Buzz Aldrin set foot on the Moon twenty minutes after Neil Armstrong. While he was collecting soil samples and taking photographs, Aldrin disappeared from the television camera for a while to dedicate himself to his first experiment: walking and jumping.
On that first visit to the Moon there were many unknowns to be resolved. The dusty surface would probably support a man’s weight without engulfing him, although just in case, Armstrong climbed down the ladder with a safety line. In low gravity he could walk, but Aldrin should test it, trying three ways: step by step, swinging from side to side and kangaroo hops. In practice, none was better than the other.
Contrary to what science fiction comics predicted in the 1950s, tracked vehicles were never used on the Moon. Perhaps out of fear that large loose rocks would damage them. The first to roll there in the early seventies were the Russian Lunokhod, robotic devices mounted on eight wheels that did not even have a steering mechanism.
To go right or left, the four wheels on one side simply stopped while the wheels on the other turned. That this solution was adopted is not surprising: the design of the chassis had been entrusted to the same engineers who had built tanks during the war.
More traditional were the electric cars used in the last three Apollo missions to allow astronauts to travel several kilometers from their ship. That vehicle was a real luxury; On the previous flight, the hard-working pilots of Apollo 14 had to be content with much more modest transportation: a simple wheelbarrow that they had to drag by hand.
The cart was designed to make it easier for them to transport the equipment needed for their experiments and collect samples. It is true that it allowed us to carry more tools, but it was not as practical as could be expected. At the slightest bump, the wheels – rubber tires – made it jump so much that part of its contents were thrown out, and the astronaut in line had to pick it up. In some particularly steep sections of the route, the two men preferred to carry her as if she were a stretcher.
The Moon was a relatively familiar environment, but as the horizons to explore expanded, new challenges arose in robot design. When they sent the first capsules to Venus, Russian engineers didn’t even know whether they would find solid ground or swampy ground. The antennas that would allow them to communicate with Earth were expelled outside at the moment of contact with the ground, but what to do if the capsule fell into a lake?
The answer was to incorporate a sugar cube into the mechanism: when it dissolved in water, it released the antenna deployment spring. Today, of course, we know that Venus is a boiling desert, the least welcoming place in our entire solar system, so no probe is prepared to land on water.
By the way, the American military adopted a similar solution with the capsules of its spy satellites, which returned loaded with compromising photos. If they fell into the sea and no one picked them up within twenty-four hours, a plug – this time of salt – would dissolve, flooding it with water to send it to the bottom, safe from curious eyes.
Russian engineers themselves faced the challenge of exploring Mars. The first vehicle to land there, the Mars 3, was not American, but Soviet, in the winter of 1971. Unfortunately, it broke down as soon as it landed and only sent a few lines of the first television image, the that corresponded to the dark firmament. Then he fell silent.
On board, the capsule carried a small rover the size of a shoe box. It did not move on wheels, but on skates that would have made it advance step by step to the distance allowed by the cable that powered it. The very design of the mechanism did not make it easy to direct. It only had a bumper to detect any obstacle. In that case, he would back away, lean a little, and try again. With communications interrupted, he was never heard from again.
To explore Mars with some mobility, NASA used vehicles with six wheels grouped together from the beginning, in a mixed rocker and bogie system. This combination of levers and joints allows them to overcome obstacles almost twice as high as the wheels themselves, always keeping them all in contact with the ground, and the body of the vehicle, level. It is such a successful design that it has later been adopted by the Chinese and Indians in their own programs.
As the surfaces of the Moon and Mars are covered in very fine dust, there is a danger of the wheel skidding, so the Russians used them with metal slats to provide more grip. In turn, in the cars of the Apollo program, they were similar in shape to a tire, but made with braided piano wire and titanium reinforcements.
On Mars, NASA started out using studded wheels, but eventually adopted titanium wheels with reinforced rubber tires. The designers at the Jet Propulsion Laboratory were so proud of their design that in the treads of the Curiosity robot, launched in 2011, they included short and long perforations in no apparent order. They corresponded to the Morse code of the letters JPL, the initials of the name of this NASA center. As the vehicle moved across the floor of Gale Crater, it left the signature of its manufacturers imprinted on the ground.
On the Moon or Mars gravity is less than on Earth, but still enough for a wheeled vehicle to have grip on the ground. Not in other places, such as, for example, in Phobos, one of the two small Martian satellites.
