Category Soviet Robots in the Solar System

The Scientific Production Organization NPO-Lavochkin was originally founded in 1937 as the Lavochkin Aircraft Design Bureau, OKB-301, named for its Chief Designer. Lavochkin produced a number distinguished fighter aircraft during WW-11

and then surface-to-air missile designs after the war, producing the first operational system for the defense of Moscow. In 1953 the SAM business was transferred to a new design bureau and OKB-301 pursued ramjet intercontinental cruise missiles as a hedge against problems with ICBM development. But the successful introduction of ICBMs in the late 1950s left OKB-301 without work. Semyon Lavochkin died in 1960 and the organization transferred in 1962 to Chelonrey’s OKB-52. The factory was closed, but reopened in 1965 as NPO-Lavochkin under the steady and capable leadership of Georgi Nikolayevich Babakin specifically to take responsibility for the robotic lunar and planetary spacecraft programs transferred from OKB-1.

The new NPO-Lavochkin realized immediate success using its inheritance from OKB-1 augmented by a history of great skill and experience in aviation technology. Luna 9 soft landed on the Moon’s surface in January 1966, and before the year was over there were three successful lunar orbiters and a second soft lander. The first successful Venus entry probe, Venera 4, followed in 1967. NPO-Lavochkin went on to continue this highly successful series of spacecraft at Venus, a successful series of lunar orbiters, rovers and sample return missions, and the singularly complex and successful Vega missions which delivered landers and balloons to Venus enroute to a flyby of Halley’s comet. LTnfortunately, NPO-Lavochkin had no success at Mars: their campaigns in 1969, 1971, and 1973 were riddled with failures, and worse was to come in 1988 and 1996. Their astronomy missions have met with better success, in particular the Granat and Astron space observatories. Today NPO-Lavochkin is the single engineering center for the production of robotic scientific spacecraft.

Russia built the first interplanetary spacecraft for launch attempts at Mars in 1960 and Venus in 1961. These two sets of spacecraft were similar, but the 1M pair built for Mars and the 1VA pair built for Venus had differences relating to the different thermal conditions expected and the communication differences involved. Each pair was identical. Only one of these spacecraft, Venera 1, survived the launch vehicle and was dispatched towards its target, but contact was lost 7 days later.

TIMELINE: JAN 1963-DEC 1965

Between their success with Luna 3 in October 1959 and the opening of 1963, the Soviets suffered two failed lunar missions, five failed Mars missions, and five failed Venus missions. During those long 39 months, Sergey Korolev’s engineers had been working on a new lunar soft-lander to take advantage of the four-stage version of the R-7. Unfortunately, this new Luna would suffer an even longer and more frustrating series of failures than the Ranger crash-lander being developed by the Americans. In fact, there would be eleven failures over the three years 1963-65 before managing a soft landing, with four of the six launch failures being caused by malfunctions of the fourth stage. Of those that were successfully deployed, Luna 4 to 8, two missed the Moon and the other three crashed onto it. The real objectives of these missions were not revealed at the time. Meanwhile, in 1964-65 the LTS finally had a string of successes with Ranger 7 to 9.

fn parallel, the Soviets were applying the lessons from Venera 1 and Mars 1 in the development of the 3MV planetary spacecraft, basically an improved version of the 2MV, for the planetary launch windows of 1964 and 1965. To gain some experience with the new spacecraft, it was decided in late 1963 to make two interim flight tests, but these spacecraft were lost to launch vehicle failures on November 11, 1963 and February 19, 1964. Undeterred, wrhen the Venus launch window opened the Soviets proceeded to launch spacecraft to Venus on March 27 and April 2, 1964. Only the second spacecraft w? as launched successfully, but because it was immediately clear that on board failures would prevent it from reaching its target it was named Zond 1 instead of being given a Venera designation. A launch to Mars – was accomplished successfully on November 30, but once again the spacecraft was sufficiently crippled that it would not make its target and so it was named Zond 2.

The loss of so much hard work must have been doubly galling with the success of the Mariner 4 flyby of Mars on July 15, 1965. As with Venus, the LTS had somehow reached Mars first! Troubled by the significant problems suffered by Zond 1 and 2, the Soviets decided to conduct another 3MV test flight. Launched on July 18, 1965,

W. T. Huntress and M. Y. Marov, Soviet Robots in the Solar System: Mission Technologies І Іл

and Discoveries, Springer Praxis Books 1, DOl 10.1007/978-1-4419-7898-1 9,

© Springer Science 4-Business Media, LLC 2011

outside a launch window, Zond. 3 was unable to reach Mars but it could fly the kind of trajectory that would be used by a real mission. The timing of the departure was arranged so that it could test its camera system by photographing the far side of the Moon. It exercised its navigation systems, propulsion system, flight and instrument operations, and returned its pictures. Unfortunately communications were lost before it reached the equivalent of Mars distance, preventing it from demonstrating its deep space capabilities.

The Zond 3 experience paid off on the flights of Venera 2 and Venera 3, both of which were launched later in November 1965, the first equipped to make a flyby and the second with an entry probe. They flew without serious problems and became the first Soviet planetary spacecraft to reach their target. But they added to rheir maker’s woes by both losing communication, Venera 2 just as it arrived and Venera 3 when
seventeen days from its target on a collision trajectory. Neither mission returned any data from Venus.

The years 1964-65 were crucial turning points in the Soviet space program. Since 1959 OKB-1 had been working on a plan to send eosmonauts on circumlunar flights, and had designed the Soyuz system for this objective. It had no plans to land people on the Moon. The Soviets initially saw the US stated intention to land a man on the Moon as mere hyperbole, but by 1964 it had become clear that major resources had been assigned to the program and that the development of the necessary rockets and spacecraft was progressing. Confident that their Soyuz could beat the Americans to a circumlunar mission but reluctant to be upstaged by a lunar landing, the Politburo directed Korolev in August 1964 to proceed with landing cosmonauts on the Moon in addition to performing the circumlunar program. However, in what would prove to be a huge management mistake, the government divided the development work for these programs amongst competing design bureaus without central leadership or responsibility. The space program was reorganized and additional resources applied. To manage all the work, new design bureaus were established and responsibilities distributed. At this point Soviet space policy underwent a fundamental change, and instead of pursuing long standing plans for the conquest of space it began to directly compete with the American program.

The other issue forcing a shake up in the Soviet space program was the long string of robotic lunar and planetary program failures between 1960 and 1965. Thus far. Korolev had been responsible for virtually all types of Soviet spacecraft and now he had been given the further task of overtaking the Americans in the race to the Moon. By his own admission. OKB-1 was overburdened and unable to devote enough time and resources to the robotic missions. In March 1965, on the advice of Keldysh, he asked his friend Georgi Babakin. who headed NPO-Lavochkin, to take over after the current production run of lunar and planetary spacecraft at OKB-1 ran its course. In April, Korolev handed over OKB-l’s plans and knowledge base to Lavochkin. The remaining robotic spacecraft were launched during the rest of the year, ending w ith Luna 8 and Venera 3, while Lavochkin designed modifications and set up to produce new’ spacecraft.

The next three sample return attempts were lost to launcher failures. In September Ye-8-5 No.403 was stranded in parking orbit when the Block D failed to restart. An oxygen fuel valve had stuck open after the first firing and allowed all the oxidizer to escape. It was designated Cosmos 300 by the Soviets, and re-entered after 4 days. In October a programming error caused the Block D to misfire and spacecraft No.404. designated Cosmos 305, re-entered during its first orbit. In February 1970 spacecraft No.405 was lost wdien a pressure sensor command error shut down the second stage after 127 seconds of flight and the vehicle was destroyed. This precipitated a review7 of the Proton launch vehicle, w hich had a miserable record with many more failures than successes in the Ye-8 and lunar Zond series at that time. Changes w ere made as a result of this review, and in August 1970 a successful suborbital diagnostic flight was flown. The following month another sample return attempt was made and, after five successive failures in a period of 15 months, success w’as finally achieved.

