How Blueshift’s technologies are driving innovation across the aerospace and defense sectors
Below is a summary of an article, which was first published by Composites World.
The aerospace and defense industries continue to influence the definition of mobility. After the launch of SpaceX’s first rocket, in 2008, a market dominated by a small number of players began to change. This change continues to drive innovation, especially in the field of electric aircraft and spacecraft. It allows for a combination that is lower-cost but has ever increasing sophistication.
Blueshift is developing technologies that are part of this innovation. In 2020, the company that was founded in 2013 launched its first product commercially: a family thermal protection system (TPS) made up of an aerogel consisting of 85 per cent air and 15 per cent pure polyimide.
The material’s porous structure can prevent thermal energy from leaking into composite structures. The thin profile format (starting with 7.5 mils) makes it easier to apply and allows for the addition of functional layers such as graphite, metals and aluminum.
AeroZero is a proprietary TPS product suite that can be used on various surfaces including carbon fibre composites. It has been proven to work in many applications including rockets and battery and exhaust systems.
TPS based on polyimide aerogel
Blueshift developed its technology after a major electronics company faced overheating problems. Tim Burbey, President at Blueshift refers to the technology the company now commercializes as ‘structured Air’.
He said: “We package air to make it more useful for product designers. It has a polymer network, but is 85 per cent air with nanosized air pockets. We have more than 30 trillion air pockets on what looks like a piece of paper.
“And you have probably heard about silica-based aerogels,” he says, “but this is a completely different product.
“When I mention structured air, it implies a material that has mechanical strength. Silica aerogels are not suitable for environments with high vibrations and do not possess good mechanical strength. The main difference between a polyimide and TPS is the ability to incorporate additional substrates. We can add graphite, aluminum or other materials which ultimately combine into a highly-functional product.”
Structured Air: Why is it necessary?
Burbey says that air is a great insulator. Air is radio frequency (RF) transparent, and this is very important for sensors and communications on aerospace vehicles. Polyimide is a chemically and high-temperature resistant polymer that provides a unique structure to help mitigate multiple thermal transfer situations, including conduction and radiant heat.
Burbey explains: “Our materials help to block the flow of heat/cold regardless of the energy source.”
The combination of polyimide and air creates a skeletal structure that slows thermal energy, limiting its penetration. This also leads to a low thermal diffusivity, meaning that more energy is needed per unit volume to change the temperature of the material. He says that the combination of these properties allows our products to excel during transient thermal events.
He adds: “For us the faster the heat transfer rate and the more extreme temperature regime, the better. Our products can be tailored to deal with conductive energy transfer which creates concentrated hot spots as well as convective transfer. We can use reflective top layers such as VDA Polyimide to absorb radiant energy.”
Modeling and optimization
Blueshift also offers modeling and simulation. Heat mitigation is required for a wide range of applications, with varying conditions and requirements. This includes vehicles that experience high-speed aero-heating from Mach 5 up to Mach 25, or when reentering the atmosphere. It also includes battery thermal runaway, and engine fires. Blueshift uses a combination of materials and custom-tailored solutions to address specific problems.
Burbey says that “modeling and simulation allows us to achieve this.” It depends on what the parts will be exposed to, the type of heating source (radiant versus conductive), and how much space you have in your configuration. Is the material in direct contact or is there a gap between it and something else? It is important to consider the time period and the heat reduction goal.
Burbey points out that Blueshift has a variety of testing capabilities to validate this modeling, including flame tests and material-level thermal analysis. He says that, “more recently, we performed a variety of flame tests in order to simulate thermal runaway for battery applications.” We’ve also had to create materials that can help reduce blasts and molten particles.
Blueshift customizes TPS to meet the needs of each application by stacking and combining layers. Burbey says that “our core technology is called AeroZero.” Blueshift’s stack-ups are multilayer versions of this technology. For example, the TripleZero version is a three layer stack with a thickness of approximately 20 mils (0.5 millimeter). We can tailor the AeroZero, for example by adding graphite to the top — which is a good heat spreader — in our AeroZero TPS Graphite version. The graphite layer distributes heat along XY plane, while the AeroZero layers significantly slows down heat penetration along Z plane.
He continues, “We have many options in superstrates to help us meet other requirements while providing the thermal protection we need.” Our standard commercial products are available in rolls up to 12 inches [305 millimeters] wide, but we plan to expand. We can also cut the materials to 4 millimeter narrow widths.
Peel and stick application for making parts
Blueshift’s materials can be integrated into composite parts and on top of them. Blueshift’s TPS line of products are supplied with a temperature-resistant, pressure-sensitive adhesive. Burbey says that the materials are peel-and stick. Our systems are applied most often after the composite has cured. This is great because we don’t need to worry about the compatibility of the material during molding. The permanent bond strength usually occurs 24+ hours following application.
The material’s peel-and stick feature simplifies and speeds up the TPS application. Its pliability and thin profile also allow engineers to design with greater flexibility. Burbey says that the space industry is a good example. In an effort to create more sustainable space solutions some companies are creating reusable rockets, for which the carbon fiber composite underneath is vital.
AeroZero TPS is less labor intensive than the cork TPS that was used in older space vehicles. This allows for easier vehicle preparation for launch. Our materials are lighter than cork and can withstand the high temperatures required during rocket ascents and reentries into the atmosphere.
Current applications and future
Blueshift’s TPS has been a great success in lightweight structures, from electric aircraft and satellites to medical devices. AeroZero TPS has also been used in battery boxes to reduce the threat of thermal runaway.
The demand for batteries with higher power density is increasing. These batteries are being developed by manufacturers in pouches or cylindrical packs that can be housed in small modules, and then stacked into complex systems. Thermal runaway is increased by limiting the high power density.
AeroZero TPS versions have been integrated in interior and exterior wall of battery modules and houses to slow down the spread of fire and explosion, as well as temperature soak. The TPS has demonstrated its effectiveness against direct flames of 1000degC for up to 60minutes without burn-through. They are being integrated into system that help to promote passenger safety.
In the aerospace industry, designers are also facing more challenges. Weight savings are becoming more important to allow reusable launch vehicles and integration of heavy battery packs that have a high power density into electrified airplanes. Material solutions must evolve beyond those developed decades ago. This also requires a balanced approach between performance, weight and flexibility.
