Venera 7: The First Landing on Another Planet

During the summer of 1990, I got a chance to check out a large exhibit of Soviet space hardware at the Boston Museum of Science (see “The Soviet Space Exhibit at the Boston Museum of Science – July 1990”). Tucked away among the displays of Phobos, Vega and other impressive pieces of planetary mission hardware was a comparatively small, egg-shaped probe painted white with “CCCP” (the Cyrillic initials for the USSR) emblazoned in red letters across the exterior. What was on display was an engineering model of Venera 7 which made the first landing on the surface of another planet on December 15, 1970 (almost 20 years before this exhibit). The culmination of over a decade’s worth of work by Soviet engineers and scientists, this historic landing was the beginning of a decade and a half of increasingly ambitious (and largely successful) missions to study our sister planet, Venus.

A model of the Venera 7 descent capsule which landed on Venus in December 1970. (A.J. LePage)

Stumbling Towards Success

Among the famous quotes from Winston Churchill is “success is stumbling from failure to failure with no loss of enthusiasm.” The Soviet Venera program to explore Venus is probably one of the best examples of this maxim. Not long after the beginning of the Space Age, OKB-1 (the Russian acronym for Experimental Design Bureau 1) run by the legendary Soviet space engineer, Sergei Korolev, which had built Sputnik, had already started work on probes to reach Venus and the Molniya launch vehicle which would send them on their way. A pair of 1VA Venus probes were launched in February 1961 but only one, eventually known as Venera 1, was successfully sent on its way to Venus. Unfortunately, Venera 1 fell silent days after launch (see “Venera 1: The First Venus Mission Attempt”).

Of the pair of 1VA spacecraft launched towards Venus in 1961, only Venera 1 survived only to suffer a series of malfunctions during its first two weeks of flight. (NASA)

Without missing a beat, the personnel at OKB-1 learned from their mistakes and designed the improved 2MV series of spacecraft for the next Venus launch window. Regretably, Soviet ambitions were thwarted when a pair of 2MV-1 Venus landers and a 2MV-2 flyby probe were stranded in Earth orbit by Molniya Blok L escape stage failures following launch in August and September of 1962 (see “You Can’t Fail Unless You Try: The Soviet Venus & Mars Missions of 1962”). Once again, Soviet engineers improved the 2MV design to create the more capable 3MV planetary probes. A pair of 3MV-1 landers were launched in March and April of 1964 but only one, Zond 1, survived launch but finally succumbed to a series systems failures less than two months later (see “Zond 1: The First Lander Sent to Venus”). Out of a trio of improved 3MV spacecraft launched to Venus in November 1965, just Venera 2 and 3 (a flyby probe and a lander, respectively) escaped the Earth only to fail days before their encounter with our sister planet (see “Venera 2 & 3: Touching the Face of Venus”).

A view of the 3MV-3 called Venera 3 with its spherical lander visible attached at the bottom.

By the time of the failures of Venera 2 and 3, responsibility for development and construction of automated lunar and planetary spacecraft had been transferred to the newly independent design bureau called NPO Lavochkin run by Chief Designer Georgi Babakin which was known for its meticulous testing and the quality of its workmanship. The engineers at Lavochkin totally redesigned the 3MV lander and its carrier spacecraft to create the much more capable 1V spacecraft. While only Venera 4 survived launch in June 1967, the spacecraft successfully deployed its lander which then returned the first in situ measurements of the Venusian atmosphere during a 93-minute descent. Originally thought to have gone silent when it hit the surface of Venus, it was later determined that it instead suffered structural failure at an altitude of 26 kilometers when the pressure exceeded 18 bars (with one bar being approximately equal to the atmospheric pressure on Earth’s surface). The surface conditions on Venus had turned out to be much more hostile than Soviet scientists and engineers had assumed when designing their lander (see “Venera 4: Probing the Atmosphere of Venus”). With only enough time to make minor upgrades to the 2V landers for the next launch window in January 1969, the landers of Venera 5 and 6 were able to penetrate more deeply into the Venusian atmosphere building on the findings of Venera 4 but still failed about a dozen kilometers above the surface (see “Venera 5 & 6: Diving Towards the Surface of Venus”).

Venera 4 being prepared for launch.

The 3V Venera Spacecraft

With a better understanding of the true nature of surface conditions on Venus, the engineers and scientists at NPO Lavochkin set out to build a much more robust 3V Venus lander for the upcoming V-70 mission. Like the earlier landers, the 3V lander was a spheroid about a meter in diameter with an offset center of gravity that would keep the blunt end pointing forward during entry without the need for an attitude control system. Beneath the ablative heat shield and layers of improved thermal insulation was a new spherical, titanium pressure vessel which housed the lander’s vital systems. Giving themselves as much margin as possible, the new 3V lander was capable of withstanding pressures of 180 bars and temperatures as great as 540° C for up to 90 minutes.

