Project Persephone

Tunnel boring machines (TBMs) are, of course, mainly used for large tunnels, big enough for car or train traffic. But there are TBMs that create tunnels as narrow as one meter. The one shown above was deployed to dig a sewer channel. These narrower TBMs have been used in small hydro power projects in the mountains of Norway, but also other places.¹ For a way to establish a projectile space launch tube under the slope of a high mountain near the equator, TBMs could excel. Unlike blasting a tunnel, the process is largely automated, and can produce a very smooth, straight channel. Almost certainly, you'd need to a tunnel lining that protects the sabot of a projectile space vehicle from the rock, but this process could also be significantly automated, by using metallic 3D printing in a "pigging" operation, such as used in oil pipeline metrology and cleaning.

Although projectile space launch arguably has little or no practical military use, there are still issues of arms proliferation with the idea, and the TBM may add to them. Projectile space launch requires energy expenditure so much like artillery, and requires at least a kickstage for orbit circularization. So it will bring in arms control questions anyway. However, the use of TBMs to establish such launch is not without military significance itself. Tunnel boring can be used by both insurgencies and in counter-insurgency operations.² Mountainous regions near the equator are both refuges and theaters of operation for insurgent groups. Project Persephone needs to stay aware of how many of its proposed technological elements are dual-use, and TBMs bid fair to be a candidate for scrutiny and for discussion with formal military agencies.

¹ https://trenchlesstechnology.com/small-diameter-tunneling-at-steep-gradients-for-mini-hydro-projects/ ⇑

² https://mwi.usma.edu/the-eight-rules-of-urban-warfare-and-why-we-must-work-to-change-them/ ⇑