Luna 16

Luna 16 was launched at 13:25:53 UT on September 12, 1970. Seventy minutes after entering parking orbit, the Block D reignited and performed the translunar injection burn. After a course correction on September 13. the spacecraft entered a nearly circular 110 x 119 km orbit at 70 degrees inclination on September 17. After gravity data had been acquired in this orbit, two orbital adjustments were made on September 18 and 19, the first into an elliptical orbit wdth its perilune 15.1 km above the landing site and an apolune of 106 km, and the second to adjust the orbit plane to 71 degrees inclination. As the spacecraft approached perilune on September 20. the extra tanks were jettisoned. The engine was ignited at perilune. 05:12 UT, and fired for 270 seconds to cancel the orbital velocity and initiate the free fall. Triggered by the radar altimeter, the engine was restarted at an altitude of 600 meters and velocity of 700 km hr. It was shut down at an altitude of 20 meters and a velocity of 2 m/s. The primary verniers were ignited for the tenninal phase, and cut off at a height of 2 meters, then the spacecraft dropped to impact at about 4.8 m/s. Touchdown occurred at 05:18 UT in the Sea of Fertility at 0.68 S 56.30 H. only 1.5 km from the planned point.

Because Luna 16 touched down 60 hours after local sunset and was not fitted w ith floodlights it did not provide any images. The drill was deployed after an hour, and in 7 minutes of operations it penetrated to a depth of 35 cm before encountering an obstacle. 1 he boom then lifted the core sample from the surface and swung it up to

the return capsule atop the ascent stage, inserting it through an open hatch that then closed. Some soil was lost from the sampler during this operation. At 07:4.1 UT on September 21, after 26 hours and 25 minutes on the Moon, the ascent stage lifted off and escaped at 2.7 krn/s. The lower stage remained on the surface and continued to transmit lunar temperature and radiation data. The ascent stage returned directly to Earth. On September 24, at a distance of 48,000 km, the straps released the return capsule. Four hours later it hit the atmosphere traveling at 11 km/s on a trajectory at 30 degrees to the vertical on a ballistic entry with a peak deceleration of 350 G. At an altitude of 14.5 km the top of the capsule was ejected and the drogue parachute deployed. At 11 km the main chute was unfurled and the beacon antennas deployed. The capsule landed at 03:26 UT on September 24, approximately 80 km southeast of the city of Dzhezkazgan in Kazakhstan.

Luna 16 proved, to contain 101 grams of lunar material. It was a triumph, and the Soviet press made the best of it, hyping the use of robots over manned missions. For the Americans, Luna 16 confirmed what they suspected about Luna 15, that it was a sample return attempt intended to upstage Apollo 11.

Luna 18

The next attempt at sample return was made one year later. Luna 18 was launched on September 2, 1971, made midcourse corrections on the 4th and 6th, and entered a 101 km circular lunar orbit inclined at 35 degrees the following day. After lowering its perilune to 18 km it was commanded to land on September 11, but the signals cut off abruptly at 07:48 UT at an altitude of about 100 meters. The main engine had run out of fuel due to excessive consumption in earlier operations, and the wreckage lies at 3.57°N 56.50°E in rugged highland terrain.

Luna 20

Luna 20 was the second attempt after Luna 18 to obtain a sample from in the lunar highlands. Launched on February 14, 1972, it was tracked by telescopes to compute an accurate trajectory, made a midcourse correction the following day and entered a 100 km circular lunar orbit at 65 degrees on February 18. It lowered its perilune to 21 km the following day. And finally, at 19:19 UT on February 21, it touched down in the Apollonius highlands near the Sea of Fertility at 3.53°N 56.55,:>E, only 1.8 km from where Luna 18 crashed. The Sun was 60 degrees above the horizon. Images of the surface were transmitted prior to the sampling operations. The drill encountered resistance, and had to be paused three times to prevent overheating. It was ultimately able to achieve a depth of only 25 cm. The recovered sample core was transferred to the return capsule.

The ascent stage lifted off at 22:58 UT on February 22, and then upon its return to Earth fell into a strong snow storm. .Although it came down over the Karkingir river 40 km north of Dzhczkazgan, when it landed at 19:19 UT on February 25 it touched down on an island. The ice, wind, and snow presented the recovery team with severe difficulties. It was recovered the following day, and when opened proved to contain only 55 grams of lunar soil.

Luna 23

The first improved Ye-8-5M sample return vehicle, No.410, became Luna 23 with a successful launch on October 28, 1974. After a midcourse correction on October 31, it entered an almost circular 94 x 104 km orbit at 138 degrees on November 2. Upon lowering its perilune to 17 km it was commanded to land on November 6. Although Luna 23 landed on target in the southern part of Sea of Crises at 12.68’N 62.28°E, it did so at 11 m/s and the impact shock wrecked the sample collection apparatus and caused other damage. No samples wjere obtained and the ascent stage was not lired. The lander continued to transmit until contact was lost on November 9.

TIMELINE: 1979-1981

The pace of planetary exploration slowed considerably after 1978, particularly in the US. There were no launches to the Moon or the planets in 1979-80. ft was a striking contrast to the hectic 1960s and 1970s. Tn fact there would be no lunar or planetary launches by the IJS during the eleven years between 1978 (Pioneer Venus) and 1989 (Galileo). Continuing their assault on Venus using the successful Venera spacecraft, the Soviets had the field to themselves. At the next Venus opportunity in 1981 they launched another pair of Venera flyby/’landcrs. Both were successful, and this time produced the first color images of the surface of the planet.

Launch date

1979

No missions

1980

No missions

1981

30 Oct Venera 13 flyby/landcr Success, first color images from surface

4 Nov Venera 14 flyby/lander Success

COLOR PICTURES FROM THE SURFACE OF VENUS: 1981

Campaign objectives:

Venera 11 and 12 had not completed the goals set for them. Whilst the experiments carried out during the descent produced a prodigious amount of information on the

W. T. Huntress and M. Y. Marov, Soviet Robots in the Solar System: Mission Technologies and Discoveries, Springer Praxis Hooks 1, DOl 10.1007/978-1-4419-7898-1 16,

© Springer Science+Business Media, LLC 2011

atmosphere, the surface science was mostly a failure. The Soviets skipped a launch opportunity in order to develop new heat-resistant technologies in order to fix these problems. In 1981 they were ready to try again with better devices and instruments, principally aiming to obtain color images from the surface and to analyze a sample obtained by a drill. The landing sites were chosen in collaboration with US scientists using maps based on the radar imaging experiment perfonned by the Pioneer orbiter in 1978. ~

As flyby spacecraft, Venera 13 and 14 were essentially identical to their immediate predecessors. The major changes for 1981 concerned the lander. In particular, metal teeth were added to the periphery of the impact ring in an effort to reduce the spin and oscillation during the descent and prevent the rough landings experienced by the 1978 missions. The camera lens cover problem was fixed, and the soil sampler was redesigned to alleviate the problem that disabled it on Venera 11 and 12.

