Megaroc was the name of the crewed derivative of the V-2 rocket proposed by the civilian British Interplanetary Society (BIS) in 1946. It preceded the first launch of the actual manned V-2 derivative, the American Mercury-Redstone Launch Vehicle, by 15 years and if successful, would have put a Brit in space in the late 1940s or early 1950s.
V-2 rocket launching during the British Operation Backfire (deutschlandmatters.com)
It was springtime in Peenemünde, Germany when Wernher von Braun, the head of the Nazi V-2 rocket program, surrendered to Allied forces. Over the next few months, as the Second World War began to wind down, the United States hired von Braun and other rocket scientists to work for its own military and the Soviet Union captured the facilities at Peenemünde while France gathered more scientists and engineers. Britain, the target for numerous V-2 attacks, took the same rockets that wrecked its cities and killed hundreds of its citizens for its own series of experimental flights.
Operation Backfire evaluated the entire V-2 rocket system and performed test launches over the North Sea. British staff also interrogated ex-Nazi personnel who worked on the V-2 program. Three rockets were launched from a concrete launch pad near Cuxhaven, a seaside town on the northern tip of Germany. Information on the handling and launch procedures are unknown other than that they were performed by German personnel . The Operation Backfire launches were filmed and the footage, commonly used in documentaries, is typically mistaken for wartime German footage because the personnel wore their original uniforms and the rockets were painted in their original color scheme. The first launch occurred on October 2, 1945 and was successful. The vehicle was called Backfire Rocket Two . Backfire Rocket One launched on October 4 but had an engine failure shortly after liftoff. The final launch took place on October 15 and was named Operation Clitterhouse. According to The Earth Gazers by Christopher Potter, the flight was to "benefit observers from America, Russia, France, the UK, and the press." Operation Backfire was a success and the rockets reached their targets located in the North Sea more accurately than the Nazi wartime ones. Afterwards, the British installations at Cuxhaven were dismantled and the concrete of the launch pad was removed. Nearby launch control shelters are supposedly still standing to this day. Some of the other V-2 rockets were taken to the Royal Air Force museum in England.
Enter Ralph. A. Smith, one of the original members of the BIS who helped re-establish the society after World War II. After fellow member H. E. Ross observed that the V-2 was "nearly big enough to carry a man", Smith proposed using a captured rocket to send a person on a suborbital spaceflight. Prior to the war, the BIS devised a plan to land men on the moon using a large multistage rocket. By the time the project gained international attention, Adolf Hitler invaded Poland and Britain declared war on Germany. Now that the society had reformed, it decided to take advantage of this newly available rocket technology and apply it towards crewed spaceflight.
According to the BIS's webpage on Megaroc, the main objective of the project was to "provide manned ascents to a maximum of 304 kilometers" (189 miles). Two windows on the fuselage would have allowed for scientific observations of the Earth and sun. Radiation communication through the ionosphere would be tested and data on human performance over a wide range of g-forces would be gathered as well. The vehicle would have been a modified, enlarged, and strengthened German V-2 rocket 57.4 feet (17.5 meters) long with a launch weight of 21.2 tons. It had a diameter of 7.3 feet (2.18 m) at its widest point. The most noticeable difference between Megaroc and the original V-2 was the omission of the iconic large aerodynamic fins and control surfaces . This reduced the vehicle's overall weight by 705 pounds (320 kg). The rocket also included a pressurized cabin instead of the original instrument bed and warhead enclosed in an aerodynamic jettisonable shroud. Two large side ports would have been used for observation, access, and egress. Such a vantage point would have also been ideal for spying on enemy territory, though only briefly. One specific instrument that would have been flown is the strobo-periscope, a modified form of the BIS pre-War coelostat . It would have provided rearward viewing after the cabin separated from the booster.
