A Trailblazer II rocket was launched on 18 June 1967 from the NASA wallops Island (Va.) Rocket Test Facility to study the properties of the reentry plasma sheath and its effects on microwave antenna performance. The reentry payload consisted of three major subsystems: a plasma diagnostic system, an S- band transponder system, and an X-band telemetry system. The flight data yielded (1) measurements of the influence of the plasma on the radiation pattern distortion, signal attenuation, and impedance mismatch for an S-band slot antenna located at the stagnation point of the nose cone; (2) measurements of the plasma sheath effects on the interantenna coupling between two S-band antennas on the nose cone; and (3) determinations of the electron density profile and gradients in the boundary layer about the nose cone.

To develop alternative solutions to Air Force problems relating to signal transmission in the presence of ionization, AFCRL undertook an extensive investigation of techniques for modifying reentry plasmas. The program included laboratory tests and a series of reentry flight experiments. This report describes the flight test of one successful technique, Teflon ablation, a passive approach that requires no internal support systems. A reentry vehicle fitted with a Teflon-coated nosecap was instrumented to measure antenna impedance mismatch, interantenna coupling, signal attenuation, and charged-particle density. The probe data showed that the local boundary-layer electron density decreased by as much as a factor of 200. The Teflon coating effected a 25-dB decrease in S-band signal attenuation. High-power antenna breakdown was modified by the presence of the ablation products. Details of the vehicle design, flight dynamics, and ablation, are presented, and the results of the Teflon-ablation technique are contrasted with those of a successful liquid-injection technique that was tested on a previous flight.

The effect of injecting an electrophilic liquid into the ionized flow field surrounding a reentry vehicle was observed during the flight of a trailblazer 2 on 28 July 1972. The report describes the rationale used to initially screen candidate additives and the experimental evaluation that finally resulted in the selection of Freon 114B2 for operational use. Injection system design and preliminary testing are discussed, and the predicted and actual performance during flight are compared. Data from on-board antennas and electrostatic probes confirmed that the additive reduced the electron density and improved transmission. A number of factors characterizing the injection are presented as a basis for analyzing the flow-additive interaction. (Author).

A simple method of simulating the variation in the amplitude of microwave signals from rocket-borne transmitters is presented. The technique reproduces signal changes caused by vehicle motion as well as those induced by plasma effects. The simulator uses a voltage controlled attenuator which is programmed to vary the output power of a test transmitter to produce the variations in signal amplitude which would be observed during a flight. An analog system which is suitable for variations of simple cyclical shape and a digital simulator which can reproduce changes of any complexity are presented. Use of the simulator before flight allows the dynamic behavior of a microwave link to be determined, permits optimum receiver and recorder parameters to be selected, increases operator confidence, and enhances flight test reliability. (Author).

This is one of a series of reports on the Trailblazer II program. The particular aspect treated here involves the unmodified expansion-region plasma and its effect on an antenna located on the vehicle shoulder. This report describes some of the theoretical approaches used, discusses the levels of approximation involved, and shows the agreement between these various methods and the test data. The failure of a single set of assumptions to yield consistent agreement over a range of altitudes confirms the need to adopt flow models appropriate to the changing regimes encountered during reentry. One significant conclusion is that performance characteristics such as reflection and interantenna coupling which depend mostly on the level of peak electron density can be represented by simple plane wave, as well as by the more sophisticated slot antenna models. The latter approach, however, is necessary to describe propagation across the entire plasma sheath.

The microstrip plasma probe, a new diagnostic tool for use in the investigation of ionized media, has been developed and successfully tested both in the laboratory and in an actual flight. It is flush mounted (therefore causes no aerodynamic disturbances); simple in geometric shape (therefore can be modified to fit curved surfaces and ruggedized to withstand shock and vibration); only a fraction of the operating wavelength in length (therefore saves on payload space); and operates with low power (therefore does not disturb the plasma which it is measuring). Experimental results, obtained from both the laboratory and from an actual flight, have been compared to theory and to experimental data from other probes. In both instances the results are close.