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Zond 1 illustration
A Russian diagram of Zond 1 with its spherical Venus lander visible on the left end. (credit: RKK Energia)

…Try, try again

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By the beginning of 1963 as the crippled Mars 1 was making its way towards the Red Planet (see “If at first you don’t succeed…” Parts 1 and 2, The Space Review, March 24 and 31, 2014), Chief Designer Sergei Korolev and his team at OKB-1 were already making plans for an improved family of interplanetary spacecraft designated Object 3MV that would be sent to Venus and Mars during the next launch windows in 1964. These new spacecraft would incorporate a laundry list of incremental improvements and design changes based on the experience with the earlier 2MV series of spacecraft. Among these was a set of experimental ion thrusters that could serve as a backup to the primary compressed nitrogen attitude control system that had failed on Mars 1.

The 3MV-3 and 3MV-4 would be four times more massive and much more capable that the American Mariner-Mars 1964 flyby mission that was also under development at this time.

Problems with the 8K78 launch vehicle (later to be known as “Molniya”), which had doomed eight out of ten planetary probes launched between 1960 and 1962, not to mention the first two out of three E-6 unmanned lunar landers launched during the first quarter of 1963, were also to be addressed with a new version called the 8K78M that would incorporate its own list of improvements, including upgraded engines and significant modifications to the Blok L escape stage, whose poor performance had stranded a half dozen planetary probes in their temporary parking orbits around the Earth.

Externally, the 3MV series of spacecraft resembled the earlier 2MV series. The 3.6-meter (12-foot) tall 3MV would consist of an orbital compartment which contained control systems, power supplies, and communications gear, as well as some instrument electronics and a planetary compartment that was geared towards specific investigations of the target planet. As before, the planetary compartment came in two varieties: one contained a film camera system and a set of ultraviolet and infrared instruments designed to study the target planet during a close flyby, while the other was a roughly spherical lander with a diameter of about 0.9 meters (3 feet) designed to detach from the orbital compartment before encounter and touch down on the target planet. Both the orbital and planetary compartments were pressurized to provide a laboratory-like environment for the internal equipment in order to simplify the design and testing of various systems as well as provide easier thermal control.

As with the 2MV, the 3MV design had four design variants. The 3MV-1 would have a launch mass of 948 kilograms (2,090 pounds) and carry a planetary compartment designed to land on Venus. Its sister craft, the 3MV-2, would have a launch mass of 935 kilograms (2,061 pounds) and sport a planetary compartment designed to study Venus during a flyby. The nominal launch window to Venus extended from late March to early April 1964. The 3MV probes would follow fast Type I trajectories to arrive at Venus in the second half of July. Because of the success of NASA’s Mariner 2 mission, in January 1963 the United States cancelled plans to launch a follow on mission using Mariner R-3 (to have been assembled from spare flight hardware) during this window, so these Soviet Venera spacecraft would be flying without competition.

Because the launch window to Mars in November 1964 was so much more favorable than the earlier launch window used by Mars 1 in November 1962, the Mars-bound 3MV spacecraft would be significantly more massive than their earlier 2MV counterparts. The 3MV-3 designed to land on Mars would have a launch mass of 1,042 kilograms (2,297 pounds) while the 3MV-4 flyby craft would weigh in at 1,037 kilograms (2,286 pounds). These craft would carry a significantly more massive instrument payload as a result. The 3MV-3 and 3MV-4 would be four times more massive and much more capable that the American Mariner-Mars 1964 flyby mission that was also under development at this time.

Engineering test flights

Korolev understood that there was a need to flight test the new 3MV design in order to iron out the problems that would inevitably crop up. To this end, Korolev envisioned flying two or three dedicated 3MV engineering missions to be launched starting in the summer of 1963. It was hoped that any problems uncovered during these test missions could be resolved in time for the 1964 planetary missions thus increasing their chances for success. Since these test missions would not be directed towards Venus or Mars, after launch they would receive the generic name of “Zond,” which means “probe” in Russian.

