When defining the ‘best’ reinforcement for any application, it should begin at the macroscopic system level while guaranteeing parameter optimization for each key attribute of the system. The following aspects are reviewed by customers who are making purchasing decisions:
- Affordability (best quality at lower cost)
- Heritage/design database (what is the company and product history)
- Structural fit and effectiveness for the application (counting moisture or fluid resistance and hot to wet properties)
- Product forms, resins accessible, and good fit with the reinforcement
- Manufacturability (counting particular capacities an individual customer may possess, for example OOA may be necessary if autoclave is not available or AFP/ATL to reduce labor costs may be mandated)
On top of the mentioned considerations, it’s necessary to drill down deeper to guarantee the ideal choice of material when it comes to satellite payload and launch applications.
The specifics of the application are what dictate the narrowing down of the selection. Materials with very high specific stiffness and strength are necessary due to the unique nature of satellite payloads. They need to be capable of surviving aggressive thermal cycling and resisting microcracking, thermal conductivity, low outgassing, and radiation resistance.
Apart from the two last properties, fiber choice is a leading or strong influencing factor in the choice of fiber. HM and UHM PAN carbon fiber have been strongly preferred by payloads, coming from several suppliers (mainly Toray, with Hexcel and Toho-Teijin contributing significantly) with some UHM pitch used (predominantly from NGF and Mitsubishi).
In addition, the type of structure to be built from the composite, such as busses, reflectors, solar array substrates, optical benches, and booms/tubes/trusses, influences the choice of a specific fiber (and resin).
Down Selection Considerations
Reinforcement (and resin) needs for launcher structures are comparable to those for aircraft structures. These are different from payloads in their overall requirement for resistance to impacts (CAI) and capacity to join structures using mechanical fasteners (OHC/FHC, OHT/FHT).
Final part size and time needed to build the composite structure are also key factors when launcher structures are considered. Out life and tool life are crucial here, as well as resin defined properties, therefore they need to be considered along with the fiber choice to guarantee success.
The choice between a fabric or a uni-directional tape for payloads or launchers tends to boil down to two considerations: the cost related to building up the composite structure and the structural efficiency. These tend to be main trades in the basic material selection. As mentioned, launchers are usually a bit different to satellite payloads in that there is a wish to build up the composite structure as fast as possible, reducing touch labor and maximizing lay-down rate and speed of ply build-up.
However, there is small trade involved. Fabrics are generally slightly costlier for the same weight of a composite placed in a structure, but usually can be applied a minimum of two times the rate of a uni-directional tape. Structures built with a high manual labor content tend to have the price of fabric overshadowed by the savings in labor. Most often, when ATL or AFP machinery is accessible, the lower price per weight of uni-directional prepreg offers a much larger benefit versus a fabric option.
This information has been sourced, reviewed and adapted from materials provided by Toray Advanced Composites - Aerospace.
For more information on this source, please visit Toray Advanced Composites - Aerospace.