AGRICULTURE
Soft Landing
When landing a SA-400 Jackal—a compact helicopter that can operate as an Unmanned Aerial Vehicle (UAV) or optionally piloted vehicle—on a moving ship, there’s little room for error.
If this 1,200-pound helicopter misses the landing site, it could end up in the water, damage the ship with its blades, or even injure people on board. These landings must be precisely executed, which is why Steen Mogensen, the CEO of Fort Collins, Colorado–based Scion UAS, and his team rely on NovAtel’s OEM615 multi-constellation GNSS receivers for the precision positioning that make such operations less hazardous.
The ability to land on a moving ship makes this helicopter well suited for military applications and is part of the reason Scion UAS received a $3 million contract from the Naval Research Laboratory (NRL) to deliver multiple SA-400 Jackal turbine-powered Vertical Take Off and Landing (VTOL) aircraft. The NRL will use the systems to develop, demonstrate and test emerging sensor systems. The Colorado-based company has already delivered two Jackals to the NRL.
Mogensen and his team have tested the Jackal’s landing capabilities more than 100 times, using a computer to land the aircraft on a large trailer pulled behind an instrument-laden truck—the company’s simulator platform for a maritime vessel.
During an August 2014 test flight, the SA-400 Jackal landed smoothly on the 16 x 20-foot trailer being towed along a runway at speeds up to 10 knots. The Jackal successfully completed 10 landings and takeoffs during this test, including straight-line approaches and 45-degree approaches to simulate ship-based operations. The company completed the final test flight in October 2014, where the NRL took delivery of the first system.
Without the precision that the OEM615 receivers provide, these successful platform landings and takeoffs wouldn’t have been possible.
“Most people think of GPS as something you have in a car that tells you how to get to the store,” Mogensen said. “All you need to know is roughly where the store is, and the GPS tells you whether to go left or right at the next intersection.”
However, Mogensen added, “If you want the GPS to tell you how to park your car in one parking spot in front of the store, you need to make sure you’re not hitting the cars next to you or hitting the store. Now the precision needs to be down to a few inches. Imagine trying to do that with your eyes closed and listening to the GPS direct you left or right. That’s what our aircraft needs when it lands on a ship. The precision must be within a foot or so of hitting the landing deck we need to be on.”
The ship is always in motion during these landings, making communication between the ship and the aircraft vital, Mogensen said. Waves can send the ship rolling, pitching and/or yawing even as the vessel is moving forward. This constant and complex movement makes it difficult to land an aircraft, and requires the high precision that NovAtel receivers provide.
“We need to communicate the location of the landing site between the ground station and the aircraft,” Mogensen said. “The landing site moves on a ship; so, you need a second set of high-precision GPS receivers onboard. The ground control station on the ship sends that information via a data link to the aircraft, allowing the aircraft to find the ship and to safely land in the correct location.”
GNSS standalone positioning could be off by many feet, which could be disastrous during one of these landings. A differential GNSS system on board the vessel tells the nearly 20 foot long Scion UAV exactly where the ship is in real-time, even as the ship’s location changes second–by–second. NovAtel’s differential GNSS guides the Jackal’s movement based on the location of the shipboard reference station, linking the movement of the two dynamic platforms.
“We can lock the two together because we can correct for where the ship is in relation to where the helicopter is,” Mogensen said, describing the need for accurate relative positioning of the two craft. “We need to know exactly where they are in reference to each other. We don’t need to know exactly where in 3D space that is, but the helicopter needs to know where the deck is so it can decrease the distance to the landing spot a few inches at a time and land exactly where you want it to land. Using the differential GPS system that NovAtel provides gives us that very high accuracy and enables us to land exactly where we want to.”
In addition to the two standard OEM615 receivers that Scion UAS uses on the ship and the aircraft, they also incorporate an additional receiver to enable the ALIGN® Heading feature that tells them the heading of both the ship and the aircraft, Mogensen said.
