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ARIANE 5 QUALIFIED FOR COMMERCIAL OPERATIONS

by Christopher Hess

Ariane 5 is qualified. Frederick Engström, Director for launchers and the Ariane-5Program at the European Space Agency ESA, wanít the only one who said that Ariane Flight 503 had been "a total success". With this third test flight of Ariane 5, a lot was at stake for the European space Industry. A failure would have had far reaching consequences.

During launch preparations the only reported anomaly was a faulty pressure valve in the cryogenic fuel supply system. The valve was replaced without affecting the planned launch. However, the original launch date, 20 October, was postponed by 24 hours, after filling the attitude control systemës hydrazine tanks, took longer than expected. The final countdown was stopped twice for a short time.

On 21t October 1998 at 18:47:21 hrs Flight 503 lifted off from ELA-3 of the European Space Flight Centre in Kourou, French Guyana. The two solid fuel boosters separated after 2 min 23 sec. at an altitude of 62 km. Almost a minute later (at 3:13) the payload fairing separated. After a flight time of twelve minutes and at an altitude of 209 km, 503 launched the re-entry capsule ARD, (Atmospheric Re-entry Demonstrator), which splashed down one hour and forty minutes later, south of Hawaii.

A further three minutes and fourteen seconds after launching the ARD, the engine of the upper stage was started in order to carry a second payload, the MSAQSAT 3 (a satellite mock up) into its geostationary transfer orbit (GTO).

Kayser-Threde, Germany had supplied MAQSAT 3 in only three months after the original payload, Eutelsat W2, was launched with an Ariane 4 Rocket a few weeks prior to 503. MAQSAT 3, which weighs 2,730 kg, had the task of duplicating the mechanical characteristics of W2. It also measures mechanic vibrations, noise and other stress parameters.

After a flight time of 33 minutes 7 seconds, the 503 upper stage engine cut off, and MAQSAT 3 received its release signal. The dummy payload stayed physically attached to the upper stage to minimise the creation of orbital debris.

The current evaluation of real-time telemetric data shows a perfectly nominal flight path for 503. The GTO parameters were well within the target area. Perigee was at 1,027 km, (prediction: 1,028+-3 km), Apogee was at 35,863 km, (prediction: 35,898 +-200 km), and the inclination was 6,999 Degrees, (prediction: 6,998+-0.054 Degrees).

André van Gaver, head of the Ariane Program Office at ESA said three weeks after the flight: îI can say today: Every aspect of the flight went very well.î The only discrepancy is that one of the solid fuel boosters was lost. Both were to be salvaged after the flight to enable analysis of their thermal characteristics.

The cause has not yet been established finally. A malfunction of the parachute system or lose connecting bolts in the centre of the booster are two of the possible causes. It is expected that the on board camera can shed light on the situation. Especially for this flight it had been fixed to the rocketís interface structure.

Measures undertaken to correct roll problems during last yearís Flight 502 were effective. The altered alignment of the turbine exhausts of main stage's Vulcain Engine has reduced the roll torque from 900Nm (502) to a nominal 100Nm. The second attitude control system, which was added to for 503, was not used in the end. It will be added for safety reasons during the next flight (504) but will be omitted in future flights.

The Flight 504 is scheduled for spring 1999, and responsibility for the Ariane-5-rocket will pass from ESA to Arianespace before that. It is planned that during 1999 four Ariane 5s will be launched from Kourou.

From page 40 of FLUG REVUE 1/99