Second Generation Veneras

By Charles S. Sheldon II*

1971-1975

THE VENUS ATTEMPTS OF 1975

Launch of Venera 9 and Venera 10

As expected, the Russians upgraded their Venus exploration effort by the use of the D-l-e class vehicle for the first time in launching Venera 9 on June 8, 1975 . It was described as a new type of Venus spacecraft. Using the standard Earth orbital platform approach, the probe was sent toward Venus, with the announced purposes of studying Venus and surrounding space, and for doing studies of the interplanetary medium on the way. Radio Moscow added that the launch vehicle was larger than the one used for Soyuz (the A-2). Ships were placed in the Gulf of Guinea , the Mediterranean , and the Pacific to support the launch, with the Molniya 1 used for relay purposes. The flight was controlled from the Deep Space Communications Center at Yevpatoriya. . .

On June 14, Venera 10 was launched, and it was announced as similar in design and mission to Venera 9. It was launched in the same manner to put it on its trajectory.

En Route to Venus

TASS announced on August 8 that the flights were going well, and that Venera 9 would reach Venus on October 22, while Venera 10 would arrive there on October 25. Soviet sources noted that while earlier Venera probes had required many commands from Earth to control their course, this time there were on-board digital computers which made many of the necessary calculations, adding flexibility to the operations. Orbital corrections were made on June 21 and October 18, and there were 90 communications sessions, for Venera 9. Presumably the handling of Venera 10 was similar.

Landing of Venera 9

On October 20, Venera 9 was divided into separate Lander and orbiter craft. On October 22 at 0658 Moscow time, the Lander entered the atmosphere of Venus at a speed of 10.7 km/sec. It was protected within a two-hemisphere shell, and was able to withstand temperatures up to 2,000° C. (20,000° C.) and 300 tons pressure. It used aerodynamic braking until it had slowed to 250 meters/sec. Then it cast loose one hemisphere and in succession used three parachutes. On the way down, it studied the cloud layers in detail. At 50 kilometers altitude it cut loose the main parachute, and relied on a disc-shaped aerodynamic brake for the rest of the descent, impacting at 6-8 meters/sec. The landing came at 0813 Moscow time. To cushion the impact, there was a compressible "doughnut" metal ring at the base of the Lander, separated by struts, and this exhausted air under impact. Because the Lander instrumentation had been pre-cooled to minus 10° C. and its exterior equipment to minus 100° C. before entry, it was able to survive in functioning condition for 53 minutes on the surface. A special system of circulating fluids distributed the heat load. The Lander carried a metal pennant with the Soviet coat-of-arms. It stood approximately 2 meters high, and was equipped with flood lights to take a surface picture.

Preliminary findings suggested that the clouds through which it passed were 30 to 40 kilometers thick, with a base 30 to 35 kilometers high. The upper layers may have contained hydrogen chloride and hydrogen fluoride, while farther down there may have been bromine and iodine. The surface pressure was about 90 Earth atmospheres and the temperature 485° C.

The real surprise was to find that the lighting was as bright as Moscow on a cloudy June day, so that the floodlights were not required. Some 15 minutes after landing, a television panoramic picture began to emerge on Earth. There was no noticeable dust, and the picture was quite clear even without further processing. Details were good out to 50-100 meters. There was a scattering of rocks 30-40 cm across, and a large stone on the apparent horizon. The panorama generally reached out to 160 meters, and the horizon may have been 200-300 meters away, but this was in doubt and probably an understatement. There was a defined curvature between surface and air at this horizon. The fact that rocks cast shadows suggested that direct sunlight was reaching the surface, in contrast to the expected solid cloud cover. Surprisingly, also, the rocks were not eroded, but showed sharp cleavages as if relatively young.

Because the landing occurred on the sunlit side away from Earth, the data had to be relayed from the surface to the orbiter for further relay to Earth. With the Sun close to the zenith, it was believed the light was probably 20 to 25 times as intense as during the Venera 8 mission where the Sun was only 4.5° above the horizon.

Landing of Venera 10

On October 23, Venera 10 was divided into separate Lander and orbiter. The Lander arrived on October 25. It approached its landing site at a 20° angle. The temperature rose to 12,000° C. and the dynamic pressure reached 168 G's during aerodynamic braking. At 60 kilometers, the parachutes opened, and then we were dropped at about 49 kilometers. At 42 kilometers, the pressure was 3.3 Earth atmospheres and the temperature was 158° C. At 15 kilometers, the pressure was 37 Earth atmospheres, and the temperature was 363° C. Some 75 minutes after entry began, the landing came at 0817 Moscow time. After this the Lander operated 65 minutes on the surface. It had also been pre-cooled inside to minus 10° C., and its interior temperature at landing was 23° C., and its pressure was 2 Earth atmospheres. The surface pressure was 92 atmospheres and the temperature was 465° C. The wind was 3.5 meters/sec. The landing occurred about 2,200 kilometers away from the Venera 9 Lander.

As with its twin, Venera 10 was successful in sending back a panoramic view of its surroundings. Picture transmission was over by 0922 Moscow time, and was relayed via the accompanying orbiter craft. This time the view showed large pancake rocks, possibly with cooled lava or other weathered rocks in between. At the control center, the telephotometer picture emerged from the receiving machine on paper tape, with breaks every so often to permit other data to be received. It took about an hour for the picture to be received.

The estimate was that Venera 9 had landed in alpine-type country about 2,500 meters elevation, while Venera 10 had landed in lower plains.

. The Venera 9 and 10 Orbiters

Both orbiters were put into their respective orbits the same day as their Landers went

to the surface of Venus. As indicated above, each served as a relay station for data from the respective Lander. Each carried a metal pennant with a bas-relief of Lenin.

The Venera 9 orbiter was estimated to be in an orbit with a high point of 112,000

kilometers and a closest approach of 1,300 kilometers, with the orbital period 48 hours, 18 minutes.

The Venera 10 orbiter was estimated to have a high point of 114,000 kilometers and a closest approach of 1,400 kilometers, with its period 49 hours, 23 minutes.

The mission of the orbiters is to explore the cloud layers of the planet, their structure, temperature, and radiation, using spectrometers, radiometers, and photopolarimeters. By using radio sounding, they were measuring the density of ions and electrons, and at high altitudes the energy spectra directly with ion traps. They were also measuring weak magnetic fields and particles in the solar wind stream.

Pictures taken in the TJV range showed dark areas of equatorial circulation, like Mariner 10. Data are taped for later replay to Earth. The most recent reference was published November 21, when Venera 9 had made 15 revolutions and been contacted 40 times. Venera 10 had made 13 revolutions and been contacted 35 times. It was then revealed that France had supplied the UV spectrometers in use. Other equipment was used to measure the ratio of hydrogen to deuterium in the upper atmosphere.

References

1. SOVIET SPACE PROGRAMS, 1971-75, OVERVIEW, FACILITIES AND HARDWARE MANNED AND UNMANNED FLIGHT PROGRAMS, BIOASTRONAUTICS CIVIL AND MILITARY APPLICATIONS PROJECTIONS OF FUTURE PLANS, STAFF REPORT , THE COMMITTEE ON AERONAUTICAL AND SPACE .SCIENCES, UNITED STATES SENATE, BY THE SCIENCE POLICY RESEARCH DIVISION CONGRESSIONAL RESEARCH SERVICE, THE LIBRARY OF CONGRESS, VOLUME – I, AUGUST 30, 1976, GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976.