The seventeen papers in this special issue are devoted to technical advances in deep-space communications and tracking.

The twelve articles in this special issue are devoted to the topic of deep space communication.

On January 14, 2005, the Huygens probe, which forms part of the joint NASA/ESA/ASI deep-space mission Cassini-Huygens, accomplished its spectacular descent through the atmosphere of Titan, Saturn's largest moon. This mission success, however, became possible only after the rescue of the endeavor from an implementation flaw that was discovered in 2000 during an in-orbit test of the Huygens relay-link receiver. The problem threatened to cripple the entire $350 million probe mission.

In digital transmission systems employing PLL repeaters, timing jitter is produced mostly by intersymbol interference (ISI). Despite the fact that IS1 represents a narrow-band disturbance to the PLL for a long chain of N repeaters, it is responsible for cycle slips of the PLL repeater. It is demonstrated that the cycle slip rate is the key parameter determining the error performance of the system. It is shown that the accumulated jitter for a large chain becomes a narrow-band process, which can be replaced by an equivalent low-pass jitter-noise process, which lends itself to analytical treatment. Numerical results of the cycle slip rate are given, based on the solution of a time-dependent Fokker-Planck equation. The results are useful for a wide range of loop transfer functions and phase-detector characteristics. The theoretical findings are confirmed by experimental results.

Phase acquisition probabilities for phase-locked synchronizers are derived. Both self- and aided-acquisition techniques are investigated and compared. It is shown that so called "hang-up" can be prevented by using initial quadrant estimation to control appropriate slew voltage applied to VCO.