Answer · confidence: partial
How did Apollo reach the Moon, and how did its speed change each step?
Research question: How did Apollo missions leave Earth orbit and reach the Moon, and how did the spacecraft's speed relative to Earth change at each step?
Apollo's route began with a launch into Earth orbit, and a parking orbit let the crew check the spacecraft close to Earth before committing to the trip to the Moon 1716. The translunar injection burn, performed by the restartable J-2 engine in the S-IVB stage, lasted about 350 seconds and changed speed by roughly 3.05 to 3.25 km/s 154. This burn turned a circular low Earth orbit into a highly eccentric one, and the Apollo XV reference reached about 10.845 km/s at engine shutdown 1226. The spacecraft then coasted on a transfer arc with its apogee near the Moon's orbital radius, timed so it arrived as the Moon approached, and lunar orbit insertion later slowed it into lunar orbit 191027. The sources do not give the spacecraft's speed during the coast itself, so that part of the question is only partly answered 19.
Checked 2026-10-22. Only documented and supported facts are used.
Dig deeper on this questionSources
[1] supported
After two standard parking orbits, the S-IVB stage was supposed to restart for translunar injection (TLI), but it failed to restart.
"Luego, después de las dos órbitas de estacionamiento estándar para comprobar la preparación del vehículo para una Inyección translunar (TLI), el S-IVB no pudo reiniciarse."Apolo 6
[2] supported
Apollo missions used circumlunar trajectories before lunar orbit insertion to provide a free return to Earth if the propulsion system malfunctioned on the way to the Moon.
"Las trayectorias circumlunares también fueron utilizadas por las misiones de Apolo antes de la inserción lunar de la órbita, para proporcionar un retorno libre a la tierra en caso de un mal funcionamiento del sistema de propulsión en el camino a la Luna."Trayectoria circunlunar
[3] supported
The spacecraft's path returns it to Earth unless its propulsion system is fired, provided it arrives properly on the leading side of the Moon.
"The result shows that the orbit will return the spacecraft to earth (unless the propulsion system is fired), provided the spacecraft is properly incident on the leading side of the moon."Elementary Analysis of Translunar Apollo Orbit (1969)
[4] supported
The Apollo translunar injection burn lasted about 350 seconds and gave a speed change of roughly 3.05 to 3.25 km/s.
"En este caso el impulso para el ITL se aplicó durante unos 350 segundos, lo que proveyó un diferencial de velocidad de 3.05 a 3.25 km/s"Inyección translunar
[5] supported
Because the S-IVB could not restart, mission controllers used the service module engine to raise the spacecraft into a high orbit, burning it for 442 seconds, longer than in any nominal lunar mission.
"Se quemó durante 442 segundos (más de lo que jamás se dispararía en una misión lunar nominal)"Apolo 6
[6] supported
On Apollo 13, after an oxygen tank rupture, the crew returned to Earth without firing the Service Module engine, but still needed a series of course corrections using the Lunar Module descent engine to maintain the free-return path.
"Esto se usó en la misión Apolo 13 , cuando una rotura del tanque de oxígeno 2 requirió regresar a la Tierra sin disparar el motor del Módulo de Servicio , aunque para mantener esta trayectoria fueron requeridos una serie de correcciones de curso usando el motor de descenso del Módulo Lunar ."Trayectoria circunlunar
[7] supported
The planned flight profile called for the service module engine to fire about five minutes after a translunar trajectory was not possible, reducing speed so the apogee dropped and the spacecraft returned to Earth as a direct-return abort simulation.
"el motor del Módulo de mando y servicio sería encendido unos cinco minutos más tarde para reducir la velocidad de la nave"Apolo 6
[8] supported
A circumlunar (free-return) trajectory takes a spacecraft from Earth around the far side of the Moon and back to Earth using only gravity once the initial trajectory is set.
"Una trayectoria circunlunar , trayectoria translunar o de retorno libre lunar, es un tipo de trayectoria de regreso libre que toma una nave espacial de la Tierra, alrededor del lado lejano de la Luna, y de regreso a la Tierra usando solo la gravedad una vez que se establece la trayectoria inicial."Trayectoria circunlunar
[9] supported
The Apollo 8 translunar injection was the first crewed translunar injection, making its crew the first people to leave Earth's sphere of influence.
"El Apolo 8 fue la primera misión con tripulación que realizó este procedimiento en 21 de diciembre de 1968 y, por tanto, los miembros de esa tripulación fueron las primeras personas que abandonaron la influencia de la Tierra."Inyección translunar
[10] supported
The translunar trajectory is timed and aimed so the spacecraft reaches near its apogee as the Moon approaches, and it then enters the Moon's sphere of influence.
