from the source and projection screen, and a magnifying lens makes the image brighter and sharper, but smaller. To move from shadowgraphy to schlieren imaging, [Degree of Freedom] positioned a razor blade in the focal plane of the magnifying lens, so that it cut off light refracted by air disturbances, making their shadows darker. Interestingly, if the light source is small and point-like enough, adding the razor blade makes almost no difference in contrast.

With this basic setup under his belt, [Degree of Freedom] moved on to more unique schlieren setups. One of these replaced the magnifying lens with a standard camera lens in which the aperture diaphragm replaced the razor blade, and another replaced the light source and razor with a high-contrast black-and-white pattern on a screen. The most sensitive technique was what he called double-pinhole schlieren photography, which used a pinhole for the light source and another pinhole in place of the razor blade. This could image the heated air rising from his hand, even at room temperature.

The high-contrast background imaging system is reminiscent of this technique, which uses a camera and a known background to compute schlieren images. If you’re interested in a more detailed look, we’ve covered schlieren photography in depth before.

Thanks to [kooshi] for the tip!

A man is shown behind a table, on which a glass apparatus like a distillation apparatus is set, with outlets leading into a large container in the center of the table, and from there to a pump.

Pulling A High Vacuum With Boiling Mercury

October 3, 2025 by 21 Comments

If you need to create a high vacuum, there are basically two options: turbomolecular pumps and diffusion pumps. Turbomolecular pumps require rotors spinning at many thousands of rotations per minute and must be carefully balanced to avoid a violent self-disassembly, but diffusion pumps aren’t without danger either, particularly if, like [Advanced Tinkering], you use mercury as your working fluid. Between the high vacuum, boiling mercury, and the previous two being contained in fragile glassware, this is a project that takes steady nerves to attempt – and could considerably unsteady those nerves if something were to go wrong.

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