Trajectory Analysis of the 1962 Soviet Venus Missions

On December 14, 1962, NASA’s Mariner 2 became the first spacecraft to return data of closeup observations from another world. What is not as widely known is that Mariner 2 had competition from a trio of much larger and more capable Soviet spacecraft designated Object 2MV with much more ambitious goals. Two of these 2MV spacecraft, each with masses in excess of a metric ton (over five times heavier than Mariner 2) carried landers and a third was a flyby probe with a much larger and more capable payload of instruments than Mariner 2 carried including an advanced, film-based imaging system. Unfortunately problems with the escape stage on the new 8K78 rocket (then the most powerful launch vehicle in the world) prematurely ended all of these missions stranding them in low Earth parking orbit. Presented here is an analysis of the trajectories available during the 1962 Venus launch window and a discussion of the most likely trajectories intended for the Soviet 2MV Venus missions.

Diagram of 2MV-1 Venus landers that were launched on August 25 and September 1, 1962. (RKK Energia)

Background

The Soviet’s 2MV series of probes launched towards Venus and Mars in the fall of 1962 consisted of a standardized spacecraft bus called the orbital compartment carrying a package called the planetary compartment which was geared towards a specific mission and target. In the case of the 2MV probes to Venus, there were two design variants: The first was designated 2MV-1 which carried a roughly spherical shaped lander, 90 centimeters in diameter designed to separate from the orbital compartment before encounter and land on the Venusian surface with data returned directly to Earth during descent and after landing. The orbital compartment would be destroyed during entry into the atmosphere of Venus. The total mass of the 2MV-1 was 1,097 kilograms.

The second variant was the 2MV-2 which was fitted with a planetary compartment that carried a film-based imaging system as well as infrared and ultraviolet instruments designed to study Venus during a flyby. No mass for the 2MV-2 has yet been disclosed but it has been generally believed to be similar to the 893.5-kilogram mass of Mars 1 (2MV-4 No. 4) which was also launched in the fall of 1962 on a similar flyby mission of the Red Planet.

For the 1962 Venus launch window, a pair of 2MV-1 landers and a single 2MV-2 flyby probe were prepared for launch to Venus on the new 8K78 rocket (later known by the name “Molniya” after the communication satellite series that also used this rocket). In addition to these three Soviet spacecraft, the Americans had prepared two smaller and much less ambitious Mariner spacecraft for this same Venus launch window. The first to be launched was the American Mariner 1 on July 22, 1962 targeted for a December 8 flyby. Unfortunately during ascent of the radio-guided Atlas-Agena B launch vehicle, loss of the radio guidance link coupled with a previously undetected error in the onboard guidance program used when the radio link was lost caused the Atlas to veer off coarse and was destroyed by range safety.

Next up was the first Soviet Venus lander attempt, serial number 2MV-1 No. 1, launched on August 25, 1962. Just before ignition of the Blok L escape stage after an hour in low orbit, four solid rocket motors were suppose to fire to settle the liquid propellants to the bottom of the tanks in preparation for engine ignition. Unfortunately, only three of these motors fired, sending the escape stage and its payload into an uncontrolled tumble preventing the stage from firing properly to send 2MV-1 No. 1 on its way to Venus. Before the next Soviet launch attempt, Mariner 2 was successfully launched towards Venus on August 27, 1962.

The second Soviet attempt, another lander serial number 2MV-1 No. 2, was launched on September 1, 1962. Again the Venus lander was stranded in its low Earth parking orbit when the main engine of the Blok L escape stage failed to ignite. The final Soviet launch attempt, the flyby spacecraft 2MV-2 No. 1, was made on September 12. This time a LOX turbopump failure in the Blok L escape stage’s main engine stranded the Venus mission in low Earth orbit. Mariner 2 would fly solo to Venus without any competition.

