WO2021032956A1

WO2021032956A1 - Unmanned aerial vehicle for transporting a payload

Info

Publication number: WO2021032956A1
Application number: PCT/GB2020/051945
Authority: WO
Inventors: John Young; Toby TOWNROW
Original assignee: Drone Evolution Limited
Priority date: 2019-08-19
Filing date: 2020-08-14
Publication date: 2021-02-25
Also published as: GB2582842B; GB2582842A; GB201911878D0

Abstract

An unmanned aerial vehicle (UAV) (100) for autonomously transporting a payload (118). The UAV (100) comprises a flight control system (122) which is configured to autonomously operate a steering and propulsion system (112) such that the UAV (100) is able to autonomously fly to a predetermined destination. The UAV (100) has a first navigation system (e.g. 128) and a second navigation system (e.g. 130), which are arranged to determine a position of the UAV (100) in dependence on different sources of data. The flight control system (122) is configured to determine whether the first navigation system (e.g. 128) and the second navigation system (e.g. 130) are providing a correct indication of the position of the UAV (100). The flight control system (122) disregards the position provided by the first navigation system (e.g. 128) and/or the second navigation system (e.g. 130) if it is determined that the first navigation system (e.g. 128) and/or the second navigation system (e.g. 130) are/is not providing a correct indication of position.

Description

Unmanned Aerial Vehicle for transporting a payload

Field of the Invention

The present invention concerns an unmanned aerial vehicle (UAV). More particularly, but not exclusively, this invention concerns a UAV for autonomously transporting a payload. The invention also concerns a payload delivery system utilising a UAV and a method of operating a UAV.

Background of the Invention

It has been identified that unmanned aerial vehicles (UAVs) (also referred to as drones) may be useful for delivering items, such as goods, supplies and equipment, to remote locations. Whilst the use of UAVs for delivering items is not yet widespread, there are a large number of possible applications. For example, a UAV could be used to deliver medical supplies or blood products to a remote medical facility, a UAV could be used to deliver purchased goods from the warehouse of a retailer to a customer, and/or a postal service could use a UAV to deliver parcels.

UAVs may be vulnerable to interference (i.e. attack) by third parties wishing to, for example, capture the UAV and its payload, disable the UAV, or destroy the UAV. Delivery systems that utilise UAVs to transport items may be particularly susceptible to interference, particularly because the UAVs of such systems may regularly fly known or predictable routes between locations. Such delivery UAVs may also be desirable targets, as it may be known that the UAVs typically carry new or valuable items which may be re-sold.

There are various ways in which a UAV may be interfered with (i.e. attacked) mid-flight. Broadly speaking a UAV may be physical interfered with, for example by entangling the UAV in a net, or using a laser or a high velocity object (such as a beanbag or bullet) to cause damage to the UAV which disables its ability to fly; or electronically interfered with, for example by signal jamming, spoofing, and electronic interruption of the drone control systems.

Signal jamming typically involves interrupting or overwhelming one or more of the signals a UAV needs to receive (from an external source) in order to successfully operate. Signal jamming can include control signal jamming, in which control signals from an operator of the drone are interfered with, and navigation signal jamming, in which navigational signals (e.g. GPS signals) from a source such as a satellite are interfered with. Signal jamming may be achieved by broadcasting electromagnetic noise at the same frequencies as the signals the UAV ordinarily relies upon receiving.

Spoofing typically involves an unauthorised third party taking over control of a UAV remotely. Spoofing may be achieved by broadcasting signals designed to impersonate the control signals used by a legitimate operator of the UAV.

Electronic interruption of the UAV control systems typically involves interrupting or overwhelming the electronic signals that are sent between, or used by, the electronic components of the UAV. This aims to prevent the affected electronic components from being able to operate as intended. Electronic interruption may be achieved by broadcasting signals at the frequencies used by the electronic components of the UAV. For example, signals may be broadcast that affect the internal bus frequencies of the UAV, such that the electronic components are unable to transfer meaningful data and control signals between themselves. Similarly, signals may be broadcast that affect the signal frequencies of the motor controllers, such that the motors are not able to operate as required for flight.

Some prior art UAVs contain ways to mitigate against some forms of interference. For example, some prior art UAVs are programmed to fly to a predetermined location (e.g. a pre-programmed ‘home’ location) in the event that control signals from the operator are jammed. However, such UAVs may struggle to make such a return flight if their GPS system is also jammed. This may leave the UAV and its payload vulnerable.

The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide a UAV, and/or a delivery system incorporating a UAV, having an improved ability to resist and/or mitigate against unwanted third party interference. Summary of the Invention

The present invention provides, according to a first aspect, an unmanned aerial vehicle (UAV) for autonomously transporting a payload, the UAV comprising: a steering and propulsion system; a flight control system; a first navigation system and a second navigation system. The first navigation system is arranged to determine the position of the UAV in dependence on a first source of data, and communicate the position so determined to the flight control system. The second navigation system is arranged to determine the position of the UAV in dependence on a second source of data, different from the first source of data, and communicate the position so determined to the flight control system.

The flight control system is configured to autonomously operate the steering and propulsion system such that, in use, the UAV is able to autonomously fly to a predetermined destination according to a flight path.

The flight control system is configured to provide commands to the steering and propulsion system on the basis of the position of the UAV, as determined by the first navigation system and/or the second navigation system, along the flight path.

The flight control system is configured to determine whether the first navigation system and/or the second navigation system are providing a correct indication of the position of the UAV.

The flight control system is configured to disregard the output, for example the position, provided by the first navigation system and/or the second navigation system if it is determined that the first navigation system and/or the second navigation system are/is not providing a correct indication of position of the UAV.

The UAV of the present invention may provide several features which may improve the ability of the UAV to resist unwanted interference (i.e. attack).

Firstly, the UAV according to the present invention is configured to fly autonomously. During autonomous flight, the UAV may require no input or command signals from an operator in order to pilot the drone to the predetermined position. This may help reduce the chance of the UAV being affected by a control signal jamming attacks and spoofing, as the UAV would not require such inputs.

Secondly, the UAV according to the present invention comprises two navigation systems. By using different sources of data, the navigation systems may able to independently provide an indication of the position of the UAV. This may reduce the chance that, if the UAV is subject to unwanted interference, both navigation systems will be affected. The chance of the UAV having at least one functioning navigation system is thus increased. Furthermore, the UAV is able to disregard position information provided by incorrectly functioning navigation systems. This may improve the chance of the UAV being able to correctly navigate to its destination when faced with unwanted interference by a third party.

