This project is devoted to the pre-development of Alphabus Central Tube (@CT), equipment which belongs to the structure subsystem of the Alphabus spacecraft. This pre-development consists in demonstrating through theoretical studies and samples manufacturing that the next spacecraft generation could benefit from new technological or industrial improvements, i.e.:
- Improved Launcher Junction Frame (LJF) design
- LJF to shell junction (without monolithic heel)
- Lay-up with laser projection
- Less stringent surface treatments on inserts
- Risk mitigation on shape defects after curing&
The issues can be divided in design and manufacturing issues:
Main design issues
- choice of the fiber wrt stiffness and mass analyses
- prediction of deformations of the tube after curing
- LJF design evolutions to insure load transfer between LJF and shell (which impact the tube diameter)
- To lower cost, mass and lay-up time of the junction between LJF and shell
Main manufacturing issues
- Feasibility or not to use a less impregnated prepreg technique for M55J to lower porosity in laminates
- Study of an alternative curing process to lower porosity and have better aligned fiber in laminates
- Study of a new method for corner manufacturing
The @ CT belongs to the @BUS primary structure which will provide a performance gap over than +50% compared to the current SPACEBUS 4000 or EUROSTAR 3000 primary structures.
The @BUS platform is expected to support up to 8.5 tons spacecraft launch mass. With regard to the Central Tube, this pre-development will enable improvements and industrialization of existing baseline (Mecabus Central Tube heritage) Several design improvements and manufacturing process evolution will issue an overall enhancement of the performances of the central tube (quality of the product and health of the composite materials).
The global shape of the tube is cylindrical. On its lower part, a ring called "launcher junction frame" (LJF) provides the fitting between the cylinder and the launcher adapter. An intermediate ring called "intermediate frame", on the outside of the @CT provides a base for several I/F. On the upper side, the @CT is connected with the first floor through the First Floor Frame (FFF) .
The interface with launcher is the standard ACU 1666mm as described in ARIANE 5 User's Manual.
According to pre-development results, this baseline could be improved/modified accordingly.
The expected project plan is built in 3 steps as follows:
Phase 1 of this pre-development has been completed with the Technology Evaluation Review held beginning of 2005.
The main results of the Phase 1 studies are:
- A possibility to fix the cylinder shell to the Lower Junction Frame (LJF) with blind bolts is identified to reduce mass and optimize production time.
- The Launcher Junction Frame (LJF) design has been studied, in order to balance the stresses in the inner and outer skins of the sandwich cylinder.
- Shape prediction analyses have been performed to envisage tolerance compliance after cylinder curing.
- Specific layup designs have been identified for optimization of the composite shell geometric tolerances after curing.
- The interest for a method of hand lay-up in combination with laser projected positioning of pre-preg patches, has been investigated.
- The Central Tube preliminary design has been established with EAR / ITAR free materials and suppliers.
- A preliminary concept baseline and production philosophy has been defined. All necessary processes and procedures are established and validated.