Experience with the previous versions of Ariane shows that systematic development is vital to ensure the launcher's steady adaptation to evolving user requirements. In the case of Ariane-5, a first evolution of the launcher was sanctioned by the Council Meeting at Ministerial Level in Granada in 1992. Preliminary studies were therefore conducted to establish a basis for the so-called 'Ariane-5 Evolution Programme', followed by an appropriate preparatory programme. The Ariane-5 Evolution Programme was formally accepted at the next Council Meeting at Ministerial Level, in Toulouse last October.
To consolidate its success, Ariane must be continually adapted to the demands of the commercial market. As that market consists mainly of communication satellites, it is the trend in the mass of those satellites that will determine the future performance requirements for the launcher. The three decisive factors are therefore:
Several industrial studies that have looked at future use of the geostationary orbit (Euroconsult survey for ESA, Arianespace market research, etc.) have confirmed the trend towards heavier satellites. The introduction of new telecommunications services, the longer operational lifetimes of the new generations of satellites (15 to 18 years), and the growth in the number of transponders per spacecraft are all contributing to an across-the-board increase in satellite mass.
By the beginning of the 21st Century, the great majority of telecommunications satellite suppliers are expected to be delivering platforms for launch into GTO with masses of 3500 to 3700kg. Consequently, an increase in performance from 5970 to 7400kg in GTO is the primary objective of the Ariane-5 Evolution Programme.
This increased performance to GTO implies a corresponding increase in launch capability for other orbits. In this context, Europe has already confirmed Ariane-5's role for low Earth transfer orbit missions to the International Space Station.
The Ariane-5E launcher is a close derivative of the initial Ariane-5 and retains the same general architecture:
The main configurations are designed for:
The Ariane Evolution Programme involves the further development of several key elements of the launcher, as outlined below.
The cryogenic main stage of the Ariane-5E launcher is powered by a Vulcain-2 engine, the thrust of which is raised to 1350kN and which carries 172t of propellant.
Figure 1. Modification to cryogenic main stage
The cryogenic main stage
The external dimensions of the stage are the same as for Ariane-5, with a height of 30m and a diameter of 5.4m. Its main elements are:
Figure 2. Modified cryogenic main stage
Equipped insulated tank
The Ariane-5E equipped insulated tank is characterised by a lowering of the common bulkhead by about 65cm compared with the current design. This results in a 65cm lengthening of the upper cylindrical section of the oxygen tank and a corresponding shortening of the first cylindrical section of the hydrogen tank.
A 16t increase in oxygen mass compared with Ariane-5 makes it necessary to reinforce the common bulkhead, the lower cylindrical section of the oxygen tank, and the two upper cylindrical sections of the hydrogen tank.
The oxygen feed line will also be shortened, but its diameter will remain unchanged despite a 23% increase in the oxygen flow rate. The oxygen tank pressure will be raised by 0.5bar to ensure a satisfactory supply to the Vulcain engine.
The hydrogen feed line and the other items forming part of the equipped insulated tank are compatible in principle with the propellant mass and thrust specified for the modified stage.
Simplified forming of the tank domes, by reducing the number of panels or the adoption of a spin-forming technique to allow single-piece manufacture, is currently under evaluation. Simplified welding and inspection procedures relying on increased automation are also foreseen. These two improvements should allow production costs for the cryogenic main stage to be reduced.
Thrust-frame, forward and aft skirts
Only the thrust-frame may have to be reinforced in view of the increase in Vulcain engine thrust. No changes are required to the other structures.
The pressurisation unit must be capable of pressurising a larger oxygen tank. The helium pressurisation system specified for Ariane-5 should be able to meet this increase in demand by using the existing margins, with no significant changes or redevelopment.
Electrical and pyrotechnic systems
The main effort with regard to the electrical systems will be on improvements aimed at reducing launcher production costs. One such action involves the bringing together of the electrical equipment common to the cryogenic main stage and the Vehicle Equipment Bay (VEB) (see later).
