Airspace concerns
The platforms at 20 km altitude (65,000 feet) are far above commercial aircraft, in unregulated airspace and present no hazard to aviation. The main airspace concern is the potential hazard of tethers to aviation.
Background: High altitude tethered aerostats are not new. There have been tethered aerostat radars suspended almost permanently at 4.8km altitude along the southern US border since 1980. The company TCOM provides a wide range of tethered aerostat solutions, primarily to the military. TCOM aerostats have flown as high as 10km.
What is new is:
Aviation is broadly divided into general aviation and commercial aviation. Airspace is regulated into classes that mandate equipment and air traffic control. Class A is airspace above 18,000 feet and below 60,000 feet. Class B, C and D is airspace below 18,000 feet near airports. These air spaces are tightly controlled and a variety of instrumentation and rules are mandated in order to enter them. Planes without instrumentation are not allowed fly in these air spaces. The primary requirement is for radios to communicate with Air Traffic Control (ATC), and transponders which identify the aircraft and provide flight information. This equipment is primarily used to guarantee separation between aircraft. Another requirement for entering Class A airspace is GPWS/TAWS equipment that warns of flight into terrain. All this equipment is currently converting to a more modern GPS based NextGen which is mandated for all by 2020.
Commercial aviation flights are controlled by ATC and are mandated to carry the instrumentation discussed above. Aircraft fly in jetways at high altitude above 30,000 feet in Class A airspace, separated by altitude within and distance along the jetway. On approaching airports planes enter Class B and Class C controlled airspace under direct air traffic control. General aviation is a large class that covers private jets and turbo props, helicopters, and light aircraft. Most of these aircraft fly below 18,000 feet and have varying degrees of instrumentation. The US has by far the largest amount of general aviation (about 200,000 planes). Most of the developing world has very little general aviation (India has about 700 planes and helicopters, mostly used for business rather than recreational use)
The FAA has the authority to designate restricted airspace. A simple way to ensure that aircraft avoid tethers is to place them in restricted bits of airspace. If this restricted space was in class A, B, C and D it would mean all aircraft exposed to tethers would carry the instrumentation that ensures they avoid them, and aircraft without instrumentation would not be exposed as they are not permitted in these air spaces.
GPWS/TAWS would indicate the restricted tether airspace to aircraft and tether mounted transponders would also indicate the position of tethers, providing a redundant backup. Planes would have to be deviating from controlled flight paths that avoid tethers for either of these systems to be needed, so there is defense in depth. A plane deviating from its flight path is far more of a danger to itself and other aircraft than a tether is a danger to that plane.
Carving out restricted airspace in Class B and C airspace may be unacceptable as this airspace is near airports. Restricting tethers from Class B, C and D airspace would expose aircraft without instruments flying visual flight rules (VFR) to tethers. This would only expose commercial aircraft to tether restricted airspace when flying in Class A airspace. VFR pilots would be breaking the rules by entering a tether restricted airspace, but if they were without instruments they would be dependent on visual aids like lights and systems like Obstacle Collision Avoidance System (OCAS) to warn them. http://www.ocasinc.com/
So broadly, all commercial passenger carrying aircraft and all general aviation aircraft with instrumentation would have less risk of flying into a tether than aircraft flying at high altitude currently have of colliding with each other or colliding with mountains. These events have very low probability of occurrence. No plane with GPWS/TAWS has ever collided with a mountain, and mid air collisions of commercial aircraft flying in Class A airspace are extremely rare.
Aircraft flying VFR without instruments would be protected by visual aids and by OCAS. Nearly all flight obstacles currently are not protected by OCAS, including the TCOM aerostats on the southern border, so our tethered stratospheric platforms would be a dramatic safety improvement. Also aircraft flying VFR are always in need of visual points of reference, and our platforms and tethers should provide such a function. Aircraft flying VFR already have a high accident rate so the safety bar is somewhat lower than that for commercial aircraft.
The risk from tethers is demonstrably low and not a major impediment to success. The ability to get small amounts of airspace designated as restricted is dependent on the regulatory environment. The developed world is highly regulated and their airspace is very busy. This makes it likely a long process, except perhaps for special cases like internet in the far north. The developing world is less regulated and their airspace is much less busy. The risk reward ratio for them is far more favorable. Essentially free large scale broadband internet for a little bit of empty airspace.
Background: High altitude tethered aerostats are not new. There have been tethered aerostat radars suspended almost permanently at 4.8km altitude along the southern US border since 1980. The company TCOM provides a wide range of tethered aerostat solutions, primarily to the military. TCOM aerostats have flown as high as 10km.
What is new is:
- the tethered platform altitude of 20km which places tether hazards in Class A airspace
- the permanent nature of the platform and tethers
- a potential increase in the number of systems deployed.
