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C.D. Fry (Exploration Physics International), T.J. Rosenberg, L. Lutz, D.L. Detrick, A.T. Weatherwax (IPST, U. MD), E. Knouse, H. Breden (Phys. Dept., U. MD), J. Giganti (Data Design Corp.)
The Planetary Surface Instruments Workshop (Meyer et al., LPI Tech. Rpt. 95-05, 1995) identified surface-based radio science instruments as key tools for observing Mars' middle atmosphere, its ionosphere and solar-wind interaction. For example, Mars has a substantial daytime ionosphere, and some important features of the Martian ionosphere can only be observed from below. One instrument, the Relative Ionospheric Opacity Meter (Riometer), is expected to work well on Mars (Detrick et al., PSS, 45, p. 289, 1997). In the past, the size, power requirements and complexity of these instruments have argued against including them on a lander or rover mission, in spite of the potentially rich science return.
We describe the development of a miniature radio receiver designed to operate as a Riometer. The development of this receiver was funded by NASA as an enabling technology for future planetary radio science missions. Our receiver includes features that are desirable for extended autonomous operation: low power consumption, wide dynamic range and linearity, computer command and data interface, and the ability to be remotely reconfigured. The receiver design provides significant improvements over previous implementations used in terrestrial riometry. The high degree of system linearity, combined with a digital feedback loop (including a low-duty calibration cycle), allows a longer measurement time. We were able to significantly miniaturize the receiver by using modern, low-power electronic components that have come on the market. We also implemented several of the subsystems in a field-programmable gate array, including the receiver detector, the control logic, and the data acquisition and processing blocks. Considerable efforts were made to eliminate or minimize RF noise and spurious emissions generated by the receiver's digital circuitry. Results of laboratory and field tests are presented and discussed.