The present invention is particularly applicable to UAVs that are configured to deliver a payload containing items such as goods, supplies and/or equipment.

Example users of such UAVs may include delivery service providers (e.g. postal services, couriers and retailers), and organisations having remote sites and which require the transfer of items between those sites. Preferably, the predetermined destination has a location that is fixed, at least for the duration of the flight. For example, the departure location may be a warehouse of a retailer and the predetermined destination may be a customer address, or the departure location may be a hospital, and the predetermined destination may be a remote medical facility.

The UAV may comprise a payload receiving portion. The payload receiving portion may be arranged to receive the payload and retain the payload during flight, the payload being removable when the UAV has reached its destination. The payload may be replaceable with the same or a different type of payload. The payload receiving portion may comprise a retaining arrangement arranged to retain the payload. The retaining arrangement may, for example, comprise a gripping mechanism arranged to grip a payload and/or a housing arranged to enclose the payload.

The UAV may comprise a third navigation system arranged to determine the position of the UAV in dependence on a third source of data, different from the first source of data and the second source of data, and communicate the position so determined to the flight control system.

The flight control system may be configured to provide commands to the steering and propulsion system on the basis of the position of the UAV along the flight path as determined by the third navigation system.

The flight control system may be configured to determine whether any one or more of the first, second and third navigation systems are (or are not) providing a correct indication of the position of the UAV. The flight control system may be configured to determine whether all of, or each of, the first, second and third navigation systems are (or are not) providing a correct indication of the position of the UAV.

The flight control system may be configured to disregard the position provided by the first, second and/or third navigation system if it is determined that one or more of the first, second and/or third navigation system are/is not providing a correct indication of position of the UAV.

Providing a third navigation system that uses a different source of data to determine the position of the UAV may provide the UAV with yet further redundancy in its ability to navigate to the predetermined destination if faced with unwanted interference by a third party.

One of the navigation systems may be a satellite based navigation system, for example a GPS navigation system. The navigation system may comprise an anti-jam antenna system. The anti-jam antenna system may comprise a Controlled Reception Pattern Antenna. The anti-jam antenna system may be a null-forming antenna system. The anti-jam antenna system may be configured to create a null in the reception pattern in the direction of a jamming signal so detected. At the time of writing, example anti-jam antenna systems are marketed by NovAtel under the registered trade mark GAJT, an example anti-jam antenna system is the GAJT-710ML Anti-Jam Antenna.

One of the navigation systems may be an optical navigation system. The optical navigation system may comprise an optical sensor, for example an image sensor such as a CCD sensor or a CMOS sensor. Preferably the optical navigation system comprises a plurality of optical sensors. The optical sensor(s) may be arranged to view at least some of the environment surrounding the UAV. The optical sensor(s) may have a field of view. Preferably the optical navigation system comprises optical sensors arranged to provide a 360 degree field of view around the UAV.

The optical navigation system may be configured to calculate a distance to an object within the field of view. The optical navigation system may comprise a LiDAR system arranged to calculate a distance to an object. The optical navigation system may be configured to calculate a distance using two or more optical sensors, the optical navigation system being configured to determine depth on the basis of the output of the optical sensors. The optical navigation system may be configured to determine distance by determining the size of a known object within an image and comparing that size to a known actual size of the object.

The optical navigation system may be arranged to determine a topography of the environment in the field of view. The optical navigation system may be arranged to determine the position of the UAV by reference to stored topographical data. For example, the optical navigation system may be configured determine the position of the UAV by comparing the topography of the environment in the field of view with stored topographical data corresponding to the environment along the flight path.

The optical navigation system may be configured to match topographical features within the field of view with known features at known positions along the flight path. The optical navigation system may be configured to determine the position of the UAV relative to one or more known features. The optical navigation system may thereby be able to derive the absolute position of the UAV within its surrounding environment. An example of a known software platform for an optical navigation system configured to determine the position of a UAV within an environment is the “Generalized Autonomy Aviation System” (GAAS).

The topographical data generated by the optical navigation system and/or topographical data stored by the UAV (reference data) may concern the topography of the surface of the earth, and preferably also artificial (man-made) objects such as buildings.

One of the navigation systems may be an All Source Positioning Navigation system. The All Source Positioning Navigation system may be arranged to determine the position of the UAV on the basis of radio frequency signals received from one or more non-navigational radio frequency source. The non-navigational radio frequency source(s) may include a telecommunication tower, a cell tower antenna, a television station broadcasting antenna, and/or a radio station broadcasting antenna. Accordingly the signals may include a telecommunications signal, a cellular signal (i.e. a mobile phone signal), a television signal, a radio signal arranged to carry audio signals. Such non-navigational radio frequency signals may be referred to as signals of opportunity. Such signals may not ordinarily be intended for navigational use (i.e. the purpose of the signal being broadcast is not to aid navigation). The UAV may comprise stored reference data concerning the position of a plurality of non-navigational radio frequency sources, wherein the signal generated by the source is associated with a known position of the source. Various techniques for determining position using signals of opportunity are known. Those techniques may be based on, for example, received signal strength, angle-of-arrival of the signals, time-of-arrival of the signals, time difference of arrival of the signals, and/or frequency difference of arrival of the signals. The All Source Positioning Navigation system may be configured to determine the position of the UAV by using the non- navigational signals to triangulate the position of the UAV.

The first, second and third navigation systems may be any one of the navigation systems mentioned herein. The different sources of data may be different forms of data (e.g. satellite data, image data and non-navigational radio signals each being different forms of data). Preferably each system is different (and hence uses a different source of data). In one example, the first navigation system is a satellite navigation system, the second navigation is an optical navigation system, and, if present, the third navigation system is an All Source Positioning Navigation system.

Preferably, the flight control system is arranged to determine which navigation system(s) are not determining a correct position of the UAV. Preferably, the flight control system is configured to disregard the position provided by the navigation system(s) determined not to be providing a correct indication of the position of the UAV.

It may be that a navigation system does not provide a correct position of the UAV if the navigation system provides a position that is not, within the error and/or tolerances of the navigation system, the same as the actual position of the UAV. Alternatively or additionally, it may be that a navigation system does not provide a correct position of the UAV if the navigation system provides output signals that do not represent a position (i.e. output signals that the flight control system cannot interpret as a position, for example the output signals may be noise or nonsensical data).

