Patent Publication Number: US-2011071706-A1

Title: Method for managing power and energy in a fuel cell powered aerial vehicle based on secondary operation priority

Description:
BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Aerial vehicles are utilized in increasingly diverse applications such as, for example, air and surface combat, reconnaissance, logistics, research, and rescue applications. Aerial vehicle designs include very diverse shapes, sizes, configurations and characteristics, wherein each of the different aerial vehicle designs can be optimized for one or more specific application. For certain applications, fuel cell powered aerial vehicles are highly desirable because fuel cells provide a robust, low vibration, low emission, high-energy density power source for the aerial vehicle. Therefore, fuel cell powered aerial vehicles can operate for extended time period and over extended distances. Further, aerial vehicles utilizing fuel cells produce low noise level and low thermal signatures, which makes detection difficult. 
     Aerial vehicles can utilize hybrid fuel cell power systems comprising a fuel cell and a secondary battery. Both the secondary battery and the fuel cell are electrically coupled to a power bus supplying power to system components of the aerial vehicle. The fuel cell can continuously convert stored fuel to electrical power to the power bus at high energy efficiencies. The secondary battery can provide electrical power to the power bus by discharging the secondary battery and can receive electrical power from the power bus to charge the secondary battery. 
     Fuel cell power and battery power can be actively managed to efficiently power components of the aerial vehicle including the propulsion module, the system control, sensing components, and payload components of the aerial vehicle. For example, the secondary battery can be discharged to meet short-term component power requirements; however, typically much less energy is stored as battery charge than is stored as fuel supplied to the fuel cell. Therefore, while the secondary battery can be discharged to power aerial vehicle components for short periods of time, when the rechargeable battery is discharged over extended periods of time the battery state-of-charge will drop to a lower state-of-charge limit making battery power unavailable. 
     Therefore, new autonomous and manual methods for efficiently controlling power and energy within aerial vehicles are needed. 
     SUMMARY 
     A method for managing power within a fuel cell power aerial vehicle is described herein. Embodiments are described with reference to fuel cell powered aerial vehicles including 
     The method within an aerial vehicle includes determining a fuel cell power limit and a battery energy reserve. The method further includes determining a flight operation power requirement. The method further includes determining priority levels of secondary operations and providing power for secondary operations based on the priority levels. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  is a side view of an aerial vehicle in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 2  is a schematic power and signal flow diagram of the aerial vehicle of  FIG. 1 ; 
         FIG. 3  is a schematic signal flow diagram of a control system of the aerial vehicle of  FIG. 1 ; 
         FIG. 4  is a view of a graphics user interface for operating the aerial vehicle of  FIG. 1 ; 
         FIG. 5  is a waypoint control map for controlling the aerial vehicle of  FIG. 1 ; 
         FIG. 6  is a flow chart diagram of a mission energy determination function for controlling the aerial vehicle of  FIG. 1 ; 
         FIG. 7  is a flow chart diagram of a system power and energy function for controlling the aerial vehicle of  FIG. 1 ; 
         FIG. 8  is a flow chart diagram of a first mission control scheme for controlling the aerial vehicle of  FIG. 1 ; 
         FIG. 9  is a flow chart diagram of a second mission control scheme for controlling the aerial vehicle of  FIG. 1 ; 
         FIG. 10   a  is a flow chart diagram of the second mission control scheme of  FIG. 9  depicting exemplary power levels when operating in a non-boost operating mode; 
         FIG. 10   b  is a flow chart diagram of the second mission control scheme of  FIG. 9  depicting exemplary power levels when operating in a boost operating mode; 
         FIG. 11  is a flow chart diagram of a third mission control scheme for controlling the aerial vehicle of  FIG. 1 ; 
         FIG. 12  is a flow chart diagram of a fourth mission control scheme for controlling the aerial vehicle of  FIG. 1 ; and 
         FIG. 13  is a flow chart diagram of a fifth mission control scheme for controlling the aerial vehicle of  FIG. 1 ; 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the fuel cell will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others for visualization and understanding. In particular, thin features may be thickened for clarity of illustration. All references to direction and position, unless otherwise indicated, refer to the orientation of the device illustrated in the drawings. 
     DETAILED DESCRIPTION 
     In the present disclosure, a method for controlling a fuel cell aerial powered vehicle is described in accordance with an exemplary embodiment. The method for controlling the fuel cell aerial vehicle has several advantages over previous method for controlling a fuel cell powered aerial vehicle. For example, the method provides more efficient utilization of the fuel cell energy, thereby increasing the stored energy to volume ratio and the stored energy to weight of the aerial vehicle. 
     Although the aerial vehicles are described herein as utilizing hybrid fuel cell power systems, in alternate embodiments the aerial vehicle utilizing hybrid photovoltaic power systems and hybrid engine power systems can utilize control concepts described herein. 
