Fifty years ago today the Soviet Union launched Zond 1 on a mission to land on Venus. Unfortunately this probe succumbed to a series of malfunctions after leaving the Earth and contact was lost on or about May 24, 1964 – two months before its scheduled encounter with Venus. Over the past couple of decades much information on Zond 1 and its even less successful sister probes has come to light enabling historians to piece together many of the details of their intended missions. Despite this, confusion still seems to exist about the true objectives of the precursor missions launched on February 19, 1964 and scheduled for launch (but not flown) on March 1. Presented here is an analysis of the trajectories available during the 1964 Venus launch window based on a contemporary NASA technical document . This analysis combined with existing information helps to clear up much of the confusion and establishes that all of these missions were actually launched towards Venus.
The primary spacecraft for the Soviet Union’s 1964 Venus missions were a pair of 3MV-1 landers serial numbers 4 and 5 built by the Soviet’s OKB-1 design bureau headed by the famed Chief Designer Sergei Korolev. With a mass of about 950 kg, they were improved versions of the pair of 2MV-1 landers unsuccessfully launched towards Venus on August 25 and September 1, 1962. The 3MV-1 consisted of a carrier bus known as the orbital compartment that would carry a spherical lander with a diameter of 90 cm and a mass of 290 kg . Before the encounter, the lander would separate from its carrier, enter the Venusian atmosphere and make a parachute descent to the surface. If all went well, the lander would return vital new data on the atmosphere and surface of Earth’s mysterious, cloud shrouded twin.
Realizing the need to test the new design before the actual Venus mission, Korolev and his engineers at OKB-1 also designed and built a stripped-down version of the 3MV-1 known as the 3MV-1A. Its intended mission was to carry a 270-kg engineering model of the Venus lander into a near-circular solar orbit inclined five degrees to the ecliptic that would return to Earth after five to six months in interplanetary space . The test lander would separate from the 3MV-1A orbital compartment and reenter the Earth’s atmosphere to test the system under conditions that realistically simulated a high-speed entry into Venus’ atmosphere. The original intent was to fly this mission early enough in 1963 so that any problems with the 3MV-1 design could be identified allowing modifications to be made to the operational 3MV-1 spacecraft before their nominal launch window to Venus during the last week of March and first week of April 1964.
After many delays, the first engineering test mission, using 3MV-1A No. 2, was launched using an 8K78 Molniya on November 11, 1963. But a problem with the launch vehicle’s escape stage stranded what became known as Kosmos 21 in a useless short-lived parking orbit . Desperate to get much needed test data on the 3MV design, the launch of a second 3MV-1A was authorized and scheduled for January 1964. More delays pushed the launch of 3MV-1A No. 4A out to February 19, 1964 [3, 4]. By this point, there were only about five weeks until the launch of the operational 3MV-1 landers so that a full six-month long Earth-return mission would be of little engineering value. Still, the problems with the earlier Soviet planetary probes, Venera 1 and Mars 1, became apparent during the first couple of days of flight so conceivably there would be enough time to uncover any hidden issues with the 3MV design and make (hopefully minor) modifications to the operational spacecraft before their launch to increase the chances of their success. But exactly what the target of the 3MV-1A mission was has been a bit of a mystery. Some reliable sources state it was aimed towards Venus [5, 6, 7, 8] but many analysts believe that it was not directed towards Venus at all since it was launched about a month before the nominal Venus launch window.
With the loss of 3MV-1A No. 4A due to a launch failure of the new 8K78M on February 19, a decision was made to launch an operational 3MV-1 early on March 1 . Since it was being launched over three weeks before the opening of the nominal Venus launch window, the exact nature of its mission objectives are uncertain. Ultimately problems encountered during the integration of the 3MV-1 to its 8K78M launch vehicle forced the March 1 launch to be scrubbed .
The first operational lander, 3MV-1 No. 5, was finally launched on March 27, 1964. After it became stranded in its parking orbit after yet another escape stage malfunction, it was designated Kosmos 27 [3, 5]. 3MV-1 No. 4, launched on April 2, was the only probe in the series to actually make it beyond Earth orbit. But early on it was discovered that its pressurized orbital compartment had developed a leak and was unlikely to make it to Venus so it received the generic name of Zond 1 instead of its originally intended designation of Venera 2 . The loss of pressure in the orbital compartment severely affected the operation of on board equipment and after a series of subsequent system failures, Zond 1 fell silent on or around May 24, 1964. Zond 1 silently flew by Venus at an estimated distance of about 100,000 km on July 19 [2, 7].
