In 1975, Soviet scientists launched two probes to Venus, which transmitted first ever images from the surface of the planet.
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At the end of 1973, the Soviet physicist Roald Sagdeev, a newly appointed director of the Space Research Institute, IKI, discussed with his colleagues the institute's future strategy for the Soviet planetary research. At the time, Soviet Union conducted a series of unmanned missions to Mars, which were expected to reach the Red Planet in February and March 1974. Although the Soviet assault of Mars reached unprecedented scale -- four probes aimed the planet -- the campaign produced rather mixed results. None of the four spacecraft were able to complete their missions successfully, even though valuable data and imagery had been returned.
The immediate impulse of the scientists at IKI was to prepare for the next launch window to Mars, opening every two years, and try again. After all, history of space exploration was full of examples where dedication, hard work and belief in success would ultimately pay off.
However, looking ahead at the 1975 launch window, the Soviet scientists had to consider one more factor -- the Americans. Although during this period, Soviet and US space programs had limited official interaction, they inherently influenced each other. Upon reviewing NASA plans for the Viking mission, scheduled for launch in 1975, Soviet scientists realized that at the present level of funding and the state of the Soviet technology, it would be very hard if not impossible to match the scale and ambition of the US project.
Rather then duplicating NASA efforts, the IKI's leadership made a controversial decision to abandon immediate plans for Mars exploration and jump-start a series of missions to Venus, known in the USSR as "Venera." "We had to work in a different "weight category": Venera-type missions were worth 100 million rubles versus the $800 million Viking," wrote in his memoirs IKI Director Roald Sagdeev. (187)
From the engineering standpoint, Venus could be reached faster than Mars -- an important factor for the Soviet scientists, facing serious challenges with the reliability of avionics onboard the spacecraft. Additionally, the same launch vehicle would be able to send heavier payload toward Venus than to Mars, therefore allowing bigger spacecraft with more redundancy built in. The Proton rocket, which after rather shaky beginning in the second half of 1960s, gradually matured as a reliable vehicle, was capable of sending 5.3 tons of payload toward Venus versus 4.6 tons to Mars, according to official specifications. (45) (According to another sources the difference is 5.4 versus 5.0 tons respectively.)(180)
However flight to Venus could hardly be called a walk in the park. The planet presented its own unique challenges, first of all hellish temperature and pressure conditions on the surface, which would make even Martian environment look benign. Yet again, launching on the mighty Proton instead of previously used Molniya rocket, enabled scientists to conceive a brand-new, heavily protected lander designed to survive on the Venusian surface and conduct sophisticated experiments.
A new generation of spacecraft for the exploration of Venus was developed at NPO Lavochkin, which had been prime manufacturer of all Soviet planetary probes, since taking over this field from Korolev's OKB-1 in mid-1960s.
During 1974 and 1975, the 4V spacecraft went through a number of endurance tests at the special thermal vacuum chamber of Department 318 of NIIKhIMMash testing center near Zagorsk (now Sergiev Posad). (129)
The new generation bus, designated 4V, had a height of 2.8 meters and a span of solar panels of 6.7 meters. A similar vehicle had already been used as a base for the Soviet Martian missions in 1973. The central section of the bus, with the height of one meter and the diameter of 1.1 meters, contained propellant tanks for the main propulsion unit. The main engine was encircled by a conical instrument compartment with the diameter of 2.35 meters at the base, which also served as an interface with the upper stage of the launch vehicle.
The 4V spacecraft was equipped with a flight control computer responsible for processing information from the star and Sun sensors and sending commands to the gyroscopes of a three-axis attitude control system, developed by NPO AP. (73)
A pair of 1.25 by 2.1-meter solar panels provided electrical power. Relatively small size of the panels took into the account higher levels of solar energy in the inner regions of the solar system, where 4V was expected to travel. However the same region of space guaranteed extensive heating of the spacecraft, which was negated by a special radiator. A system of pipes carrying coolant from the main bus went inside of the lander as well. (185)
The 4V series of spacecraft were equipped with KRD-425A engine (also known as 11D425A) developed by Alexei Isaev's KB KhIMMash design bureau in Podlipki. The engine, designed to fire as many as seven times, provided course correction during the transit journey between Earth and Venus and the insertion maneuver enabling the main bus of the spacecraft to enter orbit around Venus. (180)
In 1975, before it was launched onboard Venera-75 spacecraft, the KRD-425A propulsion system was live fired at Test Facility No. 103 of NIIKhIMMash center near Zagorsk (now Sergiev Posad). (129)
Both 4V orbiters carried following scientific payloads:
The newest element of the Venera-75 project was the lander, designed specifically for penetrating Venusian atmosphere and surviving on its surface. A -meter sphere, containing the lander was designed to protect the spacecraft from the enormous heat, reaching 10,000 C degrees, during the initial entry into the atmosphere of Venus. Shortly, before separation of the lander, the thermal control system of the main bus would cool the lander to minus 8-10 C degrees. (189, 80)
The lander itself sported internal and external layers of isolation and its body was able to withstand pressure of 10 MPa. The vehicle was topped with a sambrero-like aerodynamic brake and the parachute compartment. Inside, the lander contained communications gear, electrical battery, flight control avionics, thermal control system and an array of science instruments:
To test the landing sequence, test versions of the 4V lander were dropped from the helicopters and planes. (189)
1975 June 8: The Proton booster (8K82K) with Block D upper stage blasted off from the "right-hand" launch pad at Site 81 in Baikonur Cosmodrome at 0237 UTC, carrying the 4V-1 No. 660 spacecraft. (186) After the vehicle reached a low circular orbit around the Earth and Block D engine fired for the second time sending the probe toward Venus, the Soviet press announced the mission as Venera-9.
