One of the major limits of mass-produced batteries is the electrolyte. From lead-acid to lithium ion, there’s some temperature where the electrolyte will freeze and cause all sorts of problems, from cracked casings to various non-favorable chemical changes in the battery itself. But if there’ a solid electrolyte available, many of the downsides of charging and discharging batteries in extreme cold disappear. These batteries developed by NASA, for example, can survive some wild temperature swings.
The electrolytes used for these batteries are either a ceramic or polymer electrolyte, both of which are solid. In testing, the batteries could meaningfully operate at temperatures of -60° C and up to 80° C on the high end. Further, the solid electrolyte helps protect them even outside of these temperature ranges. Bringing the battery temperature down to -170° C was not enough to damage the battery at all, and using a small heater to bring the temperature back up to its operating range showed no capacity losses or other issues.
These batteries are eventually intended for use in some of the coldest places outside of Earth still accessible to humans (in theory) such as the south pole of the Moon where the temperatures regularly get that cold and stay cold for long periods, especially in permanently-shadowed craters or places on the Moon we might want to put some telescopes eventually. There are other terrestrial situations where these batteries might be useful as well, since they don’t need as much thermal management as other battery types.
Humanity has been sending robotic explorers to Mars since the 1970s, and for our efforts we’ve been rewarded with not only incredible imagery of the Red Planet’s magnificent desolation, but a wealth of information about the alien world and how it’s changed over the last several billion years. But comparatively, we know almost nothing about the planet’s two moons, Phobos and Deimos. In fact, as recently as the 1960s, there were some scientists that believed the unusual shape, mass, and orbit of Phobos hinted at the possibility that it was no moon at all, and was in actuality a derelict spacecraft of some type.
Martian Moons eXploration Spacecraft
Once the first Viking probes arrived at Mars, we had the photographic evidence and up-close measurements to prove that Phobos wasn’t artificial. But even today, we still don’t know exactly what it is. The data suggests that it’s not solid rock, and that large voids may be hiding under its surface. While we can be fairly sure there won’t be any mummified remains of Martian astronauts to be found within Phobos, vast deposits of ice are a tantalizing possibility.
With the launch of the Martian Moons eXploration (MMX) mission earlier this week, the Japan Aerospace Exploration Agency (JAXA) hopes to bring us one step closer to understanding the formation and structure of Phobos. Should everything go to plan, MMX will deploy a small rover to its tenuous surface in 2029, and by 2031, a sample return capsule will bring pieces of the mysterious moon back to Earth for further study.
A Delicate Operation
It’s only natural that we’d imagine Phobos and Deimos to be similar to Earth’s moon, but the reality of the situation is very different. For one thing, the Martian moons are absolutely dwarfed by our nearest celestial neighbor. Phobos has a diameter of just 22.2 kilometers (13.8 miles), and Deimos is even smaller at roughly 12.6 km (7.8 miles). For reference, Luna is approximately 3,474 km (2,159 miles) across.
Due to their low mass, putting a spacecraft into a stable orbit around either of the Martian moons isn’t really an option. Some clever maneuvering will put the MMX mission within range of both Phobos and Deimos at different points during the mission, but it won’t be able to stay around for long.
As such, final approach to Phobos will look more like a slow-motion “crash” than a traditional landing. A close comparison would be the OSIRIS-REx mission, where the spacecraft effectively “bumped” into the asteroid Bennu while collecting its samples. The impact velocity will need to be very low to prevent the spacecraft from bouncing off, and even then, some reports indicate that JAXA expects the craft to make at couple of hops before finally settling down.
The situation is compounded by the fact that we still don’t know what the surface conditions are like on Phobos. Based on previous observations, it’s expected that the moon is covered with a layer of fine regolith that could make traversal difficult for the mission’s Idefix rover. Indeed, one of the rover’s primary mission goals is to determine if wheeled motion in such an environment is even viable.
Tiny Moon, Huge Potential
Landing a crewed vehicle on Mars and successfully bringing it back home afterwards is perhaps the most daunting engineering challenge ever conceived. There’s even a solid argument to be made that it’s currently beyond our technological capabilities. The energy requirements of making a propulsive landing on the planet and then lifting off and getting back into orbit are enormous, and will very likely require in situ propellant production to refuel the craft between the two phases of the mission.
Landing on Phobos or Deimos however would require a small fraction of that energy. Moreover, due to their low orbital altitude, the moons would make ideal outposts from which to make detailed observations of Mars. This close proximity to the planet also means human operators on Phobos could directly command robotic vehicles on the Martian surface without the transmission delays that make real-time telerobotics from Earth impossible. While such a mission might not have quite the same symbolic impact of actually putting boots on Mars, it could be a valuable stepping stone towards that eventual goal.
The viability of such a landing may well depend on the findings of Japan’s Martian Moons eXploration mission. Not only in terms of the actual mechanics of rendezvousing with Phobos and touching down on it, but should the mission succeed in returning surface samples, we may be able to confirm whether or not the moon is made from ejected Martian material. Should that be the case, there will likely be even greater interest in studying the planet’s strange little moons up close.
One could make a joke about how an astronaut walking on the lunar surface is rather akin to a cat walking on the carpet in the living room, but out in space the resulting triboelectric discharge can do a lot more damage than just some stinging fingers and a bemused looking cat.
