Friday, March 01, 2013

ELEVATE PAYLOADS FROM EARTH

Tower of Babel (Gen. ch 11)
Tower of Babel
In the first recorded space project,
mankind tried to reach space via a huge structure.
Like many government projects, 
miscommunication caused severe chaos.
Unity of purpose remains important.

Eventually most materials for space borne habitats will come from space borne resources. Structural materials will likely come from asteroids and consumable fluids (fuel and life support) from comets. However, some resources will always be needed from Earth. For example, space faring humans will always need reliable, inexpensive ways to transit their home planet.
NEED TO ELEVATE RESOURCES

Some resources will always need to elevate from Earth to GEO for subsequent export throughout the Solar System.
EXAMPLE: Terraforming planets, moons and especially habitats will need plentiful supplies of Terran topsoil with unique mixture of microbes, flora seeds, worms and other organisms. Ample supplies will be crucial to continue life in extraterrestrial locations as humans know it on Earth.
EXAMPLE: Until ices are routinely obtained from space borne comets, water must come from Terra's vast oceans.  Spaceborne human vessels (habitats and g-force ships) will need considerable water supplies for life support needs which include drinking, agriculture and perhaps even recreational uses such as swimming maybe even skating.  As a bonus, water happens to be the best shielding for most types of space radiation.


EXPORTING MASS MATERIALS FROM EARTH
Transportation to orbit is often the limiting factor in space endeavors. Present-day launch costs are very high; as much as $25,000 per kilogram from Earth to Low Earth Orbit (LEO). While cheaper launch methods are required, we'll also need cleaner methods to avoid serious damage to the atmosphere from numerous launches. One possibility is air-breathing hypersonic air/spacecraft under development; another proposed project is a mass driver.
However, Thought Experiment (TE) assumes best bet for long term utility is the
SPACE ELEVATOR
In 1960, Soviet engineer, Yuri Artsutanov, conceived an "electric train to the cosmos" ; he thought it'd take 200 years to become reality. In 2010, Yuri reconsidered; he decided the first space elevator could rise into the heavens in just 30 more years.

Payloads and people could someday ride climbers attached to ribbons of super-strong material (i.e. carbon-nanotubes), reaching orbits as high as 100,000 kilometers (62,500 miles). Ribbon would stretch to a small counterweight approximately 62,000 miles (100,000 km) into space. A sea vessel resembling an oil rig will anchor the entire 100,000 km ribbon to Earth. The first space elevator will originate from a mobile platform in the equatorial Pacific.
A counterweight at the end of the space elevator will keep the ribbon taut (much like a tetherball stretching a rope from a pole).
Geosynchronous Equatorial Orbit (GEO) is the one orbit where objects  circle the globe in exactly 24 hours.  Thus, a GEO object can stay "parked" directly over any point of Earth's Equator.Platform at 0G would process climber contents. Cables would connect to the platform at both top (spaceward) and bottom (Earthward).
Habitat at 1G provides very comfortable living quarters for over 1,000 climber passengers.  Like other habitats throughout the Solar System, it would simulate Earth gravity via spin induced centrifugal force and obtain power from solar light reflected via attached mirrors.
Blocks of sea ice
would likely be
a common climber payload;
as need for water
will be great.



On Earth's equator
cable would anchor
to an offshore sea platform
(not shown).
Cost of access to outer space could greatly decrease (perhaps less than 1% of current cost). Cost of space missions has changed little during modern times. Whether the re-useable space shuttle or the expendable Russian spacecraft, the cost of launching cargo into space still remains about $25,000 per kg.