       FIG. 1  depicts an aerial vehicle  10  including a fuel cell hybrid power system  40 . The aerial vehicle  10  further includes a control system  20 , an airframe  22 , and a propulsion and flight dynamics control module  24 , a gimbaled actuator  26 , a designator  28 , a video camera  30 , and a communications system  34 . 
     The exemplary aerial vehicle  10  is an unmanned aerial vehicle (“UAV”) or alternately, an unmanned aerial system (“UAS”) configured to perform missions such as, for example, loitering, designating, identifying, traveling, targeting, tracking, sprinting and climbing as will be discussed in greater detail herein below. However, certain aspects of the method for controlling an aerial vehicle discussed herein are applicable to other aerial vehicles and can be utilized while performing other missions not specifically discussed herein. 
       FIG. 1  depicts the control system  20  outside the aerial vehicle  10  to illustrate signal communications between the control system  20  and various components of the aerial vehicle  10 , and  FIG. 2  depicts two separate boxes for control system  20  to clearly illustrate signal communications between the control system  20  and several system components. As shown in the legend  12 , power flow between components of the aerial vehicle  10  is depicted by double dashed lines  14  and signal flow is depicted by signal dotted lines  16 . The control system  20  comprises circuitry, devices, and resident program instructions that can be executed to monitor and control operation of the aerial vehicle  10 . Referring to  FIG. 3 , the control system  20  comprises distributed control and decision-making units including an autopilot controller  11 , a power system controller  13 , a payload component controller  15 , and a ground system controller  17 . The autopilot controller  11  is configured to manage the propulsion and flight dynamics module  24  of the aerial vehicle  10 . The power system controller controls power flow within the power system  40 . The payload component controller  15  is configured to manage payload component operation including gimbaled actuator  26 , the designator  28 , and the video camera  30 . The ground system controller  17  can control telemetry, can provide mission commands, can provide user information and input user command through a graphic a user interface  50  ( FIG. 4 ). 
     The propulsion and flight dynamics control module  24  comprises propulsion components, including an electric motor  52  and a propeller  54 ; steering components including a an elevator actuator  61 , an elevator  64 , a rudder actuator  62 , and rudder  66 ; and sensing components including a pitot tube  46 . 
     The electric motor  52  is signally connected to the control system  20  such that the control system  20  can command a selected electric motor power level. The electric motor  52  and a propeller  54  are coupled through a gearbox (not shown), and the electric motor  52  drives rotational movement of the propeller  54 , which provides thrust to the aerial vehicle  10 . 
     The control system  20  is signally connected to the elevator actuator  61  and the rudder actuator  62  to provide commands to control the position of the elevator  64  and the ruder  66 , respectively. Although the elevator  64  and the rudder  66  are depicted for illustration purposes, it is to be understood that flight dynamics control of the aerial vehicle  10  utilizes complex control routines for controlling the position of the flaps, elevator, ailerons, and the rudder as understood by those skilled in the art. By controlling the electric motor  52  power level along with controlling positions of any combination of slats, flaps, elevators, ailerons and the rudder of the flight, the controller  20  can control the speed, pitch, roll and yaw (thereby controlling climb and decent rate and rate of turn) of the aerial vehicle  10 . 
     Along with the pitot tube  46 , the propulsion and flight dynamics control module  24  further includes other sensing components including a pressure sensor (not shown), a temperature sensor (not shown), and a GPS unit (not shown). Each of the sensors are monitored by the control system  20  such that the control system  20  executes control algorithms based on sensed feedback to control the aerial vehicle  10 . The pitot tube  46  is provided to measure a dynamic pressure, which can be utilized in combination with the GPS unit to determine an aerial vehicle speed. 
     The airframe  22  comprises a body, a tail portion and wings. The airframe  22  provides the mechanical structure for mounting and supporting the electronics, control components and the propulsion components of the aerial vehicle  10 . The hybrid power device  40  provides power to the portions of the control system  20  residing on the aerial vehicle  10 , the propulsion module  24 , the gimbaled actuator  26 , the laser designator  28 , the video camera  30 , and the flight dynamics and propulsion control module  42 . 
     The gimbaled actuator  26  includes pivoted support and positional control for 3-dimensionally repositioning the laser designator  28  and the video camera  30  to operate at a desired line-of-sight. In an exemplary embodiment, the position of the gimbaled actuator  26  is controlled by an operator wirelessly communicating with the controller  20  through the communications system  34 . In alternate embodiments, the gimbaled device can be controlled autonomously, for example, the gimbaled device  26  can receive control algorithms for autonomously tracking a moving target by utilizing the video camera  30  and image recognition software. 
