Instrument activation is due to be completed by 22 March aboard Europe's biggest-ever observation satellite

The European Space Agency (ESA) is activating instruments on board its Envisat environmental satellite after the spacecraft's launch on 1 March by an Ariane 5 booster. Envisat's synthetic aperture radar has been switched on, with the other nine instruments due to follow by 22 March.

The Astrium-built satellite will not be fully operational until early 2003, however, by which time all the instruments will have been checked. The instrument suite will study the Earth's climate, cryosphere, ecosystem, the El Niño current, energy balance, fossil-fuel and greenhouse effects, halocarbons, infrared radiation, ozone, the stratosphere and troposphere.

The 25m- (82ft) high, 8.2t Envisat polar platform is the largest and heaviest satellite built in Europe and the largest civilian Earth observation satellite developed outside Russia.

The placing of Envisat into near-polar orbit by its Ariane 5 launcher was so precise that only minor adjustments have to be made by the satellite as it heads for its final position in an 800km (500 mile) sun-synchronous orbit, says ESA. Only 10kg (22lb) of the propellants from the reserve of the spacecraft's 319kg load will be required, the agency adds.

The launch was also a successful demonstration of the Aestus upper- stage engine after modifications following its failure last July when it stranded two satellites in low orbit. Flight V145, with the Ariane 5 featuring a new 17m-long payload fairing, was the first of the launcher model to place a satellite into sun-synchronous orbit.

Four more Ariane 5 flights are scheduled this year, including the maiden flight of the Ariane 5ECA with the ESC-A upper stage. This will increase dual-payload geostationary transfer orbit (GTO) capability to 10,000kg, from 6,000kg. A cryogenic ESC-B stage, called Vinci, is also under development, and will provide a dual-satellite GTO launch payload of 11,000kg.

The 5E/S-ESV version will have an uprated Vulcain 2 cryogenic first stage engine and the Aestus engine, providing 7,100kg GTO capability.



Source: Flight International