Space Race

ATM speaks to ADS-B Technologies chief Skip Nelson about how the Federal Aviation Administration (FAA) could provide space-based ADS-B surveillance services

Former FAA Air Traffic Organization chief Russ Chew has described global space-based Automatic Dependent Surveillance – Broadcast (ADS-B) as a ‘real game changer’, heralding what could be a major breakthrough for next generation air traffic management.

In fact, it could not only revolutionise surveillance in oceanic airspace but also provide full coverage over polar routes and remote and mountainous regions in the US where installation and subsequent maintenance of a ground station network would prove far too costly.

Chew, now with NEXA Capital Partners, told Airspace magazine: “ATC over remote areas is going to be revolutionised, because the ability to provide radar-like surveillance in these areas has never existed before”.

The industry guessed that two contenders would likely step forward to assist the FAA in the exercise which often does no more than allow the agency to prepare a more focussed request for proposals at some point in the future.

McLean, Virginia-based Iridium last year announced that its IridiumNEXT satellite constellation would include receivers that can pick up ADS-B transmissions from equipped aircraft and relay that data to air traffic control centres. The first of these Thales Alenia-built satellites will be launched in 2015, with the full constellation scheduled to be in place by 2018. Iridium, however, would not be drawn on discussing whether it had responded to the FAA request.

Anchorage, Alaska business ADS-B Technologies meanwhile did confirm in late December that it had responded to the market survey which sought to identify vendors that could provide a space-based ADS-B service from 2018, even issuing a press release to that

Low Earth Orbit System

The proposed ADS-B Technologies system would use the Globalstar second generation Low Earth Orbit constellation together with the company’s proprietary ADS-B Link Augmentation System (ALAS) avionics interface to provide real-time aircraft position information to the FAA.

In addition to FAA tracking in areas where conventional surveillance methods are either impossible or impractical to employ, aircraft would also be equipped so they could see each other and receive real time weather and airspace information from authorised sources on the ground.

ADS-B Technologies president Skip Nelson set up the business in 2004 and engaged several former FAA engineers and subject matter experts as intellectual collaborators. He was fortunate in as much that many had worked on the Capstone Programme, a FAA funded safety programme located in Alaska which had developed systems such as GPS receivers, data link transceivers and ADS-B. Nelson himself was the first pilot to fly with a certified ADS-B system back in January 2001.

His speciality is designing and deploying ADS-B systems around the world. His first contract took him to Dar es Salaam for the World Bank in 2006 before heading to China where for the Civil Aviation Flight University of China (CAFUC) he developed a large network of eight ground stations whose coverage extended from the north of Beijing to the foothills of the Himalayas. Today, nearly 500 aircraft use that system.

“The USA had started to build a very comprehensive network of terrestrial ground stations after 2008 so we worked to develop a space-based ADS-B concept for the rest of the world, a way that we could see aircraft in deep mountain passes and oceanic segments far beyond the range of terrestrial antennas,” says Nelson.

The ADS-B Technologies solution has been in operation now for more than two years, working ‘remarkably’ well, according to Nelson. “This system has the capability of giving the position of the aircraft 50ft off the water in the middle of the Pacific Ocean in real time and, as far as we know, we are the only ones to have successfully flown a space-based ADS-B system.”

Bent Pipe

Globalstar, for its part, says its unique combination of the ALAS avionics interface and its own relatively straightforward and reliable bent pipe architecture will allow virtually any 1090 MHz Extended Squitter (ES) or 978 Megahertz Universal Access Transceiver ADS-B source to report an aircraft’s position to ATC in less than 400ms.

For Nelson, an important feature of the partnership with Globalstar is that all the necessary ADS-B components remain on the ground where repairs and upgrades are easily carried out. “After all, if you put the equipment up there you can’t make a service call 480 miles up in space and you are stuck with it for the next 15-20 years,” he says.

“We prefer the Globalstar constellation because those satellites operate very much like a mirror. The satellite does nothing to the signal. We do not put any of the brains in space, there are no ADS-B -specific components on the satellite. It simply receives the signal from the aircraft and whips it right around and sends it back to the ground.”

“Simplicity may be the key to establishing the kind of reliability that a safety-oriented business like air traffic control requires,” Nelson believes. “Globalstar’s large number of ground stations means fewer and shorter hops between the satellite and the ATC point of service and thus fewer potential points of failure.”

