Orbital Analysis for Inter-Calibration Dave Mac Donnell Brooke Anderson Bruce Wielicki Don Garber NASA Langley Research Center Solar Workshop January 30, 2009

CLARREO Crossing Below Aqua 700km CLARREO 100 km nadir fov Aqua MODIS, CERES, or AIRS Crosstrack Scan Time to Achieve Viewing Angle Matches: 40 seconds per 100km orbit altitude Difference: 140 seconds above D. Garber LaRC, 7/07

Top View: CLARREO under-flight of Aqua Aqua MODIS, CERES, or AIRS Crosstrack Scan CLARREO 100 km nadir fov D. Garber LaRC, 7/07 Angle Pointing (zenith, azimuth) is required to obtain any calibration matches beyond those at nadir. Options: pointable instrument, pointing table, or S/C reaction wheels

Orbital Analysis All orbits are modeled at a 600 km altitude –Selected based on its separation from NASA missions at 705 km and NOAA missions at 824 km –Altitude separation drives the slew rates during intercalibration –The altitude may be changed to above the key intercalibration targets altitudes ( i.e. 924 km) Orbit inclinations angle are selected based on the precession behavior and the global coverage. –90 degree inclination – 0 precessions per year –74 degree inclination – 2 precession per year (at 600km) –83 degree inclination – 1 precession per year (at 600km) –97.8 degree inclination – Sun Synch (-1 precession per 600km) Ground track repeat avoidance –The ground track repeat cycle is set to greater than 50 days

Maximum Slew Rate versus Altitude Difference 3°/second for CLARREO to Aqua

Precession Rate Trade Space 600km/74.2° 600km/90° 600km/83°

Sun-Synchronous with respect to CLARREO 600km/74.2° Sun-Synch CLARREO 600km/74.2°

Sun-Synchronous with respect to CLARREO 600km/83° Sun-Synch CLARREO 600km/83°

Sun-Synchronous with respect to CLARREO 600km/90° Sun-Synch CLARREO 600km/90°

Ground Repeat Nodes for a 90 degree inclination angle orbit

Ascending Node Separation vs. Ground Track Repeat Cycle

Ground Repeat Nodes for a 90 degree inclination angle orbit

Two CLARREO Satellites 600km/90° CLARREO 1 CLARREO 2

Three CLARREO Satellites 600km/90° CLARREO 1 CLARREO 2 CLARREO 3

Solar Intercalibrations with Aqua 600km by 74 degrees Opportunities Nadir/2278 Pointing

Solar Intercalibrations with Aqua 600km by 83 degrees Opportunities Nadir/3631 Pointing

Solar Intercalibrations with Aqua Two Satellites at 600km by 90 degrees Opportunities (each) Nadir/2424 Pointing

Solar Intercalibrations with Aqua Three Satellites at 600km by 90 degrees Opportunities (each) Nadir/2424 Pointing

Solar Intercalibrations with Aqua 600km by 74 degrees and 90 degrees

Solar Intercalibrations with Aqua 600km by 90 degrees and Sun-Synchronous Opportunities Nadir/2278 Pointing

Space to Sun Azimuth/Elevation as a function of Beta-Angle

Annual Beta-Angle Cycle 600km by 74 degrees and 90 degrees

Annual Beta-Angle Cycle Two Satellites at 600km by 90 degrees

Annual Beta-Angle Cycle Three Satellites at 600km by 90 degrees

Spacecraft Configuration Challenges With spacecraft orbits that result in positive and negative beta-angles, the sun will eliminate both sides of the spacecraft. The spacecraft will likely require a 180 degree yaw when the beta-angle crosses zero. –This will maintain one side of the spacecraft as the cold side, which is suitable for radiator placement. –The solar array could maintain favorable views to the sun for power generation.

Summary The orbital analysis of the four orbital plane options are modeled and can be adjusted as needed. Pointing capability will increase the number of sample opportunities by 3 to 4 times. –Assuming 10 seconds per sample and 2 seconds buffer The beta-angle range will likely force the spacecraft to change the orientation of the spacecraft. –Nadir pointing will be maintained. –Yaw of 180 degrees is likely