Cutaway view of Megaroc (BIS)
The astronaut, called an "observer", would have worn a standard high altitude g-suit with its own air-conditioning and personal parachute. The suit included air conditioning because the cabin would not due to the short duration of the flights. A very unique feature of Megaroc's cabin was its counterbalanced cradle-type seat designed to tilt as the craft moved. Attitude stabilization was provided by hydrogen peroxide jets and the spacecraft also had automatic, manual, and emergency controls. I was unable to find any information on a proposed launch site but I feel it is safe to assume launch could have taken place either at Cuxhaven in Germany or a new facility closer to the equator. Unlike the Mercury spacecraft, this reentry vehicle did not need a special heat shield. Instead, a "reefing parachute" would have provided constant drag regardless of air-density and the velocity of descent. It would have been suitable for either a sea or land impact, fitted with a crumple skirt to absorb some shock and avoid bounce.
Megaroc had a great deal of similarities to the American Project Mercury (1958 - 1963) regarding both vehicles and mission profiles. Both were civilian projects aimed at sending a man on a suborbital flight using modified pre-existing technology. Here what a Megaroc flight would have looked like:
The rocket launches from a tower at an angle 2° from the vertical with an initial acceleration of 9.8 m/sec^2.
Constant thrust is maintained for 110 seconds or until the rocket reaches about 151,000 feet (46,000 m). By this point the rocket is accelerating about 20 m/sec^2 and the pilot is experiencing 3 g's.
A compressed-air charge separates the cabin from the hull once air density is reduced to the point where drag is negligible.
Communications switch from inside the hull to inside the cabin.
The observer performs experiments and moves freely inside the cabin.
Apogee is reached around 6 minutes and 16 seconds after launch.
At an altitude of about 70 miles (113 km) the constant-drag parachute is deployed for descent and the observer experiences 3.3 g's.
The cabin touches down on land or at sea and the chute is released to prevent the craft from being dragged along.
Megaroc was submitted to the Ministry of Supply on December 23, 1946 and promptly rejected: The country was in the process of recovering from World War II and what little money it had went to citizens who needed it the most. R. A. Smith went on to design spaceplanes and large space stations, both of which would become popular in the US in the next decade. Britain abandoned V-2 technology and shifted its focus to aviation and nuclear technology. On the other side of the Atlantic Ocean, within the next decade the V-2 would develop into the Redstone missile, the baseplate for the Juno and Saturn families of rockets.
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 According to "Report on operation 'Backfire', volume 1", German personnel working on the project consisted of prisoners of war, former members of the German military, and volunteer civilians.
 Backfire Rocket Two launched before Backfire Rocket One because One experienced issues prior to launch. A similar situation happened in 1950 with Bumpers 7 and 8, modified V-2 rockets launched by the US military. Bumper 8 launched before Bumper 7 due to an issue with 7 and became the first rocket to launch from Cape Canaveral in Florida.
 This was one of the first major rocket designs that did not follow the traditional "finned" design. It would not become standard practice for another ten years.
. The coelostat is a periscope-like device that uses two mirrors to make stars appear stationary despite the spacecraft's continuing movement.
Hollingham, Richard. “How a Nazi Rocket Could Have Put a Briton in Space.” BBC Future, BBC, 25 Aug. 2015, https://www.bbc.com/future/article/20150824-how-a-nazi-rocket-could-have-put-a-briton-in-space.
“Megaroc.” The British Interplanetary Society, 29 Nov. 2020, https://www.bis-space.com/megaroc/.
Parkinson, Bob. “A Prehistory of Outer Space.” Spaceflight, vol. 55, no. 10, Oct. 2013, pp. 374–378.
Quattromani, Nic. “Man in Space by 1948?” Let's Get Off This Rock Already!, 25 Apr. 2021, https://letsgetoffthisrockalready.com/2021/04/25/the-manned-v-2/.
"Report on Operation "Backfire" vol. 1." Smithsonian Libraries, War Office, Jan. 1946, https://library.si.edu/digital-library/book/reportonoperati1grea