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Space


First Generation Veneras

By Charles S. Sheldon II [1917-1981], was Chief of the Science Policy Research Division of the Library of Congress, Congressional Research Service

1971-1975

1961 Venus Attempts

On February 4, 1961 , the Soviet Union announced the launch of Tyazheliy Sputnik 4, of 6,483 kilograms, described as a test of an Earth orbital platform from which an interplanetary probe could be launched. The fact that this launch occurred at the correct hour for a Venus probe indicated the mission while an Earth orbital success was a Venus probe failure. In this respect, a further evolution of Soviet technology was demonstrated. The first three Luna flights had been direct ascent missions; probably starting in October I960, the change to a more powerful upper stage occurred, and the added flexibility of launch from orbit was intended, an approach which has been used ever since for deep space missions. Another launch was announced on February 12, 1961 —Tyazheliy Sputnik 5—and from this came a probe or Zond rocket carrying another Automatic Interplanetary Station (AIS) called Venera 1. The payload weighed 643.5 kilograms. It was by far the most elaborate payload combination to be unveiled to that time. For some weeks the mission went well, but at a distance of about 7.25 million kilometers from Earth, communications ceased. The payload is estimated to have passed Venus at a distance of about 100,000 kilometers on May 19, 1961 , based on its known trajectory.

1962 Venus Attempts

Venus launch windows come about every 19 months. True to practice, the Soviet Union launched multiple attempts on August 25, September 1 and September 12, 1962 carrying Venera spacecraft. All of these reached Earth orbit, but failed to launch their payloads successfully toward Venus, leaving various kinds of debris and major segments in Earth orbit. No Soviet acknowledgment of these launches has been made to this day. The United States routinely published its Goddard Satellite Situation Report including the August 25 pieces of debris in Earth orbit. But then it began to worry about the possible diplomatic consequences of such announcements, and for a time suspended publishing the statistical report altogether; and when it resumed, it skipped all Soviet objects in orbit after August 25, 1962 . However, all objects, listed or not, are assigned a sequential astronomical designator which is supposed to account for all observable objects in orbit. The omission of certain designators signaled to anyone familiar with the system that there were unacknowledged flights in orbit. In early September, press accounts rumored that the United States had begun to make secret military launches, and the Soviet representatives at the United Nations made charges against the United States to this effect. Our representative denied this and said the stories "were not wholly accurate", rather than revealing there had been a Soviet launch on September 1. The diplomatic stances adopted by both countries are not too flattering to either, in retrospect. Actually, for a long time, the September 12 Soviet launch was carried in British publications as a secret U.S. launch because of the de facto U.S. and Soviet agreement not to disclose these Soviet failures.

1964 Venus Attempts

Since ten planetary attempts had succeeded in launching only two Zond payloads, and both of these had failed to continue communications all the way to their planetary destinations, it appears the Russians launched a diagnostic flight November 11, 1963 , which was acknowledged as Kosmos 21, but it was not able to send a deep space Zond beyond Earth orbit.

Nonetheless when the Venus window came, a launch was made on March 27, 1964 . When it failed to launch a Zond, it was given the name Kosmos 27, and was passed off as a routine flight. It will be noted that this was a change of information policy, compared with the 1962-63 period when debris in Earth orbit was not acknowledged. The United States, goaded by further Soviet charges at the United Nations about project Westford, space "needles", in its counter blast named the five 1962 planetary Zond failures which reached Earth orbit together with a 1963 Soviet Moon flight failure which also was stranded in Earth orbit. The closest thing to a Soviet acknowledgment was a Soviet further complaint that the United States was attempting to register flights of other nations, which was not its business under the registration agreement of the United Nations. In any case, by assigning an arbitrary and neutral Kosmos (Space) name and number to later escape failures stranded in Earth orbit, the Soviet Union thereafter avoided this particular information problem.

