The Ferry Rocket - Trail Blazer or Unmatched Ambition?

When Von Braun was moved to the United States under Operation Paperclip in 1946, he was keen to get his ideas of spaceflight off of the ground and into the minds of the public.

His work for the US Army missile agency limited his capabilities to do this, he still found time to design a giant wheel space-station later that year (which would reappear, rejuvenated a few years later). In addition, a design was mentioned going by the designation A12, the ultimate form of the Peenemünde Aggregate programme.

Since its inception, A12 remained somewhat mysterious, with only a handful of sketches and details emerging over time. It is known that A12 was to be essentially a combination of the precursor designs into one ginormous rocket. It would have stood some 70m tall, and was 11m in diameter, and weighed 4100 tonnes (unfuelled). It was suggested that the A12 could place a 10 tonne payload into a 180 mile orbit, however what payloads that could be made by wartime Germany that could warrant such a position is up for debate. 

Such figures would have placed the rocket into a role similar to that of the Saturn 1 of later years, however there would be several severe limiting factors in its design, notably its inability to be produced quickly (or fast enough for its wartime operators), due to the sheer number of engines it would have required. Due to the fact that there were no new engine designs proposed at Peenemünde since the design of the A10, it must be assumed that the A12 would be forced to use the same engines. Present calculations posit that the A12 would have required some 50 A10 engines in the first stage alone. In addition to this requirement also weighing on the production of such the sheer number of engines, their reliability was also to be drastically affected. 

Since the V2/A4 had a less than ideal success rate ( at just 70% at its most improved at the end of the war), it is doubtful if the A12 could even dream of such figures.

Despite this, Von Braun sought to improve upon the design, and optimize it for more civilian purposes.

ENTER “THE MARS PROJECT”

In 1948, Von Braun took it upon himself to write a book, The Mars Project. It featured an idea of how a manned mission to Mars could go and be achieved by contemporary means. The book was primarily a science fiction story (one that wasn’t very good, likely one of the reasons it was never published), however the book included a technical appendix featuring all of the calculations Von Braun had done to make sure the ideas presented were feasible.

Hidden amongst the calculations, was a set on a reusable rocket to ferry equipment and men up to Low Earth Orbit. These calculations formed the basis of Von Braun's subsequent designs, so it seems appropriate to look at it in detail:

THE DETAILS

By this point, a combination of Nitric Acid and Hydrazine, with Hydrogen Peroxide used for the turbo pumps, had already cemented itself as Von Braun’s favourite fuels, due to their storability and ease of combustion. Naturally, they were the chosen fuels for his latest project. 

In what was to become the standard for these designs, no particular engine design was supplied, however the calculations were, featuring a specific impulse on the third stage (adjusted to modern day standards) seem to suggest a specific impulse of 297 seconds, although these were somewhat optimistic for its time, with the performance not being achieved until 1962.

The number of engines, once more, is not shown for each stage, although it can be presumed that it would be an inordinate number due to the relative unreliability of early liquid rocket engines. This, in tandem with the hypergolic fuels employed by the rocket would have made it one of the more dangerous rockets to fly, when compared with the rather conservative international proposals which employed LOx and Ethanol or HydroLOx.

The third stage of the vehicle was to be a winged return vehicle, in keeping with most concepts at the time, both domestic and international. Once in orbit, the third stage could deliver up to 25 tonnes of cargo, or 14.5 tonnes of “excess propellant” (for in-orbit fueling or refueling). Once the cargo had been delivered, the spacecraft could then return back to the earth. Since reentry heating had not yet been fully understood, Von Braun was unsure of how the craft could cope with reentry. So, the craft would reenter at a very shallow angle, causing as little heating as the craft could sustain. However this would have made it extremely long, causing the craft to have to travel through some 22,000km of atmosphere, over half of the Earth’s circumference. 