     The laser designator  28  provides targeting for laser guided bombs, missiles and precision artillery munitions (collectively, hereafter referred to as “laser-guided munitions”). In particular, the laser designated  28  can emit a series of coded pulses of laser-light, wherein the laser-light bounces off the target and wherein the laser-light can be detected by a seeker on laser-guided munitions. 
     The exemplary video camera  30  captures high definition video and transmits the high definition videos to a ground controller (not shown) via the communications system  34 . The ground controller can utilize the high definition videos in conjunction with video processing software to identify potential targets and to track movement of targets. 
     Although in an exemplary embodiment including three payloads, the gimbal actuator  26 , the laser designator  28 , and the video camera  30 , are discussed, in alternate embodiments, the aerial vehicle  10  can comprise various numbers of payloads and a variety of payload types. For example, and by no means limiting, the aerial vehicles  10  can include thermal infrared, video surveillance sensors, hyperspectral sensors, designators, acoustic sensors, georegistration sensors, chemical sensors, and radar and lidar sensors. 
       FIG. 2  is a schematic diagram depicting power flow  14  and signal flow  16  within the aerial vehicle  10 . The control system  20  manages power flow within the power system  40 . The power system  40  includes a power board  22  (‘POWER BOARD’), a power bus  24  (‘POWER BUS’), a battery  21  (‘BATTERY’), and a fuel cell module  23  (‘FUEL CELL’). 
     The power board  22  comprises a voltage converter for converting a fuel cell voltage to a power bus voltage and further comprises a voltage converter for converting a battery voltage to the power bus voltage. The power board sends and receives power board control signals (‘POWER BOARD CONTROL’) to and from the control system  20 . In particular, the power board  22  includes sensors to measure voltage and current outputted at the fuel cell module  23  and measures voltage and current outputted at the battery  28 . The control system  20  can monitor the sensors of the power board  22  and can control voltage conversion between the fuel cell module  23  and the power bus  24  and between the battery  21  and the power bus  24 . In alternate embodiments, other sensors and voltage converters can be utilized to meet power requirements of power consuming devices of the aerial vehicle  10 . 
     The power bus  24  comprises an electrically conductive network configured to route power from the energy conversion devices (the rechargeable battery  21  and the fuel cell module  23 ) to supply electric power to devices external to the hybrid power device  40 . Each of the devices external to the hybrid power device  40  can be connected to the power bus through power connection ports (not shown) or can hard-wired to the power bus  24 . 
     The exemplary battery  21  can comprise any of several rechargeable battery technologies including, for example, nickel-cadmium, nickel-metal hydride, lithium-ion, and lithium-sulfur technologies. In alternative embodiments, other reversibly energy storage technologies such as ultra-capacitors can be utilized in addition to or instead of the rechargeable battery  21 . Further, in alternate embodiments, multiple energy storage devices can be utilized within aerial vehicles. The control system  20  receives information from internal sensors within the battery  21 , to monitor battery state of charge (‘BATTERY_SOC’) and to monitor temperatures at multiple locations of the battery  21  (‘BATTERY_TEMP). 
     The fuel cell module  23  includes a fuel cell stack and an onboard fuel reservoir along with various pumps and/or blowers for routing air to a cathode of the fuel cell stack at a controlled rate and for routing air and fuel to a reformer and subsequently to an anode of the fuel cell stack at a controlled rate. 
     The exemplary fuel cell stack comprises a plurality of solid oxide fuel cell tubes, along with various other components, for example, air and fuel delivery manifolds, current collectors, interconnects, and like components for routing fluid and electrical energy to and from the component cells within the fuel cell stack. In alternate embodiments, an aerial vehicle can utilize various fuel cell technologies and various fuel cell shapes. The solid oxide fuel cell stack includes a thermally insulated high temperature portion that includes fuel cell tubes configured to electrochemically transform the reformed fuel into electricity and exhaust gas. The insulative body comprises porous thermally insulative material capable of withstanding the operating temperatures of the fuel cell stack, that is, temperatures of up to 1000 degrees Celsius. The fuel cell module  23  further comprises a heat exchange manifold for transferring heat from fuel cell exhaust gas to air inputted to the fuel cell stack. The actual number of solid oxide fuel cell tubes depends in part on size and power producing capability of each tube and the desired power output of the solid oxide fuel cell tubes. Each solid oxide fuel cell includes an internal reformer disposed therein for converting raw fuel to reformed fuel. 
     The fuel cell stack further includes a plurality of sensors including a fuel flow rate sensor, an anode air flow rate sensor, a cathode air flow rate sensor, an internal reformer temperature sensor and a fuel cell tube exhaust temperature sensor. The control system  20  communicates with the fuel cell module  23  via signals (‘FUEL CELL CONTROL’). By monitoring the plurality of sensors and by transmitting command signals to the fuel cell stack  23 , the controller  20  can control air and fuel flow rates within the fuel cell module  23 . The control system  20  can determine fuel consumption and a remaining fuel level by monitoring fuel flow rate within the fuel cell module  23  over time. The control system  20  provides signals to control components of the fuel cell stack including the anode air blower, the cathode blower and the fuel valve to deliver fuel and air at a calibrated rates based on a desired air/to fuel ratio and based on a desired fuel utilization level. 
