skyhook = space elevator

I wouldn't know how to answer if I had all the inputs. Still, I think the assumption is that at 60,000 miles, the thing is going to be way above a low earth orbit, and the tether (as the word may imply) will be in tension, except possibly when the elevator is at a suborbital distance from the planet.

Are you sure you got the decimal point in the right place in the distance, Neil? 60,000 miles is just way up there.

I seem to recall something about this from either Jerry Pournelle, the L5 Society, or both. His science is usually pretty good.

As Ive understood the concept, the initiation point , on earth, would be a lattice constructed tower somewhere up to 50 km high. (This is some extreme building for today and Arthur Clarkes, "Fountains of Paradise had the towers location along the equator on an island with a name like Tarolane (not sure about that name but it was near Ceylon and was at an incorrect latitude in the story)

The use of Lagrangian intervals at anL1 and L2 configuration woul have a cable connected to a satellite at geosynch orbit at L1 and then a counterweight to keep the thing from falling at L2 i think the L1 point was at 24000 mi and L2 was 140000 mi. As I understood the counterweight would be an asteroid which we would "tow" into place and connect the cable, which I also herd was now carbon fiber tubules but with a cross section more like a tear drop than rounded.
My last bit of information (I read and article in the Skeptical Inquirer last year, I beleieve)was that, if it moves forward it wouldnt be until at least another hundred years or so because the costs have to be supported by a need. We are now not needing to shuttle stuff back and forth at such a rate that would warrant a deep cut in the per pound orbital cost that such a conveyance would afford.
No matter, because It sounds really neat just to imagine the concept and do the science and to actually be able to think about feasibility of such things. This is just an example of the nimble human mind on its bright side. Then I gotta drop the glove and look at the other, darker side of our nimble minds, and get really depressed.

As you can see proposed length is up to 140,000 miles which is more
than halfway to the moon. the strain is greatest at the
geo-sycronous altitude, about 23,000 miles, so the tether is thicker
there. longer is better, as little counterweight is required and the
space craft is released at higher speed from the end for
destinations thoughout the solar system. The system to be completed in
7 years, likely will be suitable only for small unmanned probes at the
end, and only medium mass satellites at low earth orbit and
geo-stationary orbit. The latter will be the only weightless portion of
the tether. Neil

LiftPort Inc. has started a 15-year schedule to build a space elevator with no tower, just a ribbon about the width and thickness of a sheet of paper. Good FAQ's at: http://www.liftport.com/pages/index.php?fuseAction=page&pageID=1234


There used to be a lot of info at HighLift Systems, but the main guy there Dr. Bradley Edwards went to Inst. for Scientific Research.
His plan would lift a thin starter cable with a few rocket launches, simply drop one end to Earth, and use the construction equipment to anchor the high end (no asteroid needed). They'd send climbers up the thin cable to gradually deposit more and more carbon nanotubes until it's strong enough to lift real cargo. No tower involved, just a ship to hold the cable out in the ocean.

14 pages of plans, tech info, designs and schedules are here:
http://www.isr.us/Downloads/niac_pdf/contents.html

Ch.6 - "Locating the space elevator cable anchor on a movable, ocean-going platform has numerous advantages over a land-based anchor."

Ch.7 - "One additional use of the space elevator is production and delivery of a completed Mars cable (figure 7.2). The Mars cable could be produced in Earth orbit alongside an Earth elevator then released as a single unit on a trajectory to Mars. Upon reaching Mars a braking rocket or aerobraking would be required to place the cable in the proper Marssynchronous orbit."

Ch.11 - "After the first cable is complete, the second and following cables will be considerably easier, faster and cheaper to build per kilogram of capacity. Climbers can be sent up the first cable deploying and building the second cable as they climb. In this case a cable of comparable size to the original can be made in 7 months instead of the 26 months of the first."


