Several advances in the spacecraft industry have resulted in a new class of smaller spacecraft. The relative affordability of these spacecraft makes them attractive for consideration for several types of satellite missions. Studies have been performed in recent years examining the cost effectiveness of small satellite architectures utilized specifically for low Earth orbit (LEO) scientific missions. The results of these studies vary depending upon the assumptions used and the nature of the m missions addressed. This paper explores the cost effectiveness of small and large satellite architectures for post-2002 Mission to Planet Earth missions. The cost comparison examines the life cycle cost of the space, launch and ground segments of each complete mission. The analysis is based on spacecraft bus costs and historical spacecraft and launch vehicle reliabilities as well as estimations of the costs of oversight, integration and testing and operations for each of the missions. The analysis examines the architecture, single or multiple sensor platforms, best suited to orbit several sensors for LEO scientific missions.