by Brad Martin

I have purchased a stock Estes Gemini DC with the intent of using every component in it to create a rather different rocket than what is shown on the original package cover.

  My Gemini-DX will be a 5 engine cluster consisting of 4 C6-7's and  a central E9-8.  The idea is to have the boosters ejection charges reverse  with a cowling-like slice of the two smaller nose cones.  This should  make for one last smokey feeble push just before apogee.  Rocksim 's say about 3100' but I have yet to figure out ways to model  some of the subtle design mods.  One problem is how to create the model  of the booster MMT's...  An inside tube placed outside the body sims  only the CG, apparently not the CP,  So I've used 'dummy fins' of near  zero mass to help offset the CP.  I've also created a set of 'custom fins' to mimick the sliced & diced nose cone segments above, but again these are just an approximation of the real thing.  Also, I can't rotate them the way I want!  Even though these things frustrate me, I still think Rocksim is some of the best software around, and that's coming from someone that has been building 3D CAD models for over 15 years  ;}

Guesstimated timeline:
Secs/event
0.0 = power to igniters
0.1 = ignition/lift-off
0.3 = clears pad
1.8 = C6-7's burnout
3.0 = E9-8 burnout
8.8 = C6-7's ejection charge (reversed)
11.3=E9-8 ejection charge (normal)
11.4=Parachutes deployed
220 = Landing


Gemini DX - Rocksim Simulation results
Engine selection
[E9-8   ,C6-7   ,C6-7   ,C6-7   ,C6-7   ]

Simulation control parameters
Resolution: 1000 samples / second.
Simulation method: 4th Order runge-kuta.
Simulation execution time: 16.633 Sec.

Launch conditions
Altitude: 0.000 Ft.
Relative humidity: 50.000 %
Temperature: 59.000 Deg. F
Pressure: 29.914 In. Hg.
Wind speed: 0.000 MPH
Launch guide angle: 0.000 Degrees from vertical
Latitude: 90.000 Degrees

Launch guide data:
Launch guide length: 36.000 In.
Velocity at launch guide departure: 46.749 MPH
The launch guide was cleared at : 0.160 Seconds
User specified minimum velocity for stable flight: 29.999 MPH
Minimum velocity for stable flight reached at: 19.641 In.

Max data values:
Maximum acceleration: Vert: 34.978 g , Horz: 0.000 g , Magnitude: 34.978 g
Maximum velocity: Vert: 524.944 MPH , Horz: 0.000 MPH , Magnitude: 524.944 MPH
Maximum range from launch site: 0.000 Ft.
Maximum altitude: 3187.414 Ft.

Engine ejection charge data:
Conditions at engine ejection charge:
  Using a delay time of : 8.000 Seconds
     Velocity: 6.931 MPH
     Altitude: 3185.814 Ft.

Recovery system data
  P:  Parachutes  Deployed at : 11.186 Seconds
  Velocity at deployment: 0.003 MPH
  Altitude at deployment: 3187.414 Ft.
  Range at deployment: 0.000 Ft.

Time data
Time to burnout: 2.871 Sec.
Time to apogee: 11.186 Sec.
Optimal ejection delay: 8.315 Sec.

Landing data
Successful landing
Time to landing: 221.228 Sec.
Range at landing: 0.000
Velocity at landing: Vert: -10.124 MPH , Horz: 0.000 MPH , Magnitude: 10.124 MPH