BALLISTIC_MISSILE_LAUNCH_COMPUTER_GENERATOR

tool BALLISTIC_MISSILE_LAUNCH_COMPUTER_GENERATOR

tool BALLISTIC_MISSILE_LAUNCH_COMPUTER_GENERATOR
   ... weapon_tools Commands ...

   air_target_file
   surface_target_file
   gnuplot_file
   minimum_output_time
   maximum_output_time
   minimum_output_range
   maximum_output_range
   maximum_output_altitude
   limited_to_preapogee
   loft_angle
   loft_angles
   burn_time
   burn_times
   pass_1_loft_angle_start
   pass_1_loft_angle_stop
   pass_1_loft_angle_step
   pass_2_loft_angle_step
   loft_angle_range
   depress_angle_range

end_tool

Overview

BALLISTIC_MISSILE_LAUNCH_COMPUTER_GENERATOR is a specialization of weapon_tools to produce a launch computer to assist targeting and firing guided ballistic missiles. The tool will fire the defined missile type with a variety of loft angles and/or propellant burn times, and capture the resulting trajectory profiles, for use later in targeting an impact or intercept time and location for air intercepts of ballistic missiles. Any time a missile definition is modified in a way that will affect its kinematics, this generator should be re-applied to create a new launch computer data table. In order to allow the same launch data table to be used anywhere on the globe, a spherical non-rotating earth model is assumed.

Loft Angle

Large, long range ballistic missiles fire vertically, and then quickly pitch over to some nominal “loft angle”, from which a gravity-induced turn holds them on a ballistic trajectory toward the desired (maximum range) target point. The maximum achievable downrange trajectory is very sensitive to even small variations in the initial loft angle assumed (a two-degree increment in loft angle might easily make the difference between a short-range earth-impact, or going orbital with the missile). This weapon tool generator allows the user to choose a range of loft angles to use, and the angular resolution needed to iteratively converge on an “optimal” firing solution. Usually lesser range intercepts or impacts still use the same “optimal” loft angle, but prematurely terminate propulsion to cause a lower, shorter-range trajectory to impact or intercept. Alternate means of achieving shorter range impacts are lofted or depressed trajectories, where a loft angle higher or lower (respectively) than optimal is selected to achieve a desired target range impact. Lofted trajectories sacrifice a longer time of flight, and depressed trajectories may suffer aerodynamic heating issues from high speed flight in the upper atmosphere.

Usage with Guided Movers

Certain WSF_GUIDED_MOVER commands should not be used when generating data for a WSF_BALLISTIC_MISSILE_LAUNCH_COMPUTER, as they may alter the flight paths of the missile in unexpected ways, potentially leading to erroneous data being generated. These commands include, but may not be limited to, the divert commands (divert_thrust, divert_fuel_mass, divert_fuel_flow_rate, divert_altitude_limits). However, once the launch computer data has been generated, these commands can be used in the WSF_GUIDED_MOVER defined for the weapon when the scenario is being executed by mission or Warlock.

Generation Process

The generator first iteratively fires the missile at low (flat) loft angles, increasing the loft angle at each firing. Terminal impact of the missile will initially increase each time. As the optimal loft angle is approached, terminal range will reach a maximum, and then begin decreasing again. As noted in the paragraph above, this effect is highly non-linear. Because of this, a two-step iteration approach is used, beginning with a “gross” larger delta loft angle (0.2 degrees a good starting point), and when the approximate optimal loft angle is found, a “fine” iteration loop is re-run to capture a more accurate value for optimal loft angle (approximately a 0.001 degree step). This process requires either a) intelligent choices made regarding loft angle limits and increments, with human-in-the-loop adjustments, or b) a vast numbers of iterations and much computational time to generate the tables. Once the optimal loft angle (and its resulting range) is determined, then sub-optimal target ranges are achieved by lofted or depressed trajectories as noted above.

Commands

air_target_file <air-target-file-name>

Name for the output file containing the generated surface-to-air trajectory data.

surface_target_file <surface-target-file-name>

Name for the output file containing the generated surface-to-surface trajectory data.

gnuplot_file <gnu-plot-file-name>

Name of the plot file written out for post-process visualization.

minimum_output_time <time-value>

Minimum missile time of flight value below which no intercept or impact is considered valid.

maximum_output_time <time-value>

Maximum missile time of flight value beyond which no intercept or impact is considered valid.

minimum_output_range <distance-value>

Minimum missile flight ground range below which no intercept or impact is considered valid.

maximum_output_range <distance-value>

Maximum missile flight ground range beyond which no intercept or impact is considered valid.

maximum_output_altitude <altitude-value>

Maximum altitude at which an intercept solution is tested for success.

limited_to_preapogee

Flag that precludes consideration of an intercept as viable if the intercept occurs post-apogee.

loft_angle <angle-value>

Single value of loft angle to be used for trajectory propagation. Generally used only for small short range ballistic missiles. The independent variable to achieve various downrange trajectories is then propellant burn time.

loft_angles from <min-angle-value> to <max-angle-value> by <delta-angle-value>

Range of loft angles to be used for trajectory propagation tests.

burn_time <time-duration-value>

Single value of burn time to be used for trajectory propagation.

burn_times from <min-time-duration-value> to <max-time-duration-value> by <delta-duration-value>

Used for generating nominal trajectory profile launch tables (burn time) as a function of desired target range. Make sure to add in the inter-stage delay times when determining min and max duration values. Cannot be used with either loft_angle_range or depress_angle_range keywords.

pass_1_loft_angle_start <angle-value>

Beginning loft angle for pass one (coarse traversal) to find optimal loft angle. This value is highly dependent upon missile kinematics… larger (more vertical) for lumbering missiles, smaller (more horizontal) for energetic missiles. CAUTION: Choice of too high or too low a value may cause the generator to erroneously predict the optimal loft angle.

pass_1_loft_angle_stop <angle-value>

Ending loft angle for pass one (coarse traversal) to find optimal loft angle. Since iteration is with increasing loft-angle, this value must be larger than pass_1_loft_angle_start. This value is highly dependent upon missile kinematics… larger (more vertical) for lumbering missiles, smaller (more horizontal) for energetic missiles. CAUTION: Choice of too high or too low a value may cause the generator to erroneously predict the optimal loft angle.

pass_1_loft_angle_step <angle-value>

Increment value for pass one loft angle (coarse traversal). Recommended starting point is 0.2 degrees.

pass_2_loft_angle_step <angle-value>

Increment value for pass one loft angle (fine traversal). Recommended starting point is 0.001 degrees.

loft_angle_range max_angle <angle-value> max_loft <angle-value> by <angle-value>

Used only for generating lofted trajectory profile launch tables. Parameters max_angle and max_loft are both independently able to terminate the iteration loop. The max_angle parameter is an absolute value of loft angle, while the max_loft parameter is relative to the pre-calculated optimal loft angle. Cannot be used with burn_times or depress_angle_range keyword.

depress_angle_range min_angle <angle-value> max_depress <angle-value> by <angle-value>

Used only for generating depressed trajectory profile launch tables. Parameters min_angle and max_depress are both independently able to terminate the iteration loop. The min_angle parameter is an absolute value of loft angle, while the max_loft parameter is relative to the pre-calculated optimal loft angle. Cannot be used with burn_times or loft_angle_range keyword.