Autonomous Vehicles in Support of Naval Operations (2005) / Chapter Skim
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Appendix B Some Physics-Based Constraints on Autonomous Vehicles: Scaling, Energy, Sensing, and Communications
Appendix B Some Physics-Based Constraints on Autonomous Vehicles: Scaling, Energy, Sensing, and Communications
Pages 199-215
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From page 199... ...
It is important to understand how basic physics determines the variations in size, mass, and cost of autonomous systems in response to variations in the needed range and endurance for individual missions. The principal factor affecting range and endurance is energy storage.
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From page 200... ...
. Most autonomous vehicles designed for long endurance cruise at a speed that ranges from 1.3 to 5 times faster than these disturbances, so that they have sufficient command authority to loiter over a stationary point and to reach new targets of interest despite the occasional flow that exceeds the solar power flux.
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From page 201... ...
This means that unmanned aerial vehicles and unmanned underwater vehicles will have the same endurance-mass relationship. Shown in Figure B.1 is a plot of gross vehicle mass versus endurance for several vehicles, along with two curves for constant endurance per kg1/3.
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From page 202... ...
This makes chemical energy storage for aircraft somewhat more efficient than that for underwater vehicles, which generally carry both components of the chemical reaction. But an aircraft must lift its own weight, and so it requires a large wing and its associated drag, while the UUV is neutrally buoyant.
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From page 203... ...
Deploying "Predator-class" UAVs and torpedo-tube-compatible UUVs from the fleet will accomplish most missions at low cost and low risk without in-flight refueling and without onerously frequent launch and recovery. In October 1996, the Predator Marinization Feasibility Study, conducted by the Program Executive Office, Cruise Missiles and Unmanned Aerial Vehicles (PEO(CU)
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2002. Unmanned Aerial Vehicles Roadmap 20022027, Department of Defense, Washington, D.C., December.
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(Normal wing loading is about 25 kg/m2 for a sailplane -- 3 times that for a civil aviation aircraft, 9 times that for the Global Hawk, or 27 times that for a modern fighter aircraft.)
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From page 206... ...
under development is an example of this larger size, although it is still smaller than a manned aircraft designed for the same mission -- two of the UCAV-Ns fit in the space needed for a normal carrier-based combat aircraft.
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From page 207... ...
(Both C-130 transport aircraft and U-2 reconnaissance jets have successfully landed and taken off from aircraft carriers without either launch catapults or landing arrestors.2 ) The combat UAVs, as mentioned, will be comparable in mass to current manned aircraft and therefore should be able to use the same launch-and-recovery systems.
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From page 208... ...
Similar arguments about sensor apertures apply to submersibles. Thus, one finds that aerial or underwater autonomous vehicles having enough range and endurance to avoid nearly continuous launch-and-recovery operations will have a mass of 1 ton or a few tons, will move relatively slowly, will be based relatively close to the target area, and will be able to have superb sensor resolution and relative immunity from attack, especially when viewed in terms of the cost ratio compared with potential countermeasures.
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From page 209... ...
It is important to note that, while the GIG architecture includes satellite communications as part of the grid, this may not be the most important part relevant to UAV systems. Instead, a rich network of point-to-point RF communications between dozens or hundreds of unmanned vehicles will offer tremendous volumes of data through a relatively robust system.
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From page 210... ...
Also plotted in Figure B.3 is the corresponding data rate per watt for a UAV transmitting to a geosynchronous satellite, as is done by the Global Hawk and the Predator. Note that the data rate per watt is generally at least a million times worse than it is between the UAVs and the ground, despite the assumption made here that the satellite uses a large, 10 m (33 ft)
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From page 211... ...
, and thus also allow communications of modest amounts of data to units under forest canopies and in other heavily cluttered regions. It seems that the mass versus endurance argument makes the Navy the logical home for this UAV communications system.
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This architecture effectively makes autonomy enhancing but not enabling, which is reassuring considering the slow pace of autonomy successes over the past few decades. The GIG communications architecture permits telepresence for the human operator so long as the operator is in theater.
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From page 213... ...
Since navigation can be fairly accurate, it is acceptable to have a strategy by which, for example, minelike objects are cataloged along with their detailed sensor profiles, which are then reviewed by human and sophisticated offboard processing following a GIG interchange, with the UUV being sent back to those objects that are determined to be worthy of further scrutiny, tagging, or destruction. There are other attractive architectures for UUVs, such as using acoustic communications to surface transponders into the GIG network, although acoustic communications create a distinctive broadcast signature that tightly focused beams useable by UAVs will not have.
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From page 214... ...
This scaling discussion does not apply to ground vehicles, but the complexity of negotiating jungles, urban rubble piles, areas inside buildings and sewers, and so on with a ground vehicle is so daunting that it leads one to examine the ducted-fan, vertical-takeoff-and-landing, organic air vehicles and micro-airvehicles now being developed under funding from the Defense Advanced Research Projects Agency. This scaling analysis does apply to them, and since they are small, they have low range and endurance.
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From page 215... ...
that prevents appropriate levels of human involvement with the unmanned vehicles; this feature will allow the total system to have performance comparable to that of a manned system with much less cost and risk. The GIG communications architecture being deployed by the Office of the Secretary of Defense appears to offer all of the necessary features for high-speed, point-to-point communications using secure, focused beams at high frequency.
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