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3MV (Zond)

Missions to Venus

Venera-72 (Kosmos-482)

Kosmos-27: another failure

Previous chapter: Mission of 3MV-1A No. 4A spacecraft

Kosmos-27: another failure

The first follow-on 3MV vehicle arrived to Tyuratam on February 11, 1964, slightly more than a week before the launch of its Zond predecessor. (202)

On March 2, 1964, Soviet officials sent a note to the Kremlin informing the government that two 950-kilogram 3MV spacecraft with 285-kilogram landers were ready to embark on a 120-day journey to Venus. According to the document, the landers were designed to conduct a ballistic descent into the atmosphere of Venus, followed by a parachute landing. The optimal launch date for the mission would be March 27, plus or minus four days, the document said. Both Venus missions would be conducted in a midst of a busy deep-space launch campaign, also involving a pair of E-6 lunar probes:

March 21: Launch of a single E-6 lunar probe;
March 25-31: Launches of two 3MV spacecraft;
April 20: Launch of the 2nd E-6 lunar probe.

If everything went as planned, a pre-approved public statement would identify the 3MV spacecraft heading to Venus as Venera-2. (509)

On March 27, 1964, the USSR made another planetary launch attempt from Pad 1 in Tyuratam. All post-Cold War sources agree that a 8K78 Molniya rocket carried a 3MV-1 No. 5 spacecraft with a Venus lander. Essentially, it was the first fully operational 3MV spacecraft, rather than a Zond test vehicle.

Yet again, the troubled Molniya rocket continued misbehaving. As several times before, the Block I third stage and Block L fourth stage separated in the initial parking orbit, however Block L failed to perform a required engine firing to propel the spacecraft toward Venus. (52) However this time, engineers were finally able to pinpoint the exact culprit in this and in previous failures of 1VA and 2MV-4 missions. Unlike previous launches, this mission carried a Yakhont data storage unit, which recorded the telemetry during a failed attempt to fire the main engine on the Block L upper stage. As the crippled vehicle reappeared over Tyuratam during the next orbit, this information was downlinked to a ground station. (466)

The Block L stage had a so-called ignition provision unit, BOZ, which gave initial acceleration to the vehicle, ensuring that liquid propellant would flow into the main engine despite the weightless conditions of space. The BOZ unit was mounted on the truss structure, which also carried the attitude control system, a battery and related electronics. Exactly 70 seconds before the ignition of the main engine, the flight control system was programmed to switch power supply to the attitude control system from a battery on the BOZ unit to the main battery on Block L. However, due to a minor design flaw, this switch was not taking place, leaving the vehicle with disabled attitude control system, during the critical 70 seconds, when the main engine needed to fire in a certain direction. Instead of being in a stable orientation for the maneuver, the spacecraft would enter a free drift. As soon as the orientation of the vehicle violated acceptable parameters, the firing of the engine would be blocked. (52)

As the mission was stuck in a parking orbit, the USSR announced it as Kosmos-27. (202) Western radar detected three objects associated with the mission in a 237 by 192-kilometer orbit: likely, the Block I third stage, the Block L fourth stage with its payload and a fragment, probably a BOZ unit. Observers quickly identified the launch as a Venus flyby mission, with no way of knowing that it was carrying a lander as well. (185)

Just a day after launch, Kosmos-27 reentered the Earth atmosphere. (227)

Next chapter: Mission of Zond-1

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APPENDIX

Kosmos-27 mission at a glance (202):

Spacecraft	3MV-1 No. 5, Kosmos-27
Launch vehicle	8K78M (Molniya-M) No. G15000-27
Launch date	1964 March 27, 06:24:43 Moscow Time
Flight plan	Venus landing
Flight status	Failed in Earth orbit
Date of reentry	1964 March 28

Article by Anatoly Zak; last update: April 1, 2014

Page editor: Alain Chabot; last edit: March 31, 2014

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Block-I

A Block L fourth stage (foreground) and the Block I third stage of the 8K78 (Molniya) rocket during the assembly. Credit: RKK Energia

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