Venera 9 and Venera 10

In 1972 Venera 8 had shown that a lander could survive on the surface of Venus for about an hour, and Soviet planners decided the next step needed a new machine. For the first time since launches to Venus began in 1961, the Soviet Union let the October 1973 window pass while NPO Lavochkin built it, according to the Russian edition of Marov and Huntress's history of Soviet probes. The result, which the bureau calls series 4V, borrowed the heavy bus that had carried Mars 2 to Mars 7 and rode the four-stage Proton-K. Each station weighed about five times as much as the 3MV probes before it. Plans at first used the carrier as a flyby relay; NPO Lavochkin and the Space Research Institute (IKI) pushed instead for an orbiter, and won, which is how Venus got its first artificial satellites.

At the heart of the orbiter was a cylinder of propellant tanks, 110 cm across, holding UDMH and nitrogen tetroxide for a restartable KTDU-425A engine underneath. A pressurised ring 2.35 m across circled the base and held the control systems and science instruments. Two solar panels spanned 6.7 m, a 1.6 m dish talked to Earth, and helical antennas on the panels listened for the lander. Venera 9 set off weighing 4,936 kg and Venera 10 5,033 kg, of which 1,093 kg and 1,159 kg were propellant; Marov and Huntress explain the difference by a longer orbit-insertion burn planned for Venera 10. NPO Lavochkin says two near copies flew to raise the odds of success and to study the surface at two sites.

Inside a 2.4 m entry sphere, which with its contents weighed 1,560 kg, rode a 660 kg machine 2 m tall: an 80 cm titanium pressure sphere wrapped in 12 cm of honeycomb insulation and a thin outer skin, a hollow crush ring underneath to take the impact, and above it a 2.1 m disc brake topped by a cylinder that held the parachutes, the cloud instruments and a helical antenna. Before separation the orbiter blew cold gas through two pipes to chill the lander to minus 10 °C, and a store of lithium nitrate trihydrate soaked up heat as it melted, at about 30 °C according to Mitchell and 33 °C according to Marov and Huntress. The payload comprised a gamma-ray spectrometer and densitometer for the ground, photometers and nephelometers for the clouds, a mass spectrometer, thermometers, barometers, accelerometers, a cup anemometer on top of the disc, and two cameras.

A. S. Selivanov's team, with Yu. M. Gektin, built the cameras, and Mitchell compares them with the same team's Luna 9 camera: a scanning mirror fed the view to a photometer one line at a time, a principle NPO Lavochkin likens to mechanical television. Each camera looked out through a cylindrical quartz window 1 cm thick from about 90 cm above the ground, tilted down so that its strip ran from the landing ring out to the horizon on both sides. A panorama held 115 useful pixels per line, each coded in 6 bits plus a parity bit, at 3.5 s per line, so one sweep took about 30 minutes over a 256 bit/s channel. The picture size, Mitchell writes, was set by the telemetry rate and an estimated minimum lifetime of 30 minutes, although Marov and Huntress say the thermal protection was meant to keep the lander working for about two hours. Because the Venera 8 light readings had been dim, each lander also carried floodlamps.

Getting pictures home forced an unusual flight plan. Photographs needed daylight, and the sunlit side of Venus that October was hidden from Earth, so a lander there had no direct radio path. The answer was to relay through the carrier. Two days before arrival each station released its sphere on a collision course, fired its engine to move onto a flyby path, and fired again at closest approach to brake into orbit, timed so that the new satellite rose into view of the landing zone just as the lander began to transmit. NPO Lavochkin says the relay raised the information capacity of the radio link by two orders of magnitude.

The Venera 9 sphere met the atmosphere at 10.7 km/s on 22 October, 20.5° below the horizon, and peaked at about 170 g. At about 65 km, by the 1976 yearbook's account, the lid of the parachute compartment blew off and a pilot chute and a second parachute pulled away the upper part of the shell; a drag chute then opened, the transmitter came on, and four seconds later the lower hemisphere fell away. At about 62 km, now at 50 m/s, the lander opened three main canopies with 180 m² between them and spent some 20 minutes drifting through the clouds while its photometers and nephelometers worked. Near 50 km it cut the parachutes loose. For the remaining 55 minutes it fell under the disc brake alone, which the thickening air turned into a landing at about 7 m/s. The fast fall through the hot lower air was deliberate: less time there meant a cooler lander.

