Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
Issue link: https://electronicsmilitarydefense.epubxp.com/i/78772
Trends Technical Challenges For Small UAV Payloads Payload engineers push imaging technology limits under constrained SWaP budgets and deliver stabilized full motion video from small unstable airborne platforms. by Chris Johnston he small unmanned aerial vehicle (UAV) marketplace has recently displayed dramatic growth in the vari- ety of airframes and payloads. While large, familiar UAVs like Predator, Shadow, and Global Hawk garner much of the press and attention, small, unheralded UAVs deliver the majority of intelligence, surveillance, and reconnaissance (ISR) video and execute the bulk of sorties. The small UAVs are represented by micro-UAVs as tiny as a hummingbird, to UAVs that weigh 150 lbs and lift >10 kg payloads. Small UAVs are generally launched by hand, by an accelerating launcher, or are vertical take-off and landing (VTOL). Payload engineers are always faced with limited budgets in terms of mass, volume, and power for small UAVs. In parallel, however, the same engineers are asked to deliver very narrow field- of-view images, exotic on-board image processing, lossless video compres- sion, multi-color simultaneous imag- ing, and hundreds of other technically advanced attributes that are difficult to execute in a laboratory, let alone from a small aircraft buffeting in the wind. This article will discuss some of T the high-level issues that suppliers and customers need to address when considering the delivery of video to the ground from a small UAV. Defining Small UAVs Each branch of the armed services has its own definition of a UAV class, sometimes call tiers — Tier I, Tier II, and so on. There are names for UAV classes — small tactical unmanned aircraft systems (STUAS), mid-endurance unmanned aircraft systems (MEUAS), maritime tactical unmanned aircraft sys- tems (MTUAS), and so on. The most numerous UAVs are small, hand-launched aircraft powered by electric engines. Typical flight endurance is 20 to 90 minutes, and typical oper- ating altitude is hundreds of feet. The prevalence of these small, hand-launched aircraft is a testament to their value and effectiveness. Thousands of small, hand-launched UAVs have deployed with U.S. troops overseas. Payloads for these hand- launched systems are relatively simple, mostly fixed visible or thermal cameras mounted in the small airframe. Articulated 38 Electronic Military & Defense ■ www.vertmarkets.com/electronics Figure 1: Hood Technology's 4-axis gyro-stabilized imaging system, Model Alticam 11 EO/IR. payloads have only recently been introduced, and most pay- loads deliver limited functionality due to the strict mass and volume limits required for a hand-launched platform. The next step up from hand-launched is the small, tactical unmanned airborne systems, or STUAS. These are typically liquid-fueled aircraft with mission endurances from 8 to 24 hours, weigh from 40 to 150 lbs, and have the capacity to lift heavier, more complex payloads. The team at Hood Technology (Hood River, OR) was involved in the early development of two STUAS platforms, the Aerosonde and the Scan Eagle. The Scan Eagle is currently a widely deployed small tactical UAS in the U.S. fleet. The first intended uses of these aircraft were varied, but they were universally promoted as small, long-endurance aircraft with missions lasting from 12 hours to several days. In the late 1990s, the Hood Technology team contributed to the first trans-Atlantic flight of an unmanned aircraft, cross- ing the Atlantic in 26 hours. This was achieved with 1.5 gallons of fuel. An early approach was to develop useful aircraft and then determine what payloads were needed to generate commercially viable businesses. Early payloads ranged from weather sensors and geomagnetic sensors to cameras. After the first STUAS aircraft were flown and the flight attributes well understood, the trade-off between payload and flight attribute immediately ensued. Originally, it was a direct trade-off between payload mass and flight endurance. Simply put, for every gram of payload loaded onto the aircraft, a gram of fuel was removed, and the mission life was reduced. There are hundreds of sur- rounding complexities with the payload and its support, but mainly, it was a payload grams/mission duration trade-off. The earliest missions for Aerosonde and Scan Eagle STUAS-class UAVs have not yet become commercially signifi- cant. Tuna boat captains envisioned using robotic airplanes to search for schools of tuna rather than conducting searches with helicopters. Long-endurance, geomagnetic mapping missions over the northern reaches of North America were conducted. Here, the long-mission duration favored the unmanned aircraft vs. the manned aircraft.