# Strategies for Deploying a Sensor Network to Explore Planetary Lava Tubes
## 1 Introduction
### Potential Utility of Lunar Lava Tubes  
These holes have high potential as resources for scientific study as various important geological and mineralogical processes could be uniquely and effectively observed inside these holes. Although exposed lava layers could be observed on the inner walls of craters and rilles, they are covered with regolith from the surface. However, since the inner walls of these holes are nearly vertical, they exhibit fresh surfaces with a much larger section, thereby preserving more lunar volcanic history. Moreover, there is a possibility of water storage inside these lunar holes. Hydroxyl and/or water molecules can be produced by reactions of oxygen-bearing lunar materials and solar-wind protons [7]. A very speculative estimate is made for the maximum column density of the protons inside MHH, MTH, and MIH to be 0.24, 0.24, and 0.19 tons/m\({}^{2}\), possibly corresponding to water molecule densities of nearly 2.1, 2.2, and 1.8 tons/m\({}^{2}\)[8].  
In addition to scientific interest in geological and mineralogical studies, lunar holes are excellent candidates for the placement of future lunar bases. For both unmanned and manned activities on the surface of the Moon, one of the most serious concerns is radiation damage due to solar and galactic cosmic rays (SCR and GCR). On the lunar surface, the doses of radiation exceed the allowance limit of 1.2 Sv per lifelong for JAXA astronauts (\"JAXA radiation control guideline for astronauts of the International Space Station\" 2002), and far in excess of the annual dose recommended by the United States Nuclear Regulatory Committee (1 mSv/yr) (\"U.S. Nuclear Regulatory Commission Regulations: Title 10, Code of Federal Regulations, Subpart D\" 1991). Due to the limited field of view (FOV) from the bottom of these holes, they can definitely reduce the effects of cosmic rays. For a hole of the same scale of depth and diameter as MHH and MTH, the amount of GCR, including protons and heavy ions entering the hole, is less than about 10% of that striking the surface. The total dose rate of p-GCR at the floor would be less than 10 mSv/yr. The rate of n-GCR induced by p-GCR (protons and heavier ions) and heavy ions would be a maximum of several tens of millisieverts per year during the worst days at solar minimum [8]. In addition to irradiation by cosmic rays, meteorite impacts and temperature fluctuations pose a threat to astronauts and instruments operating on the lunar surface. Lunar holes would provide good protection from space particles, with the damage probability at the bottom of the hole an order of magnitude less than that on the surface. The holes will also guard astronauts and facilities from the danger of hyper-velocity secondary impacts of ejecta that are splattered by primary impact events. The lunar surface temperature varies widely, for instance, 102 K to 384 K at the Apollo 15 landing site in the Hadley rille (26\({}^{\circ}\) N, 3.6\({}^{\circ}\) E) [9] and 92 K to 374 K at the Apollo 17 landing site in the Taurus Littrow valley (20\({}^{\circ}\) N, 30\({}^{\circ}\) E) [10]. However, the temperature in a shadowed portion of the hole bottom ranges from 253 K to 303 K (\(-\)20 \({}^{\circ}\)C to 30 \({}^{\circ}\)C) in one lunar day, but the temperature ranges from \(-\)170 \({}^{\circ}\)C to 110 \({}^{\circ}\)C at the surface [8]. If the floors permit mobility, one can secure even smaller doses of radiation, lower probability of damage from meteorite impacts, and smaller temperature variations.