term systematic measurement requirements formerly planned for follow-on missions to the first series of EOS satellites, especially the PM5 series because of its focus on monitoring weather- and climate-related variables. Each NPOESS satellite is currently planned as a multisensor spacecraft. However, alternative system architectures are possible that would distribute the sensor complement among a larger number of smaller satellites.

The committee's study originated during a period when satellite builders and policymakers were engaged in a spirited debate over the feasibility and merits of substituting smaller satellites for larger systems. Advances in miniaturization were said to allow much smaller sensors that retained sufficient performance for many Earth science and operational needs. These smaller sensors could be accommodated on smaller spacecraft, which would be smaller still because of miniaturization of various spacecraft subsystems. Reducing the size, volume, and weight of both payload and spacecraft would then allow the use of either the new generation of smaller launch vehicles or clustering of spacecraft on a single launch of a larger launch vehicle. It was argued that performing missions with smaller payloads, spacecraft, and launch vehicles would lead to dramatically lower costs.

The debate over the use of small satellites had sometimes been portrayed as a dispute between innovative satellite designers and government bureaucrats or industry officials who either lacked vision or had financial incentives to maintain the status quo. The committee found that these characterizations were either inaccurate or a simplification of more complex circumstances. It is noteworthy, for example, that the historic providers of large Earth remote sensing satellites have also provided small satellite systems for space physics research, planetary exploration, and other space missions. In addition, it was evident to the committee that any credible discussion of small versus large had to include a detailed analysis of the many interrelated technical and programmatic issues associated with the design and development of satellite systems.

In responding to its charge (Appendix A), the committee set out to understand the observational needs for key NASA and NOAA Earth remote sensing programs and to determine and assess the availability and capability of sensors, satellite buses, and launch vehicles suitable for small satellite missions. Further, the committee examined opportunities presented by small satellite options with respect to mission architecture and assessed their implications for future NASA and NOAA missions.

During the study, both NASA and NOAA made programmatic decisions that affected the committee's course. NASA restructured its Earth science program such that missions that would follow the initial EOS AM, PM, and Chemistry satellites would be smaller, more flexible, and responsive to advances in technology and science. NASA also planned to integrate EOS missions with operational weather satellite programs (e.g., NPOESS) for long-term systematic measurements. Further, the NOAA-DOD-NASA Integrated Program Office opted to develop new sensors, as opposed to continuing with heritage EOS sensors, for critical NPOESS measurements through competitive procurements. Thus, both NASA and NOAA plans now recognize and embrace current capabilities and ongoing advances in sensor and spacecraft technology for future Earth observation missions. Consequently, the committee altered its planned response to its charge and de-emphasized the study of specific new technologies in favor of an increased emphasis on the implications and impact of capable small sensors and satellites on mission architecture and management trade-offs. Among the questions emphasized in this modified approach were these:

  • Are there sustained opportunities for low-cost, quick-response, focused missions, leading to a reduced "time to science" (analogous to the commercial sector's "time to market")?

  • Would affordable constellations of small satellites open the door to enhanced science via more frequent or continuous sampling strategies?


Defense Meteorological Satellite Program and the POES program. An integrated tri-agency office was established on October 1, 1994, to manage acquisition and operations of the converged satellite program.


 The EOS satellites will be launched into polar, Sun-synchronous orbits. The EOS PM satellite will cross the equator at 1330 local time. The EOS AM satellite will cross the equator at 1030 local time. The afternoon and morning crossings facilitate observations of atmospheric and land processes, respectively.

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