The same Dr. Edwards wrote "The Space Elevator: A Brief Overview of the Current Status"
http://www.eurekasci.com/SPACE_ELEVATOR/intro.html


NASA is more conservative than Dr Edwards.
From http://news.bbc.co.uk/2/hi/technology/2188107.stm



Iraqi War: $200B
Space Elevator: $10B . . . go figure

Thought I'd read somewhere last week that they'd figgered out how to make synthetic spider web... a woven square inch of that might just do the trick...

CB-The need isnt determined by the science , for, unlike the moon landings, there is no real desire to cheaply ferry goods out to space at this moment. its feasible that someone, with a good cash pile , could do it (I have no ideas about necessary permits and international treaties) If you say 50billion, then double or triple that . and, as youve said, we dont really have the space string technology ready yet.In fact, the specific type of nanotube carbon fibre material doesnt even exist. yet.

Sounds eerily like several science fiction stories I've read.

I don't expect to see it.

yeh but you have to admit that its cool. Its thinking outside the box to try to control the one item in space flight that halts many projects, cost of payload lift. Once built, if material science can catch up , it could make weekends on the moon a new tourist stop.
My only problem is that there may be some need for rocket boost at the front end , and this is the most expensive phase, so we need to carefully look at the numbers

And scifi I've read too. That was one of my favorite concepts. I'll watch and wait.

The idea definitely straddles the line between amazing and impossible. To me, watching the ideas develop over months is very interesting. There are so many different technologies involved; and the problems and solutions addressed are very creative. Better than watching football!

Ultimately the technology seems doable, and like Kennedy's moon missions it does present a clear, romantic and inspiring acheivement. Although the satellite industry is constantly growing, I'm not sure when an elevator would become profitable.

Similar to Burt Rutan's space plane and the X-Prize, I'd love the space elevator to be privately constructed, to minimize the political and military control of space. People need to do it, not agencies. Wishful thinking -- I'm curious how much support it will get.

~Here are some excerpts:~
The ribbon will have a disastrous effect on bird/other species migration?

Unlikely due to the small size and passive nature of the system.

Meteors, satellites, and space junk will hit the ribbon and break it.

o The large amount of orbital debris we have left in orbit will
eventually sever the elevator.
Low Earth objects can and will pose a serious problem. However
active avoidance can be used to avoid objects that would cause
damage. On average, an object would have to be avoided every
14 hours.
o All existing satellites cross the Equator and where could hit the
ribbon, so we'll have to get rid of them. Each and every satellite in
Earth orbit (except for those in an exact geostationary orbit) crosses
the equator twice during each and every orbit. Unless that elevator
is really good at dodging, one of these satellites is going to run into
it.
We are good at dodging, and we will avoid the satellites. We are
tracking them and will have days to weeks warning. We will move
the anchor about a kilometer each day to avoid the debris. It may well
be that in the long run (decades or centuries) we will stop putting
large numbers of satellites in Low Earth Orbit and will clean out
derelict ones already there.
The Leonids will destroy the Space Elevator.
The Leonids are a trail of dust and debris left by the Tempel-Tuttle
comet as it traverses our solar system each 33 years. The last
passage was in 1998 and the next is expected in 2031. The dust
and debris left by the comet passage disperses and leaves
the neighborhood of Earth on a timescale of years though some
debris always remains. The flux density of the debris can fluctuate
by 10,000 from year to year. The Leonid debris also has a distribution
of debris that includes dust particles and objects up to 10 cm in
diameter.
An article published by McNeil, Lai and Murad, Charge Production due
to Leonid Meteor Shower Impact on Spacecraft Surfaces, discusses
the impact probability on spacecraft and the details of the Leonid
debris. The flux density from McNeil is shown in figure 1. This flux
density is for a Leonid shower with a peak visual flux of 1000 meteors
per hour. The standard peak is 10 to 20 and the largest in 1966
was 160,000. We can calculate the probability of impact on the
elevator ribbon based on the 1000 peak number and then scale
from there.
Objects larger than about 10 cm have a finite possibility of destroying
the ribbon. Objects as large as 5 cm in diameter has a small chance
of destroying the ribbon. If we consider a weighted probability function
we might approximate the likelihood of destruction with the likelihood
of impact by a 10 cm or larger object. In our baseline, with densities of
3 gm/cm3 (estimate for the Leonid debris), this relates roughly to a
mass of about 1500 gm (4/3*3.141*53 gm/cm3*3) or a flux density of
10-17/ m2 s. A typical Leonid shower lasts roughly 2 hours or 7200 s
and the total area of the proposed elevator ribbon is 108 m2. This
gives us a probability of damage leading to destruction for each
annual passage through the Leonid debris of roughly 1/100,000 for
the showers with peak visual rates of 1000/hour. For a more
standard shower the probability would be 50 to 100 times less. For
the largest likely event (possibly in 2031) the probability would go up
by 160 to a 1/625 possibility of severe damage. These are
rough estimates and more accurate calculations are required.
However, these estimates indicate that until 2031 the danger is
probably minimal. By 2031, modifications and mitigation techniques
could be implemented to improve survivability.
-Dr. Brad Edwards
The elevator would be susceptible to a terrorist attack.
First of all, it's important to point out that there will be more than
one Space Elevator. We plan to build a second one immediately
(using the first to make it much cheaper) and expect that the second
will immediately be used to build a third, fourth, etc. An attack on any
one ribbon is unlikely because of the anchor stations' isolation and
the relatively small number of casualties that would result. Terrorists
are unlikely to be able to break the elevator anywhere higher than 15
km or so; it can then be simply flown back down to the anchor by
moving some of the counterweight mass a bit closer to Earth and will
be back in operation in a couple of days.
The first anchor will be located in the equatorial Pacific 650
kilometers from any air or shipping lanes. The ribbon would also
have restricted airspace around it. The ribbon and anchor would
be protected like any other valuable piece of property, in this
case probably by the U.S. military.
~Repairs will be necessary occasionally. At worst it will be as
dangerous as the Space Shuttle. Neil~

