Tim Furniss/LONDON
The European Space Agency (ESA) has confirmed that roughness inside the first stage engine nozzle was to blame for the roll that endangered the success of the second Ariane 5 launch in October 1997. A solution is in prospect as Arianespace prepares the launcher for fully commercial flights.
ESA looked at two potential causes for the 900Nm (Newton metre) torque roll experienced with the firing of the Ariane 502's Vulcain first stage. One possibility focused on a mechanical breakage, but ESA now believes that the problem lay with "roughness" of the internal surface of the Vulcain nozzle, causing the boundary layer of the main exhaust plume to spiral.
Although ESA has not given full details, the "roughness" is thought to involve the surface configuration of the coolant pipes that spiral around the interior of the nozzle,
An additional attitude control unit is already planned for the Ariane 503 mission, the third and final ESA funded demonstration flight, to obtain inflight confirmation of the roll problem. Asolution is also proposed to counteract the roll by a slight repositioning of the two turbine exhaust ducts that run down either side of the nozzle.
The Ariane 503, which will fly with the Aerospatiale-built Automatic Re-entry Demonstrator capsule, should be ready to launch by July. A commercial payload still needs to be found, which makes a September launch date more likely.
European commercial launcher organisation Arianespace has ruled out flying without such a payload, and is still committed to the target of launching a fully commercial Ariane 504 flight by year-end.
Talks are known to have taken place with Eutelsat, the European communications satellite organisation, on flying the Matra Marconi Space built Hot Bird 3, or an Aerospatiale Eutelsat W24 on 503.
Under an agreement with ESA, in which one of the Ariane 5s ordered by Arianespace was transferred to the 503 mission, Arianespace will pay ESA about $35 million of the commercial launch fee.
Only two of more than 40 craft on Arianespace's orderbook - the ESA Envisat and X Ray Multi Mirror telescope - are too heavy to be carried on the Ariane 4.
Source: Flight International