A cutaway of the 1948 design that appeared in Interavia in 1952

During this time, the occupants of the glider would only experience about 0.45G’s of deceleration, perfectly tolerable when compared to perhaps an Apollo crew’s 4Gs of deceleration. However, the craft may not have fared as well, as Von Braun estimated that the peak heating to be experienced by the airframe came in at almost 1005°K (781.85℃). Based upon his calculations, Von Braun concluded the craft could be constructed from contemporary steels, however he did acknowledge that “latest information” indicated that reentry heating could be up to 300°K higher than he himself had calculated, meaning heating experienced could be 1031.8℃.

Even with this rigorous calculation, the obtained results were far to conservative. When the Boeing Dyna-Soar entered development, it was calculated that the nose alone would experience almost 2140°K (1866℃, over 400° above the melting point of the steel Von Braun suggested he could make the craft from). Based on this information, the glider would have simply melted during reentry, rather than Von Braun's reasoning that it could radiate the heat at the same rate it absorbed it.

However, ever the visionary, Von Braun twigged that to successfully launch a mars mission with the rockets he had designed, it would require over 950 launches to assemble 10 spacecraft in orbit, each weighing 3720 tons each.

Naturally, he concluded that it would be far too expensive to make the boosters expendable, and so included systems that would permit their reuse and refurbishment, although they may not be as practical by modern standards. 

To reuse the first stage, a 64.5m diameter parachute was provided, which itself weighed 85 tonnes. In addition to parachute descent, final touchdown in the sea was to be cushioned by 40 tonnes of solid rocket motors to facilitate a splashdown at 304km downrange. In a fashion similar to Von Braun’s ideas in the later Project Horizon, the stage could be towed via tug back to the launch site in the pacific, and refurbished and reused.

The second stage was also recoverable, returning to earth underneath a 20.4m diameter parachute that weighed just 3 tons, with final cushioning provided by 4 tonnes of braking rockets. 

While unorthodox in its reusability, the design sounds quite modern, perhaps even comparable to the Saturn-Shuttle concept from the mid 70s. However this was not to be the final iteration of the design, far from it.

ENTER COLLIERS MAGAZINE

Popular American magazine Colliers published a series of articles detailing how man could conquer space and to show that it was indeed possible, beginning with “Man Will Conquer Space Soon!” on March 22nd 1952. 

On pages 26-27, the new “Ferry Rocket” was unveiled by Von Braun, as an upgrade to the prior 1948 iteration of the design.

However, contrary to the rockets’ almost entirely new sleek appearance, it still used almost all of the calculations Von Braun had made for the ‘48 version, so it was essentially the same rocket, although with some primary differences:

It had been decided that the 1948 rocket appeared too dumpy and squat to suitably capture the minds of the American public, so Von Braun produced a much more slender version of the design, which was further sleekened in Rolf Klep’s awesome paintings of the vehicle.

It is strange to note that Von Braun had already recognised that the somewhat boring Cylindrical forms would be much more efficient for a rocket booster, and had so implemented them onto the Redstone missile, then in development. So it is odd that he elected to retain the more conical, smooth forms of this far larger booster.

Rolf Klep's cutaway illustration made for "Man Will Conquer Space Soon"

The first stage’s diameter had remained the same, but the upper stages had become drastically smaller. In addition to this, the centrally mounted parachute canister had been dropped, instead replaced with a steel mesh drag-brake parachute stored within the fuselage of the first stage base.

The removal of the parachute canister allowed more space in the first stage to be allocated to more engines, allowing for some 52 engines to be placed inside. 43 engines would be fixed in place, but 9 engines were permitted some range of lateral motion by being controlled by a tiller bar. 

However, the problem with using the 1948 calculations began in the upper 2 stages:

The second stage diameter was reduced by 7.5m to 13.5m wide. By doing this, there was now simply not enough space to be able to meet the nozzle area required in Von Braun’s original calculations. In addition to this, Klep’s gorgeous painting showed Redstone-type low-expansion ratio engines, which would be unable to fulfill the area ratio required of the 1948 calculations, and needed for the higher performance engines the design now warranted.

