by A. T. Sayre
The terrain in the lower Melas Dorsa was more rocky and uneven than in the plain behind the Martian rover, so its progress slowed considerably. The ridges and hills rippled out in near even rows north to south and inclined at a modest but steady rate.
Rocks from the small and easily rolled over to boulders twice its size were scattered in all directions, disrupted only by narrow veins of fine sand and dirt running like cracks in the ground. The rover stuck to these smoother paths as much as possible but would have to venture through the rock field when the veins dissipated or turned too radically in the wrong direction. It might have been a smoother course to cut around to the east or west to reach its objective, a cluster of craters in central Melas Fossae, but the rover had determined the direct approach would still take less time.
The sun above and the blue halo surrounding it were the only disruption of soft brown Martian sky from horizon to horizon. The clear skies were welcome; the murky sky of the last few days had seriously depleted its batteries, and if it had continued for much longer, the rover would have been forced to shut down and spend an entire day charging.
The rover’s far left back wheel lost its grip and spun out on a flat rock just below the sand, its body jerking sideways for a moment before it stopped. That back wheel wasn’t as good as its original wheel had been. The Russian probe the rover had taken it from had been designed for the smooth Amazonis Planitia, so it didn’t have the deep treads and spikes that could grip the rocks and sharp crags in the ground. But it had been compatible, unlike most of the rest of that defunct machine, and the rover had needed a replacement. It deployed one of its long metallic arms to push itself forward and continued.
The rover spotted an odd discoloration in the side of a short scarp a few dozen meters to the east, and it stopped and rotated its main head to face it. The spot had a bright, soft white color, only dulled by the coat of Martian dust that had likely been blown thin in a storm. It was no more than a few centimeters in diameter and irregularly shaped, but it stood out clearly, as it disrupted the flowing lines in the outcropping like a mole.
The rover deployed its laser and took aim at the spot. It fired three fast, high intensity shots at it, boring a small hole. A cloud of particles hung in the air at the target, and the rover trained its spectrometer on the cloud until it dissipated.
There was the expected iron oxide in the cloud, the surface dust, as well as magnesium, magnetite, aluminum oxide, and potassium, all in small quantities. Common minerals on Mars. But there was also an abundance of calcium sulfate dihydrate in the sample. Gypsum. A sedentary mineral formed by water.
It was a particularly rare find. Gypsum had only been found in a handful of other locations, the closest being in the Meidiani Planum over three thousand kilometers away. The rover itself had never come across it. And only two of the Mars probes it had scavenged databases from recorded any sign of it. The trip to Melas Fossae would have to be put on hold.
The route to the gypsum sample meandered, moving around large rocks the rover could not roll over. Halfway to the scarp the rover came upon the edge of a sharp drop in the ground that was far too steep for it to traverse. It stopped and scanned the area.
To the west the drop of the ridge became deeper. To the east it turned into the foot of a ridgeline that meandered for approximately twenty meters until it bent back south, merging with several other ridges into a narrow plateau a kilometer away. The ground beyond the scarp appeared relatively smooth, so it could travel up and past the scarp to come at it from the other side. If there was a way back down. Here at the foot the incline wasn’t too steep, but the sides of the ridge looked impossible all the way to the horizon. Beyond that the rover could not determine; the topography maps in its database did not have the necessary detail at this small a scale. But it seemed to be the only viable option.
The ground of the ridgeline was very loose and sandy, with each turn of the rover’s wheels sending small cascades of sand sliding down behind it. It had to be very careful and deliberate in its movements to avoid tumbling down with it. At the top, it deployed its arms and pushed itself over the edge, and drove along the rounded off top slowly, leaning down one side.
By sunset the ridge had flattened out and widened, but the sides remained far too steep to descend. The scarp had long since disappeared behind the rover. Another ridgeline merged with the one the rover was on half a kilometer ahead, and perhaps by doubling back on that ridge it could find a way back down. But that would have to wait till tomorrow; with nightfall the temperature had already dropped below optimal operational levels.
