5 August 2009
- Power (Good)
Space-Based Solar Power, the PowerSat Way
A Q&A with PowerSat’s CEO
by G B Leatherwood
Here on planet Earth, we’re suffering from an energy crisis: we need gasoline to power our cars, and we need electricity to power our homes. Alternative sources of energy, such as solar and wind power, can only provide a fraction of what we need, and nuclear power has inherent risks. Of course, space enthusiasts see the answer to our problems beyond the planet. By capturing the limitless energy of the sun and transforming it into electrical energy we can use, the world will have the energy it needs without being drained of its finite resources.

Currently, the biggest obstacle to that vision is the expense of space travel. But recently the PowerSat Corporation announced the filing of U.S. Provisional Patent No. 61/177,565 or “Space-Based Power Systems and Methods.” The patent includes two technologies, BrightStar and Solar Powered Orbital Transfer (SPOT), that will enable the reduction of launch and operation costs by roughly $1 billion for a 2,500 megawatt (MW) power system.

Solar energy will be captured via solar power satellites (known as “powersats”) and transmitted wirelessly via microwave to receiving stations at various points around the globe.

PowerSat Corporation’s first patented technology, BrightStar, allows individual powersats to form a wireless power transmission beam without being physically connected to each other. This “electronic coupling,” conceptually similar to cloud computing, effectively eliminates the need to handle large (gigawatt) levels of power in a single spacecraft. Because of BrightStar, one transmission beam may now come from hundreds of smaller powersats that effectively form one large satellite array.

Space Future Journal talked with PowerSat Corp. CEO William Maness for further explanations of what a “powersat” is, how it works, how it will get into space, and when we can expect to see some tangible results from the project.

Space Future Journal: Lots of patents are filed, but most of them never get beyond the filing stage. What are your plans to make this a workable, profitable enterprise?

William Maness: The provisional patent is what starts the process. It effectively locks in the proprietary interest for up to eighteen months while the technical, financial, and regulatory details are being completed. We plan to have a BrightStar on orbit for demonstration purposes in the 2017-2018 range, or at most within three years of that.

SFJ: That’s interesting. I thought you would want the patent process to be swift.

Maness: No, actually it is in our interest to stay in the provisional stage for as long as possible to protect our interest, identify any potential challenges, and work out the details under the protection of the law.

SFJ: What do you see as the most formidable hurdle you will have to overcome?

Maness: I have to break that down into three parts: technical, financial, and regulatory. First, technical. Collecting solar energy and transforming it into usable electrical energy is being done every day with solar cell technology. However, transmitting electrical energy by wireless means has been well established and tested in the laboratory, but not in real life.

Experiments have been done in sending energy from mountaintop to mountaintop, but that’s not the same as beaming it from space to earth. The earth experiments had to traverse 200 miles of that same atmosphere, with the resultant loss of energy, but from space we only need to penetrate five miles of dense atmosphere.

This means that there is a lot less loss coming down vertically from space than sending it horizontally through the atmosphere. That’s where the big difference is.

Second, financially, it’s not as horrendous as you might think. We are taking a step-wise approach, with the interested organizations taking a sequential risk reduction approach. That is, we’re not expecting anyone to make an enormous investment all at once even before the processes are proven.

Third, regulations are mainly concerned with radio frequency allocations. The two frequencies available for this kind of transmission are 2.45 megahertz (MHz) and 5.8 MHz. We would prefer the 5.8 MHz band, but that’s the frequency most cell phones and related communication instruments use. We’re not going to ask the whole world to change its frequencies, just that we be allowed to use the higher frequency for solar power transmission. That will probably be favorably received because our beam is unmodulated, that is, it is not carrying data or voice—it’s like a bare carrier wave on the 5.8 MHz frequency. We don’t use much bandwidth or radio spectrum at all.

SFJ: How will the energy being sent down from space be collected here on Earth? I’ve seen proposals involving huge expanses of wire netting, similar to chicken wire, spread out over square miles of desert such as found in Nevada.

Maness: (Laughing) I’d have to say that the Nevada desert is probably the worst place in the country to place a receiving antenna, called a “ rectenna.” Here’s why: because of the power lost in transmitting by wire, the only way we can do it now, all electrical generating entities are geographically oriented—they have to be within 300 miles of the load they serve or rely on relay stations to compensate for the power loss. Space-based solar power is not limited like this because it’s vertical.

In your example, a rectenna in the Nevada desert could not serve Los Angeles, and certainly not Chicago or Detroit, because it’s too far away. Also, if there is a sudden need for emergency power in another part of the country, say in Chicago or New York City, the current grid system relies on what is called “wheeling,” or circulating power through the grid. That’s expensive and complicated. With the powersat system, the beam can be shifted with the click of a switch here on Earth to direct it where it’s needed.

Now I need to clarify our terminology a bit. “PowerSat” is the name of our company. Three hundred small receiving and transmission units called “BrightStar” are clustered in geosynchronous Earth orbit ( GEO) 330 miles above the earth. This cluster, or “cloud,” makes up a “power satellite” or “powersat.”