1975 June 14: The launch of the 4V-1 No. 661 (Venera-10) took place successfully at 03:00:31 UTC from the same pad in Baikonur, only six days after its predecessor.
In the course of a four-and-half-month journey two probes covered the distance of around 360 million kilometers, during which ground control stations conducted 90 communications sessions and two course corrections with each spacecraft. (183) The first maneuver placed the trajectories of both probes within 1,600 kilometers from the surface of Venus, while the second refined the landing regions and times of the entry for the landers.
1975 October 20: The Venera-9 lander separated from the orbiter. Immediately, after the separation, the orbital module conducted a maneuver which sent the spacecraft on a swing around the opposite side of the planet from the lander.
Overview of Venera-75 maneuvers:
1975 October 22: After 126 days in transit, the Venera-9 orbiter encountered Venus. Immediately after its closest rendezvous with the planet, the main propulsion unit onboard the orbiter fired injecting the spacecraft into a 1,510 by 112,200-kilometer orbit around Venus, with the inclination 34.10 degrees and the rotation period of 48 hours 18 minutes. It was the first artificial satellite of Venus. (2) The selected orbit around Venus was designed to provide at least 115 minutes of communications between the lander and the orbiter, during the latter's descent and landing. (80)
In the meantime, the Venera-9 lander plunged into the atmosphere of Venus at the altitude of 125 kilometers with the angle of 20.5 degrees relative to the local horizon and with the speed of 10.7 kilometers per second. After initial aerodynamic braking, covers of the parachute compartments were jettisoned at the altitude of 65 kilometers, the speed of 250 meters per second and acceleration of 2G. It was followed by the deployment of a small "pullout" parachute and jettisoning of the top hemisphere of the protective reentry shell of the lander. The descent velocity then decreased to around 150 meters per second.
Next opened braking parachutes, radio transmitters were activated and started relaying the data. After working for 15 seconds, braking parachutes further reduced the descent speed of the lander to 50 meters per second. At the altitude of 62 kilometers above the surface, three main parachutes with the total area of 180 square meters had deployed. Four seconds later, the lower half of the protective sphere separated from the lander and fell off under its own weight, while the lander continued slow descent through the layers of clouds under main parachutes for some 20 minutes, providing wealth of atmospheric data.
Science instruments measured wind speed, temperatures, pressure, lighting conditions and searched for the presence of water vapors. The relative mass of the water vapors in the atmosphere at the altitude of 40 kilometers was determined to be around 10 --3.
Main parachutes were jettisoned at the altitude of 50 kilometers above the surface and the lander was then in a free fall, slowing down only with the help of a disk-shaped aerodynamic break. The descent velocity increased immediately after the release of parachutes, however started decreasing again, as the atmosphere around the lander was becoming more and more dense. As the lander was approaching the surface, its instruments confirmed earlier data that the wind speed at the altitudes of up to 10 kilometers is very low -- a stark contrast to the higher altitudes (20-40 kilometers), where winds gust up to 30-36 meters per second. (123)
The Venera-9 lander hit the surface of the planet with the speed of around seven meters per second at 08:13 Moscow Time (0513 UT) on October 22, 1975. It was the daylight local time on the side of the planet not visible from Earth. (71) The impact was cushioned by compressed gas released from the inflatable doughnut-shaped amortization device. (183)
The landing site was determined to be 32 degrees north latitude and 291 degrees longitude in Beta Regio. According to later estimates, the area was some 1.5 - 2 kilometers above the average surface level. (123)
Immediately upon landing, covers protecting windows of camera compartments were suppose to jettison, providing a pair of black and white cameras with the 360-degree view of surrounding landscape. However only one cover actually separated, narrowing the view angle to 180 degrees. At the same time, a boom with soil density sensor had been successfully deployed.
During next 53 minutes, the lander streamed data to the orbiter, which in turn relayed it back to Earth. The transmission of priceless imagery started some two minutes after the landing and continued until the end of communications.
