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August 28, 2012

Earth Based Space Elevator Economics not that compelling and many hurdles beyond material we don't have

Wikipedia - For a space elevator, the cost varies according to the design. Bradley C. Edwards received funding from NIAC from 2001 to 2003 to write a paper describing a space elevator design. In it he stated that: "The first space elevator would reduce lift costs immediately to $100 per pound" ($220/kg). However, as with the initial claims for the space shuttle, this is only the marginal cost, consisting of the electricity required to lift the elevator payload, but not operating overhead and maintenance; whereas the fixed costs would be US$6 to 12 billion, for construction; and one-way designs (such as Edwards') will add to the cost of the elevators.

There are cheaper and feasible ways to lower the costs to get to earth orbit than to try to build an earth based space elevator.

The gravitational potential energy of any object in geosynchronous orbit (GEO), relative to the surface of the earth, is about 50 MJ (15 kWh) of energy per kilogram (see geosynchronous orbit for details). Using wholesale electricity prices for 2008 to 2009, and the current 0.5% efficiency of power beaming, a space elevator would require USD 220/kg just in electrical costs. Dr. Edwards expects technical advances to increase the efficiency to 2%. It may additionally be possible to recover some of the energy transferred to each lifted kilogram by using descending elevators to generate electricity as they brake (suggested in some proposals), or generated by masses braking as they travel outward from geosynchronous orbit (a suggestion by Freeman Dyson in the 1980s.

A space elevator built according to the Edwards proposal is estimated to cost $20 billion ($40B with a 100% contingency). This includes all operating and maintenance costs for one cable. If this is to be financed privately, a 15% return would be required ($6 billion annually). Subsequent elevators would cost $9.3B and would justify a much lower contingency ($14.3B total). The space elevator would lift 2 million kg per year per elevator and the cost per kilogram becomes $3,000 for one elevator, $1,900 for two elevators, $1,600 for three elevators, until construction costs are recovered, after which this drops significantly.

A fully reusable Spacex rocket could have better economics than a space elevator. A Falcon Heavy should have a one time launch cost of $1000/kg. A reusable Falcon Heavy could have costs 60 times less at a little less than $50/kg.

Various Things That We Do Not Have or Are Unable to Do Are Needed

The Earth based space elevator is 90,000 miles long. It goes past geosynchronous orbit. It is double the distance to geosynchronous at least. A space pier uses towers that are 100 kilometers tall and can use 5 GPa material. A space pier would be 1300 times shorter than a space elevator and can use materials that are 10 times weaker.

A space pier seems to strain credulity for some but is far easier to build than a space elevator

Very tall inflatable towers are under development.


7 meter proof of concept









The space elevator needs thousands of tons of carbon nanotube or graphene cables that are 5 to 10 times stronger than what we are making in any kind of volume now.

The space elevator needs better robotic climbers. Faster and more powerful climbers than what we have now. In the lower part of the climb the climbers have to deal with wind and weather without critical failure.



If you were transporting people and using a 200 kilometer per hour climber, it would need some kind of radiation shielding. The space elevator would run through the Van Allen belts. This is not a problem for most freight, but the amount of time a climber spends in this region would cause radiation poisoning to any unshielded human or other living things.

There are other safety issues.

The space elevator needs more efficient power beaming than what we have now and at a higher power level than what we have now to lower the cost of electricity used. A high density power source (for example a lightweight fusion power system) could enable climbers to carry their power. This would remove any power beaming efficiency problems. Of course a fusion powered reusable space plane would also be very economical especially if it had low capital costs from a molecular nanotechnology enabled manufacturing capability. The more technology capability that you have to make the space elevator feasible is technology that makes competing options better.

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