From: gherbert@gw.retro.com (George William Herbert)
Newsgroups: sci.space.policy
Subject: Re: SPS Questions....
Date: 26 Sep 2000 17:45:51 -0700

Scott Lowther  <lexcorp@ix.netcom.com> wrote:
>wmook@my-deja.com wrote:
>> [snip]
>> > wasigunner sez: technically feasible perhaps, in a engineer's perfect
>> > world, but not very practical for living.
>>
>> Depends on the creativity of those solving the very real problems you
>> delineate.
>>
>> > A 10-mile-high (or even 5
>> > mile-high) building would have to be essentially a closed community
>> > providing self-contained employment, health, educational, and
>> > food-supply services at periodic levels as you go up.
>>
>> Not really.
>
>Yes, really.

But not a serious problem, if you look at what it takes to supply
a small town these days in terms of shipping etc.

>> > Why? Because most
>> > people won't want to wait hours in elevators just to get to the bottom
>> > to go to work, go shopping, see a doctor, and then wait hours to get
>> > back home to the upper levels!
>>
>> This is merely an argument against elevators as they're currently
>> designed, not an argument against tall towers.
>
>Elevators are an integral part of tall towers, and designers have been
>struggling for years to come up with good, swift practical systems to
>carry passengers from Floor X to Floor Y for years... and buildings
>barely break the 1000 foot mark.

Multistory elevators have just rolled out, and multiple elevators
per track are now in use as well in some midsized applications.
There is significant inertia in play, but this problem is being
addressed today.

>> In more detail, imagine the entire exterior of a tower outfitted every
>> few yards with some sort of powered track that allows self propelled
>> and self guided elevator vehicles to move along them without cables and
>> whatnot.
>
>And what will that weigh?

Not all that much, actually.  Counterweights and cables are a significant
weight item in conventional elevators.  Such track systems are more likely
to be on internal tracks (less likely to have corrosion or inspection problems
if they're internal and easier to inspect), but they're within reach today.

>> Focusing on passengers for a minute.  One can imagine every exterior
>> room outfitted with a door (and airlock) and a parking space for
>> several vehicles.  The vehicles dock with one another having doors on
>> both sides.  A stack of vehicles forms a short hall dead ending at the
>> outermost vehicle.
>
>And what will that weigh?

I am sort of curious as to why you'd do that.

>[...]
>> In an emergency, everyone will proceed to the nearest exit.
>
>And die as the building topples over.

This would already be a problem with any modern office building.
There's nothing like the FAA evacuation time standard for tall
buildings (how long did it take to completely evacuate the world
trade center after the bomb attack...).  Arguably it should be for
a monster building... but if you look at cities, there are lots of
times that large chunks are effectively isolated with only a few
critical transit paths in or out (Manhattan.. San Francisco...
Treasure Island... Alameda...).  Say there was a massive spreading fire
on Alameda (if you're not familiar, Alameda is an island city in San
Francisco bay, connected by ... 3? bridges and 2 tunnels to the
rest of the world) which was being spread by the wind and cut people
off from most of the bridges, or the fire was sparked by earthquake
damage that took out  most of the bridges/tunnels/etc.  Tens of
thousands of people could be at risk there.  For some reason the
city fathers haven't seen a need to issue life preservers to everyone
on the island to enable them to swim to shore in the event of such
an emergency.

>> To build practical big towers we must build practical vertical versions
>> of streets, sidewalks, alleys, and so forth and vehicles to traverse
>> them.
>
>PRACTICAL being the vastly important operative word here. A system that
>may work just peachy keen for a building 2000 feet high is not likely to
>serve well a building 52,800 feet high.

No, of course not.  But it's not reasonable for people to want to move
52,800 feet faster vertically than they do horizontally today.
It takes a few minutes to either get in car, drive 10 miles, and park
and get out or to walk to public transit and ride the bus/train to
the closest destination stop and walk from there to destination.
As long as people understand that the up dimention is as far away
as the across dimention, then they'll be ok with it.  Right now
buildings are hitting the point that people are having to make that
sort of mental leap, so it should be easier in the future.

