Aerospace and Electronic Systems Magazine April 2018 - 10

Navigation and Control Architecture for Launch Vehicles
such time delay values will have to be investigated thoroughly for
its impact on stability and control.

ON-THE-FLY TRAJECTORIES
It was desirable to investigate another control scenario in which
the trajectory was not well known ahead of time but could be
changed on the fly, perhaps by a (remote) pilot or by an autonomous system that decided midflight that another trajectory was
more desirable. Therefore, the code was modified to be able to
take the current trajectory and assume that the system was going to maintain it until commanded otherwise. Because the square
wave includes periods of steady motion interspersed by sudden
trajectory changes, it was used to test this variant of the code.
As can be seen in Figure 8, the system waits until a trajectory
change is commanded before it tries to match the new trajectory.
The results are similar to the preplanned square wave trajectory,
with the difference that the control system does not anticipate the
trajectory change, although the new trajectory is still matched
within a couple tenths of a second.

ALTITUDE ANALYSIS
By the nature of the problem, launch vehicles are operating at
varying altitudes. This brings up the need for the analysis of
NRHC behavior with respect to different flight and/or operation
conditions. For this purpose, an analysis of behavior at different
altitudes has been conducted. Figure 9 demonstrates that the
NRHC and, in general, the real-time nonlinear control strategy
are able to operate reasonably in a range of flight conditions.

ROBUSTNESS ANALYSIS
SENSOR NOISE
For the purposes of this simulation, it is assumed that the current
angle of attack α is accessible and determined through a sensor

Figure 6.

Results of real-time NRHC of a biased square wave.

Figure 7.

Timing analysis of the control system.

10

IEEE A&E SYSTEMS MAGAZINE

APRIL 2018



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