Many popular accounts of the Venera-75 mission attributed the end of communications with the lander to the harsh conditions on the surface, however a respected Soviet source said the loss of signal was due to the orbiter going out of range of communications with the lander. (80)
The Venera-9 had enough time to scan 174 degrees of the panoramic view from left to right, and then 124 degrees scanning right to left. It took around half an hour to transmit all the data. Pioneering images revealed a rocky slope littered mostly with flat rocks up to 10 meters in size and surprisingly small amount of sand.
The size of most rocks was estimated to be around 50-70 centimeters and the height 15-20 centimeters. Most rocks featured sharp edges, hinting either their geologically young age, or very slow process of erosion. (188)
The lander ended up under a 30-degree angle and its cameras could only see as far as few dozen meters. Soviet scientists suggested that the material at the site represented remnants of rocks fractured as a result of the internal shifts and faults in the planet's crust. The tectonic process possibly caused a mass of debris to slide along the slope.
Another surprise was a relatively good visibility - landscape features could be discerned as far as 100 meters from the lander -- despite enormous density of the surrounding haze. One Soviet scientist apparently went far enough to compare lighting conditions on Venus with a "cloudy day in Moscow."
Along with image information, data from other instruments on the spacecraft was beaming back to Earth simultaneously. The "weather" data from the lander indicated that surrounding temperature was reaching 485 degrees C and pressure of 90 atmospheres. Under such harsh pressure, winds on the surface were rather slow and the behavior of the dust cloud raised by the landing of the spacecraft looked more like a smoke screen billowing around the submarine hitting bottom of the ocean on Earth.
(Another source quoted surface temperature of 457 degrees C.) Amount of solar radiation on the surface was measured at about 100 Watt per square meter. (123)
As the Venera-9 lander fell silent, the science equipment onboard the orbiter continued gathering information about temperature conditions at different altitudes and about composition of the planet's upper atmosphere and its cloud layers, as well as the data about interaction between the solar wind and the planet.
1975 October 23: The Venera-10 lander separated from the orbiter, while the latter conducted a maneuver to flyby Venus from the opposite side of the planet.
1975 October 25: The Venera-10 entered 113,900 by 1,620-kilometer orbit around Venus, with the inclination of 29.30 degrees and the rotation period of 49 hours 8 minutes. (2)
In the meantime, the Venera-10 lander entered the atmosphere at 0102 UT, under angle of 22.5 degrees relative to the local horizon. Repeating the Venera-9's descent sequence, it touched down on the searing surface of the planet at 0217 UT.
The landing site was located some 2,200 kilometers from that of Venera-9's, at the point 16 degrees north latitude and 291 degrees longitude.
One more time, one of the covers on the camera compartment refused to open, once again restricting field of view at the landing site to 180 degrees. Yet, the transmission of the black and white imagery and other scientific data had continued successfully for 65 minutes after the landing. (71) This time, the camera could see much farther than the one on the Venera-9 lander.
Images from the Venera-10 landing site showed bleak and almost perfectly flat desert with no apparent elevation changes. The spacecraft was sitting on a huge flat boulder with the diameter of about three meters and covered with dark spots, which were probably shallow holes filled with soil. The boulder itself, as well as similar ones visible in the distance, were themselves buried into the dark-colored soil.
The density sensor on the Venera-10 probed the surface of the rock on which the lander was sitting. The density was determined to be 2.7 - 2.9 grams per cubic centimeter, which was comparable to bazalt-type rocks on Earth. (123)
Almost three decades after Venera 9 and 10 "scanned" these truly out-of-the-world landscapes through a one-centimeter thick quartz pressure windows, Donald Mitchell, an image expert who worked for AT&T Bell Labs and Microsoft Research, reprocessed the original digital telemetry from the Soviet landers. In the case of Venera 9 and 10, he undid a pixel replication and replaced it with a higher quality interpolation filter. As a result, remarkably clear images emerged, bringing humanity closer to the forbidden world.
A display replica of a fully assembled Venera-75 spacecraft.
A primary exhibition hall in Moscow (Cosmos Pavilion at VDNKh), which used to showcase major Soviet space achievements was converted into commercial retail space with the fall of the communist system in Russia. Priceless pieces of space hardware were sent back to their cash-strapped developers. A cruise stage of the 4V (Venera) spacecraft, which once adored Cosmos Pavilion and other Soviet exhibits, was later seen on the premises of NPO Lavochkin stripped of most of its external elements.
The interface adapter for the lander is visible on top, the propulsion section is at the bottom. Tanks containing gas for attitude control are visible on the left side of the spacecraft. Copyright © 2001 by Anatoly Zak
A display replica of the Venus lander in its surface configuration. Floodlights and deployable boom with sensors are visible. Copyright © 2001 by Anatoly Zak
KRD-425A engine, which powered the 4V spacecraft bus with the portrait of Alexei Isaev, the head of KB KhIMMash, the organization that developed this system. Copyright © 2001 by Anatoly Zak