The rover stopped in a stable spot in the center of the plateau and deployed stabilizing struts to lift itself off the ground. Powerful blasts of air from its vents blew in short bursts methodically across its entire body, clearing off the day’s dust and dirt. After that was finished, the vents closed, the solar panels folded on themselves and tucked in flat against its body, its main head lowered down on top of them, and its camera lens narrowed and went dark.
The rover’s systems one by one went into standby mode to conserve energy, leaving only the barest of sensory functions operating. All except its communication system, which switched on. The rover functioned autonomously during the day, only initiating its communication system at night to upload its logs and other data gathered throughout the day’s work and to receive instructions.
The rover sent out a test signal and waited for confirmation. Thirty minutes went by. Then an hour. No reply. It sent out another signal. Still no reply. The rover ran a diagnostic on its communication systems—everything was functioning perfectly. It sent the signal again. Still nothing. The rover repeated the process. It would keep sending the test signal until a connection was confirmed.
Even though it had been a very long time since the rover had heard from home.
No confirmation. Not a word. The rover hadn’t received a single byte of information in thousands of nights. It was obvious that something had gone wrong, some reason why its signal was never acknowledged. But the rover did not have enough data to determine what it could be. Its systems were working fine, as the repeated diagnostics showed, so there was no problem on its end. But still there was no reply.
They probably didn’t know the rover was still functioning. It had survived far longer than anyone would have predicted. A few years, five at the most, was all that was expected of it. After that, the rough life of crawling along the rocks would take its toll, and the rover would cease to function, buried in the sand along with all the rest.
But the rover was still here. Still functioning. Still making its way from one point of study to the next, amassing data and exploring, because that was what it was programmed to do. And nobody had told it to stop.
It had changed somewhat since its creation, as it had needed to take parts of other machinery left on Mars to keep going. A new wheel from the Russian probe, an optic lens to replace its own cracked one, a processor from another to subsidize its own when its performance had started to lag. It had taken solar panels from a Chinese machine with more receptive photovoltaic cells and mounted them alongside its original array to improve energy collection. It added another set of arms from an Indian rover, much better at gripping than its original four, connected by an extension of its chassis that it took from an American probe at the edge of the Northern ice cap.
And as always from the probes, landers, other rovers, it took the processors and data storage units, to keep pace with the increasing sophistication of its system. It grew smarter, more resourceful, capable of more and more complex problem solving and decision making. The rover had learned so much, had grown so much, it was barely recognizable as the simple machine that had touched down on the red planet so long ago.
If someone back on Earth would make contact, would look up and see it was still there, alone in the dark on a plateau in the middle of the Melas Dorsa, just waiting for someone to acknowledge its signal, they would be amazed.
* * *
By midday the rover had traveled along the new ridge nearly halfway back to the scarp, and the incline on the eastern edge had started to ease. It still was too steep for the rover to attempt, but with the way the ridge was petering out, it seemed likely it would be manageable in another kilometer. With any luck, there wouldn’t be any further obstacles delaying it getting back to the scarp once the rover reached the ground below.
The plateau narrowed considerably and sloped down as the rover continued on to the end of the ridge, and the ground underneath started to become unstable. Chunks of dirt fell away beneath its wheels on both sides, making it slide dangerously before it could turn away. The rover pulled in its solar panels to lower its center of gravity. But that only did so much.
The rover could see the ridge line ahead grew even narrower, folding into a point and dropping sharply on both sides. It couldn’t continue forward safely. Twenty meters back, there had been a ledge descending off the east side that the rover had passed on because it was barely wide enough for its frame, but now it appeared it was the rover’s only option.
The rover reversed back up the ridgeline. The ground degraded even more. It didn’t have the same amount of traction now as it was moving against the downward slope. Every time it stopped to try to assess, it would start to slide down one side or the other.
The ground beneath its left back wheel completely disappeared, bucking the rover up and to the right. The rover’s arms shot out into the ground all around it. That stopped it from falling any farther. But the slightest movement was likely to send it over. The rover sat still as a rock, barely hanging onto its purchase, as it analyzed the situation.
