Evaluation of Dynamic Inversion as a Flight Control Methodology for Re-entry Vehicles

GN&C Design and Analysis Branch, NASA Johnson Space Center
16 February 1999 – 16 February 2000
Co-P.I. Donald T. Ward
Total award $64,307

x38  x38
Pictured above is the NASA X-38 Crew Return Vehicle (CRV), also known as the Lifeboat in Space. The CRV will provide personnel on the International Space Station with the capability to safely return to Earth in the event of an emergency. As currently designed it will carry seven people, and will be flown autonomously, i.e. no one on board need be a pilot to safely land it.

One of the flight control methodologies which will permit this capability is Dynamic Inversion. Also called Feedback Linearization, it is a non-traditional methodology for synthesizing closed-loop control laws. As opposed to traditional techniques whereby the nonlinear plant is separated into several linearized models at discrete operating points and a closed-loop controller is synthesized for each one, Dynamic Inversion seeks to synthesize a global control law from a single nonlinear model. It has been applied to paper studies of controllers for aircraft such as the F-18 HARV, and has been flown successfully on the X-36.

Specific questions to be answered by this research are:

  • Is the methodology suitable for a flight vehicle with an extreme range of operating conditions (hypersonic-supersonic-transonic-subsonic) like the X-38?
  • Is the method suitable for rapid prototyping? Specifically, is software validation of the resulting control laws straightforward and rapid?
  • For which type of applications and in what circumstances (range of operating conditions or flight regimes) is output feedback suitable as opposed to full-state feedback?
  • Is it sufficiently robust to handle flight vehicle uncertainties (aerodynamics and mass properties), atmospheric distrurbances, and effector failures?

Working with me on this program is Graduate Research Assistant:

  • Dai Ito