ASPHALT BASED THERMOPLASTIC COMPOSITE SOLID ROCKET PROPELLANTS
Their Manufacture and Use in Military, Commercial, and Small-Scale Experimental Rocket Motor Applications
Asphalt/Perchlorate composite propellants were an innovation of the early 1940s. Since their initial development, they were used principally in JATO ( Jet Assisted Take-Off ) units for aircraft of almost every imaginable type and size; ranging from small single engine planes, to the giant B-47 Stratofortress bombers. They were also used extensively in many of the early proto-type strap-on boosters for air breathing guided missiles, and pusher motors for rocket sled applications. They were used in somewhat of a lesser role as a propellant for a device called the Hydrobomb (an underwater torpedo of sorts), and as the main propelling charge in America's first long range sustained burn artillery rocket, called the Private.
When compared to other contemporary solid propellants of the day, their tenure was somewhat short lived. By 1944, their development, and state-of- the-art had run its course; and newer propellants were beginning to appear with recurring frequency. These newer propellants, with names such as Paraplex, Aeroplex , and Polysulfide, had a much wider operational temperature range, more desirable physical properties, and did not need to be processed at elevated temperatures. It was therefore, only a logical progression, that they would ultimately replace the asphalt based ones. Nonetheless, during that period of time, they were still used with a remarkable degree of success, on some pretty amazing projects.
As it turned out, some of the JATO motors that used Asphalt/Perchlorate propellants were still being produced up until the mid 1950s, due to the time lag between engineering development, and the receiving and filling of production orders. No matter what anyone says, they were a still a major stepping stone in the overall development of modern composite solid propellants, that cannot simply be glossed over.
Soon after asphalt based propellants were phased-out by the military, and commercial aerospace rocket motor industry, Amateur rocketeers rescued them, and continued using them until around 1985. By then, many of the Ammonium Perchlorate Composite Propellants (APCPs) and their associated processing technologies had been de-classified by DOD. At this juncture, even the hobbyist/experimental rocket builders became hard-pressed to find any reason for continuing their use. Even as early as 1979, groups such as the Rocket Research Institute (RRI), who had once embraced Asphalt/Perchlorate as their main-stay propellant of choice, began the transition to using APCPs.
So did some manufacturers of model rocket motors. By this time, black powder propelled model rocket motors had also reached their limit insofar as Americas regulatory agencies and the technology to support them would allow. This was most evident in the larger sized hobby rocket motors, which evolved into what is collectively known today as High Power Rocketry.
Eventually, Asphalt/Perchlorate propellants had largely out lived their usefulness for anything other than demonstrating basic propulsion principles. Of course, the same thing could be said for other amateur propellants of the day. Due to certain technological limitations (to be explained later) Asphalt/Perchlorate propellants never found their way into model, or high power rockets: which was probably all for the best.
Although it is unlikely that Asphalt/Perchlorate propellants will ever be used again for military / defense applications , the basic chemistry, and process technology is still viable. In recent years, there have been remarkable new developments in the commercial roofing industry, which ( as unlikely as it may seem ) led to the invention of a new generation of Asphalt/Perchlorate propellants, made from “super asphalts”, with significantly higher pliability, tensile strength, and elongation. This has largely been made possible through the addition of what is known generically as Kraton copolymers.
It has been suggested that these “super asphalts” could be used as a substitute for HTPB and PBAN in solid propellants for commercial space launch vehicles. Evaluations have been conducted that suggest they possess ballistic and physical properties almost on a par with existing solids, but at a considerably reduced cost. Tests are still on-going.
Be that as it may, and even if we consider only those Asphalt/Perchlorate propellants that never progressed beyond their state of the art in the early 1950s, their characteristics, and attributes are still light-years beyond those exhibited by typical amateur propellants, such as black powder, Nitrate/Sugar, and Micro-grain. They therefore, rightfully deserve their place in the sun with those other long time cherished amateur propellants.
122 pages, black and white with color cover.