The problem that NASA and other space agencies are dealing with is that the charge that builds up on a lunar-walking astronaut is very hard to equalize with something like a lunar lander. For this reason they have now set up the Lunar Grounding Challenge to consult the public whilst dangling $150,000 of rewards in front of anyone ready to pounce with a good idea.
Here on Earth we got many ways in which we can get rid of such an unwanted charge, with dry winter weather demonstrating quite effectively why humidity is a crucial factor here. With no real atmosphere on the Moon, each astronaut thus becomes a walking capacitor, which is worsened when said astronaut ventures outside of the sunlit areas and then returns to the slightly positively charged lander.
The challenge here is thus to equalize the astronaut and lander, with a design specification of a -100 kV or higher astronaut and about 100 V lander. A resulting current should not exceed 1 mA, ideally less than 0.2 mA to remain below human perception levels. If an arc exists it should not contact the suit or astronaut.
Of course, the most low-tech solution would be to use a resistor to limit the current, but at those voltage ranges it would take an awful long time to bleed off, in an environment that’s basically a perfect insulator as space will never be cold. It definitely seems like a fun challenge to sink one’s fangs into.
As NASA continues humanity’s slow march back to the Moon, different pieces of the puzzle of establishing a more permanent base there are falling into place. One of these pieces is the the Lunar Terrain Vehicle (LTR), and [Cleo Abram] and [Michelle Khare] got a look at the LTR candidate from Lunar Outpost.
Designed to help astronauts traverse the lunar surface as well as function as a semi-autonomous rover when uncrewed, the LTR will be an integral part to any future Moon base. NASA announced earlier this year that it would be moving forward with the LTR featured in this video and another from competitor Astrolab. Regardless of manufacturer, the LTR will have to deal with some wild conditions in the lunar environment.
Lunar dust is abrasive, so the LTR generates an electric current to pull the dust under the truck to prevent it from entering the cab of the vehicle as it moves along. Given the extreme temperature swings on the moon (-200˚C to 200˚C), the space truck will also be fitted with wire mesh tires as nobody wants to be changing a flat in space. The two seats in the cab are oversized and can help lift the astronauts up as space suits hamper their agility to a significant degree. There are compartments for storing samples, and the truck has a robot arm that can grab samples to bring back if no one is along for the ride.
Although for many decades the planet Mars has been prodded, poked, driven upon, flown over and especially orbited by various spacecraft, landers and rovers sent over by a certain humanoid species on Earth, the two moons that orbit Mars have featured significantly more in science-fiction and video games than in scientific literature. This is now about to change when the Martian Moons eXploration (MMX) mission launches on October 19th, which will include a sample return from Phobos.
So far these two moons of Mars – Phobos and Deimos – have only received a few cursory glances by passing spacecraft, leaving many fundamental questions surrounding their formation and composition very much open. With the MMX mission this should change dramatically, with this spacecraft intended to perform detailed measurements of both moons.
In addition a rover – called Idefix – will perform a landing on Phobos for observations of its surface. This will be quite a feat as despite this lander coming in at 25 kg, on Phobos’ surface it will weigh only 15 grams due to the low gravity, or even less than the diminutive dog companion of Obelix, with potential bouncing as we have seen with previous landing attempts on such small bodies.
After launch, the MMX mission will take a year to arrive at Mars, in August of 2027, with Idefix being released in early 2029 for its hopefully soft paws-down on the surface of Phobos where it can scurry about for a while until the main MMX spacecraft lands later for its sample retrieval and return part of the mission. If everything goes well, this would mean that a sample of Phobos should be landing in Australia in 2031.
You’ve probably heard of Mars Pathfinder, the NASA lander and its Sojourner rover that took up residence on Mars in 1997. At first, all was well, but after a few days, the lander suffered a series of total system resets. A watchdog timer detected a problem and forced reboots. [Vivek Bhageria’s] recent post looks into what happened and the eventual solution.
The root cause was priority inversion. This happens when a lower-priority task holds a resource needed by a higher-priority task and prevents the higher-priority task from executing. In this case, the operating system was VxWorks, but this can happen on any kind of priority scheduling system.
The simplified version is that there were two tasks that each used the same mutex to avoid stepping on each other. The highest priority was a data distribution task. The lowest priority task dealt with meteorology data processing. There was also a medium-priority task that handled bus maintenance.
The failure would occur when the low-priority task had the mutex and lost its time slot before releasing it. The high-priority task would then find it couldn’t take the mutex. However, the low-priority task didn’t get control again because of the medium-priority tasks waiting to run.
In effect, the high-priority task was now waiting on something that couldn’t become available until the lowest-priority task was able to run. That’s priority inversion.
Sadly, engineers noticed this happening occasionally during testing but, as we are often prone to do, they chalked it up to glitches. As one of our old bosses used to say: “If you don’t know why it happened, then you don’t know that it won’t happen again.”
VxWorks, of course, understands that this might happen and, luckily, there was enough capability on the spacecraft to turn priority inheritance on for the mutex in question. This allows the low-priority task to get a boost because a higher-priority task is waiting on it.
You can read more about the details in the post. We also covered this a decade ago with our own analysis.
Login
