What we learned from the Mars rover Opportunity
Robotics and autonomous systems will play a key role in the UAE’s Fourth Industrial Revolution—indeed, the UAE plans to send a robot to Mars by 2030—and there’s plenty going on at KU to address some of the cutting-edge R&D challenges in robotics. The KU Center for Autonomous Robotic Systems (KUCARS) focuses on three frontier robotics application themes: Robotics for Extreme Environments, Robotics for Industrial Applications, and Robotics for Infrastructure Inspection; but it’s the final frontier that’s interesting researchers in the wake of the death of the Mars Rover Opportunity.
“Certainly, a mission that had to last only three months and successfully operated for 14 years is a great achievement by itself. It is a great victory against atmospheric weather and the radiation environment,” said Dr. Elena Fantino, Assistant Professor of Aerospace Engineering. “However, the technological success of these missions has to be seen as step-by-step progress made by the several programs that NASA has designed and launched since the early years of interplanetary exploration.”
Getting there in the first place
NASA is still the only agency that has been capable of landing a spacecraft on Mars—all attempts by the European Space Agency have dramatically failed, with the recent crash of the Schiaparelli probe a fine example. The lessons learnt from this are that entry, descent and a soft landing on Mars are the components of the most critical phase in a spacecraft’s journey, and uncertainty as to atmospheric density and navigation errors make it even more strenuous.
“Landing on Mars is super hard,” explained Dr. Thomas Zurbuchen, Science Mission Director at NASA. “On average, 50 percent of the missions that go to Mars fail. We have the worst of both worlds on Mars: if you come into the Earth from the space station, the atmosphere slows you down. We have a massive atmosphere and we know how to handle this. If you land on the moon, that’s easy because there’s no atmosphere, and we use retro boosters to handle that. If you want to land on Mars, you can’t ignore the atmosphere, but it’s not going to help you. You have to use a shell, a supersonic parachute, and then the retro rockets—all autonomously—to get your spacecraft to the surface. If any of this fails, you’ll make a new crater.”
“We know that dust storms on Mars affect the efficiency of the solar cells, and this is the mostly likely cause of the termination of the Opportunity mission. The Rover was unable to produce sufficient electrical power to operate or even survive in the cold atmosphere of Mars,” explained Dr. Fantino. “This is why the Curiosity (Mars Science Laboratory) Rover carries a radioisotope thermoelectric generator (RTG) as its primary source of electrical power, rather than relying on photovoltaics.”
Navigating the unknown
The surface of Mars is rough terrain. “It’s rough to navigate and it causes stress to the robot,” said Dr. Lakmal Seneviratne, Professor of Robotics and Director of KUCARS. “One of the problems with navigating rough terrain is traction. When we walk, we know instinctively what we are walking on; but walking is very difficult, and you only realize this when you’re trying to create robots that can walk. If we have sensors, we can identify what the soil properties are, feed that back to the controller, and then they can adjust the robot’s movements to make it more effective.”
Opportunity needed a team of mission engineers, drivers and scientists on Earth to collaborate on its movements from one site to the next. The rover needed to maneuver around rocks and boulders, climb rocky slopes as steep as 32-degrees, probe crater floors and find its way across dry riverbeds—it had been designed to travel just 1,000 meters. Instead, it travelled more than 45 kilometers. But with another 144,798,455 square kilometers to explore, future rovers need to rugged enough to handle the journey.
The vast majority of space missions never return to Earth. After launch, a spacecraft’s tracking and communications system is the only means with which to interact with it. Without a consistently effective and efficient communications system between the spacecraft and the Earth, there would be no successful mission.
The demands placed on deep space communications systems are continuously increasing. According to NASA, as of March 2016, the Mars Reconnaissance Orbiter (MRO) had returned more than 298 terabits of data, but NASA estimates the deep space communications capability will need to grow by a factor of 10 each of the next three decades—to an astonishing 298,000 terabits. As we ask more detailed scientific questions, more sophisticated instruments are needed to answer them—and more data is required. Even at its maximum speed of 5.2 megabits per second (Mbps), it takes 90 minutes for MRO to send a single high-resolution image back to Earth. Understandably, the biggest obstacle to overcome is the enormous distance between us and space-faring robots. The two Voyager spacecraft are more than 15 billion kilometers away from home, and updates to the communications capability need to be extremely reliable and versatile to handle trips to (comparatively) nearby Mars and the far-flung corners of the galaxy.
The system needs to be reliable as any issues with the spacecraft can only be diagnosed, repaired, and mitigated via the communications system once it has left terra firmaon Earth. It needs to be hardy and versatile to accommodate the long system lifetime of a planetary mission. And it needs to be no heavier than a few kilograms and only consume just enough power to illuminate a refrigerator light bulb.
Much of the communication difficulty could be solved if the robots sent to Mars were autonomous. Behind many robotic systems operating today there’s a person controlling them. “They’re remote-controlled or semi-remote-controlled because autonomy is very hard,” said Prof. Seneviratne. “Robots can do three things: they move, they sense, and they intervene. They have legs, eyes, and arms. When you have a remote-controlled robot, you’ve also got the time delay. But achieving autonomy is very difficult. It’s a sensory issue—it’s both software and hardware as they form a continuum. We don’t have the feedback going into the sensors, and we don’t have the processing methods to interpret the feedback.”
The challenges are enormous.
The next step for mankind
Landing on Mars is one thing, having thriving robots is another: but the real challenge is living on Mars.
