The time it takes to fly around the Moon is not a single fixed number, but a combination of two distinct phases: the journey from Earth to the Moon and the time required to complete one revolution in lunar orbit. The total duration depends entirely on the physics of the chosen trajectory and the engineering of the spacecraft, primarily its propulsion system and its intended altitude once it reaches the lunar environment.
The Journey to the Moon (Transit Time)
The primary leg of the journey, the time it takes a spacecraft to travel from Earth and enter the Moon’s gravity, has historically been about three days for crewed missions. The Apollo missions, for example, typically covered the distance of roughly 240,000 miles in a timeframe ranging from 69 to 86 hours. Apollo 8, the first crewed mission to orbit the Moon, took approximately 69 hours to reach the point of its Lunar Orbit Insertion (LOI) burn.
This rapid transit time is achieved by using high-thrust chemical rockets, which provide a powerful, short-duration burst of acceleration known as a trans-lunar injection (TLI). Early Apollo missions used a “free-return trajectory,” designed so that if the main engine failed, the Moon’s gravity would naturally sling the spacecraft back toward Earth. This trajectory required a relatively fast approach velocity to the Moon, resulting in an initial flight time between 70 and 75 hours.
Later missions, beginning with Apollo 12, adopted a “hybrid” trajectory that took slightly longer, sometimes up to 90 hours, but offered greater flexibility in selecting landing sites. This slower approach velocity also reduced the propellant needed for the Lunar Orbit Insertion maneuver, conserving fuel for other mission objectives. Uncrewed probes, which prioritize fuel efficiency over speed, often take much longer, requiring four to five days to reach the Moon.
The Mechanics of Circling the Moon
Once a spacecraft has reached the Moon, the time it takes to complete one full orbit is dictated by the altitude and the Moon’s gravitational pull. For a spacecraft to maintain a circular orbit, it must achieve a specific orbital velocity. The Moon’s smaller mass compared to Earth means that a spacecraft needs a lower velocity to stay in orbit.
In a typical Low Lunar Orbit (LLO), generally defined as an altitude below 62 miles (100 kilometers), the orbital period is very short. For example, the Apollo command modules maintained a low parking orbit, taking approximately two hours to complete one revolution around the Moon.
The speed required for this Low Lunar Orbit is around 3,770 miles per hour (1.685 kilometers per second), allowing the spacecraft to circle the entire circumference of the Moon in that two-hour period. If a mission involves a simple circumlunar “flyby,” where the spacecraft does not enter a stable orbit but loops around the far side before returning to Earth, the time spent in the Moon’s vicinity is far longer, potentially taking several hours.
Key Variables That Determine Mission Length
The total time spent in space depends on the mission’s objective and the type of propulsion used. High-thrust chemical rockets, like those used in the Apollo program, provide a fast transit time of about three days because they generate the massive force necessary for quick acceleration. However, this speed comes at the cost of fuel inefficiency, limiting the overall mission duration.
An alternative approach is to use low-thrust, high-efficiency propulsion systems, such as ion thrusters. These systems expel ionized propellant at high speeds, making them extremely fuel-efficient, but they produce only a tiny amount of thrust. Ion-powered spacecraft require months to build up the necessary speed for lunar transit, making them unsuitable for missions requiring a rapid response or a crewed presence.
The altitude of the lunar orbit is another determining factor for the mission length. A higher orbit significantly increases the time it takes to complete one revolution, following the laws of celestial mechanics. The goal of the mission also dictates the required time in orbit; a reconnaissance mission only needs a few orbits, whereas establishing a lunar base may require weeks or months of sustained orbital operations.