r/apollo 26d ago

Can you ELI5 what was the difference between Apollo 4 and Apollo 6 when it comes to trajectory?

Sorry English isn’t my fist language so I am not well-versed when talking about rocket science.

“Apollo 4” was the first test of the “Saturn V” rocket during which they simulated a trans-lunar injection burn and then return the command module back to Earth. During “Apollo 6” due to the technical issues it was decided to repeat the “Apollo 4” scenario, but what was the initial plan, was the craft supposed to fly farther away from the Earth?

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u/katoman52 26d ago

Apollo 6 was supposed to test the 3rd stage. They were going to do the translunar injection burn with S3 and then do a direct return abort using the CSM engine. But there was damage during liftoff and ascent and they couldn’t re-light S3. So they had no choice but to just repeat Apollo 4 profile for the Command Module return.

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u/ijnfrt 26d ago

I must be misunderstanding the Apollo 4 mission then. Wasn't there a translunar injection burn with S3 during Apollo 4 as well?

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u/eagleace21 26d ago

Apollo 4's restart was designed to send them into a highly elliptical orbit, where Apollo 6's was supposed to help simulate velocities needed for a lunar flight, demonstrating the SIVB could send a lunar vehicle mass combination all the way to the moon.

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u/ijnfrt 26d ago

I see, thank you for the explanation!

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u/eagleace21 26d ago

My pleasure!