Cause for concern

As the third Ariane 5 is prepared for launch, there is anxiety about the programme

Tim Furniss/LONDON

Such is the state of the Ariane 5 programme that the third test flight of the European launcher in July will create as much tension as the first.

The launcher's maiden flight ended 30s after lift-off in June 1996 because of a design error in the attitude control system (ACS) software. The second launch last October, of the 502, suffered excessive roll torque and the subsequent premature shutdown of the Vulcain first stage engine. This would have counted as a partial failure, had it been an operational commercial mission. The 502 delivered its payload into a 520 x 26,848km orbit instead of the planned 576 x 35,830km geostationary transfer orbit (GTO). For the third flight, a second ACS will be fitted to the Ariane 503's vehicle equipment bay, to allow present attitude control performance to be doubled to counteract a roll torque of up to 2,000Nm (Flight International, 25 February-3 March).

Flight 503 is an additional European Space Agency (ESA)-funded demonstration mission scheduled for July, although it is likely to be delayed. A failure would severely embarrass Arianespace, the European commercial launcher organisation which takes over Ariane 5 commercial operations from flight 504.

The 503 will launch the ESA's Aerospatiale Automatic Re-entry Demonstrator vehicle and may carry the Matra Marconi Space Hot Bird 5 satellite for Eutelsat. Eutelsat, which is being offered a discount, has yet to decide, and other prospective clients are talking to Arianespace.

The 503 vehicle was originally one of 14 ordered by Arianespace, but was sold back to the ESA for the additional test flight. Had the original flight schedule been adhered to, the Ariane 5 would have made its maiden flight in 1995 and been handed over to Arianespace in 1996. Technical problems caused several delays.

Arianespace hopes to fly the 504 on the first fully commercial mission at the end of this year. The delays have caused Arianespace to order 20 extra Ariane 4s, extending that launcher's service life to about 2003. The plan is that the Ariane 4 and 5 vehicles will provide commercial services until the Ariane 4 is retired, now five years later than planned originally.

Up to 14 launches a year will be possible by 2000, says Jean-Marie Luton, chairman of Arianespace, eight of them by Ariane 5s, although the Ariane 5 was originally to have completed 13 launches by 2000. There are now 41 Ariane 4s remaining to be launched , in addition to 13 Ariane 5s. Arianespace plans to order 20 more Ariane 5s after a successful 503 flight, followed by 30 more. Luton wants a 50% reduction in production costs from the Aerospatiale-led industrial consortium by 2003.

Even before the Ariane 5 has flown fully commercially, plans for an uprated version are being accelerated so that the vehicle can launch a 7,000kg dual payload into GTO by 2001. "We will have to offer higher performance earlier than planned," Luton says.

ORIGINAL DESIGN

When it was designed in 1984, the Ariane 5 was to be able to place a dual payload of 5,900kg into GTO. Its raison d'etre was that, as communications technology improved, satellites would remain the same size, while becoming more powerful, requiring that two satellites weighing about 3,000kg each could be accommodated.

In fact, the trend is towards much bigger satellites, some weighing over 5,000kg alone, and even up to 7,000kg. This is not reflected yet in Arianespace's 40-plus satellite orderbook which does not include many craft that have to fly on an Ariane 5 because of their size. As a result of this future predicted trend towards bigger satellites, the Ariane 5 may be too small for some customers and too big for others. This is one reason why Arianespace is looking at other markets more earnestly than before, as well as planning to uprate the booster.

Arianespace is looking seriously at the low Earth orbit (LEO) market, which is set to explode. At least 500 satellites may need to be launched into LEO by 2003 for mobile and Internet communications purposes. The GEO market now represents only 30% of launches. "We can no longer allow ourselves to be absent from the LEO market," Luton says. This market has been partly addressed by the Arianespace-led consortium, Starsem, formed to market the Soyuz booster with Russia.

First upgrades to the Ariane 5 will involve small-scale changes to the vehicle, including adding more solid propellant, reducing margins and saving weight. The real upgrade will follow - with the effect of boosting Ariane 5's GTO capability to 8,000kg by 2003 under an ESA-funded programme to upgrade the Sociéte Européenné de Propulsion (SEP) Vulcain first stage cryogenic engine.

The upgraded Vulcain 2 was seen as the major step, but there may be plans to replace the Deutsche Aerospace Aestus second stage with a restartable hypergolic SEP engine, doubling the capacity. If this was ready in time to fly with the Vulcain 2, then a GTO payload capability increase to 9,000kg could be achieved.

A further upgrade to the Ariane 5, replacing the second stage with a restartable liquid oxygen/liquid hydrogen cryogenic engine could increase the GTO capability to 11,000kg by 2007. This stage could be an upgraded version of the HM7B used on the Ariane 4 or be based on a new SEP design. This potential link between Ariane 4 and 5 places into focus the controversial genesis of the Ariane 5 programme.

In 1987, the French-led Ariane 5 was seen first and foremost as a manned launcher to carry the French-led Hermes spaceplane into LEO, with emphasis on brute force first stage power. The commercial considerations seemed secondary. A more logical commercial course may have been to enlarge the capacity of the proven Ariane 4 design - for example, stretched stages and larger strap on boosters, in much the same way as the Atlas, Delta and Titan vehicles have grown. A brand new design for Ariane 5 may well prove to have been the wrong step.

Source: Flight International