A novel telemetry system for hypervelocity projectiles

At projectile velocities exceeding 2000 m/s ablation phenomena due to the heating by air friction may influence flight and impact behavior. Direct in-bore temperature measurements during the flight could clearly improve the theoretical modeling of the heat transfer to hypervelocity projectiles, but the temperature signals must be transmitted from the projectile to the ground station. Since the projectiles are submitted to heavy accelerations, batteries cannot be used as power supply. Therefore, at EMI a low energy telemetry concept is under investigation according to the following principle. At the projectile base a radio frequency reflector with variable reflection coefficient is installed. The reflection coefficient is controlled by an on-board local oscillator, the frequency of which is modulated by the measured signal, e.g., of a temperature sensor. The projectile base is illuminated by an unmodulated fixed frequency ground based radio frequency transmitter, and the signal reflected at the projectile base is picked up by a ground based receiver. The received signal contains the measured signal, shifted by the Doppler frequency, and the Doppler frequency itself. Since controlling the reflection factor of the projectile base only consumes a very low energy, the on-board power supply during the flight phase can be realized by a simple previously charged capacitor. Several telemetry test projectiles of caliber 30 mm have been developed and fired at successively high velocities presently reaching 1850 m/s by the aid of a light gas gun. The actual state of the work and the first results are presented