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This issue of the Johns Hopkins APL Technical Digest covers a range of scientific, engineering, and technical topics. The first two articles involve time and timing: the APL Time and Frequency Laboratory and the effects of relativity on spacecraft timekeeping. Two more articles concentrate on high velocities: scramjet inlet design and active flow control for supersonic conditions. The next two articles describe model-based conceptual systems engineering and the development of testing methods for modular spacecraft instrumentation. Next is an introduction to the characterization of chemical and biological threat agents. The issue concludes with a description of the current winners of APL Achievement Awards and Prizes.