# ERS-2 Mission Phase A

## Phase A parameters

*Phase A parameters*

- 35 days repeat cycle
- 501 orbits per cycle

*Orbit number characteristics*

- First absolute orbit number is: 1 on 21-apr-95, 03:16:54.739 UTC

- First internal track: 147 of cycle 0

*Orbit parameters*

- orbit eccentricity: 0.001165
- orbit inclination: 98.5421 deg
- asc. node Long.: 243.0078 deg
- semi-major axis: 7159495.96 m
- mean nodal period: 6035.928144 s
- mean anomaly: 270.1334 deg
- argument of perigee: 90 deg

## Formulas from Relative (track) to Absolute Orbit Numbers

ABS_ORB_NUM = REL_ORB_NUM + CYCLE_NUM*501 - 146

CYCLE_NUM = INT [ ( ABS_ORB_NUM + 145)/501 ]

REL_ORB_NUM = ABS_ORB_NUM + 146 - CYCLE_NUM*501

*Where:*

- the "Absolute Orbit Number" is counted from the beginning of the mission;
- the "Relative Orbit Number" (track), in a given cycle,
is counted starting from the first orbit East of Greenwich;
- the "Cycle Number" is increased whenever the track 1 is rivisited (note that the first cycle
(Cycle 0) was incomplete)

**This information was partly retrieved from ESA/ESRIN**