The free-return trajectory for the Apollo missions worked similarly, except the opposite (how can that be?). Instead of approaching the Moon from behind, it approached from in front, so that the Apollo spacecraft would slow down instead of speed up, then Apollo could fall back to Earth, so long as it slowed the right amount and in the right direction. Otherwise it would miss the Earth. Free-return trajectory for Apollo was a very small window.

Ames had very little money to develop and build those probes. They were very simple affairs next to the Voyagers, even after their knock-down redesign from the TOPS architecture. (As a kid, I was fascinated with the Pioneers and Voyagers, and I remember being surprised to see how small the full-scale mockup of Pioneer 10 was when my parents took us to the NASM.) I think it remains a marvel how much they were able to accomplish, having so little to work with.

But yes, they got roughed up. It was our first direct evidence of just how formidable it was going to be to operate in Jupiter’s electromagnetic field.

Richard M: Ah, but the whole point of Pioneer 10 and 11 was to characterize the environment around Jupiter so as to inform the design of the Voyager spacecraft. In that, both missions were spectacular successes, strengthened by the fact that both were able to send back a number of excellent pictures of Jupiter, plus several of its larger moons.

But….the experience of Pioneer 10 and 11 proved of great benefit to the final design of the Voyagers. Ames engineers happily passed along their data to their Voyager counterparts, who, among other things, added more radiation shielding to their vehicles.