NASA Apollo Program Atmospheric Entry Phases 1968

Video from the channel Republica Domania about Apollo program, linked on its Above Ten Thousand entry. Duration: 25:04. Language: English. Video type: Archive footage.

Educational NASA film that explains, with diagrams and maps, the atmospheric reentry phase of the Apollo command module on the way back from the Moon. It starts with the Earth-Moon geometry: the return trajectory passes over the antipode, the point on Earth opposite the Moon. The length of the splashdown point is chosen by varying the transit time by up to 24 hours, as the Earth rotates to bring the recovery forces beneath the spacecraft; the latitude, on the other hand, is nearly fixed by the Moon's declination at the time of trans-Earth injection.

It then defines the entry corridor. If the spacecraft enters too shallow, it bounces off the atmosphere and ends up in an orbit that would exhaust its oxygen and energy; if it enters too steep, the deceleration and heat exceed the limits of the crew and the structure. Since aerodynamic drag alone leaves too narrow a corridor, the center of gravity offset from the axis generates lift, and rolling the capsule orients that force upward or downward, widening the corridor: it is enough to arrive with a margin of somewhat less than 15 miles relative to the planned perigee altitude.

A 1968 NASA production, according to the title, made while the crewed missions to the Moon were being prepared, and uploaded as is.

The film follows the full sequence. After about three and a half days of return flight, the service module separates and the capsule orients itself with the heat shield forward. It enters the atmosphere at 400,000 feet (about 122 km) at about 24,500 miles per hour (about 39,400 km/h). Aerodynamic stabilization begins at 0.05 g, and between 2 and 2.5 g, capture is considered assured. In the first 70 seconds of the first control period, the most critical, the possible landing footprint shrinks from 20,700 to 2,070 miles and then to 690. A controlled skip follows, not exceeding 400,000 feet, then a second entry with another minute-and-a-half control period starting at 0.2 g, and the end of the phase at 23,500 feet (about 7,200 m), with the deployment of the drogue parachutes. Since ionization cuts off communications, the entire entry is guided by onboard calculations, one of the largest programs in the spacecraft's computer.