Venus missions

After the flights of Venera-3 and 3MV-4 No.6, a new Venus probe was launched by the Soviet Union, called Venera-4, which had to transmit data about the planet’s atmosphere and surface. This probe was the first to successfully transmit data from inside the atmosphere of a different planet. Even though it didn’t reach the surface of Venus, it did manage to transmit valuable data from Venus’ atmosphere. It was found that the atmospheric density and pressure at Venus’ surface were much higher than expected, causing the capsule to collapse prematurely. [108]

The Venera-4 vehicle was similar to that of the Venera-3: spherical in shape with a diameter of roughly 1 meter. The high reentry velocities and steep descent profile caused a maximum deceleration of roughly 300 g and the atmosphere in front of the vehicle heated up to temperatures above 11,000 degrees. After the major heating phase has passed, a drogue parachute was deployed to further slow down the capsule, followed by a single main parachute. Both parachutes were made from materials that are able to withstand temperatures of 450°C, in order to deal with the harsh atmospheric conditions on Venus. The parachute had a very unique shape, featuring a circular canopy with rectangular cut-outs.

The Venera 5 and 6 probes were already well designed by the time that Venera-4 was crushed by the Venusian atmosphere. The engineers made the necessary adjustment to make sure the probes could survive the high pressure, however, a full redesign was not feasible before the launch window. Hence the Venera 5 and 6 probes also became atmospheric probes, while a surface landing had to be postponed to Venera 7. [107]

The capsule and parachute system of Venera 5 and 6 was very similar to that of Venera 4 with several changes to increase the scientific value of the mission. The capsule shell was made stronger, more accurate scientific instruments were carried along, and the parachutes were smaller to allow for a deeper descent until the batteries ran out. Both probes continued transmitting data for more than 50 minutes until reaching an altitude of about 20 km when they were crushed by the dense atmosphere. [107][109]

After Venera 4, 5, and 6 failed to reach the surface, the USSR created Venera 7 with the data gathered from the previous mission to ensure it would reach the surface. So to land Venera 7 on the surface of Venus, they created a 490 kg egg-shaped entry capsule made out of titanium and designed to withstand 540 deg C and 180 bar for at least 90 minutes. Furthermore, to extend the lifetime, they pre-cooled the capsule to -8 Celcius.

The goal of Venera 7 was to reach the surface as fast as possible and gather data from the surface before the lifetime of the probe was at an end. In order to do this, they used the unique circumstances of the Venus atmosphere as a part of their entry system. Venera had only one parachute, which would be reefed. Right after deployment, the parachute would be 1.8 m² and be limited to fully opened by a line wrapped around the shroud lines. This reefing line had a maximum temperature limit of 200 C, well below the temperature, the probe would encounter. So once the temperatures reached 200 C, the reefing line would fail, and the parachute would increase to its final landing size of 2.5 m².

However, the actual flight was nothing as smooth as it was designed to be. Six minutes after the reefing cord melted away, the parachute ripped, and a few minutes before landing, it ripped away completely. The capsule hit the surface with 16.5 m/s. After some issues recognising the signal because Venera 7, due to the parachute failure, had landed with an antenna pointing in the wrong direction, returned data back to Earth. With this, Venera 7 became the first human-made object to transmit data from another planet's surface. [111, 113]

With the data and flight from Venera 7, NPO Lavochkin could update the design. Venera 8's pressure design limits were decreased from 180 bar to 105 bar as Venera 7 measured a maximum pressure of 92 bar at the surface. This, combined with keeping the same size as the entry vehicle, meant the resulting structure became lighter. That freed-up mass was used to upgrade the parachute system, keeping the same size but increasing the strength and adding a pilot chute. With the remaining available mass extra scientific instruments were added. Also, because Venera 7 landed in the wrong orientation after its parachute failure, a redundant antenna was added which would deploy before landing, creating a good line of sight. [111,112,113]

This meant they had a suite of instruments to cover the descent and the limited time they would have on the surface. The entry mass of both vehicles was about 1650 kg, and the final landed mass was 760 kg [129, 132]. The probes entered the Venus atmosphere and started their measurements of the atmosphere until the parachute deployed at approximately 65 km [130]. This lasted until 50 km when the parachute would be cut away, and the lander would continue under its own drag. During the descent, landers were equipped with a microphone to measure the wind velocity. These recordings are the first recordings of another planet [131]. Both landers would land with a velocity of 7.5m/s [131].

