The Silbervogel (later known as the Antipodal bomber) was a rocket-powered bomber created as a concept in the late 1930s by scientists Eugen Sänger and Irene Bredt for the Nazi regime.
The idea was based on Sänger’s extensive research into rocket engines and aerospace technology while he was a doctoral student in Vienna. He teamed up with Bredt, an expert in ram-jet engines, to begin work on creating a long-range rocket-powered bomber.
It was an advanced idea and in 1941. The German military high command considered implementing it as part of their Amerika Bomber project to create a long-range bomber aircraft that would be capable of reaching the United States.
The rocket would glide along a rail to launch itself into the air before following its mission and then landing, either at home in Germany or at a Japanese air base. The idea never progressed into the concept stage due to a sudden change in priorities for the Germans.
Despite this, Sänger’s expertise in rocket and long-range aircraft technology remained sought after by Western and Soviet powers after the war.
While studying as a PhD student at the Vienna Polytechnic Institute in 1933, Austrian aerospace engineer Dr. Eugen Sänger drafted and created a concept idea for a manned sled-type powered glider that could reach Mach 10 and glide at a 160 km altitude.
The initial design was to have a spindle-shaped fuselage and low aspect ratio wedge wings. In 1934, he revised the design into a hypersonic boost-type glide vehicle that could reach a top speed of Mach 13 at the burnout stage of its rocket motor.
It would then enter a 5,000 km long glide, reaching a stable Mach 3.3 cruising speed before coming back down to land.
Between June 1935 and February 1936, Sänger began to extensively research further ideas into a concept that resembled long-range rocket-powered plane and published a series of academic articles on the subject.
He was contacted by the German High Command, by then under the Nazi Party regime, and was asked to head a secret aerospace department and research institute in the German town of Treuen. The secret institute would help him develop and build his Silbervogel (meaning Silver Bird) idea as a manned rocket vehicle that was capable of reaching orbit.
As well as writing academic papers, Sänger was no stranger to hands-on experimental rocket making. He had been working on building various concept proposals for several years, including conducting physical research and development into liquid fuel rocket engines.
From 1930 to 1935, he conducted several static tests on a liquid-fueled rocket engine that was cooled by its own fuel by circulating it around the combustion chamber.
For the time, Sänger’s engine produced an enormous 10,000 feet a-second predicted exhaust velocity. This is particularly impressive when compared to the later V-2 rocket’s 6,560 feet second capabilities.
Around the time that Sänger began his work at Treuen, the Nazi high command began conceiving a long-range bomber project which they first termed the “Amerika Bomber” concept in 1938 before Reichsmarschall (Luftwaffe chief) Hermann Göring pushed the idea further in early 1942.
The basic concept of the Amerika Bomber was a call to manufacturers and designers to build a long-range aircraft of any type that could reach and perform bombing missions over important and strategic United States cities such as Chicago or New York before returning to back to base.
The proposal started with various conventional but updated piston propeller aircraft designs such as the Heinkel He 177 Greif and the giant Junkers Ju 390 being considered.
Other aircraft renowned German manufacturers ranging from Messerschmitt, Junkers, Focke-Wulf and the Horten Brothers also submitted design proposals to Göring and his men.
The designs began to branch away from traditional propeller aircraft towards concept designs such as the Horten Ho delta wing jet bomber or larger planes that could act as a kind of carrier of smaller bombers which would then be released once the transatlantic leg of the flight was finished.
Sänger’s Silbervogel rocket also came under the Amerika Bomber fold and research into the idea was intensified in the spring of 1942.
Sänger began working closely on the design with German engineer Irene Bredt to produce a winged rocket. Bredt was known for her studies into the ram-jet concept and would eventually marry Sänger.
The fuselage of their rocket was flattened, with the idea that this would help create lift. The wings would be short and wedge-shaped. The design also featured a horizontal tail surface located at the rear end of the fuselage which had a small fin on each end.