On April 2, 1964 , another Venus probe was launched. Because of the poor record of its predecessors, the U.S.S.R. this time simply labeled it Zond 1. However, the details announced on its course made clear that it was bound for Venus. Communications failed soon after May 14, and it passed Venus on July 19, 1964 at 100,000 kilometer estimated distance.

1965 Venus Attempts

With renewed confidence in the basic Zond bus, the launch of November 12, 1965 was named Venera 2; that of November 16 was named Venera 3; but that of November 23 was only Kosmos 96, because it failed to launch its Zond from the Earth orbiting platform Venera 2 passed Venus at a distance of about 24,000 kilometers on February 27, 1966. Venera 3 struck Venus on March 1, 1966 about 450 kilometers from the center of the visible disk. The Russians received many congratulations for these twin successes, which included sending the first manmade object to the surface of another planet. Soviet emblems were contained in the payload. A few days after the congratulations had been received; the U.S.S.R. revealed that communications had failed in both Zonds at an unspecified time shortly before the planet had been reached. This ran the total to 18 Zond payloads expended without a single bit of planetary data returned, although there were a number of engineering triumphs involved and some data on the interplanetary medium, as well as pictures of the Moon.

1967 Venus Attempts

Venera 4 was launched on June 12, 1967 , using an A-2-e vehicle like its predecessors, but carrying a heavier payload of 1,106 kilograms. Two days before arrival its mission was revealed as one to make direct atmospheric measurements. On October 18, 1967 , a capsule separated from the bus, and after aerodynamic braking, the capsule deployed a parachute, on which it hung for about 1.5 Earth hours while descending toward the surface where it deposited the Soviet coat of arms marked on a pennant of metal, as had been true of Venera 3. Its successful return of planetary data was an important first in the Soviet program. Data were refined over a period of time, apparently suggesting some problems of calibration and interpretation. At first the Russians thought they had data readings all the way to the surface, but unless a landing had occurred on a very high mountain peak, it is more likely that signals ceased at an altitude of 25 kilometers. With this assumption the Soviet data could be reconciled with the indirect U.S. Mariner readings, which were based upon interpretations of radiated and reflected energy.

The main bus of the Soviet Venera 4 carried a magnetometer, cosmic ray counters, hydrogen and oxygen indicators, and charged particle traps. It found a weak hydrogen corona at 10,000 kilometers above the surface on the night side of Venus and a magnetic field only 0.001 the strength of that around Earth, and no radiation belts. The bus was burned as it plunged into the atmosphere.

The sterilized landing capsule was an egg-shaped package about one meter in diameter, weighing 383 kilograms and protected by ablative material against the high heat of entry friction. The parachute, deployed after the speed was slowed sufficiently, was made of heat resistant material. The capsule carried two thermometers, a barometer, a radio altimeter, an atmospheric density gauge, and 11 gas analyzers. The latter took 5 readings at an altitude of 25 kilometers and others at an altitude of 23 kilometers. Signals from the capsule were received for 96 minutes both in the U.S.S.R. and at Jodrell Bank. The readings received ranged from a first temperature of 39° C. to a final reading between 263 and 277° C. The atmosphere was measured as 90 to 95 percent carbon dioxide, 0.4 to 0.8 percent oxygen, perhaps between 0.1 and 0.7 percent, but not over 1.6 percent water vapor. The remainder might have been argon or other inert gases, and if nitrogen was present, it was not identified. The final pressure reading obtained was 15 to 22 times that of Earth. Later study by both American and Soviet scientists of the Soviet data suggested the Celsius temperature at the true surface was probably about double the reading, and the atmospheric pressure was about 90 Earth atmospheres. Although the arrival of the American Mariner 5 a day later in time helped to find the correct meanings of Soviet data, the Mariner itself gave some readings whose estimates were farther off from what is the best information today. Mariner data suggested 72 to 87 percent carbon dioxide, little oxygen, and the balance being either neon or nitrogen. The surface temperature was estimated as 371° C. Mariner 5 also detected what might have been a slight magnetic field, but no radiation belt. The Russians revealed that an operating replica of Venera 4 was kept in an environmental chamber on Earth through the entire period of the flight to duplicate as nearly as possible the same circumstances so as to serve as a systems check and to give early warning of problems in order that they might be solved on Earth in timely fashion and new commands sent to the actual flight. The flight was monitored in 114 communications sessions during the several months of the voyage. Power was supplied as in the other Zond flights partly from solar cell panels, tilting them away from maximum direct exposure to the Sun as the flight moved closer to that body. Chemical batteries served as buffers. Special attention was given to communications because of the sad results on earlier flights often related to communications difficulties. As the bus approached the planet, a command was sent to orient the main antenna toward Earth and signal strength at Earth jumped 300-fold. Doppler changes in signals provided data on its speed and. stability. Once the final approach began, the ship was switched to its autonomous program. After separation of the capsule and opening of the parachute, the capsule's own directional antenna was deployed so that signals were still 20 percent the strength of those of the main; parabolic antenna of the bus.

