It's not true that only radio waves are used in space wave propagation. In fact, electromagnetic waves of various frequencies, including radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays, can all be used for space wave propagation. However, radio waves are commonly used for this purpose due to several reasons:

1. Penetration: Radio waves have the ability to penetrate various atmospheric conditions, such as clouds, fog, rain, and dust, making them more reliable for long-distance communication in space.

2. Lower Frequency: Radio waves have lower frequencies compared to other electromagnetic waves. This property enables them to diffract or bend around obstacles, such as mountains or buildings, making them suitable for long-range communication.

3. Wide Bandwidth: Radio waves have a wide bandwidth, which allows them to carry large amounts of data. This is important for applications like satellite communications and deep-space exploration.

4. Less Susceptibility to Interference: Radio waves are less susceptible to interference from other sources compared to higher-frequency electromagnetic waves. This makes them suitable for reliable communication in noisy environments, including the presence of other electronic devices.

5. Cost-Effective: Radio wave technology is relatively cost-effective compared to other types of electromagnetic waves, making it more accessible and practical for various applications.

6. Propagation Losses: Radio waves experience lower propagation losses compared to higher-frequency waves, which means they can travel longer distances without significant signal degradation.

Therefore, while other electromagnetic waves can be used for space wave propagation, radio waves are commonly chosen for their reliability, long-range capabilities, wide bandwidth, and practical advantages in terms of penetration, diffraction, and cost-effectiveness.