Touchdown came at 8 h 13 min 07 s in the yearbook, which names no time zone; read as Moscow time, that is Siddiqi's 05:13:07 UT, when the landing signal reached Earth. The ground was a slope strewn with angular rocks. The 1976 Soviet encyclopedia yearbook put its steepness at about 30°; the Russian edition of Marov and Huntress gives a 15 to 20° slope with the lander itself tilted 10 to 15° by uneven ground; Mitchell gives 20°; and a 2018 analysis by S. P. Buslaev and colleagues at NPO Lavochkin, noting that the onboard inclinometer read a lander tilt of about 30°, puts the slope at 20 to 30°, well beyond the 10° slopes the Soviet landers were designed for. Pyrotechnic charges blew off the camera caps, but one cap stuck (Mitchell blames the outside pressure), so a single camera did all the work. It swept a 174° panorama, reversed, and covered 124° of a second pass before the orbiter drew out of range after 53 minutes. At that moment the inside of the lander was below 60 °C and its equipment still working, NPO Lavochkin says.

What the picture showed was a jumble of flat and sharp-edged stones a few tens of centimetres across with finer soil between them, the white rim of the landing ring along the bottom and the horizon in the corners. Light, in the yearbook's words, was about 10,000 lux, like midday at mid-latitudes under a complete overcast. NPO Lavochkin read the scatter of rocks as a young surface, 1 to 10 million years old, and so as evidence that Venus is geologically active. The floodlamps turned out to be unnecessary and were left off later landers. Venera 8 had measured its light near the terminator, while both 1975 landers came down in early afternoon: 13:12 and 13:42 local solar time, according to Marov and Huntress. Four years earlier the Mars 3 lander had sent 14.5 or 20 seconds of image signal from Mars, which Siddiqi describes as a grey background with no detail.

Above, the Venera 9 orbiter had fired 247.3 m/s on 20 October to leave the collision course and 922.7 m/s on 22 October to brake. NSSDCA gives the orbit as 1,500 by 111,700 km with a 48.3 hour period at 34.17°, trimmed within days to 1,547 by 112,144 km. A TASS communique quoted by NPO Lavochkin marked the moment: after 136 days of flight and more than 300 million km, Venera 9 had become the first artificial satellite of Venus in history, and its lander had returned a picture of the surface at 90 times Earth's pressure and 485 °C.

Venera 10 followed three days behind. Its sphere separated on 23 October, the orbiter swerved with 242.2 m/s, and on 25 October it braked by 976.5 m/s into a 1,500 by 114,000 km orbit of 49.38 hours at 29.5°, later adjusted to 1,651 by 113,923 km. The Venera 10 lander came down on much gentler ground, about 2,200 km from its twin by the Soviet figure. Its tilt was about 8° according to NSSDCA's gallery and to Marov and Huntress, and only a few degrees according to Buslaev and colleagues. Again one lens cap stuck. The working camera scanned 63° forward, 184° in reverse and 17° forward again, by Mitchell's count, and its panorama shows broad, flat slabs with darker, finer material between them, which the yearbook read as a plain or plateau. Contact lasted 65 minutes and again ended with the relay geometry; Siddiqi notes the lander had been designed for 30.

The arrival dates are settled: the Soviet prints of the two panoramas, processed by IPPI, the Academy's Institute for Information Transmission Problems, are captioned 22.10.1975 and 25.10.1975, and the 1976 yearbook, NPO Lavochkin, NSSDCA's catalogue and Siddiqi agree. The Venera 10 touchdown time is a different matter. NSSDCA's spacecraft catalogue and Marov and Huntress give entry at 01:02 UT and touchdown at 02:17 UT. Siddiqi pairs the same 01:02 entry with touchdown at 05:17:06 UT, which would imply a descent of more than four hours, and NSSDCA's own image catalogue also says 05:17 UT. The 1976 yearbook gives entry at 7 h 00 min and touchdown at 8 h 13 min 06 s, with no time zone; in Moscow time that is 04:00 and 05:13:06 UT. NPO Lavochkin says each descent took about 75 minutes, so the first and third pairs are each self-consistent, and they sit about three hours apart, the same offset as between the yearbook's Venera 9 time and the UT that NSSDCA and Siddiqi give for it. That hints at a time-zone conversion made twice along the chain; lacking the original TASS text, this page carries all three readings.

