Using NASA's Reference Architecture: Comparing Polar and Geo Science Data Processing Systems

Today's satellite environmental monitoring of the Earth relies on two basic orbital geometries for worldwide collection of data: Geostationary and Polar Orbiting. Geostationary satellites follow a geosynchronous orbit such that from the vantage point of a terrestrial observer, the satellite appears stationary over a point on the equator. The geostationary satellite observes the same part of the Earth all times of the day. Orbital mechanics and practicalities of maintaining such a geosynchronous orbit dictate that geostationary observatories are in high Earth orbit. The other important orbital model is a polar orbiting, sun-synchronous observatory. Polar orbiters traverse from pole to pole. Over the course of a number of orbits, the entire Earth can be observed. By placing the observatory in a sun-synchronous orbit, the satellite crosses the equator at a specific mean local time at each orbit. The sun-synchronous polar satellite observes all points of the Earth at the same solar illumination angle (local sun time) of a day. Because of practicalities of orbital mechanics, sun-synchronous polar observatories are in low Earth orbit. In the abstract, all Earth orbiting satellites are commanded and controlled in the same way and satellite Earth environmental observation data is processed in the same way. Data is processed and promoted according to the international Committee on Earth Observation Satellites (CEOS) defined Level 0 represents raw instrument observations; Level 1 products represent the conversion from raw engineering units to physical sensor units and Level 2 products represent environmental science parameters derived or interpreted from the sensor observations. Thus the top-level architecture of the ground system including the mission operations and science data processing segments look strikingly similar. Given the extraordinary cost of building a ground system, combining the resources to serve the Earth environmental customers looks to be a fruitful cost saving economy of scale. But are there critical differences between the two scenarios that make such a merger less efficient? The NASA's Earth Science Data Systems Standards Process Group has developed a Reference Architecture for Earth Science Data Systems. This paper will discuss the similarities and differences between geostationary and polar environmental data systems in the context of NASA ESDS Reference Architecture to gain deeper understanding of the trade.