NASA tech aims to track tomorrow’s supersonic airliners

By Joe Stumpe|February 5, 2018

Upcoming tests of enhanced ADS-B Out radios could aid plane builders

NASA plans two flight tests this year of an enhanced ADS-B radio-and-GPS device that could help a new generation of supersonic commercial jets meet an FAA mandate that will soon be imposed on aircraft in most controlled airspace.

Starting in 2020, FAA is requiring aircraft to be equipped with Automatic Dependent Surveillance-Broadcast Out radios that broadcast a plane’s GPS position and identity. The broadcasts will be received by the air traffic control network and by any planes equipped with ADS-B In as part of a move away from reliance on ground-based radar. Current commercial ADS-B equipment would not be adequate to meet the FAA mandate if installed on supersonic aircraft.

The United States banned faster-than-sound commercial flight over land in 1973, one reason it hasn’t been tried anywhere since the Concorde was retired in 2003. But Congress has directed the FAA to study whether that restriction could be eased. Lockheed Martin and Aireon Corp. last year announced plans to build a 12-person business jet capable of flying at Mach 1.4 speed — 1,715 kph — or about 60 percent faster than current models, with operations expected to start in 2025.

“There’s a big push right now for supersonic operations, so I think there’s going to be a lot more” supersonic aircraft proposed, says Ricardo Arteaga, a NASA research engineer at Armstrong Flight Research Center in Edwards, California.

Currently, ADS-B boxes broadcast a plane’s GPS position, altitude, ground speed and identity at the rate of 1 hertz, or once per second. The rate is sufficient to meet the FAA’s allowable position uncertainty limit of 304 feet. But the magnitude of error balloons for planes at supersonic speeds — up to 679 meters at Mach 2, according to Arteaga.

Engineers at NASA Armstrong designed a prototype ADB-S radio that broadcasts at 10 hertz, or 10 times per second, with a maximum error of 68 meters at Mach 2 speed. The prototype also reduces the latency of current ADS-B boxes — that is, the time it takes to create the transmission. The prototype is a modification of an ADS version first developed for reusable space launch vehicles. Vigilant Aerospace Systems of Oklahoma City is providing software related to tracking of the F-18s by a ground station.

Arteaga said ADS-B equipment on supersonic planes also needs to transmit a more powerful signal — 250 watts instead of the current minimum of 125 watts — to help prevent collisions. That signal could be picked up at least 315 kilometers away.

The prototype supersonic ADS-B addresses these issues and more, including changes that would be needed on a supersonic plane’s display panel to accommodate incoming data.

Plans call for tests in May and August with two NASA F-18s. They will fly up to 1.4 Mach speed and 50,000 feet. The prototype passed a flight simulation test at Mach 2 speed, Arteaga said. The FAA will evaluate the results to see if the 10 hertz, 250-watt prototype should be adopted as standards for ADS-B technology on supersonic aircraft.

Enhanced ADS-B technology has a couple of other possible uses. One is the tracking of space vehicles as they re-enter airspace from low Earth orbit. Another is providing precise data for research into reducing shockwaves that are felt on the ground when a plane breaks the sound barrier — the reason the U.S. stopped supersonic flight in the first place.