The Vulcain-2 engine
The increase in engine thrust from the current 1145 to 1350kN is to be achieved mainly by stepping up the oxygen flow rate. The mixture ratio (between oxygen and hydrogen flow rates) is increased from 5:3 to 6:2.
The most important subsystems to undergo changes are the oxygen turbopump, which has to pressurise a 23% flow increase, the nozzle extension, and the combustion chamber, which has to accommodate the additional supply and cope with a higher mixture ratio.
The hydrogen turbopump as currently designed can cope with both the slight increase in flow for the enhanced version of the engine, and the pressure increase required to cool the combustion chamber more.
The gas generator must be capable of delivering a 20% increase in power to the turbopumps, which means its output must be increased. Its injector plate will be modified for this purpose.
Figure 3. Improvements to the Vulcain engine
Figure 4. Improvements to the liquid oxygen (LOX) turbopump
The operating values for the modified oxygen turbopump are:
Its main features are:
Dynamic shaft elements
Figure 5. Modifications to the combustion chamber
The operating values for the modified combustion chamber are:
The resulting main characteristics are:
Figure 6. The modified nozzle
It is possible to complement the improvements in the Vulcain engine's direct thrust with improved nozzle design.
The Ariane-5E Vulcain engine nozzle extension is characterised by a significantly higher expansion ratio (up by 30%) and by the reintroduction of exhaust gases from the turbines. The increase in expansion ratio rate is possible thanks to a better understanding of actual demand in the real operating environment of the Vulcain engine. It makes for a significant improvement in gas expansion and hence in engine performance.
The reintroduction of turbine exhaust gases enables:
This new nozzle, tagged the 'advanced divergent', has been the subject of technology demonstration activities prior to its final development.
Figure 7. The re-injection of exhaust gases
The intended enhancement of the cryogenic stage is compatible with the existing ground facilities at the launch site in French Guiana in terms of stage testing and operational implementation. The test stands in Europe used for engine and subsystem testing will, however, have to be adapted to the new Vulcain engine specifications in that:
Figure 8. Welded cylindrical booster sections
The original solid-propellent booster consists of three main segments which are bolted together. The two lower S2 and S3 segments are similar and also composed of bolted cylindrical sections.
The main enhancement to the solid booster stage for Ariane-5E lies in the planned use of an improved technology for joining the cylindrical sections, with the present seals and bolted junctions being replaced by welding. Studies are currently underway to establish the weldability of the metallic material from which the cylindrical sections are made.
This upgrade is expected to provide:
Of the possible ways of easily increasing stage performance with a minimum of development risk, whilst retaining the same stage architecture and reliability, an increase in the propellent mass to 15t has been selected. This in turn leads to an increase in both the size of the four cylindrical/spherical tanks and the height of the launcher's external structure.
The stage architecture will be based on a structure with a diameter of 4.55m, which is between the present diameter of 3.94m and the launcher's external diameter of 5.40m. Consequently, the conical structure of the equipment bay will be shortened and reinforced and its external cylindrical structure will be lengthened.
38kN of thrust will be extracted from the Aestus engine by adding a further row of injectors to the current injector plate and by enlarging the overall dimensions of the engine accordingly. In this way it will be possible to retain the existing injectors and the current chamber pressure, and hence much of the experience acquired with existing hardware (particularly with regard to high-frequency stability) will still be valid.
Figure 9. Modifications to the Engine Propulsion Stage (EPS)
A preliminary analysis suggests that chamber cooling should not be adversely affected by the increase in size.
The pressurisation unit will be modified by incorporating an additional pressurisation bottle and adapting equipment to accommodate the increased engine thrust.
The test facilities in Europe, primarily the engine and stage stands, will need to be adapted to cope with the increased flows required by the 38kN engine.
Vehicle Equipment Bay
The VEB will have to be reinforced and adapted to cope with the increased volume and mass of the storable propellant stage, the exact modifications depending on the stage configuration ultimately chosen.
