JPL’s Design for a Clockwork Rover to Explore Venus
The longest amount of time that a spacecraft has survived on the surface of Venus is 127 minutes. On March 1, 1982, the USSR’s Venera 13 probe parachuted to a gentle landing and managed to keep operating for just over two hours by hiding all of its computers inside of a hermetically sealed titanium pressure vessel that was pre-cooled in orbit. The surface temperature on Venus averages 464 °C (867 °F), which is hotter than the surface of Mercury (the closest planet to the sun), and hot enough that conventional electronics simply will not work. It’s not just the temperature that makes Venus a particularly nasty place for computers—the pressure at the surface is around 90 atmospheres, equivalent to the pressure 3,000 feet down in Earth’s ocean. And while you can be relieved that the sulfuric acid rain that you’ll find in Venus’ upper atmosphere doesn’t reach the surface, it’s also so dark down there (equivalent to a heavily overcast day here on Earth) that solar power is horrendously inefficient. Images: NASA Surface photographs from the Soviet Venera 13 probe, which landed on Venus and operated for just over two hours. The stifling atmosphere that makes the surface of Venus so inhospitable also does a frustratingly good job of minimizing the amount that we can learn about the surface of the planet from orbit, which is why it would be really, really great to have a robot down there poking around for us. The majority of ideas for Venus surface exploration have essentially been the same sort of thing that the Soviets did with the Venera probes: Stuffing all the electronics inside of an insulated container hooked up to a stupendously powerful air conditioning system, probably driven by some alarmingly radioactive plutonium-powered Stirling engines. Developing such a system would likely cost billions in research and development alone. AREE would use clockwork gears and springs and other mechanisms to provide the majority of the rover’s functionality, including power generation, sensing, locomotion, and even communication: no electronics required. A conventional approach to a Venus rover like this is difficult, expensive, and potentially dangerous, but a team of engineers at NASA’s Jet Propulsion Laboratory (JPL), in Pasadena, Calif., have come up with an innovative new idea for exploring the surface of Venus. If the problem is the electronics, why not just get rid of them, and build a mechanical rover instead? With funding from the NASA Innovative Advanced Concepts (NIAC) program, the JPL team wants to see whether it might be possible to build a Venus exploration rover without conventional sensors, computers, or power systems. The Automaton Rover for Extreme Environments (AREE) would use clockwork gears and springs and other mechanisms to provide the majority of the rover’s functionality, including power generation, power storage, sensing, locomotion, and even communication: no electronics required. Bring on the heat. Photo: Francoisguay via Wikipedia Internal view of the Voskhod spacecraft IMP “Globus” navigation instrument. In this overwhelmingly electronic world, most of us don’t have a proper appreciation for the kinds of things that can be done with mechanical computers. Two thousand years ago (give or take a century or two), the ancient Greeks constructed the Antikythera mechanism, which could calculate the position of the sun and moon, show the phase of the moon, predict eclipses, track calendar cycles, and possibly even show the locations of five planets using a carefully designed set of at least 30 bronze intermeshed gears driven by a crank. Between the 17th and 19th centuries, Blaise Pascal, Gottfried Leibniz, and Charles Babbage all developed mechanical computers that could perform a variety of arithmetic functions. And a bit more recently, in the 1940s, mechanical computers were used extensively in violently practical applications like artillery fire control systems and aerial bomb sights. The Russians used a mechanical computer called Globus for positional calculations on their spacecraft up until 2002, but in general, everything is now going electronic. This is fine and good, except for on Venus, where most electronics are impractical. JPL’s concept for AREE is to create a robot with a minimal amount of electronics, instead relying as much as possible on purely mechanical systems that can handle high temperatures for weeks, months, or even years with no problems. Jonathan Sauder is a technologist and mechatronics engineer at JPL’s Technology Infusion Group, and the lead on the AREE project. We spoke with him for more details on how the project got started, and how everything is going to work. IEEE Spectrum: How’d you come up with the idea for AREE? Jonathan Sauder: I was sitting around with a bunch of engineers, and we were working in a concurrent design session. During one of the coffee breaks, we were talking about cool mechanisms and components, and how cool would it be to do a purely mechanical spacecraft, what that would look like, and where you would use it. We realized that there are two places that make a lot of sense for something like this, where electronics don’t survive: One is Venus, because the longest we’ve been able to survive on the surface of Venus is two hours because electrical systems overheated overhead, and one is around Jupiter, because of the high radiation environment that disrupts electronics. Is it really possible to build a robotic exploration rover with no electronics? We started out in our NIAC Phase I proposal thinking that we were going to build a fully mechanical rover architecture that would not use any electrical subsystems or electronics at all, replacing all the standard electrical subsystems with mechanical computing. As we started to dig into it more, we realized that you can’t build a traditional Mars Curiosity-style rover with a centralized core processor ... Instead, what we’ve had to do is focus on something that gives more of a distributed architecture, where we have many simple mechanisms around the device, guiding it, signaling it, telling it where to go. Originally we were going to try