Failure analysis of a space elevator
Suppose the tether breaks. There are elevators 30
tons gross weight at 90,000KM at 33,000KM and at
900 meters (departed Earth one minute ago) The
tether breaks (Terrorist missile perhaps) at one KM.
Can the elevator stop ascending in 100 meters,
before it runs off the broken end in perhaps 5
seconds! Let's assume the elevator at 90,000 KM is
parked and the elevator at 33,000KM just started
accelerating toward Earth to produce a stretching
transient of the tether that will meet (and cancel)
the stretching transit from the lowest elevator at
about 20,000KM. Does it need to go away from
Earth to cancel?
In any case at least 40 tons of tension was just lost
at the low end = 30 tons of elevator + the pull of
the rollers, which were accelerating the elevator
+ 1/1000 ton of tether + the downward pull of the
anchoring tower. Since the tether is at least slightly
elastic the broken end will snap upward at perhaps
200 KMPH for 10? KM before the upward motion
falls to perhaps 1KMPH. It will be tomorrow before
any of these transients reach 20,000KM, but prompt
action is necessary to prevent the entire tether from
drifting beyond geo synchronous orbit. The elevator
at 90,000KM should be moved as fast as possible
toward geo stationary altitude, with the help of
rockets as moving it by rollers pulls the tether
farther from Earth (this reduces the weight of the
counterweight) The elevator at 33,000KM is
essentially weightless, but it can pull the tether
toward Earth with it's rollers by accelerating away
from Earth while applying breaking rockets which will
keep it at about 33,000KM. These two expediencies
my be sufficient to allow the unattached tether to
descend slowly to the anchoring tower where it can
be reattached one KM short.
Alternately a heavy lift helicopter could unroll 11 KM
from a reel on the anchoring platform and attach it to
the broken end at an altitude of about 11 KM.
Another alternative is to have a back up peice of
tether on a tower to the East extending upward about
30 KM supported at the top by a large balloon. This
could be spliced to the end of the broken tether, while
the short peice of tether fluttered down slowly to the
ocean surface. Please refute, embellish and/or agree.
Neil

Sorry, but we've been making carbon nanotubes for a year or two now. Maybe not in thousand-mile lengths, I'll grant.... and I don't know what "specific" type of nanotube you need to build an orbital tether, but we already make nanotube 'ropes'...