While a considerable wealth of information on most of the older amateur propellants is already available, through literature, and existing “tribal knowledge“, unfortunately, there is precious little technical information available on the manufacture of Asphalt/Perchlorate propellants. Other than the basic formulations, and very limited descriptions regarding their processing, the bulk of the information that does exist , is either in the Aerojet, or Caltech archives, and is not readily accessible. In the past, information held by the RRI was not disclosed outside of RRI sponsored Student Educational Rocketry Programs......... Which brings us to the reason for publishing this book.
In recent years, there have been several excellent books published on how to make Ammonium Perchlorate (AP), and Ammonium Nitrate (AN) based composite propellants. It has therefore been decided, that it is now might be an opportune time to make Asphalt/Perchlorate information available ( as well) , and thus allow the EX-HPR, and traditional experimental rocket communities to make of them as they will.
Those of us in the Rocket Research Institute, who essentially took over where the professionals left off, arent getting any younger, and have concluded that if we dont do it soon, it just might never get done. As a means of dissemination, we offer-up a historical accounting of the evolution of Asphalt/Perchlorate propellants, as they occurred in industry, as well as our own experiences in building, and launching the rockets that used them.
It is in this spirit, that we humbly offer our contribution to the collective body of knowledge of the experimental rocket community. We hope you enjoy reading the book, and can benefit from the information presented herein.
Chuck Piper, Author, Rocket Research Institute, TRA member #135 August 25, 2014, Rocket Ranch, Adobe Canyon Test Site, Patterson ,CA.
THIS PUBLICATION CONTAINS TECHNICAL INFORMATION RELATED TO THE, COMPOUNDING, MANUFACTURE, AND LOADING OF SOLID PROPELLANTS, AND THE PREPARATION AND HANDLING OF THEIR CONSTITUENT INGREDIENTS. WHILE ACCURATE IN ITS TECHNICAL CONTENT AND DETAIL, MUCH OF THE INFORMATION CONTAINED HERE-IN, MIGHT BE CONSTRUED BY TODAYS STANDARDS AS, OBSOLETE, AND OUTDATED.
IT MUST BE CLEARLY UNDERSTOOD, THAT THIS IN NO WAY MINIMIZES OR MITIGATES THE POTENTIAL HAZARDS ASSOCIATED WITH THE MIXING , HANDLING, OR OTHER PROCESSING OF THESE MATERIALS.
THE MANUFACTURE AND LOADING OF SOLID PROPELLANTS IS A POTENTIALLY DANGEROUS ACTIVITY, REQUIRING HIGHLY SPECIALIZED KNOWLEDGE, TRAINING, AND SAFETY EQUIPMENT. IN MANY INSTANCES, SPECIAL LICENSES AND / OR PERMITS FROM STATE, LOCAL, AND FEDERAL AGENCIES ARE NECESSARY.
THE OPERATION OF CERTAIN TYPES OF MACHINERY AND PROCESSING EQUIPMENT REFERENCED IN THIS TEXT ALSO PRESENTS AN ELEMENT OF RISK TO THOSE UNFAMILIAR WITH THEIR OPERATION.
FOR THESE REASONS, AND OTHERS, THE PUBLISHER UNEQUIVOCALLY STATES THAT THIS TEXT IS IN NO WAY INTENDED, IN ANY WAY, SHAPE, OR FORM TO BE USED AS ANY TYPE OF INSTRUCTIONAL MANUAL.
THEREFORE, IT MUST BE CLEARLY UNDERSTOOD, THAT THE TECHNICAL INFORMATION CONTAINED HERE-IN, IS INTENDED TO BE USED FOR HISTORICAL AND STUDY PURPOSES ONLY.
SHOULD THE READER ATTEMPT THE MANUFACTURE AND LOADING OF PROPELLANTS, OR OPERATION OF EQUIPMENT OR MACHINERY REFERENCED HEREIN, BASED UPON INFORMATION PRESENTED, THAT HE/SHE DOES SO ENTIRELY AT THEIR OWN PERIL.
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