"El instante de encendido de motores para proveer el impulso es calculado de forma tal que la nave se aproxime al apogeo al aproximarse la Luna. Finalmente la nave entra en la esfera de influencia de la Luna, realizando un paso lunar hiperbólico."Inyección translunar
[11] supported
On the return leg, the engine was to fire again to accelerate the spacecraft to simulate a nominal lunar return, at a target speed of 11,100 m/s.
"En el partido de vuelta, el motor se encenderá una vez más para acelerar la nave para simular la trayectoria de retorno nominal lunar con un ángulo de reingreso de -6,5 grados y la velocidad de 11.100 m/s."Apolo 6
[12] supported
A trans-lunar injection burn, usually by a chemical rocket engine, raises the spacecraft's velocity and changes its orbit from a circular low Earth orbit to a highly eccentric orbit.
"The large TLI burn , usually performed by a chemical rocket engine, increases the spacecraft's velocity, changing its orbit from a circular low Earth orbit to a highly eccentric orbit ."Trans-lunar injection
[13] supported
The translunar injection (TLI) maneuver is a burn that the S-IVB stage performs, and a premature S-IVB shutdown during it is the failure case this document studies. The document does not describe how the spacecraft's speed relative to Earth changed.
"The results show it is operationally feasible to perform a fixed-attitude, fixed delay time abort following a premature.S-IVB shutdown."Preliminary backup abort procedures for aborts occurring during translunar injection - Project Apollo (1967)
[14] supported
A launch vehicle first goes into a parking orbit, coasts there for a while, and then fires its engines again to enter the final desired trajectory.
"A launch vehicle follows a trajectory to the parking orbit, then coasts for a while, then engines fire again to enter the final desired trajectory."Parking orbit
[15] supported
For the Apollo lunar missions, TLI was performed by the restartable J-2 engine in the S-IVB third stage of the Saturn V rocket.
"For the Apollo lunar missions, TLI was performed by the restartable J-2 engine in the S-IVB third stage of the Saturn V rocket."Trans-lunar injection
[16] supported
For Apollo's crewed lunar missions, the parking orbit gave time to check out the spacecraft while still close to Earth, before committing to the trip to the Moon.
"For the Apollo program 's crewed lunar missions, a parking orbit allowed time for spacecraft checkout while still close to home, before committing to the lunar trip."Parking orbit
[17] documented
Apollo's route to the Moon began with a launch into Earth orbit, and the crew could manually guide the booster to that orbit if the booster malfunctioned.
"1. Launch into earth orbit: In the event of booster malfunction, the crew could terminate the ascent or take control of the booster attitude and manually guide to earth orbit."Apollo experience report: Systems and flight procedures development (1973)
[18] supported
Using a preliminary parking orbit before final injection can widen the launch window to the Moon or a planet from seconds or minutes to several hours.
"Using a preliminary parking orbit before final injection can widen this window from seconds or minutes, to several hours."Parking orbit
[19] supported
After TLI, the spacecraft coasts on the lunar transfer arc along an elliptical path about Earth with an apogee near the radius of the Moon's orbit.
"As the spacecraft begins coasting on the lunar transfer arc, its trajectory approximates an elliptical orbit about the Earth with an apogee near to the radius of the Moon's orbit."Trans-lunar injection
[20] documented
The move from Earth orbit toward the Moon was a translunar injection, a thrusting burn that the booster normally performed and that the crew could take over by following a nominal attitude-angle profile if booster guidance failed.
"2. Translunar injection: If the booster guidance failed, the crew could take control and continue the translunar injection thrusting by guiding to the nominal attitude-angle profile."Apollo experience report: Systems and flight procedures development (1973)
[21] supported
The Apollo program used parking orbits for the reasons given in the article, apart from those relating to geostationary orbits.
"The Apollo program used parking orbits, for all the reasons mentioned above except those that pertain to geostationary orbits."Parking orbit
[22] supported
A typical manned lunar mission uses five major engine firing events, each initiating a primary phase of the mission.
"A typical manned lunar mission consists of five major engine firing events."Abort Trajectories for Manned Lunar Missions (2007)
[23] supported
The TLI burn is timed so the spacecraft reaches apogee as the Moon approaches its position.
"The burn is timed so that the spacecraft nears apogee as the Moon approaches."Trans-lunar injection
[24] supported
The first step is the Trans-Lunar Injection (TLI) burn, which sends the spacecraft from Earth orbit toward the Moon, after which the spacecraft coasts.
"First the Trans-Lunar Injection (TLI) maneuver is conducted."Abort Trajectories for Manned Lunar Missions (2007)
[25] supported
A free return trajectory is a ballistic Earth-Moon-Earth path that needs no propulsive maneuvers after translunar injection.
"the spacecraft is required to depart Earth on a free return trajectory, which is a ballistic Earth-moon-Earth segment that requires no propulsive maneuvers after translunar injection."Optimal lunar orbit insertion from a free return trajectory (2012)
[26] supported
For the Apollo XV reference trajectory, the translunar injection left the spacecraft at about 321.7 km altitude with a final velocity of about 10.845 km/s at engine shutdown.
