Testing and integration

Testing

During mixing and casting, an 80 kg sample of mixture is extracted from each mixing vat.  These samples undergo various tests:

 

·         Chemical testing in a laboratory,

 

·         Test firing on the 'Baria' specimen blocks (these are like miniature segments loaded with 7 kg of propellant),

 

·         Specific sample testing to determine the mechanical resistance of the propellant and adhesives.

 

Once the segments have been weighed, they are then subjected to non-destructive testing.  Each one is examined by X-ray to verify the combined mass of the segment and its adhesives.  These tests are designed to detect any discontinuity in the propellant, as the combustion rate is dependent on continuity.  When all the tests have been completed, the segments are stored in a dedicated area then delivered to Europropulsion as required.  While this is taking place, Regulus also receives the S1 segment (which is manufactured in Colleferro near Rome) and the igniter.  These parts also undergo X-ray testing to ensure that no alterations have occurred during transportation, before being transferred to the storage area.

 

 

Intégration, assembly and delivery

Europropulsion, a subsidiary of the Italian company Avio and the French company Snecma (part of the Safran Group) takes over from Regulus to produce the solid propellant motor (MPS), then the dressed propellant motor (MPE).

 

Europropulsion's task involves assembling the stage's various constituent parts.  All integration and assembly activities take place in the Booster Integration Building (BIP), which is divided into several distinct cells: two for segment preparation, two for integration, one for tilting and one for preparing the pyrotechnic components.  Having two preparation and integration cells enables two stages to be assembled in parallel.  The segments and igniter are delivered by Regulus, whereas the nozzle is shipped directly to Europropulsion from Snecma Propulsion Solide in Haillan, near Bordeaux.
The integration process begins with the S3 segment, the lowest part of the stage, which arrives in reverse flight position (i.e. upside down).  The nozzle is then integrated using a connector which screws onto the segment's base.  After that, the segment is inverted using a special tilting device and the various segment preparation activities get underway.  Initially, these involve attaching the cable ducts and pyrotechnic charges.  This rather precise task requires a special bonding tool with a dual component adhesive.  The bonding must be completed within a limited timeframe due to the adhesive's rapid polymerisation, while also giving due consideration to any geometric constraints.  The Europropulsion engineers must then apply the external thermal protection (also using adhesive), define various operational procedures and integrate the booster structure attachment and release mechanism (DAS), which is used to attach the stage to the launcher.  Once segment S3 has been prepared and transferred to the holding area, Segments S2 and S1 are prepared in parallel in their respective cells.  Like S3, S2 must be inverted to place it in the flight position as soon as it arrives and before preparation activities can begin.  Only S1 is delivered in the flight position.  Preparation of segments S1 and S2 then commences with the bonding of the cable ducts, followed by the definition of operational procedures. 

S1, the 'star' segment Unlike the other two constituent segments of the MPS which have conical cores, the core of the S1 segment is star-shaped.  This unusual shape is due to the higher combustion rate required in this segment, which has to ignite the other two segments. Since the propellant burns in parallel layers, the internal pressure at any time is a result of the shape of the combustion surface.