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ERS-1

ERS-1 was the European Space Agency's first major Earth-observation satellite, launched in 1991. Its radar and other instruments helped establish Europe as a major provider of space-based environmental measurements, particularly of oceans, ice and land surfaces.

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Object identity

NORAD ID
21574
COSPAR ID
1991-050A
Operator
Not listed
Country
Not listed
Launch date
Not listed

Immediate discovery

Why this satellite matters

Synthetic-aperture radar is one of its best mathematical stories: motion along the orbit is used to synthesize an antenna much larger than the physical one, improving ground resolution through signal processing.

Understanding the mission

Science and engineering ideas

Synthetic-aperture radar is one of its best mathematical stories: motion along the orbit is used to synthesize an antenna much larger than the physical one, improving ground resolution through signal processing.

Mission

Mission and purpose

The current public orbital catalog identifies this object, but verified mission-specific information may be limited. TransitSatellite will expand this page when authoritative information is available.

  • Synthetic-aperture radar is one of its best mathematical stories: motion along the orbit is used to synthesize an antenna much larger than the physical one, improving ground resolution through signal processing.

Design

Engineering

Synthetic-aperture radar is one of its best mathematical stories: motion along the orbit is used to synthesize an antenna much larger than the physical one, improving ground resolution through signal processing.

Real orbital values

The mathematics

The current two-line element set reports approximately 14.3957 revolutions per day. Dividing 1,440 minutes by that value gives an estimated orbital period of 100 minutes.

Period

100 min

Representative speed

26,902 km/h

Representative altitude

767 km

Inclination

98.78°

These are representative calculations derived from current orbital elements, not fixed physical specifications. Altitude and speed change around an elliptical orbit, and predictions change as new orbital elements are published.

Launch record

Launch and deployment

ERS-1 launched on 17 July 1991 aboard an Ariane 4 from Kourou, French Guiana.

TransitSatellite does not estimate historical launch weather. Temperature, clouds, wind, holds, and scrub reasons will appear only when supported by traceable historical sources.

Orbit

LEO orbit explained

Low Earth orbit is the region closest to Earth used by most crewed spacecraft, many science missions, Earth-observation satellites, and large constellations. Objects move quickly and commonly complete an orbit in roughly 90 to 130 minutes.

LEO can provide detailed Earth views, lower communications delay, and easier access than higher orbits, but it covers less area per spacecraft and is more affected by atmospheric drag.

Live TransitSatellite experience

See ERS-1 moving now

Open the live tracker to view its current calculated position, trajectory, orbital information, visibility tools, and Save and Share controls.

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Learning

Questions to explore

  • What can an orbit tell us before the mission is fully identified?
  • Why are stable catalog identifiers important?

Evidence

Sources and data notes

Current identity and orbital elements come from CelesTrak’s public GP data. Calculated orbit values are derived from the current TLE and may change after catalog updates. Mission-history claims are added separately and require authoritative sources.

Catalog updated

Sep 17, 2026, 1:04 AM UTC

Story review

1970-01-01T00:00:00.000Z