I.e., how long does it take for you to walk to a bus stop,
the bus to arrive, the bus to drive 10 miles, and you get out?
For me, that's a half hour to 40 min on the route I take down
to the BART station to commute to work when I don't need the
car during the day.

>>[...]
>> > The upper floors, at least, would need to be pressurized to keep
>> > people alive, necessitating airlocks at some level,
>>
>> Yes.  This is unusual in today's construction.  But you've provided no
>> technical reason this can't be done.
>
>MASS. MASS. MASS. MASS. MASS. MASS. MASS. MASS. MASS.

I am about to horribly mix metric and US units.  Flamers will
be vacuum-sealed for freshness.

If the tower is 100 meters in diameter and pressurized to 8 PSIG,
and you use relatively mundane fiberglass epoxy pressure vessel
technology, then we're talking about needing... let's see...
100m = 3936 in ~= 4000 in, r~=2000 in, force on shell is 8 psi * 2k
in or 16k PSI, which is less than an inch of fiberglass to hold that
with adequate civil engineering safety margins etc etc etc.
Call it an inch, at density 1.5, to be pessimistic.  The floor is
3 meters tall, 100 m diameter is 314 meter circumfrence, 950 square
meters of pressure vessel surface area per floor, times 2.5 cm is
about 24 cubic meters, about 36 tons.

Floor design dead mass plus live mass has to be practically at least
100 pounds per square foot, 100 m is 328 feet, radius is 164 feet,
squared times pi is about 85,000 square feet, 8.5 million lbs,
about 4 thousand tons.

Adding 1% to building weight to hold air in is a practical solution,
I think.

>[...]
>> There may be situations where huge collections of people will come
>> together for specific purposes.  Perhaps for security reasons,
>
>Perhaps not. A ten mile high tower would have every nut with a bomb
>spooging his shorts.

The design criteria to deal with that problem are a headache but are
manageable.  You can make the buildings pretty resistant to damage.
But it does need to be addressed, along with the "747 crash landed
on the 30,000 foot floor" and "a news helicopter hit the #41 support
cable" and "someone brought in fifty tons of paint which caught fire
on the 25,000 foot floor" and "Oops, is that a tornado?".


-george william herbert
gherbert@retro.com

From: gherbert@gw.retro.com (George William Herbert)
Newsgroups: sci.space.policy
Subject: Re: SPS Questions....
Date: 27 Sep 2000 13:33:34 -0700

Scott Lowther  <lexcorp@ix.netcom.com> wrote:
>George William Herbert wrote:
>> Scott Lowther  <lexcorp@ix.netcom.com> wrote:
>> >wmook@my-deja.com wrote:
>> >> [snip]
>> >> > wasigunner sez: technically feasible perhaps, in a engineer's perfect
>> >> > world, but not very practical for living.
>> >>
>> >> Depends on the creativity of those solving the very real problems you
>> >> delineate.
>> >>
>> >> > A 10-mile-high (or even 5
>> >> > mile-high) building would have to be essentially a closed community
>> >> > providing self-contained employment, health, educational, and
>> >> > food-supply services at periodic levels as you go up.
>> >>
>> >> Not really.
>> >
>> >Yes, really.
>>
>> But not a serious problem, if you look at what it takes to supply
>> a small town these days in terms of shipping etc.
>
>Errr.... problem. If I want to get a gallon of water ten miles from here
>in a small town, it's a simple matter of plumbing and perhaps some
>pumps. But getting it TEN MILES STRAIGHT UP? This is a whole different
>weird area unrelated to the logisitcs of a small town.

Getting it ten miles straight up is roughly fifty one thousand foot lifts,
five hundred one hundred foot lifts.  They have boost pumps and staged
storage up on large skyscrapers today; you just need more of them on a
ten mile sized structure (and more energy input, etc).

Quantitatively more, but qualitatively the same solution used today
in large buildings.

