If we were reasonably sure there’s liquid water within a few hundred meters of the surface, then bringing along well drilling equipment would be worth the substantial mass required to obtain it. A fair amount of research has been done on this topic; for an excellent primer, see “Drilling Operations to Support Human Mars Missions” (Frankie, Tarzian, and Lowther: 1998, Pioneer Astronautics) for a discussion of one proposed approach, along with some of the challenges. That paper assumes a fair amount of well drilling knowledge, so let me provide a couple introductory items I learned from more Earthbound resources before sending you off for this homework. The site https://www.drillyourownwell.com is dedicated to just what it sounds like—hand-drilling very shallow irrigation wells with extremely simple equipment. Alas, we discover the most critical ingredient for water well drilling is...water. As the drill bit cuts through the ground, water is used as a “drilling fluid” to wash the cuttings up to the surface. Water can also be mixed with bentonite to make “drilling mud,” which is more efficient, but it still needs water.
A quick side note here—recall the movie, “Armageddon,” in which a team of professional oil well drillers, including Bruce Willis, [spoiler alert] save the planet by becoming erstwhile astronauts, drilling a hole into an asteroid, and dropping a nuke down the shaft. They didn’t use any drilling fluid in the movie, which raises the question—how did they get the cuttings out of the hole? They could have used something as simple as pressurized air, since the asteroid had almost no gravity, but the story didn’t consider the problem at all. We don’t get the luxury of Hollywood writing.
The Pioneer Astronautics paper proposes using liquid CO2 as a drilling fluid. This requires that the well be pressurized, but it turns out that’s not unheard of. The proposed well also uses a non-rotating shaft with a hydraulically powered rotating drill head. At Drill Your Own Well, there’s a great video of a rotating shaft, but a little online research reveals that deep drilling often uses a stationary shaft and then has a complicated, hydraulically powered drill bit on the business end of the well. In Pioneer’s “Drilling Operations,” liquid CO2 is used as the hydraulic fluid to power the drill bit as well as being the drilling fluid. CO2 requires about five atmospheres to maintain liquid form, or about 75 psi. The proposed well uses a four inch borehole, minimizing the amount of force we need to counterbalance. (Warning: researching well drilling online is likely to cost you as much time as using Google/Bing maps and wondering, “Where does that railroad track go?”)
A final introductory aspect is that drilling mud is important to balance the weight of the drill string—the mud provides buoyancy for the drill pipe and drilling head.
The paper is available at https://marspapers.org, but unfortunately does not include any of the figures or tables referenced by the text. (I asked Pioneer Astronautics for a complete copy, but received no response.) Still, with careful reading, we can get a pretty good idea of what the authors were thinking 20 years ago under a very different reference architecture. To avoid too much repetition, the rest of this post assumes you’ve read it. It’s worth the time.
Welcome back. A couple items immediately come to mind from the Pioneer Astronautics paper. First, a Starship-based architecture makes this approach eminently feasible, even early on. The aft cargo pods of a Starship seem like a perfect place for a wellhead, and the overall mass of a Starship means the vehicle can handle the 10,000 psi expected of a “kick.” With a four inch borehole, the kick will produce about 62 tons of force—a Starship logs in at 100+ tons. Of course, we’ll need a better understanding of how kick forces operate in 0.4 gee, but we seem to be in the ballpark.
Further, the power requirements for the proposed drilling operation are actually quite feasible with solar power given the enormous capacity of Starship. We should also be able to bring more bits than proposed, more pumps, and more tools—also the sort of equipment that would likely be quite happy in aft cargo compartments. The proposed plan budgets just over seven tons for drill pipe, so we can easily bring more, and potentially trade more mass for greater corrosion resistance, if desired. And, in addition to the capacity of our primary drill ship, drill pipe certainly seems like the sort of non-complicated cargo that a bare-bones Starship freighter might haul.
There is the issue of how to connect the wellhead to our drilling platform. Starship’s cargo bay should be reconfigurable to support the operations described in “Drilling Operations,” to include pressurized operations, crown block and draw works, additional drill pipe, etc. The mud pump and baffles would be set up on the surface, since the cuttings will need to be periodically dumped. The one problem is that Starship has a pair of very large tanks between the aft cargo compartments and the main cargo compartment, so the drill ship will need a special configuration. It seems relatively straightforward to modify the tanks with a six inch (or so) raceway from top to bottom to allow the drill string to pass through. There doesn’t seem to be a particular reason why the drilling equipment can’t simply be positioned in line with one of the aft cargo compartments, thus minimizing changes to the engine configuration.
The second item immediately obvious from the Pioneer Astronautics paper is that we first need to establish the presence of liquid water deeper below the surface. The “strip mining” option seems to be something we can verify as a precursor mission, which means it’s automatically available as a backup. But, before we send a Starship (or two) with well drilling equipment, we really need to be sure there’s water down there. That means more than a couple seismic instruments; we’ll need a whole suite of gear. That’s up next.