Soviet Diagram of the Venera 3V lander. From the bottom label and working clockwise, these are shock damper, pressure shell, instrument commutator, insulation, internal heat shield, top release, parachute, antenna, ventillator, radio, transmitter and spacecraft adapter. Click on image to enlarge. (Roscosmos)

Other changes were also made to the 3V lander. The size of the parachute was decreased from 15 square meters used on Venera 5 and 6 to just 2.5 square meters. Despite the smaller size of the canopy which could now withstand temperatures as great as 520° C, it would still allow a safe landing given the newer estimates of the surface conditions. To further hasten the descent to the surface, a cord was wrapped around the parachute shroud lines to keep it from fully opening with an area of 1.8 square meters. The cord was designed to release the shroud lines to allow full opening of the parachute when the temperature exceeded about 200° C. The descent was now expected to take about an hour compared to the lander’s design life of 90 minutes.

Because of the increased mass of the more robust 3V lander, it carried a smaller suite of instruments compared to its predecessors. In addition to a densitometer, the 3V lander carried resistance thermometers capable of measuring temperatures in the 25° C to 540° C range as well as a set of aneroid manometers to measure pressures between 0.5 and 150 bars. The telemetry system, which would transmit data directly to Earth at a rate of one bit per second, now employed a temperature-stabilized crystal oscillator so that the line of sight velocity of the descending lander could be measured to an accuracy of ±1.5 meters per second. With the Earth only 10.3° from the local vertical at the expected landing site, the Doppler velocity measurements were relatively insensitive to horizontal winds providing a single measurement accuracy of only about ±8 meters per second. Integrating the Doppler velocity measurements, however, would provide an independent means of reconstructing the near-vertical descent of the 3V lander supplementing the data from the lander’s radar altimeter. Since the 3V lander was now expected to reach the surface, it also carried a gamma ray spectrometer to measure the concentrations of radioactive potassium, uranium and thorium in order to gauge the composition of the surface materials. The total mass of the 3V lander now swelled to 490 kilograms – 85 kilograms heavier than the earlier 2V lander.

The 3V carrier for the lander was little changed from its immediate predecessors save for incremental improvements in its various systems based on ground testing and flight experience. About 3.5 meters tall, including the lander, the core of the carrier consisted of a 1.1 meter in diameter cylinder that was about as tall. This pressurized compartment housed the carrier’s various systems and maintained their temperature between 15° C and 25° C using a forced gas system. The circular radiator for this system was mounted on the anti-Sun side of the spacecraft and served as the hub for an umbrella-like, deployable high gain antenna 2.3 meters in diameter used to support long-range UHF band downlink and uplink. The thermal control system was also used to pre-chill the lander to a temperature of -8° C before deployment to help maximize its life in the hot atmosphere of Venus.

A Venera 3V spacecraft being prepared for launch. (Roscosmos)

Mounted on top of this compartment was the propulsion system consisting of a pressure-fed KDU-414 engine and its propellant tanks. This system would be used to perform a pair of midcourse corrections (one shortly after leaving the Earth and another prior to the Venus encounter) in order to fine tune its trajectory. On the sides of the main compartment were a pair of deployable solar panels with a span of over four meters and an area of 2.5 square meters which provided electrical power to the spacecraft’s systems. In order to accommodate a heavier lander, the 3V carrier sported fewer scientific instruments to save mass. Only a solar wind charged particle detector was carried this time. All together, the upgraded 3V spacecraft had a launch mass of 1,180 kilograms. This was 50 kilograms heavier than Venera 5 and 6 but still well within the lift capability of the 8K78M Molniya rocket for this Venus launch window.

The V-70 Mission

As was done for the earlier V-67 and V-69 missions, the Soviet V-70 mission to Venus would launch a pair of the improved 3V spacecraft towards Venus during the August 1970 launch window. The first, 3V No. 630, successfully lifted off from the pad at Area 31/6 in the Baikonur Cosmodrome at 8:38:22 AM Moscow Time (05:38:22 GMT) on August 15, 1970. The first three stages of the 8K78M Molniya successfully placed the Blok L escape stage and its 3V payload into a temporary 182 by 202 kilometer Earth parking orbit with an inclination of 51.7°. After coasting in orbit to reach the optimum injection point, the Blok L main engine ignited at 07:59 GMT and sent what was now called Venera 7 into a 0.69 by 1.01 AU solar orbit which would reach Venus on December 15 after a transit of 120 days.

The launch of Venera 7 on August 15, 1970.

The second 3V spacecraft, No. 631, lifted off at 8:06:09 AM Moscow Time (05:06:09 GMT) on August 22 and into its temporary parking orbit. Because of the malfunction of a transformer in the Blok L power system, the stage’s engine ignited late and burned for only 25 seconds instead of the required 244 seconds. The significant underburn stranded what was now called Kosmos 359 in a 208 by 890 kilometer orbit with an inclination of 51.1° which decayed on November 6. Venera 7 was on its own.