to do a number of our scientific measurements mechanically as well. As we started to look into that, we just couldn’t quite get the resolution of data that you need to image or measure things like temperature and pressure. There are some various high-temperature electronics that have been developed—silicon carbide and gallium systems—that do operate at high temperatures. The problem is that they’re at a really low level of integration. So what that means is that you can’t do traditional electrical systems with them, and you can’t do anything close to what would be required for a rover. So our idea is to built a mobility platform that would be able to locomote, seeing new places and operating for a lot longer than you could with the systems that currently exist. Image: ESA/J. Whatmore/NASA/JPL-Caltech An early concept image for the AREE featuring a legged design. Where did you begin with the design for AREE? The primary goal is to first design our locomotion architecture to be as robust as possible. And then the second goal is to use as many simple, distributed, reactive mechanisms as we can to sort of guide the rover as it works its way across the surface of Venus. You’ll notice that in some of our earlier images, the rover looked a lot like Theo Jansen’s Strandbeests, these semi-autonomous creatures that roamed the beaches of the Netherlands. A Strandbeest operates off just a couple simple sensors, which control whether the legs move backwards or forwards, and it has built-in logic to avoid soft sand and water. Early on in our conceptual development, we actually worked with Jansen: He came to JPL for a two-day collaborative engineering session, and we were getting all his expertise in 30 years working with Strandbeests. One of the first things he mentioned was that the legs have to go. And you know, when the person who’s created the Strandbeest tells you the legs have to go in your Venus rover, it means you probably need to find a different architecture. The key issue is that, while the legs work great on flat soft beaches, once you start getting to more variable terrain (like an unknown Venus environment), the legs will not be stable enough and the rover will have a very high probability of tipping over and getting damaged. That’s what inspired our architecture change from Phase I to Phase II, where we went from this really cool-looking legged rover to a maybe slightly less cool-looking but much more robust and probably much more implementable rover that looks like a World War I tank. Image: NASA/JPL-Caltech The Phase II concept for AREE features tank treads for locomotion and an internal wind turbine. There are several significant advantages to the tank design, besides just not tipping over quite as often. Since it’s vertically symmetrical, if it does flip over for some reason, it can keep on going. This is by no means the final design, and the JPL team is starting to look at wheels as well, since wheels may be more robust due to fewer moving parts. Can you describe how AREE will be able to navigate across the surface of Venus? Basically what we’re doing is developing some very specialized systems in terms of obstacle avoidance and determining whether there’s enough power to move or not, rather than a standard centralized system where you have a rover that can do multiple processes or be reconfigured or changed at any time via software. We’re trying to make the mechanisms as simple as possible, to do one specialized task, but to do that specialized task really well. Maybe it’s when the robot bumps into an object, it’ll flip a lever, which causes the rover to drive backwards a little bit, rotate by 90º degrees, and drive forwards. We can only do one obstacle-avoidance pattern, but you can repeat that multiple times and be able to eventually able to work our way around an obstacle. Image: Jonathan Sauder/NASA/JPL-Caltech Obstacle avoidance is another simple mechanical system that uses a bumper, reverse gearing, and a cam to back the rover up a bit after it hits something, and then reset the bumper and the gearing afterwards to continue on. During normal forward motion, power is transferred from the input shaft through the gears on the right hand side of the diagram and onto the output shaft. The remaining gears will spin but not transmit power. When the rover contacts an obstacle, the reverse gearing is engaged by the synchronizer, thus having the opposite effect. After the cam makes a full revolution it will push the bumper back to its forward position. A similar cam can be used to turn the wheels of the rover at the end of the reverse portion of the drive. How are AREE’s capabilities fundamentally unique from other Venus lander proposals? Right now there are several Venus mission concepts, each of which would cost as much as what a Mars Curiosity rover would or more, that either land in one location, or they get two locations of data. Most proposals are highly complex and looking at 2 to 24 hours on the surface. We’re looking at extending that amount of time to a month, essentially, with this rover concept, and that’s really where the key innovation comes in: Being able to sample multiple locations on the surface of Venus and understanding how things change with time. Image: Jonathan Sauder/NASA/JPL-Caltech AREE compared to other proposed Venus rovers and concepts. Can you describe your vision for AREE, if everything goes as well as you’re hoping? The ideal robot would be something that could go into some of the roughest terrain on Venus called the tessera, which is this very rough and rocky lava. Our goal would be to track this rover during its mission on that terrain, taking geological samples as we travel to help us understand how Venus evolved. For the ideal rover, it’d be nice to get a little bit larger than 1.5 meters: Right now it’s restricted by the heat shield size. If we could, we would expand the rover to 2.5 meters in order to overcome larger obstacles and get more wind energy. Eventually, the goal would be to place a rover that would essentially be a Venus juggernaut that can get over most obstacles and keep trekking forward, driving itself along slowly but steadily, collecting