Can a LEO Architecture Fully Replace GEO Measurements for Low-Light Imagery and Hyperspectral IR Sounding?

The NOAA/NESDIS Geostationary Extended Observations (GeoXO) program has been examining the viability of making persistent low-light imagery measurements from geostationary orbit in order to satisfy the requirements of persistent imagery over the Western Hemisphere. Their studies have shown that, because of stray light issues, the ability to make low-light measurements from geostationary orbit is technologically difficult. In addition, the GeoXO program is developing other high update rate sensors for hyperspectral infrared (IR) soundings and atmospheric composition radiances. The latter two are intended to be manifested on a satellite to be positioned over a latitude near the center of the conterminous United States (CONUS).

Building upon the GEO/LEO Architecture Study conducted in 2022, NESDIS examined in more detail the trades and potential constellation designs to make low-light measurements over the Western Hemisphere from different orbits. The study team looked at constellations that would inform NESDIS leadership of the feasibility and costs of replacing the GEO low-light capability with data obtained only from LEO satellites. Similarly, as a risk reduction activity, the study team looked at constellations that would provide moderate update rate (e.g., one hour) hyperspectral IR sounding and atmospheric composition measurements over CONUS. The study started with establishing the measurement trade space which included variations in geographic coverage, update (or revisit) rate, and instrument capability. The authors considered several primary factors that influenced constellation design and lifecycle cost:

1. Performance Requirements;
2. Availability Requirements;
3. Orbital Consideration (e.g., is the 1330 orbit required, sun synchronous or non-sun synchronous orbits);
4. Constellation Size;
5. Launch Cadence;
6. Design Life Trades;
7. LEO/GEO Trades; and
8. Aggregation vs. Disaggregation.

Each factor was carefully considered to allow NESDIS not only to understand the trades, but also the ramifications of replacing GEO capability with LEO configurations. The authors will describe the study and identify several key recommendations.