Payload

Flyby spacecraft

1. KONUS gamma-ray burst detector

2. SNEG gamma-ray burst detectors (France-USSR)

3. Magnetometer (Austria)

4. High energy particle cosmic ray detector

5. Solar wind detectors

The flyby spacecraft carried a reduced payload to facilitate an increased payload on ihc lander. Updated forms of the cosmic ray experiment and the two gamma-ray investigations were included, and an Austrian magnetometer on a 2 meter boom was attached to one of the solar panels.

Flyby payload mass: 92 kg Lander

Entry and descent

1. Accelerometers for atmospheric structure (110 down to 63 km) and then lander impact analysis

2. Temperature and pressure sensors

3. Gas chromatograph for atmospheric composition

4. Mass spectrometer for chemical and isotopic composition

5. Hydrometer for water vapor content

6. Nephclomcter for aerosol studies

7. X-ray fluorescence spectrometer for elemental composition of aerosols

8. Spectrophotometer for spectral and angular distribution of solar radiation

9. Ultraviolet photometer 320 to 390 nm

10. GROZA-2 radio for electrical activity and microphone for acoustic and seismic events

11. Doppler experiment for wind and turbulence Surface

1. Panoramic color imaging system with two cameras

2. Drill and surface sampler

3. X-ray fluorescence spectrometer for surface rock elemental composition

4. Rotating conical soil penetrometer (PrOP-V)

5. Chemical oxidation state indicator

Several of the instruments were improved from their Venera 11 and 12 versions, including the camera, drill, spectrophotometer, x-ray spectrometer for aerosols, mass spectrometer and gas chromatograph. The hydrometer humidity sensor and chemical oxidation state indicator were new; the latter being a simple chemical indicator to search for traces of oxygen in the atmosphere. The spectrophotometer measured the full spectrum from 470 to 1,200 nm using a wide-angle sky view and an array of six narrow-angle directional views. The gas chromatograph was equipped with a better detector, could sense more species, and was capable of operating in the cloud layer. l he mass spectrometer was improved to provide 2 to 40 times better mass resolution with 10 to 30 times greater sensitivity. The anomalous krypton reading of the 1978 missions was understood and corrected. The GROZA-2 instrument now; included a modified 10 kHz detector, a new7 detector in the 2 kHz band, and was better able to search for seismic events after touchdown.

The panoramic imaging system was fitted with an improved lens cover. The large increase in bandwidth for the transmission to the flyby relay spacecraft allowed each camera to have clear, red, green, and blue filters. Each camera was to cycle through its 180 degree panoramic image four times, one for each filter, taking almost an hour to complete. To ensure that a color section would be transmitted if the lander lasted only 30 minutes, one camera first scanned a full 180 degrees through the clear filter and then scanned each of three 60 degree sections in turn with red, green and blue filters.

It is a testament to the technology of the Venera landers that so many instruments were mounted outside and hence exposed to the pressure, temperature and corrosive atmosphere of Venus. These included the drill, penetrometer, mass spectrometer, gas chromatograph, hydrometer, aerosol x-ray spectrometer, oxidation state indicator, and the GROZA radio sensors and microphone. The cameras and nephelometer were mounted inside with special housings attached to the pressure vessel to enable them to observe out through windows and prisms. The platinum thermometer and aneroid pressure instrument used external sensors with wires fed through ihe pressure vessel.

The drill sampler was on the base of the lander. The machining of this device had to take account of thermal expansion at 500"C, and the process of drilling, sampling and analysis had to complete within the 30 minute guaranteed lifetime of the lander. A telescoping drill head was to bore into the surface for about 2 minutes, reaching as much as 3 cm into solid rock and coring a 2 cc sample. Information on the speed and

movement of the drilling rig. depth of drill penetration, and magnitude of the current drawn by the elec trie motor while drilling, provided information on the physical and mechanical properties of; the surface. After the few grams of material gained by the drill had been deposited on a tray, this would be moved pyrotechnically through a three-stage airlock to transfer it from the ambient 90 bar pressure to just 0.06 bar in the analysis chamber of the x-ray fluorescence spectrometer, which used plutonium, uranium-235 and iron-55 sources. The gas pumping for this transfer was enabled by a vacuum reservoir on the base of the lander.

The dynamic penetrometer was designed to determine the mechanical properties of the surface material, whether rock or soil. It consisted of a cone-shaped die that could pivot on the end of a lever and fall forward onto the ground. Л sighting device within the field of view of one of the cameras determined the depth of penetration. After penetration, a spring would cause the die to rotate in the soil and the angle of its turn would be displayed on the sighting device. A cable unit was also attached to one end of the die and an electronic unit within the lander could measure electrical resistance.

Lander payload mass: 100 kg

Mission description:

Landers

Venera 13 was launched on October 30, 1981, and made midcourse corrections on November 10 and February 21, 1982. It released its entry capsule on February 27 at a range of 33,000 km from the planet, and this entered the atmosphere on March 1. The accelerometer was turned on at about 100 km altitude and provided data on atmospheric density until parachute deployment. The parachute opened at 62 km and was jettisoned about 9 minutes later at an altitude of; 47 km. The descent instruments were activated just after the parachute opened, and the descent time from parachute opening to landing was just over an hour. The lander hit at 7.5 m/s. bounced once, and came to rest on a fiat, crumbly surface in an elevated hilly landscape at 7.55 :S 303.69 :E. It was 03:57:21 UT, 09:27 Venus solar time, and the solar zenith angle was 36 degrees. The surface transmission lasted 127 minutes.

Venera 14 was launched on November 4, 1981. and required three midcourse corrections to reach Venus. This was because the first one on November 14 w as not executed properly. After a compensating maneuver on November 23, the final trim maneuver was made on February 25. 1982. The entry system was released on March 3, and this entered the atmosphere on March 5. The parachute opened at 62 km and w as jettisoned at 47 km. The lander touched down at about 7.5 m/s on a low lying plain at 13.055 S 310.19’E, 950 km southwest of; its partner. It was 07:00:10 UT, 09:54 Venus solar time, and the solar zenith angle was 35.5 degrees. The surface transmission lasted 57 minutes.

Venera 13 and 14 experienced the same electrical anomaly as had Venera 11 and 12 at 12.5 km altitude. The science sequences worked very well on descent for both

landers and also on the surface. Immediately upon landing, the lens covers popped off and imaging began. A black-and-white contingency image was transmitted first, followed by the color panoramas. The drill experiment was also started immediately after landing and the entire process of drilling, sampling, and analysis took a little over 32 minutes. Venera 13 obtained a 2 cc sample and Venera 14 obtained a 1 cc sample, each from a depth of 3 cm. The Venera 13 penetrometer worked well, but by bad luck on Venera 14 this experiment deployed on top of an ejected lens cover. The microphones picked up aerodynamic noise during the descent, the sounds of the landing, and then the deployment of the lens covers, the drilling noise and sampler pyrotechnics, winds at the site, and other sounds of the lander at work.

Flyby carrier spacecraft:

The flyby carriers each passed Venus at an approximate closest point of approach at

36,0 km and entered heliocentric orbit where they continued to return data on the Sun, including flares. As tests to assist in planning late midcourse maneuvers for the Halley’s comet encounters by the Vega missions, Venera 13 fired its engine on June 10, 1982, and Venera 14 did so on November 14, 1982.