And plenty of nanotubes...

Walmart & China partners in progress?
Every time we shop at Walmart the Chinese warchest for a lunar base gets a boost; dont believe me? Try and buy a pair of shoes that's not made in the Peoples Republic.
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We are the failed generation, history will look back and call this world wide lull in manned space activity as the equivalent of the dark ages in the design and production of manned space vehicles.
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We don't have an answer to the British French Concorde in aviation circles(expensive and too small to be practical)but it pointed to a future that no civil aerospace firm in America ever claimed. What a shame! Materials, computer modeling , rapid prototyping and finite element analysis and other advances since the 60's and yet none of the major players or their investors seem to have been able to translate that into a practical design. Mock-ups and test beds are everywhere.. funding is spent and projects shelved or moth balled for lack of a viable commercial design.
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NASA for all of the money the American taxpayer has given them has failed, they have failed to educate and build any sort of public interest in the future of manned spaceflight. Time after time they have proven themselves unresponsive to public requests for the re-imaging of certain features on Mars.
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The arrogance of the high cabal continues and as we watch the Chinese prepare to go to the moon, with a moon base planned.. My question for NASA is: What have you been doing for the last 3 decades? Have you designed a heavy lift rocket using all of the advances available?
Mars has been waiting and we are waiting.. we want a manned mission to Mars... but maybe a long duration Lunar mission needs to be undertaken as proof of concept first.(Mars Direct would be better but we'll take what we can get)
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The privately funded X-prize competition has placed the ball into the private sector's court. A ballistic sub orbital toss into space with a 14-day turn around before repeating the same sub orbital flight again. While it may capture the world's attention briefly, it should also focus attention on NASA's lack of progress in the development of manned space flight abdicating leadership and ceding the vanguard to the private sector.
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We need to be manufacturing in orbit, the things we need to colonize space.. how can we do that without reliable , cost efficient launch systems? We have had 30 years..Its time to bring things to a halt and take a serious look at where we have been, where we want to go and what its going to take to get there.
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Salute the past and then grasp the reins and lead on to the future. First a launch system less complex more efficient, second an expanded space station committed to the building in orbit of technologies in support of manned Lunar and Mars missions. La Grange points, Space Elevators and more unmanned missions would have to wait.
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We need to get control of the monolith that is NASA and all of the funding that it uses and start directing the development in a War time footing effort to make a manned mars mission a reality within THIS decade or you can wait another 30 years for nothing to happen.
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I challenge NASA to prove me wrong... show me where, when and how we are going anywhere.. show me the plans , the launch vehicles and the ability to get things done
The moon missions took a decade, you have had 30 years lead-time from the word go. You have 5 years now.. show me something .. anything I can believe in... We have all been waiting for far too long

some1 may have already said this but i didnt bother reading - there will not be the weight of the cable nor space station on the tether. The space station will be at a higher orbit than what is neccicary for a stationary orbit, it will be like flying a kite, the tension will be pulling up, above the centre of gravity of the cable+space station then the remainder of the cable will be dangling from that centre of gravity. The tension at the tether will be zero assuming there is no wind and the astronaughts and mechanice remain perfectly still.

someone may have already said this but I
didn't bother reading - there will not be
the weight of the cable nor space station
on the tether. ~the station will be
approximately weightless if it is near
the center of gravity, but the cable will
have weight almost as much as it's mass
near the ends. The center of gravity will
shift thousand of kilometers from the
geo stationary orbit altitude, as the
elevators move up and down, if the
tether is as low mass as the optimists
hope. It may be necessary to make
adjustments to prevent breaking the
tether as the weight will not be felt
instantly, but will travel up and down
the cable at a few thousand kps,
perhaps a few hundred kps. Can
anyone make a good guestimate of
how fast these transients = traveling
waves will travel. Neil~