The units function just the same as the hundreds of solar collectors found on the International Space Station and the multitudes of satellites and spacecraft such as the Mars and moon rovers. The BrightStars communicate with each other and the earth controllers via microwave transmissions, precisely focusing the energy beam to where it’s needed on earth.

SFJ: A question frequently raised is, “What if the microwave beam strays from its intended target and fries a nearby community? Or what if birds or airplanes fly through the beam? Will they be fried?”

Maness: Again, this is really two questions. First, for some reason, highly unlikely but possible I suppose, the beam [could] var[y] from its intended target. In the millisecond it takes for the target to discover that it’s not receiving its signal, the beam shuts down. In other words, it can’t stray. If the beam doesn’t reach the target, it stops.

Second, the power of the microwave beam itself is smaller than what we normally use for a cell phone. That’s one reason why this won’t be used as a military weapon, as some fear. It’s just too weak. I suppose if you were standing directly under the rectenna trying to make a call on your cell phone, you’d experience some interference, but that’s about all. In fact, birds and airplanes fly through microwave beams all the time without harm. It’s not strong enough to harm the birds, and the aluminum shells of airplanes deflect the waves without any effect.

SFJ: Let’s talk about the rectennas themselves. How are they constructed? How big are they? How will they be protected from sabotage or vandalism?

Maness: As you described earlier, the receiving material itself is basically a wire mesh. In North America, the “footprint” is calculated to be an ellipse approximately one mile wide by one-and-one-half miles long. The mesh will be supported on poles 30 to 60 feet tall, much like the current power and telephone poles. One of the beauties of this system is that since it is wire mesh, it will not interfere with crops or animals under it. Rain and sunshine pass right through it. The microwave energy does not penetrate the mesh, so there’s no danger there. In fact, once the novelty wears off, those near the rectenna will probably not even notice it’s there.

The rectennas will of course be fenced in and monitored, so the opportunity for sabotage or vandalism is no greater than any other power generation plant.

SFJ: Now let’s talk about getting all these hundreds of “small” satellites into orbit. I put “small” in quotes because that seems like a relative term depending on who you talk to.

Maness: Right. When space solar power was first proposed forty years ago, a very large satellite collector to generate gigawatts of electricity was envisioned. Since then the technology has evolved rapidly and continues to do so with the development of ever-thinner film just microns thick and very flexible. This helped us with the development of BrightStar, since we can make them much smaller and thus easier and cheaper to put in orbit.

In physical dimensions, the BrightStar weighs about ten tons and is designed to ride atop an Atlas V or SpaceX Falcon 9 to low Earth orbit ( LEO). The BrightStar will take care of its own propulsion from LEO to GEO. In terms of physical dimensions, the inflatable stowed BrightStar will fit inside the payload envelope of both the Atlas and Falcon,, or 4.5 meters in diameter by 11.3 meters long, tapering to match the payload shroud. Deployed, each BrightStar looks like two thin plates, supported inside the rim. The larger of these two “disks” is the photovoltaic array and is 350m in diameter, separated and supported by an inflatable torus with a diameter of two meters. The smaller disk is the transmitter, about 100m in diameter, also thin-film in construction supported by the same inflatable outer rim. Each BrightStar will generate about 17 megawatts (MW) on orbit.

Conventional liquid-fueled rockets lift the BrightStar into LEO. From there each BrightStar will continue on its way powered by its own electric ion propulsion engine. In this way we save 67% of the weight needed to reach GEO, and ion propulsion doesn’t care much about orbital parameters. Granted, it may take six months or so to reach GEO, but the cost is relatively insignificant.

SFJ: Seems like we’re still fighting the lack of inexpensive reusable rockets to get your system in place. What we still need is a Henry Ford in the rocket industry.

Maness: And maybe Elon Musk, with the rapid advances he’s making now, is that fella.

Not only that, but I’m not in the launch business. I want to say to the industry, “I need to send 300 ten-ton satellites into LEO and spend $4 to $5 billion to do it.” And next year, we’ll do it again. We provide a credit-worthy, repeating-load customer to launch service providers. It is up to them to capitalize and risk-manage their own programs.

SFJ: You said earlier that there is little chance for microwave energy being used as a weapon. What interest, if any, has the US government or any other government shown in your process?

Maness: In fact, there has been some interest, but not for weaponry. It has been speculated that this would be a way to provide electrical power to remote or forward military operations not dependent on ground-based generation and transmission. Many other non-military opportunities may arise.

SFJ: I saw a sign in a doctor’s office the other day that I thought you might like. It said, “Those who say it can’t be done should refrain from interrupting those who are doing it!”

Maness: (Laughing) That’s exactly right. I wish I’d said that!

For more complete descriptions of the PowerSat Corporation and its current status, go to PowerSat.com.
Share |
G B Leatherwood 5 August 2009
Please send comments, critiques and queries to feedback@spacefuture.com.
All material copyright Space Future Consulting except as noted.