The first Zond version would be a stripped down model of the Venus lander craft designated 3MV-1A. Originally envisioned to have a launch mass of 800 kilograms (1,760 pounds), this spacecraft would carry little scientific instrumentation and a lightweight 275-kilogram (606-pound) entry probe. The 8K78 rocket would be used to launch the 3MV-1A into a nearly circular solar orbit inclined about five degrees to the ecliptic. About nine days after launch, a course correction maneuver using the propulsion system employing the KDU-414 engine would be performed. In this solar orbit, the probe would recede to a maximum distance of 12 to 16 million kilometers (7.5 to 10 million miles) before returning back to the vicinity of the Earth five to six months after launch. About 10 to 15 days before reaching Earth, the 3MV-1A would make one more course correction to refine its final approach trajectory. Before reaching the Earth, the entry probe would detach from the orbital compartment and reenter the atmosphere at a speed in excess of 11.5 kilometers per second (7.2 miles per second) to simulate the conditions of an entry into the Venusian atmosphere. After reentry, the parachute system would be tested and, presumably, the lander would be recovered. In addition to giving Korolev’s engineers a chance to test the 3MV-1 design on a long mission, it would be the first spacecraft ever to return to the Earth from interplanetary space, giving the Soviet Union yet another space first.

Since these test missions would not be directed towards Venus or Mars, after launch they would receive the generic name of “Zond,” which means “probe” in Russian.

The second Zond variant would be a stripped down version of the Mars flyby spacecraft designated 3MV-4A. Originally envisioned to have a launch mass of 996 kilograms (452 pounds), this spacecraft would carry a planetary compartment equipped with an updated miniaturized film-based imaging system and other scientific instruments. The 3MV-4A would use an 8K78 to send it on a simulated trajectory towards the orbit of Mars. At a distance of 40,000 to 200,000 kilometers (25,000 to 124,000 miles), the 3MV-4A would turn its camera back towards the receding Earth and acquire a sequence of photographs that would be subsequently developed automatically on board. The spacecraft would then transmit its scanned photographs and other data gathered on the interplanetary environment out to distances as great as 200 to 300 million kilometers (124 to 186 million miles) as part of a long distance communications test. The 3MV-4A mission, if successful, would provide the first images of the Earth taken from deep space and give the Soviets another long distance communication record in addition to a much needed engineering test of the 3MV-4 design.

On March 21, 1963, the Soviet government officially approved the 3MV program. It would consist of one or two 3MV-1A flights and a single 3MV-4A flight to be launched in 1963 as well as a total of six operational 3MV spacecraft to be launched to Venus and Mars in 1964. As had happened all too frequently in the past with other projects, however, design and construction of the new 3MV took longer than expected. However, by July of 1963 Korolev had set the launch schedule for the Zond tests. A 3MV-1A would launch sometime between September 1 and October 15 (with the optimum launch date being October 12) on an Earth-return mission. This launch date would allow the 3MV-1A to be visible high in the sky as viewed from Soviet tracking stations during most of its mission and would result in a return just as the launch window to Venus was opening. While this would be too late to make any major changes to the design of the 3MV-2 Venus lander, it would still allow any problems with the basic 3MV design to be uncovered early enough to make changes a few months before the Venus launches. The 3MV-4A Zond mission was scheduled for launch in March 1964 with sufficient time to make any needed changes to the Mars-bound 3MV design to be launched eight months later.

The Zond missions

Continued delays in the preparation of the first 3MV-1A ended up pushing its launch date out by several weeks, but by early November 1963 it was finally ready. Less time would be available to correct any problems uncovered by this flight but it was felt to be vitally important. On November 4, the Central Committee officially approved two TASS press releases for the upcoming mission. If the test craft was successfully placed on its interplanetary trajectory, it would be called “Zond 1.” But if it got stranded in its short-lived parking orbit by another launch vehicle failure, it would receive a generic “Kosmos” designation to avoid the international treaty and public relations issues that had arisen as a result of the unannounced 2MV launch failures towards Venus and Mars a year earlier.

On November 11, 1963, 8K78 serial number G103-18 lifted off from Site 1/5 at the Baikonur Cosmodrome in Soviet Kazakhstan carrying 3MV-1A No. 2 on an Earth-return mission. But as had happened eight times before, the Blok L escape stage failed to function as intended. During its coast in parking orbit, attitude control was lost and the Blok L ended up firing its engine in the wrong direction, stranding the rocket and its payload in Earth orbit. The orbit of what was now called Kosmos 21 decayed three days later. This would be the first of many failed lunar and planetary missions to be hidden (rather poorly, I might add) by the Kosmos designation.

