NASA is phasing the Space Shuttle out of service. Without the Space Shuttle, how will we send people into space? The Saturn V rockets of the Apollo program were effective, but they used vast amounts of fuel. It is time for some innovation. We have relied on chemical fuel rockets for half a century. We need a better way of getting to space.
One major drawback for chemical rockets is the weight of the fuel itself. The fuel's combustion has to generate enough thrust to lift both the fuel and the rocket/payload. The Space Shuttle has a mass of 100,000 kilograms, but when combined with its rockets there are 2,000,000 kilograms that need to lift off the ground. The energy for thrust is stored in the fuel's chemical bonds, and the energy density is limited. It might be better to store the energy on the ground, and beam that energy to the spacecraft during liftoff. That way, a lot of energy can be combined with less fuel to produce the same or more thrust. A powerful laser facility would act as a launch base. With a constant supply of energy, it could launch commercial satellites much more often—and more cheaply—than rockets. If you want to launch two rockets in one day, then you need to build two rockets. With laser propulsion, you only need to build one laser facility and fire up the lasers twice.
A vessel built for laser propulsion focuses (with optics or heat exchangers) laser beams from the ground to ignite either some propellant or just the air below. A continuous or pulsating (depending on the type of laser) explosion is created, but without combustion of conventional rocket fuel. The vessel gets its propelling energy from the light of the laser beam, not chemical bonds in expensive fuel, and the “lightcraft” is propelled upwards. This is the principle behind laser propulsion.
Scaling up payloads should be easier with laser propulsion. With rocket-propelled spacecraft, you need more or bigger rockets to launch heavier payloads. As mentioned earlier, the weight of the fuel itself is a problem. But with laser propulsion, you can simply add more lasers on the ground and aim them all at the same point. This way you get more thrust without adding more heavy fuel tanks.
One problem is keeping the lightcraft stable during launch. Current scaled-down prototypes spin at high rates in order to fly straight up. Such spinning might not be desirable for a full scale lightcraft. If the whole vessel rotated while carrying passengers, they would get sick, or worse. Perhaps a large gyro could be used instead of spinning the whole craft, but that would add to the overall weight.
Another obstacle for laser propulsion is the power of lasers. It takes about one megawatt of laser power to lift one kilogram of lightcraft into space. The Space Shuttle weighs about 100,000 kilograms so launching a lightcraft as massive as a Space Shuttle would require around 100,000 megawatts (100 gigawatts) of laser power. To put this into perspective, think about some real-world lasers and their outputs. Common laser pointers have power ratings under 5 milliwatts (0.000005 megawatts). The military laser, ZEUS, has a power rating of 10 kilowatts (0.01 megawatts). The Nova laser, part of a nuclear fusion project, was capable of 16 terawatts (16,000,000 megawatts) in very short bursts. Roughly, you would need 10,000,000 ZEUS lasers to send a Space Shuttle into low orbit, or 500,000 to send a 5,000 kg Apollo lunar module. Considering the energy supply for such laser power, a nuclear power plant generally produces around 1,000 megawatts of electricity.
The limitations in engineering and powering of lasers makes lightcraft best suited for very small satellites. This could be beneficial for research institutions and companies that want to put equipment into orbit but cannot afford big rockets. Also, cargo and spacecraft could be sent up in pieces, then assembled in orbit. Perhaps in the future rockets will be limited to large payloads, and lasers will routinely launch anything under a certain weight limit. With technology improving all the time, microsatellites might become common and affordable.
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