Which scientific concept relates to the maximum speed required for a spacecraft to overcome gravitational pull?

The concept that relates to the maximum speed required for a spacecraft to overcome gravitational pull is escape velocity. This is defined as the minimum speed an object must reach to break free from the gravitational attraction of a celestial body without any further propulsion.

Escape velocity depends on both the mass of the body from which the object is escaping and the distance from its center. For example, on Earth, the escape velocity is approximately 11.2 kilometers per second. It’s important to note that this speed must be reached irrespective of the direction of launch; as long as the object is traveling at or above this speed, it can escape the gravitational influence of the planet.

While lift-off speed refers to the speed necessary for a spacecraft to begin its ascent, and orbital speed pertains to the speed needed for an object to maintain a stable orbit around a celestial body, neither directly relate to the ability to escape gravitational pull. The term "velocity of escape" might convey a similar idea as escape velocity, but it is not the commonly accepted term in physics literature. Thus, escape velocity is the correct choice as it accurately describes the threshold needed to overcome a planet’s gravity.