As far as his views on likely rival propositions go, Nelson believes Iridium can only be proposing that the FAA support the business in developing a system for the future. “Iridium’s plan is to start launching satellites in 2016 equipped with unique hardware on each of the 66 or more satellites. We maintain that our system is much more straightforward and reliable.”

He says Iridium is a different architecture, a different philosophy; one that uses more satellites and which because of its netted communications structure, is just not as well suited to ATC applications as the GlobalStar constellation is.

“Our concept is this: if Eurocontrol was to adopt this system for the North Sea, say, they would at least want the information landed somewhere in Europe. They wouldn’t want to take a feed from Arizona as Iridium offers.

“GlobalStar has a lot of stations and is willing to build more. It is already planning to launch six more satellites in late Spring and we are in talks with them about adding more satellites to meet the requirements of CAAs – most notably the FAA and Eurocontrol – around the world,” says Nelson. “This should also promote global harmonisation since it means that more nations will be able to land their own surveillance data inside their own borders with a standardised set of protocols.”

Four-Digit Figure

ADS-B Technologies’s ALAS device is roughly the size of two packs of cigarettes and comes in at a budget-friendly four digit figure, according to Nelson. What is more, it is a peripheral device that does not interfere with any existing avionics, and merely represents an alternative delivery mechanism.

With Globalstar acting as a data provider functioning very much like an internet service provider with participation metered, Nelson says the industry now needs to develop new financial models to adapt to a future new 24/7 transmission environment.

“This is, as Russ Chew points out, a game changer in all respects which includes the economic and business dimension. This is what we call a keydown technology; it transmits continuously and we have never had something that has been connected 100 per cent of the time before.”

In terms of how space-based ADS-B surveillance will develop, Nelson thinks that the US will evolve into a combination of the already very successful ITT network  and a space-based system, one that provides an extrapolation of the terrestrial system providing the potential for supporting the mainland network  in an emergency situation.

“As far as the rest of the world outside Europe, the USA and perhaps Australia, we see great potential for space-based ADS-B as the primary ATC systems,” says Nelson. “China would seriously like to find a way to manage air traffic in western China from Chengdu to Lhasa over the Himalayas. We’ve already done some consulting on that and calculated what a radio station would cost at 15,000 and 17,000ft and we know that one satellite

Coronal Mass Ejection

And, how reliable is the ASD-B safety case in terms of solar activity where particularly potent coronal mass ejections could knock out satellite communications? “Frankly, we are going to have problems and possibly of a scale similar to the Iceland volcano events of recent years. That’s the baseline safety factor and then there is the exposure of satellites to gamma radiation, a double impact that might not be seen in a terrestrial scenario. The brightest brains in the world are seriously divided on the impact of solar events,” says Nelson.

Still, Nelson insists that his solution offers one of the most secure ATC surveillance systems which effectively guarantees encryption due to the nature of the signal. “Essentially, the ASD-B signal is sent in a sealed box car where only an authorised user can open it.”

On December 28, six more second-generation Globalstar satellites were successfully launched from the Baikonur Cosmodrome in Kazakhstan, using the Soyuz launch vehicle representing Globalstar’s third multi-satellite launch in a little more than a year.

“This means that Globalstar is now three-quarters of the way toward its goal of launching 24 new high speed, high capacity satellites capable of supporting our NextGen space-based air traffic management system,” said Nelson. “It also means that we are on track for full scale operational testing by late 2014, should the FAA or any other civil aviation organisation require it. We would like to see the FAA support test or demonstration flights within the next year. My business would be able to do it within six months.”

ADS-B: What is it?

  • ADS-B is a technology that broadcasts an aircraft’s call sign, position, altitude, velocity and other data, twice a second.
  • ICAO has identified ADS-B as a main component in future ATM surveillance and is actively supporting ADS-B implementation. ICAO has revised key documents such as PANS–ATM Doc 4444 to reflect the change from radar surveillance to also use ADS-B for 5 NM en route separation.
  • ADS-B relies on aircraft broadcasting their identity, position and velocity, and this signal can be captured by receivers on the ground (ADS-B out) or on board other aircraft (ADS-B in). ADS-B is recognised as an essential element in SESAR and in the FAA’s NextGen programme.
  • The benefits of ADS-B over radar surveillance, according to Eurocontrol, are its low cost when compared to other surveillance alternatives (up to 1/10 of a radar system with system coverage), its high accuracy, and the support of airborne surveillance applications which will enable many future safety capabilities. Source: ATC Global Insight

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