Surface measurements also exist in several versions. TASS gave 485 °C at the Venera 9 site in 1975, and NSSDCA repeats it. The 1976 yearbook and NPO Lavochkin's project page give 460 °C and 90 atm for both sites. The Russian edition of Marov and Huntress gives 455 ± 5 °C and 85 ± 3 bar at Venera 9 and 464 °C and 91 ± 3 bar at Venera 10. Wind from the cup anemometers was 0.4 to 0.7 m/s at Venera 9 and 0.8 to 1.3 m/s at Venera 10 in the yearbook; NSSDCA and Air & Cosmos print an unattributed 3.5 m/s. The gamma-ray spectrometers found potassium, thorium and uranium at levels the yearbook matched with basalt. The densitometer, a paint-roller-shaped probe with a caesium-137 source laid on the ground after landing, gave about 2.8 g/cm³. NPO Lavochkin adds that 5 to 10 percent of the Sun's energy reaches the ground, scattered by the clouds.

During each descent the nephelometers fired pulses of light into the passing air and measured how it scattered. The Russian edition of Marov and Huntress says these readings for the first time revealed the structure of the clouds of Venus: a main deck from about 65 km down to 49 km in three layers, 62 to 57, 57 to 52 and 52 to 49 km, holding three sizes of particle between about 0.5 and 6 micrometres. The measured refractive index, 1.46, fitted sulfuric acid better than water. Below 49 km a thinner haze reached down to about 25 km, with largely clear air beneath. Two instruments disappointed. The mass spectrometers misbehaved, which Marov and Huntress blame on an unsuitable cleaning procedure before launch and probable fouling of the inlets by cloud particles, and a high ratio of argon-36 to argon-40 that they recorded went unpublished at the time. The near-infrared water-vapour photometer gave figures that later spectroscopy showed to be wrong, though the 1976 yearbook had reported them.

With the landers silent, the orbiters turned to the planet. Venera 9's line-scanning cameras, one violet and one ultraviolet, returned 17 cloud surveys between 26 October and 25 December 1975, Mitchell reports. Siddiqi says no pictures from the Venera 10 orbiter were ever released and that it is unclear whether it carried a camera; NSSDCA says some reports indicated one, and Marov and Huntress list separate camera passbands for each orbiter. Radiometers found cloud-top brightness temperatures of 233 to 235 K on the day side and about 244 K at night. A nightglow spectrometer recorded a glow unlike Earth's night sky, later identified as molecular oxygen bands, and on Venera 9 it also saw flashes that NPO Lavochkin still presents as lightning 25 times more energetic than Earth's; Mitchell writes that they are believed to be lightning, while Marov and Huntress note that Venera 10 did not confirm them, so the question stays open. Radio signals grazing the planet in 50 occultation sessions (NPO Lavochkin; Mitchell counts 19) showed a night-side ionosphere changing shape from day to day, and a bistatic radar experiment bounced 32 cm signals off 55 strips near the edge of the disc at about 10 km resolution. The magnetometers found no field of the planet's own, and the plasma instruments sampled both sides of the bow shock.

One orbiter instrument came from France. Jacques Blamont, his student Jean-Loup Bertaux and Vladimir Kurt built a photometer to measure sunlight scattered by the hydrogen around Venus in the Lyman-alpha line, and its readings gave a temperature of about 450 °C at the base of the exosphere, according to both Air & Cosmos and Marov and Huntress. Blamont, quoted by Air & Cosmos, said that the instrument worked perfectly on both satellites, but that his team learned nothing about where it sat, when it was switched on or where it pointed, and got measurements from five orbits in all. Accounts of the French share differ: NSSDCA credits a French 350 nm ultraviolet photometer, Siddiqi French-made ultraviolet cameras, and Marov and Huntress a French ultraviolet spectrometer plus French work on the photopolarimeters.