     Exemplary fuels for utilization within the fuel cell stack include a wide range of hydrocarbon fuels. In an exemplary embodiment, the fuel comprises an alkane fuel and specifically, propane fuel. In alternative embodiments, the fuel can comprise one or more other types of alkane fuel, for example, methane, ethane, propane, butane, pentane, hexane, heptane, octane, and the like, and can include non-linear alkane isomers. Further, other types of hydrocarbon fuel, such as partially and fully saturated hydrocarbons, and oxygenated hydrocarbons, such as alcohols and glycols, can be utilized as fuel that can be converted to electrical energy by the fuel cell stack. The fuel also can include mixtures comprising combinations of various component fuel molecules examples of which include gasoline blends, liquefied natural gas, JP-8 fuel and diesel fuel. 
     Referring to  FIG. 4  a user interface  70  is provided to allow a user to select priorities levels of secondary operations and to control parameters of the aerial vehicle  10 . As used herein, the term “secondary operations” refer to operations that are not included in the flight operation power requirement that is, operations not required to maintain the aerial vehicle in flight. 
     The user interface  70  includes a priority selector  72 , a speed controller  74 , an altitude controller  76 , a gimbaled actuator selector  78 , a video selector  80 , a designator selector  82 , a battery boost selector  84 , a fuel cell boost selector  86 , a directional variance selector  88 , a flight speed and altitude display  90 , a fuel gage  92 , a fuel duration gage  94 , a battery state of charge gage  96 , a hybrid power display  98 , and a battery duration display  99 . 
     The priority selector  72  determines priority of secondary power operations including meeting a target speed, meeting a target altitude, providing power to the gimbaled actuator  26 , providing power to the video camera  30  and providing power to the laser designator  28 . Although the priority selector allows a user to select priority in meeting a target speed and altitude along with priorities of each of the payloads, the control system  20  selects a higher priority for meeting a minimum speed and minimum altitude required for flight over the priority of each of the secondary power operations including the payload operations. 
     The speed controller  74  allows a user to select a target speed between a minimum speed and a maximum speed, and likewise, the altitude controller  76  allows a user to select a target altitude between a minimum altitude and a maximum altitude. The control system  20  controls the flight dynamics module  72  and provides power to the engine  52  based on the target speed and altitude. 
     The gimbaled actuator selector  78  allows a user to determine whether the gimbaled actuator  26  is an “on” state receiving power from the power system  40  or in an “off” unpowered state. Likewise, the video selector  80  and the designator selector  82  allow a user to determine whether each of the video camera  30  and the designator  28  are in an “on” state or an “off” state, respectively. When either the video selector  80  or the designator selector  82  is in an “on” state the control system  22  automatically selects the gimbaled actuator  26  as a priority higher than the video camera  30  and the designator  28 . 
     The battery boost selector  84  allows a user to select whether the aerial vehicle  10  is operating in a base battery operating mode (‘OFF’) or whether the aerial vehicle  10  is operating in a battery boost operating mode (‘ON’). When the aerial vehicle  10  is operating in the base battery operating mode, the control system  20  selects a base battery upper power limit, and the control system  20  controls power flow from the battery  21  to the power bus  24  such that the base battery upper power limit is not exceeded. When the aerial vehicle  10  is operating in the battery boost operating mode, the control system  20  selects a battery boost upper battery power limit, and the control system  20  controls power flow from the battery  21  to the power bus  24  such that the battery boost upper power limit is not exceeded. 
     For each set of operating conditions, the battery boost upper power limit is a higher power than the base battery upper power limit such that when the aerial vehicle  10  is operating in the battery boost operating mode, a higher battery discharge rate and a lower minimum battery state of charge are allowed by the control system  20 . In one embodiment, the battery boost upper power limit and the base battery upper power limit are dynamically determined based aerial vehicle operating (present and future) conditions and specifically based on a battery state of charge, a battery temperature, and a measured battery output power. 