A "space elevator" system could make travel to Geosynchronous Equatorial Orbit (GEO) a routine, inexpensive event; this could transform the global economy. Mechanical lifters could attach and climb the ribbon, carrying cargo and humans into space, at only $100 per pound ($220 per kg).
Dr. Bradley Edwards of the Spaceward Foundation: "Previously the material challenges were too great. But now we're getting close with the advances in creating carbon nanotubes and in building machines that can spin out the great lengths of material needed to create a ribbon that will stretch up into space".
According to Edwards: "Current estimates put the cost of building a space elevator at $6 billion with legal and regulatory costs at $4 billion." By comparison, acquiring space shuttle system cost about $19.5 B; cost per shuttle mission is about $500M.
The space elevator could be used for satellite deployment, defense, tourism and further exploration. A spacecraft would climb the ribbon of the elevator and then would launch toward its main target once in space. This type of launch would require less fuel than would normally be needed to break out of Earth's atmosphere. Some designers also believe that space elevators could be built on other planets, including Mars.
*********CONTENTS*********
. Ribbon Conveyor Belt
The carbon nanotubes composite ribbon will be just a few centimeters wide and nearly as thin as a piece of paper. Long carbon nanotubes -- several meters long or longer -- would be braided into a structure resembling a rope. Manufacture a long ribbon of nanotubes; then, wind it into a spool and launch into orbit. When the spool reaches geostationary orbit (35,790 km above Earth's surface), start unspooling in two directions simultaneously; both downward toward the Earth and upward away from Earth. When the downward ribbon reaches Earth's atmosphere, it would be caught and then lowered and anchored to a mobile platform in the ocean. Similarly, the upward boundward ribbon would attach to the counterweight.
Redundant Strands
Space elevator must have redundant strands for reliability and to enble simultaneous lifters to travel both up and down.

If elevator system has only one lifter and one ribbon; then, space elevator can only handle one lifter per cycle (several weeks). Awaiting cargo loads will form a very long queue.

On the other hand, ribbon can be more like a conveyor belt with several lifters interspersed along its length. Then, quantity of concurrent lifters on one strand is only limited by load capability.  If one strand could carry one lifter every 5,000 km; then, a lifter would be available every day and theoretical number of lifters on one strand could be as many as 7.
SUMMARY: Effective Space Elevator Needs Conveyor Belt Ribbon
to continuously cycle both up and down.
While this ribbon is still notional, other elevator components can be constructed with known technology.
Thus, by the time the ribbon is complete, other components can also be ready (perhaps by 2028).

A sea vessel resembling an oil rig will anchor the entire 100,000 km ribbon to Earth. The first space elevator will originate from a mobile platform in the equatorial Pacific.

The entire elevator system can reposition by moving the anchor along Earth's equator (east or west). The anchor design shares many required characteristics with the Sea Launch ocean-going launch platform.
Counterweight spins around the Earth, keeping the ribbon taut for the robotic lifters to ferry loads up and down.
Putting the counterweight on the end of the ribbon might prove challenging. One option for a counterweight calls for using left over ribbon material and associated equipment.Another option calls for capturing an asteroid.
NOTE: The counterweight is NOT at geosynchronous orbit; thus, it will tend to orbit as determined by its distance from Earth's center, a much slower orbit then geosynchronous (once per 24 hours). However, space elevator concept calls for counterweight to be "tethered" to the geosynchronous station thence to the "anchor" at Earth's surface. This centripedal force overcomes the counterweight's orbit to keep it directly above the geosync station which is in turn, directly above the anchor. Thus, the frequent "tetherball" analogy.
Robotic Lifter
Solar powered robotic lifter will climb the ribbon into space. Traction-tread rollers will grip the ribbon to accomplish the climb. A geostationary orbit (GEO) distance from earth surface is about 35,790 km; thus, at 200 kph, one lifter might take about 7.5 days {35,790 km/(200 km/hr) 179 hrs} from Earth's surface to GEO; then, another 7.5 days back to the surface (i.e. one lifter cycle ≈ 15 days).

Operational lifters could climb the space elevator frequently. Their payload capacity will be about 14 tons of payload with a volume exceeding 15,000 cubic meters (m3). Cargo will range from satellites to solar-powered panels and eventually human passengers.

Downward lifters can use Earth’s gravity to power their return trip; they would use their rollers and the ribbon to limit their velocity to 200 kph and to guide their downward path.
Risk Analysis: (Few space elevator vulnerabilities include:)
HIGH WINDS
The lowest few kilometers of the tower would feel wind loads, but the required equatorial location of the tower base avoids the trade winds and the jet streams. See Space Elevator paper by Jerome Pearson (USAF's original "thought leader" on space elevator).
Anchored at the Equator, ribbon would experience very low average wind speeds.  Jet streams are limited to temperate latitudes; and hurricanes never occur at less than 5° latitude.
On the other hand, tropical tornadoes produce winds as high as 150 m/s.   Fortunately,  the large tensile strength reserve of the tower at the base could handle these winds.
TERRORISM

The anchor's isolated location will considerably lower the risk of terrorist attack. For instance, the first will be in the equatorial Pacific, 404 miles (650 km) from any air or shipping lanes.

