Project LOTiS

An addendum to TeamIndus’ Lunar Base

A NASA concept for an inflatable lunar base.

Recently, Team Indus writer Jatan Mehta (who is also the mastermind behind The Space Perspective publication) wrote an awesome article on Team Indus’ Medium publication about the possibilities of colonizing the moon. The article went into great detail about the benefits of setting up a permanent colony on our nearest celestial neighbor, as well as addressing many of the greatest challenges in doing so.

One challenge involved in erecting a permanent colony on Luna which was not directly addressed in the article is the connection between the cryogenic water ice located within the shadowed craters on the poles, and the lunar base itself. A permanent lunar base would require a constant power source. Because solar power is currently the cheapest and most reliable power source for near-sun space applications, building a base directly atop these ice deposits in the shadows of the craters would not be prudent. Instead, a Moon base would likely need to be located on peaks of eternal sunlight on either the North or the South pole of the Moon.

Craters of eternal darkness, located on the South Pole of the Moon. For our project, we chose Shackelton Crater as our point of origin.

The Lunar Environment

The challenge of autonomously transporting frozen ice across the surface of the Moon may seem trivial at first glance. We are already on the verge of developing self-driving semi trucks capable of following directions across hundreds of kilometers, coping with thousands of other vehicles on the road, and executing a series of complex decisions regarding potential hazards along the way. But there are some very important, non-trivial differences between the transportation of goods here on Earth, and the transportation of cryogenic ice on the Moon.

Whereas humans are here to stock semi trucks to make sure that everything is packed correctly, this luxury is not available on the Moon. Instead, cryogenic ice located in the lunar craters would have to be mined and transferred to our transportation vehicle completely autonomously, since direct communication with the Earth is impossible within the polar craters of the Moon. This ice is likely to not be purified at this stage, containing a sludge of both lunar regolith and water ice.

Once filled, this transportation vehicle would require the ability to traverse the distance between the polar craters and mountains amidst sticky, statically charged lunar soil. Unlike Earth dirt, which is thick and heavy, lunar regolith is very tenuous and fine. This regolith would stick to everything; cameras, solar panels, radiators, and other external components. This trek may be in excess of 100 kilometers along a path that isn’t paved, marked, or mapped.

Color-coded elevation map of our chosen ground path (red line) between Shackelton Crater and Malapert Mountain (~140 km).

After several hours or even days, this vehicle would need the ability to guide itself into an unloading zone where the sludge of regolith and water ice could be filtered somehow, and the remaining waste regolith could be emptied elsewhere on the lunar surface. This vehicle would then be required to make the return voyage back down the mountainside, into the dark crater, and back to the harvesters to start the process all over again. To ensure financial efficiency, this vehicle would need to be made sturdy enough to withstand years on the lunar surface, repeating this perilous trip perhaps hundreds of times.

Team LOTiS

In my senior year of aerospace engineering, I took a course called Spacecraft Systems, where we were divided into groups of six and allowed to invent a project of our choosing involving the course material. This was the challenge that our group tackled; theorizing and designing a near-future lunar vehicle capable of transporting 100 tons of cryogenic water per year from polar lunar craters to bases located on the peaks of eternal sunlight. Though out project was geared more towards the financial aspect of this lunar water (setting up a refueling post at Earth-Moon L4 or L5 to save money on deep space launches), the design works equally well in tandem with TeamIndus’ lunar base concept. We called ourselves Team LOTiS, or Lunar Transportation Services (Pronounced like “Lotus”. No one really knows what the “O” or the “i” stood for).

Team LOTiS’ logo, combining design elements of the lotus flower, and a crescent moon.

Among the first decisions that we executed as a group was deciding which method of transportation we would use to move 100 tons of cryogenic ice from the poles to the nearby mountains each year. We arrived at three viable options: rockets, rails, or rovers. Rockets require a source of fuel. This fuel could come from the water you are collecting by splitting it into hydrogen and oxygen, but this would ultimately detract from the collected volume of H2O for your lunar base. This, along with the fact that precision rocket maneuvers on the Moon would be difficult and dangerous, caused us to reject this idea. A rail system on the Moon would eliminate the potential hazards that a rover would face, such as regolith, craters, and boulders. However, constructing a 100+ kilometer rail system on the Moon would probably take years and cost more money than it is really worth.

This left us with one option; a lunar transportation rover. The next question we tackled was how big the rover should be. A simple case study showed that the larger we could make our lunar rover, the better. A larger rover requires less trips per year, thus inducing less wear and tear on the moving parts of the vehicle and increasing it’s lifespan. Our rover size was limited to existing or near-future space launch vehicles, the largest of which being NASA’s SLS Block 2 which can ferry a 10 meter long, 48,000 kg payload to a Trans Lunar Injection (TLI) orbit. This became our main design constraint.