     The base battery upper power limit is a battery power level associated with long-term battery durability. The boost upper power limit may degrade operational lifetime of the battery  21  and therefore, is preferably only utilized for short time periods. However, during certain situations, it is desirable for the battery to exceed the base upper power limit, for example, to complete a significant mission objective, to maintain the aerial vehicle in flight, or to prevent damage to components of the aerial vehicle  10  and therefore, the boost battery operating mode can be selected in these situations. Further, for operations that only occur for short time period, for example targeting utilizing a laser designator, it may be more preferable to operate the battery in the boost battery operating mode than utilizing a heavier, higher power battery within the aerial vehicle  10 . Further, it may preferable to operate in the aerial vehicle in the battery boost operating mode to power the propulsion module when at least one of a steep climb rate or a high velocity is required. For example, high power propulsion may be desired when performing evasive maneuvers, when tracking a target, or for traveling a desired distance in a desired time period. In one embodiment, the battery boost operating mode allows the battery  21  to operate under the lower state of charge limit of the base battery operating mode. For example in one embodiment, when in the battery  21  is the battery boost operating mode, the battery  21  can operate at less than half the lower state of charge limit of the base battery operating mode. 
     The fuel cell boost selector  86  allows a user to select whether the aerial vehicle  10  is operating in a base fuel cell operating mode (‘OFF’) or whether the aerial vehicle  10  is operating in a fuel cell boost operating mode (‘ON’). When the aerial vehicle  10  is operating in the base fuel cell operating mode, the control system  20  selects a base fuel cell upper power limit, and the control system  20  controls power flow from the fuel cell module  23  to the power bus  24  such that the base fuel cell upper power limit is not exceeded. When the aerial vehicle  10  is operating in the fuel cell boost operating mode, the control system  20  selects a fuel cell boost upper battery power limit, and the control system  20  controls power flow from the fuel cell module  23  to the power bus  24  such that the fuel cell boost upper power limit is not exceeded. 
     For each set of operating conditions, the fuel cell boost upper power limit is a higher power level than the base fuel cell upper power limit such that when the aerial vehicle  10  is operating in the fuel cell boost operating mode a high maximum fuel cell power level can commanded by the control system  20 . To command higher operating power, the control system  20  can increase the current drawn from the fuel cell module  23  and can increase the fuel consumption within the fuel cell module  23 . By operating in the boost operating mode, the boost operating mode may operate at a higher temperature. In an exemplary solid oxide fuel cell, the fuel cell operates at an operating temperature of greater than 25 degrees Celsius when in the boost operating mode than when operating at a base upper power limit of the base operating mode. 
     The fuel cell boost upper power limit and the base fuel cell upper power limit are dynamically determined based fuel cell operating power, fuel flow rate, and a measured fuel cell temperature (that is, one of the temperature measured at the internal reformer or the temperature measured at the exit end of the fuel cell tubes). The base fuel cell upper power limit is a fuel cell power level associated with long-term fuel cell durability. The boost fuel cell power limit may degrade operational lifetime of the fuel cell module  23  and therefore, is preferably only utilized for short time periods. For example, operating the aerial vehicle in the boost fuel cell operating mode can elevate the fuel cell operating temperature and increase the fuel cell power draw, thereby increasing the rate of failure due to thermal stress and oxidation of fuel cell components. In one embodiment, operating the fuel cell in the boost operating mode can degrade the nominal operating life of the fuel cell module  23  by greater than 25%, and more specifically greater than 50% over operating the aerial vehicle  10  in the base operating mode. 
     During certain situations, it is desirable for the fuel cell module to exceed the base fuel cell upper power limit, for example, to complete a significant mission objective, to maintain the aerial vehicle in flight, or to prevent damage components to the aerial vehicle  10  and therefore, the boost fuel cell operating mode can be selected in these situations. Further, for operations that only occur for short time period, for example when targeting utilizing a laser designator, it may be preferable to operate the aerial vehicle  10  in the boost fuel cell operating mode rather than utilizing a heavier, higher power fuel cells that add weight and volume to the aerial vehicle  10  and that are less efficient during nominal operating conditions of the aerial vehicle  10 . Further, it may preferable to operate in the aerial vehicle  10  in the fuel cell boost operating mode to power the propulsion module when at least one of high climb rate or a high velocity is required. For example, high power propulsion may be desired when performing evasive maneuvers, when tracking a target, or for traveling a desired distance in a desired time period. 
     The directional variance selector  88  allows a user to select an angle of deviation from a straight-line path to a designate a path the aerial vehicle  10  can travel for power conservation purposes. For example, if a straight-line path to a designated waypoint is straight into a headwind, it may be desirable for the aerial vehicle  10  to travel at a deviated path to avoid the headwind and therefore maintain higher state of charge levels within the battery  23  and provide greater levels of power reserve for secondary operations. 
     The flight speed and altitude display  90  displays the current measured air speed and the climb rate or decent rate of the aerial vehicle  10 . 
     The fuel gage  92  depicts the fuel level (“FUEL”) within a fuel tank of the aerial vehicle (not shown). The control system  20  determines the fuel level based on a fuel tank capacity and based on information provided by a microprocessor of the fuel tank and based on the fuel flow rate determined by the fuel flow sensor of the fuel cell module  23 . 
