Space waves are characterized by which true property?

• A. They pass through the ionosphere.
• B. They bounce off the ionosphere.
• C. They travel along the ground.
• D. They are not used in navigation.

Answer: (A)

Space waves propagate as line-of-sight signals that travel directly through the atmosphere and into space, not by bouncing off the ionosphere. At the higher frequencies used for aviation navigation (VHF/UHF), the ionosphere is essentially transparent, so these waves pass through it and reach receivers that are within line of sight. This is what enables navigation aids like VOR and ILS, which rely on direct, ground-referenced transmissions. In contrast, lower-frequency waves can be reflected by the ionosphere (skywave) or can travel along the Earth’s surface as ground waves, which is why those behaviors are not characteristic of space waves. Therefore, the true property is that space waves pass through the ionosphere.