PRODAS Presentation: C 6DOF Simulation

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PRODAS Presentation C 6DOF Simulation Philip
V. Hahn Dr. Robert Frederick
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Overview

• Desire 6DOF modeling and simulation of
  Squib-Controlled Spinner
• Tools
• PRODAS
• C
• CMD (C Model Developer)
• Simulation tool provides a framework to run the
  simulation.
• References
• Modeling and Simulation of Aerospace Vehicle
  Dynamics, Peter H. Zipfel.
• CMD Manuel
• Dr. Costello (via email and PowerPoint
  presentations)

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Scenario

• Gun-launched spinning projectile with squibs to
  provide lateral diversion
• Threat Rockets and mortars fired at close
  (2-8km) range
• Intercept Zone 0.5-1.5 km ( gt Mach 1.0 velocity
  at intercept)

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Projectile Specification
CG and CP shift during flight (as a function of
Mach number)
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Classes and Object Oriented Programming
Class we are deriving from (Inheritance)
Name of the class we are creating
Constructor, used to set up initial conditions at
object creation
class Projectile public Block
public Projectile(string infile, Output
obj) void init(void) void
update(void) void rpt(void) // accessor
functions protected
Called once at start of simulation
Called every iteration. Contains the differential
equations we need to solve.
Reporting function, used to control text output
to console
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Inputs

• Aerodynamic coefficients are extracted from
  PRODAS PR3 file.
• Search for basicAeros to find the aero
  coefficient table.
• Implemented as 1-D text tables with linear
  interpolation.
• Initial velocity, diameter, mass, roll rate, and
  moments of inertia
• appropriate windows in PRODAS.
• Initial Elevation and Azimuth
• Elevation is implemented as theta
• Azimuth 90 is implemented as psi.
• All inputs are located in a text file and
  extracted on program execution.

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Diagram of Program Class Structure
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Evolution of the code

• Implementation of quaternions to replace Euler
  angles
• Separation of competencies from functions into
  individual classes
• Atmosphere
• Aerodynamics
• Earth model
• Quaternions
• Airframe (core differential equations)
• Implementation of guidance class and squib class

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Summary of Control Logic and Assumptions

• Nominal Z and Y values are stored in a text
  table
• We are assuming lateral thrusters, and thus we
  cannot influence Z.
• We take the difference between our position and
  the value stored in the table
• Transform the values to body coordinates using
  an inverted Direct Cosine Matrix
• Convert from X and Y values in body coordinates
  to Phase and Magnitude
• Wait for the following criteria to be met
• Proper timing (each squib has a dedicated time
  slot)
• Miss distance gt 2 meters
• Phase is /- 10 degrees of the direction we want
  to fire.
• Once all three conditions are met, we fire the
  squib
• Integration refines for the very short event.
• Text table defines thrust curve shape
• (Highly simplified Dr. Costello can provide a
  more in-depth discussion)

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Results Comparing to PRODAS
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Guidance results

• Getting close to PRODAS GNC
• My problem is getting the smear to line up the
  same

Coarse integration can cause us to miss the left
side of our window and shift the thrust vector.
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Future Work

• Implementation of a no-roll frame
• dp/dx0, phiconstant, ? spin angular
  velocity.
• Refining Dr. Costellos guidance module in my
  C Simulation
• Has only been working for 3 days
• My simulation increases the integration step
  once the squib fires, may be prudent to increase
  it earlier to avoid the smear problem (at a cost
  of time).
• Explore drop-in replacements for the trajectory
  tracking module
• Some form of predictive correction (proportional
  navigation?)
• We have target trajectories for a mortar and
  rocket defined
• Mortar/Rocket can be implemented as a class and
  flown in real time.
• Adding in error sources
• IMU class guidance wont have perfect knowledge
  of the state variables
• Turning on the flight computer after the gun is
  launched
• Using a magnetometer to detect gravity /
  orientation / rates

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Additional Materials

• PRODAS File
• CMD Source Code
• CMD Manual
• Questions