Speakers at the 9th Annual Conference on European Space Policy wasted no time in addressing the somewhat worrying failure of several Galileo onboard clocks, as revealed by European Space Agency Director General Johan-Dietrich Woerner at a press briefing earlier in January in Paris. He made clear at the time that the clock failures, while indeed troubling, had had no effect on the operational integrity of the Galileo system.

Certain sources, however, seemed to want to jump on the clock story as another confirmation of a misguided and failed approach of the entire Galileo program, if not the entire European Union. Reactions from some quarters involved crying out, “There they go again, another gaffe for Galileo!”, and then watching as the relevant officials squirmed.

Yes, curious as it may seem, there are some people who enjoy watching officials squirm.

But there was no squirming at the conference in Brussels. Elzbieta Bienkowska, European Commissioner (EC) for single market, industry, entrepreneurship and SMEs, confirmed Woerner’s assessment of the operational status of all Galileo satellites, and not before reminding the assembly of the successes of 2016, including the first-ever four-at-a-time launch last autumn, and the successful declaration of Galileo initial services in December.

“A number of clocks have failed,” Bienkowska said. “Every large-scale project, in particular technology-intensive ones, face high risks. Galileo is no exception. Such things can happen, as we also learned from the experience of other navigation satellite systems. This is why we have four clocks onboard each satellite, to cope precisely with clock failures. To work properly, a satellite needs only one clock. All the satellites in orbit to deliver initial services are operational.

“We are monitoring the situation very closely,” she said. “As always, on technical issues, the Europe Space Agency is leading an in-depth technical investigation of the clock failures and is already implementing corrective actions together with the industry.”

So, the common message coming out of ESA and the EC is, in short, “smooth sailing.” The policy of installing more clocks than needed seems to have paid off. Despite the failed clocks, which number about six, all of the orbiting Galileo satellites still have at least two functioning clocks.

Bienkowska said she has recommended the setting up of a joint steering group chaired by the EC, along with industrial partners and ESA, to look into the clock failures and then make clear policy and industrial recommendations.

These clear policy recommendations are pertinent, because, as we know, Galileo is not just a technology program but a policy-driven program. It was Woerner who said during his press briefing in Paris that the decision to install the now-failing, but more importantly ‘made-in-Europe’ rubidium clocks onboard Galileo was a political decision, not a technical one, linked to the central EU policy goal of maintaining European autonomy in space.

Woerner also granted that while no orbiting satellite has been rendered inoperable due to a clock failure, impending launches could be delayed as the investigation plays itself out.

Later, Bienkowska proclaimed the important role of space, including Galileo, in European security and defense. She concluded by encouraging, among other things, “…faith in the added value of Europe…” and she called space, “…one of these – maybe the only one of these – concrete and positive examples of what we can do together in Europe.”

Godspeed, Antonio Tajani
The really bad news at the conference was the announcement that scheduled opening speaker and longtime Galileo advocate Antonio Tajani would not be appearing, due to responsibilities under his “new mandate.”

We remind readers that Tajani, the former vice-president of the European Commission, was recently voted into the Presidency of the European Parliament. Commentators expressed pleasure in knowing that our old friend is traveling in ever higher circles, and everyone in the European space community will now be expecting to feel his support from that new and even more influential position.

So, it was Tajani’s replacement speaker, European Member of Parliament Jerzy Buzek, who set the tone for the conference. He called in his opening address for a more concerted effort towards bringing space-based data and services to the people, for the benefit of society, but especially for the European economy.

Buzek mentioned increasing competition from a dynamic United States, and he spoke of the need to inspire the next generation of Europeans, a theme that has been repeated over and over for years.

The audience was then treated to a stimulating address by another highly placed personality, the High Representative of the Union for Foreign Affairs and Security Policy and Vice-President of the European Commission Frederica Mogherini, who said, about European space activities, “There is a clear link with our security and defense.”

Mogherini thanked Bienkowska, “…for the wonderful work we’ve done together with really a team spirit, that sometimes is new in our institutions…”

The EC’s new Global Strategy for Foreign and Security Policy, unveiled last summer, Mogherini said, is meant to encompass all the fields and all the tools of relevance to the EU’s external action, including space.

“We stress the need for cooperation,” she said, “and to develop some kind of common governance of space activities. We all understand that space is essential to our security and to our economy, so we have a strong and clear interest to promote the autonomy and security of our space-based services.”

This, by the way, is the same Frederica Mogherini who, just a few days later, would have very strong words for the incoming American administration in response to the announcement of new restrictions for people wanting to enter the United States.

