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  Chapter 3  Pencil rocket in Ogikubo  
Ogikubo Hospital

We calculated backwards to find out how big the diameter of the rocket body should be if we used a 9-mm diameter propellant. This propellant burns both from inside and outside, so it burns by 1.5-mm from both sides. To calculate how many seconds it takes to burn a 1.5-mm propellant, we needed data called burning velocity. I asked NOF for the data and calculated that when the temperature goes up high, the propellant is already finished burning. So I reported to Professor Itokawa that Geralmine could tolerate the heat from the combustion. He then said to me, "Let's use this!" (Toda)

First of all, we had to conduct tests to verify the propellant's burning velocity. We assumed the burning velocity from the given data and calculated the amount of gas generation and the pressure produced by this gas. We then produced the experiment equipment. (Kakimi)

We initially burned a piece of propellant in this equipment and it burned without any trouble. To tell the truth, we wanted to burn up to 12 pieces at once, but we just gradually tried two and three pieces at a time. After successfully testing four pieces at once, we jumped to eight pieces. We dug a hole like an octopus trap on the grounds of Fuji Seimitsu in Ogikubo and were burning these propellants. When it came to the test on eight pieces, a big noise suddenly sounded and something rose higher and higher. (Kakimi)

I didn't recognize what went off right away because I had a preconceived idea that eight pieces of propellants wouldn't be strong enough to cut the bolt based on my calculations, but my judgment was wrong. When I glanced inside the hole, there was no rocket nozzle. It was when I was pondering what had happened, that the nozzle suddenly fell to the ground with a big bang. The ground was very hard, but the nozzle still buried itself about one-meter into the ground. I thought the nozzle had simply toppled over in the pit but when I dug up the ground I discovered it was actually our nozzle. This combustion equipment had been bolted with eight 12-mm long nickel chrome molybdenum alloy bolts with nuts. All eight bolts were cut off. It was a surprise. (Kakimi)

One of the scattered nuts had landed at neighboring Ogikubo Hospital and unfortunately had penetrated into a patient's room. The hospital reported to us that following the loud bang, some unusual material had fallen into their building, so we went there and discovered that the nut had crashed through the roof and penetrated into the room. Ogikubo Hospital used to be attached to Nakajima Aircraft Industries, so the issue didn't become that big, but because of this accident we moved the test pit to Kawagoe. (Kakimi)

After investigating several things, I found the data on the burning velocity was incorrect. Thus, the amount of the gas generation was ridiculously high and the internal pressure became too high to support the bolts and they were blasted off into the air. (Kakimi)

The Pencil rocket

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