The flight control system may be configured to determine whether the output of the navigation systems (e.g. the first, second and/or third navigation systems) are each providing an indication of position (i.e. are each providing data which the flight control system can interpret as a position, whether correct or incorrect). The flight control system may be configured to disregard the output provided by any navigation system where it is determined that said output that does not represent a position. The flight control system may be configured to, if the output of at least two navigation systems are providing an indication of position, compare the positions provided by those navigation systems.

The flight control system may be configured to compare the position provided by each of the navigation systems and determine, on the basis of the comparison, whether any of the navigation systems (e.g. the navigation systems so compared) are not providing a correct indication of the position of the UAV.

For example, the flight control system may be configured to compare the position provided by the first navigation system and the position provided by the second navigation system and determine, on the basis of the comparison, whether the first navigation system and the second navigation system are providing a correct indication of the position of the UAV (or whether either of the first navigation system and the second navigation system are not providing a correct indication of the position of the UAV).

Similarly, the flight control system may be configured to compare the position determined by each of the first, second and third navigation systems and determine, on the basis of the comparison, whether any one or more of the first, second and third navigation systems are (or are not) providing a correct indication of the position of the UAV.

The flight control system may be configured to compare the positions determined by the navigation systems by calculating a distance between the positions.

The flight control system may be configured to determine whether the navigation system(s) are providing a correct indication of the position of the UAV by calculating the distance between the positions so determined, and comparing that distance to a threshold value. The flight control system may be configured to determine that one or more of the navigation systems are not providing a correct indication of position when said distance between the determined positions exceeds a threshold value.

The threshold value may be fixed during a flight (i.e. from take-off to landing). The threshold value may, for example, be 10 metres, or 15 meters. The flight control system may be configured to dynamically determine the threshold value, for example in dependence on the flight conditions and/or the flight path.

The position determined by each navigation system may be subject to an error (an inaccuracy). For example, the position indicated by a satellite navigation system may have an error of ±5 meters under open sky. The error of each navigation system may be an inherent property of the navigation system (e.g. of the hardware used). The error of each navigation system may also be a result of the environment surrounding the UAV. For example, the position indicated by the satellite navigation system may increase to ±10 meters in heavily built up areas. This may, for example, be due to some satellite signals being blocked or reflected off buildings.

Preferably, the threshold value is determined in dependence on the error of each navigation system. For example, the threshold may be a percentage (e.g. 50%, 100% or 150%) of the sum of the errors of the navigation systems whose positions are being compared.

In a UAV with only two navigation systems, it may be difficult, only on the basis of a comparison between the positions determined by the navigation systems, to determine which navigation system is not providing a correct indication of position. Therefore the flight control system may take into account further information in order to determine which navigation system is not functioning correctly.

For example, the flight control system may store the past position information provided by each navigation system. The flight control system may be configured to compare the position most recently determined by a navigation system with preceding positions determined by the navigation system. The flight control system may be configured to calculate whether the most recently determined position may be reached from the preceding positions. If the flight control system determines that the most recently determined position was impossible for the UAV to reach from the previously determined position, this may be indicative that the navigation system in question is not providing a correct position of the UAV. In an example, the navigation system may provide a series of substantially continuous latitude and longitude measurements. If the navigation system suddenly provided a latitude and longitude measurement a significant distance away (e.g. more than 500 meters away), then the flight control system may determine this is a not a correct indication of position of the UAV. In embodiments with three or more navigations systems, it may be possible to determine which navigation system is not providing a correct indication of position by calculating which position so determined is significantly different from the other two positions (e.g. because it is at a distance from the other two positions by more than a threshold value). If the position provided by all three navigations systems differ by more than a threshold value from each other, then it may be an indication that two or more of the navigation systems are not functioning correctly, for example due to a multifaceted attack on the UAV. If more than three navigation systems are present, then the position determined by all or some of the navigation systems may be compared to work out which navigation system(s) are not providing a correct indication of position.

In alternative embodiments, the flight control system may, if it determines that one or more of the navigation systems is/are providing a false indication of position, disregard the position provided by one of the navigation systems (e.g. the first navigation system), the choice of navigation system to disregard being predetermined. The flight control system may be configured to disregard the position provided by each of the navigation systems in a predetermined order. Such a configuration of the flight control system may be applicable, for example, where one of the navigation systems is more likely to be attacked and is most likely to be responsible for the discrepancy between the positions provided by the navigation systems, and/or if the flight control system is unable to determine which navigation system is not providing correct position information.

In some embodiments, the flight control system may be configured to monitor the output signals of the navigation systems, the outputs being monitored in order to (i) determine if the output signals corresponds to a position (incorrect or correct), (ii) disregard any output signals which do not correspond to a position, (iii) if there are two or more navigation systems having output signals that correspond to a position, determine the differences between those positions, and/or (iv) if those differences indicate one of those positions are incorrect, for example because the difference exceeds a threshold value, disregard the position provided by at least one of those navigation systems. It will be understood that the position data provided by the navigation system(s) may be disregarded for the purpose of commanding the steering and propulsion system in order to fly the UAV along the flight path.

The UAV may be configured to, when the flight control system determines that a navigation system is again providing a correct indication of the position of the UAV, following a period in which the navigation system was determined not to have been providing a correct indication of position, restore the use of the position information that was previously disregarded.

The UAV may be configured to undertake a defensive manoeuvring procedure should the UAV determine that it may be being interfered with, for example due to at least one navigation system unexpectedly ceasing to provide a correct position to the flight control system. The defensive manoeuvring procedure may be arranged to move the UAV further from the location in which it may be being interfered with. The defensive manoeuvring procedure may involve one or more of the following changes to the flight of the UAV as compared to the planned flight path: increase in altitude, increase in airspeed, and alterations to heading.

The UAV may comprise a cellular network transmitter and receiver (e.g. a 3G, 4G and/or 5G transmitter and receiver) for facilitating communication with the UAV during flight. The UAV may be configured to open a datalink with a base station in the event the flight control system determines that all of the available (on-board) navigation systems are not providing a correct indication of the position of the UAV. The datalink may be used to send command signals to the UAV concerning the flight of the UAV, for example the datalink may be used to pilot the UAV, optionally manually, in the event that the UAV is unable to navigate itself along the flight path.

The UAV may be configured, at least in certain operating modes, to disregard any external command signals, for example radio frequency command signals, received by the UAV. The UVA may be configured, at least in certain operating modes, such that the destination of the UAV is unalterable by external command signals sent to the UAV during the flight. The UAV may be configured, at least in certain operating modes, to only act on encrypted external command signals received by the UAV. The flight control system may be configured to decrypt the encrypted external command signals prior at acting on them. The UAV may only act on encrypted external command signals which it is able to decrypt, for example because it holds the encryption key. The flight control system may be configured to receive an encryption key prior to flight.