     The fuel level indicator depicts a series of bars such that a ratio of filled-in bars to total bars is indicative of the fuel level within the fuel reservoir. 
     The flight duration gage  94  displays an estimated operating life of the aerial vehicle  10  until refueling is required. The operating life can be calculated utilizing one of a variety of methods for predicting operating life based on, for example, the fuel level within the fuel reservoir, average fuel consumption levels, short-term and long-term external device load history, power generation, and user defined parameters. 
     The battery state of charge gage  96  depicts a battery state-of-charge of the battery  21  by showing a series of bars within the battery icon. The battery state-of-charge indicator depicts the series of bars such that a ratio of filled-in bars to total bars is indicative of the state-of-charge of the rechargeable battery  21 . 
     The hybrid power display  98  graphically depicts hybrid power utilizing a plurality of triangle shaped indicia. The plurality of triangle shaped indicia include indicia pointing toward the battery indicating charging and indicia pointing away from the battery indicating discharging. The amount of filled-in indicia indicates the charge/discharge rate. 
     The battery duration display  99  indicates an amount of time until the battery  21  is discharged to a lower state of charge limit, wherein supplemental power form the battery  21  is not utilized to power electric vehicle components when the battery  21  is fully discharged to the lower state of charge limit. 
     Referring to  FIG. 5 , a waypoint map  100  depicts waypoints  101 ,  102 ,  103 ,  104 , and  105 . In an exemplary waypoint based control scheme described herein, the control system  20  selects a mission to be completed operating the aerial vehicle between waypoints. The missions include a base travel mission  111  (‘BASE TRAVEL’) selected at waypoint  101 , a designate target mission  112  (‘DESIGNATE TARGET’) selected at waypoint  102 , a follow mission  113  (‘FOLLOW’) selected at waypoint  103 , a climb mission  114  (‘CLIMB’) selected at waypoint  104 , and a sprint mission  115  (‘SPRINT’) selected at waypoint  105 . 
       FIG. 6  shows a mission energy determination function  144 . The mission energy determination function  144  includes a total mission energy and peak power calculator  146  (‘MISSION ENERGY AND PEAK POWER’) and an available system energy and power availability calculator  148  (‘AVAILABLE ENERGY AND POWER’). The total mission energy and peak power calculator calculates total mission energy and peak power based on the target speed and target altitude, the payload power requirements for the mission, and the mission duration. The mission energy determination function  144  is executed prior to beginning each mission and is continuously executed during the mission to determine whether sufficient power and energy is available to complete each mission, whether boost commands are required to provide sufficient power and energy to complete each mission, or whether the mission must be aborted due to insufficient power or energy. In one embodiment, the mission determination function calculates power and energy required for a plurality of missions prior to beginning a first mission of the plurality. For example, the mission determination function can calculate the energy required for a designate target mission subsequently followed by a follow mission. 
     Certain missions described herein are boost-enabled missions in which the control system  20  is permitted to utilize the fuel cell boost operating mode and the battery boost operating mode to complete mission objective. Other missions described herein in are boost disabled missions in which boost can be command to allow flight operation of the aerial vehicle, but cannot be commanded to complete mission objectives. Further, during certain types of missions the mission abort function is unavailable. 
     Referring to  FIG. 7  a system power and energy function  120  comprises a fuel cell power determination function  140  and a battery energy determination function  142 . The fuel cell power determination function  140  determines long-term steady-state power (“POWER  1 ”), that is overall power continually supplied by the fuel cell module  23  for use by the aerial vehicle  10  based on the measured fuel flow rate (‘FUEL FLOW RATE’), the measured fuel cell power, the measured fuel cell temperature, and the signal indicating whether fuel cell boost operating mode is active (‘FUEL CELL BOOST’). The fuel cell power determination function  42  determines overall supplemental energy (‘SUPPLEMENTAL ENERGY  1 ’) available as battery charge, based on the measure battery state of charge (‘BATTERY STATE OF CHARGE’), the measured battery power (‘BATTERY POWER’), the measured battery temperature (‘BATTERY TEMP.’), and a signal indicative of whether battery boost operating mode is active (‘BATTERY BOOST’). 
     The battery power determination function  142  determines the overall battery supplemental energy “Energy Supplement 1” available through battery discharge to supplement the stead-state fuel cell power during the mission. For certain types of missions, the aerial vehicle  10  will operate in a holding pattern at a waypoint to charge the battery above a selected state of charge level (for example, above 95% state of charge) before beginning the mission. Further, during some missions, the battery discharge reserve is determined as a continuous power level applied throughout the duration of the mission. For some missions, a portion of the battery discharge reserve remains in reserve for performing a specific operation during a selected time period of the mission; for example utilizing a laser designator to designate a target. 
