Compact Modular Telemetry System for Wind Tunnel Test Data

The CMTS is an air gapped telemetry system specifically designed for wind tunnel testing.  The wind tunnel application presents a number of factors that are almost diametrically opposite those experienced in conventional telemetry design.  The environment through which the radio frequency (RF) link must pass is bounded by metallic walls that are highly reflective with a very short pathlength requiring unusual treatment to ensure transmission integrity.  The required throughput of up 50 channels at a10 kHz rate, is consistent with modern telemetry capabilities.  The environmental conditions encountered over the range of testing performed at the Arnold Engineering Development Complex (AEDC) present other unique challenges.  For example, at Mach 10 the freestream temperature in the tunnel is only a few degrees above the liquefaction point.  Surfaces in contact with the airstream are heated to many hundred degrees.  The aerodynamic heat conducts into the model raising the internal temperature of the telemetry electronics.  CMTS includes an environmental control system and has the capability to include active cooling via gas or liquid heat exchange. In proposing the Phase I effort, the RF link was the most significant challenge for the system.  CMA built an electromagnetically similar surrogate tunnel having the dimensions of the AEDC VKF-A wind tunnel.  An extensive test program characterized RF transmission in the tunnel environment in both the L and S band frequency ranges.  Testing included all common modulation formats including continuous wave (CW), amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), and shaped offset quadrature phase shift keying modulation (SOQPSK).  CMA successfully demonstrated an end-to-end, bidirectional telemetry link using Range Commanders Council (RCC), Interrange Instrumentation Group (IRIG) approved, SOQPSK telemetry system. The proposed Phase II program builds upon the information gained in the Phase I program, particularly with regard to antenna configuration, antenna matching, and issues in the highly reflective RF environment (including self-modulation, cross modulation, multipath transmission, and carrier phase offset).  The program leverages the use of existing, IRIG approved telemetry technology and equipment where possible, significantly reducing risk.   CMTS is modular by design.  Multiple conceptual designs are prepared including a plate configuration (for inclusion inside models or inside an afterbody), a cylinder configuration (for sustained hypersonic testing), a tray model (a combination of the plate and cylinder arrangements), and a stationary configuration (for mounting on or below the sting). The proposed program is accomplished in 19 months.  A prototype system is built in the plate configuration.   The prototype is demonstrated in the AEDC facility, including integration of the telemetry system with the AEDC data system.