Wednesday, February 4, 2015

Space1 Model Space Program Part 2 Rocket Parts

Last time we introduced the idea of running your own space program at the small model rocket hobby level. This time we will look at finding some parts to build your own rocket at extremely low cost.

Eggs make perfect nosecones
The first objective is to collect together all the parts needed to build a rocket. It's estimated a small rocket (1.5 or 1.75-inches in diameter) can build for about $3 using common materials. A larger 2.5-inch rocket could cost about $5. This compares to store kits ranging from $20 to $50.

You will need some extra things like a motor and a launcher, and we'll talk about these things in more detail later.

Some parts come in packages with enough material for several rockets. Some parts are purchased as "spares" for future rockets of varying sizes. We will calculate the cost of each part used, for just one rocket.

Ok, so let's make a quick trip to the dollar store to make our first purchases. We found three different size eggs. Although there is no such thing as an Easter egg in Taiwan as Easter is generally not celebrated (most people are atheist or Buddhist), packaging in the shape of an egg was found.

Two smaller egg packages held a kind of silly putty and the largest egg held a LEGO knockoff copy by the Chinese brand Wange. The larger egg contained many small treasures, ideal for building rocket devices and a tiny surprise. More on this later.

The first purchase was an egg shaped package for the rocket nosecone. This was found in 3 sizes, small at 1.5-inches diameter, medium at about 1.75-inch and a large at 2.5-inches. The cost was 15, 20 and 80 NT dollars respectively. This amounts to USA cost of $.50, $.66 and $2.66.A toilet paper roll tube is 4-inches long, a diameter of 1.75-inches and perfectly fits the medium size egg.

Rocket shock cord from elastic band
The final item purchased is elastic for sports pants waist band. Number 2 is the width size at .25-inch and 20 yards is the length. It should be enough elastic shock cord material to make 40 rockets. The cost is NT$40 or US$1.33. That figures to about US$.04 per rocket.

As this has an exterior fabric base it will be fireproofed for protection against the ejection charge. However, we are working on a new design that insulates the parachute and the shock cord from the hot ejection charge. More about this later too.

The material has a stretch rate of 
6-inches at rest and stretches to a max of one foot long. The material is rather consistent in this regard, with a ratio of 1:2 as 1-foot will stretch to about 2'2". The material has a stable spring constant, as a test, stretching a six inch length fifty times, has no apparent deviation. Breaking point is undetermined. In a poundage test pull, the material did not break under 200 pounds momentarily applied.