1964 Venus Trajectories
There were two families of low energy launch opportunities to Venus available in early 1964. These are illustrated in the contour plot in Figure 1 taken directly from Reference . In this figure, contours of C3 launch energy are plotted as a function of launch date (X-axis) and time of flight (Y-axis). As can be seen, the most energetically favorable family of trajectories that allowed for the largest possible launch mass (or the longest possible launch window for a payload of a given mass) were the Type II trajectories where the spacecraft travels more than 180° in its orbit around the Sun from launch to its encounter with Venus. Assuming a launch energy requirement comparable to that used by the Mars 1 spacecraft launched in November 1, 1962 , the launch window for Type II trajectories would run from about mid-February to mid-May. Unfortunately, the minimum energy Type II trajectories have times of flight on the order of 165 to 195 days (with shorter times later in the window) and communication ranges of around 105 to 165 million km at the time of encounter (with shorter ranges coming earlier in the window) .Although energetically less favorable, the Type I trajectories, where the spacecraft travels less than 180° in its orbit around the Sun from launch to its encounter with Venus, were far more desirable because of their significantly shorter times of flight. Keeping the flight time as short as possible was a very important consideration for not only Soviet but American engineers as well in these early days of the Space Age when the lifetime of most early spacecraft was usually quite short. Again assuming C3 launch energy requirements comparable to the Mars 1 mission in 1962, the launch window for Type I trajectories to Venus in 1964 ran from about mid-March to mid-April. Although the launch window was shorter, the minimum energy Type I trajectories had much shorter times of flight compared to the Type II ranging from about 100 to 126 days (with shorter times of flight occurring later in the launch window). Likewise the communication range from Earth to Venus at the time of encounter was also shorter with Type I trajectories falling in the 50 to 64 million km range . With mission times as much as half as long and communication ranges as much as half as far with only a relatively minor payload penalty, the Type I trajectories to Venus would have been preferred.
Since the mission of the 3MV-1 was to land on Venus, the characteristics of the encounter with Venus were important particularly the approach velocity. The conditions for the 1964 Venus launch window are illustrated in Figure 2 which was taken directly from Reference . In this figure, contours of C3 launch energy are plotted as a function of launch date (X-axis) and asymptotic approach speed with respect to Venus (Y-axis). As can be seen, the Type II trajectories tended to have a lower approach speed earlier in the launch window with lower-energy Class I orbits (where the encounter with Venus occurs before the spacecraft’s perihelion) tending to provide the lowest possible approach speed compared to the Class II orbits (where the spacecraft encounters Venus after perihelion). The faster and more desirable Type I trajectories displayed the opposite trend: Class II orbits later in the window offered slower approach speeds than Class I orbits earlier on. Attempts to fly higher energy Class I trajectories that would further decrease the time of flight would very quickly increase the approach speed and tax the heat shield on the landers.For this particular launch window, Soviet planners traded the length of the Type I launch window for payload mass. The 3MV-1 were about 55 kilograms heavier than the Mars 1 spacecraft so they taxed the performance of the 8K78M somewhat more shortening the available launch window in the process. In addition, there was the need to launch an unmanned E-6 lunar lander on a 8K78M during its narrow launch window around March 21 . Since the sole launch pad at this time available for supporting the 8K78M could be refurbished and launch another 8K78M in just three days, the nominal launch window for the 3MV-1 landers ran from about March 24 to the first few days of April 1964.
Zond 1 (3MV-1 No. 4)
Zond 1 is the simplest mission to analyze since its launch and encounter dates are known as well as its goal of landing on Venus. Zond 1 was launched on April 2, 1964 and reached Venus the following July 19 (albeit in a non-functioning state) yielding a time of flight of 108 days. Based on the trajectory analysis for that day [9, 11, 12], the following information is derived:
Table I: Zond 1 Trajectory Synopsis
|Launch Date||Apr 2, 1964|
|Arrival Date||Jul 19, 1964|
|Time of Flight (days)||108|
|Launch energy, C3 (km2/s2)||12.4|
|Asymptotic Speed WRT Venus (km/s)||6.0|
|Entry Speed (km/s)||12.0|
|Distance to Venus at Encounter (million km)||59.7|
The launch energy requirements for the trajectory chosen for Zond 1, denoted as “4” in Figures 1 and 2, was only slightly higher than the minimum energy for a Type I transfer trajectory on this launch date with a time of flight just one day longer.
