65: 3. Launch Mechanics, Primitive Technology, and Trans Lunar Injection. Bob Zimmerman discusses how Apollo 8 launched on December 21, 1968, the first day of its window, following a smooth ride on the powerful Saturn 5 rocket. Engineers had mitigated the "po

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John Batchelor

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🗓️ 8 November 2025

⏱️ 8 minutes

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Summary

3. Launch Mechanics, Primitive Technology, and Trans Lunar Injection. Bob Zimmerman discusses how Apollo 8 launched on December 21, 1968, the first day of its window, following a smooth ride on the powerful Saturn 5 rocket. Engineers had mitigated the "pogo" vibration effects that plagued earlier test flights. After one Earth orbit to verify systems, they performed the Trans Lunar Injection (TLI), firing the upper stage Saturn engines to accelerate toward the moon. This moment marked the first time humans were visibly leaving Earth orbit, an experience Jim Lovell described as the Earth shrinking rapidly, like the exit of a tunnel. The Apollo capsule's onboard computer system was highly primitive, inferior to a simple digital watch calculator. Astronauts had to manually enter long strings of numbers dictated by ground control to execute maneuvers, although Borman maintained the use of a manual override for absolute precision.
1966 APOLLO 1

Transcript

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0:00.0	I'm John Batchel with my colleague Bob Zimmerman.
0:07.6	His book is Genesis, The Story of Apollo 8, the First Man Flight to Another World.
0:13.1	It is December of 1968.
0:16.4	The mechanics of launch give them a six-day window.
0:20.4	And what does that mean, Bob, six-day window and what does that mean bob six-day window
0:22.7	it means they they can launch within that six-day period and do their mission of the
0:28.4	moon and the earth is in the same is in the right position to do so they were fortunate they
0:33.4	were no delays they launched at the very first opening of the window and launched on December 21st on their way into Earth orbit.
0:42.6	And then they spent about one full orbit in Earth orbit testing their systems out to make sure everything was working because they didn't want to leave Earth orbit unless they knew everything was okay.
0:53.4	And then once they had done that and they reached the point in the Earth orbit,
0:57.9	where it was time to fire the upper stage Saturn engines that would power them to the moon,
1:04.0	they got the go-ahead from Capcom.
1:07.0	That's the guy who talks to them from the ground.
1:09.0	And in this case, it happened to be, it's always an astronaut.
1:11.4	In this case, it happened to be Mike Collins, who was on the Apollo 11 mission that
1:15.8	was to follow.
1:17.0	And Mike Collins said to them, your goal for TLI.
1:20.4	TLI is trans lunar injection.
1:22.4	That's the technical term they gave to that firing of that engine.
1:25.3	So the astronauts fired the engine.
1:26.8	And for the first time,
1:28.3	in all missions that had been sent with people into space, these guys were going somewhere.
	...

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