The following is the starting strategy for the n-prize competition.

The satellite has a fixed weight range, and limited purpose. The only challenge seen here is to pick cheapest electronic components.

The most used vehicle for putting satellites into orbit is the rocket. Development of a cheap rocket, capable of launching satellites into space, is the main focus of Alchemy team.

The rocket is divided in three parts: the payload (here, the satellite), the control system and the motor. The control system is not critical: there are a lot of choices for how to control the rocket frame in flight, and the satellite ‘brain’ and sensors can be re-used. The strategy for the competition is to technically improve a cheap and available fuel up to the point where it is reliable enough for space travel.

The cheapest and widest available rocket fuel is the candy fuel. It is safer than BP and easier to work with. It also doesn’t need hard to find, forbidden or more important, dangerous chemical substances, like APCP. However there is a problem with the performance: the Isp is just a bit lower than needed for putting a satellite into LEO(low earth orbit). While the maximum theoretical Isp is about 160 seconds, in practice values around 130 s are obtained. For reaching 9km/s of delta-v (7.8km/s for the satellite velocity, 1.2 km/s for gravitational and atmospheric drag), with a single stage a mass ratio of 1170 is needed. Supposing the air frame, motor casing and control system can be squeezed in 1kg, over a ton of fuel is needed. Since 1kg of fuel costs a bit less than a pound, almost all budget is spent on fuel alone. Three stages will only see the rest of the budget is spent on fuel tanks and separation system.

Instead of potassium nitrate, ammonium nitrate will be used. It is cheaper and provides a higher Isp. No Al or Mg, since they are considered dangerous to work with. They’re also expensive. Instead table sugar and carbon black only are considered. The challenge is to stabilize the phase change and to cast the fuel in a decent shape without lowering the Isp too much. A low burn rate is not a bad thing. Also ignition is not considered a problem, since candy fuel can be used as a primer.

The strategy is reduced to two objectives: casting the ammonium nitrate propellant with either sugar or carbon, and stabilizing the phase change without lowering the specific impulse too much. Actually if the fuel can be cast in solid grains, phase stabilization might not be needed. Caseless, nozzleless motors can be built with candy fuel retaining about 65% of theoretical specific impulse. The only problem of phase volume change is additional stress on motor case. Testing should make sure the phase change causes no cracks.

Once phase stabilized AN is cast into grains, the victory is a matter of time.


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