Here's why:

* Low Density: Aluminum is incredibly lightweight, making it ideal for applications where weight is a critical factor, like aircraft and rockets.

* Strength and Durability: Despite its low density, aluminum is surprisingly strong and durable, making it suitable for structural applications.

* Corrosion Resistance: Aluminum forms a protective oxide layer that resists corrosion, which is essential for aircraft and rockets operating in harsh environments.

While other metals like titanium and magnesium are also used in aircraft and rockets, aluminum remains a primary choice due to its combination of lightness, strength, and affordability.