It may be there's another planet that will soon share that title: Venus. NASA is currently investigating a robotic explorer to land on Venus and explore. Unlike the rovers on Mars, this rover has decidedly steampunk character to it; it's all mechanical.
If there's any planet that seems like a good definition of hell, Venus is a strong candidate with a surface temperature of approximately, 450ºC or 850ºF, which is high enough for paper to spontaneously combust and melt lead. The atmosphere is a mix of carbon dioxide, nitrogen, and sulfur dioxide, while the surface pressure is 92 bar or 1,334 psi. The atmosphere is dense enough to crush a submarine. Some data says Venus' atmosphere undergoes critical refraction and it's possible for light to circle the planet, above the surface. Ray tracing computer modeling suggests that with a strong enough telescope, a hypothetical astronaut in the right place could see himself in the distance.
The electronics geeks, hams and experimenters might have had the thought "hot enough to melt lead? What about solder?" and it is. Parts can be welded onto a substrate, but "hot enough to melt solder" is an important consideration. The NASA lab planning the mission, NASA’s Innovative Advanced Concepts Program (NIAC) had developed a conceptual robot based on mechanical computers and WWI tanks because mechanical parts should survive the environment. Called AREE (Automaton Rover for Extreme Environments), the design has been referred to as a Steampunk Robot or Clockwork Rover. Shades of Babbage's Analytical Engine!
AREE was first proposed in 2015 by Jonathan Sauder, a mechatronics engineer at JPL. He was inspired by mechanical computers, which use levers and gears to make calculations rather than electronics.Venus has had only two robotic missions land on its surface, both from the former Soviet Union, the Venera and Vegas landers. They were able to function only for minutes: specifically 23 and 127 minutes before the electronics failed in the oppressive environment. To survive on Venus long enough to do any good science clearly requires thinking well outside the proverbial box.
Sauder said these analog technologies could help where electronics typically fail. In extreme environments like the surface of Venus, most electronics will melt in high temperatures or be corroded by sulfuric acid in the atmosphere.
"Venus is too inhospitable for kind of complex control systems you have on a Mars rover," Sauder said. "But with a fully mechanical rover, you might be able to survive as long as a year."
AREE includes a number of other innovative design choices.
Mobility is one challenge, considering there are so many unknowns about the Venusian surface. Sauder's original idea was inspired by the "Strandbeests" created by Dutch artist Theo Jansen. These spider-like structures have spindly legs that can carry their bulk across beaches, powered solely by wind.
Ultimately, they seemed too unstable for rocky terrain. Sauder started looking at World War I tank treads as an alternative. These were built to roll over trenches and craters.
Another problem will be communications. Without electronics, how would you transmit science data? Current plans are inspired by another age-old technology: Morse code.
An orbiting spacecraft could ping the rover using radar. The rover would have a radar target, which if shaped correctly, would act like "stealth technology in reverse," Sauder said. Stealth planes have special shapes that disperse radar signals; Sauder is exploring how to shape these targets to brightly reflect signals instead. Adding a rotating shutter in front of the radar target would allow the rover to turn the bright, reflected spot on and off, communicating much like signal lamps on Navy ships.
A mission like this would be interesting from the technology-geek standpoint, but one has to wonder if there might be ways to cool electronics to get more science done. NASA's Space Technologies Directorate talks about RTG-powered refrigerators (Radioisotope Thermal Generator - the type of power generator powering the Voyagers and some other deep space probes) has some high level summary.
Two enabling technologies, RTG powered cooling systems and high temperature electronics, have been proposed to enable long duration in-situ Venus operations. The former is highly complex and requires billions in R&D to cool a small chamber of electronics, while the latter is not close to the integration level required for a rover....That last paragraph makes it sound like the mechanical AREE might be getting close to being approved to go to Venus. For real.
...The automaton rover is designed to reduce requirements on electronics while requiring minimal human interaction and based on the subsumption architecture from robotics, where simple reactions of the rover lead to complex behavior. AREE combines steampunk with space exploration to enable science measurements unachievable with today’s space technology.
In Phase 1 purely mechanical rover technologies were compared to a high temperature electronics rover and a hybrid rover technologies. A purely mechanical rover, while feasible, was found to not be practical and a high temperature electronics rover is not possible with the current technology, but a hybrid rover is extremely compelling. Phase 1 mitigated our highest risks, demonstrating passive signaling was possible, the power budget balanced, and the rover fits within current EDL systems. Building on the design created in Phase 1, the objective of this proposed work is to finalize the trades with regards to implementation of locomotion and signaling systems, develop an end to end rover design, and perform Venus environmental testing of a representative prototype.