Results:

Venera 13 lander:

Descent measuremen ts:

The microphysical properties reported by the nepheiometers indicted, three distinct layers in the main cloud system: a dense top layer from 60 km (the altitude at which the measurements began) down to 57 km, then a transparent layer from 57 to 50 km, and finally the densest layer from 50 to 48 km. Doppler measurements gave a wind profile. Interestingly, the humidity sensors on both Venera 13 and 14 indicated ten times more water in the atmosphere than was determined spectroscopically in the 46 to 50 km range. The water mixing ratio was determined from several instruments and, despite some conflicting values, it seemed to be greatest in the cloud formation

region between 40 and 60 km with less water above and below the cloud layers. The amount of water vapor at 48 km was estimated at 0.2%. The mass spectrometer was not opened until below the cloud layers to preclude it being clogged by aerosols, and it provided altitude profiles of a number of atmospheric constituents between 26 km and the surface. These findings include a neon isotope ratio slightly higher than for Earth but less than for the Sun, a small krypton mixing ratio significantly less than that measured by the gas chromatograph and by Venera 11 and 12, and an argon-40 mixing ratio about four times lower than for Earth. The gas chromatograph detected some new species including molecular hydrogen, hydrogen sulfide, and carbonyl sulfide. Other species detected included molecular oxygen, water vapor, krypton, and sulfur hexafluoride.

The coronal discharge detectors of the GROZA-2 experiment established that no vehicle discharges were responsible for the very low frequency bursts interpreted as lightning by the Venera 11 and 12 experiments. No lightning or electrical discharges were detected.

Surface measurements:

Venera 13 obtained both black-and-white and the first color panoramic images from the surface of Venus. These show the lander ring base with triangular ‘crown’ points for lander stabilization during the descent, the ejected camera covers, the color test pattern strips, the deployed PrOP-V penetrometer, and the exhaust port of the aerosol x-ray fluorescence instrument on the lander ringjusl to the left of the penetrometer. The landing site appeared to be composed of bedrock outcrops surrounded by dark, fine-grained soil. The Venera 13 and 14 panoramas both showed llat, layered stones with a dark soil between them, and scattered small grains to compose a scene reminiscent of the floor of a terrestrial ocean. The photometers noted dust raised by

the landing, but it quickly settled and the resulting sedimentation was apparent by comparison of sequential images through different filters.

The Venera 13 site showed dark, flat rocks distributed over a darker crumbled soil surfaee with some low, rolling ridges in the background. The cameras returned four panoramas each, one in each filter: clear, red. green and blue; the latter three for the color image. However, precise color balancing was difficult to achieve in processing the filter data because the deployed calibration strips were affected by heat, pressure, and the orange sky. and because the radiometric response of the camera was not well known.

The drill sample analysis indicated a potassium-rich basalt of a type that is rare on Earth. The penetrometer showed the load-bearing capacity of the soil to be similar to heavy clays or compacted dust-like sand. These are both consistent with the surface characteristics derived from stress-strain profiles measured in the mechanics of the landing, which indicated a surface covered by a weak, porous material similar to the properties of weathered basalt. The electrical resistivity of the surface was surprising low. in the semi-conductor range, perhaps due to a thin film of conducting material on insulating soil particles.

The exposed-surface chemical test on both landers for the oxidation state of the Venusian atmosphere seemed to indicate a reducing carbon dioxide-rich atmo­sphere instead of an oxidizing one, but the experiment may have been compromised by the dust disturbed upon landing. Due to the short lifetime on the surface, the GROZA-2 acoustic experiment was designed to detect the micro seismic events that commonly occur at a rate of about one every few’ seconds on Earth. No events were detected by Venera 13, but tw7o such events may have been noted by Venera 14. The Venera 13 microphone recorded the aerodynamic noise of the descent, and on the surface this data gave w ind speeds of 0.3 to 0.6 m/s. Successive pictures through different filters show ed dust being blown off the lander ring. The temperature at the landing site was 465°C and the pressure was 89.5 bar. Only 2.4% of sunlight reached the surface. Some minor changes in illumination were observed, perhaps due to clouds, but the overall impression was of a dead calm, murky atmosphere over a flat volcanic plain.

Venera 14 lander:

Deseent measurements:

The Venera 14 lander conducted the same observations as Venera 13. both during its descent and w hile on the surface, obtaining very similar results. The combined mass spectrometer results were:

the isotopic ratios were:

13/12 carbon 40/36 argon 38/36 argon 20/22 neon

and the combined gas chromatograph results were:

water vapor molecular oxygen molecular hydrogen krypton

hydrogen sulfide carbonyl sulfide sulfur hexafluoride

The x-ray fluorescence instrument measured the composition of the aerosols from 63 to 47 km. It detected both sulfur (1.10 + 0.13 mg/m3) and chlorine (0.16 + 0.04 mg/mJ) and the chlorine abundance was considerably knver than the measurement by Venera 12. This more precisely calibrated instrument measured a sulfur/’chlorine abundance ratio compatible with sulfuric acid aerosols. The aerosols in the region between 6.3 and 47 km were composed principally of sulfur compounds with some chlorine compounds. The abundance ratio of sulfur and chlorine varied with altitude. The highest density aerosols were in the range 56 to 47 km. The x-ray fluorescence instrument of Venera 13 did not operate properly.

Surface measurements:

Unlike Venera 13, the Venera 14 photometers detected no dust raised on landing. It came down on a smooth level plain with flat, layered rocks which had very little soil

between them. The composition of the drill sample indicated a low-potassium basalt similar to that of terrestrial mid-ocean ridges. A lower sulfur content than Venera 13 may well indicate that the Venera 14 site is younger. The surface properties inferred from the dynamics of touchdown indicated a surface similar to the Venera 13 site, but possibly covered with a layer of weaker, porous material. No penetrometer data was obtained from Venera 14 because the instrument swung down onto a jettisoned lens cover. The audio sensor reported two sounds that could have been distant and small seismic events. The temperature at the site was 470=,C and the pressure was 93.5 bar. Hie amount of sunlight reaching the surface was 3.5%.

X-ray fluorescence soil analysis results were:

The surface composition measurements from Venera 8, 9, 10, 13 and 14 at sites around the planet were all consistent with basalts of compositions similar to those on Earth. The great variety of igneous and metamorphic rocks widespread on Earth was not evident, most likely owing to the lack of water on Venus.

Venera 13 and 14 flyby spacecraft:

Both ilybv spacecraft collected data on the solar wind and solar x-ray Hares. They participated in an interplanetary network to triangulate on gamma-ray bursts, in this case detecting about 150 events. Later in the decade, the Vega spacecraft were to use a flyby of Venus to set up an encounter with Halley’s comet, so after leaving Venus behind Venera 13 and 14 fired their engines to rehearse the maneuvers that would be required by those later missions.

Whereas in the US the National Academy of Sciences is an advisory body to the government, the Soviet Academy of Sciences had governmental and implementation roles. It was integral to the Party, and made decisions on the worthiness of proposed space projects, approving those to be undertaken. However, the Ministry of Machine Building allocated the funding for these projects. The President of the Academy, Mstislav Keldysh, was a powerful and highly influential figure in the Soviet space program during his tenure. Before he became President of the *Acadcmy in 1961, he was head of the Institute of Applied Mathematics (TPM) and kept this position until his death in 1978, when IPM was named the Keldysh Institute. It played a major role in space navigation and mission design.