Kosmos 27 (3MV-1 No. 5)
The failed mission of Kosmos 27 is slightly more difficult to analyze since only its launch date of March 27, 1964 is currently known. But since Kosmos 27 was the same type of craft as Zond 1 with the same mission, it is reasonable to assume that it would have been launched on a near-minimum energy, Type I trajectory to Venus just like Zond 1. The minimum energy Type I trajectory on this date had a time of flight of 114 days resulting in an encounter date of July 19 or the same day as Zond 1 [9, 13]. Since at this time it seems that the typical Soviet practice was to space out planetary encounters a couple of days apart to ease demands on tracking and ground controllers, it is reasonable to assume that the intended encounter date would have been two days earlier than that of Zond 1 or July 17 yielding a time of flight of 112 days. Based on the trajectory information for this launch date and assumed encounter date of July 17 [9, 11, 12], the following information is derived:
Table II: Kosmos 27 Trajectory Synopsis (Assumed Jul 17 Encounter)
|Launch Date||Mar 27, 1964|
|Arrival Date||Jul 17, 1964|
|Time of Flight (days)||112|
|Launch energy, C3 (km2/s2)||12.5|
|Asymptotic Speed WRT Venus (km/s)||6.4|
|Entry Speed (km/s)||12.2|
|Distance to Venus at Encounter (million km)||57.8|
This trajectory, denoted as “3” in Figures 1 and 2, has a C3 launch energy requirement only slightly greater than the minimum for this date and is comparable to that of Zond 1 launched six days later. The approach speed towards Venus is slightly higher but the only way to decrease this would be to fly a higher energy Class II trajectory with a longer time of flight. Obviously minimizing the time of flight was more important and this entry velocity was not a concern.
3MV-1A No. 4A
The engineering test flight of 3MV-1A No. 4A was launched on February 19, 1964. As can be seen in Figure 1 and was discussed earlier, there are no low-energy Type I trajectories on this date leading some analysts to conclude that this mission was not launched towards Venus at all despite claims to the contrary from many reliable sources [5, 6, 7, 8]. The minimum energy for a Type I trajectory for this launch date has a C3 of 21.1 km2/s2 and a time of flight of 138 days [9, 13]. I have yet to locate a good model for the performance of the 8K78M Molniya launch vehicle for escape trajectories. However, given that a modern Soyuz FG launched from an equatorial site like Kourou  might be just capable of sending a 800-kilogram payload (the originally envisioned launch mass of the 3MV-1A design ) on such a trajectory today, it seems highly unlikely that the lower-performance 8K78M Molniya launched from Baikonur 50 years ago would have been capable of doing so supporting the speculation of some analysts.
However, the primary mission of 3MV-1A was to provide engineering information that could help discover any hidden issues with the 3MV design. The problems with the previous Soviet planetary probes, Venera 1 and Mars 1, were uncovered within the first couple of days of their flights. Hopefully any problems uncovered during the 3MV-1A test flight would prove to be minor allowing last-minute modifications to be made to the operational 3MV-1 probes being prepared for launch. A launch on February 19 would provide up to a month’s worth of engineering data before the opening of the nominal Type I launch window used by Kosmos 27 and Zond 1. Since reaching Venus was not the primary objective of the mission but apparently still a secondary one, it seems likely that 3MV-1A No. 4A was launched on a lower energy but longer Type II trajectory towards Venus.Figure 3, which was taken directly from Reference , shows the minimum C3 launch energies as a function of launch date for Type I and II trajectories (upper and lower curves, respectively) towards Venus in 1964. For the 3MV-1A launch date of February 19, the minimum energy for a Type II trajectory is 14.9 km2/s2 (denoted by “1” in Figure 3) which is slightly less than the C3 of 15.2 km2/s2 for the 894 kg Mars 1 mission  launched in 1962 on an 8K78 (denoted by the blue horizontal line in Figure 3). The 8K78M launch vehicle would have had sufficient performance to launch a 3MV-1A with a mass as great as about 900 kg on a Type II trajectory towards Venus with a time of flight of 193 days resulting in an arrival date of about August 30, 1964 – six weeks after the scheduled arrival of Zond 1. It is likely that there was not much expectation that the 3MV-1A would survive this longer trip to Venus but it was still possible it would be able to provide additional information on Venus (not to mention propaganda points for a successful encounter with Venus) after it had performed its primary function of supplying vital engineering information for the upcoming 3MV-1 probes.
