TRANSLUNAR INJECTION

The use of a parking orbit provided a full revolution of Earth in which to confirm that the S-IVB stage and the spacecraft were fully operational prior to attempting the TLI manoeuvre. The alternative would have been to time the launch to enable the S – IVB to undertake a single long burn directly onto a translunar trajectory. Such a manoeuvre was viable, but offered fewer contingency options. Specifically, if the spacecraft were to be found to have a fault that would require an abort and return to Earth, it would already be outbound by the time this became evident. However, the time spent in parking orbit posed a thermal issue for the S-IVB, which held liquid hydrogen at -423°F and liquid oxygen at -293°F. Nevertheless, the designers had cleverly exploited this fact, because as heat leaked in and caused the hydrogen to boil, the gas was vented through two small aft-facing nozzles for ongoing ullage to maintain the propellants settled in their tanks.

The burn was to begin at 002:44:14 and nominally last 5 minutes 47 seconds, but the Instrument Unit was programmed to terminate the manoeuvre when the desired velocity had been attained, and would therefore cut off early if the engine were to overperform and extend the burn if the engine underperformed. Armstrong was to allow it an additional 6 seconds before intervening, and asked Collins to monitor the duration and yell out at 5 minutes 53 seconds.

When Apollo 11 again came into range of Carnarvon, McCandless called with good news, “You are Go for TLI.”

“Thank you,” Collins acknowledged.

The S-IVB terminated its hydrogen venting, pressurised its propellant tanks, and ran through the pre-start sequence for the J-2 engine.

NASA had equipped several KC-135 aircraft as Apollo Range Instrumentation Aircraft, and stationed them in a line across the Pacific between Australia and the Hawaiian Islands. “They’re going to try uplinking both on S-Band and on VHF,” McCandless advised. “So if you make sure your S-Band volume is turned up, we’d appreciate it. We should have continuous coverage from now on, right through the TLI burn.’’

“Very good,’’ acknowledged Armstrong.

McCandless established a relay through ARIA 4 but the signal was noisy, so he switched to ARIA 3, which was much clearer. The aircraft relayed telemetry to Houston. “We just got telemetry back down on your booster,’’ McCandless advised, “and it is looking good.’’

“Everything looks good here,’’ Armstrong confirmed.

Although Apollo 11 would be the third mission to perform the TLI manoeuvre, it was by no means routine, as any major engine burn represented a potential point of catastrophic failure. The manoeuvre began in the vicinity of the Gilbert Islands, about half-way between Australia and Hawaii. The Instrument Unit was in control, but it provided cues to the spacecraft, and illuminated a lamp immediately prior to igniting the J-2 engine.

“Whew!’’ exclaimed Armstrong on the intercom circuit when the engine lit.

“We confirm ignition,’’ called McCandless, “and the thrust is Go.’’

“Pressures look good,’’ Armstrong noted.

“About 2 degrees off in the pitch,’’ Aldrin pointed out.

“I wouldn’t worry too much about that,’’ Armstrong advised.

The Real-Time Computer Complex was using the ARIA data to calculate the S – IVB’s departure trajectory, and any emergency course correction that the spacecraft would have to make in the event a shortfall in velocity.

“One minute,’’ called McCandless. “Trajectory and guidance are looking good, and the stage is good.’’

For the crew, the burn was silent. Although the engine was 110 feet behind and directed its plume aft, Collins noticed intermittent flashes of light through his side window. “Don’t look out of window 1,’’ he chuckled, “because if it looks like what I’m seeing out of window 5, you don’t want to know.’’

“Oh, I see a little flashing out there, yes,’’ Armstrong said.

From the centre couch Aldrin’s field of view was limited, but he looked across Collins, “Damn. Kind of sparks flying out there.’’

There was a lurch when, as programmed, the S-IVB adjusted the ratio of fuel to oxidiser being fed to the engine.

McCandless provided a reassuring update, “Thrust is good.’’

As the S-IVB consumed propellant and its structural dynamics altered, it began to vibrate. On Apollo 8 the amplitude of the vibration had caused Frank Borman to

consider aborting the burn. As the rattle built up, Aldrin became concerned that it might shake loose the Maurer camera that he had mounted in window 4. Collins, not wanting the camera to fall on his helmet, checked that it was secure.

As they climbed, they emerged from Earth’s shadow rather earlier than if they had remained in low orbit. The sunlight that suddenly flooded in made it difficult to read the instruments, but Armstrong had had the foresight to mount a card in his window to serve as a shade. “I’m glad I got my card up!’’

“Neil, that was a hell of a good idea,’’ congratulated Collins. “I can’t see very much.’’

“You are Go at 5 minutes,’’ McCandless advised.

As long as the J-2’s burn continued to within about 45 seconds of the intended duration, the mission would be able to continue by having the CSM later employ its main engine to make up the velocity shortfall. A greater shortfall would require an abort in which the CSM cancelled the result of the interrupted TLI and pursued a trajectory designed to end with a landing in the primary recovery zone, where the US Navy had ships already on station.

The S-IVB’s acceleration built up as it consumed its fuel and became lighter.

“What kind of g we pulling?’’ Aldrin asked.

“1.2, or 1.3 g, maybe,’’ Armstrong replied.

“Gee, it feels a lot more than that.’’

“Here we go,’’ announced Collins, as the nominal time for cutoff approached.

Two or three extra seconds passed, then the engine shut down.

“Shutdown!’’ called Armstrong.

Prior to the TLI manoeuvre, the vehicle had been in a nearly circular orbit at an altitude of about 100 nautical miles. The burn was to accelerate by 10,435 feet per second, to a velocity of 35,575 feet per second at an altitude of 174 nautical miles. At cutoff, it had attained 35,579 feet per second and 177 nautical miles, which was excellent by any measure. On the ground, the mass of the space vehicle had been 6.5 million pounds; at insertion into orbit it was slightly less than 300,000 pounds; it was now 138,893 pounds.

“Houston, that Saturn gave us a magnificent ride,’’ Armstrong announced. “We have no complaints with any of the three stages.’’ It was another great success for Wernher von Braun’s rocket team at the Marshall Space Flight Center.

The TLI manoeuvre inserted the vehicle into an elliptical orbit with an apogee beyond the orbit of the Moon. It did not shoot the spacecraft directly towards the Moon, but some 40 degrees ahead of the current position of the Moon in its nearly circular orbit of Earth. However, as the spacecraft neared apogee in three days’ time, the gravitational field of the now-present Moon would deflect its trajectory. If the spacecraft were to do nothing, it would pass around the ‘leading limb’ on a figure-of – eight ‘free return’ path that would send it back to Earth. However, the plan was to fire the main engine while behind the Moon in order to slow the spacecraft and enter lunar orbit.