[ExI] Fwd: Village in space, was marmalade agenda

[Keith Henson]

For the last few months I have been skipping the posting from this
group.  But if you happen to wonder what I have been doing . . . .

I think there is only one of you (Spike) who follows this on power
satellite economics.

Best wishes,

Keith



---------- Forwarded message ----------



On Tue, Nov 1, 2016 at 8:33 AM, Jim Plaxco <JimPlaxco at chicagospace.org> wrote:
> On 10/31/2016 8:00 PM, Keith Henson wrote:

snip

>> _If_ we can start out building power satellites from the ground and
>> make a profit doing so, such a foothold might lead in directions of a
>> lot of people living out there and tapping asteroids or the moon for
>> resources.
>
> Or it may be through the use of zero-gee research and manufacturing that
> yield high value knowledge and/or products.

So far this has failed.  One of the more promising projects was
growing large hard-to-crystallize proteins in zero g so the structure
could be determined by X-ray crystallography.  Alas, the people
involved delayed getting around to doing it for so many years that an
alternative method, femtosecond lasers, was developed that gets
entirely around the need for large crystals.

>> There needs to be some physics done before the artists get on it.
>
> Since when have artists needed physics?  ;-)

Point taken.  :-)  A physics correct Pegasus with a 7 foot long
breastbone would be something to behold.

A counter example though is Don Davis who is devoted to getting the
physics right in his paintings.  I can't find the art, but we had a
discussion decades ago about the radiators and I think he produced a
version of the Bernal Sphere that got the radiators right.  (The X
cross ones are not an optimal solution because they "see" each other
instead of deep space.)

Long travel times are dictated by orbital mechanics and reaction mass
efficient spiral orbits.  The travel time makes it desirable to keep
the workers in space for years to decades.  If we are going to have
people in space for long times, we have to provide artificial gravity
and shielding.

The two interact.  If we need a large radius to keep the rotation rate
down, the minimum size goes up and the efficient use of shielding goes
down.  "It is generally believed that at 2 rpm or less, no adverse
effects from the Coriolis forces will occur, although humans have been
shown to adapt to rates as high as 23 rpm.[6]"
https://en.wikipedia.org/wiki/Artificial_gravity

For the same thickness of shielding, the Stanford Torus used a lot
more mass than the Bernal Sphere designed the same year.  (Roughly the
area of a torus to a sphere.)  Mined from the moon or asteroids, mass
is relatively inexpensive.  Brought up from Earth, it's relatively
expensive.

For construction-worker housing, there is a long list of
considerations.  We need to start with some estimation of how many
people and how many cubic meters they need.  For example, 11 cubic
meters is considered the minimum in the UK for working space.

http://www.hse.gov.uk/contact/faqs/roomspace.htm

The ISS and an Ohio Class Subs have 152 and 42 cubic meters person respectively.

http://www.milsf.com/ship-size-tonnage-and-crew/

We have to pick a number for the size of the habitat and the
population--just to get some numbers for the artists.  For a first
try, how about 1/10th of the diameter of O'Neill's Island One?  That
was 500 meters diameter and held about 10,000 people.  For this one, I
am going to assume 50 meters and 400-500 people.  That makes the
radius 25 m, the spin rate 5.98 RPM, and the volume 65450 cubic
meters.  If the population is 400 people, they have163.6 cubic meters
per person.  For a population of 500 it would be a bit over 130 cubic
meters per person.  If the people come up 100 at a time inside cargo
stacks, 400 (in 4 cargo stacks) might be the starting population.
That gives plenty of cargo mass (60,000 tons) for the habitat and
construction frame.

The surface area of a 50-m sphere is 7854 square meters, requiring
40,000 tons of shielding or about 1.2 power satellites worth of mass.
At the density of water, the shielding would increase the size of the
outer sphere to 60 meters.  If we animate it, we have to decide on
rotating or stationary shielding.  I am inclined to stationary
shielding, but really stationary, not rotating backwards slowly, means
we have to build a second habitat shell without shielding to counter
the momentum from spinning up the first one.

