To carry out its mission ERS-1’s orbit had to enable its instruments to scan along predetermined paths designed to give optimum coverage for a set number of orbits. To achieve this, ERS-1 was a three-axis-stabilised, Earth-pointing satellite in yaw steering mode (YSM). The elliptical orbit was sun-synchronous, near-polar, with a mean altitude of 785 km, an inclination of 98.5° and a local solar time at the descending node of 10:30 a.m.


orbit_ers2_1 orbit_ers2_2
ERS-1 orbit Heavens Above

Orbit parameters

35-day orbit

Main characteristics
Semi-major axis 7159.5 km
Eccentricity 0.0001042
Argument of perigee 92.4836°
Inclination (sun-synchronous) 98.543°
Auxiliary data
Mean altitude 782 km
Nodal period 50 min 25.5 s
Repeat cycle 35 days
Number of passes per cycle 1002
Ground track separation at Equator 80 km
Acute angle at Equator crossings
Longitude at Equator of pass 1
Orbital velocity 7.45 km/s
Ground scanning velocity

For the other repeat periods:

3-day 35-day 168-day
semi major axis 7153.138 7159.496 7147.191
inclination 98.516 deg. 98.543 deg. 98.491 deg.
mean altitude 785 km 782 km 770 km
orbits per cycle 43 501 2411

Further information on ERS (ESA website)