Hypersonic vehicle model and control law development using H(infinity) and micron synthesis
Abstract
The control system design for a Single Stage To Orbit (SSTO) air breathing vehicle will be central to a successful mission because a precise ascent trajectory will preserve narrow payload margins. The air breathing propulsion system requires the vehicle to fly roughly halfway around the Earth through atmospheric turbulence. The turbulence, the high sensitivity of the propulsion system to inlet flow conditions, the relatively large uncertainty of the parameters characterizing the vehicle, and continuous acceleration make the problem especially challenging. Adequate stability margins must be provided without sacrificing payload mass since payload margins are critical. Therefore, a multivariable control theory capable of explicitly including both uncertainty and performance is needed. The H(infinity) controller in general provides good robustness but can result in conservative solutions for practical problems involving structured uncertainty. Structured singular value mu framework for analysis and synthesis is potentially much less conservative and hence more appropriate for problems with tight margins. An SSTO control system requires: highly accurate tracking of velocity and altitude commands while limiting angleofattack oscillations, minimized control power usage, and a stabilized vehicle when atmospheric turbulence and system uncertainty are present. The controller designs using H(infinity) and musynthesis procedures were compared. An integrated flight/propulsion dynamic mathematical model of a conical accelerator vehicle was linearized as the vehicle accelerated through Mach 8. Vehicle acceleration through the selected flight condition gives rise to parametric variation that was modeled as a structured uncertainty. The muanalysis approach was used in the frequency domain to conduct controller analysis and was confirmed by time history plots. Results demonstrate the inherent advantages of the mu framework for this class of problems.
 Publication:

NASA STI/Recon Technical Report N
 Pub Date:
 October 1994
 Bibcode:
 1994STIN...9512838G
 Keywords:

 Aerodynamic Characteristics;
 Control Systems Design;
 Dynamic Models;
 Hypersonic Vehicles;
 Mathematical Models;
 Propulsion System Configurations;
 Robustness (Mathematics);
 Single Stage To Orbit Vehicles;
 Angle Of Attack;
 Ascent Trajectories;
 Atmospheric Turbulence;
 Flight Characteristics;
 Inlet Flow;
 Oscillations;
 Payloads;
 Stability;
 Structural Analysis;
 Spacecraft Design, Testing and Performance