The payoff of unmanned aircraft systems (UAS) for military, law enforcement and scientific missions is constrained by the airspace they can share with manned aircraft. As of May 2011, one Broad Area Maritime Surveillance system Demonstrator (BAMS-D) was providing 50 percent of the Intelligence, Surveillance and Reconnaissance (ISR) imagery for the U.S. Navy’s 5th fleet in the Arabian Gulf. The Northrop Grumman RQ-4A Global Hawk nevertheless depends on off-board sensors to keep clear of other aircraft. Capt. Robert Dishman, Naval Air Systems Command (NAVAIR) program manager for Persistent Maritime UASs explains, “We’ll be tethered to a ground-based radar, or if we’re to operate outside the littoral regions, we’ll be tethered to a ship, AWACS or E-2. That’s very limiting.”
The Increment I MQ-4C BAMS expected operational in 2015 will be the first UAS with a Due Regard sensor to cue ground operators to conflicting air traffic. Autonomous airborne and ground-based Sense-And-Avoid (SAA) technology must be integrated with new certification, training and operating standards to steer unmanned air vehicles (UAV) through shared sky.
Like most UAS integrators, MQ-1 Predator/Reaper/Gray Eagle manufacturer General Atomics Aeronautical Systems Inc. (GA-ASI), based in San Diego, has SAA plans. Tests of the Automatic Dependent Surveillance-Broadcast (ADS-B) and Traffic Alert and Collision Avoidance System (TCAS) found shortcomings in algorithms certified for civil aircraft.
“They never considered the flight profiles of UAVs,” said GA-ASI Director of Strategic Development Scott Dann. “Our aircraft traditionally fly slower than a lot of aircraft in commercial-use airspace.” Dann chairs the FAA Aviation Rulemaking Committee looking at UASs in the National Airspace System (NAS). “The airspace issues are not unsolvable, but they probably are bigger than any one company or one agency to solve... I don’t think there’s going to be a silver bullet. It’s going to take a concerted effort,” he said.
The Department of Defense (DoD) Airspace Integration Plan lays out incremental steps to fly unmanned systems in the NAS, and a Joint Concept of Operations gives the armed services common UAS practices, procedures and flight standards. “Our ultimate goal is predictable, safe behavior,” said Mary Ottman, deputy product director for airspace integration concepts with the Project Office for UAS (Product Office for Airspace Integration), part of the Program Executive Office for Army Aviation and Missile Command (AMCOM) in Redstone Arsenal, Ala. “We want these guys to always act the same way.”
The DoD UAS Task Force organized in 2007 includes FAA, Department of Homeland Security (DHS) and NASA in a NAS Access Plan for Federal Public Unmanned Aircraft Systems. Like other government operators, DHS and NASA fly UAVs outside U.S. restricted airspace only with FAA Certificates Of Waiver or Authority (COA) that define each operation. U.S. Customs and Border Protection and the Coast Guard, for example, jointly operate the Guardian/Predator-B UAS under a COA that sets safe operating altitudes, de-conflicts traffic and formalizes recovery procedures in the warning area off the Florida Space Coast. FAA has about 270 COAs in effect, most of them good for one year. Typical approval time is now 60 days for new COAs and 30 days for renewals.
COAs enable NASA to use Ikhana/Predator, Global Hawk and smaller UASs successfully, but the space agency finds lack of routine access to the NAS a significant limitation. In May, NASA received approval and funding for a five-year project on UAS Integration in the NAS at Dryden Flight Research Center. With FAA input, Phase 1 of the project will validate key technical areas for modeling, simulation and flight test.
Phase 2 generates methodology for developing UAS airworthiness requirements, and data to develop certification standards and regulatory guidance. Beginning in fiscal 2012, NASA will flight test SAA technologies developed by the DoD.
The first Army Gray Eagle UAS company to deploy in Operation Iraqi Freedom flew over 4,500 hours from July 2009 to June 2010. Helicopter pilot Capt. Travis Blaschke commanded the Quick Reaction Capability-1 (QRC-1) unit at Forward Operating Base (FOB) Taji. “We shared airspace with an entire aviation brigade that’s 300 aircraft in and out of the FOB every day,” he said.
With four MQ-1C Gray Eagles, QRC-1 was a 1st Division asset tasked by ground commanders for Reconnaissance, Surveillance and Target Acquisition like manned Apache and Kiowa Warrior helicopters. “We would base the airspace upon the ground space the division was allocated,” says Blaschke. “Really, our airspace was all of Iraq if the mission dictated we go outside Baghdad.”
UAVs shared a runway with manned aircraft, and Ground Control Station (GCS) operators switched from tower to air traffic control (ATC) to transit controlled airspace. ATC divided Iraqi airspace into 30-km blocks and assigned altitude bands –– low for helicopters, medium for all manned and unmanned aircraft and high for manned aircraft alone. “We’re kind of connecting the blocks to get from the location we’re at to our final mission location,” said Blaschke. “We’re also requesting an altitude... You can be stacked from 2,000 feet all the way up to 13,000 feet. Every 500 feet, there’s a different aircraft in that airspace.” ATC cleared blocks enroute. “If there’s an operation in a sector, they’ll tell us to avoid three blocks or four blocks if they need us to deviate.”
