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The USSR repeats secret lunar space tug test attempt One year after the failed launch of the first L1E test flight, Soviet engineers made another try to test their Block D lunar space tug on Dec. 2, 1970. This time, the secret mission went much better but more than half a century later there are still many questions about its flight plan and the spacecraft design.
The L1E No. 2 mission at a glance:
A second copy The critical importance of the Block D stage for the Soviet lunar program and other projects prompted the effort to launch the second L1E spacecraft which had been in the production pipeline from the beginning of the Block D test flight program around 1967. At the time of the first spacecraft failure due to a botched launch late in 1969, the second L1E was in advanced stages of assembly. The specially modified Block D stage No. 26, allocated to the L1E No. 2 mission, was also available. (1075) On April 20, 1968, interim head of the TsKBEM design bureau Yuri Semenov, signed the technical assignment for the construction of an experimental ground unit for the future L1E spacecraft. The construction of the two flight vehicles was proceeding as well. The bodies of two ships were ready by January 1969 and mockups were also under construction. However on both vehicles, engineers were struggling to ensure tight seal on the unique "see-through" tank sections of the Block D stage, which were designed to enable outside cameras to document fluid dynamics in the tank interior. As of May 7, 1969, the second L1E mission was scheduled for launch in December of that year, or just a month after the flight of its predecessor. Obviously, the failure of the L1E No. 1 in November 1969 severely derailed these plans. On July 6, 1970, Head of TsKBEM, Vasily Mishin jotted down a note indicating that only 1.5 months were required for preparing the (second) L1E launch, but in reality, the vehicle would not reach the launch pad until December of that year. (774) L1E-2 mission lifts off The UR-500K rocket carrying the 7K-L1E No. 2 spacecraft lifted off on Dec. 2, 1970, at 20:00 Moscow Time, from the "Left" pad at Site 81 in Tyuratam. (400) This time, the ascent to orbit apparently proceeded exactly as planned, inserting the spacecraft and the Block D upper stage into a 190 by 300-kilometer initial orbit, even though it was likely too short-lived for its parameters to be cataloged by Western radars. During the mission, officially announced as Kosmos-382, a total of three major maneuvers were detected. According to one hypothesis, the first two burns simulated the insertion into orbit around the Moon and the maneuver to enter pre-descent orbit planned for the L3 expeditionary complex. The other theory was that the mission simulated the planned maneuvers of the lunar orbiting vehicle, expected to serve as a payload in the upcoming test launch of the N1 Moon rocket, which ultimately took place in June 1971. As of 2025, no contemporaneous sources were available to the general public detailing the flight program of the Kosmos-382 mission or even confirming the overall design of the L1E spacecraft. Western tracking data showed that as soon as the spacecraft reached its apogee over the Southern Hemisphere during the first revolution around the Earth, the first maneuver stretched the orbit into a long ellipse boosting the apogee to an altitude of 5,038 kilometers, while raising a perigee to 303 kilometers. The maneuver required estimated 982 meters per second in velocity change. Soviet sources also gave very similar orbital parameters (320 by 5040 kilometers) for the Kosmos-382 mission. The USSR recorded the inclination of that orbit as 51.5 degrees, indicating a small, but significant in terms of propellant, change from the 51.6 degrees normally used by the Soviet spacecraft for their initial parking orbit. (2) On Dec. 4, 1970, the second major burn of the Block D engine mostly lifted the perigee of Kosmos-382, placing the spacecraft into a 1,616 by 5,071-kilometer orbit, at a cost of 285 meters per second in estimated velocity change. Soon thereafter, two objects were detected separating from the main spacecraft. One of them was interpreted as a rocket stage, however, there is no information from the Soviet sources whether the Block D and the L1E spacecraft were expected to separate. The final detectable burn around Dec. 7, 1970, which could simulate the deorbiting burn of the LK/Block D stack in lunar orbit, in reality boosted the perigee of the Kosmos-382 mission even further, placing the vehicle into the a 2,577 by 5,082-kilometer orbit around the Earth and increased its inclination to 55.87 degrees, where the spacecraft would remain for decades. (50) The published notes by Vasily Mishin later confirmed that the L1E No. 2 spacecraft operated until Dec. 7, 1970, when it completed its mission with the seventh firing of the Block D engine at 19:00 Moscow Time. Possibly, the four firings missing from the Western record were simply too small to be detected, but there are no enough historic record to reconcile this discrepancy. According to a post-flight review chaired by Mishin on Dec. 14, 1970, Block D fired a total of seven times during the flight of L1E No. 2, which was the main achievement of the project, essentially certifying the capabilities of the Block D stage for the L3 lunar expeditionary project. Ironically, in its subsequent decades-long career, Block D would never have to pass such an endurance test. The Kosmos-382 mission also recorded the thermal regimes of the oxygen tank on the Block D and tested the operation of the 110K attitude-control tracker on the L1E spacecraft. The dynamics of the vehicle were also recorded. Finally, the engineers studied various phenomena inside the Block D stage, such as the boiling of the cryogenic oxygen, as well as watched condensation and separation between gas and liquid under conditions of weightlessness. (774) Western analysts noticed that the format of the telemetry transmissions from Kosmos-382 was similar to those from the known failed launch of a Proton rocket in November 1969, so the link between the two L1E missions was established very early on. The mission was also correctly characterized as related to the Soviet lunar program, but that where the known information would mostly end. (50) It took another 50 years to all but confirm that the L1E vehicle was probably very similar to the L1A prototype spacecraft launched on the N1 rocket, even though no actual blueprints of the L1E spacecraft had been published by the end of the first quarter of the 21st century.
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