Wireless Week has a story on Sanswire Technologies:
Sanswire Technologies is keeping its dream alive of creating a national wireless broadband network with a re-designed satellite-like, high-altitude airship, the Statellite [sic].
Rather than orbiting like a traditional satellite, a Statellite is stationed in the stratosphere. At an altitude of 13 miles, the ship can provide a wireless transmitting platform that can see an area of up to 300,000 square miles.
The company plans to launch a series of the units in the United States to create a national wireless broadband network, enabling subscribers to access the Internet wirelessly at high speeds anywhere in the United States, as well in parts of Canada and Mexico.
"The new design will give us much more flexibility. Not only will we be able to offer wireless broadband services to our subscribers, but the platform can also be used to transmit other wireless services such as cellular, MMDS, fixed wireless telephony, HDTV and 3G/4G mobile," said Michael Molen, Sanswire's CEO.
The figure of 300,000 square miles struck me as quite large. It implies a radius of 309 miles, which -- though I'm most definitely not a wireless engineer -- seems far for inexpensive, bidirectional, broadband communications.
To get some idea of the size of 300,000 square miles, here's a circle of that size centered on downtown Chicago (click on any image for a larger view).
Here's the same circle from a continental view.
13 miles equals 68,640 feet; I presume they're really talking about 70,000 feet and rounding to the nearest mile. A handy calculator tells us that from 70,000 feet, the distance to the horizon is actually 356 miles.
Now, even at a distance of only 309 miles, an object at 70,000 feet is going to hang low on the horizon. From the table found on this page, at 70,000 feet, the elevation from 300 miles away is 0.4 degrees -- in other words, slightly less than the width of the Sun or a full Moon in the sky (see here for more on estimating angles in the sky). That's not much -- easily less than treetops or nearby buildings. (As a point of reference, DirecTV's satellites 1, 2, and 3 have elevations of up to 21 degrees above the horizon throughout Alaska, and many Alaskans must buy larger-than-DBS dishes in order to have a hope of receiving a signal.)
10 degrees above the horizon -- the width of one's fist (with thumb tucked in) at arm's length -- seems more reasonable to me. That equates to a range of just under 75 miles. A radius of 75 miles equals a coverage area of 17,671 square miles, which doesn't sound nearly as impressive as 300,000, but if they're just talking about covering major cities, it's not bad at all.
Here's a circle with a radius of 75 miles centered on the Empire State Building.
With a range of 75 miles, it would take only three stationary airships to cover the Boston-New York-Washington corridor.
I may be wrong about this, and the true range may be 309 miles, but even at 75 miles, it's an interesting proposition, at least for well-populated areas. The "BosNYWash" corridor has an estimated population of 40 million, and is the largest, most densely populated megalopolis in the US, and why not start with the best case? Three hovering airships to serve a total available market of 40 million people sounds great to me.
On the other hand, Sanswire claims that it will only take 12 airships to provide coverage "anywhere in the United States and parts of Canada and Mexico." I've played with my mapping program, and I just can't get this to work -- I can't make 12 circles with a radius of 309 miles each completely cover the continental US. The area of the continental US is 2,870,084 square miles, but the US is irregularly shaped, and a circular coverage pattern implies overlap in any case.
So, at the end of all this, I'm intrigued by Sanswire, but I have a few questions:
- By a coverage area of 300,000 square miles per airship, does Sanswire mean to imply a range of 309 miles?
- At an airship altitude of 70,000 feet and a range of 300 miles, the airship will be only 0.4 degrees above the horizon. How will users experience reliable communication at such a low elevation?
- At a line-of-sight distance of 309 miles, what sort of power will be required to transmit to the airship? What does this imply for portable communications devices?
- How can Sanswire provide service to anywhere in the continental US with only 12 satellites, each with a range of 309 miles?
I'm interested in the answers to these questions, both from readers with technical knowledge and from the Sanswire people themselves (whom I'll invite to respond here).