Also unlike in the US, where university laboratories and NASA’s various field centers prepared scientific experiments for planetary missions, in the USSR the research institutes of the Academy of Sciences filled this role. These institutes were established by the Academy, but were funded through MOM. In the early years, the leading player was the Vernadsky Institute, more formally known as the Institute of Geochemistry and Analytical Chemistry. In 1965, at about the same time as Korolev transferred the robotic program to NPO-Lavochkin, the Soviet Academy of Sciences under Keldysh’s initiative established the Institute for Space Research (IKI; Institut Kosmicheskikh Issledovanii), which gradually built up its role in scientific missions, including providing flight instruments, and by the 1970s was a fierce competitor to Vernadsky. With Roald Sagdeev’s appointment as Director in 1973, IKI assumed scientific leadership of deep space missions. After Sagdcev quit in 1988. Vernadsky shared leadership under Valery Barsukov until the latter died in 1992. Today IKI is the leading space science institution. The institutes develop flight instruments and NPO-Lavochkin is responsible for the spacecraft and operations.

After the failures of the 1M and 1VA missions, a new multi-mission spacecraft was designed 1’or missions to Mars and Venus. The 2MV modular spacecraft had a mass of approximately 1,000 kg. The core of the spacecraft was a cylindrical pressurized ‘orbital’ module that had the propulsion module attached at one end and the payload at the other end. The payload could consist of either an entry probe or a pressurized module with instruments for flyby observations. Solar panels, antennas, thermal control devices, navigational sensors and several science instruments were attached to the side of the main module. The communications, attitude control and thermal control systems for the 2MV were greatly improved over the 1M and 1VA, and the same propulsion system was provided for midcourse trajectory corrections.

Four variants were designed. The 2MV-1 and 2MV-2 were Venus models, and the 2MV-3 and 2MV-4 were Mars models. The -1 and -3 versions were equipped with appropriate entry vehicles, and the -2 and -4 carried instruments for a flyby mission. Six spacecraft were launched, three to Venus (two probes and one flyby) in August and September 1962, and three to Mars (two flybys and one probe) in October and November 1962, Unfortunately all but one was lost to launch vehicle failures. The Mars 1 spacecraft launched on November 1, 1962, flew for almost 5 months before communications were lost on March 21, 1963, at what was then regarded as the vast range of 106 million kilometers from Earth. In view7 of this engineering success, the 2MV general design set a long-term precedent for Russian planetary spacecraft, particularly for Venus where this type of spacecraft was used until 1975.

Campaign objectives:

After having focused for several years on Mars and Venus, the Moon reasserted itself as a priority in concert with the progress of the manned space flight program. The 1959 Soviet plan to send cosmonauts on circumlunar flights had also envisaged robotic orbiters and landers. An early proposal for a Yc-5 lunar orbiter to respond to the first American attempts at small lunar orbiters was canceled along wdth its three-stage 8K73 launcher in favor of launching Ye-6 landers and Ye-7 orbiters using the four-stage 8K78 ‘Molniya* developed for planetary missions. These new spacecraft were also to exploit the design and flight experience of the second generation Mars and Venus spacecraft launched in 1962. The 2MV was a modular spacecraft with a common flight module and a mission-specific flyby or entry probe payload module. Unlike the earlier Luna spacecraft, which were launched directly towards the Moon, the Ye-6 series and all subsequent lunar missions were placed in Earth orbit for later injection onto a lunar trajectory by the restart able fourth stage.

The early Ye-6 series, built at OKB-1, was designed to accomplish the first lunar soft landing. Unfortunately, it suffered eleven straight failures between January 1963 and December 1965. Four spacecraft were lost to booster failures, two were stranded in Earth orbit by fourth-stage failures, two failed in transit and missed the Moon, and three failed at the target by crashing.

The years 1962-65 were dismal for Soviet robotic lunar and planetary exploration. The early sueecsses of Luna 1, 2, and 3. and the encouraging but ultimately fruitless flights of Venera 1 and Mars 1. had built expectations for more success. But by the end of 1962 the Molniya launcher had failed in all but one of ten launches and the truncated flight of Mars 1 had revealed the shortcomings of the 2MV series. These problems were addressed with the 3MV series, essentially the same spacecraft with advanced engines and avionics, and these advances were incorporated into the first Ye-6 series. Nevertheless by the end of 1965 three 2MV Mars missions, three 2MV Venus missions, two test and one 3MV Mars missions, one test and five 3MV Venus missions, and eleven Ye-6 lunar missions – a total of twenty-six missions had been lost without a single success at the assigned targets. Ironically, in the midst of this awful record, one of the test 3MV Mars spacecraft did achieve a measure of success at the Moon, when Zond 3 provided far-side photography of better quality than that from Luna 3. It was the only lunar accomplishment in this period. Such a long string of failures could well have shut down an American program, so vulnerable to public criticism, but in the Soviet Union it led to the determination to succeed, although not without a great deal of internal criticism by the government and outright threats of punishment.

Spacecraft:

The Ye-6 spacecraft consisted of three sections totaling 2.7 meters in height. The first section consisted of the Isayev mideourse correction and descent engine, which produced a thrust of 4.64 tons using hypergolic nitric acid/amine propellants. Four smaller 245 N thrusters mounted on outriggers were used for attitude control during the descent. The main pressurized cylindrical compartment containing avionics and communication equipment was mounted above the engine. Л pair of cruise modules were attached to the central cylinder. One held both attitude control thrusters for the translunar flight and a radar altimeter to trigger the landing sequence, and the other contained avionics sensors for attitude reference and control during the cruise. Both were discarded after the altimeter triggered the landing sequence. The lander capsule was strapped to the top of this stack. Unlike their planetary cousins, these spacecraft carried no solar panels because the flight time for the carrier module and the time on the surface for the lander were sufficiently short that the batteries would not require a recharge.

A new autonomous control system, the 1-100. was made for the Ye-6 which not only controlled the spacecraft but also the attitude and firings of both the third and fourth stages of the launcher. This approach deviated from usual practice but saved a great deal of w eight by eliminating the third and fourth stage controllers with their associated cabling and connectors. However, this had never been tried before, and w ould be the cause of further problems for a launcher that had already failed in nine out of ten attempts.

The lander capsule comprised a 105 kg hermetically sealed 58 cm sphere encased in tw’o hemispherical airbags sewn together. It carried communications equipment, a program timer, heat control systems, batteries, and scientific instruments including a television system. Once the lander was on the surface, it would deploy four petals to

expose its upper hemisphere and raise four 75 an antennas. The batteries were to supply power for a total of 5 hours over a period of 4 days, with its activities being driven either by timer or by command from Earth. The mass distribution was biased towards the bottom to assist the lander in turning upright on the surface when the petals were opened. The ideas of using air bags for impact and articulating petals to ensure a final upright stance on the surface were both quite clever, but not patented, and so the Americans adapted them for the pyramidal lander of the Mars Pathfinder mission in 1996.

After a direct approach to the target site on the Moon, the landing sequence was initiated at an altitude of 8,300 km. The attitude thrusters stabilized any roll that the spacecraft might possess and aligned the vehicle to the lunar vertical. At about 70 to 75 km altitude the radar altimeter was triggered, sending a signal to jettison the two cruise modules, inflate the airbags to 1 bar and ignite the main engine. At this time its speed relative to the Moon was about 2.630 m/s. The engine was to be shut off at an altitude of 250 to 265 meters and the four outriggers ignited for terminal descent. When a 5 meter long boom made first contact with the surface, the capsule would be ejected vertically to reduce its velocity to 15 m/s. The impact would be absorbed by the airbags. Four minutes after landing, the airbag cover would be severed along the joining seam and discarded. One minute later the lander would right itself by opening the four spring-loaded petals that formed its upper hemisphere, then raise its antennas.

The sites that could be reached by this type of mission were severely constrained, because the final approach of the translunar trajectory had to be perpendicular to the surface to direct the entire thrust of the retro-rocket straight downward. The control system of the vehicle was incapable of dealing with lateral velocity components. In practice, this limited the targets to western longitudes at latitudes that varied with the time of the year.