samples and weather data as it goes. Image: Jonathan Sauder/NASA/JPL-Caltech The concept of operations for traversing across Venus plains and to the tessarae. During the primary mission of 116 Earth days (one Venus diurnal cycle), the rover will traverse 35 km. An extended mission will traverse up to 100 km over the course 3 years. At this point, you may be wondering just why the heck it’s worth sending a clockwork rover to explore the surface of Venus if we’re never going to hear from it again, because without electronics, how can it send any data back to us? There are certainly ways to store data mechanically: It’s easy to temporarily store numbers, and you can inscribe about 1 megabit of data onto a metal phonograph record. But then what? One idea, which is somehow not as crazy as it sounds, would be to use hydrogen balloons to hoist these metal records into the upper atmosphere of Venus, where they would be intercepted by a high altitude solar powered drone (!), which would then read the records and transmit their contents to a satellite in orbit. The researchers also considered a vacuum tube radio, but while vacuum tubes are quite happy to operate at high temperatures, they’re vulnerable to becoming de-vacuumed in the Venusian atmosphere. To get data back from AREE, the researchers want to use radar reflectors. A radar reflector mounted on the back of the rover could be seen from orbit, and by putting a shutter in front of the reflector, the rover could transmit something like 1000 bits every time a satellite passed over it. The solution that the AREE researchers came up with instead is this: radar reflectors. A radar reflector mounted on the rover could be seen from orbit, and by putting a shutter in front of the reflector, the rover could transmit something like 1000 bits every time a satellite passed over it. Adding multiple reflectors with different reflectivity along with shutters operating at different frequencies could allow a maximum of 32 unique variables to be transmitted per day. You wouldn’t even need to be transmitting specific numbers to send back valuable data, Sauder says, because just putting a reflector underneath a fan could be used to measure relative wind speeds at different locations over time. So now that you’ve got this ingeniously capable and robust robotic rover that can survive on Venus, the final thing to figure out is what kind of scientific exploration it’ll be able to do, and that’s a particularly difficult question for AREE, as the NIAC Phase 1 proposal explains: One of the greatest weaknesses of a purely mechanical system is its ability to make science measurements. Beyond communications, one of the key areas that could effectively use high temperature electronics is the instrument. More complex measurements, especially those related to geologic measurements, require electronic solutions. Late last year, NASA announced HOTTech, the Hot Operating Temperature Technology Program, which is providing funding to support “the advanced development of technologies for the robotic exploration of high-temperature environments … with temperatures approaching 500 degrees Celsius or higher.” The AREE team hopes that HOTTech will result in some science instruments that will be able to survive on their rover, although if not, they also have some ideas for a few interesting ways of doing science without any electronics. These include measuring wind speed from a wind turbine, temperature and pressure from thermally expanding materials, and chemical properties from rods that react to certain desired chemicals. Image: Jonathan Sauder/NASA/JPL-Caltech AREE stores wind power in a composite clock spring, much like a pocket watch. The mechanical system shown above can measure the energy stored in the rover’s springs, and uses a clutch to deliver power to the locomotion system when enough has been stored up. If you only want the rover to run after a certain amount of time, or after other conditions have been met, mechanical logic gates can be added to incorporate the output of a clock, or other sensors. To be clear, it’s not like Sauder and his team are trying to make all of this mechanical stuff for fun: It really is necessary to explore Venus affordably for longer than just a day or two. “Our goal with this project is specifically not replicate things that have already been done or will soon be done in the high temperature electronics area,” Sauder says, “but provide a set of mechanical solutions for things that might take longer to develop where there is no clear current solution.” The technology that’s being developed for AREE has applications elsewhere in the solar system, and not just in high radiation environments like Jupiter’s moon Europa. Right here on Earth, AREE could be useful for taking samples from very close to an active volcano, or from within highly radioactive environments. Another advantage of AREE is that it can be completely sterilized at a very high temperature without affecting its functionality. If, say, you find a lake under the icecap on Mars with some weird tentacle-y things swimming around in it, you could send a send in a sterilized AREE to collect a sample without worrying about contamination. At this point, AREE has received Phase 2 NIAC funding for continued development. The team is working on a more detailed study of the locomotion system, which will likely involve swapping the tank treads out for something wheel-based and more robust. They’re also developing a high temperature mechanical clock, one of the fundamental parts of any autonomous mechanical computer, and Sauder says that he expects some exciting results from building and testing a radar target signaling system within the next year. We're certainly excited: this is one of the most innovative robots we've ever seen, and we can't wait for it to get to Venus. The Automation Rover for Extreme Environments team, led by Sauder, also includes Evan Hilgemann, Michael Johnson, Aaron Parness (whose research we’ve written about before), Bernie Bienstock, and Jeffery Hall, with Jessie Kawata and Kathryn Stack as additional authors on the NIAC Phase 1 final report, which you can read here.