It should be noted that even if the 2MV-1 landers did survive launch as well as the transit to Venus, they were doomed to failure from the start. Soviet engineers had assumed that the pressure and temperature on the surface of Venus were no higher than 5 bars and 77° C, respectively. We now know that the surface conditions are much more extreme than had been generally believed at this time with values of 92 bars and 480° C, respectively. The 2MV-1 landers would have been crushed at an altitude of about 35 kilometers or more by excessive external pressure. While the landers would have returned scientifically valuable in situ measurements of the properties of the Venusian atmosphere during their parachute descent, they would never have survived to the surface.

1962 Venus Trajectories

For the 1962 launch opportunity to Venus, there were two types of trajectories available: relatively fast Type I trajectories where the spacecraft would travel through less than 180° in its orbit around the Sun before its encounter with Venus and longer Type II trajectories where the spacecraft would travel through more than 180° in its orbit around the Sun before its encounter. As can be seen in the plot of minimum C₃ launch energy as a function of launch date in Figure 1 (taken directly from Clark et al.), typically Type I trajectories were energetically more favorable than the Type II trajectories during most of the 1962 window. It was only after about September 7, 1962 that the Type II trajectories were energetically more favorable than the Type I. But in this early era when spacecraft longevity was an issue, the minimum energy Type I trajectories with their transit times that were 70 or more days shorter than the Type II were much preferred despite their modest payload penalty late in the 1962 Venus launch window.

Figure 1: Plot of minimum C3 launch energy as a function of launch date for Type I and Type II trajectories (taken from Clark et al). The three red “+” show the conditions for the following assuming minimum energy trajectories: 1) 2MV-1 No. 1, 2) 2MV-1 No. 1 and 3) 2MV-2 No. 1. Click on image to enlarge. (JPL/NASA)

The C₃ launch energy requirements for Type I and II trajectories as a function of launch date and time of flight are illustrated in the contour plot shown in Figure 2 (taken directly from Clark et al.). The minimum launch energy towards Venus occurred on August 23 with a C₃ of 8.7 km²/s². For minimum energy Type I trajectories, the general trend was towards significantly shorter times of flight for later launch dates. Minimum energy trajectories during this Venus launch window were energetically much more favorable than the Mars launch window in late October to early November 1962 allowing the Venus-bound 2MV spacecraft to be up to about 200 kilograms more massive than their Mars-bound counterparts. The distance to Venus at the time of encounter tended to increase slightly with launch date for minimum energy trajectories. These factors made the period from about mid-August to early September 1962 the most desirable launch window towards Venus with the later half of the window being preferred because of the significantly shorter times of flight to Venus.

Figure 2: This plot, taken from Clark et al., shows contours of C3 launch energy plotted as a function of launch date (X-axis) and time of flight (Y-axis). The three red “+” show the conditions for the following assuming minimum energy trajectories: 1) 2MV-1 No. 1, 2) 2MV-1 No. 1 and 3) 2MV-2 No. 1. The blue “+” indicate the trajectories of the following: 4) Mariner 1 and 5) Mariner 2. Click on image to enlarge. (JPL/NASA)

Since a pair of 2MV-1 spacecraft were intended to land on Venus, the approach velocity was also an important consideration in trajectory choice. For the 1962 Venus launch window, contours of C₃ launch energy as a function of launch date and asymptotic approach speed with respect to Venus is shown in Figure 3 (taken directly from Clark et al.). The general trend for minimum energy trajectories is for lower approach speeds with later launch dates. Increasing the launch energy to decrease the time of flight on Class I trajectories (where Venus is encountered before the spacecraft reaches the perihelion of its transfer orbit) quickly increases the approach velocity taxing the capabilities of the landers’ heatshield. While Class II trajectories (where Venus is encountered after the spacecraft reaches the perihelion of its transfer orbit) with modestly higher energies might decrease the entry velocity by as much as a couple of hundred meters per second, this modest advantage is offset by an undesirable increase in the time of flight. Taking together the launch energy, time of flight and approach velocity considerations, near-minimum energy trajectories during the second half of the 1962 Venus launch window from late August to early September would have been most desirable.