“Human exploration of outer space began as a space race between the U.S. and the Soviet Union,” she said. “Today the Cold War is over, and I believe it is over forever. I not only believe it, but I hope it.”

Looking at the larger picture, she discussed preventing a new arms race and moving towards better global governance: “We often refer in the European Union to the fact that we invest in a rules-based global order. We don’t have so many actors that are investing in a truly rule-based global order, so we have a special responsibility as Europeans to play a role, to link up with the others that share our same agenda and to try and bring this agenda forward.”

She added, “We are engaging with our tools, our diplomacy, our political weight – because indeed we have some – and our capabilities. Europe’s strategy of autonomy includes Galileo.

“Strategic autonomy benefits not only our citizens and states, but also our partners, because the development of a full spectrum of security capabilities will make us a stronger partner for our friends around the world that are demanding more and more from the European Union to be a security provider around the world, including our American friends. So, we can set our partnerships globally on a more equal footing, sharing more equally the costs and the responsibilities of our common security.”

“Europe,” Mogherini concluded, “can and should be a space power, but it can only do so as a true union.”

This all developed against the backdrop of what some have called an existential crisis for the EU itself. And that existential crisis has a name…

Brexit
The breaks in between conference sessions featured much chatter about recent events. This being the new year and all, when people like to take a deep breath, look back and look forward. Brexit and the election of a new American president were on people’s tongues, with tones varying from amused to frustrated to nearly passionate. Everyone’s got a right to their opinion.

And the topic of Brexit also spilled onto the podium, with several speakers specifically alluding to “what’s happened,” not without the urging of at least one mischievous session moderator.

European Member of Parliament from Britain Clare Moody got the ball rolling, explaining to the conference why she thought Britain should have stayed in the EU: “We are united in diversity. It is by working together that we can achieve success in our endeavors in space. It is as a British MEP that I particularly recognize and cherish our ability to combine our efforts.”

Moody reminded participants of what she had said at the same conference a year ago. “I said then that space policy was one of the very many good reasons that the UK should have stayed – should stay – in the EU. My view on that hasn’t changed, although you may have noticed that the politics have gotten a little bit more tricky back in the UK.”

Moody continued on the theme of world politics: “Space is where we work with countries that we sometimes find more difficult to work with here on Earth.” She was also happy to note that ESA had endorsed the new EU Space Strategy and that the EC sees ESA as, “…a valuable, full and equal partner in developing space programs.”

This is an important point indeed for Great Britain, whose membership in ESA, if not in the EU, will ensure its continued presence in big-league European space projects such as Galileo.

During a question-and-answer session on space services integration, Jadwiga Emilewicz, Undersecretary of State for the Ministry of Economic Development of the still relatively young EU Member State Poland, was asked about the impact of Brexit on European space policy. “Thank you for the question which is not very directly connected with the topic of our discussion,” she responded, to the delight of some listeners, “although Brexit is interfering on almost every single discussion within the European Union.”

Brexit is important, Emilewicz said, but it will not interfere with the goals of Europe’s space policy. “I would say that if we want to achieve those ambitious goals, it could not be achieved without the active role of the United Kingdom.”

For his part, Woerner, during his press briefing in Paris a week earlier, had already addressed the question of Britain’s self-removal from the European Union. “ESA is an intergovernmental organization, so we are not part of the EU, so therefore there is no direct impact. The UK has clearly indicated that their membership in ESA is not in question. It’s more or less the opposite; they are increasing their contribution strongly.”

So, there is no immediate impact on Galileo, Woerner said. “We will see what happens in the future and how the UK and the EU really define the details, but for us the relationship with the United Kingdom is of very great importance, so we will do our very best to see that their Brexit does not have some negative influence on the space sector.”

The Wider and Oh-So-Bothersome World
While some speakers showed little fear of tackling head-on the touchy issues of the day, others preferred to work around them. Asked whether, in the wake of recent political events, the EU should not move towards breaking off completely from any sort of dependence on the United States, including in the space sector, Wales’ own Lowri Evans, Director-General of the Commission’s DG GROW, chose to dodge, slightly, expounding instead on the value and merits of European competitiveness, public funding and downstream operators.

“The return on investment that we get as public funders of space depends on how much we can actually galvanize the new start-ups or people that are not traditional space actors,” Evans said, “to really create new value added that is created in Europe, made in Europe.”

She did refer to competition with the United States in general, saying, “This is a services economy, a burgeoning services economy, and we are determined to do everything we can there. Because, to take up the American analogy, if we are not activists here, from a public regulatory and financial perspective, we will leave the space data world to people like Google. We’re not going to do that. We’re not going to leave it to the American multi-nationals.”