     The fuel cell power function  140  determines overall system power based on a current fuel flow rate (‘CURRENT FUEL FLOW RATE’), a current fuel cell power level (‘CURRENT FUEL CELL POWER’), a current fuel cell temperature level (‘CURRENT FUEL CELL TEMP.’), and a fuel cell boost activation signal (‘FUEL CELL BOOST’). 
     The battery power function  142  determines overall battery supplemental energy based on a battery boost activation signal (‘BATTERY BOOST’), a current battery power (‘CURRENT BATTERY POWER’), and a current battery state of charge (‘BATTERY STATE OF CHARGE’). 
     Referring to  FIG. 8 , a base travel mission control scheme  111  includes the system power and energy function  120 , an environmental power reserve function  122 , a flight operation power function  116  and a secondary operation priority function  118 . The base travel mission is a standard operating mode for traveling between locations. The base travel mission control scheme  110  actives boost operating mode when boost operating mode is required to maintain the aerial vehicle  10  in flight, but does active boost operating mode to accomplish secondary mission objectives. 
     The environmental power function  122  determines an overall environmental power reserve (‘ENVIRON. POWER  1 ’) based on an aerial vehicle headwind speed, an aerial vehicle altitude, an aerial vehicle speed, and an environmental lift factor. The aerial vehicle altitude and speed can be determined by an onboard global positioning sensor (not shown). The environmental lift factor predicts influences of a thermal current due to altitude changes and due to changes in terrain (determined for example utilizing GPS navigation and reference map software providing information about the terrain. The environmental lift-factor can be calculated based the pitch of the aerial vehicle, the altitude change rate, the propulsion power levels, and the positions of aerial vehicle components. 
     The flight operation power function  116  determines minimum power levels required to maintain the aerial vehicle  10  in flight. The flight operation power function  116  includes a minimum dynamics and communications power function  124  and a minimum propulsion power function  126 . 
     The minimum dynamics and communications power function  124  subtracts the power and energy levels required to operate the actuators  61  and  62  and the communications system  34  of the aerial vehicle  10  from the overall system power and the overall battery supplemental energy, respectively to determine a second system power (‘SYSTEM POWER RESERVE  2 ’) and a second battery supplemental energy (‘ENERGY SUPPLEMENT  2 ’), respectively. 
     The minimum propulsion power function  126  determines a power requirement for providing propulsion to maintain the aerial vehicle above a lower speed limit and a lower altitude limit, each of which are indicative of minimum requirements required to maintain stable aerial vehicle flight. The environmental power function  122  inputs the overall environmental power reserve and the system power reserve. The minimum propulsion power function  126  determines whether the minimum speed and altitude can be met by the overall environmental power reserve. If the minimum speed and power is exceeded by the overall environmental power reserve, the minimum propulsion power outputs the remaining environmental power reserve (‘ENVIRON. POWER  2 ’) to the secondary operation priority functions  118 . If the minimum speed and altitude the aerial vehicle  10  cannot be met by the overall environmental power reserve, the control system  20  calculates propulsion power and energy requirement for maintaining the aerial vehicle  10  above the lower speed limit and lower altitude limit and subtracts the propulsion power and energy requirements, respectively from the second system power and the second battery supplemental energy to determine a third system power (‘POWER  3 ’) and a third battery supplemental energy (‘ENERGY SUPPLEMENT  3 ’), respectively. 
     The third system power and the third battery supplemental energy are provided to a boost determination function  128 . The boost determination function  128  determines whether to command a fuel cell boost (‘FUEL CELL BOOST’) to maintain the aerial vehicle in flight based on the third system power. Further, the boost determination function  128  determines whether to command a battery boost signal (‘BATTERY BOOST’) to activate the fuel cell boost operating mode based on the third battery supplemental energy. 
     The secondary operation priority functions  118  prioritizes secondary functions including providing sufficient power reserve to continuously operate the gimbaled actuator  130 , providing sufficient power to operate the designator for a target designation time period  132 , providing sufficient power to operate the video camera continuously  134 , providing sufficient power to operate at a target flight speed  136  and at a target flight altitude  138 . It is to be understood that battery charge and discharge rate requirements are relatively constant for operating the gimbaled actuator, operating the video camera, and for operating at the target flight speed and altitude and therefore, utilize system power. However, since the laser designator is only operated for a short time period, typically in the range of five minutes or less, the time required for laser-guided munitions to reach the target, and utilizes relatively high levels of power during that time period, the battery discharge rate requirements increases substantially during laser designator operation thereby utilizing battery supplemental charge. 