"The primary values utilized were the translunar injection altitude and final velocity which convert to 321.7 kilometers and 10.845 kilometers per second respectively."Abort Trajectories for Manned Lunar Missions (2007)
[27] supported
After TLI, the spacecraft coasts toward the Moon until it reaches the lunar interface, where the Lunar Orbit Insertion (LOI) burn slows it into a circum-lunar orbit.
"Once the TLI burn is completed the spacecraft coasts until the lunar interface has been reached."Abort Trajectories for Manned Lunar Missions (2007)
[28] supported
The LOI burn injects the spacecraft into Low Lunar Orbit, typically about 100 km above the lunar surface, where it serves as the parking orbit for the service and command modules.
"The LOI propulsive burn injects the spacecraft into a circum-lunar orbit. The circum-lunar orbit, also known as Low Lunar Orbit (LLO) is typically on the order of 100 km above the lunar surface"Abort Trajectories for Manned Lunar Missions (2007)
[29] supported
The Apollo trans-Earth injection burn, which sent the spacecraft back toward Earth from lunar orbit, gave a posigrade speed increase of about 1,000 m/s over roughly 150 seconds. This document does not describe the outbound trans-lunar injection that first left Earth orbit.
"An Apollo TEI burn lasted approximately 150 seconds, providing a posigrade velocity increase of 1,000 m/s (3,300 ft/s)."Trans-Earth injection
[30] supported
Apollo 8 was the first crewed mission to leave low Earth orbit and to orbit another celestial body.
"Apollo 8 was the first crewed mission to leave low Earth orbit and to orbit another celestial body, and Apollo 11 was the first crewed mission to land humans on one."Apollo program
[31] supported
On Apollo missions, the trans-Earth injection burn was performed by the restartable Service Propulsion System engine on the Service Module, after the Lunar Module was undocked.
"On the Apollo missions, it was performed by the restartable Service Propulsion System (SPS) engine on the Service Module after the undocking of the (LM) Lunar Module if provided."Trans-Earth injection
[32] supported
The first three lunar missions (Apollo 8, 10 and 11) used a free return trajectory, a flight path coplanar with lunar orbit that would allow a return to Earth if the service module engine failed to achieve lunar orbit insertion.
"The first three lunar missions (Apollo 8, Apollo 10 , and Apollo 11) used a free return trajectory , keeping a flight path coplanar with the lunar orbit, which would allow a return to Earth in case the SM engine failed to make lunar orbit insertion."Apollo program
[33] supported
The first Apollo trans-Earth injection was performed by Apollo 8 on December 25, 1968.
"It was first performed by the Apollo 8 mission on December 25, 1968."Trans-Earth injection
[34] supported
On later missions, lighting conditions at the landing site required a lunar orbital plane change, which needed a course change maneuver soon after trans-lunar injection (TLI) and eliminated the free-return option.
"Landing site lighting conditions on later missions dictated a lunar orbital plane change, which required a course change maneuver soon after TLI, and eliminated the free-return option."Apollo program
[35] supported
Apollo 6 attempted a demonstration of trans-lunar injection, but three engine failures, including failure of the S-IVB restart, occurred during the flight.
"Uncrewed, second flight of Saturn V, attempted demonstration of trans-lunar injection, and direct-return abort using SM engine; three engine failures, including failure of S-IVB restart."Apollo program
[36] supported
Apollo 6 was intended to test whether the Saturn V's third stage, the S-IVB, could propel itself and the Apollo spacecraft to lunar distances.
"Apollo 6 was intended to demonstrate the ability of the Saturn V's third stage, the S-IVB , to propel itself and the Apollo spacecraft to lunar distances."Apollo 6
[37] supported
To send the command and service module back to Earth, the service module engine fires during trans-Earth injection.
"Trans-Earth injection The SM engine fires to send the CSM back to Earth."Apollo program
[38] supported
After Earth orbit, the S-IVB was supposed to restart for trans-lunar injection (TLI), but it failed to restart.
"Then, after the standard two orbits to assess the vehicle's readiness for trans-lunar injection (TLI), the S-IVB was ordered to restart, but failed to do so."Apollo 6
[39] supported
Because the S-IVB restart failed, mission control used the service module's SPS engine to raise the orbit to a high apogee instead of sending the spacecraft toward the Moon.
"The SPS engine burned for 442 seconds to get to the planned"Apollo 6
[40] supported
Without enough propellant for a second SPS burn, the spacecraft entered the atmosphere at 10,000 m/s rather than the planned 11,000 m/s that would have simulated a lunar return.
"There was now, however, not enough propellant to speed up the atmospheric reentry with a second SPS engine burn"Apollo 6