NASA’s SLS Block 2 is the largest, near-future deep space launch vehicle.

To limit the chance of tipping over, we allotted a height of 4 meters from wheel base to roof. This constrained our cryogenic ice container to a spherical diameter of 2 meters to allow for a half meter of hull above and below the container for elemental protection, and a meter of ground clearance for potential lunar obstacles. This diameter is enough to transport about 17 tons of mixed lunar sludge, about 50% of which was assumed to be cryogenic ice. To achieve our goal of 100 tons of water ice, our rover would need to complete 12 trips to the polar craters each year.

Because our rover would be making trips into dark craters, we decided that our vehicle should be powered by a combination of both solar panels, as well as rechargeable lithium ion batteries for periods of darkness. After some research, we found that solar panels with efficiencies in excess of 40% would likely be commercially available within the next ten years. Using four, 2 x 3 meter sun-tracking solar panels (effectively taking up the length of our hull), our rover would have a power availability of about 15 kilowatts in times of sunlight; the power consumption of about 10 toaster ovens.

It is important that we have access to the full 15 kilowatts of power for the duration of our mission. Because the Moon has no atmosphere, we don’t have to worry about cloud cover or atmospheric sunlight variation. Instead, we had to worry about the sticky, positively charged lunar regolith which is constantly being kicked up by our wheels and wreaking havoc on all of the systems of the rover, including our solar panels. To rid of this regolith, a parallel electrode system can be used to create an unstable electric field which repels lunar dust away from critical systems.

Indium-tin parallel electrode regolith removing system (wow, that’s a mouthful). The left image is before the device is turned on, and the right is after.

Collected power would be divided between the active thermal control system keeping our electronics and our ice container cool in the sunlight (134 W), our on-board electronics and computers (295 W), our communication systems (35 Watts), our differential wheel motor controls (600 Watts), and our electric transportation engine (power usage varies with load & hill grade). Batteries would be charged from excess power while the rover is travelling down the slope from the mountain bases to the crater; this is when transportation power usage is lowest. Because of the extreme grades of travelling back up the crater walls and mountainsides with a full load of water ice, extra power from the batteries will be required in tandem with the solar panels to execute the return trip.

To ensure safe passage on the lunar surface, five radio towers would need to be erected on nearby lunar mountains to provide communication coverage to the rover between the crater and the lunar base. RFID beacons would be used on the lunar surface to guide the rovers along a pre-chosen path free of debris and heavy terrain. In the rare cases of meteor impacts or moonslides which could create unexpected terrain, cameras would be installed across the hull to provide information about the rover’s immediate external environment.

Map of coverage for 5 radio towers located along our path from before. Yeah, this is better than AT&T coverage.

Once the rover reaches it’s destination on top of the peak, it needs a way to deposit the water ice into a processing facility without the sludge of regolith which is mixed in. Simple. Just connect the rover’s ice container to a chamber at the base and turn off the rover’s thermal control system. Sunlight will heat the rover and the ice container until the water ice inside the container sublimates away into the vacuum of the chamber. Once all of the ice has sublimated into the chamber at the base, the only thing remaining inside the rover’s container is the waste regolith. This waste can simply be dumped at a safe distance from the facility with a hatch built into the bottom.

Our Design

Once all of the finer details had been worked out, we put it all together! After several iterations in our design, here is what we settled on:

Team LOTiS’ final rover design! On the left is an external image, and on the right is a semi-transparent view of the innards.

Let’s break the design down a little bit:

Labeled 3D models of our rover.

Such a lunar rover would be the largest object we have ever put on another world, having a dry mass of more than 8 tons. Each of the six wheels are taller than most human beings, and size of the structure is comparable to that of a construction dump truck. But it works! And we could actually get it to operate on the moon with near-future technology.

Size comparison between LOTiS and other space rover designs (also, our professor).

Conclusion

What does this mean for the TeamIndus lunar base concept? Just another reason that we should start packing! Our entire project emphasized the capabilities of just one lunar rover. With the aid of several LOTiS rovers, the needs of a human lunar colony could be easily met with enough water to spare to set up another facility dedicated to placing a profitable refueling post at Earth-Moon L4/L5.

Humanity’s future is in space. How fortunate we are to have such a pristine stepping stone as the Moon for our endeavor into the final frontier. For eons, humanity has looked to the stars, our drive for exploration fueled by the presence of our looming, unavoidable Moon. One day, bases all across the solar system may be erected for scientific advancement, profitability, and the survival of our species. But it all has to start somewhere. And what better place to begin that quest than on our very own Moon?

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