The Soviet circumlunar plan

The Soviets hoped to send cosmonauts around the moon in Zond...but they only sent turtles.

Separate from their plans for a manned lunar landing—which planned to use the (then) new Soyuz spacecraft, the gigantic N-1 launch vehicle, and a tiny one-manned lander—the Soviet Union had a separate program to send cosmonauts to loop around the moon.

Of course, they really wanted to do this before the Americans. And they began testing the hardware—called Zond—for just such a mission. They launched unmanned tests of the Zond, using the (seemingly) trusty Proton booster. In 1968, they launched Zond 4, Zond 5, and Zond 6 achieving some success, but leaving some serious worries.

For example, Zond 5 looped around the moon, successfully returning a “crew” of turtles and other biological specimans to earth…but landed off target.

Zond 6 repeated the feat, but lost cabin pressure, killing the biological specimans, and landed very, very hard.

Even the Soviet Politburo balked at sending actual cosmonauts on the next flight—which would have been in early December 1968. If successful, a manned Zond 7 would have beaten the Americans who put their Apollo 8 crew in lunar orbit near the end of that month.

It’s a very good thing the Soviets decided not to send cosmonauts. Aleksei Leonov and Oleg Makarov had trained for the mission. They sent that Zond unmanned instead—later, in January 1969—and the booster failed; the vehicle was destroyed.