An introduction to the analysis of satellites orbiting the earth

NASA's interest in the possible use of smaller satellites for its Earth Observing System EOS 2 —the space-based component of the Office of Earth Science's Earth Science Enterprise—arose from budgetary pressures, the desire within the scientific community for more missions and shorter mission time lines, the perception that there are both gaps and unrealized opportunities in the enterprise's space segment, and the determination of NASA officials to accelerate the infusion of new technologies into their space programs. In the literature, the term covers everything from a satellite weighing from a few to 1, kg. Such satellites, which tend to cluster in the to kg range, can provide robust payload accommodations for one or more instruments and are suitable for launch on the new class of low-cost, small expendable launch vehicles or as part of a multisatellite launch on a larger expendable launch vehicle.

An introduction to the analysis of satellites orbiting the earth

NASA's interest in the possible use of smaller satellites for its Earth Observing System EOS 2 -the space-based component of the Office of Earth Science's Earth Science Enterprise-arose from budgetary pressures, the desire within the scientific community for more missions and shorter mission time lines, the perception that there are both gaps and unrealized opportunities in the enterprise's space segment, and the determination of NASA officials to accelerate the infusion of new technologies into their space programs.

NASA's particular interest in NPOESS involves its potential to fulfill long-term systematic measurement requirements formerly planned for follow-on missions to the first series of EOS satellites, especially the PM 5 series because of its focus on monitoring weather- and climate-related variables.

Whispers from the Sky

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.

An introduction to the analysis of satellites orbiting the earth

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 Athe 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.

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? The committee explored the scientific merits and technical capabilities of small satellites; the development status e.

The criteria used to assess small satellite utility and to examine mission architecture trade-offs included performance capability, risk, mission flexibility and robustness, and the potential for streamlined management processes-all with a focus on the potential for lower mission-life-cycle costs.

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Several case studies Appendix D were examined to assess the reality versus the promise of small satellites to date and to help identify paths to greater success in the future.

Both operational and research programs were considered, and the distinction between them underlies much of the discussion in this report. Characteristics of operational programs include an established community of data users who depend on a steady or continuous flow of data products, long-term stability in funding and management, a conservative philosophy toward the introduction of new technology, and stable data-reduction algorithms.

Research programs often require greater measurement accuracy, more attention to calibration, programmatic flexibility, and faster time to science; depending on the cost of the mission, they can be more tolerant of risk. The study emphasized the launch and space segments of Earth observation missions.Introduction to Weather Satellites.

The world’s first meteorological satellite, a polar-orbiting satellite, was launched from Cape Canaveral on 1 April Named TIROS for Television Infrared Observation Satellite, it demonstrated the advantage of mapping Earth’s cloud cover from satellite altitudes. GPS satellites are at 12, miles, high enough to be accessible to large swaths of the Earth.

Others that need a closer look at Earth are lower. For comparison, the International Space Station is only about miles high, and very few satellites are lower than that. Assembled by experts at the Union of Concerned Scientists (UCS), the Satellite Database is a listing of the more than operational satellites currently in orbit around Earth.

It consists of a science component and a data system supporting a coordinated series of polar-orbiting and low-inclination satellites for long-term global observations of the land surface, biosphere, solid Earth, atmosphere, and oceans" (EOS Project Science Office, ).

While satellites in orbits between km and km can provide an excellent introduction to satellite communications and support experimental payloads, their altitude limits both the amount of time the satellite is available in any one part of the world and maximum communication range (footprint).

Satellites in orbit observe the same point on earth in regular intervals, known as revisit times.

An introduction to the analysis of satellites orbiting the earth

These times vary depending on orbit, altitude, location, swath, etc. and are crucial for time-series analysis and detecting change.

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