The initial departure from the Earth orbiting platform would have made Venera. 4 miss the planet by 60,000 kilometers, so a midcourse correction was applied July 29, to aim it for the visible center of the planet. During its entry, it is believed the capsule withstood temperatures in the range of 10,000 to 11,000° C. The capsule had been desired to withstand pressures up to 100 atmospheres and loads up to 300 G (compared with the 10 to 12 G a man can withstand for the same length of time).

Just five days after the launch of Venera 4, Kosmos 167 was sent to Earth orbit and from its timing and behavior it was intended to be the second Venera of the 1967 window, but the Zond rocket failed to fire, leaving it stranded in Earth orbit.

1969 Venus Attempts .

On January 5, 1969 , Venera 5 was launched toward Venus using the same A-2-e Launch vehicle as its predecessors. The payload weighed 1130 kilograms. From the outset it was identified as intended to gather additional atmospheric data. The probe carried not only the usual metal pentagon with the Soviet coat of arms, but a bas-relief of Lenin’s head. The Zond rocket, escape stage "e" was fired from its orbiting platform over Africa . Most details of the flight were as already described for Venera 4. This bus jettisoned its capsule to hit the atmosphere at a speed of 11.17 kilometers per second, which was reduced aerodynamically to 210 meters per second when the parachute was opened For 53 minutes while suspended from the parachute, data were returned about the atmosphere. Further details are discussed in connection with the following flight.

Venera 6 was launched five days after Venera 5, January 10, 1969 . It was a close duplicate of its immediate predecessor, of identical weight, and carrying the same symbols and instrumentation. It, too, was slated to land on the night side of Venus, as were Venera 3, 4 and 5. Venera 6 reached Venus on May 17, a day after Venera 5. The hope in running two flights so close to the same pattern was to improve the cross calibration of results for consistency in data readings.

During the course of the flights, some 1.500 commands were sent to the two stations in 136 communications sessions (73 to Venera 5 and 63 to Venera 6). Semi directional antennas were used in the first two months of the voyages, and then the parabolic antennas of 2 meters diameter were aligned whenever high capacity data links were needed. Considerable information was stored in tape recorders on board, which could be emptied during a communications session, ready for refill with fresh data.

As with Venera 5, Venera 6 deployed its parachute after slowing down aerodynamically and data were returned for 51 minutes.

The Russians supplied further information on orientation of the bus. When it was time to use the high gain directional antenna, the Sun seeker searched for the Sun, and then using the Sun direction as an axis the ship was rotated until the Earth tubs found Earth at which point it locked on and the antenna was correctly pointed.

