Is It Time for Unmanned Aerial Systems to Get Certified GNSS?

While the FAA is moving ahead with plans for UAS/UAV to have regular access to U.S. airspace by 2015, a number of barriers remain. For UAVs to be treated like manned aircraft, their systems likely need to be qualified to the same standards as civil avioncs — this is a challenge, as each UAS has largely unique systems. UAS equipment standards are emerging, but threats to GNSS abound and defense/mitigation is required. The coming AUVSI convention in Las Vegas in August may provide some answers.

Today’s demand for a wide range of unmanned aerial systems (UAS) has resulted in a lots of different types flying today in many applications. With no apparent standard avionics fit or uniform safety standards, each UAS type is basically configured for specific tasks. As commercial applications for UAS emerge, major market growth is anticipated. One forecast indicates that the UAS market could reach $7.26 billion this year alone. The promise of new and better ways to reduce costs, improve safety, and for more efficient operations is feeding a real market expansion.

However, in the U.S. the FAA currently requires each UAS commercial project desiring access to controlled airspace to obtain an FAA-approved Certificate of Authorization (CoA). While the FAA has made efforts to speed up approvals, this process has put a damper on widespread commercial adoption of UAS. Nevertheless, opportunities abound in pipeline and transmission line inspection, crop spraying, expanded law enforcement/security, and hundreds of other applications. The FAA may have felt some pressure to move forward, because Congress has put in place the Modernization and Reform Act of 2012, which calls on the FAA to fully integrate unmanned systems, including those for commercial use, into the national airspace by September 2015.

Cadence Technologies SR-20.

Meanwhile, a project called the Unmanned Aircraft Systems Integration in the National Airspace System (or UAS in the NAS) undertaken by NASA’s Dryden Flight Research Center at Edwards Air Force Base, California, seeks to reduce technical barriers related to safety and operational challenges associated with enabling routine UAS access to the NAS.

Civil aircraft and UAS may co-exist after September 2015.

NASA Predator test vehicle.

Europe is also undertaking a study on the integration of unmanned aerial systems (UAS) in non-segregated airspace for the future “Single European Sky”. The study, known as ICONUS (Initial CON OPS for UAS in SESAR), will be carried out by a consortium within the European air traffic management program called SESAR. The group is led by France’s ONERA, and includes AVTECH (Sweden), CIRA and Deep Blue (Italy), ENAC (France), and INTA (Spain) — all have significant experience with UAS. The study will allow the definition of the requirements, capabilities, and the equipment that UAS will need to operate safely and efficiently in the coming European SESAR environment.

In the U.S., the RTCA SC-203 committee is busy drafting UAS operational requirements, and there has been significant progress towards ultimately publishing Minimum Aviation Performance Standards (MASPS), including requirements for navigation. Europe also has similar activities under way aimed at improving UAS access to their airspace.

The big picture is that requirements for unmanned aircraft are being brought into conformance with the standards applied to the performance and behavior of manned aircraft. Navigation requirements for UAS are expected to specify that systems will need to be qualified to Minimum Operational Performance Standards (MOPS). This means that on-board electronics, including GNSS systems, will probably need to be FAA TSO qualified, just as they are now for manned aircraft.

But why do we need to investigate certified avionics now? In the scheme of things, +2 years of breathing space to certify UAS avionics systems is not long before the September 2015 deadline. FAA airborne software and hardware qualification will take mucho time and effort to implement, and reconfiguration of systems, interfaces, and operating procedures may take even longer.

UAS manufacturers have the option to move forward in stages — for instance, by selecting a few existing airborne qualified OEM avionics, they could minimize the internal effort to comply. And as the first UAS with certified avionics emerge, they will probbaly get good support from FAA to adopt the rules of operating in the U.S. NAS. Embedding an existing certified GPS receiver in UAS avionics will reduce the level of internal work needed and will allow more effort for developing commercial market opportunities which are looking to quickly adopt UAS.

And while this is going on, efforts are in full swing to change the navigation landscape in the U.S. and Europe over the next few years. So it would be better to be ready with a capable GNSS receiver that is already built to meet the challenges of the FAA NextGen and SESAR environments.

The L5 civil GPS frequency may likely be operational around the time that UAS unrestricted access becomes possible. GPS L1/L5 dual-frequency operations will enable higher navigation accuracy, reliablity, and integrity. The FAA is already developing NexGen WAAS to include L5, and revisions to the GPS MOPS to include L5 are anticipated to begin shortly, in time for a usable GPS L5 constellation in 2015/2016.

The FAA is already preparing for L5 avionics, and industry investigative work is under way. It’s possible that GPS L1/L5 may well meet the accuracy and integrity requirements for CAT II/III automated landings. And in Europe, Eurocae work is expected to gain momentum for the Galileo E1/E5a MOPS as the Galileo satellite navigation system is launched and becomes operational.

The new GNSS environment also includes WAAS/SBAS precision approach (LPV) capability — LPV is available now in the US and will soon be in wider operation in Europe. And Automatic Dependendant Surveillance (ADS-B) is being rolled out in the U.S. and around the world. ADS-B is being mandated within the U.S. NAS as the means for air traffic control to track all aircraft, so UAS avionics will need to include certified ADS-B Out capability.

