Zond 6 was the 13th launch of the Soviet ‘Zond’ space program. This program, started in the early 1960’s and had two distinct eras of different spacecraft. The first of which, used in the initial three launches, was based on the 3MV Planetary Probe. However, after two failed attempts to explore Venus and Mars, the Probe was used to photogrpah the backside of the moon for the second time in history and was then retired from the Zond program.

That brings us to the era which includes the Zond 6 mission. This era was dominated by a stripped-down Soyuz spacecraft which included service and decent modules but no orbital module. This series of missions was intended to be a first step towards manned cirumlunar flights. The first successful circumlunar flght of the series was the Zond 5 on September 15th, 1968 which was shortly followed by the Zond 6, 50 years ago today.

Zond 7K-L1 Spacecraft, Image Source

The 7K-L1 represented a lot of firsts for the Soviet space program. This was the first Soviet spacecraft to utilize an onboard flight control computer, the Argon-11s. This spacecraft would also be the Soviet’s first attempt at circumlunar navigation which would be a larger challenge than the earth orbiting missions of previous Soyuz spacecraft. Instead of simply having to attain an orbital velocity, this time the spacecraft would have to attain orbit around Earth and then fire its engines a second time (Number 3 in the photo below). This second firing, known as trans-lunar insertion, is required to escape Earth’s gravity and begin the journey to the moon.

L1 Flight Profile, Image Source

At a little past 7 p.m. on November 10th, 1968, the Zond 6 mission launched from Baikonur Cosmodrome on board a Proton-K rocket. The rocket performed a successful launch and trans-lunar insertion and the spacecraft was on its way to a successful circumlunar mission. On November 14th Zond 6 flew around the moon taking numerous photographs of the near and far sides of the moon using its AFA-BAM camera. In total, 169 photographs were taken between 2,430 km and 9290 km. A copy of one of the few images from the mission ever published can be seen below displaying the Earth over the horizon of the moon.

Zond 6 Photograph, Image Source

With the mission complete it was time to bring the spacecraft back down to Earth’s surface. The intention was to utilize a technique known as ‘skip reentry’ to decrease the craft’s velocity to allow for a safe and stable reentry. However, on November 17th, a few hours before reentry, an O-ring failed causing depressurization and the unfortunate death of all animal test subjects onboard.

Following this, the parachute was deployed too early and resulted in the crash landing of the spacecraft near the intended landing zone in Kazakhstan. This crash resulted in the complete destruction of all but 52 of the photographs. At the time, as a propaganda move, the Soviet Union announced publicly that the mission was a complete success. Despite the unsuccessful reentry attempt, this mission was indeed a huge success and milestone in the space age. This was one of human’s first ever looks at the far side of the moon and assisted in reassuring the scientific community that it would indeed be possible to get humans to the moon and back. In hindsight, this was one of the many steps along the way to one of human’s greatest achievements in the form of the manned Apollo missions.