Blast-off from the Moon’s Surface

The pyrotechnic noises at descent stage separation were loud, but ascent-engine ignition was inaudible.

Continuing First Men on Moon,
our selection from Apollo 11 Mission Report by NASA Mission Evaluation Team and by The Astronauts: Neil Armstrong, Edwin “Buzz” Aldrin, and Michael Collins published in 1971. The selection is presented in eight easy 5-minute installments. For works benefiting from the latest research see the “More information” section at the bottom of these pages.

Previously in First Men on Moon

Time: July 21, 1969
Place: Sea of Tranquility

Because of the bulk of the extravehicular mobility unit, caution had to be exercised to avoid bumping into switches, circuit breakers, and other controls while moving around the cockpit. One circuit breaker was in fact broken as a result of contact (section 16).

Equipment jettison was performed as planned, and the time taken before flight in determining the items not required for lift-off was well spent. Considerable weight reduction and increase in space was realized. Discarding the equipment through the hatch was not difficult, and only one item remained on the platform. The post-ingress checklist procedures were performed without difficulty; the checklist was well-planned and was followed precisely.

Lunar Rest Period

The rest period was almost completely unsatisfactory. The helmets and gloves were worn to relieve subconscious anxiety about a loss of cabin pressure, and they presented no problem. But noise, lighting, and a lower-than-desired temperature were annoying. The suits were uncomfortably cool, even with the waterflow disconnected. Oxygen flow was finally cut off, and the helmets were removed, but the noise from the glycol pumps was then loud enough to interrupt sleep. The window shades did not completely block out light, and the cabin was illuminated by a combination of light passing through the shades, warning lights, and display lighting. The Commander rested on the ascent engine cover and was bothered by the light entering through the telescope. The Lunar Module Pilot estimated that he slept fitfully for perhaps 2 hours, and the Commander did not sleep at all, even though body positioning was not a problem. Because of the reduced gravity, the positions on the floor and on the engine cover were both quite comfortable.

Launch Preparation

Aligning the platform before lift-off was complicated by the limited number of stars available. Because of sun and earth interference, only two detents effectively remained from which to select stars. Accuracy is greater for stars close to the center of the field, but none were available at this location. A gravity/one-star alignment was successfully performed. A manual averaging technique was used to sample five successive cursor readings and then five spiral readings. The result was then entered into the computer. This technique appeared to be easier than taking and then entering five separate readings. Torqueing angles were close to 0.7° in all three axes and indicated that the platform drifted. *

[* NASA Editor’s note: However, platform drift was within specification limits.]

After the alinement, the navigation program was entered. It is recommended that future crews update the abort guidance system with the primary guidance state vector at this point and then use the abort guidance system to determine the command module location. The primary guidance system cannot be used to determine the command module range and range rate, and the radar will not lock on until the command module is within a 400-mile range. As this range is approached, the abort guidance system provides valid data.

A cold-fire reaction control system check and an abort guidance system calibration were performed, and the ascent pad was taken. Approximately 45 minutes prior to liftoff, another platform alinement was performed. The landing-site alinement option at ignition was used for lift-off. The torqueing angles for this alinement were approximately 0.09°.

In accordance with ground instructions, the rendezvous radar was placed in the antenna SLEW position with the circuit breakers off for ascent to avoid recurrence of the alarms experienced during a descent.

Both crewmembers had forgotten to watch for the small helium pressure decrease indication that the Apollo 10 crew experienced when the ascent tanks were pressurized, and the crew initially believed that only one tank had been pressurized. This oversight was temporary, but it delayed the crew verification of proper pressurization of both tanks.

Ascent

The pyrotechnic noises at descent stage separation were loud, but ascent-engine ignition was inaudible. The yaw and pitch maneuvers were smooth. The pitch- and roll-attitude limit cycles were as expected and were not accompanied by physiological difficulties. Both the primary and the abort guidance systems indicated the ascent to be a duplicate of the planned trajectory. The guided cut-off yielded residuals of less than 2 ft/sec; and the in-plane components were nulled to within 0.1 ft/sec with the reaction control system. Throughout the trajectory, the ground track could be visually verified, although a pitch attitude confirmation by use of the horizon in the overhead window was difficult because of the horizon lighting condition.

Rendezvous

At orbital insertion, the primary guidance system showed an orbit of 47.3 by 9.5 miles, as compared to the abort guidance system solution of 46.6 by 9.5 miles. Since radar range-rate data were not available, the Manned Space Flight Network quickly confirmed that the orbital insertion was satisfactory.

In the preflight planning, stars had been chosen that would be in the field of view and that would require a minimum amount of maneuvering to get through alinement and back in plane. This maintenance of a nearly fixed attitude would permit the radar to be turned on and the acquisition conditions to be designated so that marks for a co-elliptic sequence initiation solution would be immediately available. During the simulations, these preselected stars had not been correctly located relative to the horizon, and time and fuel were wasted in first maneuvering to these stars, then failing to mark on them, and finally maneuvering to an alternate pair. Even with these problems, the alinement was finished approximately 28 minutes before the co-elliptic sequence initiation, and it was possible to proceed with radar lock-on.

All four sources for the co-elliptic sequence initiation solution agreed to within 0.2 ft/sec, an accuracy that had never been observed before. The Commander elected to use the primary guidance solution without any out-of-plane thrusting.

The co-elliptic sequence initiation maneuver was accomplished by using the plus Z thrusters, and the radar lock-on was maintained throughout the firing. Continued navigation tracking by both spacecraft indicated a plane-change maneuver of approximately 2.5 ft/sec , but the crew elected to defer this small correction until terminal phase initiation.

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