Space elevator economics

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With a space elevator, materials could potentially be sent into orbit at a fraction of the current cost. It is the aim of this article to compare the speculative total costs of a future space elevator with the speculative total future costs of rocketry and other alternatives.

Costs for well-tested systems to low earth orbit are from about $7,500 per kilogram for a Soyuz launch [1] (http://www.astronautix.com/lvs/soya511u.htm) to about $40,000 per kilogram for a Pegasus launch today (2004) [2] (http://www.astronautix.com/lvs/pegasus.htm) [3] (http://www.theculture.org/rich/sharpblue/archives/000066.html) . Some systems under development, such as new members of the Long March CZ-2E, offer rates as low as 5,000$/kg, but (currently) have high failure rates (30% in the case of the 2E). Various systems that have been proposed at varying points in history have offered even lower rates, but have either failed to get sufficient funding (Roton, Sea Dragon), are currently under development, or most commonly, have financially underperformed (as in the case of the Space Shuttle). NASA is trying with its Space Launch Initiative (SLI) to drive rocket launch prices down via a second generation reusable launch vehicle.

Geosynchronous rocket launchers deliver 2-3x less payload to GEO than to LEO as they require additional fuel to reach the higher orbit which cuts into the payload; and hence the cost is proportionately greater. The bulk costs to Geosynchronous orbit are currently about $20,000 per kilogram for a Zenit-3SL launch.

It is difficult to define the lower limit on the cost of rocket launch. While fuel costs per payload can be fairly well defined, a rocket system is comprised of tradeoffs. For example, Liquid Oxygen and Liquid Hydrogen give a better impulse than many other fuels, but require insulated cryogenic tanks that require inspection, pressure release for vaporizing fuel, and give less launch readiness. Better engines can increase thrust, but often suffer increased wear. A rocket is far more than the fuel to get it to orbit, and despite trillions of dollars being spent on space exploration, rocket costs have changed relatively little since the 1960s. [4] (http://www.theculture.org/rich/sharpblue/archives/000066.html) It is, however, logical that rockets will be cheaper in the future as materials technologies advance - especially those that would enable a space elevator. However, studies have shown that the main cost driver on launch is volume; the more launches a system performs the cheaper it becomes.

Government funded rockets have not historically repaid their capital costs, and do not necessarily try, although some of the sunk cost is often quoted as part of the launch price. A comparison can therefore be made between the marginal costs of fully or partially expendable rocket launch and space elevator marginal costs. It is unclear at present how many people would be required to build, maintain and run a 100,000km long Space Elevator, and consequently how much that would increase the elevator's cost.

For a space elevator, the cost varies according to the design. Using the design specs developed by Dr. Bradley Edwards, referring to the marginal cost, "The first space elevator would reduce lift costs immediately to $100 per pound" ($220/kg) [5] (http://isr.us/SEHome.asp?m=1).

Development costs might be roughly equivalent, in modern dollars, to the cost of developing the shuttle system.

The marginal or asymptotic cost of a trip would consist solely of the electricity required to lift the elevator payload, maintenance, and in one-way designs (such as Edwards'), the cost of the elevators.

The gravitational potential energy of any object in geosynchronous orbit, relative to the surface of the earth, is about 50 MJ of energy (about 15 KWh) per kilogram of that object. (See geosynchronous for details).

Given current power grid costs and the current 0.5% efficiency of power beaming, a space elevator would require $350/kg just in electricity costs. However, electricity costs are exceptionally difficult to predict; consider both the currently rising price of electricity compared against the nebulous possibilities of fusion power, or the solar power that could be generated by a GEO object (like that at the end of a theoretical space elevator).

By the time the space elevator is built, Dr. Bradley Edwards expects technical advances to increase the efficiency to 2%. (see power beaming for details).

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 a private communication to Russell Johnston in the 1980s).

Other non-rocket technologies have also been proposed that offer more encouraging results for low-cost payload launch (see spacecraft propulsion).

For the space elevator, the efficiency of power transfer is often a limiting issue. In most designs, the concept of a superconducting cable for transferring power - even if incredibly light - will add hundreds of tons of weight to the cable, easily breaking it. Consequently, power beaming is nearly always viewed as the only efficient mechanism for power transfer.

The cost of the power provided to the laser is also a limiting issue. While a land-based anchor point in most places can use power at the grid rate, this is not an option for a mobile oceangoing platform. A specially built and operated power plant is likely to be more expensive up-front than existing capacity in a pre-existing plant.

Finally, up-only climber designs must replace each climber in its entirety or carry up enough fuel to return it to earth - a potentially costly venture.

Space elevators have high capital cost but low operating expenses, so they make the most economic sense in a situation where it would be used over a long period of time to handle very large amounts of payload. The current launch market may not be large enough to make a compelling case for a space elevator, but a dramatic drop in the price of launching material to orbit would likely result in new types of space activities becoming economically feasible. In this regard they share similarities with other transportation infrastructure projects such as highways or railroads.

Note that governments generally do not historically even try to repay the capital costs of new launch systems from the launch costs. Several cases have been presented (space shuttle, ariane, etc), documenting this. Russian space tourism does partitially fund ISS development obligations however. See [6] (http://www.isr.us/SpaceElevatorConference/pdf/Kare/Workshop2_kare.pdf) for a projection of different costs of several very different launch systems.

This document includes the claim that it seems that governments are not willing to pay the capital costs of a new replacement launch system. Only if that new system provides, or appears to provide, a way to reduce their overall projected launch costs (including any new capital costs of the new system), have they been willing to fund a program. This was why the Space Shuttle program proceeded. Governments tend to prefer to cut costs in many cases, spending more money is something they are usually loathe to do; unless it results in lots of votes.

Additionally, according to a paper presented at the 55th International Astronautical Congress in Vancouver in October 2004, the Space Elevator can be considered a megaproject and the current estimated cost of building it ($6.2 billion) is rather favourable when compared to the costs of constructing bridges, pipelines, tunnels, tall towers, high speed rail links, maglevs and the like. It is also extremely favourable when compared to the costs of other aerospace systems as well as launch vehicles. [7] (http://www.spaceelevator.com/docs/iac-2004/iac-04-iaa.3.8.3.09.raitt.pdf)

Total cost of a privately funded Edwards' Space Elevator

A space elevator built according to the Edwards proposal is estimated to require $40billion. This includes all operating and maintenance cost. If this is to be financed privately then perhaps a 15% return would be required - i.e. $6bn annually. The SE would lift 2,000,000 kg per year and the cost per kilogram lifted is therefore $3,000. Despite all that precedes this section of the article some well-founded estimates of future rocket all-in costs are similar.

Additionally, in potentially the same time frame as the elevator, the Skylon spaceplane (not a conventional rocket) is estimated to have an R&D and production cost of about $15 billion. The vehicle has about the same $3000/kg price tag. Skylon would be suitable to launch cargo and particularly people to low/medium Earth Orbit. The space elevator can only send cargo although it can do so to a much wider range of destinations. [8] (http://isr.us/Downloads/niac_pdf/chapter7.html)