§ 5.12.9 Bootstrapping to SPS -- Electric Power Utilities for Space with Wireless Transmission
Contrary to the Department of Energy studies, it is not necessary to build dedicated SPS platforms from scratch. For business, it's not necessary to fund SPS as a crash program to supply energy to Earth. Instead, there is a profitable, gradual bootstrapping approach.
Most every space related product and service discussed elsewhere in PERMANENT needs electric power. There's no need to list all the applications again here. The demand for electric power in space will undoubtedly continue to grow at an exponential rate. Eventually, it will be more economical to supply standard plug-in power modules made from solar cells manufactured in space for use in space, made from silicon, one of the most abundant elements in asteroids and on the Moon.
There are advantages to manufacturing silicon semiconductor solar cells in space, as discussed elsewhere.
A closely related technology which will probably be pressed into use first, and definitely in conjunction with expansion of space power capacity, will be wireless transmission of power, i.e., via radio beam operating at high frequency. That is the main topic of the rest of this section.
Whatever entity implements this technology in the marketplace is sure to become the power utility for space development, and eventually a beamed power utility for ground based users, too.
The demand for wireless power might unfold according to the following:
It should be emphasized that the practical and economical path to development of SPS will be power satellites becoming the electrical utility of outer space before they beam down power to Earth's economies. This could be either as a result of the growth of SPS platforms in space which start to supply some of their power to ground based consumers, or evolution to new SPS platforms to serve Earth specifically.
Indeed, it's likely that the first application of beamed power for space development will be to beam it up from Earth's surface to a rectenna in space.
Beamed power, or "wireless power transmission", using the same technologies proposed for SPS, has been demonstrated for decades on Earth. In 1964, a microwave helicopter was developed, and beamed power was considered for defense aircraft that needed to stay in the air over a particular place for long times without landing for refueling, e.g., air-launchable nuclear missiles which were mobile to evade a possible first strike. The specific SPS beam itself was tested during the SPS studies of the 1970s. The Japanese had planned a project to beam power from Earth to space as part of their SPS 2000 project, though it was later postponed indefinitely due to budget cuts.
Several applications of beamed power are worth discussing in some detail:
High Altitude Long Endurance (HALE) aircraft platforms for cellular/voice/data services
An emerging application of great potential for beamed power comes from the blooming cellular voice and data communications market, which has led several companies to do serious research on designs of flying communications antenna platforms located over cities for wireless communications. These are called High Altitude Long Endurance (HALE) platforms, and can be either dirigibles (i.e., balloons) or winged aircraft (i.e., airplanes or helicopters). These HALE platforms would replace today's cellular relay antennas based on the tops of towers and buildings, giving much better coverage and superior signals. They will relay communications from ground user to ground user, as well as between satellite above and local ground user below. They would be pilotless and remote controlled.
The two problems with HALE platforms that are the driving forces in their economics and feasibility are:
Beamed power satisfies both of these needs.
Beamed power to satellites and interorbital vehicles
Beaming power to objects in orbit (either ground to orbit, or orbit to orbit) would use the same technology as for HALE platforms. There is a difference in that objects in orbit are always moving. Automated slewing of the antenna is one obvious solution. Alternatively, phasing of the transmitted beam can provide the functional equivalent of slewing and has been used for mobile communications for a long time (keeping focussed on a small receiver at a distance without mechanical slewing) as well as in beamed power aircraft experiments.
As discussed in the PERMANENT section on emerging communications satellite constellations for cellular services, some of those near-term satellites are going to need substantial power sources.
Many communications satellites built by Hughes use "ion drive" electric powered thrusters for stationkeeping, as discussed in the section on transportation. Hughes has also developed an upper stage capability for delivering the satellite to geostationary orbit using electric propulsion. The NASA Deep Space 1 probe launched in October 1998 is relying 100% on electric propulsion to fly by an asteroid. The Russians have been using electric propulsion for more than 10 years on their military satellites.
A disadvantage of electric propulsion is the mass of the power plant required to deliver the maximum power to the thrusters.
By replacing the power plant with a rectenna and beaming the electrical power up to the spacecraft from Earth, we may be able to achieve significantly lighter and less expensive satellites.
