Thursday, October 9, 2014

Yes, the Aggregat 4 (and von Braun) was a Pretty Big Deal

Those of my readers with significant aerospace knowledge are probably slightly concerned by the title. Has this blog so quickly devolved into writing about obvious content? Will my next post be about how the sky is blue, or water is wet?
No, I will not be writing about the wetness of water or the blueness of the sky. However, in my recent travels on the internet, I came across a person who made the bold claim that “von Braun’s work was just scaled-up rip-offs of Goddard’s”. That said person, when pressed on this claim, chose to resort to insults rather than providing facts to back up their statement is a topic for another day.
The intent of this article is not to downplay Robert Goddard’s achievements in the field of rocketry. His work was an inspiration to aerospace engineers and scientists worldwide. Indeed, von Braun himself acknowledged Goddard’s achievements, saying in 1963; 

"In the first third of this century, interest was limited to a few lone-wolf scientists who were often labeled "crackpots." One such "crackpot," Dr. Robert H. Goddard, is now credited with being the first to fly a liquid rocket, complete with a "re generatively cooled" combustion system and a simple guidance system to keep it on course. Dr. Goddard, a truly great man, was a professor of physics at Clark University in Worcester, Mass. His rockets, which were flown starting in 1926, may have been rather crude by present-day standards, but they blazed the trail and incorporated many features used in our most modern rockets and space vehicles.”

Had Goddard received as much funding and resources as von Braun, he might well have been able to create a rocket like the A4. Alas, he did not, and such speculations will remain just that, speculations.
This post is also not intended to unnecessarily glorify Nazi engineering or practices. The usage of slave labor in the assembly of the V2 rockets was a horrendous atrocity. While the advances in aerospace technology caused by the A4/V2 are numerous, they were most certainly not worth the lives of thousands of innocent men. Also, to head off any wehraboos who might be reading this article, the A4/V2 was a major technical achievement, but useless as a weapon. The German state would have been better suited investing the time and resources spent on the V2 (according to some accounts more than the Manhattan Project cost) on simpler and more mundane projects with a greater chance of success. Not that it would have made a difference in the final outcome.

Now, onto the main topic. According to the Encyclopedia Astronautica, the largest rockets Goddard ever tested were the P-C series, which he built in 1939-1941. These rockets were fueled with liquid oxygen and gasoline; this propellant combination was a precursor of later kerolox rockets such as the Saturn V. This combination, when used in the P-C’s engine, resulted in just over 3 kilonewtons of thrust. With a total mass of roughly 220 kilograms, and a height of almost 7 meters, the P-C series were nothing to sneeze at. Certainly better than anything I could put together in my garage. However, let’s compare them to the A4.
The A4 was roughly 14 meters tall, twice the height of the P-C. Moreover, it had a mass of over 12,000 kilograms, more than an order of magnitude greater than Goddard’s rocket. Not only this, but the engine in the A4 produced nearly 100 times as much thrust as the one on the P-C, and used a different propellant combination (liquid oxygen and alcohol). 

If you are still unconvinced, here’s a visual comparison. First, a picture of the P-C, from Astronautix. 

Not the greatest picture, but it does show the internals clearly visible, as well as an indication of the relative size.

Now, the A4;


It is highly obvious that the two rockets are of completely different scale. Considering that the gulf between the A4 and Goddard’s earlier efforts is even larger, it is clear that the A4 is not simply one of Goddard’s rockets with the dimensions changed to metric (as one person on the internet claimed).
Of course, some might argue that the A4, and other rockets in the Aggregat series are simply scaled up versions of Goddard’s rockets. Since scaling up a rocket is trivial (according to these people), von Braun and friends didn’t actually do any new work. Ignoring that it is clear that the A4 is not a P-C (or any other of Goddard’s rockets) with the dimensions multiplied by some number, let’s take a look at whether scaling up a rocket to a bigger size is actually trivial.
During the 1950s and early 1960s, kerosene/liquid oxygen (kerolox) was a commonly used propellant combination in the American space program. Many rockets, including the Atlas ICBM and the Saturn I used kerolox engines in the first stage. However, the most famous usage of this propellant combination was the Saturn V, whose F-1 first stage engines were quite possibly the most powerful in the world (depending on whether you count the multi-nozzle RD-170).
By the time the Saturn V was developed, the US space program had several years of experience with kerolox engines. While none of them were as large as the F-1, it should have been trivial to scale an existing design up to that size, right? Wrong. The F-1 suffered from massive combustion instability issues, which took several years to resolve, and represented a major setback in the program. (More can be read about the development of the F-1 here;
In addition to issues with combustion instability in the F-1, the Saturn V had several other kinks that needed to be worked out during its development, including pogo oscillations that nearly resulted in the loss of the (fortunately unmanned) Apollo 6. Clearly, making a bigger rocket by simply scaling up existing designs is not trivial. This is due to the inherent nonlinearities and complexities in large systems such as space launch vehicles. In the 1960s, when computer simulation technology was in its infancy, it was impossible to predict exactly how a large system such as a Saturn V might behave (even today it is difficult). In the 1940s, when computer simulation technology was nearly nonexistent, and slide rules were the computational tool du jour, it would have been impossible.
What if it was argued that von Braun’s earlier work, such as the A1, was a copy of Goddard’s? This question is more interesting. Indeed, the rockets of the L-B series, which Goddard tested from 1930-1937, are comparable, or even larger than, von Braun’s efforts from the same period. Also, while Goddard’s L-B rockets flew successfully multiple times, the A1 was tested a single time, which ended in failure. But was the A1 merely a crude copy of the L-B, as has been claimed? Or was it a native, if somewhat inferior, design. Let’s compare pictures of the two.

This is a diagram of the A1.
And here’s the L-B:

As can be seen, the two rockets are distinct designs, with different proportions. While the A1 was undoubtedly influenced by Goddard’s work, it is a unique design, so far as I can tell. Of course, even if the A1 were a clone of a Goddard rocket (a dubious assertion), this would not discount von Braun’s later work.

In conclusion, Goddard’s contributions to rocketry and the aerospace sciences are numerous. They went criminally unrecognized, and had they received the attention they deserved, spaceflight could have been advanced several years. However, they do not diminish the magnitude of the accomplishments of later engineers, such as von Braun. While von Braun’s work may have been inspired and influenced by Goddard’s, being influenced by others is a natural part of science and engineering. Is Einstein’s work diminished because it was based on that of Maxwell and others? I think not.


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