The UAV is preferably able to autonomously land at the predetermined location. The UAV may be able to recognise a landing site and land at the landing site autonomously,

The UAV may comprise radio frequency shielding. The flight control system, the steering and propulsion system, the first navigation system, the second navigation system, and/or the third navigation system (or any parts thereof) may be shielded by the radio frequency shielding. Of course this excludes any components/parts of said systems, such as antenna, which are required to be unshielded in order to correctly function.

The UAV may comprise a collision avoidance system. The collision avoidance system may be arranged to determine whether following the flight path would result in the UAV colliding with an object. The collision avoidance system may be arranged to alter the flight path if it is determined that the UAV would, if flight along the flight path were to be continued, collide with the object; the flight path being altered in a direction in which collision with the object is determined to be avoided. The collision avoidance system may use components of, or form an integral part of, the optical navigation system. The collision avoidance system preferably is configured to alter the flight path of the UAV to avoid both stationary and moving objects.

The UAV may comprise one or more sensors (separate from the aforementioned navigation systems) arranged to measure heading. The UAV may comprise one or more sensors (separate from the aforementioned navigation systems) arranged to measure airspeed. The UAV may comprise one or more sensors (separate from the aforementioned navigation systems) arranged to measure altitude. The flight controller may be arranged to provide an estimate of the position of the UAV on the basis of a position previously determined by one of said navigation systems, and the measurements of heading and airspeed, and optionally also altitude. The UAV may comprise any one or more of the following: a tachometer, an air pressure sensor, a barometer, an altimeter (e.g. a pressure altimeter, a laser altimeter), a wind speed sensor, a magnetometer, a compass (e.g. a gyrocompass), an angle of attack sensor, an accelerometer, a gyroscope. The UAV may be arranged to use the output of any of the aforementioned devices/sensors to corroborate and/or assist the determination of position by any one of the navigation systems. For example, the altimeter and compass may be used to help narrow down the pool of reference data used by the optical navigation system when determining position.

The UAV may comprise an outer material configured to reflect at least 25%, at least 50% or at least 75% of incident laser radiation. The reflectance of the material may be at least 25%, at least 50%, or at least 75% in the visible spectrum, and preferably also in the IR and/or UV spectrum. This may lessen the heating caused by incident laser radiation can thus reduce the chance that the UAV suffers damage as a result of a laser attack. Preferably a majority of the under surface of the UAV comprises said reflecting material. The material may be titanium.

The steering and propulsion system may comprise one or more rotors arranged to propel and/or steer the UAV during flight. The steering and propulsion system may comprise four rotors, optionally only four rotors (i.e. the UAV may optionally be a quadcopter). The steering and propulsion system may comprise six rotors, optionally only six rotors (i.e. the UAV may optionally be a hexcopter).

The rotors may each be surrounded by a wall extending at least partly, and preferably completely, around an edge of the area swept by the rotor blades. The rotors may each be contained within a duct. Surrounding the rotors blades may reduce their vulnerability to physically attack and/or interference. For example, it may reduce the chance of the rotors becoming entrapped in a net.

The UAV may be battery powered. The UAV may comprise one or more electric motors to power the rotors. Preferably each rotor is powered by its own electric motor. The UAV may have a span of less than 2 meters, or less than 1 meter (span being the maximum horizontal distance from one side to the opposing side of the UAV, including any rotors). The UAV may have a maximum weight (without a payload) of less than 50kg, or less than 20kg, or less than 10kg.

The present invention provides, according to a second embodiment, a payload delivery system comprising a UAV and a base station. The UAV may be a UAV according to the first aspect of the invention. The base station is arranged to communicate the position of the predetermined destination to the UAV, preferably prior to flight. The base station may be arranged to communicate the flight path to the UAV, preferably prior to flight. The base station may be arranged to charge the UAV, optionally when the UAV has landed thereon. The base station may be arranged the charge the UAV via induction charging.

The flight control system and/or the base station may be arranged to determine a flight path for the UAV from the take-off location to the location of the predetermined destination. The flight path may take into account the topography of the environment between the take-off location and the location of the destination. The flight path may take into account any no-fly zones in which UAV flight is not permitted, for example over densely populated areas.

The payload delivery system may comprise a landing site. The landing site may comprise a landing position indicator detectable by the UAV. The flight control system may be configured to cause a landing of the UAV in response to detection of the landing position indicator. The landing position indicator may provide the UAV with an indication of the preferred landing position. The landing position indicator may be visual indicator, which may be detectable by an optical sensor on board the UAV. The landing position indicator may comprises a laser emitter. The landing position indicator may comprise a machine readable code. The machine readable code may, in the simple cases, be a shape that the flight control system may be able to determine from an image of the landing site. The machine readable code may be a QR code or the like.

The landing site may be provided by a second base station. The base station at the landing site may be arranged to exchange a landing token with the UAV to verify that the UAV is at the correct landing site.

The present invention provides, according to a third aspect, a kit of parts for a payload delivery system, the kit comprising: a UAV, a base station, and a landing site. The UAV, the base station and/or the landing site may be in accordance with any aspect of the present invention.

The present invention provides, according to a fourth aspect, a method of operating a UAV, the method comprising the steps of: providing a UAV according to the present invention; using the first navigation system to determine the position of the UAV according to the first source of data; using the second navigation system to determine the position of the UAV according to the second source of data; determining whether the first navigation system and the second navigation system are providing a correct indication of the position of the UAV; and disregarding the position provided by the first navigation system and/or the second navigation system if it is determined that the first navigation system and/or the second navigation system are/is not providing a correct indication of position of the UAV.

The method may comprise a step of comparing the positions so determined by the first navigation system and the second navigation system. The method may comprise a step of determining, on the basis of said comparison, whether the first navigation system and the second navigation system are providing a correct indication of the position of the UAV.

The step of comparing the positions so determined by the first navigation system and the second navigation system may comprise calculating the distance between the position determined by the first navigation system and the position determined by the second navigation system. The step of determining whether the first navigation system and the second navigation system are providing a correct indication of the position of the UAV may comprise determining whether the distance between the positions exceeds a threshold value. If the threshold value is exceeded, the flight control system may deem that at least one of the first and second navigation systems are not providing a correct indication of the position of the UAV. The method may comprise a step of determining a threshold value on the basis of the accuracy of the first and the second navigation systems.

