A fleet of small spacecraft (“cells”) in low Earth orbit combine to form an integrated Earth observing system providing many observations previously requiring distinct sensing systems. Each cell performs a few relatively primitive functions, including emission, reception, sampling, and recording of radio and microwave signals. Each cell observes over a spherical field of view, samples the received signals independently at many small antenna elements, and stores the data from each element. Data from all cells are sent to a common location where they can be combined in diverse ways to realize a wide range of observing functions. These functions may include ionosphere and gravity field mapping; atmospheric radio occultation; ocean, ice, and land altimetry; ocean scatterometry; synthetic aperture radar (SAR) imaging; radar sensing of soil moisture, land cover, and geological surface properties; and interferometric SAR sensing of surface change. The system can also provide real-time messaging, navigation and surveillance functions.