Aviation is broadly divided into general aviation and commercial aviation. Airspace is regulated into classes that mandate equipment and air traffic control. Class A is airspace above 18,000 feet and below 60,000 feet. Class B, C and D is airspace below 18,000 feet near airports. These air spaces are tightly controlled and a variety of instrumentation and rules are mandated in order to enter them. Planes without instrumentation are not allowed fly in these air spaces. The primary requirement is for radios to communicate with Air Traffic Control (ATC), and transponders which identify the aircraft and provide flight information. This equipment is primarily used to guarantee separation between aircraft. Another requirement for entering Class A airspace is GPWS/TAWS equipment that warns of flight into terrain. All this equipment is currently converting to a more modern GPS based NextGen which is mandated for all by 2020.
Commercial aviation flights are controlled by ATC and are mandated to carry the instrumentation discussed above. Aircraft fly in jetways at high altitude above 30,000 feet in Class A airspace, separated by altitude within and distance along the jetway. On approaching airports planes enter Class B and Class C controlled airspace under direct air traffic control. General aviation is a large class that covers private jets and turbo props, helicopters, and light aircraft. Most of these aircraft fly below 18,000 feet and have varying degrees of instrumentation. The US has by far the largest amount of general aviation (about 200,000 planes). Most of the developing world has very little general aviation (India has about 700 planes and helicopters, mostly used for business rather than recreational use)
The FAA has the authority to designate restricted airspace. A simple way to ensure that aircraft avoid tethers is to place them in restricted bits of airspace. If this restricted space was in class A, B, C and D it would mean all aircraft exposed to tethers would carry the instrumentation that ensures they avoid them, and aircraft without instrumentation would not be exposed as they are not permitted in these air spaces.
GPWS/TAWS would indicate the restricted tether airspace to aircraft and tether mounted transponders would also indicate the position of tethers, providing a redundant backup. Planes would have to be deviating from controlled flight paths that avoid tethers for either of these systems to be needed, so there is defense in depth. A plane deviating from its flight path is far more of a danger to itself and other aircraft than a tether is a danger to that plane.
Carving out restricted airspace in Class B and C airspace may be unacceptable as this airspace is near airports. Restricting tethers from Class B, C and D airspace would expose aircraft without instruments flying visual flight rules (VFR) to tethers. This would only expose commercial aircraft to tether restricted airspace when flying in Class A airspace. VFR pilots would be breaking the rules by entering a tether restricted airspace, but if they were without instruments they would be dependent on visual aids like lights and systems like Obstacle Collision Avoidance System (OCAS) to warn them. http://www.ocasinc.com/
So broadly, all commercial passenger carrying aircraft and all general aviation aircraft with instrumentation would have less risk of flying into a tether than aircraft flying at high altitude currently have of colliding with each other or colliding with mountains. These events have very low probability of occurrence. No plane with GPWS/TAWS has ever collided with a mountain, and mid air collisions of commercial aircraft flying in Class A airspace are extremely rare.
Aircraft flying VFR without instruments would be protected by visual aids and by OCAS. Nearly all flight obstacles currently are not protected by OCAS, including the TCOM aerostats on the southern border, so our tethered stratospheric platforms would be a dramatic safety improvement. Also aircraft flying VFR are always in need of visual points of reference, and our platforms and tethers should provide such a function. Aircraft flying VFR already have a high accident rate so the safety bar is somewhat lower than that for commercial aircraft.
The risk from tethers is demonstrably low and not a major impediment to success. The ability to get small amounts of airspace designated as restricted is dependent on the regulatory environment. The developed world is highly regulated and their airspace is very busy. This makes it likely a long process, except perhaps for special cases like internet in the far north. The developing world is less regulated and their airspace is much less busy. The risk reward ratio for them is far more favorable. Essentially free large scale broadband internet for a little bit of empty airspace.
Illustration of impact on airspace
The picture below shows a screenshot of an aviation chart covering a part of northern California and Nevada. As can be seen the airspace is quite busy. San Francisco international airport has a large class B airspace. Other major airports with Class C airspace are at San Jose, Oakland, Sacrament and Reno. Other busy airports are at Fresno, Monterey, Stockton, and Modesto. There are numerous small airfields. Beall and Travis are busy air force bases. There is a large Military Operations Area (MOA) in the top left. To the East of Reno there is Fallon Naval air station and several large MOAs and restricted flight areas. The red borders are Temporary flight restricted areas (TFR). Some are for forest fires. The circle around Beall AFB seems permanent and related to flying drones.
Two green squares have been added to represent the airspace needed for two StratoSolar systems that could provide all energy to the entire region shown. This region has a population of over ten million and encompasses the Bay Area and Sacramento. The areas selected are only to illustrate the general StratoSolar selection criteria. They are over very lightly populated land, are not on major airways and are close to the dense urban population centers. As can be seen the restricted area needed is small compared to the other various uses of this airspace.
Two green squares have been added to represent the airspace needed for two StratoSolar systems that could provide all energy to the entire region shown. This region has a population of over ten million and encompasses the Bay Area and Sacramento. The areas selected are only to illustrate the general StratoSolar selection criteria. They are over very lightly populated land, are not on major airways and are close to the dense urban population centers. As can be seen the restricted area needed is small compared to the other various uses of this airspace.
