Introduction:
In order to understand why only rocket engines can be propelled to space, it is important to consider the unique characteristics and capabilities of these engines. While there are several factors that contribute to the ability of rocket engines to reach space, one key differentiating factor is that they are not air-beating engines.

Explanation:
Rocket engines are specifically designed to operate in the vacuum of space, where there is no air or atmosphere. This fundamental difference sets them apart from other types of engines, such as jet engines, which rely on the presence of air to generate thrust.

1. Air-beating engines:
Air-beating engines, such as jet engines, work by taking in air from the surrounding atmosphere and compressing it before burning fuel in the combustion chamber. The hot exhaust gases are then expelled at high speeds, creating thrust. However, in order to generate this thrust, air-beating engines require a continuous supply of air, which is not available in the vacuum of space.

2. Rocket engines:
Rocket engines, on the other hand, do not rely on the presence of air to generate thrust. They carry both fuel and oxidizer onboard and use a process called combustion to produce high-pressure and high-velocity exhaust gases. This expulsion of gases at high speeds creates a reactionary force known as thrust, propelling the rocket forward.

3. Generating high thrust:
Rocket engines are capable of generating very high thrust, which is essential for overcoming Earth's gravity and reaching the speeds necessary to escape the Earth's atmosphere. The high thrust is achieved by the combustion of fuel and oxidizer, which produce a large amount of hot gases that are expelled at high velocities.

4. Propulsion efficiency:
While rocket engines may not have the highest propulsion efficiency compared to other types of engines, such as turbofan engines used in commercial aircraft, they are specifically designed for the unique requirements of space travel. The focus of rocket engines is on generating high thrust rather than maximizing efficiency. This is because the main objective of a rocket is to reach space, where the absence of air resistance allows it to continue moving without the need for further propulsion.

Conclusion:
In conclusion, only rocket engines can be propelled to space because they are not air-beating engines and do not rely on the presence of air to generate thrust. They are specifically designed to operate in the vacuum of space and can generate high thrust, which is necessary for overcoming Earth's gravity and reaching the speeds required for space travel. While they may not have the highest propulsion efficiency, their unique characteristics make them the ideal choice for space exploration and satellite launches.