The Septentrio AiRx2 receiver comes out of the box as a certified L1 GPS with ADS-B and WAAS LVP, but is also ready for GPS L5 and Galileo E1/E5a.

Photo: Septentrio

And yet, even as greater steps forward are being taken to enhance how GNSS is used in this wider definition of aviation, which will soon include UAS, a team at the University of Texas was busy demonstrating how a UAV could be maliciously side-tracked (see article in the August issue of GPS World). Their recent tests at White Sands Missile Range used a spoofing set-up built in their lab to significantly affect the trajectory of a Hornet Mini UAV. Admittedly, the GPS on this vehicle was not a qualified airborne receiver, but there were other sensors on board the vehicle which may have been able to indicate that the GPS had been hijacked. The spoofing set-up used a high-power directional signal to overwhelm the real GPS signals and “distract” the GPS on-board receiver. Nevertheless, they were able to force the hovering UAV down towards the ground — somewhat reminiscent of the Iranian downing of a U.S. surveillance drone in December last year.

How could this happen when there was also an inertial sensor and a radio-altimeter on the UAV? A good question, which UAV manufacturers will need to consider when they implement their on-board Kalman filters, knowing that spoofing is now an additional threat to combat. But, couldn’t we detect that high-power RF spoofing signal at the front-end of the GPS receiver? Even if only to tell the on-board systems that there could be Hazardous Misleading Information (HMI) about? Or run separate GPS and GPS/inertial position solutions, detect significant divergence, and set the same warning flag? And multi-constellation, multi-frequency receivers, and even controlled radiation pattern antennas — all things to investigate, and even more effort for the aviation receiver guys who are always working tirelessly to improve the integrity of GNSS positioning.

Of course, if you hijack a UAV with a high-power spoofer, you are also spoofing civil transports operating in the same airspace — so now there is the potential to trigger a federal investigation. And it will probably be easier to detect this stuff with moving airborne sensors rather than the fixed ground equipment used to find jammers on trucks at Newark Airport, and lots of pilots likely providing real-time location information on radios if their GPS goes even a little haywire — all would help to quickly locate and shut down any spoofer. Nevertheless, it’s a threat to be mitigated.

In South Korea, the effects of intermittent North Korean jamming of GPS to disrupt navigation at sea, on land, and in the air in the south may have contributed to the recent fatal crash of a Schiebel Camcopter S-100 drone — a 150-kilogram rotorcraft capable of 220 km/h flight, which should have coped with loss of GPS as the Camcopter has multiple inertial measurement units that “allow safe operation and recovery in the absence of GPS signals.”

Schiebel Camcopter S-100.

Schiebel, however, has indicated that information recovered to date indicates that after the loss of GPS signals to the aircraft’s receivers, there may have been incorrect handling and operator errors which resulted in an unfortunate chain of events that ultimately led to the crash.

Emergency procedures “to ensure a safe recovery in such a situation” do not appear to have been “correctly and adequately followed,” Schiebel alleges.

NovAtel may have found one way to help mitigate spoofing on UAVs — they just released a combined civil/SAASM GPS receiver, the OEM625S, aimed specifically at UAVs. Granted, the idea is to add SAASM anti-spoofing capability to a number of UAVs which currently use NovAtel commercial receivers — mostly in military systems. And of course that may well be motivated by the desire to avoid any further Iranian incidents!

BAE Systems has obviously been thinking of giving GPS a back-up for just those situations where jamming or even spoofing is detected. BAE’s system was just announced at the Farnborough Air Show in the UK and is still in the research phase, but looks extremely promising. Known as Navigation via Signals of Opportunity (NAVSOP), it interrogates the radio environment for the ID and signal strength of local digital TV and radio signals, plus air traffic control radars, with finer-grained adjustments coming from cellphone masts and Wi-Fi routers. Mapping the locations of all these sources might be quite an undertaking, and given that these are all non-safety-of-life commercial signals, the sources are subject to the vagaries of power outages, regular maintenance, and breakdowns. Nevertheless, with such a multitude of signals, NAVSOP could well turn out to be a viable back-up for GNSS.

Meanwhile, the Association for Unmanned Vehicle Systems International (AUVSI) big show is set to run August 6-9 in Las Vegas. With more than 500 exhibitors, attendance is expected to be more than 8,000 people from all over the world. All the key manufacturers, suppliers, and users of UAS are expected to be there, so it’s a great opportunity to meet people working with UAS and see some of the hardware and systems. Hopefully we will be able to get a feel for how the industry sees the onset of commercial market opportunities and the changes this may mean to systems and vehicles. It will be my first time walking round all these exhibits and seeing the live demos, so I’m very excited to be able to find out even a little about what makes this industry tick! More on this later…

So, shared access to civil airspace, wider applications in commercial operations, and changes in equipment qualification — along with potential solutions for GNSS jamming and spoofing — lots to consider for the UAS industry.

Tony Murfin
GNSS Aerospace