Figure 1. Ariane-5 on the launch pad
Ariane-5's solid-rocket boosters are designed for high reliability and minimum cost. Already during the preliminary design stage, the possibility of recovering the boosters after flight was therefore considered to be of great interest for meeting both of these goals. To ensure enhanced reliability during the entire production phase, there will be stringent post- flight inspection of the spent boosters. The possibility of refurbishing and reusing the recovered boosters has, however, been rejected. It is currently considered a non-cost-effective option because of the specific design and reliability complications that this would incur. It is currently planned to recover four boosters per year.
The Ariane-5 heavy-lift vehicle currently under development is the successor to the Ariane-4 generation of launchers. Specific Ariane-5 design goals are:
Ariane-5 is being developed under the auspices of ESA, which has entrusted the prime contractorship for the programme to the French National Space Agency (CNES).
For the first two minutes of Ariane-5 flight, propulsion will be provided mainly by two large solid boosters (EAPs), assisted by the cryogenic main stage, which forms the lower composite of the launcher. The upper composite includes the Vehicle Equipment Bay (VEB), a storable-liquid-propellant stage, a fairing, and a dual-launch Ariane support structure (SPELTRA) and adapters (Fig. 1). Payloads are housed under the fairing and in the case of a dual launch within the SPELTRA.
Figure 1. Ariane-5 on the launch pad
The twin solid boosters have been designed and developed by:
The EAP stage (Fig. 2) consists of:
Figure 2. One of the Ariane-5 boosters
The total mass of the EAP stage is 277 tons at lift-off, decreasing to 40 tons at the end of a two-minute burn. The boosters are then separated from the main stage and are ready to enter their recovery phase.
Moscow's Scientific Research Institute for Parachute Construction (SRIPC), which has much experience in recovery systems, has been helping with the development of the Ariane-5 booster recovery system. SRIPC has been involved in all Soviet manned space recovery systems, including that for the Soyuz capsules.
One of the challenges in developing the Ariane-5 Booster Recovery System (BRS) has been that of working with a variety of such organisations with different technical and managerial methods. The excellent cooperation that has been established between the different organisations involved, coupled with the extensive ground testing and simulation that have been conducted have contributed to the present high degree of confidence in the system that has been developed.
Fokker Space and Systems has been responsible for the BRS system studies and hardware development management. SRIPC and Spain's Confecciones Industriales Madrilenas (CIMSA), in the form of Union Temporal de Empresas (UTE), develops, qualifies and produces the BRS parachutes, canister and the control box, including the altitude-determination system.
For the nose-cone release system, the pyrotechnic pistons are developed by Aérospatiale (F) and the pyrotechnic chain by Dassault (F) as an Aérospatiale sub-contractor.
The maritime segment is designed by the German company Harms- Bergung and the maritime operations in French Guiana will be managed by CNES.
The reduction in launcher payload capacity due to the inclusion of the Booster Recovery System (BRS) is small, and the system can be omitted when necessary for launch performance reasons.
All BRS elements are housed in the booster's front skirt. The BRS is equipped with its own power supply and control system and has limited electrical connections to the stage. The control system maintains the BRS in a 'dormant state' during Ariane's ascent phase and for up to 10 seconds after EAP separation. This ensures that there is no possibility of accidental operation of the parachute chain and no electrical interference with the launcher systems.
Before splashdown, the EAP stage is decelerated to a speed of 27 m/s and reoriented into a vertical nozzle-down position with a 10 degrees maximum impact angle. A four-stage parachute system is used, which includes an auxiliary parachute, a cluster of three drogue parachutes, a main parachute, and an additional chute to limit the speed increase during the main parachute's deployment (Fig. 3 and Table 1).
Figure 3. Schematic of the Booster Recovery System's operation.
