Mariner 10, 1974
We did Mariner 10 while I was out at Kitt Peak. That one went to Venus and then to Mercury. We went around the planet, and then around the Sun to shoot back to Mercury. Orbiting Mercury, we always came back to the same place at the same time. The last time we passed, we ran out of gas. The control is done by gas jets.
They actually flew it around the Sun the last time using the solar panels to stabilize it, because they knew they were going to run out of gas. So they used the solar panels to fly it like a sailboat. Then as they approached Mercury, they turned on the gas jets and stabilized it, and we did our experiments until the power passed.
I got involved during the Apollo program in Mariner 10, which was the first flight to Mercury. That was a reconnaissance flight to just see what was on Mercury, and to plan for an orbiter. It wasn’t supposed to be a definitive mission; reconnaissance was all it was. That was a successful mission.
Nobody’s ever been back to Mercury since 1975. I was on the planning committee to send an orbiter there. It never happened, for two reasons. One, people looked at Mercury and said, “Oh, well, it’s just like the Moon, so it’s not interesting.” Which is baloney, but that was the perception at the time. The other reasons is, to send a mission to orbit Mercury is an extremely difficult task, and extremely expensive. They haven’t been to Mercury until recently [with the MESSENGER mission].