Abstract : This final report describes a program to develop an instrument capable of measuring electron density in the 50 to 160 kilometer altitude region and capable of surviving a 60,000 'G' shock encountered during launch from a cannon. This report is in two parts: The first describes various techniques and instruments capable of measuring electron density in this altitude region. The second section describes the design techniques as well as flight results from these probes. Both dc and ac Langmuir probes were chosen as the best instruments for fulfilling the system requirements.