TOUGHEST ROBOT EVER
To build a rover that can survive in the crushing pressure and temperature of Venus, we need to rethink everything...
Crash. The Soviet probe Venera 7 speeds down through Venus' thick atmosphere, landing hard on the surface, when the parachute does not function properly. For 23 minutes, it sends data back to Earth, before falling silent. The scanty measurements tell a story of an extremely hostile environment. Surface temperatures are close to 475 °C – enough to melt lead – and the pressure, which is more than 90 times that of Earth’s surface, would crush most submarines. Venus is more extreme than anyone had ever imagined, so no wonder the probe quickly succumbs to the devastating conditions.
Venera 7 was the first probe to land on Venus on 15 December 1970, and for the next 15 years, only nine other Russian and one American probes managed to follow suit. Since the space race calmed down in the 1980s, Venus has only been visited by orbiters, but NASA still dreams of exploring our neighbouring planet’s surface once again. So, engineers have designed the robust AREE rover, which can resist the intense pressure and the high temperatures.
The rover will study the planet’s surface and determine what caused the runaway greenhouse effect on Venus. However, the studies cannot be carried out using instruments like those on the Martian rovers. Instead, AREE must carry out its pioneer work by means of springs, gears, and Morse-like code.
Rover to explain disaster course
In spite of its hard landing, the Venera 7 mission was successful. It was the first time that a probe sent a signal to Earth from the surface of another planet, and although subsequent Venus probes lived longer, none of them kept up a signal to Earth for more than two hours and seven minutes. The brief lives of the probes are a major part of the reason why our closest neighbour has been visited so rarely since 1985. When equipment is to be brought to the surface of Venus, it must first pass through clouds consisting of sulphuric acid droplets, and at lower altitudes, other highly corrosive chemical compounds such as hydrochloric acid and hydrogen fluoride exist. On the planet's surface, the pressure could easily destroy sensitive instruments.
However, the high temperatures are the major problem, as they will melt some metals and overheat all electric systems. The electric resistance of the circuits will increase with temperature, meaning it will be more difficult for a current to flow through the electronics. But what is worse, the transistors of modern microchips are based on silicon, which loses its semiconductor properties in the heat, making computer units break down.
The mere identification of a heat-defying material that can protect individual microchips cause problems for engineers.
Old inventions inspire rover
To overcome the planet’s harsh conditions, astronomers and engineers from NASA’s Jet Propulsion Laboratory have designed a rover that would be able to function on Venus for months. Known as the Automaton Rover for Extreme Environments, AREE, the project has been on the drawing board since 2015.
Inspired by reliable clockworks and mechanical machines of the past, scientists imagine a mechanical rover controlled by gears and energized by springs, that are powered by the wind. All parts are to be made of special metal alloys and synthetic fibre materials that can resist the high temperatures. The design of the rover is inspired by the World War I tanks, which were built to climb steep obstacles such as bomb craters and trenches. Due to volcanic activity on Venus, a crawler would also have to be able to handle different types of terrain.
At the centre of the rover, there is a simple wind turbine, that can generate wind energy 24/7. The low surface wind speed of averagely 0.6 m/second is sufficient to make the wind turbine rotate in the thick atmosphere. By making the rover be stationary for seven hours, energizing a spring by means of wind power, the rover can drive 100 m in one hour, as the spring is automatically released. During the planned 116 Earth days of the mission – corresponding to one Venus day – the rover can drive 35 km in the Sekmet Mons lava field, which has a versatile geological history.
In order to make sure that the rover does not drive in a circle, but rather explores a long cross section of Venus, a mechanical system must continuously count the number of revolutions of each tread of the vehicle. If one tread is ahead of the others, the rover must have turned, and so, the device makes sure to get it back on track again. A similar system ensures that the rover continues in the same direction if it encounters an obstacle and has to reverse to take a slightly different route.
Data sent as flashing code
However, the Venus rover cannot handle all tasks with mechanics. Particularly the more detailed geological measurements require electronic sensors. The inventors trust physicists and engineers from NASA’s Glenn Research Centre to develop new electronics, which can function at temperatures of about 500 °C. In 2016, scientists managed to make simple circuits based on the extremely durable silicon carbide material function under conditions like those on Venus for 21 days. However, the simple circuits cannot make up a real computer, and moreover, scientists would like to get data that spans a longer period of time.
Apart from the electric components, the rover will be assisted by a satellite orbiting Venus, which is not exposed to the harsh conditions of the rover. The satellite is to aim an ultra-strong radio signal at four radar targets on the top side of the rover. Scientists explain that the targets function as inverted stealth planes that become invisible by bending radar waves. Instead, the radar targets concentrate the radar signal back to the satellite. By means of gears, the rover’s measurements are transferred to four rotating discs with holes in them, that alternately hide and show the radar targets. So, the reflected radar signal is interrupted in a rhythm that reflects the collected data and sent back as a type of flashing Morse code in the same way as the signal lamps of ships. Finally, the satellite sends the about 1,000 bits of data collected per day to Earth.
Mechanics allow visit to Mercury
Venus is highly influenced by volcanic eruptions, and the surface is covered in lava fields. NASA’s scientists hope that a new mission can teach them more about how periods of volcanic activity have shaped the surface over billions of years and perhaps spot mineral evidence of a time, when the planet was a much more friendly place to be. Although the conditions sound overwhelming, prolonged meteorological and geological studies of the barren desert surface are important in order to understand why the planet’s greenhouse effect went berserk. More than 2.5 billion years ago, Venus was not just like Earth in size, it also included oceans and perhaps even life. So, Venus is also known as Earth’s twin. Data from the mechanical rover is to help scientists solve the mystey of why Venus was transformed. This is not only important to Earth’s future, rather also to the possibility of exploring the prospects of life on other planets orbiting remote stars.
A mission to the surface of Venus has not yet been planned, but with AREE, it might be done. The responsible scientists emphasise that a mechanical rover could also explore Mercury, whose surface has not yet been visited. On Earth, it can be used to observe active volcanoes. No matter what, the robust vehicle is in for a hot future.
96.5 % of Venus' atmosphere is carbon dioxide, whereas nitrogen makes up 3.5%.