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An analysis of differential charging between dielectric surface materials and the frame of a DSCS-III geosynchronous spacecraft is presented. Charging levels measured by surface potential monitors (SPMs) covered with samples of Kapton and Astroquartz have been recorded for one half of a solar cycle. Both seasonal and solar cycle effects are seen in the daily peak levels of the SPM voltages, with local maxima occurring near the equinoxes and a general trend increasing as solar max is approached. Charge neutralization by an onboard Xe plasma contactor was demonstrated to be effective throughout the mission, with a mean voltage reduction of 86% for Astroquartz and 74% for Kapton. Though a statistical analysis shows a general correlation between the fluence of charging electrons with SPM voltages, the event-specific correlation contains enough variance to cast doubt on the usefulness of an electron sensor as a differential charging alarm. We have found that a Kapton-covered SPM may be better suited than an electron sensor as a differential charging alarm. Index Terms--Geosynchronous orbit, satellite charging, space environmental effects, space weather.

The Compact Environmental Anomaly Sensor (CEASE) is an instrument designed to provide real-time space environment hazard warnings to the host spacecraft. In this paper, we report on the first year of on-orbit operation of this instrument and describe its performance with particular emphasis on its engineering, hazard-warning function. Index Terms--Dosimetry, proton radiation effects, radiation detectors, satellites.

The solar cycle dependence of dose rates in the low-altitude 'horns' of the outer zone electron belt is examined using data from TSX5/CEASE (solar maximum epoch) and APEX/PASP+ (solar minimum epoch). It is found, after normalizing the dose rates to account for the different shielding geometries, that the ratio of PASP to CEASE dose rates is ~4 for L > 4. This is contrary to the equal dose rates predicted by the NASA AE8MIN and AE8MAX models. Index Terms--Electron dose, low earth orbit, radiation belt, solar cycle variation.

Optically sampled analog-to-digital converters (ADCs) combine optical sampling with electronic quantization to enhance the performance of electronic ADCs. In this paper, we review the prior and current work in this field, and then describe our efforts to develop and extend the bandwidth of a linearized sampling technique referred to as phase-encoded optical sampling. The technique uses a dual-output electrooptic sampling transducer to achieve both high linearity and 60-dB suppression of laser amplitude noise. The bandwidth of the technique is extended by optically distributing the post-sampling pulses to an array of time-interleaved electronic quantizers. We report on the performance of a 505-MS/s (megasample per second) optically sampled ADC that includes high-extinction LiNb[O.sub.3] 1-to-8 optical time-division demultiplexers. Initial characterization of the 505-MS/s system reveals a maximum signal-to-noise ratio of 51 dB (8.2 bits) and a spur-free dynamic range of 61 dB. The performance of the present system is limited by electronic quantizer noise, photodiode saturation, and preliminary calibration procedures. None of these fundamentally limit this sampling approach, which should enable multigigahertz converters with 12-b resolution. A signal-to-noise analysis of the phase-encoded sampling technique shows good agreement with measured data from the 505-MS/s system. Index Terms--Analog--digital conversion, distortion, electrooptic devices, intermodulation, microwave receivers, pulsed lasers, signal sampling, time-division multiplexing.