4.1.5.2. ERS-1 orbits

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.

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)