Figure 3: This plot (taken from Clark et al.) shows contours of launch energy plotted as a function of launch date (X-axis) and asymptotic velocity with respect to Venus (Y-axis). The three red “+” show the conditions for the following: 1) 2MV-1 No. 1, 2) 2MV-1 No. 1 and 3) 2MV-2 No. 1. Click on image to enlarge. (JPL/NASA)

2MV Trajectory Analysis

While the launch dates of the three Venus-bound 2MV spacecraft are known, the intended encounter dates have yet to be revealed. Since subsequent missions to Venus and Mars tended to use near-minimum energy trajectories towards their targets, it is likely that these Venus missions did as well. Table I summarizes the analysis for minimum energy trajectories for the three launch dates based on the data from Clark et al. and as shown in Figures 1, 2 and 3.

Table 1: Summary of 2MV Trajectories to Venus (Assuming Minimum Energy Trajectories)

During this time, it was normal Soviet practice with multiple planetary spacecraft to space the encounter dates about two days apart to spread out the workload for tracking and ground control crews.  This was certainly the case for the 2MV missions to Mars launched two months later whose intended encounter dates are currently known. Following minimum energy trajectories naturally spaces the December 16 and 18 encounter dates of the 2MV-1 No. 2 lander and 2MV-2 No.1 flyby spacecraft, respectively, by the desired two-day interval. A minimum launch energy trajectory for the August 25 launch date of 2MV-1 No. 1, however, has an encounter date that is just a day earlier than for No. 2. However, just a slight increase in its launch energy could easily allow a December 14 encounter date which not only produces the desired two-day interval between landing attempts, but is coincidentally the same encounter date as the American Mariner 2 spacecraft. If 2MV-1 No. 1 had been launched on a trajectory with a C₃ of 9.5 km²/s² like No. 2, the time of flight of 2MV-1 No.1 would have been short enough to easily beat Mariner 2 to Venus with the penalty of a only a insignificantly higher entry velocity. Beating the intended Mariner 1 encounter date of December 8, had its launch been successful, would have been more problematic.  But until more information on the intended encounter dates of the 2MV Venus missions is released from Soviet archives, this is only speculation.

While the C₃ for a minimum energy trajectory for the 2MV-1 lander-bearing spacecraft were in the 8.8 to 9.5 km²/s² range, the C₃ for the minimum launch energy for the sole 2MV-2 flyby probe which was launched towards the end of the window to Venus was a significantly higher 12.3 km²/s². The 2MV-2 could have been launched on a Type II trajectory with a C₃ energy as low as 10.5 km²/s² but the time of flight would have been about 70 days longer significantly reducing the chances that the spacecraft would survive to Venus. This spacecraft could have also been launched as early as about July 19 on a Type I trajectory with the exact same C₃ of 12.3 km²/s². Unfortunately the time of flight would be about 146 days with an encounter date of December 12. An encounter only about six days earlier with a time of flight 48 days longer was obviously a risk not worth taking.

In order for the 8K78 to launch the 2MV-2 on its higher energy transfer trajectory to Venus, it must have been lighter than the 1,097-kilogram 2MV-1 spacecraft. Mars 1 with a mass of 893.5 kilograms was launched on November 1, 1962 with a C₃ of 15.2 km²/s². The Venus-bound Zond 1, with a mass of about 950 kilograms launched with an improved 8K78M on April 2, 1964, had a C₃ launch energy of 12.4 km²/s² – almost the same value as a minimum energy trajectory for 2MV-2 No. 1. More details are needed to determine the payload capabilities of the early 8K78 and 8K78M launch vehicles but it seems possible that 2MV-2 No. 1 could have had a launch mass as great as almost 950 kilograms if it had been intended to follow a minimum energy Type I trajectory.

