In recent years, there has been an increased need for surveillance capabilities in both civilian and military arenas. Mobile unmanned sensor fleets have long been envisioned as a tool for acquiring such intelligence. We describe a geolocation system as a payload for unmanned aerial vehicles. In particular, we address the issues that arise in designing an inexpensive, distributed, mobile, RF sensor processing system: low payload cost; power-limited components; real-time constraints; absence of common clocks; and varying environmental conditions. We also target, qualitatively, the tradeoff decisions across the dimensions of accuracy (of time of arrival estimates and the final geolocation), computational effort, physical dimensions, and operational logistics. The final system architecture, algorithms, and accuracy figures are also described.