The method may comprise a step of determining which navigation system or systems is/are not providing a correct indication of position. The step of disregarding the position provided by the first navigation system and/or the second navigation may comprise disregarding the position provided by the navigation system deemed not to be providing a correct indication of position.

The present invention provides, according to a fifth aspect, a method of delivering a payload, the method comprising the steps of: providing a UAV according to the present invention; providing the UAV with the payload such that the UAV can carry the payload during flight; communicating to the UAV the predetermined destination for delivery of the payload; calculating the flight path to be followed by the UAV to the predetermined destination; and initiating flight of the UAV so as cause the payload to be delivered to the predetermined destination. Preferably, the UAV flies autonomously to the predetermined destination without the need for external commands from an operator of the UAV. The present invention provides, according to a fifth aspect, a flight control system for a UAV. The UAV being a UAV according to any preceding aspect of the invention.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the methods of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa. In particular, the methods of the invention may comprise any steps in which it is herein described the UAV, or components thereof, may carry out (i.e. are configured / arranged to carry out).

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 shows a plan view of a UAV according to a first embodiment of the invention;

Figure 2 shows a side view of a UAV according to a first embodiment of the invention;

Figure 3 shows the architecture of the control system of the UAV according to a first embodiment of the invention; and

Figure 4 shows a payload delivery system according to a second embodiment of the invention.

Detailed Description

Figure 1 shows a UAV 100 according to a first embodiment of the invention. The UAV 100 comprises a main body 102 housing a control system 104 and a power system 105 comprising batteries. Six outwardly extending arms 106 are mounted to the main body 102. A rotor 108 driven by an electric motor 110 (not shown in Figure 1) is mounted upon each of the arms 106 (for clarity only one arm 106 and rotor 108 are labelled in Figure 1). Each of the rotors 108 is contained in a duct 113 which surrounds the lateral sides of the rotor 108. The ducts 113 may help protect the rotors 108 from damage. The rotors 108 and motors 110 collectively form part of a steering and propulsion system 112 (not indicated in Figure 1). By altering the speeds of the rotors 108, the UAV 100 can be steered and propelled in a known manner.

In alternative embodiments of the invention, the UAV 100 may comprise fewer rotors 108, for instance in alternative embodiments the UAV 100 is a quadcopter comprising four rotors. In alternative embodiments of the invention, the UAV 100 may comprise more than six rotors 108.

As shown in Figure 2, the UAV 100 further comprises a payload receiving portion 114 mounted to the main body 102. The payload receiving portion 114 comprises a housing 116 for receiving a payload 118 therein. A door 120 of the housing 116 is closable so as to retain the payload 118 during flight.

The outer surfaces of the main body 102 and the payload receiving portion 114 are covered in a reflective material to reflect incident laser radiation. In embodiments, the reflectance of the reflective material is at least 50% across the visible spectrum.

Figure 3 shows the architecture of the control system 104. The control system 104 comprises a flight control system 122 configured to communicate with a motor controller 124 of the steering and propulsion system 112. The motor controller 124 is in communication with each motor 110 and controls the power that each motor 110 receives from the power system 105. The flight control system 122 is configured to instruct the motor controller 124 to operate in a way that allows the UAV 100 to fly in a controlled manner.

The control system 104 further comprises a plurality of navigation systems 126. The UAV 100 comprises three navigation systems in total, a satellite navigation system in the form of a GPS navigation system 128, an optical navigation system 130, and an All Source Positioning Navigation system 132.

The GPS navigation system 128 calculates the position of the UAV 100 in a known manner by receiving and processing signals broadcast by satellites. The GPS navigation system 128 comprises an anti-jam antenna system comprising a Controlled Reception Pattern Antenna. The Controlled Reception Pattern Antenna is arranged to analyse the signals received and, if a jamming signal is detected, create a null in the reception pattern in the direction of the jamming signal in a known manner. The optical navigation system 130 comprises a plurality of image sensors distributed so as to provide a 360 degree field of view of the environment surrounding the UAV 100. The optical navigation system 130 comprises software that is able to determine, from the images received from the image sensors, the topography of the environment surrounding the UAV 100. In other words, the software is able to determine a three dimensional representation of the environment surrounding the UAV 100, including the shape of visible features (e.g. including width, height and visible depth of those features).

In alternative embodiments, the optical navigation system comprises a laser scanning system to derive the topography of the environment around the UAV 100.

The optical navigation system 130 further comprises stored topographical data of the environment in which the UAV 100 is to operate. Said topographical data comprises topographical measurements of both natural features (e.g. the relief of the land) and man-made features (e.g. buildings, roads, etc.) present in the environment, along with the positions of those features. The stored topographical data for the proposed operating area is loaded into the UAV 100 prior to take-off.

The optical navigation system 130 is configured to match at least some of the features in the environment surrounding the UAV 100 (as imaged by the image sensors) with corresponding features in the stored topographical data. On the basis of the distance and orientation of the UAV 100 to those features (as deduced from the images so captured) the optical navigation system 130 is able to calculate the position of the UAV 100 within its surrounding environment.

The All Source Positioning Navigation system 132 comprises a radio frequency receiver arranged to detect non-navigational signals (i.e. signals of opportunity) broadcast by cell towers, television station antennas and radio station antennas. The All Source Positioning Navigation system 132 comprises stored data concerning the locations of the sources of said non-navigational signals. The All Source Positioning Navigation system 132 is configured to use the non-navigational signals to triangulate the position of the UAV 100. In embodiments, the All Source Positioning Navigation system 132 comprises multiple antenna in order to help determine the location of the signals relative to the UAV 100.

In alternative embodiments, the control system 104 only comprises two navigation systems (e.g. only the GPS navigation system and the optical navigation system); and in further alternative embodiments, the control system comprises more than three navigation systems.

As is apparent, each of the navigation systems 128, 130, 132 are arranged to independently determine a position of the UAV 100 using a different source of data. The navigation systems 128, 130, 132 are each arranged to output the position that they determine and communicate that position to the flight control system 122.

The flight control system 122 is configured so as to be able to autonomously fly the UAV 100 to a predetermined destination that has been input into the flight control system 122. The flight control system 122 is configured to calculate, prior to take-off, a flight path to the predetermined destination. In alternative embodiments, the flight path may be input into the flight control system 122, rather than the flight control system 122 working out the flight path itself.