Venera 7 quickly settled into its routine for the four-month cruise to Venus. The spacecraft performed its first midcourse maneuver on October 17 when it was 17 million kilometers from the Earth. A second correction on November 17 at a range of 31 million kilometers further fine tuned the trajectory to a point near the nightside equator about 2,000 kilometers from the terminator.

On December 10, Venera 7 detected a solar flare providing vital data on the event from its unique perspective five days out from Venus. On December 12, with Venera 7 some 1.3 million kilometers from Venus, the spacecraft was commanded to charge the lander’s batteries and chill it to -8° C in preparation for landing. By the time it had reached Venus, ground controllers had conducted 124 communication sessions with the spacecraft. The carrier automatically released its lander at 04:58:44 GMT on December 15 when the spacecraft lost its Earth lock as it reached the upper atmosphere of Venus. The lander encountered the atmosphere at an altitude of 135 kilometers with a speed of 11.5 kilometers per second at an angle of 60° to 70° to the local horizontal. While the carrier burned up, the lander experienced peak braking loads of 350 g as the heat shield temperature spiked to 11,000° C.

By the time the Venera 7 had descended to an altitude of 54 kilometers with a speed of 200 meters per second, the lander deployed its parachute as it sensed the atmospheric pressure had reach 0.7 bars. Immediately after parachute deployment, Venera 7 began broadcasting data back to Earth starting at 04:59:28 GMT. At 05:08:41 GMT, the cord holding the parachute’s shroud line gave way with the ambient temperature at 325° C allowing the canopy to open fully. This quickly decreased the descent speed from 27 to 19 meters per second. Things began to go wrong at 05:15:46 GMT when the parachute unexpectedly ripped resulting in a sharp jump in the descent speed from 15 to 26 meters per second.

Plot of temperature and descent velocity as a function of Earth receipt time (Moscow Time). To convert to spacecraft time (GMT), subtract 3 hours, 3 minutes and 22 seconds. Click on image to enlarge. (Avduevsky et al.)

As Venera 7 continued its quick descent, Doppler tracking data showed that it was beginning to swing back and forth with a period of 30 seconds or so as the parachute continued to disintegrate. The damaged canopy finally collapsed at an estimated altitude of 3 kilometers with the lander freefalling for the next three minutes. Venera 7 impacted the surface at a speed of 16.5 meters per second (the equivalent of a fall off of a five-story building here on Earth) at 05:34:10 GMT on what is today known as Navka Planitia at 5° S, 351° E. The lander’s signal was lost on impact and then regained briefly a second later before disappearing into the noise. It now appeared that Venera 7 had failed on impact.

As the V-70 mission engineers and scientists reviewed the descent data from Venera 7, they discovered the commutator (the electromechanical device which cycled the input of the telemetry system from one instrument to the next repeatedly) had malfunction. The only data transmitted during the abbreviated 35-minute descent were temperature readings – fortunately a very useful data set that allowed the atmospheric properties to be derived. The Doppler velocity data also showed that the upper atmosphere was moving rapidly in a retrograde direction in agreement with ground observations of the planet’s faint cloud features. At lower altitudes the winds dropped to less than 2.5 meters per second.

A plot of atmospheric pressure versus height based on measurements from Venera 4 through 7. Click on image to enlarge. (Avduevsky et al.)

While it was initially feared that Venera 7 failed at landing, over the course of the next couple of days as the lander’s radio transmissions were processed it was discovered that the lander had indeed continued to transmit from the surface for 23 minutes. Apparently the Venera 7 lander had bounced upon impact and settled on the Venusian surface with a tilt of about 50°. Instead of being almost directly above the lander, the Earth was now in one of the sidelobes of its antenna resulting in the signal having just 1% of its expected strength. With the last of the data by the Venera 7 lander transmitted at about 05:57:08 GMT, it was found that Venus had a surface temperature of 474°±20° C. Extrapolating from the earlier results from Venera 4, 5 and 6, it was estimated that the surface pressure 90±15 bars.

For the first time in history, a spacecraft had transmitted data from the surface of another planet. The Soviet press hailed the historical achievement on December 18 when it became clear the V-70 mission had succeeded. With the conditions at the surface of Venus finally pinned down with in situ measurements, efforts at NPO Lavochkin turned towards analyzing the failures of the Venera 7 flight in order to construct an improved lander for the anticipated launch of the next Venera mission in March of 1972 (see “Venera 8: The First Characterization of the Surface of Venus“).

Follow Drew Ex Machina on Facebook.

General References

V. S. Avduevsky et al., “Soft Landing of Venera 7 on Venus Surface and Preliminary Results of Investigations of the Venus Atmosphere”, Journal of the Atmospheric Sciences, Vol. 28, No. 3, pp. 263-269, March 1971

Brian Harvey, Russian Planetary Exploration: History. Development, Legacy and Prospects, Springer-Praxis, 2007

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

Nicholas L. Johnson, Handbook of Soviet Lunar and Planetary Exploration, Univelt, 1979