European Remote Sensing Satellite, ERS-1

Summary:

This document contains information about the ERS-1 satellite. A description of the mission is provided as is information about the spacecraft and its environment. The ground data system is briefly described.

Also see the ERS-2 documentation.

Table of Contents:

• 1 Source/Platform or Data Collection Environment Overview
• 2 Ground Segment Information
• 3 References
• 4 Glossary of Terms
• 5 List of Acronyms
• 6 Document Information

1. Source/Platform or Data Collection Environment Overview:

Source/Platform or Data Collection Environment Long Name, Source/Platform Acronym:

European Remote Sensing Satellite, ERS-1

Source/Platform Introduction:

ERS-1 is a European Space Agency (ESA) satellite devoted to remote sensing from a polar orbit. It provides global and repetitive observations of the environment using techniques which allow imaging to take place irrespective of weather conditions. ERS-1 has a sun-synchronous, polar, near-circular orbit with a mean altitude of 785 km.

Collection Environment:

Satellite

Source/Platform Program Management:

The European Space Agency (ESA), joined by Norway and Canada

 

Source/Platform Mission Objectives:

Data generated by the ERS-1 mission contributes to:

• Improved understanding of ocean-atmosphere interactions
• Advances in knowledge of ocean circulation and energy transfer mechanisms
• Improved estimates of the mass balance of the Arctic & Antarctic ice sheets
• Better monitoring of dynamic coastal processes
• Improved pollution monitoring
• Improved detection and management of land use changes

Source/Platform Parameters:

ERS-1 was launched on 17 July 1991 by an Ariane 4 launcher from Kourou, French Guiana. Its total mass is 2157.4 kg, 888.2 kg from the payload and 1257.2 kg from the platform. The peak power supplied to the payload is 2600 W, payload average power is at most 550 W. The voltage of the power supply varies between 23 V and 37 V with a maximum on-board energy of 2650 WH. ERS-1 is a 3 axis stabilized spacecraft with a design lifetime of two to three years.

ESA sponsored the mission. The prime contractor is Dornier (Federal Republic Germany). Co-contractors include Fokker (The Netherlands), Laben (Italy), Matra (France), MDA (Canada), Marconi (United Kingdom) and Selenia (Italy).

Coverage Information:

ERS-1 has a sun-synchronous, near polar, near circular orbit at a mean altitude of 785 km and an inclination of 98.5 degrees. During the initial three months of the commisioning phase, the satellite had a 3-day repeat cycle at an altitude of 785 km (this is known as the reference orbit). Subsequent satellite height adjustments have provided two multi-disciplinary phases with a 35-day repeat cycle, two ice phases with 3-day repeat cycles and two geodetic phases with 168-day with cycles. The majority of the mission has been performed in the 35-day repeat cycles. ERS-1, operating in-tandem with ERS-2, is expected to remain in a 35-day repeat cycle for the rest of its mission. Since ERS-1 has no on-board recorders except for an on-board tape recorder for bitrate data, AMI data can only be obtained if there is a ground station in view of the orbiting satellite.

Attitude Characteristics:

ERS-1 is three axis stabilized, Earth pointed. Absolute rate errors in each platform axis are no greater than 0.0015 degree-seconds (3 sigma). Maximum errors are:

• Bias and long term drift errors - 0.11 degrees worst case in pitch and roll, 0.21 degree in yaw
• Harmonic & random errors - 0.03 degrees in pitch and roll, 0.07 degrees in yaw

Predicted orbit accuracy is nominally 30 m (radial), 15 m (cross-track) and 920 m (along-track). Definitive, or in ESA terminology restituted orbit, accuracy is 25 m (radial), 15 m (cross-track) and 60 m (along-track).

Data Collection System:

Data system monitoring is done via an on-board computer with a word length of 16 bits. The payload memory capacity is 20K words max. The payload data exchange is done by an On Board Data Handling (OBDH) type bus. The number of payload users is 8 redundant. Instrument data does not get processed by the on-board computer prior to transmission.

Communication Links:

ERS-1 has two telemetry systems - an S-band (2 kbits/sec) Telemetry, Telecommand and Control (TTC) system for housekeeping purposes and an X-band Instrument Data Handling and Transmission (IDHT) system for the science data. Three data streams are transmitted from the IDHT. The first, a dedicated X-band link, contains the high-rate data from the SAR image mode, with auxiliary data and a copy of the S-band telemetry data, at a total rate of 105 Mbits/sec. The other sensors have their data combined, again with a copy of the S-band data and satellite ephemeris information into a low-rate data channel operating at 1.1 Mbits/sec. This channel is continuously recorded by an on-board tape recorder which is replayed at 13.6 times the original speed over the ground stations to form a second data channel at 15 Mbits/sec. It will share the second X-band link with the live transmission of the combined low-rate data, which constitutes the third data stream.

