The special material is
Aluminum and Composite Fibre Reinforced Plastic
Carbon Fiber Reinforced
Polymer - CFPR
- has a very high strength for a
- reflects well heat
- does not rust
It may not be the best. But it is practically the most fitting
substance that can be used to optimized on multiple criteria.
While traveling through the atmosphere at very high velocity, there is a lot of stress on materials. The materials could vibrate while traveling and that requires strength. The radiation of Sun heats the spacecraft a lot. So it has to withstand high temperature.