Experimental Determination of the Impulse Coupling Coefficient – Standardization Issues S. Scharring a , J. E. Sinko b , A. Sasoh c , H.-A. Eckel a and H.-P. Röser d a Institute of Technical Physics, German Aerospace Center, Stuttgart, Germany b Micro-Nano Global Center of Excellence, Nagoya University, Japan c Department of Aerospace Engineering, Nagoya University, Japan d Institute of Space Systems, University of Stuttgart, Germany Abstract In research on beamed energy propulsion, the momentum coupling coefficient c m is a central figure of merit to characterize a propulsion system. The determination of c m is based on the measurement of imparted impulse and laser pulse energy. Nevertheless, the knowledge of laser pulse length, laser spot area and ablated mass is of great importance for the comparability of experimental results in laser ablative propulsion. The use of a great variety of measurement techniques for these parameters throughout the scientific community implies the risk of misunderstandings and might impede the comparability of results. In this paper, we present critical issues concerning the measurement of the aforementioned key parameters with respect to possible standardization issues. As an example, a simple laser propulsion experiment will be presented and compared with an experimental model from a different research group. 1. INTRODUCTION Measurement techniques and experimental standards used by laser propulsion groups around the world often differ significantly even for commonplace measurements. Comparability is enhanced when similar measurements and standards are widely used. Thus, our intention for this paper is that it may spur the acceptance of common standards for measurements and data analysis to enable laser propulsion researchers to more rigorously test the validity of their own data as well as assess its importance in relation to previous studies. The recent collaboration between the German Aerospace Center (DLR) and Nagoya University (NU) spurred a discussion which brought to light some key issues relating to standardization for laser propulsion. For example, how many measurements are necessary? What equipment, and what diagnostics, are necessary and sufficient? How can common measurement errors be avoided? Upon reviewing the literature, we found that in general, difficulties in laser ablation propulsion measurements stemmed from misinterpretations or misunderstandings of five primary laboratory parameters; specifically, the laser pulse energy, laser pulse length, laser spot area, imparted impulse, and ablated mass. Therefore, in the interests of standardization, we will focus our discussion on these parameters. Some aspects have already been sketched in [1] and will be presented in more detail in this paper along with results from recent experiments. 2. METHODS AND PARAMETERS In laser propulsion, the momentum coupling coefficient c m plays a central role. Its most common unit, N/MW, indicates that it is a technical figure of merit giving the average thrust caused by a laser with a certain average power. In the case of pulsed laser propulsion, however, the defining fraction is usually augmented by time yielding the following definition: (1) c p E m L = ∆ Volume 3 · Number 1 · 2011 33