The fuel would be carried in two large tanks fitted on each side of the fuselage which would run from the wings to the aft end of the rocket. Oxygen tanks would be attached one on each side of the fuselage, located forward of the wings.
Power would be provided by a large rocket engine based on Sänger’s designs that could produce up to 100 tons of thrust and would be mounted in the fuselage rear. The engine was flanked by two auxiliary rocket engines to provide liftoff power.
For the takeoff launch, the rocket would be propelled down a 1.9 mile long monorail track by a rocket-powered sled that developed a 600-ton thrust for 11 seconds. The track was angled at 30 degrees to allow for the Silbervogel to be propelled into the air once the guide rail came to an end.
After takeoff, the rocket would quickly reach an altitude of 5,100 feet and a speed of 1149 miles per hour. At this point, the main rocket engine would kick in and fire for eight minutes, burning 90 tons of fuel to propel the Silbervogel to its maximum speed of around 13724 miles per hour and to an altitude of over 90 miles in the air. Some sources even predicted that the rocket would climb to a height of 174 miles.
The Silbervogel’s long-range flight would be achieved in a series of short bursts or skims. As the Silbervogel accelerated and descended under the pull of gravity, it would then hit the denser air at about 25 miles above the earth and almost skim like a stone through the air. These skims would help to cool the bomber after encountering the intense frictional heating in the denser air. The skims would gradually be decreased until the aircraft would glide to a normal landing speed using its conventional tricycle landing gear to land safely on a runway.
The pilot would sit in a pressurized cockpit in the forward fuselage and a tricycle undercarriage was fitted for a gliding landing. A central bomb bay was fitted and designed to carry a single 8000-pound free-falling bomb with no guidance.
No defensive armament was fitted to the rocket. The designers believed that the speed and velocity would enable it to outrun enemy fighters and fly high above American air defences.
The empty weight of the rocket was approximately 22,000 pounds at the end of the design process.
The rocket’s development hit a snag when Sänger and Bredt calculated that the heat generated on the rocket’s body as it descended from orbit would be enough to melt the fittings and cause the fuselage to burn up and explode. A heat shield was subsequently fitted.
The Nazis began building a full-scale launching and testing facility for the rocket in June 1941, but the project was put on hold following the German invasion of the Soviet Union under Operation Barbarossa.
As the Nazi war machine became bogged down and halted on the Eastern front, the focus of the German military high command shifted to placing priority on producing existing designs to meet the needs of the German war effort.
Undaunted, Sänger continued to work on the idea and proposed two variants of the Silbervogel to the Luftwaffe in December 1941: the manned Antipodenferngleiter (antipodal long-range glider) and the unmanned Interglobalferngleiter (intercontinental long-range glider).
Both essentially followed the same fuselage design although the unmanned version could carry a larger bomb payload.
It was imagined that the manned version would fly from Germany to drop its bomb on an American city or industrial target before the pilot would land it at an airbase in Japan.
However, the project did not enter the testing phase.
As the war began to turn against Germany, Sänger was ordered to move away from experimental prototypes and focus on ram-jet production to help the Luftwaffe quickly deploy jet-powered aircraft against advancing Allied forces to claw back air superiority.
Sänger helped to work on emergency projects such as the Škoda-Kauba P14 jet fighter, however like the Silbervogel the P14 jet was also not tested or put into production before the end of the war.
Sänger held onto his research, and despite initial attempts by Nazi officials to censor or prevent him from publishing his ideas in the public realm, he continued to study rocket design after the war with his academic publications and blueprint ideas filtering abroad into the hands of foreign governments.
Following the defeat of the Nazis, Sänger and Bredt moved to France and worked as engineers for the French Air Ministry.
Around this time Sänger was the target of a failed kidnap and bribery attempts by the KGB and Stalin. They had become aware of Sänger’s work and the Silbervogel concept and wanted Sänger and Bredt brought to the Soviet Union to resume and recreate it.
When the attempts failed, Stalin instead demanded that Soviet scientists work on their own version incorporating Sänger’s philosophy into their labour, although none of their work reached the production stage.