The main events (1-10) are listed in Table 1
Altitude Events (referenced to Fig. 3) Initiated by
0 Launch phase (1) +/- 10 km Removal of first safety barrier in control system Pressure (switching of baro relay) (1) 59 km Booster separation from central stage (2) Electrical signal Removal of second safety barrier in control system. Supplied by booster Arming of safety device (BSA). 150 km Culmination of ballistic phase (3) 8.5-27 km Removal of third safety barrier in control system Pressure (switching of baro relay), initiation of Altitude Determination System (ADS) (3) 4.8-5.2 km Ignition of nose-cone release expandable tube (4) Altitute from ADS Ignition of nose-cone separation pistons Time delay from ADS Separation of nose cone Separation piston force + aerodynamic force Release and deployment of auxiliary parachute Noise cone movement Release and deployment of drogue parachutes Auxiliary parachute force De-reefing of three drogue parachutes, Built-in cable cutters in four steps (5) with pyrotechnic delay 1320-2770 m Activation of drogue strap release pyros and release Time delay from ADS of drogue parachutes (6) Release and deployment of additional parachute (7 & 8) Drogue parachute force 1200-2640 m Release and deployment of main parachute (7 & 8) Drogue parachute force De-reefing of main parachute, in four in steps (9) Built-in cable cutters with pyrotechnuc delay 0 Splashdown at v < 27 m/s (10)
These six parachutes are packed in separate bags , compressed to reduce volume, and housed in the parachute canister. The auxiliary parachute is linked to the nose cone by a 15-metre strap. The drogue parachute is connected to the booster via a removable anchor bracket. The main and additional parachutes are connected to the booster skirt via a fixed anchor bracket. All of these elements, including the moving parts of the anchor brackets, are delivered in kit form ready for use.
The canister (Fig. 4a and Fig. 4b) is made up of welded aluminium skin panels with a beam-reinforced bottom and four connection brackets to the first ring frame at the top section. Four struts located in the middle of the shell and connected to the third ring frame prevent any lateral motion under the 18 g maximum ascent and re-entry flight loadings.
Figure 4a.
Figure 4b. The parachute canister
Both anchor brackets for the drogue and main parachutes are made of titanium alloy to save weight, but must be strong enough to transfer shock loadings of up to 132 tons at parachute opening.
The nose-cone release system (Fig. 5) uses an expandable tube to break the connection ring to the cone and prevent any fragment generation towards the parachute pack. The cone is jettisoned at 27 m/s with the help of four pyrotechnic pistons installed on the first ring frame of the booster. These pistons and the tube are activated simultaneously by a pyrotechnic chain. The pyro command is generated by the control system and secured by a safe-and-arm device (BSA). The safe position is maintained until the end of the ascent flight to avoid any risk of premature separation.
Figure 5. The booster's nose cone
The control system consists of a control box (Fig. 6b), an altitude determination system (ADS), and a power supply. The three sub- systems are fully redundant to ensure a high degree of reliability. Power is supplied by two nickel-cadmium batteries. The control box is activated just before booster separation by a command from the on-board computer.
Figure 6a. The control system and its layout
Figure 6b. The control box
The parachute system is integrated into the skirt during the booster's final assembly in Kourou, French Guiana. This operation is carried out using a special jig to give the parachute system the necessary 12 degrees inclination in the skirt (Fig. 7). Two removable guide rails prevent any contact between the parachute system and the booster during installation, and align the positions of the threaded holes for connection. The two brackets of the drogue and main parachutes are connected with their counterparts on the top ring. Once the pyrotechnic chains have been connected, the nose cone closes the front skirt of the booster.
Figure 7. Integration of the parachute system into the skirt
Qualification testing of the parachute chain has included three release tests from a helicopter with a mass of 5 tons for the qualification of the drogue parachute, and five release tests from aircraft with a mass representative of the booster for the qualification of the overall parachute chain (Fig. 8). A failure during one of the drop tests led to a redesigning of the main parachutes, which were subsequently successfully requalified.
Figure 8. One of the parachute release tests
The canister and control box have also been flight-qualified and all tests have been successfully completed.
The nose-cone separation static test has already been completed and the dynamic test respecting the real dynamic pressure conditions is presently being prepared in Russia.
Qualification of all pyrotechnic devices, including safety testing (e.g. ignition of reefing cutter in folded parachute pack) has also already been completed.
The two boosters will fall back into the Atlantic Ocean approximately 500 km down range of the Kourou launch site. Impact will occur nozzle-first, with the main and supporting parachutes remaining attached to the booster's front skirt. After impact, the booster will stabilise in a vertical position with about 10 m of it above the water.
A specially equipped vessel will be waiting, approximately 8 km from the expected splash-down point, to tow the two boosters to Kourou harbour, to be dismantled ready for post-flight examination, first in Guiana and later in Europe. To facilitate the search process, both boosters will be equipped with Sarsat localisation and homing beacons.
Prior to towing, each booster will be rotated into a horizontal position using a special inflatable buoy installed in the booster's nozzle by divers. Air will then be injected to expel the water from the motor. The total recovery operation, including towing back to Kourou harbour, is expected to take about 80 hours.
All booster recovery qualification tests have been completed apart from two nose-cone separation tests. The flight-model boosters for the first launch of Ariane-5 (V501), presently expected to take place in April 1996, have already been delivered to the Kourou launch site.
ESA Bulletin Nr. 85.