Based on the trajectory information for this launch date and assuming a minimum energy Type II trajectory [9, 11, 12, 13], the following information is derived:
Table III: 3MV-1A No. 4A Trajectory Synopsis (Assumed Minimum Energy Type II Trajectory)
|Launch Date||Feb 19, 1964|
|Arrival Date||Aug 30, 1964|
|Time of Flight (days)||193|
|Launch energy, C3 (km2/s2)||14.9|
|Asymptotic Speed WRT Venus (km/s)||4.5|
|Entry Speed (km/s)||11.3|
|Distance to Venus at Encounter (million km)||106.3|
This trajectory, denoted as “1” in Figures 1 and 2, has a C3 launch energy requirement greater than those of Kosmos 27 and Zond 1 but less than Mars 1. While the 193-day time of flight for this mission was over 80 days longer than minimum energy Type I trajectories to be used by Kosmos 27 and Zond 1, it was still shorter than the then record long 230-day flight attempted by Mars 1 over a year earlier. If this craft had survived the extra long trip to Venus, its lander would have had the added bonus of having to endure a slightly more benign entry into the Venusian atmosphere compared to the typical conditions during the nominal Type I launch window in late March (assuming that the engineering version of the lander 3MV-1A No. 4A presumably carried on this flight was even capable of attempting such a landing).
3MV-1 Launch Scheduled for March 1
In light of the launch failure of 3MV-1A No. 4A test flight, the mission of the operational 3MV-1 that was scheduled to be launched on March 1 (over three weeks before the opening of the nominal Venus launch window) starts to make sense. As before, there were no low-energy Type I trajectories available on this date. The minimum energy of a Type I trajectory on this date had a C3 of 17.3 km2/s2 with a time of flight of 131 days [9, 13]. It seems unlikely that there would have been enough time to strip several tens of kilograms or more off of one of the 3MV-1 probes so late in their preparation during the 11 days between the loss of 3MV-1A No. 4A and the planned March 1 launch date so that it would be light enough for the 8K78M to launch it towards Venus on a Type I trajectory.
The other option available is obvious upon examination of Figure 3. The minimum C3 launch energy for a Type II trajectory on this launch date (denoted by “2” in Figure 3) is essentially identical to the launch energy of Kosmos 27 and Zond 1 (shown as a horizontal yellow line in Figure 3) which followed faster Type I trajectories to Venus later in the month. This can not be a coincidence and it seems almost certain that the March 1 launch was intended to follow a longer Type II trajectory towards Venus. Even though the time of flight of this trajectory was about 80 days longer than the preferred Type I trajectory (increasing the chances that the probe would not survive long enough to function during its encounter with Venus), a 3MV-1 launched on this date could still provide as much as three weeks of useful engineering data that could improve the chances of success for the sole remaining 3MV-1 spacecraft. And if the 3MV-1 launched on March 1 did survive all the way to Venus, it would be able to execute its original Venus landing mission.
Based on the trajectory information for this launch date and assuming a minimum energy Type II trajectory [9, 11, 12, 13], the following information is derived:
Table IV: 3MV-1 Trajectory Synopsis for March 1 (Assumed Minimum Energy Type II Trajectory)
|Launch Date||Mar 1, 1964|
|Arrival Date||Sep 5, 1964|
|Time of Flight (days)||188|
|Launch energy, C3 (km2/s2)||12.5|
|Asymptotic Speed WRT Venus (km/s)||4.7|
|Entry Speed (km/s)||11.4|
|Distance to Venus at Encounter (million km)||113.2|
This trajectory, denoted as “2” in Figures 1 and 2, has a C3 launch energy requirement essentially identical to Kosmos 27 and Zond 1. While the 188-day time of flight for this mission was about 80 days longer than minimum energy Type I trajectory used by Zond 1, it was still shorter than the then record long 230-day flight attempted by Mars 1 and would reach Venus around September 5, 1964 (about 48 days after Zond 1 following its faster Type I trajectory). If this craft had survived the extra long trip to Venus, its lander would have had the advantage of enduring a slightly more benign entry into the Venusian atmosphere compared to the typical conditions during the nominal Type I launch window in late March.
