A New Real-Time Guidance Strategy for Aerodynamic Ascent Flight
- Paper number
IAC-05-C1.8.02
- Author
Dr. Takayuki Yamamoto, Japan Aerospace Exploration Agency (JAXA), Japan
- Coauthor
Dr. Junichiro Kawaguchi, Japan Aerospace Exploration Agency (JAXA)/ISAS, Japan
- Year
2005
- Abstract
Reusable Launch Vehicles (RLVs) are conceived to constitute the future space transportation system. If these vehicles use air-breathing propulsion and lifts off horizontally, the ascent path had better make good use of the aerodynamic effects. The optimal steering for the vehicles exhibits completely different behavior from that in conventional rockets flight. This is because both thrust and lift depend on the atmospheric dynamic pressure and a new steering strategy is sought. While there have been many studies dealing with numerical optimization problems for the ascent flight, there have been few studies as for real-time guidance methods that are actually applicable to these vehicles with satisfactory and robust performance. The authors proposed the trigonometric function form as the steering law by means of series expansion of optimality conditions, which are expressed in terms of both adjoint variables and the effective thrust-to-lift force ratio. This method shows a good performance, however, the parameters have to be optimized and solved for the boundary conditions in real-time. And the computation load is too heavy to be performed by onboard computers. In this paper, here is proposed first another new guidance strategy, which is implemented in real-time basis. This method derives from the optimality condition as for steering, which is expressed by new parameters. Assuming the effective thrust-to-lift force ratio is constant, an analysis concludes that the steering is expressed by only four parameters including the total flight time. The steering function takes the form comprised of Linear and Logarithmic parameters. In order to verify the feasibility of the parameterized steering function derived, a comparison between the numerical optimization results with that via the parameter optimization is performed and shows the acquired terminal horizontal velocity is almost same for both cases. This supports the parameterized Liner Logarithmic steering law. In application of the strategy to the guidance, if the deviation from nominal ascent path is caused by the vehicle model errors or perturbations, the parameters in the steering function have to be re-calculated. Here is shown that there exists a simple linear relation between the terminal states and the parameters to be corrected. And the relation easily makes the parameters determined to satisfy the terminal boundary conditions in real-time. The paper presents the guidance results for the practical application cases with certain constraints such as the dynamic pressure limit admitted, and with certain disturbances such as wind gusts. The results show the guidance is well performed and satisfies the terminal boundary conditions specified. This guidance strategy does not include the optimization process during the flight but contains a simple two-by-two linear algebraic equations process with forward integration. The strategy built and presented here does guarantee the robust solution in real-time excluding any optimization process, and it is found quite practical.
- Abstract document
- Manuscript document
IAC-05-C1.8.02.pdf (🔒 authorized access only).
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