The flight path takes into account the topography of the environment between the take-off location and the location of the predetermined destination. Both natural features and artificial features (e.g. buildings) between the locations are taken into account when the flight path is calculated to reduce the risk that the UAV may collide with known objects.

The flight control system 122 is further configured to verify that the flight path to the predetermined destination is achievable on the basis of the battery life of the UAV 100. In alternative embodiments, the flight control system 122 is also configured to take into account other factors when verifying the flight path, such as weather conditions and payload weight.

In flight, the flight control system 122 is configured to instruct the motor controller 124 to operate the motors 110 in dependence on the position of the UAV 100 along the flight path such that the flight path is followed as closely as possible by the UAV 100.

The flight control system 122 is further configured to monitor the outputs of each of the navigation systems 128, 130, 132 and determine whether the navigation systems 128, 130, 132 are, or are not, providing a correct indication of the position of the UAV 100. The flight control system 122 disregards, for the purpose of piloting the UAV 100, the position information provided by any of the navigation systems 128, 130, 132 which are deemed not to be providing a correct indication of position. A navigation system is deemed not to provide a correct position of the UAV 100 either because (i) the navigation system provides output signals that do not represent a position (i.e. output signals that the flight control system cannot interpret as a position), or (ii) the navigation system provides a position that is not, within the error and/or tolerances of the navigation system, the same as the actual position of the UAV 100.

Accordingly, in a first step towards determining whether the navigation systems 128, 130, 132 are providing a correct indication of the position of the UAV 100, the flight control system 122 determines whether the output of each navigation system 128, 130, 132 is representative of a position, and is not, for example, simply electromagnetic noise or nonsense data. If any of the navigation systems 128, 130,

132 are providing an output which cannot be interpreted as a position, then the output of those navigation systems 128, 130, 132 are disregarded for the purpose of piloting the UAV 100 along the flight path.

In a second step towards determining whether the navigation systems 128,

130, 132 are providing a correct indication of the position of the UAV 100, the flight control system 122 compares the positions provided by each of the navigation system 128, 130, 132 deemed to be providing an output representative of a position. The comparison is made by determining the distance between each of the positions. If the distance or distances exceed a threshold value, then the flight control system 122 determines that at least one of the navigation systems 128, 130, 132 (whose position is being compared) is not providing a correct indication of the position of the UAV 100.

The threshold value is set in dependence on the accuracy of the navigation systems 128, 130, 132 being compared. In embodiments, the threshold value is a sum of the known errors of the navigation systems 128, 130, 132 being compared.

Once it is established that one of the navigation systems 128, 130, 132 (whose position is being compared) is providing an incorrect indication of position, the flight control system 122 is configured to determine which navigation systems 128, 130,

132 is providing that incorrect position.

In the event that the positions determined by all three of the navigation systems 128, 130, 132 are being compared (because all three systems are providing an output representative of a position - which may be correct or incorrect), then the flight control system 122 may be able to determine which of the navigation systems 128, 130, 132 is providing an incorrect indication of position by determining which two positions are close together (i.e. within a threshold value of each other), and which position significantly differs from the other two positions (i.e. is beyond a threshold value of both positions). The flight control system 122 is then able to deem the outlying position as incorrect, and the position data from the corresponding navigation system is disregarded.

In the event that the positions determined by only two of the navigation systems 128, 130, 132 are being compared (because only two systems are providing an output representative of a position - which may be correct or incorrect), then the flight control system 122 has to consider other data in order to determine which navigation system 128, 130, 132 is providing an incorrect indication of position.

The flight control system 122 is configured to achieve this by comparing the position most recently determined by each navigation system 128, 130, 132 with preceding positions determined by the navigation system 128, 130, 132. The flight control system 122 is then configured to calculate whether the most recently determined position can be reached from the preceding positions. If the flight control system determines that the most recently determined position was impossible for the UAV 100 to reach from the previously determined position, the flight control system 122 deems that the presently determined potion is incorrect and the position data from the corresponding navigation system is disregarded.

The UAV 100 further comprises a range of on-board sensors 134 which are also in communication with the flight control system 122. The sensors 134 include a compass 136 configured to determine a heading of the UAV 100, a laser altimeter 138 configured to determine the altitude of the UAV 100, an accelerometer 140 and an airspeed sensor 140. The flight control system 122 also uses the outputs from these sensors 134 to determine whether it is possible for the most recently determined position to be reached from the previously determined position.

If the flight control system 122 determines that more than one of the navigation systems 128, 130, 132 are providing a correct indication of position, then the flight control system 122 may choose from which navigation system 128, 130, 132 the position data should be taken when instructing the motor controller 124 to operate the motors 110 to cause the drone to fly. In embodiments, the flight control system 122 reverts to using the position provided by the most accurate of the available navigation systems 128, 130, 132. In alternative embodiments, the flight control system 122 takes an average of the positions so determined.

The UAV 100 further comprises a 5G cellular network transmitter and receiver 142. The flight control system 122 is configured to open an encrypted data link to an operator via the 5G connection in the event that the flight control system 122 determines that none of the navigation systems 128, 130, 132 present are providing a correct indication of the position of the UAV. The flight control system 122 comprises a stored encryption key in order to decrypt encrypted navigational commands from an operator.

The incorrect functioning of one or more of the navigation systems 128, 130, 132 is also an indication that the UAV 100 is being interfered with (i.e. attacked) by a third party, for example by jamming of the GPS navigation signal, or by shining a laser into the image sensors of the optical navigation system 130. The UAV 100 is configured to alter the flight path if it determines such interference is taking place.

The flight path is altered according to a defensive manoeuvring procedure which involves increasing the altitude and airspeed of the UAV 100 and altering the heading so as to take a longer distance, and less predictable, route to the predetermined location. For example, the route may comprise one or more seemingly random changes of direction.

The UAV 100 is operable in a plurality of different operating modes. In a manual operating mode the UAV 100 is able to be controlled by an operator via radio frequency signals. In an autonomous operating mode, which is preferably used to deliver a payload, the flight control system 122 is configured to disregard any external command signals sent to the UAV 100. An exception is made if it becomes necessary to establish an encrypted 5G datalink in the event all of the navigation systems 128, 130, 132 are not providing a correct indication of position.

