The EOS Chemistry mission is the third of the 'flagship' missions of NASA's Earth Sciences Enterprise, following EOS AM and EOS PM. Design work on the Chemistry spacecraft has started under NASA contract NAS5-32954. This spacecraft is the second of the EOS Common Spacecraft, EOS PM being the first one. The design has recently been successfully completed with spacecraft CDR this June, and it is now in the fabrication phase for the PM mission. This design of the spacecraft will be summarized. The Chemistry mission will carry four new scientific instruments. These instruments place some new requirements on the spacecraft to accommodate them, but these are satisfied with relatively small 'kits' that are added to the Common Spacecraft design. This design of the Chemistry configuration of the Common Spacecraft will be presented. We have explored the cost effectiveness of small and medium satellite architectures for hypothetical future Earth Science missions. These cost comparisons include the life cycle cost of space, launch and ground segments of each complete mission and are based on actual costs of existing missions. We find that the lowest cost approach under a wide variety of assumptions is to use a medium size spacecraft carrying a suite of instruments.