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StatusOngoing
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Status date2014-08-04
Objectives
The approach was to analysis state-of-the art grounding methods and new developed grounding methods and to compare the hole grounding path from the single MLI layers to the S/C interface. Beside the pure technical point of conductivity also other points like mass, flexibility, manufacturability and costs have been considered.
The goal of this study was to develop an improved MLI electrical bonding method, with a separate view on 3 different sections of the grounding path:
a) Connection of conductive MLI surfaces to MLI blanket bonding points
b) Related electrical bonding connection to the spacecraft structure
c) Connection between the MLI bonding point and the structure bonding point
Requirements for Function & Performance, Environment, Physic & Resource and General requirements have had to be taken into account.
Challenges
N/A
Benefits
With the selected grounding method and routing methods (depending on structure material and temperature) MLI blankets can be easily removed. An indirect BL connecting between blanket and provides high flexibility for handling with MLI blankets during test campaigns or for late S/C is given.
The benefits shortly summarized:
- No grounding interface management with MLI supplier.
- Simpler structure panel design.
- Late design freeze of structure panels.
- Structure panel simplification (no grounding inserts) and therefore less manufacturing effort.
This leads to significant less engineering, design, management and manufacturing costs on panel / S/C side especially for higher levels
Features
The selected grounding method and routing methods are a combination of well-known materials, products and methods in the space industry with slight adaptions.
The grounding is ensured through a rivet via Stand-off and e.g. a conductive tape directly to the structure or to a given grounding area. The deleted grounding via wire to a grounding insert is the main benefit.
Trade-offs performed for different, tested MLI grounding methods have led to the selection of a Multi-Layer-Insulation Bonding Point, which combines the extensive heritage of the State of the Art washer grounding method with a newly introduced grommet or hollow rivet.
After further properties comparison between the grommet and a hollow rivet the aluminium rivet has been selected for any further testing. The reasons for this selection have been
- the same manufacturing effort
- overall a lower el. resistance (Rivet to layer)
- a lower magnetic moment due to the rivet
- consists of standardized parts (with different lengths if needed for thick lay-ups)
- standardized, low cost riveting tools are available.
This properties result in lower manufacturing costs and a better electrical and electro-magnetic performance.
For structure grounding 4 different methods have been detected which all guarantee a reliable sufficient grounding.
These methods are via Chofoil, metallic foil & conductive tape, metallic foil & screw, as well as via electrically conductive, acrylic Adhesive. Also a combination of different grounding methods including the State of the Art method via Bonding Lead is possible.
For a selection for a specific grounding the surface temperature, the surface material and the given requirements need to be taken into account.
Plan
Within 2 Phases several State of the Art and new innovative grounding methods have been tested and assessed. To receive an objective view on the complete grounding path each of the following sections have been tested and assessed separately - MLI grounding point (between each layer), on the routing, between MLI and S/C I/F point, as well as the S/C I/F point itself (structure grounding).
5 different MLI grounding points have been taken into account with 7 different connectors and 2 different fixation methods to the S/C.
Current status
N/A