This article - Small Satellites Launch Big Plan: Start-Up Proposes - WSJ.com - Dec.31.07 (subscription required) reports on an interesting spinoff company from JPL called GeoOptics LLC. The firm intends to use a constellation of 24 microsats to implement a technique called GPS Radio Occultation to obtain high resolution data world wide on atmospheric temperatures, pressures, and humidities. The satellites will do this by examining the modifications to GPS signals from their transits through the atmosphere. Similar radio signal occultation techniques have been used to examine the atmospheres of Mars and other planets. See the GeoOptics website for introductory level overviews of their plans.

The article says "the project is projected to cost less than $2.5 million a satellite, including launch". The firm "has commitments of about $50 million, and the initial cost is projected at about $100 million".