Lander payload:

1. Panoramic camera

2. Radiation detector

The camera weighed 3.6 kg and drew 15 W. It was a single photometer directed at the zenith inside a pressurized glass cylinder and used a nodding and rotating mirror to scan the scene both horizontally and vertically. It could expose a full 360 degree panorama in an hour with a resolution of 5.5 mm at a distance of 1.5 meters. Three small dihedral mirrors on deployable poles facilitated 3-dimensional view s of small strips of the surface. Calibration targets were dangled from the four whip antennas.

which also provided a measurement of the lander’s tilt on the surface. The radiation detector was a miniature gas discharge Geiger counter.

Mission description:

Six of the first eleven Ye-6 spacecraft were lost to launch vehicle failures, and none of those that flew to the Moon achieved a soft landing.

The first spacecraft to launch, Ye-6 No.2, was stranded in Earth orbit on January 4, 1963, when the failure of the PT-500 transformer in the power supply of the new I-100 controller prevented the fourth stage from reigniting. This was the sixth failure for the fourth stage out of eight attempts to use it. The object was designated Sputnik 25 by the Americans but was not acknowledged by the Soviets, and it re-entered the following day. The second attempt with Ye-6 No.3 on February 3. 1963, failed even to reach orbit because the 1-100 provided an improper pitch angle to the trajectory control system after the separation of the core stage. The third stage did not fire and the remaining stack fell into the Pacific near Hawaii – although this was commented upon by the American press no explanation was forthcoming from the USSR.

With the I-100 control unit fixed, Ye-6 No.4 was successfully sent towards the Moon on April 2, 1963, as Luna 4. The Soviet press announced the launch, saying that scientists were w’orking on the task of landing on the Moon, and pontificated on the possibility of human flights. But the mood soon changed. By the next day it was clear that the navigation system had malfunctioned and that it would not be possible to make the planned mideourse correction. Luna 4 missed the Moon by 8.336 km at 13:25 UT on April 5, and a miffed Soviet press claimed that a flyby was all that had been intended. The spacecraft ceased to transmit on April 6. The Soviet Academy of Sciences undertook a review7 of the program, but could not determine precisely why Luna 4’s navigation system had failed. However, some issues were identified, and it W’-as apparent that the rushed program was suffering quality control problems. It was decided to add a backup radio direction finding system, but this took time and it was a year before the next launch.

Unfortunately Ye-6 No.6 failed to reach orbit on March 21, 1964, when the third stage had an oxygen valve problem, failed to deliver full thrust, and cut off early. An upper stage failure also caused the loss of Ye-6 No.5 on April 20, 1964. when the command to fire the fourth stage failed. Suspicion fell on either the PT-500 current converter or the 1-100 controller, and extensive new testing began on these devices. It took almost a year to complete testing and modifications. The sixth attempt with Ye – 6 No.9 on March 12. 1965, was lost w7hen the fourth stage did not ignite due to a failed transformer in the power system. Unlike the ease for the first Ye-6 launch, the spacecraft was acknowledged by the Soviets and designated Cosmos 60, but it was obviously a failed lunar mission. After so many problems, the entire guidance and control system for the upper stages was reworked using a new three-phase converter, and separate guidance systems installed on the third and fourth stages. This change did not even get a test when the seventh attempt on April 10, 1965. failed because a

failed oxidizer pressurization system prevented the third stage engine from igniting, and the spacecraft. Ye-6 No.8. never reached orbit.

But Ye-6 No.10 was successfully dispatched towards the Moon on May 9. 1965. and announced as Luna 5. During the mideourse maneuver attempt on May 10. the gyroscopes in the I-100 guidance system were not given sufficient time to warm up and the spacecraft began to spin around its longitudinal axis. Engineers brought the spacecraft back under control and attempted the maneuver a second time, but sent it an incorrect command. By the time this was diagnosed it was too late to perform the maneuver. With the spacecraft on course to hit the Moon, albeit obliquely, it was decided to attempt to initiate the terminal maneuvers to exercise the system, but the guidance failed again and the engine did not fire. On May 12, the spacecraft hit the Moon at 1.6 S 25"W instead of the planned site at 31’S 8°W. becoming the second Soviet spacecraft to do so. Moscow, without portraying the mission as a failure, said a lot of information had been obtained ‘for the further development of a system for a soft landing on the Moon’s surface’’.

Ye-6 No.7 was launched on June 8. 1965, and successfully sent toward the Moon as Luna 6. The mideourse correction on June 9 began well, but a command error prevented the engine from cutting off, and it fired until the fuel was exhausted. This deflected the trajectory to such an extent that the spacecraft missed the Moon by 160,935 km on June 11, 1965. However, the engineers successfully put it through all of its landing sequence events.

An attempt to launch Ye-6 No. l 1 was canceled on September 4. 1965. when the core stage avionics failed in pre-flight testing. The vehicle was returned to the barn for major repairs to its control system. A month later, on October 4, this same rocket successfully dispatched Luna 7. This time the mideourse maneuver was performed successfully, making this the first Ye-6 in ten launches to be given the opportunity actually to attempt a lunar landing. However, in making its approach it lost attitude control, which prevented the retro-rocket from firing, and it crashed in the Ocean of Storms at 22:08:24 UT on October 7, at 9.8 N 47.8 W, west of the crater Kepler. An optical sensor had been set at the wrong angle and had lost sight of Earth during the attitude control maneuver immediately prior to starting the retro-rocket. As Moscow reported in its first admission of a failure. "Certain operations were not performed in accordance with the program and require additional optimization.”

Leonid Brezhnev, who had ousted Khrushchev the previous year, called Korolev to Moscow7 to account for the long string of failures. Korolev’s political charm stood him in good stead as he explained the difficulties and promised success with the next mission, due to launch in December. Although he did not deliver on this promise, he never had to face the new7 leadership again because he died during colon surgery on January 14. 1966. After the Moscow summons. Boris Chertok. a deputy at OKB-1. investigated the reliability and testing of spacecraft subsystems, and identified a lack of integrated testing of some subsystems during spacecraft assembly as a particular problem. Although corrective action was taken for the next launch, this was not in itself sufficient.

On December 4. 1965. Yc-6 No. l2 was launched into a lower inclination parking

orbit than its predecessors, at 51.6 degrees instead of 65 degrees. This allowed for a mass increase beyond 1.500 kg. The fourth stage then sent the spacecraft towards to Moon as Luna 8. The midcourse maneuver went well the following day, but alas the second Ye-8 to be presented with an opportunity to make a lunar landing failed. Just prior to retro-rocket ignition, the two airbags were inflated, as planned, but one was pierced by an improperly manufactured mounting bracket on a lander petal and the thrust of the escaping gas caused the spacecraft to spin. As a result, the retro-rocket cut off after just 9 of the required 42 seconds. The spacecraft crashed in the Ocean of Storms at 21:51:30 UT on December 6, at 9.ГК 63.3 W. to the west of the crater Kepler. The bracket problem was fixed, and on future missions the airbags would be inflated only after the retro-rocket had completed its burn.

Luna 8 was the eleventh straight failure in the Ye-8 program and the last before NPO-Lavochkin took over management of the Soviet lunar and planetary programs.

Results:

None.