Traditionally a magnetometer, an instrument that measures the strength and direction of the Earth’s magnetic field, has been used to obtain heading measurements. However, these devices simply aren’t reliable in an environment filled with metal or magnetic fields, such as a ship with steel construction and electric motors, which is why Scion UAS uses NovAtel’s heading solution instead.
With the NovAtel solution, the Jackal can perform high-precision landing on a moving target, Mogensen said. The unmanned helicopter typically lands within six inches to a foot of the optimal landing spot, which Mogensen said “is pretty good for a large vehicle like the Jackal coming down in a moving scenario.”
Beyond Precision
While precise positioning is vital to successfully landing an aircraft like the Jackal on a moving platform, so is stability, Mogensen said.
“Helicopters don’t want to fly. They want to fall out of the sky,” Mogensen said. “Keeping a helicopter stable is difficult. For that reason we use the autopilot, but it needs input on not only where the helicopter is in 3D space, but what the attitude of the helicopter is at any one moment. We need to know if it is twisting or turning. We can use input from the GNSS receivers to see exactly how the aircraft is moving in space, and we can use that to correct the helicopter’s attitude and keep it stable.”
The team also uses other sensors to measure acceleration of the aircraft in all directions, and that information combined with the GNSS data tells them exactly what the helicopter is doing so that they can make any necessary corrections.
Why NovAtel
Mogensen and a few of his Scion UAS colleagues had used NovAtel technology in the past; so, it just seemed natural to turn to the GNSS manufacturer for the precision GNSS capabilities they needed for the Jackal.
Mogensen worked with NovAtel at his previous company to build a much smaller helicopter, he said. Back then he didn’t have the need for the advanced features like he does now, such as the differential GNSS and the heading system. Because Mogensen and his colleagues had been so impressed with NovAtel’s products and services previously, they were confident that the company could deliver when he needed a more complicated solution.
“We’ve been happy not only with the quality of the product but also the support,” Mogensen said. “When you’re relying on a product that comes from another country, it’s a little bit of a gamble, but in this case the relationship with NovAtel has been very good. The support is there when we need it, and it’s accurate and to the point.”
Living in the Commercial World
While there’s certainly a place for the Jackal in military operations, the UAS also has the potential to provide benefits in a variety of commercial areas, from search and rescue to precision agriculture, Mogensen said.
The technology is there, but like the rest of the unmanned industry, Scion UAS has to wait for the Federal Aviation Administration (FAA) to approve rules and regulations for operating a UAS in national airspace. The FAA released proposed rules for small UASs earlier this year, but it will likely be a while before they are officially implemented. In any case, this first set of proposed rules doesn’t cover systems as large as the Jackal.
Even so, Scion UAS is focusing on developing commercial applications in order for the systems to be ready for such missions once the regulations are finally in place. One of the biggest areas Mogensen said the Jackal can help with is search and rescue. The helicopter not only has the ability to find missing persons but, with a seat installed inside the aircraft, it can also carry a person to safety. Once the Jackal lands at a rescue site, rescuers can speak through an onboard sound system and direct the person to climb onboard.
“All they have to do is sit still and tighten their seatbelts. The helicopter takes care of the rest,” Mogensen said. “There’s no other system on the market that can transport a person in the helicopter while flying completely autonomously. You can imagine the applications for something like that in public safety.”
Agriculture is another industry Mogensen sees embracing systems like the Jackal, making it possible to apply chemicals to crops without risking the pilot’s life. Many pilots are injured or even killed during spray applications, Mogensen said. Flying a fixed wing airplane or a helicopter close to the ground, trees and power lines can lead to accidents. If a UAS is performing the spraying, the worst thing that can happen is loss of the equipment.
Mining exploration, power line and pipeline inspections are other activities that Mogensen hopes will benefit from the Jackal in the future. With the help of NovAtel, the UAS is in a prime position to perform such commercial applications once the FAA allows it.
“There are a lot of applications in the civilian market, now we just need the permission and acceptance from the general public and the government to use these systems to perform these missions,” Mogensen said. “And everybody is basing their systems on GPS technology. NovAtel is one of the biggest precision navigation companies in the world and that’s who we’re choosing to work with.”