But then the entire left side of the ridge fell away and took the rover with it.
The rover flipped and tumbled, scraping its way down the course ridge, pinballing off hard earth and rocks in its path. It was powerless to stop or even just slow itself, so it did the only thing it could—pulled in its arms and head tight against its body to save them from breaking off, and waited to reach the bottom.
It fell over a steep drop and began to cartwheel end over end, picking up speed, bouncing in the air in high arcs, before slamming back down and continuing to roll. Near the bottom it glanced off a large boulder, sending it twirling in the air. It landed flat on its back and skidded along until coming to rest a few meters away from the ridge.
The rover lay there a long time as the sun moved across the sky. The faint hum of its internal motors was silent. It was as still as the rocks and hills around it.
It was near sunset before the rover let out two sharp beeps, and its hum returned as its systems rebooted. Its wheels twitched and rolled in the air for a moment, before the rover’s gyroscope came online letting it know it was upside down.
The rover dug its right side arms into the ground and pushed itself upward, walking the arms closer and closer, to push itself on to its side and farther. With one last heave the rover fell back down onto its wheels with a bounce.
It did a check of its internal systems. Everything seemed to be online and functioning properly. The visual, motor, energy systems, all reported nominal. Its processors and memory storage were also undamaged.
Externally there was more. There were no cracks in its body, and its main head seemed undamaged. But one arm hung crumpled down its side and was unresponsive. It examined the arm. It was barely attached, only hanging on by a half ripped flat cable. At some point in the fall it must have taken the brunt of a hit right at its joint.
The rover deployed its solar panels. Two of them were barely functional. The fall had cracked one of them straight through, and the other would not fully open. The others worked fine, but the rover’s solar harvest ability was severely compromised.
The strut on the front right wheel was bent outward, tilting the rover forward, and when it moved, the wheel wobbled on its axle, causing the rover to jerk up and down randomly. It managed to stabilize itself by supporting its front with one of its remaining arms like a crutch.
The rover grasped the dead arm and ripped it away from its body, dropping it on the ground. That could be done without. Even the loss of the solar panels wasn’t a deathblow. But the wheel and strut needed to be replaced. And soon. There was no way to know how long it could last.
The rover scanned its database. The closest machine to its location was a European rover lying defunct in the Solis Planum, nine hundred kilometers to the west. Its strut system was similar enough to the rover’s, at least as a stopgap until it could reach something more suitable. It might be able to make it that far before the wheel broke off completely. If it moved slowly, and avoided the rougher terrain. And got a little bit of good fortune.
And it didn’t have much choice but to try.
* * *
It took nearly a month to get out of the Melas Dorsa. Normally it would have taken just a few days. But the rover wasn’t capable of managing anything but the easiest terrain. It had to go north for many days before there was an opening to the west it could manage. And then it had to turn south again after only a few kilometers when its way was blocked by sharp cliffs that stretched all the way to the horizon. Days were spent exploring down narrow valleys, looking for a gap in the hills, only to find impassable walls or rocky fields it couldn’t manage anymore and turning back. All done at an agonizingly slow pace. Even with the help of the arm, its bad wheel kept deteriorating, putting more stress on the rest of the rover’s body. By the time the rover had found a path to the smooth ground below the Toconao crater, it couldn’t do more than ten kilometers a day.
The remaining wheels with the arm were compensating for the extra weight as best as they could, but the jarring up and down tilt of moving was causing havoc on the rover’s internal systems, loosening connections and bolts a fraction at a time. The effect accumulated and efficiency had dropped system wide. The rover had to shut down its gyroscope completely because its constant rolling was disorientating. That at least saved some energy, as the extra strain of the rover’s limp across the planet used up more than its already compromised solar panels could fully replenish.
The going was easier once out onto the hills to the west of the crater, and on through to the top of Solis Dorsa. The land was more fluid. Lines of ripples in the sand stretched east to west, and the rover rode along inside them like tracks, up and down the gentle inclines. The obstacles were minimal, only occasionally forcing the rover to reroute. The rover’s degradation slowed, but didn’t completely reverse.