Only a small portion of the tether's length will be within reach of any attack, (15 km or below). 

As a valued global resource, the space elevator will likely be protected by specially trained military forces.
SATELLITE COLLISIONS
A space elevator would present a significant hazard to the many deployed satellites. In fact, all objects in stable orbits with perigees below GEO altitude (35,800 km) will eventually impact the cable. To avoid satellites; the entire system will actively avoid them.

"Our plans are to anchor the ribbon to a mobile platform in the ocean," said Tom Nugent, of LiftPort. "You can actually move your anchor around to pull the ribbon out of the way of satellites."
SPACE DEBRIS
Unlike satellites, it's highly impractical to pro-actively avoid the numerous space debris which range in size from 0.1 cm to many cm in diameter.  However, the space elevator cable can provide an unexpected benefit; it can be a "space broom" to sweep the skies clean of unwanted orbital debris both manmade and natural.
To rapidly repair associated damage to the cable, one might deploy armies of "nanomites"; tiny robotic entities which could exist throughout the very long cable. These nanobots would actively detect debris impacts and fix damage; they might even retrieve debris for analysis.
BEST RISK MITIGATION: Redundancy; always have a spare tether ready to go.
Operational Analysis: A Summary
(Space elevators will make GEO trips more frequent and more affordable.)
How frequent?? At 200 kph, just one lifter can maintain a payload cycle to geostationary orbit of 15 days (7.5 days to ascend to GEO Node, and 7.5 days to return).  While a chemical rocket can reach the GEO much quicker, its launch cycle requires several months. Furthermore, rocket cost per cycle is many millions of dollars (typical cost: $100,000,000 per launch), much greater than forecast cost of Space Elevator.
Thus, Space Elevator can more easily upload mass materials.
----a. Terran top soil contains life forms (helpful bacteria, seeds, worms, bugs, etc.) required to terraform nonterrestrial bodies such as habitats, moons and rocky planets. Without it, agriculture will prove impossible. Radiation and low temps will sterilize the outer layers of topsoil but inner layers should protect sufficient lifeforms to terraform.
---b. Huge volumes of water will be needed, but an endless supply is readily available at the sea based, Marine Anchor.
---c. Frozen Treats. During ascent, unprotected packages will freeze solid to become a nice neat package for later defrost.
---d. Easy Dropoff. With a transponder, each payload could join a series of orbiting objects at geostationary orbit to be picked up as needed.
TE assumes a habitat will need an enormous amount of water; perhaps 3,000 metric Tonnes (mTs) of water to supply a typical mission. Earth's oceans can easily supply this amount; however, lifting this large mass from Earth's surface to GEO will definitely require a resource such as the space elevator.
In addition, Terran topsoil and many other miscellaneous items must also ascend to orbit. If a "lifter" can transport 10 mTs per lift, it will take 300 cycles to export sufficient water for one mission. Assume an equal requirement for Terran top soil for another 300 cycles. Further assume another 400+ cycles for other payload requirements then one habitat might need 1,000 lifts of 10 mTs for just one mission.
With only one strand of ribbon and one lifter; then, SE needs a 15 day cycle for each 10mT load up to GEO. At that rate, each g-force mission needs 15,000 days (about 41 years) to completely supply the habitat.
With redundant strands and multiple lifters, capacity could conceivably increase to 1 load per day. Once each day, a lifter begins its climb on Up-link strand; 7.5 days later, the lifter reaches GEO.  Lifter cannot use same strand to return because 6 other lifters are also ascending to GEO.  Thus, lifter discharges its payload and is ferried over to Down-link strand dedicated for downward travel and starts is descent.  7.5 days later, it arrives at Marine Anchor to start another 15 day cycle. Thus, total time to supply habitat reduces from 15,000 days to 1,000 days or about 3 years.













FINAL NOTE
Relevant Links





At 100,000-km,
space elevator will extend to
 about a fourth of the distance 

to Luna, our moon.









VOLUME 0: ELEVATIONAL
VOLUME I: ASTEROIDAL
VOLUME II: INTERPLANETARY
VOLUME III: INTERSTELLAR




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