List of Sensors/Instruments:

Active Microwave Instrumentation (AMI):

AMI combines the functions of a Synthetic Aperture Radar (SAR) and a Wind Scatterometer (WNS). The AMI measures wind fields and wave spectra over the open ocean and records all-weather, fine resolution images over the ocean, polar ice, coastal zones and land. The AMI has an image mode (swath) SAR. SAR mode and Wind/Wave mode are mutually exclusive during operation.

Radar Altimeter (RA):

RA provides measurements of altitude, significant wave heights and surface wind speed over the ocean and various parameters over sea ice and ice sheets.

Along Track Scanning Radiometer (ATSR):

ATSR is an experimental four channel infrared radiometer which provides precise and accurate measurements of sea surface temperatures and cloud top temperatures.

Microwave Sounder (MWS):

MWS is a two-channel passive microwave radiometer that provides information on the total precipitable water vapor and the total liquid water content of the atmosphere.

Precise Range and Range-rate Equipment (PRARE):

PRARE is an experimental instrument providing high precision orbit data in support of the altimeter mission. This instrument does not work.

Laser Retroreflector (LR):

LR permits the use of ground based laser ranging to determine precise orbit and calibration information in support of the altimeter mission.

2. Ground Segment Information:

Tracking and Control:

The primary Tracking, Telemetry and Command (TT&C) station is located in Kiruna, Sweden with a backup in Villafranca, Spain. Activities performed include: monitoring and control of all satellite systems and sub-systems, attitude/orbit prediction, determination and orbit/attitude control, operating the ESA S-band network throughout all mission phases and payload performance monitoring for the purposes of mission control.

Data Acquisition and Processing:

Data acquisition and processing covers the following tasks: payload data acquisition at X-band, including playbacks of on-board low bit rate (LBR) recorded data; recording of raw data on High Density Digital Tapes (HDDTs) and routing of data (optical disks and Computer Compatible Tapes (CCTs)) to National Processing and Archive Facilities (PAFs); Fast Delivery (FD) processing of SAR and LBR instrument data; and dissemination of FD products, via land lines and/or satellite links. These functions are performed by the ESA ERS-1 ground station network, the ESA data processing facilities and the national and foreign acquisition facilites located around the world.

Latitude Crossing Times:

The time ERS-1 first crossed the equator (ascending node) for each phase is listed below (in UTC):

• Phase A - 1991:212:20:52:38.283 - Commissioning (3-day repeat)
• Phase B - 1991:362:07:36:18.607 - Ice (3 day repeat)
• Phase C - 1992:093:15:58:38.119 - Multi-Disciplinary (35 day repeat)
• Phase D - 1993:357:17:39:06.043 - Ice (3 day repeat)
• Phase E - 1994:100:17:39:05.093 - Geodetic (168 day repeat)
• Phase F - 1994:271:02:30:56.813 - Geodetic (168 day repeat)
• Phase G - 1995:080:09:01:49.350 - Multi-Disciplinary (35 day repeat)

3. References:

See the European Space Agency's on-line documentation.

4. Glossary of Terms:

See ASF's Glossary for terms related to ASF. See the EOSDIS Glossary for a more general listing of terms related to the Earth Observing System project.

5. List of Acronyms:

This list defines acronyms found within this document. See ASF's Acronym List or the EOSDIS Acronyms List for more.

AMI:

Active Microwave Instrumentation

ASF:

Alaska SAR Facility

ATSR:

Along-Track Scanning Radiometer

CCT:

Computer Compatible Tape

EOSDIS:

Earth Observing System Data and Information System

ERS:

European Remote Sensing satellite

ESA:

European Space Agency

FD:

Fast Delivery

HDDT:

High Density Digital Tape

IDHT:

Instrument Data Handling and Transmission

LBR:

Low Bit Rate

LR:

Laser Reflector

MDA:

McDonnell Detweiler Associates

MWS:

Microwave Sounder

OBDH:

On-Board Data Handling

PAF:

Processing and Archive Facility

PRARE:

Precise Range and Range Rate Experiment

RA:

Radar Altimeter

SAR:

Synthetic Aperture Radar

TTC:

Telemetry, Telecommand and Control

TT&C:

Telemetry, Tracking and Control

UTC:

Coordinated Universal Time

WNS:

Wind Scatterometer