Woerner — at the earlier press briefing in Paris — had also addressed the change of American administrations, which, as usual, will involve a change in the NASA administration. “We are in contact with the transition team in order to ensure that ESA remains a strong partner of NASA in the future,” Woerner said.

There was nothing controversial here, even though one journalist wanted to know what would happen if the new American administration should decide to apply the same logic to its partnership with ESA as it has in its comments about unfair burden sharing within NATO.

Woerner provided a suitably respectful response, indicating essentially that ESA doesn’t work that way and its partnership with the United States is not under threat, so far.

Power to the People
The incoming American administration has been referred to on both sides of the Atlantic as “populist,” with all the varied connotations associated with that term. It was hard not to sense a tiny bit of “people power” creeping into the European Space Policy Conference, as exemplified by comments from various speakers.

If you recall, there was Buzek’s call for more “services for the people” and Evans’ emphasis on “Made in Europe.” Additionally, Pierre Delsaux, Deputy Director-General of the European Commission’s DG GROW, said, “We have several hundred people in this room, but we have millions and millions of real people outside, and we need those people to understand why space is important.”

Emilewicz believes everyday people in Poland need to know how important space is, but they also need to know that space is the EU and this is why they pay taxes. So, the people of Europe need to be considered and their support must be actively sought. Not that these aren’t the kinds of messages one always hears when European Space Policy is touted, but it did seem a little more palpable this time around.

MEP Cora van Nieuwenhuizen talked about the need for public awareness and support for space activities. “It’s not only necessary that all my colleagues in the European Parliament know that it’s really important, but you also need the support from your constituencies, so for that reason we need the general public to know a little bit more about what is happening.” She said people in the street in her constituency still don’t understand the full depth of penetration of space technologies in their daily lives.

Executive Vice-President, Head of CIS, Airbus Defence and Space Evert Dudok said, “If people don’t know why we invest in space, then what the heck… We have to do much more on applications that people can use.”

Bringing all the people together by bridging the digital divide was another people-centric priority highlighted by Jean-Loic Galle, President and CEO of Thales Alenia Space.

Back to Galileo
Participants were pulled back to the meat of the meeting by ESA Director of NAV Paul Verhoef, who hailed ever closer and ever more satisfactory cooperation between his Agency, the EC and the European GNSS Agency (GSA).

When discussing the launch of Galileo Initial Services, he sounded quite proud.

“It shows the world that we are progressing. Obviously, for many years there has been an undertone of ‘this system which is costing too much and it is too late’. So, I think that we have now put this behind us; the event in December was fantastic, also because it was mentioned around the world,” he said.

Verhoef said ESA’s United Space of Europe and Space 4.0 initiatives, and the EC’s new Space Strategy are all moving in the right direction, with the future focus on applications and integration of space services with terrestrial technologies. He cited the example of autonomous driving as one area where Europe can and should be moving forward very rapidly, working to integrate space-based navigation and Earth-observation services, a variety of ground-based technologies, the world of sensors, and all of the traditionally non-space user communities.

It is important, Verhoef said, for the space sector to put itself forward to provide better access to the space technologies that can make this integration happen. To this end, he stated, “We are trying to set up a common front office, if you will, between the application areas of navigation, communication and Earth observation, supported by our technical people at ESTEC (European Space Research and Technology Centre, Noordwijk, Netherlands), in order to offer a way into the ESA system for those who think that space can offer a contribution to their solution.

“So from our side,” he said, “we are trying to reposition ESA in this new world. We have a sector that is confident in its capabilities and open to the challenges that lie ahead.”

Finally, it was GSA Executive Director Carlo des Dorides who drew all the strands together, emphasizing the importance of public support, the rapid adoption of Galileo services and their integration into a multi-GNSS and multi-system environment, as well as the development and economic exploitation of useful applications.

For des Dorides, the current role of the GSA is to make the European Space Strategy concrete, in a future where Galileo and GNSS will be, “…one element of an overall multi-system, providing positioning and navigation, so the answer will not be GNSS only.”

The new emerging paradigm for navigation and positioning, he said, has ubiquity as a key element: “Navigation and positioning data must be available with seamless continuity wherever it is needed, so urban canyons, mountains, tunnels, in the parking area, in the garage.”

Positioning data must be robust and secure, he added, and there will be a new emphasis on “ambient intelligence.”

“This is the capacity to interact with the external world, and, more and more, between users,” des Dorides said.