Various improvements aimed at reducing costs will be made to the VEB, most involving the simplification or grouping together of electrical equipment.
One such possibility is to group the switching units currently located between the equipment bay and the cryogenic main stage. Bringing them together in the equipment bay would allow the number of units, and hence production costs, to be reduced.
Ariane-5 dual-launch system
Figure 10. Modified dual-launch system
The dual-launch system (Sylda-5) proposed for Ariane-5E is a structure entirely within the fairing which can accommodate a satellite with a diameter of 4m in the lower position. This represents ample capability in the short term given currently competing platforms and launchers, and it is still possible to launch satellites with diameters up to 4.57m in the upper position.
The overall height of Sylda-5 is 5.08m. Its estimated mass of between 400 and 500kg (precise figure to be confirmed at the start of Ariane-5E development) represents a saving of at least 350kg compared with the current Speltra. The fact that it is also both simpler and lighter will allow production costs to be reduced significantly.
Estimated performance gains
Table 1 shows the expected performance gains on the basis of studies to date for the Ariane-5E reference mission, namely a launch into Geostationary Transfer Orbit (GTO):
It can be seen that a 1500kg increase in performance can be obtained without the EPS modification, which could be retained for a later upgraded version of Ariane-5E.
Table 1. Ariane-5E performance gains
Increase in lift-capability to GTO
Cryogenic main stage
Solid booster stage
Storable propellant stage
Ground and transport facilities
The integration and launch facilities in Kourou and the transport facilities for the launcher elements, which represented a significant investment for the Ariane-5 programme, can be reused for Ariane-5E without major change.
The launch trajectory will make it necessary to reopen the Libreville telemetry station, which is used for Ariane-4 but was not envisaged to be needed for Ariane-5.
Not only will the Ariane-5E cryogenic main stage have the same external dimensions as the current stage, but all of the interfaces now used for handling, transport, storage and operation will also be retained. Only the Vulcain engine nozzle will call for special checks.
The modifications to the solid boosters will not affect either their transport or the associated ground operations in Kourou.
The only changes to the Vehicle Equipment Bay are those needed to adapt it to the possible modified storable-propellant stage version, which has no influence on the ground facilities.
The Sylda-5 structure will require only relatively minor adaptations as regards the handling of the new structure and the integration of payloads.
Figure 11. Launcher development planning
The aim is to have the Ariane-5 growth version operational in 2003 so as to be able to continue systematically performing dual GTO launches under attractive conditions. The steady evolution in performance needs makes it desirable, in as far as the launcher's design allows, to have a number of 'intermediate' versions available. This will allow the launcher's lift capability to be increased gradually as the growth version is developed. The development of Sylda-5 will allow the GTO lift capability to be increased by around 300kg from the end of 1997, and the remaining gain will be achieved at the end of 2003. Due to the blocking of the modification of the EPS stage, the schedule has been limited to the preliminary design studies.
Development costs will have to be kept as low as possible. Consequently, the development effort has been limited to include only that work strictly necessary for the goals to be achieved efficiently and economically. It is particularly important that we capitalise on the experience gained, in order to ensure that European industry maintains an engineering capability in this field.
Recurrent production/launch costs
The already stiff competition between the various companies offering launch services on the open market is bound to become even tougher. The reduction of launch costs therefore has to be a major objective for the Ariane-5 Evolution Programme.
The Ariane-5 Evolution Programme has been agreed by the Ariane Launcher Programme Board as defined in the Programme Proposal, with the exception of the EPS modification, which has been frozen. The main objective is to achieve an increase of 1400kg in perfomance for the GTO reference mission, and the target date for completion of the programme is 2003. The main modifications are now well-defined and all of the various contractors are already working hard to achieve both of these goals. There is an intermediate milestone in 1997 provided by the availability of Sylda-5, which will already provide a 350kg increase in payload capability to GTO.