These two Venus probes were also matched by a replica in an environmental chamber on Earth for diagnostic purposes. The claim was these latest Zonds were built to a higher standard of resistance to heat, and pressure than Venera 4. The resistance of ships to G load was raised to 450 as opposed to 300 of the earlier model. Instruments in the probe bus were supposed to function between 0 and 40 degrees Celsius, but in actual fact were held between 10 and 25 degrees. Because of the more rugged construction and better protection, the parachute size was cut to one third that of Venera 4 to permit a more rapid descent through the atmosphere to enhance the chance of survival closer to the surface.

While discussing these craft, the Soviet Chief Designer predicted that future automated craft would fly to Mars, dig samples, and return these to Earth.

In March 1970, the scientific findings of Venera 5 and 6 were released for comparison with Venera 4 with these results:

TABLE 2-1.-ATMOSPHERE OF VENUS, EARLY SOVIET DATA

Atmospheric components Venera 4 final data Venera 5 and 6
C02 (percent) 90+/- 97+/- 4
N2 (percent) <-7(possibly<-2.5) <-2
O2 (percent) 0.4-1.5 <-0.1
H2O (at P 0.6 atm)mg/liter 1-8 ~11

Source: Vinogradov, Acad. A. P., et al.:” Study of the composition of the Venerian Atmosphere on Venera 5 and Venera 6 automatic stations. Doklady Akademii Nauk SSSR, Vol. 180, No. 3, PP. 552-554.

It will be observed that the two sets of results bear a relation, but that the later readings brought some noticeable shirts in the conclusions. Especially, the Soviet position had shifted from an estimate of surface pressure from 22 atmospheres to 100 atmospheres, and the temperature from 280° 0. to 500° C.

1970 Venus Attempts

Venera 7 was launched on August 17, 1970 with an A-2-e launch vehicle and weighed 1,180 kilograms, the heaviest yet of the Zond payloads sent to the planets. It followed the familiar pattern of placement in Earth parking orbit with the use of a Tyazheliy Sputnik. >From this platform the Zond rocket was fired toward the end of the first revolution to send it toward Venus. The mission was described as designed to conduct further studies of the atmosphere of Venus, as well as other studies of the planet.

On December 12, 1970 , as Venera 7 approached Venus, the solar cells of the main bus were used to charge the batteries of the landing capsule, and the temperature of the capsule was lowered to minus 8 degrees Celsius. On December 15. only 14 seconds later than estimated, Venera 7 entered the atmosphere of Venus at 7:58:44 Moscow time. This signal reached the Soviet Union at 8:02:06 . The speed was close to 11,600 meters per second, about as estimated. As soon as the atmosphere affected the stability of the vehicle so that it lost its lock, this automatically triggered the separation of the landing capsule. After aerodynamic braking slowed the capsule to 250 meters per second, the parachute system was deployed, and the antenna was extended. Its signals to Earth continued for 35 minutes. In light of the limitations with its predecessors, this capsule had been made still heavier and shaped as a perfect, sphere for greater strength, and with no holes drilled through its shell which might prove weak points during entry. Instead, only after the top hatch blew off to deploy the parachute and antenna were the sensors exposed.

With no more news at the time from Soviet sources, "Western observers concluded once again that the environment of Venus had been too much for the capsule. But apparently after the 35 minutes of strong signals ended, the Russians continued to tune in the hiss of electronic a dual antenna system was used on the capsule. In addition to one directly on the capsule, a second tossed to one side on landing was also used. The first 13.3 minutes of data came from the main antenna, and the next 20 minutes from the secondary antenna, and then the remaining 30 minutes came from the main antenna again.

Analysis of the soil of Venus, a new feature, was incomplete, but suggested a soil density of 1.5 grams per cubic centimeter. The soil showed 4 percent potassium, 0.0002 percent uranium, and 0.00065 percent thorium. This suggested rock similar to granite.

On March 31, Kosmos 482 was launched at the right time to be a Venera flight. Again, there was payload separation from the orbital launch platform, but an early cutoff which left the Zond rocket and payload in an eccentric orbit with the apogee sufficiently high that the payload remains in orbit now more than three years later.

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.



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