>> >[...]
>> >> In an emergency, everyone will proceed to the nearest exit.
>> >
>> >And die as the building topples over.
>>
>> This would already be a problem with any modern office building.
>> There's nothing like the FAA evacuation time standard for tall
>> buildings (how long did it take to completely evacuate the world
>> trade center after the bomb attack...).  Arguably it should be for
>> a monster building... but if you look at cities, there are lots of
>> times that large chunks are effectively isolated with only a few
>> critical transit paths in or out (Manhattan.. San Francisco...
>> Treasure Island... Alameda...).
>
>Again, this analogy doesn't hold together that well. If I'm cut off in a
>small part of twon, that's perhaps bad... but at least I don't need to
>worry about a window blowing out and dealing with explosive
>decompression, bitter cold, oxygen deprivation, the carbon fiber walls
>catching fire, etc.

I would like to see carbon fiber in an epoxy matrix burn in anything
but a LOX environment... it has always been pretty darn inert when I've
seen it post-accident or during one.

Obviously, some of the environment more closely resembles a space station
in terms of how critical a failure is as you pass say the 4km mark,
and that all becomes much more critical at pressures where human life
simply cannot be sustained without pressurization or supplimental oxygen
or both (above 7km or so).  When I work the numbers, 10 miles is about
3 PSI, so with pure oxygen at ambient pressure you won't die but will
be extremely incapacitated / uncomfortable.  Having pure O2 breathing
aparatus available in case of depressurization, and having internal
floor bulkheads so that a depress will only have limited areas of effect,
would be necessary for such a structure.

>> >> To build practical big towers we must build practical vertical versions
>> >> of streets, sidewalks, alleys, and so forth and vehicles to traverse
>> >> them.
>> >
>> >PRACTICAL being the vastly important operative word here. A system that
>> >may work just peachy keen for a building 2000 feet high is not likely to
>> >serve well a building 52,800 feet high.
>>
>> No, of course not.  But it's not reasonable for people to want to move
>> 52,800 feet faster vertically than they do horizontally today.
>
>Well.... maybe. How long do you have to wait in line to go that 10 miles
>straight up? At 8:50 AM or 5:01 PM, the lines could get pretty bad.

It sometimes takes a half hour to me to get a BART train.
I live 12 miles from work (across a bridge) and it sometimes
takes me 90 min to drive home if I have to do it during rush
hour now.

>> I.e., how long does it take for you to walk to a bus stop,
>> the bus to arrive, the bus to drive 10 miles, and you get out?
>
>Zero minutes. Buses are the work of the Devil. I drive myself.

You'll love California, then...

>> >> > The upper floors, at least, would need to be pressurized to keep
>> >> > people alive, necessitating airlocks at some level,
>> >>
>> >> Yes.  This is unusual in today's construction.  But you've provided no
>> >> technical reason this can't be done.
>> >
>> >MASS. MASS. MASS. MASS. MASS. MASS. MASS. MASS. MASS.
>>
>> I am about to horribly mix metric and US units.  Flamers will
>> be vacuum-sealed for freshness.
>>
>> If the tower is 100 meters in diameter and pressurized to 8 PSIG,
>> and you use relatively mundane fiberglass epoxy pressure vessel
>> technology, then we're talking about needing... let's see...
>> 100m = 3936 in ~= 4000 in, r~=2000 in, force on shell is 8 psi * 2k
>> in or 16k PSI, which is less than an inch of fiberglass to hold that
>> with adequate civil engineering safety margins etc etc etc.
>> Call it an inch, at density 1.5, to be pessimistic.  The floor is
>> 3 meters tall, 100 m diameter is 314 meter circumfrence, 950 square
>> meters of pressure vessel surface area per floor, times 2.5 cm is
>> about 24 cubic meters, about 36 tons.
>>
>> Floor design dead mass plus live mass has to be practically at least
>> 100 pounds per square foot, 100 m is 328 feet, radius is 164 feet,
>> squared times pi is about 85,000 square feet, 8.5 million lbs,
>> about 4 thousand tons.
>>
>> Adding 1% to building weight to hold air in is a practical solution,
>> I think.
>
>A few points:
>1) This analyses means no windows. That'd suck.

