Kuiper skids to a halt in the sand, running towards the camera.

Radioing the Moon

Kuiper blueshifts.

On this day in 1946, we made our first round-trip visit to the Moon (using radio waves!) Before this, we weren’t positive if radar could even get past Earth’s ionosphere, let alone bounce off an object ~240,000 miles away and return. Although radar had a huge impact on World War II, it was still a fairly new technology at the time.

“Project Diana” (named after the goddess of the Moon) was a proof of concept by the US Army Signal Corps. They were tasked to demonstrate whether it might be possible to utilize radar to detect an incoming long-range ballistic missile. As they had no missiles readily available in space, they decided to use the moon as a proxy. The project took place at Fort Monmouth in Wall, New Jersey.

The earliest moonshot took some heckin’ engineering. Because both the Earth and the Moon are constantly moving, the engineers had to account for the Doppler effect. You’re likely familiar with the way a fire truck siren changes pitch as it’s heading towards you vs. heading away; that’s Doppler in action.

When a fire truck is approaching you, your ears hear sound waves more frequently (resulting in a higher perceived siren pitch.) That’s called “blueshifting.” As it gets further away, your ears hear sound waves less frequently (resulting in a lower perceived pitch.) That’s “redshifting.”

The complex calculations that made Project Diana possible were done by American astrophysicist Dr. Walter McAfee. His contributions to science opened the way to satellite communications and space travel, but he almost didn’t get the chance. Dr. McAfee was rejected from jobs at several federal agencies. At the time, the vast majority required a photo to be submitted with a job application, and Dr. McAfee was Black.

Fort Monmouth did not require a picture, and requested that Dr. McAfee report to work immediately. When he (nervously) arrived and introduced himself, the head of engineering personnel was thrilled. He said, “By God…we’ve been getting people who want to pass themselves off as mathematicians or mathematical physicists and they don’t have anything. Now we’ve got one.”

Original post: https://www.instagram.com/p/Bse5S5DjtoY/

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