ALOS Data Users Handbook

ALOS Data Users HandbookIn this method, the orbit is theoretically always fixed and is located on RSP ± 0 km in order not to take eachperturbation into consideration.(2) Orbit DeterminationThe ALOS Tracking and Control System determines satellite orbit by using SN or GN.Although the timing which carries out orbit determination is a nominal 4 times per week (Tuesday, Thursday,Saturday, Sunday), it will judge whether it considers as either of three patterns carried out 3 times per week(Tuesday, Thursday, Sunday), or every day based on the accuracy evaluation result of the orbitaldetermination error during the initial phase.(3) Orbit ControlManeuvers will be performed so that ALOS can keep the following orbit accuracy• Longitude Repeatability: +/-2.5km above equator• Local Time at DN: 10:30 AM ± 15min.A maneuver (delta V) will be performed every Saturday. However, the maneuver will be canceled if deemedunnecessary during an evaluation conducted every Tuesday. The plan of orbit control of the following day ismade available to the related organizations via EOC every Friday.Inclination will reduce at the rate of about 0.033 deg. / year by solar gravity mainly and will vary localcrossing time at the descending node. To correct this error, an inclination maneuver will be performed aroundthe middle of the mission period (2.5 years after launch). The inclination maneuver is a ΔVy maneuveraccompanying a 90 deg. yaw around maneuver.In addition, the orbit control of ALOS will be carried out as that it keeps the nadir of the satellite less than 0.1degrees (TBD) to the geocentric.5-11