Satellites in low orbit have energy storage systems for providing electricity when they are in the Earth's shadow, e.g., batteries. By locating power transmitters around the Earth, they can reduce battery storage, too.
We may also gain greater fuel efficiency due to the lighter satellite and the practical ability to deliver more energy to each unit of propellant. Stationkeeping by electric propulsion could occur while the power is being beamed up from Earth.
As space is developed, launch rockets will begin delivering their payloads to low Earth orbit - just above Earth's atmosphere. Lifting up from Earth is by far the most dangerous, difficult and expensive leg of the trip. From there, the cargoes will be picked up by space trucks and hauled to their final orbital locations. The most economical cargo vehicles will use electric propulsion.
By equipping electric vehicles and satellites with just a beam receiving antenna instead of an entire power plant, we can reduce their mass substantially and hence improve fuel efficiency.
Notably, fuel efficiency is proportional to the speed of the propellant ejected (by conservation of momentum), whereas the energy required is proportional to the square of the speed of the propellant (kinetic energy). Thus, the greatest efficiencies will come from beamed power, and the most economically competitive trucking services will rely on beamed power.
There is also a high radiation belt in a medium Earth orbit called the Van Allen Belt. Any solar cell powered vehicle passing through this belt will experience a slight degradation in performance due to the damaging effects of this radiation on solar cell panels. However, a receiving antenna is far less susceptible than a solar cell power plant would be.
Every satellite orbiting Earth needs stationkeeping due to the gravitational effects of the Moon and the Sun on their circular orbits. Satellites in low Earth orbit also experience drag due to the outer fringes of the Earth's atmosphere. Stationkeeping thrusting keeps them from falling into the atmosphere and crashing onto Earth, as well as maintaining an optimal orbit for delivering their service.
Electric propulsion uses electricity to accelerate a propellant for thrust, instead of a chemical explosion as with conventional rocketry. It is much more fuel efficient than conventional chemical rocketry. The disadvantage is that it needs high electric power, though only occasionally and for relatively brief times. That electric power can be beamed.
Beamed power to orbital and lunar industry
Since it is much less expensive and compact to produce a rectenna than to produce a power plant, future industry in space may buy power from a utility company which beams the electricity.
Large electric power plants would provide economies of scale, offering power cheaper than users could produce it themselves. They could sell the electricity at prices per kilowatt hour, just as for consumers on Earth. After all, industries and consumers on Earth don't produce their own electricity. We just connect to the utility company. The only difference in space is that the connection is wireless.
Satellites, space stations and industries are unlikely to consume energy at a continuous rate equal to their maximum capacity. Onboard excess capacity is often wasted. Thus, consuming beamed power on an as-needed basis would be more efficient than blasting up one's own power plant sized for maximum power consumption. It would be more efficient to consume the proper amount of energy from the utility when it is desired or scheduled. In this manner, an SPS can produce a "baseline" power output and schedule in consumers for varying loads. Of course, consumers could also store energy locally to handle quick variations of power needs.
On the moon, there are two week lunar nights followed by two week lunar days. If lunar applications are to use cheap solar rather than nuclear power, they'd be prime users of power beamed down from orbit. There will be enough power available to keep factories running full steam and even to illuminate the surface being mined, to assist in vision as well as warm up the surface in the frigid lunar nights.
Space based industry will be a major beneficiary of beamed power. The entire payload can be devoted to the industry, without needing to blast up the power plant.
Beamed power vs. energy storage
Industry located in low Earth orbit is in the shadow of the Earth half the time. Onboard solar power suddenly drops from peak to zero. Satellites in low Earth orbit spend half their time in shadow. They could get power from a power utility in a polar orbit (whereby the beam would never strike the ground below).
Beamed power relieves the satellite of needing to carry energy storage devices, e.g., heavy batteries, plus excess power plant to charge the batteries during the sunlit time. That's expensive. All they would need is a relatively lightweight rectenna.
Conclusion regarding wireless power transmission
The applications of beamed power have already arrived in the form of present day satellites and emerging HALE platforms, and there is no end in sight for follow-on applications. Whatever entity implements this technology in the marketplace is sure to become the power utility for space development, and eventually a power utility for ground based users, too. Proximity to market is not much of an issue. You can offer energy to users almost everywhere.