Which artificial satellite allowed scientists to realize that navigation based on satellite signals was possible?

The correct choice highlights the significance of Sputnik I in the development of satellite navigation. Launched in 1957 by the Soviet Union, Sputnik I was the first artificial satellite to orbit the Earth. Its deployment marked a pivotal moment in space exploration and technology, demonstrating that it was indeed possible to send objects into orbit and be able to receive signals from them.

This capability laid the groundwork for understanding how satellite signals could be used for various applications, including navigation. The radio signals emitted by Sputnik I were detected by ground stations on Earth, allowing scientists to study the effects of the satellite's orbit on signal propagation. This led to the realization that, with the proper technology, satellites could be used as reliable reference points for determining one's position on the planet.

In contrast, the other options do not represent significant milestones in satellite navigation development. Voyager 1 is known for its role in deep space exploration, while the Hubble Space Telescope is primarily focused on astronomical observations. Apollo 11, though historic as the first manned moon landing, did not contribute to the foundational understanding of satellite navigation systems. Thus, Sputnik I stands out as the catalyst for the concept of navigation based on satellite signals.