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An Optimization Analysis of the GCOM-C1 and Sentinel-3A Missions for Improved Ocean Color Imaging Coverage Presented to CGMS-41 Working Group II, WGII/9 in response to CGMS Action 40.17 Brian D. Killough NASA, Langley Research Center. Background.

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  1. An Optimization Analysis of the GCOM-C1 and Sentinel-3A Missions for Improved Ocean Color Imaging CoveragePresented to CGMS-41 Working Group II, WGII/9in response to CGMS Action 40.17Brian D. KilloughNASA, Langley Research Center

  2. Background • The CEOS Systems Engineering Office (SEO) was asked to examine the coverage capabilities of a virtual satellite constellation using GCOM-C1 and Sentinel-3A. • The goal is to improve the daily coverage available for ocean color imaging by suggesting minor adjustment to their planned orbits. • The SEO utilized its COVE tool (next chart) to conduct the analysis. • Conclusion: With minor adjustments to the planned orbit of GCOM-C1 (4 km altitude, <0.1 deg inclination, 2 min LST), the constellation can maximize the daily coverage potential and remove the oscillations in relative spacing between adjacent swaths that create periods of poor coverage.

  3. CEOS Visualization Environment (COVE) Did you know ....There are 1046 Earth orbiting missions • Browser-based tool using Google-Earth to display satellite coverage swaths and calculate coincidence scene locations. • Automated daily satellite position data from CelesTrak. • Saved bookmarks and states, Google-Earth KML and Shapefile compatibility, collaborative sessions. • Output: position, UTC time, viewing angles, solar angles, day/night, and EXCEL tables • Large mission database: 126 missions, 263 Mission-Instrument combinations COVE is a FREE tool ! Visit: www.ceos-cove.org

  4. Assumption • GCOM-C1 Mission, SGLI-VNR Instrument • Launch in mid-2014, Altitude 796km, 10:30am LTDN, 34-day orbit repeat, Swath 1150km. • Sentinel-3 Mission, OLCI Instrument • Constellation of two satellites (A and B), phased 180-degreesSentinel-3A launch in April 2014, Altitude 800 km, 10:00am LTDN, 27 day orbit repeat, Swath 1240km. • Orbit Analysis • Simple J2 orbit propagator • Arbitrary launch date and propagation start time. • Other Assumptions • Modifications were only considered to the GCOM-C1 orbit since Sentinel-3A and 3B are both impacted by changes and their optimized performance, as a pair, would be lost.

  5. Analysis Results • Due to differences in orbits, the ground swaths of the satellites drift relative to each other. The swath spacing will oscillate between extremes over a 3 month period. • This oscillation results in complete overlap (top figure) and non-overlapping coverage (bottom figure). • Even in the non-overlapping case, minor gaps are present between satellite passes.

  6. Optimization Results • With small modifications to the GCOM-C1 orbit, it is possible to remove the oscillation in the ground coverage pattern produced by the virtual constellation. • Increase the GCOM-C1 altitude by 4km and adjust the orbit inclination by <0.1-deg to achieve a 27-day orbit repeat, similar to Sentinel-3A. • Following altitude and inclination adjustments, there is a need to adjust the local crossing time to achieve the desired separation at the equator. • Moving the LTDN to 10:32am achieves the consistent daily coverage shown on the right. Additional adjustments to the LTDN can remove this small overlap, if desired.

  7. Additional Considerations • The optimized coverage pattern (previous chart) requires the two spacecraft to be flying in a tight formation separated by only a few seconds. This change may require increased fuel consumption. • Significant coordination will be required by the operations teams during launch, orbit insertion, and daily operations of the constellation. • Once Sentinel-3B launches, significant overlap will exist between GCOM-C1 and Sentinel-3B (figure on right) • Unless there is a secondary benefit to redundant coverage, either GCOM-C1 or Sentinel-3B’s coverage is largely redundant. • If the 3-satellite constellation is not desired, GCOM-C1 can perform a small propulsive burn to return to its original orbit and both teams can return to independent operations. Optimized ground coverage for GCOM-C1 (RED) and Sentinel-3A (BLUE) with the addition of Sentinel-3B (GREEN). Little gaps exist in this scenario.

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