High-altitude platforms, or HAPs, are unmanned aircraft that stay in the air for an extended period of time in order to provide service to a fixed geographic area. The US government currently operates HAPs that stay aloft for a day or longer, but as solar power improves, the duration is expected to improve dramatically. The Boeing SolarEagle, which will begin testing next year, is expected to stay up for five years at a time.
One reasons to expect HAPs to quickly displace satellites for many uses is cost. A modern communications satellite costs hundreds of millions of dollars to build, deploy, and operate. Launch costs alone can exceed $100 million. Drones are cheap by comparison. A single Predator drone reportedly costs only $4 million, and we can naturally expect the cost of drones to fall more as they become more common.
A major reason drones are so much cheaper to build is that they are more serviceable. Satellites need to be constructed with small tolerances and meticulous care because they usually cannot be repaired while in orbit. A small bug that is not discovered until after launch could result in a total loss of equipment and launch costs. In contrast, drones can be ordered to return home to receive updates if a problem is discovered, which saves on up-front development costs.
HAPs are also superior to communications satellites because of the shorter distance that their radio signals need to travel. Geostationary satellites orbit at a height of 35,786 km. In contrast, most HAPs are expected to operate in the lower parts of the stratosphere, at an altitude of around 20 km. This is high enough to be above the weather and out of the way of commercial airplanes. It takes 119 milliseconds for light to travel from Earth to a geostationary satellite, or 238 milliseconds round trip. This is slow enough to make Internet use over a satellite link very unpleasant. But a radio signal can travel 20 km in under 0.07 milliseconds, so a round trip from the surface of the Earth to a HAP and back would take only 0.14 milliseconds, which is not even noticeable to a human being. The shorter distance for HAPs also means that weaker radios can be used. This means less energy use and better battery life for transmitters at both ends, and it means that the electromagnetic spectrum can be used more efficiently.
Satellites also suffer from the scarcity of orbital slots. Because geostationary orbit must take place exactly 35,786 km over the Equator, and because of the potential for interference from strong radio signals, there are a limited number of orbital slots. Countries at the same longitude are in competition with each other for these slots—a slot that serves New York City could also serve Bogotá. To solve this problem, orbital allocations are currently coordinated through the ITU (yes, that ITU). In contrast, there is no scarcity of space in the sky for HAPs. They don’t have to operate at an exact height or latitude, and there are few international externalities associated with HAP use.
Perhaps the most exciting aspect of HAPs is the possibility of inter-HAP communication. Imagine a mesh network of stratospheric drones functioning as high-altitude Internet infrastructure. One HAP every 600 miles or so would be sufficient to cover the globe. Such an arrangement would be much harder for governments to monitor and censor than the current system, in which some countries are served by only a handful of cables. It would also enable a more competitive local broadband market, since terrestrial services (and the regulators who impede them) would have to compete with the cost of an uplink to the HAP mesh.
HAPs won’t eliminate all satellites. In fact, they are likely to rely on GPS satellites in order to be able to maintain a fixed position over the Earth. There may be some other activities for which satellites remain the better option. But at least for communications, HAPs are likely to carry the day. They are cheaper, more serviceable, lower-latency, more efficient, and not limited by altitude or latitude restrictions. This exciting new use of drones is further evidence that airspace is our next great, disruptive platform for commercial and social innovation.