Once they arrived at the surface, the landers would transmit data for another 127 and 57 minutes for Venera 13 and 14, respectively, where it made the first colour images of Venus's surface. Venera 13 and 14 both collected two soil samples, one sample from the surface and the other with its onboard drill. Finally, Venera 13 and 14 were equipped with cameras with red/green and blue filters. Which, when combined, would create the first colour images of Venus.

In each VeGa entry system, there was one lander and one balloon. These would separate at 65km when the top half of the entry sphere, which contained the balloon, would separate from the bottom half, the half with the lander. The landing sequence of the lander was similar to the Venera landers before it. Deployment of its parachute was at an altitude of 63km, and it would be released at 47km. After which, it would land at its terminal velocity of 8m/s [170].

The landers that touched down on the 11^th and 15^th of June 1985 were virtually identical to Venera 13 & 14 [169,170]. They had a mass of 716 kg at touchdown, a wide array of measurement equipment for analysing the atmosphere during the descent, and a drill and spectrometer to take and analyse a soil sample [1,2]. Both VeGas had a lifetime of under an hour (56 and 57 minutes) after touchdown on the surface. After which, having completed all their scientific tasks, VeGa 1 and VeGa 2 succumbed to the extreme environment, and contact was lost with the landers.

The balloons, which separated from the lander at 65km, first deployed a 35 m² parachute to decelerate the system to 8m/s [170]. Once at 55km, the 3.4m diameter balloon would be filled with Helium. Once the balloon was filled, the parachute and filling system would be released at 50km, and the balloon would increase its altitude again until it reached its cruising altitude of 54km [170]. The entire system had a mass of 123 kg at entry and 20kg in its final cruising configuration [170]. On board, it had a temperature and pressure sensor, vertical wind anemometer, light level photometer and a nephelometer for measuring the density and particle size of local aerosols [169,170]. Its battery pack would allow for a lifetime of 46 hours. The data collected would be transmitted directly back to earth [170].

The VeGa landers would mark the end of the Soviet planetary missions to Venus. The Soviets launched, over a 24-year period, 29 missions towards to planet, of which fifteen successfully delivered three entry probes, ten landers, two balloons and four orbiters to Venus [170].

DAVINCI+ is a proposed mission of NASA to study the atmosphere and surface of Venus by descending a probe into the planet’s thick atmosphere. In the past, atmospheric probes and landers have been flown by both the United States (Pioneer program) and more extensively by the Soviet Union (Venera and VeGa programs). Although more recent probes have been studying Venus from orbit, DAVINCI+ will be the first probe to enter Venus’ atmosphere since VeGa did in June 1985. 

DAVINCI+ was a revival of an earlier, similar project proposal with the name DAVINCI, which had a similar mission profile and design. The design of the DAVINCI+ probe has likely not yet been frozen, however early renders indicate that the probe will use two parachutes, featuring a disc-gap-band, to slow down the capsule during its hour-long descent. [42, 43]

RocketLab plans to launch a privately funded mission to Venus using its Electron launch

vehicle. They are aiming to launch during the 2023 Venus launch window. The mission will use the company’s high energy Photon as a cruise stage and communications relay to bring the atmospheric probe to Venus upon which it will release the probe on a direct entry trajectory. The roughly 20kg probe will not have a parachute or any other deployable of decelerator and will feature an integrated, non-detachable heat shield. The probe will enter through the atmosphere and will take measurements of the cloud layer to determine if it contains substances that are indicative of biological life. Once the probe has passed through the cloud layer it will begin to relay its findings back to the spacecraft in orbit. Due to the lack of any form of method to decelerate the vehicle will impact the surface ballistically and be destroyed. The aim of this mission is to search for signs of life on Venus but also to demonstrate the feasibility of conducting planetary science with small spacecraft.