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VEGA - RACS

VEGA Small Launcher - RACS

Hydrazine Roll and Reaction Control System (RACS)

Exploded view of AVUM 4th Stage

Since 1998, the Italian Space Agency and the European Space Agency have been developing the 'Vega' small expendable launcher. Named after the second brightest star in the northern hemisphere, the first launch of Vega is planned for 2007, from Europe's Spaceport in French Guiana. The Vega Launch Zone is being built on the old ELA1 zone that was previously used for Ariane-1.

Vega is tailored for the three satellite categories:
Micro-satellites : up to 300 kg
Mini-satellites : from 300 to 1000 kg
Small satellites : from 1000 to 2000 kg

The four stages of VEGA comprise:
1st Stage: P80 solid rocket motor
2nd Stage: Zefiro 23 solid rocket motor
3rd Stage: Zefiro 9 solid rocket motor
4th Stage: Bipropellant Attitude and Vernier Module (AVUM)

Based on a reference performance of 1500 kg into a 700 km-altitude polar orbit, Vega is ideally sized for economically placing up to 2000 kg into the polar and low-Earth orbits used for many scientific and Earth observation missions. Unlike most small launchers, Vega will be able to place multiple payloads into orbit.

Cost, reliability and availability is optimised by using advanced low-cost technologies, use of existing Ariane production facilities and flight qualified hardware, the availability of an existing launch zone, its surrounding infrastructure and facilities, and by introducing an optimised synergy with existing production facilities used for Ariane launchers.

ESA Vega brochure

Roll and Attitude Control System (RACS)

The hydrazine RACS is mounted to the AVUM 4th stage and is designed to fulfil the following functions:

An important technical challenge is for the RACS to be able to provide the high thrust necessary for launcher roll control, yet provide very low minimum impulse bits to the AVUM for final payload pointing before separation. Moreover, to assure reliability, a simple RACS system is required. Fortunately, such a system has already been space qualified, and proven to be 100% reliable on all Ariane 5 launches to date.

As with Ariane 5, the multi-role functions of VEGA's RACS are simply achieved by using a hydrazine bladder tank in blow-down mode, feeding clusters of thrusters mounted to the AVUM. Unlike the Ariane 5 ACS, which may use two to four bladder tanks and 2 modules of three or four thrusters, depending on the mission; VEGA requires just one bladder tank and two thruster clusters.

VEGA Roll and Attitude Control System Schematic

RACS Cost, Reliability and Availability
To assure that VEGA RACS has the highest possible reliability at low cost, maximum use is made of existing hardware derived from the Ariane 5 ACS. Reliability is further assured since the hydrazine thrusters and components selected are also space proven on numerous satellites and spacecraft - as well as on Ariane 5. The existing production also assures readily available hardware whilst minimising delta qualification for VEGA.

Multi-Role Modular RACS

RACS Layout within AVUM showing external Thruster Clusters

Thruster Cluster beneath Aerothermal Cover		Thruster Cluster Assembly

Thruster Cluster Feedthrough

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