How Composites and Prepregs Figure Into Launch Vehicle Design

Getting a space vehicle off the ground is no easy task. And of course, it needs to be done before that vehicle breaks through the atmosphere and goes into orbit. It is done with launch vehicles. Here at Axiom Materials, we know that launch vehicle design and manufacturing is heavily reliant on composite prepregs.

Both composites and prepregs play a vital role in aerospace design. Combine the two and you are looking at applications that would be more difficult with dry composites requiring manual resin application.

For the record, a prepreg is a composite that comes from the factory already saturated with resin. Prepregs merely need to be laid out and cured. Their big advantage over traditional composites is even distribution of the resin. You get a higher quality finished product, which is critical to designing and building launch vehicles.

Where Prepregs Are Used

Prepregs are used for specific applications in launch vehicle design. They are ideal for primary structures due to their strength to weight ratios. On average, a carbon fiber reinforced polymer (CFRP) is stronger than traditional aluminum but with a 20-25% weight reduction.

Prepregs are deployed to build payload adapters, which are large scale composite structures designed for the next generation of launch vehicles that will carry all sorts of payloads into orbit. We also see prepregs being deployed in fairings, fairing jaws, and cryotanks.

All such applications have two things in common: weight savings and performance improvements. Launch vehicle design must maximize performance in order to make space travel financially worthwhile. And one of the best ways to keep customers happy is to give them high-performance vehicles that improve the bottom line with lower weight that saves fuel and increases capacity.

Prepregs and Manufacturing Processes

As previously mentioned, manufacturing with composite prepregs is a bit different compared to traditional composite layups. Manufacturers tend to rely on advanced techniques to create the complex composite structures necessary for launch vehicles. Here are three such processes:

• AFP – Also known as automated fiber placement, AFP combines advanced automation with traditional layup principles to build large composite structures with both speed and precision. AFP can make comparatively quick work of most launch vehicle components.
• OOA – OOA (out-of-autoclave) processing allows for cost-effective fabrication of larger common lightweight structures for which low void content is required. It is more time-consuming than AFP, but it is an exceptionally reliable process.
• Filament Winding – Filament winding is not normally the first thing that comes to mind when launch vehicle design comes up. Nonetheless, it is a reliable technique for building spherical and cylindrical structures. Think feel tanks and motor casings.

Regardless of the manufacturing process, composite prepregs speed up manufacturing in addition to improving overall quality. Having composites already saturated with resin removes a very time-consuming step.

They Have Their Challenges

Composite prepregs offer enough advantages that engineers are happy to utilize them in launch vehicle manufacturing. But prepregs do have their challenges. First and foremost is limited shelf life.

By virtue of being saturated with resin, a prepreg has partially cured when taken out of its packaging. Layup must be completed in a timely manner. Not only that, even unopened prepregs will not last forever on the shelf.

By contrast, dry composites have a virtually unlimited shelf life. Fabricators can also take a bit more time on layups because they are applying resin as they go. That makes dry composites more forgiving.

Regardless of the challenges, composite prepregs are a preferred option for launch vehicle design and manufacturing. Their offerings are extensive, surpassing those of dry composites in several key areas.