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Pen rocket control


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so, see ....

The problem statement is really simple,

make a 150mm max pen rocket, with solid engine(sugar and kno3 composition)

but, it gotta achieve a min altitude of 10 meter, and land back ......

Things i think we'll need is ,

  1. oxidizer fuel proportion thrust control,
  2. stabilization solution for balance,
  3. and many more

and no electronics allowed, 

What u guys think ........ 

Edited by Vulcan
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  • 2 weeks later...

The lack of reaction control systems or telemetry will mean uncontrolled thrust instabilities. Even if you were able to use non-powered linkage in the rocket to counteract these variances in flight; the small size and complexity of parts are prone to fail under the force and heat of the propellent.

You theoretically could machine a part with stability fins. To keep the dimensions of a pen I would start the design with an ID of 8mm where the propellent will be stored. You will want to make this as long as it needs to establish a stable center of gravity with the propellent mass in mind. You can play with the OD in order to establish an equilibrated design giving you structural integrity and a proper center of mass. 

Empty Mass = mE 

Propellent Mass At Launch = mp = mp1 + mp2 + mp3

Propellent Mass During Coast = mpC = Δmp2 + mp3

You're going to find it difficult to make a composite rocket propellent that is able to give you launch, coast, and recovery capabilities in such a small constraint. Your launch phase mwill have to supply enough energy to overcome all the compositions. In flight, the coast phase will have to sustain the momentum of the launch phase and account for the changing mass while it burns off this section of solid fuel. To recover (i.e. a parachute) you will need an ejection charge. 

Rocket Composition


The efficiency of the propellent is entirely depended on your personal level of skill in chemistry. So to make the presumption of the ability of this theoretical design to go farther than 10 meters would be speculatory at best. 

But you could test it before designing to establish the propellent force. 

  1. Make a batch of C12H22O11.
  2. Make a suspended test fixture with an ID of 8mm and length of 110mm (matching you rocket design and compensating for the recovery components).
  3. Link a Force Gauge (pushing end) to the pushing end of the test fixture.
  4. Measure equal sections of propellent.
  5. Insert propellent into the test fixture making sure it's done the same way each test.
  6. Ignite and record findings.
  7. Do this 10 times and average.  

If this overcomes the mass of the rocket than you can move on to how long it will overcome the mass to make a prediction of the flight path and stability characteristics of the rocket. 

By no means am I a rocket scientist, but I do have working exposure to missiles to include hypersonic missiles. I hope this can put you in the correct headspace and orient you in the correct position.

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