Each night as it rested its beaten body, it continued to send its signal into the dark back home. And there was still no reply. The same ritual as always. Send the signal, wait for a reply. No response, send it again. No response. Run a diagnostic, send it again. No response. No contact. The same fruitless act, sending out a call into the black sky above, trying to get anyone to notice one lowly machine all alone in a vast, vacant wasteland. Its increased need for help didn’t change anything.
But then, halfway across the upper Solis Dorsa, the rover started to receive the beacon signal.
It was barely distinguishable from normal background interference at first, like some kind of natural occurrence. And at first the rover dismissed it as such. But as it slowly traveled westward it got stronger. After a week it was unmistakably artificial. Three quick beeps, repeated over and over. Every night exactly the same. It wasn’t the long awaited signal from home, but localized, coming from the Sinai Planum northwest of the rover’s location. The rover had no record of any probes, landers, or craft of any kind in that area. And no probe would have a need for a location beacon to begin with.
But a spaceship would, to mark its landing site for its crew to follow back from their expeditions around the planet.
The rover changed course and moved at a vigorous pace toward the beacon, pushing itself far more than was safe. It couldn’t be sure how long the ship would be there. As it was, it would take the rover weeks to reach it. It tried repeatedly both day and night to contact them, but there was no reply. They were deaf to the rover’s calls. Or ignoring them. Or possibly using a frequency for communication outside of the rover’s range. A change in communication frequency—that had always been an explanation for why it had not been able to contact home for so long. One the rover had long ago determined most likely.
But the reason ultimately was moot. What mattered now was that they could leave at any moment, without even knowing the rover was racing to meet them.
In just a couple of weeks, it was halfway there. The strain on its system had increased, and its batteries were slowly depleting. But the rover would not slow down. It moved even faster when it made it into the Sinai Planum, where the ground flattened out considerably. Each day bringing it closer.
The rover stopped trying to contact home. It monitored the beacon continuously instead, both day and night, looking for any variations in the pattern or a change in signal strength. Anything that would suggest the ship was preparing to leave before the rover could reach it. But the only change was that the signal was getting stronger as the rover approached. All night it would listen to that simple signal that confirmed the spaceship’s presence.
The rover reached to within one hundred kilometers. Then almost eighty the next day. Under seventy. Just a few more days. The rover risked a steep rise sixty kilometers from the ship because going around it would add another day, and nearly fell again going down the other side. But it was so close now. Fifty kilometers.
With forty kilometers to go, the rover ran straight through the night instead of shutting down and planned to do the same the next. It would bring its energy reserves dangerously low, but as long as the days were sunny and clear, the rover calculated it would have just enough left to get to the ship before the batteries were empty.
There was a haze in the sky both days, and the rover didn’t collect the energy it needed. It wouldn’t have enough to make it now. But the rover pressed on through the second night anyway. It shut down all systems not integral for travel, but that only saved a negligible amount. The beacon was only ten kilometers away. It couldn’t stop now when it was so very close. Through that last night, the rover’s energy dwindled, and it slowed even further, moving only intermittently.
A few hours before dawn, it could move no more and halted at the crest of a hill. One more revolution of the wheels and step of its arm would drain it completely and permanently. There was only enough left in the battery to keep its processors functioning at minimal. In such a weakened state, it had no control left—it barely had the processing power left to know there was anything to control.
The rover’s lens and arms fell limp at its sides, its traveling light went dark, and it disappeared into the black of night.
The morning sun rose and shined on the rover’s solar panels. By midmorning its energy reserve was back up to 10 percent, and the rover came back to life. The beacon signal was still there, strong as ever. And only three kilometers away, directly in front of it, down the hill and on the plain below. And with a few more joules of energy stored away, it would have enough to make it.
But when the rover scanned the area and spotted the craft, it determined there was no rush.
Copyright © 2020. Rover by A.T. Sayre