As many of the electronic components of the UAV 100 as practical, including the flight control system 122 and motor controller 124, are shielded by radio frequency shielding to reduce the susceptibility of the components to electronic interference. Of course some components, such as antenna of the GPS navigation system 128, must remain unshielded. The shielding forms a Faraday cage around the components. The UAV 100 also comprises a collision avoidance system 144 which monitors the outputs of the image sensors of the optical navigation system 130 and determines the possibility that following the flight path would result in the UAV 100 colliding with an object. If the collision avoidance system 144 determines that the UAV 100 would, if flight along the flight path were to be continued, collide with an object, the collision avoidance system 144 commands the flight control system 122 to alter the flight path in a direction in which collision with the object is determined to be avoided. In making its determination, the collision avoidance system 144 takes into account the current heading and airspeed of the UAV 100, as well as the positions of other objects in the environment surrounding the UAV 100.

Figure 4 shows a payload delivery system 150 according to a second embodiment of the invention. The payload delivery system 150 comprises a UAV 100 according to the first embodiment of the invention, a first base station 152 and a second base station 154.

Each of the first and second base stations 152, 154 comprise a landing site 156 for the UAV 100. The first and second base stations 152, 154 comprise an induction charger 158 arranged to charge the batteries of the UAV 100 when the UAV 100 is on the landing site 156. In alternative embodiments, a contact charging arrangement may be provided.

In alternative embodiments, the UAV 100 comprises an alternative power source to the batteries or an additional power source. In such embodiments, the base stations 152, 154 alternatively or additionally comprise a system for replenishment of that power source. For example, in embodiments, the UAV is powered by gas and the base station comprises a system to replenish the gas.

The base stations 152, 154 and the UAV 100 are also arranged to transfer data between each other when the UAV 100 is on the landing site. In embodiments, a wired data connection may be established; in alternative embodiments, the data connection is wireless, for example via Wi-Fi or infrared. Prior to take-off, the data being transferred includes at least the location of the predetermined destination, and can also include the encryption key for encrypted 5G communication, the details of the payload 118 including payload weight, landing codes, map updates, the locations of established no-fly zones, the flight path etc. The landing site 156 on each base station 152, 154 comprises a landing indicator in the form of a machine readable code arranged so as to be identifiable to the image sensors of the UAV 100 when the UAV 100 is near the base station 152, 154, for example within 20 meters of the base station 152, 154. The machine readable code allows the UAV 100 to precisely locate and track the landing site 156 when it arrives at its destination, at which point the position provided by the navigation systems 128, 130, 132 might not be accurate enough to guarantee the UAV 100 lands on the landing site 156.

In alternative embodiments, the base stations 152, 154 comprise a laser guidance system arranged to emit one or more laser beams which the UAV 100 is able to track and thereby locate the landing site 156.

In use, the UAV 100 is initially provided on the first base station 152. A payload 118 is loaded into the housing 118 of the payload receiving portion 114 and is secured therein. The first base station 152 communicates to the UAV the location of the predetermined destination to which the payload 118 is to be delivered, the second base station 154 being located at that location of the predetermined destination.

The flight control system 122 then calculates a flight path to the predetermined destination taking into account the topography of the environment between the first and second base stations. The flight path is a path in three dimensional space and so specifies the direction as well as the altitude the UAV 100 is to fly at. The flight path is then verified to ensure the UAV 100 has sufficient range to complete the flight with a suitable margin.

Flight of the UAV 100 is initiated, either by an operator or automatically, and the flight control system 122 continuously sends appropriate commands to the motor controller 124 so that the motors 110 are controlled in a way that the UAV 100 flies autonomously according to the flight path. The flight control system 122 receives heading and altitude inputs from the compass 136 and altimeter 138, respectively, along with position data provided by the GPS navigation system 128 as a basis for the navigation of the UAV 100.

During flight, the optical navigation system 130 and All Source Positioning Navigation system 132 also provide positional information to the flight control system 122. The flight control system logs the position provided by each navigation system 128, 130, 132 and also continuously compares the positions by calculating a distance between them.

If at least two of the positions so determined begin to differ by more than a threshold value, then the flight control system 122 deems that at least one of the positions is incorrect, and also that the UAV 100 may be being interfered with. The flight control system 122 thereafter instructs the motor controller 124 to fly the UAV 100 according to the defensive manoeuvring procedure. Simultaneously the flight control system seeks to determine which navigation system 128, 130, 132 is determining an incorrect indication of position by determining which position is outlying in comparison to the other two positions. If all positions differ significantly, then each position is compared to the previously logged positions to gain an indication of which navigation systems 128, 130, 132 may not be functioning correctly.

The flight control system 122 disregards the output provided by any of the navigation systems deemed to be providing a false indication of position. If, for example, the position provided by the GPS navigation system 128 is deemed to be incorrect, then the flight control system 122 disregards the position provided by the GPS navigation system 128 and begins to pilot the UAV 100 in accordance with the position determined by the optical navigation system 130.

If all the navigation systems 128, 130, 132 are either deemed to be providing an incorrect indication of position or an output that does not correspond to a position, then the UAV 100 establishes an encrypted 5G datalink with an operator in order to receive navigational commands.

If the flight control system 122 establishes that one or more of the navigation systems 128, 130, 132 again begin to provide a correct indication of position, then autonomous flight on the basis of that position data may be restored.

Additionally during flight, the collision avoidance system 144 continuously monitors the outputs of the image sensors of the optical navigation system 130 and, if it determines there is a likelihood of collision, commands the flight control system 122 to alter the flight path to avoid the collision.

Upon nearing or reaching the predetermined position, the machine readable code at the landing site 156 of the second base station 154 comes into view of the image sensors of the optical navigation system 130. At a similar time the UAV 100 exchanges landing codes with the second ground station 154 to verify that the landing location is correct. The flight control system 130 can then track the location of the landing site 156 and pilot the UAV 100 towards it for landing.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

In alternative embodiments of the invention, the UAV flies according to the position provided by one navigation system, the other navigation system or systems remaining inactive (i.e. not actively outputting an indication of position to the flight control system). The flight control system may activate the other navigation system(s) if it determines that the presently used navigation system ceases to provide a correct indication of position (e.g. on the basis of a comparison of current and previous positions of the system, or due to the system providing an output not representative of a position). The initially used navigation system is then deactivated or the output provided by that system is otherwise disregarded. In such an embodiment the UAV switches between the navigation systems as it deems necessary to obtain an accurate indication of its position.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

1. An unmanned aerial vehicle (UAV) for autonomously transporting a payload, the UAV comprising: a steering and propulsion system; a flight control system; a first navigation system arranged to determine a position of the UAV in dependence on a first source of data, and communicate the position so determined to the flight control system; a second navigation system arranged to determine the position of the UAV in dependence on a second source of data, different from the first source of data, and communicate the position so determined to the flight control system; wherein the flight control system is configured to autonomously operate the steering and propulsion system such that, in use, the UAV is able to autonomously fly to a predetermined destination according to a flight path; wherein the flight control system is configured to provide commands to the steering and propulsion system on the basis of the position of the UAV, as determined by the first navigation system and/or the second navigation system, along the flight path; wherein the flight control system is configured to determine whether the first navigation system and the second navigation system are providing a correct indication of the position of the UAV; and wherein the flight control system is configured to disregard the position provided by the first navigation system and/or the second navigation system if it is determined that the first navigation system and/or the second navigation system are/is not providing a correct indication of position of the UAV.

