At the end of World War II the United States famously snapped up as many German scientists as it could with Operation Paperclip. While they were from a wide variety of disciplines, the ones most remembered today were the rocket designers and, as London and Amsterdam were still sporting spectacular V-2 craters, public interest in them was high at the time.
By the end of 1945 most of them would relocate to the United States, but in the period immediately following the end of fighting in Europe they were still in Western Europe and being interrogated by US intelligence personnel keen to learn about a line of weapons development in which the Nazis had jumped far ahead of the rest of the world.
It was in this setting that a few articles were published in major US newspapers and magazines (Time, Life, the New York Times and others) during July 1945 outlining one bit of information the US was getting from the captured scientists. All the articles were based on a single news conference held in Paris at the end of the previous month. While the conference apparently covered a wide variety of weapons that had been under development when the war ended, the articles picked up on one spectacular one and focused on it: the Sonnengewehr, quickly dubbed the “Sun Gun”.
The Sun Gun idea had been brought to the attention of the US by a group of scientists and engineers at Hillersleben, Germany (now part of the town of Westheide in Saxony-Anhalt, which was once part of East Germany). Though mostly unassociated with Wernher von Braun’s more-famous group they too had experience with rocketry, having worked on rocket-assisted artillery weapons and tank shells during the war.
As reported, in an unfortunately garbled way that makes it clear the reporters didn’t understand the underlying physics, the Sun Gun would have been a disc-shaped space station in a 3100-mile (5000-kilometer) orbit; some sources say 5100 miles, but this seems unlikely as German engineers would have expressed themselves in kilometers and that would be an unwieldy 8208 of them. Either way, neither would have been geosynchronous, an oddity pointed out even by some of the reporters in 1945.
Regardless, the station would have been coated with metallic sodium—chemically reactive and so easy to tarnish in the atmosphere, but which would stay clean in vacuum—polished into a mirror. The mirror would be pointed at a receiver off the coast of Europe and used to boil ocean water for power, but when the need arose it could be used on military targets—it had a projected ability to heat anything on the surface to 200 Celsius. Other numbers are scant and not clearly from the scientists themselves, but one that raises an eyebrow is that the mirror would have had an area of 5000 square miles (a round number in non-metric units, which is suspicious, and matches a diameter of 128.4 kilometers). Other sources suggest a much more realistic 9 square kilometers.
Life magazine was the most expansive on the topic, and published several drawings on the construction and operation of the station. Unfortunately their accompanying text and some of the details in the illustrations themselves suggest that the article’s authors were engaging in speculation on both topics. For example, they have the station being built of pre-made sections—cubes, oddly enough, which makes it a bit hard to produce a disk—when there’s reason to believe that it would have been made on a skeleton of long cables reeled out from a central station. Also contrary to this, Life has the inhabitable area around the edge of the disk, though this would have turned the Sonnengewehr into a “filled-in” version of the torus-shaped stations so favoured by von Braun during his lifetime
Immediate post-war reports to the contrary, it’s very unlikely that there was any sort of official work done on the Sonnengewehr beyond some tentative memos and discussions. If nothing else, consider the sheer mass of material that would have to be lifted into high orbit to build it. One source suggests one million tonnes of sodium metal, a figure considerably larger than the mass of everything ever lifted into orbit by all the world’s nations between 1957 and the present day.
Instead it seems to have been at best something batted around as a possible ultimate destination—even the scientists involved were thinking along the lines of the year 2000—in the culture of grandiosity that Nazism embraced and that also produced things like the Landkreuzer P. 1500 and Hitler’s architectural enabler Albert Speer. Even the mainstream rocketry program at Peenemünde was looking to run before it learned to walk, and this was just an extreme example of this attitude in the embryonic German space program. It may not have even been as tentative as that: at worst, it was merely discussions of an idea floated by the father of German rocketry, Hermann Oberth, in 1929.
Any gloss of reality the Sonnengewehr got likely came once the war was over and the Hillersleben group were under the control of the American military. In that precarious situation they would have been searching for anything to impress their captors of their usefulness and the Sun Gun inflated from cafeteria-table discussions to the preliminaries of a project. It did get them a little attention at the time, to be sure, but its sheer fantasticalness made it quickly drop back out of the limelight.