Safe Two Hundred Person L5 Space Station

Pekka Janhunen, who designed the electric sail, has proposed a 200 person L5 space station that would have safe long term radiation shielding and rotate for one G of gravity.

The proposed station would weigh 89000 tonnes and provides 60 square meters (646 square feet) of floorspace per person. The radiation shield is made of asteroid rock, augmented by a water layer with 2 % of the mass for neutron moderation, and a thin boron-10 layer for capturing the thermalized neutrons.

Nextbigfuture notes that just bundling 12 Starships in place of each sphere would have a similar volume. The old proposals for using Space Shuttle Fuel Tanks again show how a Starship shortcut for minimal construction could be done. SpaceX Starships are made out of steel, so welding and cutting the steel could be manageable. The outer Starships could be filled with supplies, water and fuel which would make it easy to create the radiation shielding.

Al Globus and Strout used the OLTARIS tool to simulate the GCR (Galactic cosmic rays ) equivalent radiation doses (millisievertrates) behind various thicknesses of different materials. They recommend 20mSv/year as the equivalent dose level during the solar minimum when the galactic radiation is at maximum.

20 mSv/year shield using 2 % of water.
Material   Thickness   kg/m2          Role   
Iron         2.3 cm    180         Structural wall
Dry regolith 3.34 m    8683        Shield
Water        17.7 cm    177        Neutron moderator
Boron-10      0.4 mm    1          Neutron absorber
Total         3.5 m     9041

Globus and Strout also require that the absorbed dose for pregnant women be less than 6.6 mGy/year, or 5 mGy per pregnancy. This condition is satisfied since the absorbed dose at the center of the sphere during solar minimum is 4.0 mGy/year.

If SpaceX Starship reaches $30/kg, the first 200-person settlement could probably be built without space manufacturing. Each settler might need initial capital of∼$21M. Space Manufacturing and space resources can reduce the cost of the station by a factor of four.

SOURCES- Arxiv Pekka Janhunen, SpaceX Starship alternive by Brian Wang
Summary Written by Brian Wang, Nextbigfuture.com