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1.4.3 L1 Mission Descriptions
Dates are launch to reentry (where applicable).
| Cosmos 146 | March 10-18, 1967 | |
| First flight of a Soyuz-based L1 vehicle in space. The version flown was, however, simplified, because the flight was intended primarily as a test of the Block D fourth stage of the Proton launch vehicle. The Block D engine fired twice in the course of the flight. | ||
| Cosmos 154 | April 8-10, 1967 | |
| Block D could not fire, possibly because of premature ejection of its ullage motors (used to settle fuel in the stage after weightless coast in parking orbit). Because of this, Cosmos 154 failed to test the high-velocity reentry characteristics of the L1.[1] | ||
| Launch failure | September 28, 1967 | |
| One of the six engines in the Proton first stage failed to operate. The emergency escape system dragged the descent module free of the errant rocket. | ||
| Launch failure | November 22, 1967 | |
| One of the four engines in the second stage of the Proton failed to operate. The emergency escape system activated. The land landing rockets fired prematurely during parachute descent. | ||
| Zond 4 | March 2-9, 1968 | |
| First L1 spacecraft called Zond. Zonds 1 through 3 were interplanetary probes unrelated to Soyuz. The unmanned Zond 4 spacecraft flew to lunar distance, but away from the Moon. It was lost during reentry because of an attitude control failure.[2][3] | ||
| Launch failure | April 23, 1968 | |
| Escape system triggered mistakenly during nominal Proton second stage operation. | ||
| Zond 5 | September 14-21, 1968 | |
| Successfully circumnavigated the Moon, but its guidance system failed, resulting in an unplanned splashdown in the Indian Ocean. It was recovered and shipped to the Soviet Union via India. | ||
| Zond 6 | November 10-17, 1968 | |
| Tested the worldwide tracking system set up for Soviet manned lunar missions and photographed the Earth. During reentry, the descent module depressurized. | ||
