Engine or stage?
On Vega—like on Ariane 5—the same name designates the solid-rocket booster stages and their engines: P-80, Z-23 and Z-9. This stems from the booster’s architecture and the way it burns its fuel: the stage and the engine are one and the same.
P-80 first stage
Vega is one of the world’s fastest launchers off the pad in its category, ‘roaring’ from ELA-1 and reaching Mach-1 in just 30 seconds. This feat is made possible by its P-80 solid-booster first stage, developed with CNES oversight starting in 1999.
The ‘P’ stands for poudre (‘solid propellant’ in French), and 80 for the 88 tonnes of fuel it is carrying when Vega lifts off. Between 1999 and 2006, the P-80 programme drew on a CNES initiative originally dubbed ‘Ariane 2010’ aimed at identifying new technologies capable of improving performance—thrust, reliability, vibrations, etc.—while cutting costs, especially in the domain of solid propulsion. The P-80 was developed foremost as the first stage of Vega, but it was also a technology demonstrator. The advances it has accomplished therefore cover all the main elements of a solid-rocket booster:
- Engine casing: made of carbon fibre pre-impregnated with epoxy resin, filament-wound around a metal mandrel with its own internal thermal insulator coating. In 2006 the P-80 became the largest filament-wound monolithic engine ever built.
- Thermal insulation: this consists of an innovative low-density rubber coating reinforced with aramid fibres and glass microspheres.
- Solid propellant: the engine’s performance is enhanced by the density of the fuel, which is the result of a new mixture richer in aluminium than for Ariane 5.
- Nozzle: thanks to a new and simplified architecture, the nozzle and its attachment system are less costly, involve fewer parts and use more-innovative materials than the technologies developed in the 1990s for Ariane 5.
- Igniter: like the nozzle, the system has been simplified with respect to the solid-booster technologies available for Ariane 5.
- Nozzle activation: an electro-mechanical system—rather than a heavier and more-complex hydraulic system—controls the nozzle and applies commands from the flight computer on the AVUM stage. The nozzle can be gimballed 6.5 degrees.
The empty weight of the P-80 before fuelling is just 8.55 tonnes. It is 11 metres long and 3 metres across. It was tested for the first time in Kourou in 2006.
Ignition of the P-80 marks lift-off: the stage is designed to operate for 107 seconds, generating 3,000 kN of vacuum thrust, after which it is separated from the Z-23 second stage by a pyrotechnic charge and 6 small retrothrusters to keep it clear of the launcher.
Z-23 second stage
As soon as the P-80 separates from the launcher at an altitude of over 55 km and a speed of about 2,000 m/s, the Z-23 second solid-booster stage kicks in. The Z stands for zefiro (‘wind’ in Italian) and 23 designates the mass of fuel at lift-off. The Z-23 is shorter than the first stage (8.4 m) and above all sleeker (1.9 m across), giving Vega its unique profile on the launch pad. While the Z-23 may be smaller, with 1,100 kN of thrust it still packs plenty of punch to boost Vega out of the atmosphere before it cuts off at an altitude of over 140 km after reaching a speed of around 3.9 km/s.
Avio S.p.a has overseen development of the Z-23 since 2000. The engine uses the same solid propellant as the P-80 and is filament-wound with carbon fibres impregnated with epoxy resin. The Z-23 underwent its qualification test firing in Sardinia on 27 March 2008.
The Z-23 burns for 71.6 seconds and is also controlled by the flight computer on the AVUM stage. It is separated from the launcher by a spring and pyrotechnic cutter system.
Z-9 third stage
The Z-9 fires at an altitude of over 150 km, a few seconds after separation of the Z-23 stage and a few seconds before Vega’s fairing is jettisoned. It employs the same HTPB solid-propellant technology as the lower stages, only is not quite as powerful. The Z-9 carries 10.5 tonnes of fuel and burns for 117 seconds, generating a maximum thrust of 313 kN. The stage takes the AVUM/payload composite to near-orbital velocity, falling away after boosting it to 7.5 km/s.
The Z-9 has the same 2000s development heritage as the Z-23 stage. It was hot-fired for the first time in 2005 by Avio S.p.a. The Z-9 is 1.9 m across and 3.9 m long, and is assembled at Avio’s facility in Colleferro, Italy. The Z-9 is separated from the upper stage by an electromechanical spring system that dispenses with the need for pyrotechnic devices. The interstage includes a dual system of separate antennas to ensure the launcher range-safety auto-destruct command is received in the event of an anomaly, as well as a radar transponder to track its trajectory from the ground.
AVUM fourth stage
Vega’s fourth or upper stage is designated AVUM, for Attitude and Vernier Upper Module. It comprises a propulsion system, avionics and the flight computer that controls the three lower stages to achieve the trajectory specified in the flight plan.
The AAM (AVUM Avionics Module) controls the launcher during its flight, processes telemetry data, distributes electrical power and manages thermal control and the range-safety system. All of these processes are automated and only the auto-destruct system is engaged manually from the ground.
The stage’s main MEA engine—an upgrade of the Russian RD-869 engine—is built by Ukrainian firm KB Yuzhnohe. It runs on UDMH-nitrogen peroxide liquid propellant stored in four spherical 142-litre tanks and can be restarted 5 times (thrust: 2.45 kN). Six small hypergolic thrusters fed from a central 40-l nitrogen gas tank are also used to control the stage’s attitude.
Depending on the mission profile, AVUM fires one last time once the payload has been successfully deployed, and then de-orbits or is injected into a ‘graveyard’ orbit from where it will re-enter the atmosphere after 25 years.
Vega’s fairing gives the launcher an aerodynamic profile and protects its payload, notably from the effects of atmospheric drag. It is jettisoned by pyrotechnic devices once the upper composites are outside the atmosphere, in the first seconds after the Z-9 stage fires. The fairing consists of two symmetrical half-shells, is 2.6 m across at its widest point and 7.88 m long, and has an aluminium honeycomb and carbon fibre reinforced polymer (CFRP) sandwich structure and cork thermal shielding.
Vega has a range of adapters for different payloads. For single-satellite launches, customers can choose between the PLA 937 VG or PLA 1194 VG adapters, depending on the kind of coupling architecture they require. Payload separation is achieved by a clamp-band system and four mechanical springs.
For dual-payload launches, Vega’s VESPA (Vega Secondary Payload Adapter) system is capable of accommodating the first satellite (maximum 1 tonne) in the top position and the second smaller and lighter satellite (maximum 600 kg) in the lower position underneath, where there is also room for 6 nanosatellites.