Space elevator economics

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This article compares space elevator economics with the economics of alternatives like rockets.

The costs of using a well-tested system to launch payloads are high. Prices range from about $4,300/kg for a Proton launch^[1] to about US$40,000/kg for a Pegasus launch (2004).^[2]^[3] 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 have offered even lower rates, but have failed to get sufficient funding (Roton; Sea Dragon), remain under development, or more commonly, have financially underperformed (as in the case of the Space Shuttle). (Rockets such as the Shtil-3a, which offers costs as low as $400/kg rarely launch but has a comparatively small payload, and is partially subsidised by the Russian navy as part of launch exercises.)

Geosynchronous rocket launch technologies deliver two to three times smaller payloads to geosynchronous orbit than to LEO. The additional fuel required to achieve higher orbit severely reduces the payload size. Hence, the cost is proportionately greater. Bulk costs to geosynchronous orbit are currently about $20,000/kg for a Zenit-3SL launch.

Rocket costs have changed relatively little since the 1960s, but the market has been very flat.^[3] It is, however, quite reasonable to assume that rockets will be cheaper in the future; particularly if the market for them increases.

Rocket costs are significantly affected by production volumes of the solid parts of the rocket, and by launch site costs. Intuitively, since propellant is by far the largest part of a rocket, propellant costs would be expected to be significant, but it turns out that with hydrocarbon fuel these costs can be under $50 per kg of payload. Study after study has shown that the more launches a system performs the cheaper it becomes. Economies of scale mean that large production runs of rockets greatly reduce costs, as with any manufactured item, and reuseable rockets may also help to do so. Improving material and practical construction techniques for building rockets could also contribute to this. Greater use of cheap labour (globalisation) and automation is practically guaranteed to reduce manpower costs. Other costs, such as launch pad costs, can be reduced with very frequent launches.

Government funded rockets have not historically repaid their capital costs. 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 launches and space elevator marginal costs. It is unclear at present how many people would be required to build, maintain and run a 100,000 km space elevator and consequently how much that would increase the elevator's cost. Extrapolating from the current cost of carbon nanotubes to the cost of elevator cable is essentially impossible to do accurately.

For a space elevator, the cost varies according to the design. Dr. Bradley Edwards, who has put forth a space elevator design, has stated that: "The first space elevator would reduce lift costs immediately to $100 per pound" ($220/kg).^[4] However, as with the initial claims for the Space Shuttle, this is only the marginal cost, and the actual costs would be higher. 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 not solely consist of the electricity required to lift the elevator payload. Maintenance, and one-way designs (such as Edwards') will add to 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 (15 kWh) of energy per kilogram (see geosynchronous orbit 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 electrical costs. By the time the space elevator is built, Dr. 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).

For the space elevator, the efficiency of power transfer is just one limiting issue. The cost of the power provided to the laser is also an 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 ocean-going platform. A specially built and operated power plant is likely to be more expensive up-front than existing capacity in a pre-existing plant. Up-only climber designs must replace each climber in its entirety after each trip. Return climbers must carry up enough fuel to return it to earth, a potentially costly venture.

Space elevators have high capital cost but presumably low operating expenses, so they make the most economic sense in a situation where they would be used to handle many payloads. 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. In addition, launch costs for probes and craft outside Earth's orbit would be reduced, as the components could be shipped up the elevator and launched outward from the counterweight asteroid at a lower cost in both funding and payload (since most probes do not land anywhere and almost none that do need to carry fuel for launch away from their destination - most probes are on a one-way journey).

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.

It has been suggested that governments are not usually willing to pay the capital costs of a new replacement launch system. Any proposed new system must provide, or appear to provide, a way to reduce overall projected launch costs. This was the impetus behind the Space Shuttle program. Governments tend to prefer to cut costs in many cases. Spending more money is something they are usually loath to do.

Alternatively, according to a paper presented at the 55th International Astronautical Congress in Vancouver in October 2004, the Space Elevator can be considered a prestige 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 not entirely unfavourable when compared to the costs of other aerospace systems as well as launch vehicles.^[5]

[edit] Total cost of a privately funded Edwards' Space Elevator

A space elevator built according to the Edwards proposal is estimated to cost $40 billion. This includes all operating and maintenance costs. If this is to be financed privately, a 15% return would be required ($6 billion annually). The space elevator would lift 2 million kg per year and the cost per kilogram becomes $3,000. Some well-founded estimates of future rocket costs are similar.

For comparison, 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 $3,000/kg price tag. Skylon would be suitable to launch cargo and particularly people to low/medium Earth orbit. The space elevator can move only cargo although it can do so to a much wider range of destinations.^[6]