modular radiation buffers

Here's something that's been lurking in my idea file for a while, and
I don't seem to be doing much with it, so I may as well throw it out
here for your consideration.

Problem: we can't put enough shielding into a space suit to protect
workers in open space -- not by a long shot. Outside work can be
suspended during solar flares, but cosmic radiation is constant, and
has cumulative health effects. Anything we can do to protect workers
while in open space will lead to improved health, or longer allowed
construction times per worker, or both.

This idea is to build partial radiation shelters in open space by
connecting large triangular shields (or "buffers") into any desired
configuration. The buffers should be cheap to construct, and provide
not only radiation shielding, but some other services as well (such
as power outlets and a stable work platform).

Thickness
Space construction workers may be considered radiation workers; U.S.
standards (at least in the 1970s) limited such workers to 5 rem/yr
(http://www.nas.nasa.gov/About/Education/SpaceSettlement/spaceres/
II-1.html). The buffers are designed of such a thickness that, if a
worker were completely enclosed by them, his exposure would be less
than that (ignoring for now the gaps between the buffers). This
requires 280 g/cm^2 of shielding mass (ibid).

Lunar regolith has a density of 1.7 to 1.9 g/cm^3 (http://
est.msfc.nasa.gov/workshops/LRSM_docs/Day1/Batiste.pdf, which sites
Scott, 1987). Taking the low end of this range to be conservative,
this yields a thickness of 165 cm.

Construction
The large buffer triangles would be built from a latticework of small
aluminum (or other convenient metal) triangles, connected together to
form a three-dimensional mesh or cage in the shape of the buffer.
The inside of this cage would be filled with bags of lunar regolith.
Cables and tubing, as needed, would be run along the three edges,
inside the mesh. Finally, a vertex unit would be attached to each of
the three main vertices of the buffer triangle. Each vertex unit
includes several power sockets, an Ethernet port, a powered cable
winch, and small RCS thrusters.

Buffers would be assembled in space, from small components delivered
by ship or mass driver from the lunar surface: palettes of smaller
triangles (perhaps 50 cm on a side), bags of regolith, and the
cabling and other fixtures. We should find some way of snapping the
smaller triangles together that can be done quickly by hand, yet will
hold strong -- perhaps with something like U-shaped brackets and pins.

Note that the mesh of small triangles means that every buffer
provides a very useful surface, covered with places to clip on a
safety line, lamp, or any other equipment.

Configuration
A single buffer is useful by itself, as it can shield workers near it
from a portion of the sky, and provide a platform with simple station-
keeping capability (via its RCS). When more buffers are available,
they can be assembled into larger configurations as follows. First,
a worker connects a small (probably palm-sized) computer to the
desired buffer, either wirelessly or by plugging into one of its
ethernet ports. It uses this to activate the buffer's RCS, flying it
over to the general area of the existing buffer structure and
bringing it to an approximate stop. Then a cable is extended from
the winch of the existing structure, and a worker attaches this to
the corresponding vertex of the new buffer; this can be repeated for
other vertices as needed for the desired configuration. The winches
are then activated to reel in the new buffer and hold it firm.
Finally, workers visit each vertex and connect the power, networking,
and gas lines, to integrate the new buffer with the existing buffer.

By suitably choosing which vertices are connected to which others,
almost any shape of protected space can be created. (Though this
point needs to be explored in more depth.)

Comments?

Joe Strout
Inspiring Applications, Inc.
http://www.InspiringApps.com