Tube v Pit

 I admit, I’m not a fan of the pit.

Smithsonian Magazine reported on the recent research paper: Thermal and Illumination Environments of Lunar Pits and Caves:

The Moon is known for its extreme surface conditions, with temperatures dipping well below negative 200 degrees Fahrenheit at night and above 200 degrees Fahrenheit during the day. But the harsh lunar environment just started looking a bit more welcoming after a recent discovery found that the satellite's underground caves and pits keep a consistent temperature around 63 degrees.

A team of scientists studied these lunar pits across a football field-sized area of the Moon's Mare Tranquillitatis, or “Sea of Tranquility”, reports Shauneen Miranda at NPR. In their study, which was published in Geophysical Research Letters in July, they document how the pits that form above caved-in lava tubes create potentially ideal conditions for human habitation under the lunar surface.

I have heard more than one space enthusiast say that we now have new evidence that lava tubes are much warmer than we thought – 63 degrees F! No, no, no, no, they didn’t exactly say that. Lava tubes or caves without skylights (aka pits) have a much colder stable internal temperature of around -20 C (-4 degrees F).

I also have a problem with the wording “…the pits that form above caved-in lava tubes create potentially ideal conditions for human habitation under the lunar surface”. I don’t think pits create potentially ideal conditions for human habitation under the lunar surface. I’m okay with saying that “some equatorial lunar pits potentially create ideal stable temperatures for a considerable distance on either side of the tube underneath the pit”. The farther away from the equator, the less direct sunlight reaches the floor of the pit so they wouldn’t get nearly as warm as the Tranquillitatis pit which is right smack on the equator. So why would a lava tube near the lunar equator with a large hole in the roof not be ideal conditions for human habitation?

Let me compare Tube Town (my imaginary lunar base) to a lunar base under the skylight in Mare Tranquillitatis.  

Tube Town

Features:

• Drive-in entrance in Eudoxus crater which contains sintered launch pads and propellant tanks
• Unpressurized motor pool that protects humans, bots and rovers from micrometeorites and radiation while being charged and repaired
•  The unpressurized section at the far end of tube provides secure cold storage for water ice, volatiles, food and other supplies
•  Two human airlocks (each with capacity of 12 people) and de-dust mitigation area 
•   One giant airlock in the middle of the waterless concrete first wall accesses the high bay for     spacecraft 
• Five pressurized living areas (160m tall ceiling and 400m wide on average) at nearly 1 atm of pressure and warmed to avg of 68 degrees F. (Factory 600m long, Commons 400m long, Recreation 200m long, Quarters 200m long and Farm 400m long) totaling around 500,000 cubic meters of pressurized, dust-free usable space, in shirt sleeve conditions

Mare Tranquillitatis Pit

Features:

•         Two 100m elevators for transport of all people, supplies, and equipment from lunar                       surface down to floor of the pit
•         Two unpressurized tubes either side of the heat sink
•         No airlocks, no de-dust
•         A collection of pressurized inflatable habitats and structures (brought down the                               elevators)
•         62 degrees F but spacesuits must be worn when outside the habitats. Small hab for                         growing food, small hab for recreation, small habs for sleeping quarters 

Which one sounds like ideal conditions for human habitation under the lunar surface?