With the launch failure of the first Zond engineering test mission and the continued unsatisfactory condition of the 3MV spacecraft under final assembly and test, by the end of December 1963 a second 3MV-1A mission was officially approved for launch in January 1964 on the first improved 8K78M, with the 3MV-4A test flight to follow in the April-May time frame after the launch of the Venus missions. While a longer test flight would have been preferred, at least the new 8K78M could be tested and a few weeks of flight experience could be gained before the launch of the Venus missions in two months. Since the problems with Venera 1 and Mars 1 occurred during the first few days of their missions, it was hoped that any hidden problems with the 3MV design would become apparent early enough—and be minor enough—so that the operational 3MV craft could be modified before launch. Eventually it was decided that no 3MV-2 flyby probes would be launched towards Venus during the 1964 window and that all resources would be instead concentrated on preparing just a pair of 3MV-1 landers.

Kosmos 21 would be the first of many failed lunar and planetary missions to be hidden (rather poorly, I might add) by the Kosmos designation.

Still more delays pushed the launch of the 3MV-1A test flight out further, towards the very beginning of the 1964 Venus window. Additional issues with the scheduling of E-6 lunar landing missions, also being developed at OKB-1 at the same time, complicated matters further. Officials finally decided that the 3MV-1A test flight would now take place at the very beginning of the Venus launch window in late February 1964. The 8K78M had sufficient payload capability to launch the lightweight 3MV-1A on a longer Type II trajectory that would reach Venus around the end of August. While it is likely that there was little expectation that this test mission would actually survive the six-plus months needed to reach Venus, it would still provide a vital test of the new 8K78M launch vehicle and a month’s worth of in-flight engineering data that could help improve the chances of success for the pair of operational 3MV-1 landers. After the next E-6 lunar lander was launched during its narrow window around March 21, launch opportunities to Venus on the faster Type I trajectories that would get the landers to Venus in the last half of July became available over the course of the following couple of weeks.

The Venus missions

On February 19, 1964, the first of the improved 8K78M rockets, serial number T15000-19, lifted off carrying 3MV-1A No. 4A on the last chance at a test flight of the Venus probe design. But just as the Blok I third stage was suppose to ignite, failure occurred once again. Liquid oxygen leaking from a bad valve seal froze a kerosene fuel line, causing it to break. This resulted in an explosion and the loss of the launch vehicle with the debris falling to Earth 85 kilometers (53 miles) north of Barabinsk in Siberia.

With the loss of the last available 3MV-1A test craft, it appears that a rather drastic decision was made. Apparently desperate to get some test flight data to improve the chances of reaching Venus, officials decided to launch one of the pair of operational 3MV-1 spacecraft early at the beginning of March on a Type II trajectory to Venus that would provide three weeks of flight data before the opening of the faster Type I launch window later in the month. While the longer, six-month trip time increased the chances that the 3MV-1 would fail before reaching Venus in early September, it would seem that it was felt to be less risky than launching a pair of untried spacecraft with absolutely no test. But the launch of 8K78M serial number T15000-22 for March 1, 1964, was ultimately scrubbed because of problems encountered during prelaunch integration of the 3MV-1 with the 8K78M. In order to resolve the problem, the launch was postponed to the opening of the Type I launch window at the end of the month. The 3MV-1 would now have to fly untested.

As the final preparations for the pair of 3MV-1 landers were being made, the focus shifted to the launch of the unmanned lunar lander, E-6 No. 6. The E-6 Luna program was coming out of a self imposed year-long stand down as major problems with the E-6 uncovered during the first three attempts in early 1963 were fixed. It was hoped that the E-6 problems were resolved and that this flight would beat America’s delayed Surveyor lunar lander by a year or more. On March 21, 1963, 8K78M serial number T15000-20 lifted off carrying the new E-6. But a series of problems with the 8D715P engine on the Blok I third stage culminated in its premature shutdown 487 seconds into the flight. The rocket and its payload were destroyed during reentry.

