Small Unmanned Aerial Systems (sUAS) can provide valuable intelligence in support of disaster response. In a quickly deployable package, they can be launched to expand the coverage area of search parties, collect critical data prior to conducting specific rescue or firefighting tasks, and survey damages. In areas with complex terrain and poor visibility, sUAS may be the only option for aerial data collection. The following paper will explore the requirements derivation process for a disaster response sUAS.
Mission
The proposed sUAS will be primarily marketed towards law enforcement, firefighting, and other crisis response organizations as a solution for man-portable tactical reconnaissance. Fire Apparatus identifies DJI and FireFly UAS as the most prevalent in fire fighting use (Petrillo, 2016), which the new vehicle aims to replace through superior performance. It will be designed around the following core tasks:
- Identifying distressed persons
- Characterizing compromised structures
- Surveying damage and safety hazards
- Providing situational awareness to distributed team members
Base Requirements
The Request for Proposal (RFP) contained baseline requirements for transportability, cost, air vehicle element, command and control element, payload, datalink, and support equipment. Three will be broken down into derived requirements.
Payload
5.1 Shall be capable of color daytime video operation up to 500 feet AGL
5.1.1 Shall provide 90% probability of recognition in clear daytime lighting conditions between one hour after sunrise until one hour prior to sunset.
5.1.2 Shall provide 90% probability of detection in degraded conditions defined as lighting within one hour of sunrise/sunset, haze, light fog, smoke, and dust.
5.1.3 Shall meet 5.1.1 and 5.1.2 criteria at a slant range of 700 feet.
5.2 Shall be capable of infrared (IR) video operation up to 500 feet AGL
5.2.1 Shall provide 90% probability of recognition in unobscured atmospheric conditions outside of the thermal crossover period (within one hour of sunrise/sunset).
5.2.2 Shall provide 90% probability of detection in degraded conditions defined as the thermal crossover period, haze, light fog, smoke, and dust.
5.2.3 Shall meet 5.1.1 and 5.1.2 criteria at a slant range of 700 feet.
5.3 Shall be interoperable with C2 and data-link
5.3.1 Shall receive uplinked commands from the air vehicle using RS-232 interface.
5.3.2 Shall return feedback/status messages to the air vehicle using RS-232 interface.
5.3.3 Shall compress time-stamped sensor metadata and raw video into H.264/AVC compliant transport stream (MISB, 2010).
5.3.4 Shall export compressed video via RS-422 interface to air vehicle transmitter.
5.4 Shall use power provided by air vehicle element
5.4.1 Shall operate from 22.2VDC power source.
5.4.2 Shall not exceed 1,000mAh power consumption in any mode of operation.
Datalink
6.1 Shall be capable of communication range exceeding two miles line of sight (LOS)
6.1.1 The air vehicle and controller shall automatically detect co-channel interference.
6.1.2 Upon detecting co-channel interference, the air vehicle and controller shall automatically switch frequencies within 500ms.
6.2 Shall provide redundant communication capability (backup) for C2
6.2.1 Shall have a primary Frequency Hopping Spread Spectrum (FHSS) Federal Communications Commission (FCC) compliant S-band datalink.
6.2.2 Shall have a secondary Frequency Hopping Spread Spectrum (FHSS) Federal Communications Commission (FCC) compliant UHF-band datalink.
6.3 Shall use power provided by air vehicle element
6.3.1 Shall operate from 22.2VDC power source.
6.3.2 Shall not exceed 2,500mAh power consumption in any mode of operation.
Support Equipment
7.1 Design shall identify any support equipment required to support operation
7.1.1 Shall include a 115VAC field battery charger capable of charging two batteries in one hour.
7.1.2 The vehicle shall save recorded photos on a removable Secure Digital Extended Capacity (SDXC) card in JPEG format.
7.1.3 The vehicle shall save recorded videos on a removable Secure Digital Extended Capacity (SDXC) card in MPEG-4 format.
Design Overview
Fielding the tactical crisis response sUAS will be largely an integration effort between several mature technologies. The vehicle will be a tilt-wing configuration with four wingtip electric motors turning fixed pitch propellers. This blends the rotary wing ability to takeoff/land vertically and hover, with the speed and endurance of a fixed wing. The payload will be similar to the combined electro-optical (EO)/infrared (IR) system under development for the Insitu ScanEagle (Insitu, 2015), providing greater data on the ground scene on the same sortie without having to modify the vehicle. A key feature for this sUAS will be the capability to stream full-motion video and associated metadata to dispersed ground parties. While many commercially available sUAS are able to distribute video from their control stations via web streaming (ex. YouTube), this service may be unavailable during a crisis as cell networks are damaged or overloaded. The proposed sUAS will transmit its video feed to tablets and smart phones, enabling recovery personnel to share a common operating picture. Onboard flight control will be accomplished by dual redundant sensor and processing modules that will compare outputs prior to sending commands to effectors. To enable high downlink speeds, the primary datalink will use an S-band FHSS protocol. In the event all available S-band channels become unusable, a backup UHF datalink will provide essential control and telemetry functions for safe recovery. The power system will consist of two commonly available 22.2VDC 11,000mAh batteries.