The control scheme leveraged the precision of the MQ-1C navigation suite. “Our triple-redundant GPS systems keep us from deviating on our side of the system. It’s very reliable and consistent,” he said. Approved approaches integrated returning UAVs with manned traffic patterns. “They knew the altitude we’d be at. They knew our rate of descent. There’s not the variation you’d see from one manned pilot to another.”
The Raytheon AN/AAS-53 electro-optical (EO) payload on the Gray Eagle also gave operators situational awareness on takeoff and landing. “The payloads are used just as you’d use your eyes as a manned pilot,” said Blaschke. “You’re ensuring prior to pressing the takeoff button that there’s nothing in your pattern.”
While the Army adapts similar control procedures to the smaller AAI RQ-7B Shadow UAS, the Navy faces special airspace issues with the MQ-8B unmanned helicopter at sea.
Two Northrop Grumman Fire Scouts share the frigate USS Halyburton with a manned SH-60B Seahawk off the Horn of Africa. Integrated air operations fly manned and unmanned aircraft at the same time. With positive radar control, the shipboard tactical controller ensures safe separation between the UAV and other aircraft. The MQ-8B also has an Identification Friend or Foe (IFF) transponder interrogated and tracked by both ship and Seahawk for safety.
Within the NAS, Army UAS training and test flights outside restricted or COA airspace now require manned chase aircraft or ground observers for safety. At the Army UAS test field in El Mirage, Calif., any aircraft entering the joint-use airspace forces the UAS to land. Army Ground Based Sense-And-Avoid (GBSAA) efforts aim to mix ground sensors and apply new maneuver algorithms and concepts of operation to steer UAVs away from conflicting traffic.
A proof-of-concept demonstration in April fused three Lightweight Surveillance and Target Acquisition Radars (LSTAR) from SRC, based in North Syracuse, N.Y.
“We’re making this system sensor-agnostic where we can use existing radars, FAA radars, whatever, to determine where this aircraft is in the sky,” said Ottman at AMCOM. The Air Force, Navy and Marine Corps are evaluating the Raytheon AN/MPQ-64 Sentinel air defense radar and various airport surveillance radars for GBSAA.
Based on the Army Lightweight Counter-Mortar Radar (LCMR), the small, three-dimensional LSTAR shows GCS operators if conflicting traffic is above or below the UAS, and it has the waveforms, signal processing algorithms and electronically scanned antenna to spot small threats in ground clutter.
According to LCMR co-inventor and SRC Vice President Tom Wilson, “The criterion for SAA is to make sure you can detect and track everything in the airspace that could collide with a UAS. That includes an ultralight flying slow at low altitude with a small radar return, or a parachutist.”
The L-band radars in the El Mirage demonstration also had classifier algorithms “tweaked” to discriminate large birds. Off-radar software and a custom display marked traffic with a simple red or green light –– a red light meant the UAS had to land.
The next phase of GBSAA testing will put two LSTARs at Dugway Proving Ground in Utah this summer. “Instead of landing when someone enters your airspace, you want the UAV to have the option to stay in the sky,” said Ottman. “We’re going to use those sensors to get out of the way.”
The Air Force leads an Airborne Sense-And-Avoid Advanced Technology Development (ATD) to put Unmanned Sense, Track and Avoid Radar (USTAR) on the RQ-4A Global Hawk. Colorado Engineering, based in Colorado Springs, is developing the C-Band, pulsed-Doppler, electronically scanned array. The Air Force is also developing an X-Band electronically reconfigurable array radar to fly Multi-Sense Detect, Sense and Avoid (MSDSA) tests this July. The Navy wants a Due Regard Air-to-Air Radar Subsystem (AARS) with human pilot-in-the-loop to operate the MQ-4C BAMS outside off-board radar coverage. “The FAA and the authorities do get a little nervous if you say you’re going to maneuver an aircraft without pilot intervention,” said Capt. Dishman at NAVAIR. Initial studies considered EO sensors to mimic a pilot’s eye. “What we found was that’s fairly limiting with environmental effects, clouds, rain. If you put a radar on board, you can get great detection ranges in a wider variety of environmental conditions.”
ITT Electronic Systems Radar Reconnaissance and Acoustic Sensor business, in Van Nuys, Calif., is developing the AARS radar to fly on the second BAMS test article in the fall 2012. The Navy selected a Ku-band radar to avoid interference with BAMS primary sensor, and used modeling and simulation to define a field of regard 110 degrees to either side of the aircraft and plus or minus 30 degrees in elevation. ITT made the radar software DO178-compliant for the FAA, and drew on thin tile array technology to achieve a target weight around 65 pounds.
With three electronically scanned arrays above the BAMS EO sensor and Electronic Support Measures antenna, the new radar provides desired coverage and generates target tracks quickly enough for avoidance maneuvers. The Navy is working with the Air Force Research Laboratory (AFRL) on follow-on algorithms that will recommend maneuvers for approval by a pilot on-the-loop. “What we really we want to get to is fully autonomous Sense-And-Avoid and integrate that right in with the flight control system,” says Dishman.
While the Navy BAMS will also use ADS-B and the TCAS Traffic Advisory mode to show operators traffic with transponders, the DoD is investigating visible band sensors to detect non-cooperative aircraft. In January, AFRL and the Army put miniature EO cameras on a Shadow UAV. AFRL also plans to demonstrate Short Wave Infra-Red (SWIR) SAA technology on a Reaper in Fiscal 2012, and it is investigating active Laser Detection and Ranging to reduce false alarms versus passive EO.