The habitat spin axis has to be equatorial N/S to avoid gyroscopic
torque issues, i.e., parallel to the Earth's axis.  10,400 km altitude
is about in the middle of the Van Allen belt gap and a 6-hour orbit.
Not sure this makes a lot of difference, but it will keep the space
workers in sync with the ground if their working times depend in any
way on the direction of light.

The habitat location in the construction frame will be on the near
(Earth) side because new power satellites spiral outward.  In the
artwork we will show two of them, one with and one without shielding.

The North direction will have a concentrating mirror focused on the
axis of the habitat.  The light level inside is set at 400 watts per
square meter with reference to the central cross section, or about 800
kW.  That's enough for plants (salad greens only; most food comes up
with the power satellite parts).

The habitat also needs power to run fans, pumps, a few lights and a
lot of computer workstations and low latency teleoperator stations.
Detailed design will modify this, but I am going to initially figure a
kW/person load or ~400 kW.  Assume 40%-efficient concentrated PV that
is 1000 kW input, which adds to the 800 kW from the raw sunlight
input.  The cells will be on a flange around the window and rotate
with the habitat avoiding slip rings.  For light concentrated to 100
kW per m^2, the window and PV flange would have an area of about 18
square meters, the window being 3.2 m diameter, the flange with PV and
water cooling, 5 meters.  The concentrating mirror would be 47.7 m,
but 50 m is close enough for the artwork.

The cooling loop has to reject ~1800 kW.  If the radiator runs at 20
deg C, the rejection rate is 400 W/m^2, making the radiator area ~4500
square meters.  Eventually the second habitat will get shielding and
be occupied, so the total radiator area for the two of them will be
~9,000 square meters.  To make the analysis simple, the radiator will
radiate only one direction with non-imaging type reflectors so all
sides of the radiator pipes see 2.7 deg K.  This assumes low-
pressure, condensing steam as the working fluid, and tapered radiator
tubes.

It will take an extensive fault tree analysis to determine what might
fail and what the habitat spacing should be to keep one failure from
propagating to the other.  For the present, the center- to-center
distance on the habitat spheres will be set by the radiator dimension
of 67 m square x 2 or 135 m.

Depending on the time of the year, the Sun will be eclipsed part of
the time by the Earth.  Worst case, the Earth subtends 2 times
sin(6300/16,770) or 44 deg.  [Earth will be *HUGE*]  (44/360)*6 hr is
.72 hrs or 44 minutes (need to figure umbra/penumbra).  That makes the
average heat and light input ~88% of peak during the worst of the
eclipse season.  It also mandates a substantial energy storage.  The
ISS has the same eclipse problem but the eclipses are shorter.

Given various losses and filters to keep out the less useful
wavelengths, the reflecting mirror to get the light in will be 67
meters in diameter.  One of the mirrors will be set 70 meters above
the other so the habitat mirrors don't shade each other as the whole
thing goes around the Earth every 6 hours.  The mirrors track the Sun,
going a full circle every 6 hours.

The frame holding the habitats is a 45-deg, chopped-off corner 200 m
wide of a square structure that spreads out to 3.2 km wide.  The edge
with the habitat is closest to Earth and has space-anchor attachments
at the 45-deg corners.  The anchors are in the tons to tens of tons
range and, with tens of km of length, the attachment strings provide
hundreds of newtons of tension (an effect of being deep in the Earth's
gravity well).

A great deal of care will have to be taken to assure that cargo stacks
don't run into the space anchors.  This should not be too hard since a
cargo stack gains about 220 km in the last orbit.

The two outer edges of the square will be where power satellites are
connected (dry dock edges) or possibly we truncate the frame either
one or two power satellites wide.  The other two sides of the square
(or triangle) will be used to dock cargo stacks.  The stacks will be
moved up by an elevator one layer at a time and disassembled from the
top down.  This keeps the cargo stacks from eclipsing the habitat
light and power mirrors.  There is plenty of room to dock several
cargo stacks.  Construction power can be from PV hanging under the
construction frame (south side).  Transport on the frame is by tracked
vehicles.  (Credit to John Strickland.)

Sorry for the extreme data dump.  It will look simple as an animation.
If you are good at visualization and see a problem, please let me
know.

Keith

PS.  When we cut a new power satellite loose, do we smash a bottle of Champagne?