     Each of the fourth system power (POWER  4 ) the fifth system power (POWER  5 ), the sixth system power reserve (POWER  6 ), the seventh system power (POWER  7 ), and the eight system power (POWER  8 ) indicate system power levels after accounting for the secondary function  130 ,  132 ,  134 ,  136 , and  138  respectively. Likewise, each of the fourth battery supplemental energy level (ENERGY SUPPLEMENT  4 ), the fifth battery supplemental energy level (ENERGY SUPPLEMENT  5 ), the sixth battery supplemental energy (‘ENERGY SUPPLEMENT  6 ’), the seventh battery supplemental (‘ENERGY SUPPLEMENT  7 ’), and the eighth battery supplemental energy (‘ENERGY SUPPLEMENT  8 ’) indicate the battery supplemental energy levels accounting for the secondary function  130 ,  132 ,  134 ,  136 , and  138  respectively. 
     Each of the third system power reserve, the fourth system power reserve (SYSTEM POWER  4 ), the fifth system power reserve (SYSTEM POWER  5 ), the sixth system power reserve (SYSTEM POWER LEVEL  6 ), the seventh system power reserve (SYSTEM POWER LEVEL  7 ), and the eight system power reserve (SYSTEM POWER LEVEL  8 ) indicate system power levels after accounting for the secondary function  130 ,  132 ,  134 ,  136 , and  138  respectively. 
     Referring to  FIG. 9 , a control scheme for the target designate mission  112  includes the system power reserve function  120 , the environmental power reserve function  122 , the flight operation power function  116  and a secondary operation priority function  168 . The designate target mission pilots the aerial vehicle proximate a target and projects a series of coded laser pulses at the target such that the target can be located by laser-guided munitions. The designate target mission provides boost enablement to accomplish mission objectives. Therefore the ninth system power reserve is utilized by the boost determination function to determine whether sufficient power is required for each of the aerial vehicle secondary operations  130 ,  132 ,  134 ,  136 , and  138  during the mission, and the boost determination function output commands to operate in the fuel cell boost operation mode (‘FUEL CELL BOOST’) and to operate in the battery boost operating mode (‘BATTERY BOOST’) when the fuel cell boost operating mode and the battery boost operating mode are required to meet mission objectives. 
       FIG. 10  A and  FIG. 10  B demonstrate show exemplary power levels for the target designate mission  112  control scheme with boost operating mode disabled ( FIG. 10  A) and with boost operating mode enabled ( FIG. 10  B). Referring to  FIG. 10  A, when boost operating mode is disabled, overall system power level is 250 W and the control system  20  subtracts power level the each of the steady state (“S. S.”) operation functions  120 ,  124 ,  126 ,  130 , and  134  in their prioritized order as shown. Since the battery recharge operation  134  has a high priority level than the target speed function  136  and the target altitude function  138 , the control system  10  will not utilize system power to meet speeds and altitude levels above the minimum speed and altitude level unless the battery is fully charged, that is charged to 2500 W min of power. An alert  139  will be sent to a user wherein the user can choose to meet target speeds and altitude levels even when the battery is not fully charged and the user can choose to utilize power from battery discharge to meet the target speed and altitude levels. 
     Referring to  FIG. 10B , the control system can select the boost operating mode to meet mission objectives, thereby allowing the fuel cell to provide 300 W of available system power. 
     Referring to  FIG. 11 , follow mission control scheme  115  includes the system power reserve function  120 , the environmental power reserve function  122 , the flight operation power function  116  and a secondary operation priority function  178 . The secondary operation power function  178  includes a target speed/altitude/direction determination function  150  that receives a predicted target position from the target position estimator  152  and determines an optimized flight speed, altitude and heading based on the predicted target position. When executing the follow mission  109 , the aerial vehicle tracks and follows a target, for example a ground vehicle as is traveling and evasively maneuvering. The follow mission  109  provides boost enablement to accomplish mission objectives. Therefore the sixth system power reserve utilizes by the boost determination function to determine whether sufficient power is required for each of the aerial vehicle secondary operations  130 ,  134 , and  150  during the mission. 
     Referring to  FIGS. 12 and 13  a climb mission control scheme  116  includes the system power reserve function  120 , the environmental power reserve function  122 , the flight operation power function  116  and a secondary operation priority function  188  and a sprint mission control scheme  117  includes the system power reserve function  120 , the environmental power reserve function  122 , the flight operation power function  116  and a secondary operation priority function  198 . The control scheme for the climb mission  116  and the sprint mission  117  each allows boost enablement to accomplish mission objectives. Therefore the seventh system power reserve utilizes by the boost determination function to provide sufficient power for each of the aerial vehicle secondary operations  130 ,  134 ,  136 , and  138  during the mission. 
     The exemplary embodiments shown in the figures and described above illustrate, but do not limit, the claimed invention. It should be understood that there is no intention to limit the invention to the specific form disclosed; rather, the invention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined in the claims. Therefore, the foregoing description should not be construed to limit the scope of the invention.