The analysis of the trajectories of the various Soviet Venus probes of 1964 seems to resolve the lingering confusion about the nature of the 3MV-1A launch of February 19, 1964 and the scheduled launch of an operational 3MV-1 on March 1. While the primary objective of 3MV-1A No. 4A was to provide a much needed test flight of the 3MV-1 design, the launch energy requirements for a Type II trajectory to Venus were low enough on February 19 that a 3MV-1A with a mass of no more than about 900 kg could have been launched towards Venus as a secondary objective using the 8K78M rocket. Such a trajectory would provide up to a month’s worth of flight data that could have increased the chances of success for the operational 3MV-1 landers to be launched starting in late March 1964 during the preferred Type I trajectory window. If 3MV-1A No. 4A managed to survive the long flight of about 193 days, it would provide a bonus encounter with Venus around August 30.
With the loss of the last 3MV-1A test craft, it appears that the decision was made to launch an operational 3MV-1 three weeks early on March 1, 1964 in a last ditch attempt to get some much needed flight data on the 3MV design. While it was impossible for the 8K78M to launch a 3MV-1 with a mass of about 950 kg on a Type I trajectory to Venus on this date, the launch energy requirements for a minimum energy Type II trajectory were essentially identical to those of the faster Type I trajectories attempted by Kosmos 27 and flown by Zond 1 later in the month. While the long time of flight of 188 days decreased the chances that it would survive until its encounter with Venus around September 5, the flight data gathered would have likely improved the chances of success for the remaining operational 3MV-1 lander making the gamble worthwhile. In the end this mission was scrubbed because of problems uncovered during the integration of the payload with the launch vehicle.
Without any test flights, 3MV-1 No. 5 was launched on March 27, 1964 with the encounter with Venus likely scheduled for July 17 using a near-minimum energy Type I trajectory. A malfunction of the escape stage of the 8K78M stranded this payload in its parking orbit and it was designated Kosmos 27. The last available lander, 3MV-1 No. 4, was successfully launched on April 2 into a 108-day Type I trajectory to become Zond 1. But a loss of pressure in its orbital compartment and a series of subsequent equipment failures disabled the craft before its expected July 19 encounter with Venus. The 3MV design would require more work before the next Venus launch window in November 1965.
1) V.C. Clark, Jr., W.E. Bollman, R.Y. Roth and W.J. Scholey, “Design Parameters for Ballistic Interplanetary Trajectories Part I. One-way Transfers to Mars and Venus”, Technical Report No. 32-77, JPL, January 16, 1963
2) Wesley T. Huntress and Mikhail Ya. Marov, Soviet Robots in the Solar System, Springer-Praxis, 2011, pp. 133-137
3) Bart Hendrickx, “Managing the News: Analyzing TASS Announcements on the Soviet Space Program (1957-1964), Quest, Vol. 19, No. 3, pp. 44-58, 2012
4) Timothy Varfolomeyev, “Soviet Rocketry that Conquered Space Part 5: The First Planetary Probe Attempts, 1960–1964”, Spaceflight, Vol. 40, No. 3, pp. 85–88, March 1998
5) Boris Chertok, Rockets and People Volume III: Hot Days of the Cold War (ed. Asif Siddiqi), SP-2009-4110, NASA History Division, 2009, p. 389
6) Timothy Varfolomeyev, “Soviet Rocketry that Conquered Space Part 6: The Improved Four-Stage Launch Vehicle, 1964-1972”, Spaceflight, Vol. 40, No. 5, pp. 181-184, May 1998
7) Timothy Varfolomeyev, “The Soviet Venus Programme”, Spaceflight, Vol. 35, No. 2, pp. 42-43, February 1993
8) Brian Harvey, Russian Planetary Exploration: History, Development, Legacy and Prospects, Springer-Praxis, 2007, p. 70
9) V.C. Clark, Jr. et al., ibid, “Venus 1964: Time of flight vs launch date”, Figure 6-1, p. 108
10) V.C. Clark, Jr. et al., ibid, “Mars 1962: Time of flight vs launch date”, Figure 11-1, p. 252
11) HORIZONS Web-interface, JPL, http://ssd.jpl.nasa.gov/horizons.cgi
12) V.C. Clark, Jr. et al., ibid, “Venus 1964: Asymptotic speed with respect to Venus vs launch date”, Figure 6-17, p. 124
13) V.C. Clark, Jr. et al., ibid, “Venus 1964: Minimum injection energy vs launch date”, Figure 4-2, p. 66
14) Arianespace, Soyuz CSG User’s Manual, Issue 1, Rev. 0, Fig. 2.12, p. 2-16, June 2006
15) Brian Harvey, Race Into Space: The Soviet Space Programme, Halsted Press, 1988, pp. 87-88