In-bore measurements using an optical data link [in EM railguns]

Previous efforts to obtain information from onboard sensors involved writing the data to an EPROM located in the launch package, performing a "soft" catch of the projectile, and recovering the chip in order to download the data. This method requires soft catch capability and has been limited to velocities of less than 1 km/s. The authors have developed a method to measure in-bore quantities on board a railgun launch package and transmit the information out of the barrel in real time using an optical data link. The onboard transmitter, which is mounted on the front end of the launch package, is either a repackaged laser diode or a high intensity LED. During launch, light pulses are transmitted down the bore, reflected off a mirror just outside the muzzle, and received with a telescope and attached photomultiplier tube. Successful operation has been achieved for accelerations up to 105 kgees and velocities up to 2.0 km/s. An analog encoded version of the system has been built and used to perform an armature voltage measurement.