
Re: Why stop at 5 years?
"They sure did. Because there was no alternative. Computers and robotics in the 60/70s were nowhere near as advanced as they are today"
Yes there was.
Apart from physically "walking on the moon" the entire Apollo mission from launch to splash down could have been run automatically via Mission Control and the two Apollo Guidance Computers - one in the CSM and one in the LM.
They never did a fully automated lunar landing for one reason only - astronauts egos wouldn't permit it. In fact a fully automated "test landing" was discussed but killed because if the first Apollo LM landed with nobody onboard, the American public would rightly have said - "why are spending all the money to send men when a machine can do it?"
Launch was handled entirely by the IM computer in the Saturn V and Mission Control. The "astronauts" were just passengers, or as the oft used expression so aptly put it, "spam in a can".
Getting a man on the moon - i.e. Apollo - was all about beating the Soviet Union in space for political reasons.
Voyager 1 & 2 were designed and built using 60's/70's technology and BOTH are still exploring.
https://science.nasa.gov/mission/voyager/where-are-they-now/
The first space shuttle computers (five per shuttle) used core memory! How advanced the technology is nowhere near as important for spacecraft as reliability and ability to "harden" them for use in space.
Though I entirely agree with your point about robotic spacecraft. You didn't clearly state the biggest disadvantage to using humans - the expect to come back,alive.