Tim Furniss/LONDON

The lift-off of the second Ariane 5 has been put back from the end of September, possibly to November, but the 100th Ariane launch was completed from the Guiana Space Centre, Kourou, in French Guiana on 24 September,

The Ariane 502 development flight from the ELA 3 launch pad is viewed as the most critical launch in the history of Europe's space programme following the failure of the first test flight in June 1996.

Although a launcher countdown demonstration test has been completed successfully, the European Space Agency (ESA) has abandoned the September date so that it can spend more time analysing the launcher's "dynamic behaviour".

Flight data received from the 501 launcher before it was destroyed indicated instabilities in lateral-acceleration loads, which are thought to have been caused by a higher-than-predicted amount of gimballing of the Vulcain cryogenic first-stage main engine, resulting in a greater use of lubricating oil for the engine actuators.

Computer simulations indicated that the oil might could be exhausted before the Vulcain completes its planned 580s consumption if this rate of gimballing re-occurs.

The problem may be the result of a computer glitch which, if corrected, may allow the launch to take place as early as 15 October.

A delay to November will result if ESA decides to add "electronic filters" to the vehicle's control system to limit gimballing to the amount that is necessary without compromising vehicle performance and safety.

The discovery of higher acceleration loads led to concerns about the way in which the original 502 payload complement was mounted in the payload shroud and caused ESA to drop the German amateur-radio satellite, the Amsat, from the flight because it was not designed to cope with the new, ultra-conservative rise in lateral launch loads from 2.5g to 5.8g.

The 502 will now carry the two original load-measuring payloads (called Maqsats) and a student satellite (called the Teamsat) into geostationary transfer orbit (GTO) on a demonstration of a typical commercial launch. The larger Maqsat will also be placed into GTO.

The Ariane 5 commercial user manual does not include these new loads, which ESA says are being applied strictly for the 502 mission as an "-ultra-cautious margin and will have no influence on Ariane 5 commercial flights".

ESA, which is funding the planned 503 final development mission in March 1998, is still looking for a commercial customer willing to fly the booster as a cut-price alternative to a fully commercial, operational Arianespace- controlled launch. The agency needs to sell the 503 launch to meet its Ariane 5 budget.

While ESA struggles to get the Ariane 5 programme successfully launched, the Arianespace V100/ Ariane 42L booster has carried the Intelsat 803 communications satellite into GTO - the 100th flight since the first Ariane was launched in December 1978.

Various Ariane versions have carried 180 satellites into orbit, with 43 more on the orderbook.

Source: Flight International