Built for three months at Venus, the orbiters lasted at least that long; how much longer depends on the source. NPO Lavochkin says Venera 9 existed until 27 April 1976, after a Soviet statement of 22 March 1976, cited by Siddiqi, that the main orbital task was complete. For Venera 10 Siddiqi has data until at least June 1976, and Air & Cosmos prints 15 September 1977 without naming its source. NSSDCA and Marov and Huntress say the transmitters failed after about three months, although the same Russian edition also credits the orbiters with more than a hundred further orbits, over 200 days at about 48 hours each. McDowell's GCAT catalogue still lists both in Venus orbit, but no source consulted reports a later observation, and JPL's Horizons lookup found no Venera craft on 5 November 2026. Mitchell's catalogue says the Venera 9 orbiter's digital image data and ephemeris have become available. Both orbiters are listed among what we left at Venus.

Both landers came down near Beta Regio, in NSSDCA's words. E. L. Akim and V. A. Stepanyants placed Venera 9 within 150 km of 31.01° N, 291.64° E and Venera 10 within 150 km of 15.42° N, 291.51° E, and in 2001 A. M. Abdrakhimov of the Vernadsky Institute mapped both circles on Magellan radar mosaics. In each, about 60 percent of the ground is wrinkle-ridged plains of mafic lava, which he judged the likeliest material under each lander, and the flat view at Venera 10 fits plains better than the tessera that fills about 15 percent of its circle. Mitchell reports that high-resolution radar suggests the Venera 9 slope is a wall of the rift valley Aikhulu Chasma. NSSDCA's rounder coordinates (31.7° N, 291° E and 16° N, 291° E) sit 93 and 80 km from these centres. Six sources checked give a separation of about 2,200 km (NSSDCA's gallery says 2,100), although the published centres are about 1,650 km apart by calculation. More in landing on Venus.

Copies of the first pictures from the surface came off a phototelegraph machine at the deep space communications centre in Yevpatoria, where Leonid Ksanfomaliti watched the Venera 9 strip emerge on 22 October 1975. The pictures were printed in First Panoramas of the Surface of Venus, a 1979 collection edited by M. V. Keldysh. Don P. Mitchell rebuilt the complete transmissions from surviving 6-bit digital data, some of it found on tapes exchanged between the Soviet Union and Brown University, and from photographs in that book. His three-stage Venera 9 panel, ending with gaps filled by an inpainting algorithm, carries his credit in Siddiqi's Beyond Earth and appears uncredited, with a Venera 10 counterpart, on NPO Lavochkin's anniversary page. Ted Stryk's enlargements for The Planetary Society head this page.

A single stone on the Venera 9 panorama has had a second career. Symmetric and about 40 cm across (30 cm in a 1978 description), it was called by geologists a strange stone with a rod-shaped protrusion and a knobbly surface. A 1978 book, Planets Rediscovered, quoted in Nauka i Zhizn, noted that the object had not moved in the eight minutes before the camera swept back over it and judged it most likely an oddly shaped stone, perhaps a volcanic bomb. In the same magazine in 2012 Ksanfomaliti, of the Space Research Institute, argued that it and objects on later panoramas may be signs of life, and quoted the camera designer Gektin as saying his team disliked that interpretation but could find no other explanation for what they saw. The 1978 book had also warned that the picture was too coarse for detail; see life on Venus.

Its design outlived the mission. Mitchell counts ten Venus missions flown on this bus between 1975 and 1984, from Venera 9 through Venera 11 and 12, Venera 13 and 14 and the radar mappers Venera 15 and 16 to the Vega pair. The pair's record card, signed by a Soviet sport federation commissioner, claimed an absolute world record for mass placed in Venus orbit and noted pennants bearing Lenin's bas-relief on the orbiters and state emblems on the landers.