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Apollo Atmospheric Entry Phase 1968 NASA JSC-345; Mission Planning and Analysis Division (MPAD) -

Apollo Atmospheric Entry Phase 1968 NASA JSC-345; Mission Planning and Analysis Division (MPAD) por Jeff Quitney   5 mess atrás

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"Explains the geometry of return trajectory and reentry into the Earth's atmosphere by the Apollo spacecraft, as well as the problems involved and the methods and actions for overcoming these problems." Produced by NASA Houston Manned Spacecraft Center 's Mission Planning and Analysis Division for Project Apollo.

NASA film JSC-345

Originally a public domain film from NASA, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).



Entry Control

The entry aerodynamics for the Apollo CM are closely related to the AGC entry control logic (ref. 1); therefore, a brief description of the control programs is included (fig. 6(a)). After the CM separated from the SM and prior to reaching the entry inter- face at 400 OOOfeet, the spacecraft was oriented in pitch with its stability axis along the AGC-estimated relative wind-velocity vector with a bank-angle attitude of 0 O, or lift up (fig. 6(b)). Pitch and yaw attitude control was maintained until 0. 05g deceleration was reached. The spacecraft attitude was then maintained by aerodynamic forces and moments.

Control of the rotational rates was retained in the rate damping mode. The roll rate gyro was coupled to the yaw electronics to give coordinated roll control about the velocity vector rather than about the spacecraft body X-axis. At the entry interface, the initial roll program of the INITIAL ENTRY phase was in command. The AGC esti- mated a 2084-nautical-mile inertial range to the targeted landing point and a 7.9- nautical-mile cross-range error at this time.

When 0. 05g was sensed (0. 05g interface), the AGC automatically began the entry computations. A post-0. 05g test determined if the lift vector, which was up initially, should be rolled down to ensure atmospheric cap- ture. A decision was made to continue the flight with the lift vector up. When the aerodynamic deceleration level exceeded 0. 2g and the altitude was decreasing at a rate less than 700ft/sec, control was transferred to the HUNTEST phase.

During the HUNTEST phase, steering was performed by a constant-drag routine until the difference between the desired and the predicted range was less than 25 nautical miles, and the predicted skip velocity was less than orbital velocity. To obtain the proper trajectory conditions, the Apollo 4 mission was flown lift vector down for approximately 22 seconds during the phase immediately after peak g.

The UPCONTROL phase was entered at the same time that the lift vector was rolled back to lift vector up. In the UPCONTROL phase, the bank angle was controlled between 40 and 90 to provide the skip-velocity vector re- quired to match the predicted range with the calculated range to target.

Normally, the KEPLER, or BALLISTIC, phase would have been entered next, when the total deceleration had fallen below 0.2g. Since the spacecraft never reached this required condition during the UPCONTROL phase, the KEPLER phase was bypassed, and at a time near the maximum skip altitude of 241 602 feet, the FINAL ENTRY phase was entered.

In the FINAL ENTRY phase, or second entry, the CM was steered to the target point based on a linear perturbation about a stored reference trajectory. All steering calculations ended when the earth-relative velocity fell below 1000 ft/sec. At drogue parachute deployment time, the AGC indicated a target overshoot of 2. 3 nautical miles...


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