Aerogel is regarded as the lightest solid in the world. Due to its high specific surface area and low thermal conductivity, it is widely used as a heat-resistant material for aerospace vehicles. In 1999, the National Aeronautics and Space Administration (NASA) developed a silica aerogel with a density of 3 mg/cm³, making it the lightest solid material at that time. However, due to the brittleness and humidity sensitivity of the silicon aerogel material, its application was limited. NASA has been supporting research on durable aerogels for many years. 
Silica aerogel material 
In response to the demand for a lightweight and flexible supersonic inflatable decelerator material for spacecraft landing, researchers at NASA Glenn Research Center (GRC) first conducted a study to enhance its durability by using polymer-reinforced silica aerogel. They found that the polymer-reinforced silica aerogel had a density twice that of silica aerogel, a surface area reduced by 30% to 50%, but its strength increased by two orders of magnitude. 
Polymer reinforcement of silica aerogel enhances durability 
Nevertheless, its strength still fails to meet the requirements for the deceleration material of spacecraft. Subsequently, in collaboration with the University of Akron, they developed polyimide aerogel cross-linked with octaphenyl (POSS), resulting in a polyimide aerogel with a density of 0.12 g/cm³ and a porosity of 90%. This material can withstand a temperature of 1100 °F for 90 seconds, ensuring that it will not burn when entering the atmosphere; its strength is five times that of polymer-reinforced silica aerogel, and it can be made thinner (0.5 mm in thickness) to meet the requirements of being foldable and stored in the spacecraft, effectively overcoming the shortcomings of silica aerogel in terms of weight, cost, flexibility, and durability. 
Flexible polyimide aerogel 
Based on aerogel and fiber materials, NASA began to develop multifunctional composite materials that can meet the requirements of structural materials and thermal protection materials for spacecraft. For instance, researchers at NASA's Kennedy Space Center (KSC) developed a manufacturing method for a multifunctional aerogel/fiber hybrid laminated composite material. By selecting different fiber layers (such as polyester, carbon fiber, Kevlar® fiber, Spectra® fiber, Innegra fiber or their combinations), different thicknesses of aerogel layers, and different composite structures, different functions or multifunctional composite materials can be produced. This lightweight and high-strength multifunctional composite material can meet the requirements of aerospace vehicles in terms of thermal protection, impact resistance, energy absorption, and sound insulation, and can be applied in many fields such as automobiles, ships, buildings, liquefied natural gas transportation, sports equipment, and military protection. 
Aerospace application case: Inflatable reducer 
In order to realize the manned Mars landing plan, NASA is developing heavy-load transportation technology. The Hypersonic Inflatable Aerodynamic Decelerator (HIAD) is a solution that can provide effective payload and volume benefits for spacecraft braking. In 2006, NASA established a project named "Advanced Inflatable Decelerators for Atmospheric Entry" (PAIDAE), and developed a HIAD consisting of an outer layer, an insulation layer, and an airtight layer with a diameter of 3 to 12 meters.