Constant Dynamic Pressure Trajectory Simulation in POST
Author(s)
Olds, John R.
Budianto, Irene A.
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Abstract
Future space transportation vehicles way well
rely on high speed airbreathing propulsion (ramjets
and scramjets) to supply much of their motive power.
Because of the tradeoff relationship between engine
thrust and vehicle airframe weight, ascent trajectories
are typically simulated using a constant dynamic
pressure phase during airbreathing acceleration. That
is, dynamic pressure is increased to benefit vehicle
thrust up to some fixed limit imposed by the vehicle
structure. The constant dynamic pressure portion of
the trajectory typically begins around Mach 2 or 3 and
continues to the maximum airbreathing Mach number
or until some convective aeroheating limit is reached.
This paper summarizes comparative research on
three candidate guidance methods suitable for
simulating constant dynamic pressure trajectories.
These are generalized acceleration steering, linear
feedback control, and cubic polynomial control. All
methods were implemented in POST (Program to
Optimize Simulated Trajectories) - an industry
standard trajectory simulation code. Both quantitative
and qualitative comparisons of these methods (i.e. in
terms of computer processing time, number of
required iterations for convergence, sensitivity to
quality of initial values, accuracy and program
robustness) are presented. Of the three methods, the
linear feedback control approach is found to be the
most efficient and robust, with good accuracy.
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Date
1998-01
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