“The reason we’re talking about sending people to Mars is because sending robots there is very difficult to do,” explained Dr. Seneviratne.
Space agencies and aerospace companies around the world continue to address the challenges of living in space, such as using existing resources, options for disposing of trash, and more. Missions to the moon are about 1,000 times farther from Earth than missions to the International Space Station, requiring systems that can reliably operate far from home, supporting all the needs of human life. Then, there’s the 34 million mile trip to Mars to consider.
“Between sending robots to Mars and sending humans to Mars is a huge step. You just need to think about the amount of resources needed to facilitate human life—all the water, for example,” said Dr. Fantino.
The atmosphere on Mars is mostly carbon dioxide, the planetary surface is too cold to sustain human life, and the gravity there is just 38 percent of Earth’s. Innovative companies have been designing habitat prototypes that are self-sustaining, sealed against the uninhabitable atmosphere, and capable of supporting life for extended periods without support from Earth. Environmental control and life support systems are nothing new—thanks to the International Space Station—and crew are used to air locks and docking ports. But ISS crew members and astronauts are used to short missions in space.
Spaceflight of any kind presents unique stressors, from high G forces, increased radiation and microgravity, to sleep deprivation and nutritional complications. A mission to Mars and back would take a minimum of 520 days and see the crew journey around 360 million kilometers from home—that’s 520 days experiencing microgravity, confinement, stress from high expectations and risk of equipment failure, and microgravity-induced changes such as alterations in body fluid distribution.
“This is a fascinating topic—combining advanced machines and bioengineering healthcare solutions in pursuit of one goal: human presence in space,” explained Dr. Cesare Stefanini, Associate Professor of Biomedical Engineering and Director of the Healthcare Engineering Innovation Center. “With robots, we can remotely—but physically—access space and other planets, and with bioengineering, we can make human life in space possible. This has happened already, and the goal now is to extend our reach in terms of distance and ‘sojourn’ time.”
From Dr. Stefanini’s point of view, there are two primary factors conflicting with life in space: microgravity and the presence of radiation. Other aspects, such as circadian rhythm, absence of atmosphere and extreme temperature ranges can be addressed and compensated with engineering solutions in a relatively easy way, but the two main aspects are less easy to tackle, with potentially severe consequences.
“Microgravity is the word used to refer to a whole set of physical phenomena that occur in a vehicle in orbit—it is not the lack of gravity,” explained Dr. Fantino, “In low-earth orbit, the gravity (or better, the gravitational acceleration) is still more than 90 percent of the gravity on the surface. And gravity is the only reason a satellite can be in orbit around Earth, around Mars, or in interplanetary space (around the Sun). What causes ‘microgravity’ is the fact that in the frame of reference of the vehicle (spacecraft, or platform, or satellite), people and objects feel the same acceleration towards the Earth and this acceleration is the cause of the orbital motion. Gravity is not felt as force that pulls downwards, but as a force that pulls an object in a circle. An astronaut floats inside the ISS because both the astronaut and the ISS move on the same circle around the Earth—it’s a different experience of gravity. But this enables all sorts of chemical and physical phenomena (such as the fact that particles don’t settle in a solution because they are not pulled downwards) that has paved the way to a new branch of scientific research.”
What effects then does microgravity have on the human body?
“Microgravity impacts on the properties of bone, making them less dense and strong; cardiovascular physiology (heart atrophy); and vision due to damage to the eye from increased intracranial pressure,” said Dr Stefanini. Equally, there’s a risk to immune health as studies have demonstrated a key role for microgravity in microbial physiology: bacteria can proliferate more readily in space, which suggests that this environment is better able to initiate growth that could lead to contamination, colonization and infection. A total of 234 species of bacteria and microscopic fungi were identified in the Mir space station environment between March 1995 and June 1998, and if these bacteria can survive the extreme conditions of spaceflight, they pose a considerable risk of contaminating not just the crew on board, but also wherever they may land. “To counteract this,” said Dr. Stefanini, “we need to restore gravity, and solutions can be developed by implementing artificially-generated inertial forces, for example via rotating systems.”
Since Yuri Gargarin, over 450 people have travelled into space, but only those on Apollo missions have ventured beyond the first 500km of the low-Earth orbit. Low-earth orbit has a protective measure for humans planet-side and in space: the Earth’s magnetic field deflects a significant amount of radiation, but beyond the Van Allen radiation belt, where charged particles are trapped in this magnetic field, astronauts are exposed to solar and cosmic radiation. A 520-day round-trip to Mars would mean an astronomical amount of exposure for the crew on board.
“Radiation in space is characterized by high energy and carcinogenicity, especially for long missions such as the one for reaching Mars. Shielding is more difficult than in terrestrial applications, but the development of new materials opens the door to potential solutions,” explained Dr. Stefanini.
Exploration of the moon and Mars is intertwined: the moon provides the opportunity to test new tools, instruments and equipment that could be used on Mars to build self-sustaining life-support systems away from Earth. Sending humans far from Earth raises another intriguing problem: the one of space medical treatment and how to intervene on a patient by remote presence. Again, robots can be of great help (e.g. tele-operated surgical systems), allowing for surgeons on Earth to operate at very long distances. “This is already a reality,” said Dr. Stefanini, “The technology is there.”
NASA plans to send someone to Mars by 2040 but there’s a lot of work to be done in the meantime. The Mars Rover Opportunity lies in its most appropriate final resting place in Perseverance Valley—a symbolic end for the first robot on Mars.
News and Features Writer
26 March 2019