Another possibility worth considering is that 2MV-2 No.1 had a launch mass closer to Mars 1 after all and instead of being launched on a minimum energy trajectory, it was launched with a higher C₃ similar to the 15.2 km²/s² of Mars 1. This would have placed the 2MV-2 No. 1 flyby probe on a trajectory with a time of flight as short as about 83 days allowing the spacecraft to pass its heavier lander-laden 2MV-1 sisters to reach its target as early as December 4 easily beating not only Mariner 2 but also Mariner 1 to Venus in the process. And since this spacecraft did not carry a lander, the higher encounter velocity resulting from this faster trajectory would have been of no concern.  Once again, more information from Soviet archives will be required to determine which option was chosen: A spacecraft with a mass of as much as 950 kilograms launched on a near-minimum energy trajectory to follow the 2MV-1 landers or a lighter spacecraft with a mass closer to that of the 893.5-kilogram Mars 1 launched on a faster trajectory to precede the 2MV-1 landers beating Mariner 1 and 2 to Venus in the process.

Summary

The Soviet’s 2MV Venus missions unsuccessfully launched in late August to early September 1962 could have followed near-minimum energy trajectories that would have reached Venus on or about December 14, 16 and 18. The 2MV-1 No. 1 lander could have easily been launched into a slightly higher energy transfer trajectory that could have allowed it to reach Venus with its lander slightly earlier than NASA’s Mariner 2 December 14 encounter date.

Two possibilities are identified for the 2MV-2 No. 1 flyby spacecraft’s trajectory to Venus with its September 25 launch date. It could have had a mass of as much as 950 kilograms (which is heavier than generally believed) and followed a minimum energy trajectory that would have brought it to Venus after the pair of 2MV-1 landers around December 18. Alternatively, it could have had a launch mass closer to its 893.5-kilogram sister craft, Mars 1, and followed a much faster, higher energy trajectory to Venus that would have preceded the 2MV-1 landers beating NASA’s Mariner 1 and 2 to the first planetary encounter by as much as four or ten days, respectively. More information from Soviet archives will be needed to resolve these possibilities and determine if the Soviets would have actually beaten the Americans to Venus. This analysis, however, strongly suggests that it was well within the realm of possibility.  Given the problems encountered by Mariner 2 during its 129-day lifetime (which was more than sufficient to reach Venus on its 109-day transfer trajectory), one must question the chances of Mariner 1 reaching Venus in operating condition on its longer 139-day trajectory to Venus even if it had survived launch. But even if the 2MV spacecraft did not beat Mariner 2 to Venus, the successful flyby of Venus with the more capable 2MV-2 and the information returned about the Venusian atmosphere during the 2MV-1 landing attempts would have easily eclipsed the achievements of the diminutive Mariner 2.

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Related Reading

“If At First You Don’t Succeed… Part I”, The Space Review, Article #2477,  March 24, 2014 [Article]

“If At First You Don’t Succeed… Part II”, The Space Review, Article #2480,  March 31, 2014 [Article]

“Trajectory Analysis of the Soviet 1962 Mars Missions”, Drew Ex Machina, May 2, 2014 [Post]

“Trajectory Analysis of the Soviet 1964 Venus Missions”, Drew Ex Machina, April 2, 2014 [Post]

General References

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
p. 65, Fig 4-1 “Venus 1962: Minimum injection energy vs launch date”
p. 81, Fig 5-1 “Venus 1962: Time of flight vs launch date”
p. 100, Fig 5-20 “Venus 1962: Asymptotic speed with respect to Venus vs launch date”

Wesley T. Huntress and Mikhail Ya. Marov, Soviet Robots in the Solar System: Mission Technologies and Discoveries, Springer-Praxis, 2011

Andrew J. LePage, “Trajectory Analysis of the Soviet 1964 Venus Missions”, Drew Ex Machina, April 2, 2014 [Post]

Andrew J. LePage, “Trajectory Analysis of the Soviet 1962 Mars Missions”, Drew Ex Machina, May 2, 2014 [Post]

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

HORIZONS Web-interface, JPL [Link]

Mariner-Venus 1962 Final Report, SP-59, JPL/NASA, July 1965