New Delhi: Dispatching a rover and a lander to Venus is challenging because of the extreme surface conditions, with temperatures easily reaching 465°C,
and the pressure reaching 90 bar. That means the pressure in the Venusian atmosphere at the surface is 93 times that of Earth at sea level. These are temperatures and pressures in excess of the tolerances of conventional spacecraft systems. Electronics fail roughly between 150°C and 250°C, with pressure crushing structures just as being a kilometre under water would on Earth. The heat melts lead and causes rapid degradation of material, with even the most robust metals such as titanium facing limits when it comes to protecting the sensitive science instruments necessary for observations.
The Soviet Venera landers achieved the only successes on the surface between 1970 and 1982. Venera 7 was massively overbuilt, and survived for 23 minutes. The Venera 13 and 14 probes were designed to survive for around 32 minutes. Venera 13 transmitted for a record 127 minutes, while Venera 14 survived for 57. No surface mission has survived for more than a couple of hours. No mobility was ever attempted, with a focus on pre-cooling, insulated pressure vessels and circulating fluids marginally extending the mission lives. The descent required heat shields and parachutes capable of extreme entry dynamics, with thick clouds blocking optical navigation. Apart from the crushing pressure and extreme temperature, the spacecraft also have to deal with corrosion by sulphuric acid, which forms the clouds and rains down on Venus.
A Rover requires entirely novel technologies
No rover has operated on the surface of Venus, because extending survival from a few hours to days or months for meaningful mobility requires breakthroughs well beyond current technology. Standard digital computers and batteries cannot function, the power sources and actuators cannot use electronics. Communication is complicated by the thick atmosphere, that limits data rates. Terrain navigation requires obstacle avoidance that do not use visible sensors, as cameras and processors would fail immediately.
NASA has explored wind-powered mechanical systems using analogue computers and clockwork mechanisms. Radar retroreflectors could transmit data to orbiters, which is a complex mechanism where the orbiter has to watch for clockwork movements by the rover on the ground. The rover would have to move about blind, depending on rollers and physical bumpers for detecting obstacles, as electronics and vision systems are impossible. These are all conceptual though, and there is no Venus lander and rover mission in progress anywhere in the world.