2. A UAV according to claim 1, wherein the flight control system is configured to compare the position provided by the first navigation system and the position provided by the second navigation system and determine, on the basis of the comparison, whether the first navigation system and the second navigation system are providing a correct indication of the position of the UAV.

3. A UAV according to claim 2, wherein the flight control system is configured to compare the position determined by the first navigation system and the position determined by the second navigation system by calculating the distance between the positions, and wherein the flight control system is configured to determine whether the first navigation system and the second navigation system are providing a correct indication of the position of the UAV by determining whether the distance between the positions exceeds a threshold value.

4. A UAV according to any of claims 1 to 3, wherein the first navigation system is one of a satellite navigation system, an optical navigation system and an All Source Positioning Navigation system.

5. A UAV according to claim 4, wherein the second navigation system is another of the satellite navigation system, the optical navigation system and the All Source Positioning Navigation system

6. A UAV according to claim 4 or 5, wherein the satellite navigation system comprises an anti-jam antenna system.

7. A UAV according to any of claims 4 to 6, wherein the optical navigation system comprises an optical sensor having a field of view, and the optical navigation system is arranged to determine a topography of the environment in the field of view and determine the position of the UAV by reference to stored topographical data.

8. A UAV according to any of claims 4 to 7, wherein the All Source Positioning Navigation system is arranged to determine the position of the UAV using radio frequency signals received from one or more non-navigational radio frequency source.

9. A UAV according to claim 8, wherein the non-navigational radio frequency source or sources include a telecommunication tower, a cell tower antenna, a television station broadcasting antenna, and/or a radio station broadcasting antenna.

10. A UAV according to any of claims 4 to 9, wherein the first navigation system is the satellite navigation system, and the second navigation system is the optical navigation system.

11. A UAV according to any preceding claim, further comprising a third navigation system arranged to determine the position of the UAV in dependence on a third source of data, different from the first source of data and the second source of data, and communicate the position so determined to the flight control system; wherein the flight control system is configured to determine whether each of the first navigation system, the second navigation system and the third navigation system are providing a correct indication of the position of the UAV; wherein the flight control system is configured to disregard the position provided by the first navigation system, the second navigation system and/or the third navigation system if it is determined that one or more of the first navigation system, the second navigation system and/or third navigation system is/are not providing a correct indication of position of the UAV.

12. A UAV according to claim 11, when dependent on claim 10, wherein the third navigation system is the All Source Positioning Navigation system.

13. A UAV according to any preceding claim, the UAV comprising a cellular network transmitter and receiver, the UAV being configured to open a datalink with a ground station in the event the flight control system determines that all of the navigation systems aboard the UAV are not providing a correct position of the UAV.

14. A UAV according to any preceding claim, wherein the UVA is configured such that the destination of the UAV is unalterable by external command signals sent to the UAV during the flight.

15. A UAV according to any preceding claim, wherein the UAV comprises radio frequency shielding, the flight control system being shielded by the radio frequency shielding.

16. A UAV according to any preceding claim, further comprising a collision avoidance system, the collision avoidance system arranged to determine whether following the flight path would result in the UAV colliding with an object, the collision avoidance system being arranged to alter the flight path if it is determined that the UAV would, if flight along the flight path were to be continued, collide with the object, the flight path being altered in a direction in which collision with the object is determined to be avoided.

17. A UAV according to any preceding claim, wherein the steering and propulsion system comprises one or more rotors arranged to propel and steer the UAV during flight.

18. A UAV according to claim 17, wherein the rotors are contained within a duct.

19. A payload delivery system comprising a UAV according to any preceding claim, and a base station, wherein the base station is arranged to communicate the position of the predetermined destination to the UAV prior to flight.

20. A payload delivery system according to claim 19 , further comprising a landing site comprising a landing position indicator detectable by the UAV, the flight control system being configured to cause a landing of the UAV in response to detection of the landing position indicator.

21. A payload delivery system according to claim 20, wherein the landing position indicator comprises a laser emitter and/or a machine readable code.

22. A kit of parts for a payload delivery system, the kit comprising: a UAV according to any of claims 1 to 18, a base station according to claim 19, and a landing site according to claim 20 or 21.

23. A method of operating a UAV, the method comprising the steps of: providing a UAV according to any of claims 1 to 18; using the first navigation system to determine the position of the UAV according to the first source of data; using the second navigation system to determine the position of the UAV according to the second source of data; determining whether the first navigation system and the second navigation system are providing a correct indication of the position of the UAV; and disregarding the position provided by the first navigation system and/or the second navigation system if it is determined that the first navigation system and/or the second navigation system are/is not providing a correct indication of position of the UAV.

24. A method of delivering a payload, the method comprising the steps of: providing a UAV according to any of claims 1 to 18, providing the UAV with the payload such that the UAV can carry the payload during flight, communicating to the UAV the predetermined destination for delivery of the payload, calculating the flight path to be followed by the UAV to the predetermined destination, initiating flight of the UAV so as cause the payload to be delivered to the predetermined destination.

25. A method according to claim 24, wherein the UAV flies autonomously to the predetermined destination without the need for external commands from an operator of the UAV.

26. A method of determining the position of a UAV, the method comprising the steps of: using a first navigation system to determine a position of the UAV in dependence on a first source of data; using a second navigation system arranged to determine the position of the UAV in dependence on a second source of data, different from the first source of data; calculating the distance between the position determined by the first navigation system and the position determined by the second navigation system; and determining whether the first navigation system and the second navigation system are providing a correct indication of the position of the UAV by calculating whether the distance between the positions exceeds a threshold value, the first navigation system and/or the second navigation system being determined not to be providing a correct indication of the position of the UAV if the distance exceeds a threshold value.

27. A flight control system for a UAV according to any preceding claim.