~Here are some excerpts from Dr Edwards
about the space elevator;~
The Concept
The NASA Institute for Advanced Concepts
(NIAC) Phase I study examined the entire
system in detail and found a space elevator
design that will work with current or
near-future technology, a method to
deploy the elevator, and specific scenario
for safe operation.
Current research on the space elevator is
continuing to refine the design and bring
the required technology to completion as
quickly as possible.
In simple terms, the space elevator is a
ribbon with one end attached to the Earth's
surface and the other end in space beyond
geosynchronous orbit (35,800 km altitude).
The competing forces of gravity at the
lower end, and outward centripetal
acceleration at the farther end, keep the
ribbon under tension and stationary over
a single position on Earth. This ribbon,
once deployed, can be ascended by
mechanical means to Earth orbit. If a
climber proceeds to the far end of the
ribbon and releases, it would have
sufficient energy to escape from Earth's
gravity and travel to the Moon, Mars,
Venus and the asteroids.
For the last two years a detailed design
study of the space elevator concept has
been funded under NASA's Institute for
Advanced Concepts (NIAC). The NIAC
work produced a detailed description of a
possible space elevator program. Initially,
a small, carbon-nanotube-composite
ribbon (10 to 20 cm wide and microns thick)
capable of supporting 990 kg payloads
would be deployed from geosynchronous
orbit using four rockets and a
magnetoplasmadynamic upper stage.
Climbers (230) are sent up the initial ribbon
(one every 3 to 4 days) adding small ribbons
alongside the first to increase its strength.
After 2.3 years a ribbon capable of
supporting 20,000 kg cargo climbers would
be complete. The power for the construction
and cargo climbers (100kW to 2.4 MW) is
beamed up using a free-electron laser
(840 nm) and 13 m diameter segmented
dish with adaptive optics, identical to the
one being constructed by Compower Inc.
and received by GaAs photocells
(80% overall efficiency at this wavelength)
on the climber's underside. This power,
converted to electricity, would be used by
conventional, niobium-magnet DC electric
motors and a set of rollers to pull the
climbers up the ribbon at speeds up to 200
km/hr. The spent initial spacecraft and
construction climbers would become
counterweights at the space end of the
100,000 km long ribbon. An ocean-going
platform, based on the current Sea Launch
program, would be used for the Earth
anchor and located in the equatorial
Pacific. Major risk of damage to the ribbon
comes from meteor impacts and atomic
oxygen erosion; both can be mitigated
through several methods (curved ribbon
design, metal coating) and are discussed in
detail in the NIAC Phase I final report.
Modifications to this baseline scenario are
expected to greatly improve the deployment
and reduce the risk and construction costs
~Neil

skyhook = space elevator
I found some more numbers for The space elevator, and
the arithmetic does not seem to check, but that does
not mean we should not start work on various phases
of the Space Elevator. Perhaps most worrisome is the
CNT is not yet available in commercial quantities, so
we have trust the word of promoters regarding it's
performance, reportedly 40 times stronger than
anything else, and 3 square millimeter cross section will
hold 40 tons plus the mass of 6? million tons, yet a ribbon one micrometer = one micron
thick and 50 millimeters (0.05 square milimeters) wide
will support it's own mass plus one ton in reduced
gravity. The mass is 5000 tons. The average gravity is
perhaps 10% of Earth's sea level gravity. The ribbon is
tappered to a maximum width of 115 millimeters at GEO
stationary orbit altitude = 0.115 square millimeters. If
we figure an average cross sectional area of 0.1
millimeters, a length of 100 billion millimeters =
100,000 kilometers; the total volume of the ribbon is
ten billion cubic millimeters = ten million cubic
centimeters which weighs 5 million grams; so the
average density is 0.5 which is reasonable as carbon is
a low density element and the nano tubes are hollow.
However 5 million grams is only 5 tons. Can anyone
explain these apparent errors?
There are more details at www.isr.us/Downloads/niac_pdf/chapter1.html Neil