Earlier, we lamented the loss of Red Dragon and the precursor missions that might have been. But, perhaps we lamented too soon. Musk has been pretty clear that the first robotic ships on Mars will do things that are essentially precursor missions, just using a full-size ship instead of a Red Dragon. That makes our precursor missions a lot more interesting.
For starters, we want to keep risk manageable, and we only have so much time to program autonomous actions into the rovers. It seems likely, for example, that once those solar power fields are set up, the rovers won’t spend a lot of time amongst the panels clearing off dust. Too much can go wrong. We might need a contingency plan here in case of a major dust storm, but let’s set that aside for now.
This leaves the autonomous tractors available for exploring the local area, using a variety of scientific instruments—whatever we can fit on the trailer, and maybe even on custom trailers. We have two years, more or less, and can recharge the vehicles at will. (We might even want to equip the trailers with a solar panel once they’re done hauling cargo for now. Then, as we tow them around on excursions, we have an emergency charging capability to get back to the ships.) We might consider bringing the tractors back on board during Martian winter to minimize thermal cycling. It might also be worth bringing one on board in the event of a major dust storm. (We’d probably want at least one available on the surface for contingency ops.)
We should also ponder what sort of equipment would be appropriate for the aft cargo compartments. (In the new design, it looks like there are still three.) The upside of these compartments is that we can probably just drop things onto the Martian surface without breaking them. The downside is that they’re right next to the engines, so the vibrations are going to be insane. We’ll note these items as we go along, but we can identify one right now.
If it can survive the vibration environment, one piece of equipment we’d really like on the surface quickly is a suite of seismic instruments, so we can take advantage of the next ship’s landing to gather data about the local geology. Raptor engines blasting the surface and a solid thump of a couple hundred tons ought to beat a little seismic explosive charge. For redundancy, a twin set of instruments would be very desirable.
We want to understand the local geology for two reasons. First, it may be unlikely, but we’d really like to know if there are any voids that could threaten follow-on landings. The last thing we need is a beautiful 4K video from Constellation showing Heart of Gold breaking through the surface and tipping over on landing. Second, a major task for the first ships is to verify the presence of water/ice.
Musk has been explicit about this, but without any specifics. We have a couple options here. First is figuring out how much water is present as ice in the soil just below the surface, a few centimeters or so. Second is figuring out whether there’s actually liquid water farther below the surface.
For the first, returning to https://planetaryprotection.arc.nasa.gov/file_download/90/29-Sanders.Mars.ISRU.PP_Sanders.V2.pdf, slides 10 and 11 illustrate the sort of “small” prospecting gear we might use. And https://www.nasa.gov/sites/default/files/atoms/files/mars_water_isru_planning-hangout-5-24-16.pdf slides 11 and 12 give us a sense of how large an area, and how much depth, we might need to excavate. The presentation shows multi-centimeter depth, not multi-meter depth. This is extremely promising, since that suggests we simply need front-end loaders to get the “ore” we need to process.
Thinking about how this might work with the robotic precursor ships, our first observation is that we literally need a front-end loader, not a tractor with a robot arm. Specifically, we’re suggesting an industrial-grade vehicle, not anything remotely like a Curiosity or the Phoenix lander. Although it can be lighter construction than would be needed on Earth, at the low end, we’re looking at something from the Northern Tool & Equipment line (see: tractors); at the high end, the Caterpillar 900 series. This will be an electric vehicle, of course, and we’ll need to determine whether hydraulics can be an option at Mars temperatures. Since it will be electric, we probably want to drag a power cable out to the work area so it can recharge in between loads. That presumably means we also need a small robot arm on the loader so it can plug itself in. This has the added advantage that we can put the loader to dual use, picking up things we want to look at more closely, for example, a scientifically interesting rock. We might just look at it with the loader’s cameras, or we might bring it back for a true science rover to examine.
We’ll be loading some sort of (electric) dump truck, which will haul our cargo back to the ships for analysis. Eventually, they’ll be hauling this ore to a processing point next to Nostromo, but for now, we have a stationary lab that will determine the water content. We won’t actually do anything else with the product, yet, other than dump it in a convenient pile. Nevertheless, we probably want two dump trucks, so we can get a better sense of timing. The loader scrapes off a few centimeters of soil with each pass, loading the truck. The truck heads back for analysis. Meantime, a second truck is arriving at the loading point. The two trucks cycle between the loader and lab, primarily to let us verify the process, to include timing. For full-scale propellant production, should there be two trucks per loader? Three? Four? Keep in mind both loader and trucks will need periodic recharge. It seems the best way to be sure about this will be to first test the arrangement on Earth, and then verify it, day after day, on Mars. Of critical importance—determining whether the loader has enough power to actually scrape off those few centimeters, or whether the surface material is too hard. If it’s too hard, we’ll need some alternatives. For now, let’s assume the loaders will be successful, even if we have to take smaller bites. Watching the road and subdivision construction near my house, it certainly seems there are ways to mechanically break up hard soil. We can reexamine this assumption later.
Accessing ice will likely require removing a lot more overburden, which was also examined in our references above. Before we start digging deep, we’ll want to take lots of those surface samples to be confident this landing site can provide water from the soil. After that, then we can explore whether the site also has ice, and how deep it might be. Confirming ice would let us radically change our approach, dramatically reducing the amount of bulk ore to be processed—as long as it’s not too deep. See slides 10-13 in the “Mars ISRU hangout” pdf.
But, as long as we’re digging, we might consider whether we can combine activities. We have two years, after all. Once we have power to the ships, and we’ve established that the site has accessible water, what’s next? While there are plenty of possibilities for robotic ships, there’s one overriding concern for the crewed ships that will follow: radiation protection. Specifically, we might as well see whether we can dig a deep enough, large enough trench to place a hab brought by the first crewed missions. We could then process the removed material and use it to cover the hab. In the digging process, we will identify exactly what we’ll find a few meters under the surface, and incidentally bring tears of joy to planetary geologists everywhere.
Digging more than a few centimeters deep will likely require a jackhammer attachment on the loader. If you’re searching, try “hydraulic hammer,” but that reminds us of our earlier question about what sort of hydraulics will work at Mars temperatures. We’ll set the hydraulics concern aside for now, just noting that we need some way of breaking up the surface. Zubrin recommends explosive charges, which might also be a good thing to test out before we have people around.
Arguably, though, a better solution is to drill for water. We’ll talk about that next.