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Apollo 6 - . Payload: Apollo CM 020/ SM 014 / Apollo LTA-2R / S-IVB 502. Mass: 36,806 kg (81,143 lb). Nation: USA. Agency: NASA Houston. Program: Apollo. Class: Moon. Type: Manned lunar spacecraft. Spacecraft Bus: Apollo CSM. Spacecraft: Apollo CSM. Duration: 2.43 days. Decay Date: 1968-04-04 . USAF Sat Cat: 3170 . COSPAR: 1968-025A. Apogee: 184 km (114 mi). Perigee: 183 km (113 mi). Inclination: 32.5000 deg. Period: 88.20 min.
Apollo 6 (AS-502) was launched from Complex 39A at Kennedy Space Center. The space vehicle consisted of a Saturn V launch vehicle with an unmanned, modified Block I command and service module (CSM 020) and a lunar module test article (LTA-2R).

Liftoff at 7:00 a.m. EST was normal but, during the first-stage (S-IC) boost phase, oscillations and abrupt measurement changes were observed. During the second-stage (S-II) boost phase, two of the J-2 engines shut down early and the remaining three were extended approximately one minute to compensate. The third stage (S-IVB) firing was also longer than planned and at termination of thrust the orbit was 177.7 x 362.9 kilometers rather than the 160.9-kilometer near-circular orbit planned. The attempt to reignite the S-IVB engine for the translunar injection was unsuccessful. Reentry speed was 10 kilometers per second rather than the planned 11.1, and the spacecraft landed 90.7 kilometers uprange of the targeted landing point.

The most significant spacecraft anomaly occurred at about 2 minutes 13 seconds after liftoff, when abrupt changes were indicated by strain, vibration, and acceleration measurements in the S-IVB, instrument unit, adapter, lunar module test article, and CSM. Apparently oscillations induced by the launch vehicle exceeded the spacecraft design criteria.

The second-stage (S-II) burn was normal until about 4 minutes 38 seconds after liftoff; then difficulties were recorded. Engine 2 cutoff was recorded about 6 minutes 53 seconds into the flight and engine 3 cutoff less than 3 seconds later. The remaining second-stage engines shut down at 9 minutes 36 seconds - 58 seconds later than planned.

The S-IVB engine during its first burn, which was normal, operated 29 seconds longer than programmed. After two revolutions in a parking orbit, during which the systems were checked, operational tests performed, and several attitude maneuvers made, preparations were completed for the S-IVB engine restart. The firing was scheduled to occur on the Cape Kennedy pass at the end of the second revolution, but could not be accomplished. A ground command was sent to the CSM to carry out a planned alternate mission, and the CSM separated from the S-IVB stage.

A service propulsion system (SPS) engine firing sequence resulted in a 442-second burn and an accompanying free-return orbit of 22,259.1 x 33.3 kilometers. Since the SPS was used to attain the desired high apogee, there was insufficient propellant left to gain the high-velocity increase desired for the entry. For this reason, a complete firing sequence was performed except that the thrust was inhibited.

Parachute deployment was normal and the spacecraft landed about 9 hours 50 minutes after liftoff, in the mid-Pacific, 90.7 kilometers uprange from the predicted landing area (27.40 N 157.59 W). A normal retrieval was made by the U.S.S. Okinawa, with waves of 2.1 to 2.4 meters.

The spacecraft was in good condition, including the unified crew hatch, flown for the first time. Charring of the thermal protection was about the same as that experienced on the Apollo 4 spacecraft (CM 017).

Of the five primary objectives, three - demonstrating separation of launch vehicle stages, performance of the emergency detection system (EDS) in a close-loop mode, and mission support facilities and operations - were achieved. Only partially achieved were the objectives of confirming structure and thermal integrity, compatibility of launch vehicle and spacecraft, and launch loads and dynamic characteristics; and of verifying operation of launch vehicle propulsion, guidance and control, and electrical systems. Apollo 6, therefore, was officially judged in December as "not a success in accordance with . . . NASA mission objectives."