With two successive failures of the new 8K78M, it was now the turn of the 3MV-1 Venus landers. With its earlier problems now resolved, 3MV-1 No. 5 was launched on March 27, 1964, on 8K78M serial number T15000-22. This time the first three stages of the new 8K78M worked as intended to place the Blok L escape stage and its Venus-bound payload into a low parking orbit. But during the unpowered coast, attitude control was lost and the Blok L never ignited its 11D33 engine. Stranded in Earth orbit, the rocket and its payload were designated Kosmos 27. Despite the failure, one of the many improvements made to the new Blok L paid off this time. Data from the various systems gathered by the new telemetry system were recorded and radioed back to ground controllers on the next orbit, allowing engineers to diagnose the failure like never before. This failure (and probably a couple of earlier failures) were found to be the result of a fault in the design of the wiring of a key control system in the Blok L. Fortunately, the fix involved only 20 minutes of a technician’s time with a soldering iron to resolve for the next launch attempt.

With its wiring fault fixed just in time for the end of the Venus launch window, 8K78M serial number T15000-23 lifted off the morning of April 2, 1964, at 2:42:40 UT carrying 3MV-1 No. 4. This time all four stages of the 8K78M worked, sending what was to be called Venera 2 on its way to Venus and the first attempted landing on another planet. However, before the triumphant launch announcement could be made, controllers discovered a major problem during the first communication session with the receding probe. The pressurized orbital compartment was leaking and all its gas would be lost within a week, severely compromising the ability of its equipment to operate. With bleak prospects for success, the Soviets announced the probe simply as Zond 1, making no mention of its mission to Venus.

Because of the torque from the leak in the orbital compartment, Soviet engineers were able to pin down the problem quickly as a bad weld near the quartz window for the probe’s star and Sun sensors. While it would not help Zond 1, future 3MV craft would have their welds X-rayed as a new quality control check. While the probe was still fully functional and engineers formulated a contingency plan to keep the spacecraft operating as long as possible, Zond 1 made a course correction maneuver the day after launch at a distance of 563,780 kilometers (350,390 miles) to refine its trajectory. This was the first time the KDU-414-based propulsion system had been used on a Soviet planetary mission.

The last public announcement about Zond 1 came on May 19 and all communications were lost on May 24. The now silent Zond 1 flew by Venus on July 19.

By April 9 the pressure in the orbital compartment had dropped to the point where it became unreadable by the onboard sensors. Since the Zond’s main transmitter required a pressurized compartment to maintain thermal control and suppress arcing in its high voltage circuitry, ground controllers routed communications through one of the redundant pair of transmitters in its 290-kilogram (640-pound) lander. Obviously Soviet engineers had learned the same hard lessons of redundancy that their American counterparts had during the failures of the Ranger program. With some measure of command, control, and communications, Zond 1 proceeded to gather limited data from its instruments about the interplanetary environment. Its new ion thrusters were also tested but were found to operate erratically, possibly due to the loss of pressure in the orbital compartment.

Continued tracking of Zond 1 showed that it would still miss Venus by a large margin, so on May 14, a second course correction was attempted. At a range of 14 million kilometers (8.7 million miles) from Earth, the KDU-414 engine ignited for a second time changing the velocity of Zond 1 by 50 meters per second (110 miles per hour) before the engine apparently cut off early. Still 20 meters per second (45 miles per hour) shy of the required velocity change, Zond 1 would now miss Venus by about 100,000 kilometers (62,000 miles).

As the cruise to Venus continued, more problems cropped up, including the apparent loss of one of its star sensors. Zond 1 was placed into a flat spin to stabilize the orientation and keep the solar panels pointing towards the Sun. Unfortunately, the high gain antenna could no longer be used so contact via the lander’s communication systems could only be maintained until about the middle of June before it was too far away—a full month before reaching Venus. As luck would have it, though, Zond 1 would not last that long. The last public announcement about Zond 1 came on May 19 and all communications were lost on May 24. The now silent Zond 1 flew by Venus on July 19.

With this latest failure, Korolev and his team at OKB-1 were left scrambling to diagnose and correct the problems uncovered with the 3MV and the 8K78M. The 3MV-4A test flight was postponed and plans for the upcoming launch window to Mars in November 1964, which now would be competing with a pair of smaller American Mariner spacecraft, had to be reconsidered.


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