Phobos is a rock that does not reach thirty kilometers in diameter. Certainly a captured asteroid, of such low mass that it has not even been able to sink in on itself and adopt a spherical shape. Its gravity is two thousand times less than on Earth; If an astronaut were to walk there one day, he would have to be careful: a jump with some momentum could put him into orbit.
Russia has tried to explore Phobos a couple of times (with little success). Just a look from above. The last attempt involved detaching a pair of scout robots by simply dropping them. In a vacuum, a parachute would be useless, and the weak gravity doesn’t even justify a braking rocket. All you need to do is pad your instruments a little so that they don’t get bruised on impact after a slow-motion fall that could take more than a quarter of an hour.
One of the two probes was a static station; the other had to move to investigate at least two or three different locations. As? With so little weight the wheels have no traction, and making a robot with legs was too complicated.
In the end, the solution was to build a ball-shaped capsule, with a single foot hidden inside. Firing it using a pneumatic piston, as if kicking the ground, would be enough to send it dozens of meters away, after the corresponding rebounds. Thus, from jump to jump it could cover a good area of ????terrain.
The designers of the European probe Philae, the first destined to land on a comet, encountered a similar problem. As a target, one called Churyumov-Gerasimenko (the surnames of its discoverers) was chosen, whose severity is even lower than that of Phobos.
It was feared that the probe would bounce when it hit the ground, so they installed a double safety system. Already about to make contact, it would launch a pair of harpoons that would have to be stuck into the ground to anchor it. At the same time, on each leg she carried a drill bit with which to pierce the ice, giving her three more points of grip.
Upon landing in November 2014, both systems failed. And as was predictable, the Philae bounced and bounced until it landed in the worst place: a crevice in the ground where it did not receive sunlight to recharge its batteries.
It took specialists at the European Space Agency months to sift through hundreds of photos of the comet in search of their missing spacecraft. In the end, they located her tilted, with one paw sticking out of the crack. She had stopped broadcasting almost a year earlier.
For its part, JAXA, the Japanese Aerospace Exploration Agency, turned to the toy industry to design a mobile robot to send to the Moon. It was a simple plastic ball, heir to the transformers tradition. When it reached the ground, it opened into two hemispheres that would serve as wheels and raised a micro television camera with which to document its adventures.
The first model of the robot-transformer was a passenger on the Hakuto-R, a private ship that crashed last year. The attempt was repeated a few weeks ago with the Japanese SLIM probe, whose landing on the moon was somewhat surreal. At a very low altitude it lost one of its two braking thrusters. Literally, its nozzle fell off and fell to the ground.
It says a lot about the skill of the Japanese programmers that, despite such a catastrophic failure, the software continued to control the ship, which landed on the Moon in one piece, even if it was on its nose. By then, the ball-robot had already jumped into motion and deployed its camera, and was able to send the image of the vehicle almost embedded in the ground.
The inventiveness of designers has no end. Some ships headed to an asteroid have deposited simple cube-shaped boxes there, but they can also move; Inside they have an off-center counterweight that is rotated by an electric motor. With each rotation, the box shakes and turns over, that is, one more step on a slow path to explore the terrain.
Others use more pedestrian methods. The Swarm, built by a Mexican university, consisted of four tiny, identical, coaster-like robots. The carrier vehicle – the American Peregrine, which also failed to reach its objective a few weeks ago – carried a small catapult to launch them to the ground without further consideration, as soon as the moon landing was completed. No one could guarantee that they would fall face up, so they had photocells on both sides. Just in case.
Perhaps the most ambitious experiment in mobility has been the use of the Ingenuity helicopter on Mars. Designed simply as a test to carry out only five flights in that tenuous atmosphere, it completed 72, establishing its distance record at seven hundred meters, at a speed of over 20 km/h.
Unfortunately, on its last landing, Ingenuity’s rotor scraped against the ground, damaging the tip of a blade. With this small imbalance, it is no longer able to fly, so it has been permanently abandoned in a sandy area near the edge of the Jezero crater, while the Perseverance mobile robot continues on its way.
But the experience acquired with that helicopter will continue. NASA has already designed another drone model with four rotors and much more payload capacity. It is called Dragonfly and should be sent to explore Titan, Saturn’s mysterious moon, in 2028.