The next sample return attempt with spacecraft Yc-8-5M No.412, the tenth in the scries, was lost when the Block D failed during its first burn and was unable to reach parking orbit. The final attempt, with No.413, was successful. Luna 24 was launched on August 9, 1976, made a midcourse correction on the 11 th, and entered a circular lunar orbit at 115 Icm with an inclination of 120 degrees on August 14. It adjusted its orbit to 120 x 12 km on the 17th and at 02:00:00 UT on the 18th it landed in darkness at 12.75°N 62.20°E in the Sea of Crises, only about 2,400 meters from the Luna 23 lander and near the Luna 15 target. The focus of the Ye-8-5M series was to obtain a deep core from the surface of the lunar mascon in Mare Crisium. The drill was able to reach the planned depth of 2.25 meters at a slightly inclined angle that equated to a vertical penetration of 2 meters. The sample was transferred to the return capsule and then at 05:25 LIT on the 19th the ascent stage lifted off. The capsule landed 200 km southeast of Surgut in Siberia at 17:53 UT on August 22. It proved to contain a sample of 170.1 grams.

End of the Moon, but the beginning for a propulsion stage

Luna 24 was the last of the Luna series and the final Soviet lunar mission. A third rover was built and another sample return spacecraft tvas prepared, but in 1977 the

Figure 11.30 Luna 16 recovery and soil sample (below). The balloons were inflated post­landing to right the capsule for antenna exposure.

launcher for the rover was requisitioned for a communications satellite and attention swung towards the ill-fated 5M Mars sample return project. Later all lunar and Mars plans were canceled in favor of continuing the successful Venus missions.

However, the reliable Ye-S cruise stage was modified to produce the autonomous propulsion stage for the 1988 Plrobos spacecraft, and went on to become the Fregat upper stage that is currently used by Proton-K and Soyuz launchers.

Results:

The altimeter on Luna 15 returned data during the descent until loss of signal, and this provided useful in forma lion on the mean density of the lunar soil. The sample that Luna 16 got from the Sea of Fertility was a dark, powdery mare basalt similar to that obtained by Apollo 12 in the Ocean of Storms. In 1971 three grams of Luna 16 soil were exchanged with NASA for three grams of Apollo 11 samples and three grams of Apollo 12 samples. The Vernadsky Institute of Geochemistry in Moscow* conducted analyses of the soils returned from these missions. Some samples were donated to other countries including France. Austria and Czechoslovakia. Although small, the Luna 20 soil from the highlands differed significantly from the Luna 16 mare sample. It was clearly lighter in color, with larger panicles. More than half of the rock particles were ancient anorthosite compared to less than 2% in the Luna 16 sample. Tw o grams were exchanged for one gram of highlands material obtained by Apollo 15, and US scientists were able to date the Luna 20 sample at 3 billion years. The 2 meter core from Luna 24 exhibited layering that clearly indicated successive deposition. Small portions of this core were exchanged with US scientists.

TIMELINE: 1982-1983

The final missions in the Soviet Venera series were launched in June 1983. Having achieved most of their objectives with the Venera landers, these two spacecraft were outfitted with large radar antennas replacing the entry system and sent to Venus as orbital radar mappers. Both were successful, with their radars discerning the surface through the ubiquitous clouds to map from 30"N to the north pole with a resolution of about 2 km.

Launch date

1982

No missions

1983

2 Jun Venera 15 orbiter Successful radar mapper

7 Jun Venera 16 orbiter Successful radar mapper

PIERCING TIIE CLOUDY VEIL OF VENUS: 1983

Campaign objectives:

After six consecutive successes of their heavy Venus landers starting with Venera 9, the Soviets decided to send radar imaging orbiters in the 1983 opportunity instead of more landers. In 1978 the US Pioneer 12 orbiter had obtained radio altimetry data of the entire planet at the very low resolution of 150 km. and operated the altimeter in a side-looking mode to obtain a narrow equatorial strip of topography at a resolution

W. T. Huntress and M. Y. Marov, Soviet Robots in the Solar System: Mission Technologies and Discoveries, Springer Praxis Hooks 1, DOl 10.1007/978-1-4419-7898-1 17,

© Springer Science+Business Media, LLC 2011 of 30 km. This data was used to target the Venera 13 and 14 landers in 1981. The 1983 Venera radar or hi tors were intended to use hi sialic radar techniques ю improve the resolution to 2 km or better, albeit only over about 25% of the planet.

Venus had become more or less a ”Red ‘ planet, left almost exclusively to Soviet exploration. After the Mariner 5 flyby in 1967 it was over a decade before the US revisited the planet, and the two small Pioneers in 1978 were primarily focused on the ionosphere and atmosphere. But at that same time the US was also developing a proposal for a Venus Orbiting Imaging Radar (VOIR) mission. NPO-Lavochkin had been working on a Venus radar mapper since 1976 and, after having pioneered local surface imaging, the Soviets wanted to conduct their radar mapping mission before the Americans. As events transpired, they did not have to compete, since VOIR was canceled in 1981 and replaced by a simpler, less costly mission named Magellan that was noi launched until 1989. In essence all that NPO-Lavochkin had to do was to replace the entry system of its spacecraft with a side-looking radar to obtain imagery and electrical properties of the surface of the planet, and to add a radio altimeter to measure the topography on the ground track. But modifying the spacecraft to carry the radar was not without challenge.

Rumors of a Soviet Venus radar mapping mission began to circulate in the US in 1979, as NASA was trying to obtain funding for its VOIR mission. Familiar with the heavy nuclear-powered RORSAT orbiting radars the Soviets used to track Western navies, most observers in the IJS did not believe they had the technology to build a lightweight low-power synthetic aperture radar. It was indeed a struggle, particularly the data storage and computing requirements, and the launch had to be slipped from 1981 to 1983, but ultimately it performed rather well.

Spacecraft:

Venera 15 and 16 were the first in this series of carrier vehicles to be modified in a significant way since Venera 9. The bus was lengthened by 1 meter to accommodate the 1,300 kg of propellant needed to put such a heavy craft into orbit around Venus. The load of nitrogen for the attitude control system was increased from 36 to 114 kg to permit the large number of attitude changes that the orbital mission would entail. Two more solar panels were added outboard of the standard pair to provide the extra power to operate the radar system. The parabolic antenna was enlarged by 1 meter to a diameter of 2.6 meters to increase the bandwidth from 6 to 108 kbits/s and a new 5 cm band telemetry system was introduced to communicate with the 64 and 70 meter ground stations. The spacecraft were identical, and consisted of a cylinder 5 meters long and 1.1 meters in diameter. A 1.4 x 6.0 meter parabolic panel antenna for the synthetic aperture radar (SAR) was installed at the top, in place of the entry system. The entire SAR system weighed 300 kg. A 1 meter diameter parabolic dish antenna was mounted nearby for the radio altimeter. The electrical axis ol’the radio altimeter antenna was aligned with the long axis of the spacecraft, and the SAR was angled 10 degrees off this axis. During imaging, the radio altimeter would be lined up with the local vertical and the SAR would look off’ to the side by 10 degrees.

