Ariane 5 Returns to Flight With Launch of ESA’s Envisat

An Ariane 5 successfully launched Envisat from Kourou, pad ELA 2 at 0107:59 UTC (5:07 p.m. PST February 28) on March 1. The satellite will monitor changes to Earth’s environment. The Ariane 5 flew a course due north from the Kourou, injecting the satellite into its orbit 27 minutes after launch. Provisional parameters at injection were an altitude of  7,152.4 km for a target of 7,152.4 km (+/- 7.5 km) inclined to the equator at 69.8 degrees for a target of 70.3 degrees (+/- 1.9). The spacecraft will orbit in a sun synchronous orbit at 800 km inclined at 98.54°. This Ariane 5 was the first flight to be equipped with the long payload fairing, measuring 17 meters.

The satellite deployed its 10 meter solar array 59 minutes after launch. In three days the first instrument, the Advanced Synthetic Aperture Radar (ASAR), will be activated. This will be used to take radar images of the Earth's surface. The other nine instruments will be activated over the next 20 days. Envisat will start returning data from the ASAR after two months. Some of the instruments will not begin sending back information until the end of 2002.

Ariane 5 has now launched 11 times, experiencing three failures. The Ariane 5 was grounded after the last August 2001 failure and underwent more than 300 engine test firings prior to its return to service. Analysis determined that the upper stage problem was caused by the presence of water in fuel lines. The water was the result of ground tests by the manufacturer to certify that the plumbing could withstand design pressures.

The US$2.2 billion (EURO 2.3 billion) Envisat will gather information on greenhouse gasses, global warming, the status of the ozone layer as well as monitoring the oceans, Arctic and Antarctic ice melting and rain forests. Three instruments on Envisat will monitor the Earth's surface. One will measure ocean temperature accuracy; another will monitor ocean wave patterns, polar ice and forest cover; and a spectrometer will chart the chemical content of the oceans, including chlorophyll. Another four altimetry instruments will track the spacecraft’s height above surface features. Some will track cloud altitude, others the height of polar ice and ocean waves. The remaining three instruments will monitor the atmosphere. One will monitor the ozone level high in the atmosphere. Another will look at pollutants and other chemicals in the same atmospheric region. The Scanning Imaging Absorption Spectrometer for Atmospheric Chartography, or SCIAMACHY is planned to monitor the carbon dioxide level. The head of the study says, “It's not a foregone conclusion that we can do it.” The spacecraft is designed to operate in sun-synchronous orbit for five years.

The satellite was built for the European Space Agency by a consortium of 50 companies. Astrium was the prime contractor responsible for the production of Envisat. Massing more than 8,111 kg (17,844 lbm), the spacecraft will be positioned at an altitude of 800 km with an inclination of 98.54 degrees, with an orbital period of 100 minutes. For most instruments, the satellite will provide global coverage every three days, with exact revisit coverage every 35 days. Ground equipment for Envisat was built by a consortium of 20 companies led by Alcatel Space.

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