European Space Agency Earth-observing satellite program
This article is about the European satellite program. For the 1960s United States Air Force satellite program also abbreviated ERS, see Environmental Research Satellite §TRS_Mk._1.
ERS-1 carried an array of Earth-observation instruments that gathered information about the Earth (land, water, ice, and atmosphere) using a variety of measurement principles. These included:
SAR (synthetic-aperture radar) operating in C band can detect changes in surface heights with sub-millimeter precision.
WindScatterometer used to calculate information on wind speed and direction.
MWR is a Microwave Radiometer used in measuring atmospheric water, as well as providing a correction for the atmospheric water for the altimeter.
To accurately determine its orbit, the satellite included the PRARE (Precision Range and Range-Rate Equipment) and a laserretroreflector. The PRARE became non-operational shortly after launch; later analysis concluded that the failure was due to a memory latchup caused by radiation.[3] The retroreflector was used for calibrating the radar altimeter to within 10cm.
Mission
ERS-1 had various mission phases using 3-day and 35-day repeat cycles. During the geodetic mission, ERS-1 was put in two long repeat cycles of 168 days, which is equivalent to a single 336-day cycle. The geodetic mission allowed for accurate mapping of the Earth's bathymetry and geoid over the seas using the Radar Altimeter.
On 10 March 2000, ERS-1's attitude control system failed due to a gyroscope malfunction and its mission was officially declared finished.[3]
Its successor, ERS-2, was launched on 21 April 1995, on an Ariane 4, from ESA's Guiana Space Centre near Kourou, French Guiana.[5] Largely identical to ERS-1, it added additional instruments and improved existing instruments including:
When ERS-2 was launched, ERS-1 shared the same orbital plane. This allowed a tandem mission, with ERS-2 passing the same point on the ground 1 day later than ERS-1. ERS-2 has a repeat cycle of 35 days.[4]
ERS-2 operated without gyroscopes from February 2001, resulting in some degradation of the data provided by the instruments. The tape drive aboard failed on 22 June 2003, leaving the instruments operating only within visibility of a ground station. After the tape drive failure additional ground stations were brought online to increase the data gathering abilities of the satellite. The Wind Scatterometer and GOME were the only instruments of their kind until the launches of MetOp-A and Envisat, respectively.
The successor to ERS-2 was the Envisat satellite, launched 1 March 2002. Envisat contained improved versions of many of the instruments onboard ERS-2. However, even after the launch of its successor, the operational life of ERS-2 was extended until 2011, when the decision was made to end the mission. Over a series of burns in July, August and September, ERS-2 was finally depleted of all fuel on 5 September 2011. At 13:16:38 the batteries were switched off and the satellite decommissioned. The spacecraft was left in an orbit where it will reenter the Earth's atmosphere and safely disintegrate within 25 years, in accordance with international standards.[6]
In the final stages of emptying the fuel tanks, it was estimated that they would be empty after a 40-minute burn on 2 September 2011. However, the spacecraft survived both this manoeuvre and a second 40-minute burn on 3 September. On 5 September a third burn was initiated. The fuel tanks were finally drained, and the spacecraft orbit was lowered from 785 to 573km above Earth.[7]
In February 2024, ESA reported that ERS-2 was expected to reenter in an uncontrolled fashion, some time between 16 February and 22 February 2024.[8]
The satellite reentered at 1717 UTC on 21 February, in the Pacific Ocean between Alaska and Hawaii.[9][10]
↑Cuthbertson, Anthony (21 February 2024). "Satellite crash – live: Out-of-control ERS-2 heading for Earth". The Independent. Retrieved 21 February 2024. The European Space Agency has finally confirmed that the two-tonne satellite reentered the Earth's atmosphere somewhere between Alaska and Hawaii.
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ). Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).
Launches are separated by dots ( • ), payloads by commas ( , ), multiple names for the same satellite by slashes ( / ). Crewed flights are underlined. Launch failures are marked with the † sign. Payloads deployed from other spacecraft are (enclosed in parentheses).
