A guest post by Joseph Friedlander
What qualifies as a supertall tower? In any era, a tower well beyond the previously built engineering limits. Many people think of towers as linked to the egos of builders, the peaks of finance (there is a theory of large amounts of simultaneous tall structures marking the pre-crash financial frenzy of an overheated economic boom--sort of a climax forest of real estate finance before the clear-cutting of an oncoming depression). But here we speak not of cost, not of even too many of the engineering concerns but simply outlining some of the uses and concerns of supertall tower building.
A previous post on the uses of Supertall Towers for travel and space access
Height regime (arbitrary selections based on various thresholds)
1 kilometer (where we are now, about)
3 kilometers --a good first target, high enough to smash all records, low enough to be routinely buildable.
5 kilometers (near strength limit of iron without tricks like staging/tapering)
8 kilometers (just under Everest height, near strength limit of aluminum without tricks like staging/tapering)
20 kilometers (U-2 height, good for space launch (around 90% vacuum thrust on the pad, easier Max Q, less gravity and drag losses)
30 kilometers (Martian height, 99% of air below you, darkening sky, kilometer per second rotary tether assist launch known possible because the SR-71 travelled at that speed at this height)
50 kilometers (99.9% of air below you)
75 kilometers (probably low limit of rotary tether launch at high fraction of orbital speed)
100 kilometers (Become an astronaut by taking an elevator-- major tourism potential above that of simple sightseers-- also 1 millionth atmospheric pressure at sea level)
130 kilometers-- 80 miles (Just below 90 mile stable orbit, high enough to be below low perigee satellites, and above height where loss of signal for reentry, so extremely light if any nose cone or fairings needed-- just launch spacecraft or shoot mass driver and the unshielded spacecraft saves great mass and the launch sequence saves a pyrotechnic event which can fail.)
Geosynchronous height-- If you can build this tall, you can simply leap off and you're in orbit. But above this height, you can get free launch assist, from the rotation of the Earth, at high sublunar heights enough energy for a minimum energy transfer to Saturn-- of course, you need to launch at the right time for that to work.
Advantages and Uses of Supertall Towers
- Line of sight and sheer height (for individuals)
- People will pay for the view
- People will pay to get married/eat/impress people and clients in an exclusive place
- People will pay to get official astronaut certification
- Sports/bungee jumping/glide jumping/rappeling/space parachuting
- Line of sight and sheer height (applications)
- Drop tower for near zero gravity processing
- Drop tower for movie studio (the movie Apollo 13 used a zero gravity trajectory plane for filming and 30 seconds for a take was sufficient)
- Pressure work (surface lab, tall standpipe, think Pascal's Barrel)
- Observation, sensors, scanning radar, surveillance, placement of microwave antennas
- Cheaper replacement for satellites with most of the coverage, stronger signal strength (closer to user)
- Above a good fraction of the atmosphere
- Vaccum processing much easier with lower outside ambient before pumpdown-- huge vacuum chambers possible if you have the lift capacity
- Astronomical observatories --academic and personal (rent space for your remote controlled scope on top)--Imagine the Keck Observatory above the atmosphere--
- Massive solar power payback possible if you pay attention to conflict between incoming winds and furling thin reflectors-- Above the clouds (certain rare high clouds excepted) nearly 40 percent of a day may give productive power as opposed to typically 10 percent on the ground.
- Laser frequencies usable without much attenuation for massive data transfer without optical fibers between two high towers
- Laser/particle beam/mass driver/ rotary tether/ other methods of direct space launch to orbit or escape (height required varies by method)-- 100 times cheaper space possible.
- Possibility of catching incoming orbital or lunar payloads deborbiting and using the energy as a power source in near vacuum. Literally 1% of the Moon's mass incoming could power civilization for geological eras of time with very little increase in gravity.
- Possibility of intercity travel far faster than we have now. I wrote about that here --http://nextbigfuture.com/2011/02/heinlein-style-spaceflight-with.html Note that
- Possibility of effective missile defense by laser without attentuation (But see last point in entry below)-- the cheapest means of anti-anti missile defense is to target your tower!
- Enemies of Towers
- Government permission required (active or passive-- they say no, it's over before it starts)
- NIMBY-- This is the flip side of long line of sight-- I don't want to see your tower from 300 km away in my pristine wilderness...
- Earthquakes --You think they are tough on the ground? Try it in a space tower
- Wind-- Say after me, class-- statics is not dynamics. First they teach statics, then they teach dynamics. There is a reason.
- Resonance-- Rotary space launch tethers need to be precisely balanced and other resonance sources kept well under control
- People with weapons who want to target your tower-- Governments, terrorists, criminals, kids with a new rifle just looking for a target. It is hard enough keeping a tower standing against nature. You don't want people gunning for you too.
From Professor A.A. Bolonkin's paper on optimal steel towers found on arXiv here:
In my post on his AB Matter concept --if buildable could lead to 'cable cars to the planets' and space towers literally in Jovian gravity with no taper-- foundations secured by the clever means of literally sticking through the Jovian core with no fear of the fearsome temperatures within.
If Bolonkin's AB Matter can be built it would enable towers and space cable cars of unspeakable capacity and utility. Not to neutron stars or worse but many unreachable places would soon be easy to reach. Gas giants, even other stars. Even probing within the Sun.
The limit of AB Matter tether launch is probably 1/6 lightspeed or so.