Takayuki Yamamoto

The Japan Aerospace Exploration Agency (JAXA) makes the world's first solar power sail craft IKAROS demonstration of photon propulsion and thin film solar power generation during its interplanetary cruise. The spacecraft deploys and spans a membrane of 20 meters in diameter using the spin centrifugal force. It also deploys thin film solar cells on the membrane, in order to evaluate its thermal control property and anti-radiation performance in the real operational field. The spacecraft weighs approximately 310kg, launched together with the agency's Venus Climate Orbiter, AKATSUKI on May 21, 2010. This paper presents the summary of development and operation of IKAROS.

On the ascent path of the vehicles like spaceplanes, the optimal steering shows the different behavior from that of conventional rockets. This is because both thrust and lift force varies depending on the change of the atmospheric dynamic pressure. This indicates that it is required the new guidance strategy for these kind of vehicles. In this paper, we propose a new guidance strategy which has only four parameters to be determined. This method is derived from some analytical assumptions and approximates the steering in simple linear and logarithmic function. Only by carrying out the numerical integration of this, the parameters are easily determined to satisfy the terminal boundary conditions.

This paper newly presents what the optimal guidance strategy is for the vehicles, which fly along the so-called aerodynamic ascent path. As commonly utilized, the paper first shows the optimization results via the DCNLP method, while the paper secondly shows the other results via the SQP, direct optimization method. The latter is efficiently and easily carried out taking the advantage of the steering angle expressed in a certain orthogonal functions. The primary result of the paper is the analytical description of the steering law, that relates to the optimization discussion. It is clearly concluded that a conventional linear tangent law is applicable only to non-lift vehicles. The conclusion, at the same time, indicates that the optimal guidance should take trigonometric functions in addition to those in the conventional linear tangent law. The results presented in the paper further extend the optimization process to the guidance scheme with numerical demonstrations. Since the linearized translation motion fits better for the analytical model, the results of the paper successfully could show the practical validity of it. The examples include the cases with the vehicle parameters varied from nominal and the sensitivity to those is also examined.