The Space Shuttle, officially known as the Space Transportation System (STS), was a complex, partially reusable spacecraft that operated from 1981 to 2011. This vehicle was capable of launching like a rocket, maneuvering in orbit, and gliding back to Earth for a runway landing. To achieve orbit, the Shuttle had to overcome Earth’s gravity and attain a specific velocity dictated by the laws of orbital mechanics.
The Specific Orbital Speed
The velocity required for the Space Shuttle to maintain a stable orbit around Earth was approximately 17,500 miles per hour (28,000 kilometers per hour). This tremendous pace is known as orbital velocity, and it is the speed at which the spacecraft’s inertia perfectly balances the planet’s gravitational pull. This speed varies slightly depending on the altitude of the spacecraft.
To grasp the magnitude of this speed, consider that a typical commercial airliner travels at about 550 miles per hour. The Space Shuttle moved through space at more than 30 times the speed of a jet. Attaining this velocity was the primary goal of the Shuttle’s ascent phase. The main engines accelerated the Shuttle to this speed in just over eight minutes of powered flight.
Balancing Gravity and Motion
The reason the Space Shuttle had to travel at 17,500 miles per hour relates to the physics of overcoming gravity without escaping it entirely. People often misunderstand orbital flight, believing that spacecraft escape the force of gravity, but this is not the case. Earth’s gravity remains a significant force even in Low Earth Orbit, but the Shuttle’s high horizontal speed prevents it from falling back to the surface.
This dynamic is conceptually described as being in a state of continuous “freefall.” Imagine throwing a baseball from a high mountain; if thrown fast enough, its trajectory would curve downward, but the Earth’s surface would curve away beneath it at the same rate. The Shuttle’s orbital velocity was the speed necessary for it to perpetually “miss” the Earth as it falls toward it.
This speed creates a balance where the inward pull of gravity is precisely matched by the outward tendency of the spacecraft’s motion, known as inertia. If the Shuttle traveled much slower, the orbit would decay rapidly, causing the vehicle to re-enter the atmosphere. Conversely, if it moved significantly faster, it would achieve escape velocity and fly away from Earth. The specific velocity of 17,500 mph was the equilibrium for maintaining orbit.
Contextualizing the Orbit: Altitude and Duration
The Space Shuttle’s speed was maintained within Low Earth Orbit (LEO). Mission parameters generally placed the Shuttle in an altitude range between 185 and 330 nautical miles (about 340 to 610 kilometers) above the Earth’s surface. The exact altitude was determined by the mission objective, such as servicing the Hubble Space Telescope or docking with the International Space Station.
This relatively low altitude meant the Shuttle completed a full circuit around the planet in about 90 minutes. At this speed, the crew experienced approximately 16 sunrises and sunsets every 24 hours, a consequence of their rapid movement around the globe.
Orbital mechanics dictates an inverse relationship between altitude and speed. The lower the orbit, the stronger the gravitational pull, and consequently, the faster the required orbital velocity. While 17,500 mph is the general figure, a slightly higher orbit required a slower speed to maintain the necessary gravitational-inertial balance.