Sport Rocketry

38 JANUARY/FEBRUARY 2020 SPORT ROCKETRY Figure 2. SS-25 missile. Source: ITAR-TASS/Andrey Smirnov. gle-warhead RT-2PM Topol, also known by the U.S. and NATO designator SS-25. The SS-25 remains in the Russian force today, but is being gradually replaced by newer ICBM designs that carry more war- heads per missile. All Minuteman variants were designed for basing in underground silos to protect against any attack other than a direct hit by another nuclear weap- on (the United States has never deployed a mobile ICBM). The Russian SS-25, on the other hand, comes in both silo-based and road-mobile versions. Modeling ICBMs in Sport Rocketry Given their historical significance, the Minuteman II and the SS-25, and ICBMs in general, are compelling candidates for scale models in hob- by rocketry. While some ICBMs are ar- guably among the most boring looking rockets ever devised (no offense, Trident D5), the Minuteman II and SS-25 are both visually striking, with multiple tran- sitions—one corre- sponding to each of their three stages— and an assortment of uncommon features. However, ICBM models are almost absent in model and high power rocket- ry. For some build- ers, this could reflect an aversion to what might be character- ized as the darkest side of rocket sci- ence. However, the prevalence of models of shorter-range nu- clear missiles, including Lance, Pershing, and Honest John, suggests that physical characteristics of ICBMs are the primary deterrent to a wider presence in the hobby. To rocketeers with even limited expe- rience, the technical challenges of model- ing ICBMs are evident. First and foremost, many ICBMs do not have fins, which is okay for sophisticated guided missiles but not so great for those us who must rely on simpler means of aerodynamic control. Clear plastic fins are always an option, but some might find this approach less than satisfying. Second, rockets with three or four transition sections look nice but are more difficult to build than something with a single airframe diameter. Finally, be- cause some ICBM design details are pro- tected as state secrets, suitable scale data may be hard to come by. Despite these challenges (and, let's be honest, partly because of them), I set out to design and scratch build high-powered semi-scale models of the Minuteman II and SS-25 ICBMs. The silo-launched Min- uteman II would serve as my NAR Level II certification rocket, and a road-mobile SS-25 would do the same for Level III. Within this endeavor, one objective was striving for realism in certain elements that I deemed critical. This included small things, like using sep- arate parachutes for the body and nosec- one, because the latter is designed to come down, but in a man- ner that does not in- volve being tethered to the body. It would also include more in- volved undertakings, such as constructing a unique tube-based launch system for each rocket that was true to the actual mis- sile. Dedication to re- alism was admittedly far from complete, and did not extend to staging, guidance, or (of course) any inclu- sion of nuclear mate- rial. Minuteman II Model At 6'2" in length and with a maximum body diameter of 7.7", my model Minute- man II is approximately 1:10 scale (ac- cording the Boeing.com website, the actual missile is about 59 feet in length and 6 feet in diameter). When loaded with an Aero- Tech K550W motor, it weighs approxi- mately 22.5 pounds. See Figure 3. Figure 3. Minuteman II model flies on an AeroTech K550W.

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