Yoji Shirasawa

Small-scale Experiments and Simulations of Centrifugal Membrane Deployment of Solar Sail Craft "IKAROS"

ecently, a variety of solar sail spacecrafts using thin large membranes have been developed in US, Europe and Japan. In Japan, centrifugally deployed solar sails have been mainly investigated 1 . A solar power sail demonstration spacecraft “IKAROS” was developed by Japan Aerospace Exploration Agency and was launched on May 21th, 2010 by H-IIA launch vehicle. 2,3 Figure 1 shows an overview of “IKAROS” in space. The square solar sail with 20 meters in diagonal and 7.5 micrometers in thickness was successfully deployed by centrifugal force using no extendable booms. The sail consists of four trapezoidal petals which were folded up into strips and rolled up around the spacecraft in stowed configuration. The deployment of the membrane consists of two stages. In the first stage, the strips are quasistatically reeled out. In the second stage, the strips are dynamically unfurled. Since on-ground dynamic deployment experiments of the large membrane are impossible, small-scale experiments and numerical simulations are necessary to predict the deployment dynamics. In this paper, a deployment experiment of a smallscale square membrane similar to “IKAROS” is conducted in a vacuum chamber and corresponding numerical simulations are performed by employing a spring-mass system model. The deployment behavior is discussed and the results of the experiment and simulations are compared to examine the validity of the simulations.

Shape Parameters Estimation of IKAROS Solar Sail Using In-Flight Attitude Determination Data

IKAROS is the Japanese deep-space solar sail technology demonstration mission launched in 2010. IKAROS is a spinner spacecraft with the 20m-span solar sail kept extended by the centrifugal force. During its solar sailing flight from Earth to Venus, IKAROS showed a unique attitude behavior due to solar radiation pressure attracted on the sail. This paper proposes a generalized model of spinning sail-craft, which clearly explains the attitude behavior observed in IKAROS. Then it is shown that this behavior has a clear dependency on the sail shape and the optical property distributions on the sail. We show the estimation results of the on-orbit sail shape using this new model.

Windmill Torque Estimation of Spin-type Solar Power Sail with Shape Control

Solar Power Sail Demonstrator ”IKAROS”, which is a spin-type solar power sail, has been successful in a technology demonstration in space. During the period of the operation, the stretched shape of IKAROS was expected to be a flat shape. But the pictures taken by the monitor cameras revealed that the sail became an unexpected shape because of a curving of the thin-film solar cells. It was also confirmed that “windmill behavior” which constantly reduces the spin rate. In this study, it is suggested that the control method of the windmill torque with the shape control evens in the range of curving of thin-film solar cells. For instance, a twist angle is given to each petal by changing the tether arrangement of the main body in order to control the direction of the windmill torque. This method is expected to save the large fuel to fix the windmill torque under a severe weight request. In addition, the validity of the control method is evaluated by a FEM analysis which is specialized to the thin-film analysis.