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Space launches are expensive, with typical costs of $5,000-$10,000 per pound of payload. Fuel is a significant cost, with 25-50 pounds of fuel required per pound of payload. Building larger rockets can reduce costs, but the most promising solutions involve fuelless or fuel-efficient launches. These include using an air-breathing engine or electromagnetic accelerator, or building a space elevator using carbon nanotubes. The latter is currently expensive, but prices are falling, and it may be economically feasible by 2020.
Launching into space has always been very expensive. A typical launch cost is $5,000 – $10,000 USD per pound of payload. Launching a 1,000-pound (450 kg) satellite can therefore cost up to $10 million USD. Ever since we started launching objects into space, scientists have looked for ways to reduce launch costs to open up this frontier for more companies, governments and individuals. However, little progress has been made so far.
One component of the cost of a space launch is fuel. For every pound of payload launched into low Earth orbit, 25-50 pounds of fuel are required. Typical rockets are powered by a combination of liquid hydrogen and oxygen, both of which must be kept at very low temperatures using many tons of cryogenic cooling equipment. Think of a rocket as a very expensive refrigerator the size of a tall building.
To reduce launch costs, one approach is to build a larger rocket. Thanks to economies of scale, larger rockets tend to cost less per pound than smaller rockets. However, that only goes so far. Larger rockets can reduce launch cost per pound by a factor of two or three, but not much more.
The most promising routes to substantially reduce launch costs involve solutions where the payload does not need to carry fuel with it during the climb. This is one of the costliest elements of a conventional rocket launch: A rocket must carry enough fuel to not only propel its payload, but also any remaining fuel as it climbs. The bottom of the atmosphere is the densest and most energy-expensive to traverse, but it’s also where the rocket itself is heaviest, requiring very large fuel tanks.
There are several proposals for fuelless or fuel-efficient space launches. One is to use an air-breathing engine (reactor) for the first stage of ascent, using atmospheric oxygen as the oxidizer rather than on-board oxygen. This was the approach used by SpaceShipOne, the first spacecraft built by a private company. Another, more futuristic approach would be to build an electromagnetic accelerator, or railgun, to fire a payload fast enough to reach orbit. Unfortunately, most payloads fired into orbit by a railgun would experience accelerations of at least 100 gravities, enough to kill humans. Therefore, if an electromagnetic accelerator were built for space launches, it would probably only be used to send supplies, such as water or steel, rather than astronauts or satellites.
An even more futuristic approach to reducing launch costs would be to build a space elevator, a tether that stretches from the equator to a counterweight orbiting 36,371km (22,600 miles) above the Earth. The only known material strong enough to be used for such an elevator without collapsing under the force of gravity would be carbon nanotubes. Currently, carbon nanotubes cost around $25,000 USD per kilogram or $25 million USD per ton. Even creating an elevator for the seed space would require about 20 tons, which at today’s prices would cost $500 million. It’s quite expensive, but nanotube prices are falling, and many scientists believe that building a space elevator could be economically feasible by 2020.
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