Or windows with equivalent structural strength to the fiberglass.
Or more than 1% of the building floor weight dedicated to the
pressure vessel.

The analysis was intended to demonstrate that pressurization is in rough
terms small compared to other weights in the building.

>2) What are the health hazards (fire, outgasing of volatiles, etc) of
>that much fiberglass?

If we can make spacecraft using it, we should be able to make buildings
out of it.  Epoxy is fairly inert in a fire.

>3) How well will the fiberglass stand up to the condition found in the
>stratosphere?

There are well understood lifetime analysis tools for aircraft use of
fiberglass and other composites.  Or, if you don't like fiberglass,
use aluminum for the walls, or steel, etc.  If you use T-1 steel,
and a factor of safety of 3, you need around a half inch of it, weighing
around 100 kg/m^2, 95 tons instead of 36 tons; around 3% of the floor
weight instead of 1%.  Adding windows might bring that as high as 10%.
Still minor compared to basic floor weight.

>4) You didn't seem to include the weight addition of making each floor
>it's own pressure vessel, for obvious saftey requirements in the event
>of a blowout (airplane hiots, window pops out, fire, something). Assume
>0.1 inch thick fiberglass, 2000 inches radius... 1256637 cubic
>inches/205925919 cubic cm/308 tonnes per floor. Adding these pressurized
>floors to everything above the 8 psi level (aprox. 16,000 feet) means
>that 3680 floors have pressurization bulkhead floors. If we assume that
>the bulkheads start at zero thickness at 16,000  feet and go to the full
>0.1 inch thickness at 52,800 feet, that averages to 0.05 inches thick
>for 3,680 floors, or a total extra mass of 566,720 tonnes. This, of
>course, does not include the mass of the columns that would be needed
>every few meters at the least to maintain the floors in the event of a
>blowout.

You don't need every floor to be airtight, but every second, or third,
or fifth or something.  Details TBD based on safety assumptions.

Actually sealing the floor should require not a lot more additional
structure than the basic floor weight.

>And a final point: a building ten miles high is going to be stretching
>materials tech to the bleeding edge and beyond just to build the thing.
>An extra 1% may kill it as dead as cleanly as an extra 1% might kill an
>SSTO.

A needle 10 miles high is going to be stretching a lot of things;
something with a reasonable taper ratio ten miles high is a different
story (say, a 1 mile wide base, and half mile top).  Both are possible.

Again, please don't take my discussions here for actual support of
the idea of 10 mile tall buildings.  Like a dam across the Congo at
Leopoldville and Orion launch vehicles, this is one of a number of
interesting but fundamentally unlikely or impractical engineering
projects which exercise engineering and analysis skills but are not
likely to ever get built.  It's fun to analyze them and talk about
them from time to time, but that's different than expecting
them to get built.  Among other things, I find it improbable that
more humans will ever live on earth than the insolation can support
food production for in high efficiency agriculture, which works out
to around a trillion people.  If those trillion people each have
100 square meters of home and 100 square meters of work and 100
square meters of transportation/access areas and 200 square meters
of recreation area per person (500 m^2 total) that works out to
5E14 m^2 or 5E8 km^2 required for the whole maximum credible
population of Earth.  That's a building area equivalent to just
two thousand kilometers on a side and 125 stories, which is a trivial
fraction of the Earth's total surface area, at building heights
roughly what we're doing now.  I can see buildings getting taller than
they are now as it becomes more cost effective to make big buildings
but I realistically think that the limit will end up being something
like 3-4 km, the sort of heights that humans inhabit in quantity
on existing terrain, but not higher than that, as the added system
requirements for life support at altitude are too expensive to
be practical.  Engineering projects for non-habitation purposes
I can see, but not buildings for live/work.  There's just no reason
to build them.


-george william herbert
gherbert@retro.com