A New Method for Terminal Area Guidance for future Reusable Launch Vehicles

Paper number

IAC-05-C1.8.05

Author

Mr. James Chartres, University of Adelaide, Australia

Coauthor

Mr. Michael Graesslin, University of Stuttgart, Germany

Coauthor

Dr. Gerald Schneider, University of Adelaide, Australia

Year

2005

Abstract

The next generation of reusable launch vehicles will require significant improvements in guidance algorithms in order to reduce cost, increase safety and flexibility, whilst allowing for possible autonomous operation. Recently improved guidance studies have concentrated on the ascent and hypersonic re-entry phases of flight. Currently there has been little investigation into the terminal flight phase where the increased flexibility of improved guidance algorithms could provide a significant benefit.

This paper presents a new method for developing trajectories and guiding a vehicle during the terminal flight phase, starting at the final conditions of hypersonic re-entry and steering the vehicle to the automatic landing interface (ALI). Most methods for terminal area guidance (TAG) are based on the Shuttle Orbiter's Terminal Area Energy Management (TAEM) method. This paper outlines a possible new method using non linear programming (NLP) techniques to define a trajectory based upon steering commands with respect to a vehicle state parameter such as flight time or energy.

The guidance algorithm uses a two stage method; using a simplified restoration method to perform updates to the onboard flight path prediction and an optimisation step utilised to reduce a specified cost function. The cost function can be used to provide safety margins within the trajectory whilst minimising or maximising a target, such as reducing the required control effort. The guidance algorithm was tested using Monte Carlo simulations for verification with numerous off-nominal conditions such as atmospheric uncertainties, poor aerodynamic modelling, initial condition deviations and sensor errors for vehicle states. The simulation environment consisted of two systems with different models for aerodynamics, atmospheric conditions, earth shape and gravity. A simulator with high order models acting as a real world environment was connected to the guidance algorithm, representing the onboard computer of the vehicle, using low order models such that it can run in real time.

The guidance algorithm was applied to the proposed future reusable launch vehicle Hopper previously studied under the German ASTRA (Advanced Space Transportation for Reusable Applications) program. Hopper is a horizontal take off, horizontal landing sub-orbital vehicle which launches an expendable upper stage to place payloads into orbit. The results provided by the Monte Carlo simulations are presented and analysed revealing that the new guidance method is applicable to the terminal flight regime. The guidance algorithm is able to deliver the vehicle to the required final conditions whilst conforming to flight restrictions and coping with the various off-nominal conditions.

Abstract document

IAC-05-C1.8.05.pdf

Manuscript document

IAC-05-C1.8.05.pdf (🔒 authorized access only).

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