Moreover, the third stage now suffered the same problem, being reduced from 9.8m to 5.8m when the third stage engine took up the entire base of the stage in the original calculations. 

The return glider was now vastly expanded upon from the original 1948 proposal. It had 5 engines in the base of the glider, for both accelerating up to orbit and decelerating from it. Crew was also indicated, with 7 crew members in total, each with their own pressurized “escape capsule”, which in the event of an emergency, could safely return to earth under their own power and parachute. 

The cargo capacity, however, was massively reduced from its predecessor to just 10 tonnes to LEO, 11.5 when carrying “excess propellant” for fueling in orbit. 

Von Braun envisioned that the rocket would fulfill a role similar to that of the space shuttle of the future, simply ferrying men and equipment up to a given orbit to facilitate either crew transfer or orbital assembly.

WHAT IF?

It is at this point one may wonder, what it would be like if such a vehicle had indeed been manufactured to these specifications. Would it even work? Would it be safe for crewed launches? 

To begin with, one must examine the infrastructure that would be required of the rocket, then proceed onto the feasibility and reliability of the vehicle itself.

 In order to launch a rocket, one needs a launch site, this much is obvious. Where said launch site should be is more debatable. It should be as close to the equator as possible, with a large expanse of either empty terrain or ocean down range to allow for safe landing of rocket stages. In addition, the chosen area should have enough space to accommodate the personnel necessary to launch the rocket, and the facilities necessary to maintain and construct them.

Von Braun’s chosen site meets only 1 of these criteria, this being the Johnston Atoll in the Pacific Ocean. By all accounts it does make sense to start operations here, as it has plenty of room for launch sites, being almost completely level. In addition it is surrounded by almost the entire Pacific Ocean, making stage recover safe and simple. 

What it does not have room for, however, is anything else required of a major launch site. 

At the time of the article’s  publication in March 1952, the atoll was scarcely a square half mile in size. There is no conceivable way that Von Braun could hope to get the number of launch sites and personnel required of his enormous missions onto such a tiny island without enlarging or with dredging at great expense.

Moving swiftly on, once more Von Braun had chosen his favorite fuel combo in Nitric Acid and Hydrazine. While they can be stored for many months, they would be extremely expensive to acquire.  

The first stage alone would require over 4,800 tonnes of Nitric Acid and Hydrazine, which at the time would have cost $303,792, a small fortune for the time. 

Applied to the other two stages, each launch would have cost $911,376 in fuel alone. Such figures would only get worse once Von Braun proposed the missions the rocket could be used on. 

He suggested that the Ferry Rocket would largely ferry cargo up to a space station for the crew to assemble in-situ. For example, if his later mars mission profile were pursued (which employed the same ferry rocket), it would have to haul 1870 tons of cargo to orbit for assembly.

To do this Von Braun proposed a fleet of 3 Ferry Rockets to perform 400 total launches (335 to haul cargo, 65 for crew rotation), launching 3 times EVERY 48 HOURS FOR 8 MONTHS. Extrapolating the fuel costs it would come to a staggering $110,884,383 for the entire programme! That’s $1,314,607,586.00 today! 

It is absolutely unthinkable that the US could possibly pay for such exorbitant costs when it was still recovering from WW2, and with little backing from a public that wouldn’t really see the point in doing so

TO CONCLUDE

While Von Braun was a true visionary of his day, the fact remains that the designs he produced were wildly optimistic for even the 1960s, let alone the 1950s. 

Very little of the Ferry Rocket went on to live through subsequent designs, and that is probably for the best, however pretty the designs might have been

REFERENCES

1952 iteration statistics: http://www.astronautix.com/v/vonbraun1952.html

1948 iteration statistics and general information: http://www.astronautix.com/v/vonbraunconceptvehicle.html