Launch mass: 5,250 kg (Venera 15) 5,300 kg (Venera 16)

Fuel mass: 2,443 kg (Venera 15) 2,520 kg (Venera 16)

Payload:

1. Polyus-V synthetic aperture radar (SAR) operating at a wavelength of 8 an

2. Omega radiometric altimeter

3. Thermal infrared (6 to 35 microns) Fourier emission spectrometer (IFSE, DDR-USSR)

4. Cosmic ray detectors (6)

5. Solar plasma detectors

6. Magnetometer (Austria)

7. Radio occultation experiment

All of the components of the SAR and radio altimeter were shared except for the antennas. The electronics cycled the 80 W traveling wave tube oscillator between the antennas every 0.3 seconds. An onboard computer controlled their sequencing and operation. The SAR antenna would illuminate the surface over 3.9 milliseconds with 20 cycles of 127 phase shifts for cross-track encoding. Spacecraft motion over that same interval swept out a 70 meter virtual antenna. After each transmission, the antenna was switched to the receiver, which digitized the magnitude and phase of the reflected radar pulses and stored the data as 2,540 complex numbers in a solid-state memory buffer. To keep up with the radar illumination cycle of 0.3 seconds, the data were read out alternately onto two tape recorders to complete a period of 16 minutes

ol mapping during a periapsis pass. Each such pass produced about 3,200 return images to compose a data strip approximately 120 x 7,500 km. Once the data were received on Earth, each individual 3.9 millisecond return was divided by time delay mto 127 ranges across-track and 31 ranges along-track and then processed to correct for atmospheric, geometric, and orbital effects. The individual return images for a pass were then assembled to yield, an image strip representing the slope, roughness, and emissivity of the surface of Venus.

During altimetry, the antenna would transmit a code sequence of 31 pulses, each of 1.54 microseconds duration. After transmission, the antenna was switched to the receiver, which recorded the reflection of the pulses from the surface over a period of 0.67 millisecond. The oval footprint of the altimeter radio beam was 40 km cross-track and 70 km along-track. After onboard processing of the return waveform, the data were stored on the tape recorder for later transmission to Earth, which further processed the data to correct for atmospheric, geometric, and orbital effects to yield altitudes. A low resolution mode was used until the orbital elements were precisely determined, and then it was switched to a high resolution mode. In combination with Doppler analysis, the high resolution mode reduced the footprint to 10 x 40 km with an error of about 1 km. The vertical accuracy was about 50 meters.

It was also decided to include an infrared Fourier-transform spectrometer supplied by East Germany. This weighed 35 kg and was intended to provide a higher spectral resolution than the infrared radiometer operated by the Pioneer 12 orbiter. ft divided the spectrum into a continuous set of 256 channels over the range 6 to 35 microns. It had a field of view of 100 x 100 km, and provided 60 complete spectra along each periapsis pass. The objectives were to obtain atmospheric temperature profiles from the 15 micron carbon dioxide band in the 90 to 65 km altitude range, the temperature of the upper cloud deck, the abundances of aerosols, sulfur dioxide and water vapor in the atmosphere, and data on the thermal structure and dynamics of the clouds and atmosphere.

The cosmic ray and solar wind experiments were similar to those flown on every Venus mission since Venera 1.

Mission description:

Venera 15 was launched on June 2. 1983, and conducted midcourse corrections on June 10 and October 1 before entering orbit around Venus on October 10. Venera 16 was launched on June 7, conducted midcourse corrections on June 15 and October 5. and entered orbit on October 14. Their orbital planes were inclined about 4 degrees relative to one another, so that any area that was missed by one spacecraft should be able to be imaged by the other. Venera 15 made an orbital trim on October 17, and Venera 16 did so on October 22. Each operating orbit was inclined at 87.5 degrees to the equator, with the periapsis at 1,000 km and the apoapsis at — 65,000 km and a period of 24 hours. The periapsis was positioned at about at 62 N and each periapsis passage would image the surface on a 70-degree arc. Both spacecraft began science operations on November 11. Small burns w’ere made from time to time to preserve the periapsis. accommodate high gain antenna position changes as the Sun-vehicle – Earth angle decreased, and maintain the 3 hour interval between the periapses of the two spacecraft.

Mapping and altimetry would typically begin at 80"N on the inbound side of the pole and continue over the pole down to 30 N on the retreating side. Radar imaging w as conducted continuously w ith a best resolution of about 1 km. The data collected on each 16 minute periapsis pass was stored on the tape recorders, then replayed to Earth during a daily 100 minute communications window prior to the next periapsis. During each 24 hour interval Venus would rotate on its axis by 1.48 degrees, and so successive mapping passes partially overlapped one another. At that rate. 8 months was required to cover all longitudes. The 24 hour orbit was necessary to enable the spacecraft downloads to be synchronized with the receiving stations in the USSR. Several orbital corrections w ere made during the mission to maintain the period and shape of each orbit. In June 1984. Venus went through superior conjunction and no transmissions were possible while it passed behind the Sun as seen from Earth. This provided an opportunity to conduct radio occultation experiments to study the solar and interplanetary plasma. After conjunction. Venera 16 rotated its orbit backwards 20 degrees relative to its partner to map areas missed prior to superior conjunction, and mapping was concluded shortly thereafter, on July 10.

Between them, the two spacecraft were able to image all of the planet from 30: N to the north pole, or about 25% overall. The resolution of 1 to 2 km w;as similar to w hat could be achieved by the 300 meter Arccibo radio telescope dish operating as a radar, but it w? as limited to equatorial latitudes and could not get the accompanying altimetry.

Venera 15 reportedly exhausted its supply of attitude control gas in March 1985. but Venera 16 continued to transmit data from its other instruments until May 28 of that year. No attempts w ere made to change orbits for higher resolution or increased coverage.

Results:

Together, the two spacecraft imaged from 30°N to the north pole at a resolution of 1 to 2 km. The primary product consisted of 27 radar mosaics at a scale of 1:5,000,000 of the northern 25% of the planet. The results confirmed that the highest elevations, meaning those which stand more than 4 km above the plains, have greatly enhanced radar reflectivity.

The radar experiments produced major discoveries about the surface of the planet, imaging new types of terrain that included:

Coronae large circular or oval features with deep concentric rings

Domes flat, nearly circular raised features some with central calderas

Arachnoids – collapsed domes with radial cracks

Tessera – large regions of linear ridges and valleys

Prior to Venera 15 and 16, the coronae glimpsed by Arecibo had been thought to be impact features filled with lava. About 30 coronae and 80 arachnoids were in the area mapped. As no evidence of plate lectonics was evident, the coronae, domes and arachnoids were all postulated lo be surface expressions of mantle plumes heating an immobile crust. There wjere no direct terrestrial analogs. The tessera appeared to be the oldest crustal regions on the planet, and were often overlapped by lava flows.

Even if large ohjects that penetrate the thick atmosphere are destroyed before they can reach the ground, they can create a shock wave that leaves an impression on the surface. There were about 150 craters in the area surveyed. Analysis of the cratering data led to a very young age of 750 + 250 million years, consistent with the idea of catastrophic resurfacing making the tessera, and large scale ‘blistering’ over mantle plumes between resurfacing events.

The altimeter produced extensive data on topography in the northern hemisphere. In combination with the radar data, scientists w’ere able to produce detailed maps of the surface.

The infrared spectrometer on Venera 16 malfunctioned, but the one on Venera 15 worked in orbit for 2 months before it too failed. The spectra clearly resolved carbon dioxide, water vapor, sulfur dioxide, and sulfuric acid aerosol. This data was strong confirmation that the particles in the upper cloud layer were a 75 to 85% solution of sulfuric acid. The aerosol distribution and mixing ratios for sulfur dioxide and water vapor were determined in the altitude range 105 to 60 km. The thermal structure and optical properties of the atmosphere were also determined in this altitude range. The clouds ranged from 70 to 47 km, but in the polar region the clouds were 5 to 8 km lower and the air above 60 km was warmer than in equatorial regions. The average surface temperature was measured at 500°C. but some warmer spots were detected along with some cooler regions. There were no features in Ihe spectrum to suggest the presence of organic compounds.

The two orbiters produced 176 radio occultation profiles between October 1983 and September 1984.