Doppler-radar: a possibility to monitor projectile dynamics in railguns

A precise and continuous measurement of the velocity of projectiles inside the barrel would permit to improve the understunding of the dynamic behavior of railguns. Friction-related questions, the mechanical stability of projectiles, or mass loss of armatures are problems to be mentioned in this context. One possibility to monitor the projectile dynamics is the use of a conventional Doppler-radar. In this paper, the experimental setup of a W-band Doppler system and its application at railgun experiments are described. First results obtained using a 15 x 30 [mm.sup.2] rectangular caliber railgun are presented. The maximum muzzle velocity for the series of experiments is about 1300 m/s. Depending on the quality of the electrical contact between rails and armatures, a very good agreement between the projectile dynamics measured by the Doppler-radar and the information given by several B-dot signals recorded at several positions along the barrel is obtained. If no electrical arcs are formed during the shot, the projectile is properly detected until it reaches the muzzle of the launcher (l = 3 m). Some aspects of friction are discussed to illustrate the evaluation of the data obtained. Index Terms--Armature, Doppler-radar, railgun.