Test & Evaluation Criteria
Payload
Section 5 requirements can be accomplished independent of vehicle testing in an enclosed facility that provides control of ambient lighting and simulating various visibility conditions. In order to expand the operational field of regard, all sensor requirements will need to be satisfied at a slant range of 700 feet (equates to a 45 degrees sensor depression angle). Sensor fidelity will be tested using the U.S. Air Force Equivalent Bar Chart, which establishes a normalized, objective means of determining if a sensor can be expected to meet certain thresholds (McShea, 2010).
5.1.1 Illumination will be varied from 10.8-10752 Lux (average twilight to full daylight) to meet the “recognition” threshold (object is present and can be classified) to 90% certainty.
5.1.2 The EO sensor fidelity will be tested in degraded conditions from 10.8-1.08 (average twilight to deep twilight) in artificial fog down to visibilities of 2 miles, to meet the “detection” threshold (object is present) to 90% certainty. It will be assumed that the vehicle will not be operated beyond visual line of sight.
5.2.1-3 The IR sensor fidelity will be tested similarly to the EO sensor, with average bar target radiances varied 200-500 degrees Kelvin.
5.3 All of these requirements can be tested concurrently with 5.1 and 5.2 by connecting the sensor to RS-232 and RS-422 compatible receivers with H.264/AVC video decoding software and displayed.
5.4 The payload will be exercised to worst-case conditions, as determined through analysis of individual subcomponent current requirements. Measurements will be recorded and multiplied by a safety factor of 25%.
Datalink
All datalink requirements will be tested using a production-ready article (to identify any electro-magnetic interference in the final design) placed in an anechoic chamber equipped with precision transmitters and frequency controllers.
6.1 The vehicle will be operated in a representative manor while a specific S-band frequency is jammed. The UAS’s FHSS algorithms should skip to alternate frequencies, with no interruptions to control or downlinked video observed by the operator.
6.2 The vehicle will be operated in a representative manor until broadband S-band noise is injected. The UAS should automatically transition to the backup UHF datalink, with no apparent loss of control observed by the operator (loss of downlinked video is acceptable).
6.3 The datalink will be exercised to worst-case conditions, as determined through analysis of individual subcomponent current requirements. Measurements will be recorded and multiplied by a safety factor of 25%.
Support Equipment
Support equipment requirements can be tested concurrently with other developmental test events.
7.1 The suitability of the battery charger can be tested as soon as a design decision is made on the specific battery. Since the support equipment should exhibit a high degree of reliability for first responders, criteria provided in MIL-STD-810 Environmental Engineering Considerations and Laboratory Tests should be followed while measuring charging times.
7.2-3 As soon as a complete system is assembled, media recording can be verified concurrently with other events. After each flight, files on the SD card should be checked for time stamp errors and corruption.
Development Process
The Rapid Application Development (RAD)(OIS, 2008) model will be used to accelerate the “10 Phases of Development” (Austin, 2010). Since a conceptual design has already been established based on similar products, the process will begin with preliminary design. This phase, along with detailed design, prototyping, and test are forecasted to take three years (roughly half of Austin’s recommendation) due to low technical risk and the use of Concurrent Development (CD). CD compresses development timelines by simultaneously completing multiple phases of the acquisition process. In this case, development of the vehicle and payload will run in parallel, which makes interface control a key focus area. Prototyping and early flight test can also overlap to identify and correct any deficiencies as early as possible. The certification process will also start one year prior to fielding. While a production-representative article may not be available at that point, certification can be started on the premise of similarity with other certified systems, contingent on final verification results. A Gantt Chart will be used to track progress, manage resources, and maintain timelines. The team will also employ Agile Manufacturing principles (Sarhadi, Gunasekaran, & Yusuf, 1999) to accelerate the prototyping, production, and support phases, by leveraging Computer Assisted Drafting (CAD) and 3-Dimensional printing for example.
References
Austin, R. (2010). Unmanned aircraft systems: UAVs design, development and deployment. Reston, VA: American Institute of Aeronautics and Astronautics.
Insitu. (2015). ScanEagle Product Card. Retrieved November 22, 2016, from https://insitu.com/images/uploads/pdfs/ScanEagle_SubFolder_Digital_PR080315.pdf
McShea, R. E. (2010). Test and evaluation of aircraft avionics and weapon systems. Raleigh, NC: SciTech Pub.
Motion Imagery Standards Board. (2010). Constructing a MISP Compliant File/Stream (MISB TRM 0909.2).
Petrillo, A. (2016, July 6). Drones Poised to Be Used on More Fire Scenes Across the United States. Retrieved November 30, 2016, from http://www.fireapparatusmagazine.com/articles/print/volume-21/issue-6/features/drones-poised-to-be-used-on-more-fire-scenes-across-the-united-states.html
Office of Information Services. (2008). Selecting a Development Approach (United States, Department of Health and Human Services, Center for MEDICARE & MEDICAID Services).
Sarhadi, M., Gunasekaran, A., & Yusuf, Y. Y. (1999). Agile manufacturing:: The drivers, concepts and attributes. International Journal of Production Economics, 62(1), 33-43. doi:10.1016/S0925-5273(98)00219-9
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