Editing Apollo 8 (section)

===Parameter summary===

[[File:Apollo 8 TLI.jpg|thumb|upright=3.0|Mission profile]]

As the first crewed spacecraft to orbit more than one celestial body, Apollo{{nbsp}}8's profile had two different sets of orbital parameters, separated by a translunar injection maneuver. Apollo lunar missions would begin with a nominal {{convert|100|nmi|km|sigfig=4|adj=on}} circular Earth parking orbit. Apollo{{nbsp}}8 was launched into an initial orbit with an [[apogee]] of {{convert|99.99|nmi|km}} and a [[perigee]] of {{convert|99.57|nmi|km}}, with an [[inclination]] of 32.51° to the [[Equator]], and an [[orbital period]] of 88.19 minutes. Propellant venting increased the apogee by {{convert|6.4|nmi|km}} over the 2{{nbsp}}hours, 44 minutes, and 30 seconds spent in the parking orbit.{{sfn|Orloff|2000|p=45}}

This was followed by a [[trans-lunar injection]] (TLI) burn of the [[S-IVB]] third stage for 318 seconds, accelerating the {{convert|63650|lb|kg|abbr=on}} command and service module and {{convert|19900|lb|kg|abbr=on}} LM test article from an orbital velocity of {{convert|25567|ft/s|m/s}} to the injection velocity of {{convert|35505|ft/s|m/s|abbr=on}}{{sfn|Orloff|2000|p=46}}<ref name="PressKit"/> which set a record for the highest speed, relative to Earth, that humans had ever traveled.{{sfn|Phillips|1975|p=178}} This speed was slightly less than the Earth's [[escape velocity]] of {{convert|36747|ft/s|m/s}}, but put Apollo{{nbsp}}8 into an elongated elliptical Earth orbit, close enough to the Moon to be captured by the Moon's gravity.{{sfn|Woods|2008|pp=108–109}}

The standard lunar orbit for Apollo missions was planned as a nominal {{convert|60|nmi|km|adj=on}} circular orbit above the Moon's surface. Initial lunar orbit insertion was an ellipse with a [[perilune]] of {{convert|60.0|nmi|km}} and an [[apolune]] of {{convert|168.5|nmi|km}}, at an inclination of 12° from the lunar equator. This was then circularized at {{convert|60.7|by|59.7|nmi|km}}, with an orbital period of 128.7 minutes.{{sfn|Orloff|2000|p=46}} The effect of lunar [[mass concentration (astronomy)|mass concentrations]] ("mascons") on the orbit was found to be greater than initially predicted; over the course of the ten lunar orbits lasting twenty hours, the orbital distance was perturbated to {{convert|63.6|by|58.6|nmi|km}}.{{sfn|Orloff|2000|p=39}}

Apollo 8 achieved a maximum distance from Earth of {{convert|203752|nmi|smi km|abbr=off|sp=us}}.{{sfn|Orloff|2000|p=39}}