That includes human users but also things, the internet of things, which, across the globe, already include more connected things than connected people.

In sum, the 9th Annual Conference on European Space Policy saw leaders and members of various space-linked communities taking stock, discussing challenges and sketching a future based on strong cooperation and united effort, with an eye toward, but not cowed by, the “interesting times” we live in.

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Thalwil, Switzerland-based u-blox has launched the ZOE-M8G, an ultra-compact GNSS receiver module, especially designed for markets where small size, minimal weight and high location precision are essential.

The device offers exceptionally high location accuracy by concurrently connecting to GPS, Galileo and either GLONASS or BeiDou. According to the company, it also provides industry-leading -167 dBm navigation sensitivity, which is said to make it ideal for wearable devices, unmanned aerial vehicles (UAVs) and asset tracker applications.

Thalwil, Switzerland-based u-blox has launched the ZOE-M8G, an ultra-compact GNSS receiver module, especially designed for markets where small size, minimal weight and high location precision are essential.

The device offers exceptionally high location accuracy by concurrently connecting to GPS, Galileo and either GLONASS or BeiDou. According to the company, it also provides industry-leading -167 dBm navigation sensitivity, which is said to make it ideal for wearable devices, unmanned aerial vehicles (UAVs) and asset tracker applications.

The new device helps simplify product designs because it is a fully integrated, complete GNSS solution with built-in SAW-filter and low-noise-amplifier (LNA). This means it can be used with passive antennas, without the need for additional components, and doesn’t compromise performance.

The module measures 4.5mm x 4.5mm x 1mm. Due to its very small size, a complete GNSS design using the module takes approximately 30 percent less printed circuit board (PCB) area compared to a conventional discrete chip design with a CSP chip GNSS receiver.

Uffe Pless, product marketing, positioning product center at u-blox, said: “When you’re designing products such as smart watches, fitness trackers, asset trackers, UBI dongles and even drones, every square millimeter and every gram counts. The u-blox ZOE-M8G makes it significantly easier for product designers to achieve precise location tracking while keeping within their strict form factor and weight restrictions.”

Samples of the u‑blox ZOE‑M8G will be available in February 2017 and volume production will start in October 2017.

Earlier the company said its M8 series of GNSS modules were used in the development of the drone technology for participation in the United Kingdom’s Direct Line Insurance Fleetlights Initiative. The modules provide accurate positioning to a formation of multiple drones that can travel up to 30 mph — while maintaining a distance of approximately two meters between the aircraft, the company said.

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Horten, Norway–based Sensonor AS is in serial deliveries supporting the STIM210, which is designed to provide high accuracy inertial data for the AXD-LNS Land Navigator Solution. The Land Navigator went into regular production in late 2016, following five years of development.

Horten, Norway–based Sensonor AS is in serial deliveries supporting the STIM210, which is designed to provide high accuracy inertial data for the AXD-LNS Land Navigator Solution. The Land Navigator went into regular production in late 2016, following five years of development.

The GMA AXD-LNS is a high performance navigation system intended for a wide range of applications, such as advanced navigation displays and advanced navigation control systems in armored vehicle programs. Because of its high-stability MEMS sensor-based architecture, the AXD-LNS equipment is easily configured for platform stabilization applications. In a GPS-denied environment, the system exploits the velocity aiding with help of the high accuracy inertial data to provide a continuous navigation solution.

The AXD-LNS product specifically addresses the stabilization and guidance needs of the defense market, and all of its components comply with the demanding standards of safety and reliability used in this field.

STIM210 is a small, lightweight and low power, ITAR free high performance tactical grade gyro module with three gyros. According to the company, the STIM210 is closing the performance gap to FOG (fiber optic gyro) and is a powerful alternative to current solutions in the market. STIM210 is currently deployed in applications like unmanned aerial vehicles, satellites, portable target acquisition systems, land navigation systems, turret stabilization, missile stability and navigation, and mortar aiming systems. STIM210 has been in regular production since 2010 and is part of the STIM gyro and IMU family that has fielded more than 50,000 gyros worldwide.

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TRAK Microwave, a brand of London, England– and Stuart, Florida–based Smiths Interconnect, has released its 8835 GPS Clock, a GPS time and frequency instrument. The 8835 GPS Clock is designed to deliver optimal power and interoperability options while maintaining GPS accuracy and reliability.

TRAK Microwave, a brand of London, England– and Stuart, Florida–based Smiths Interconnect, has released its 8835 GPS Clock, a GPS time and frequency instrument. The 8835 GPS Clock is designed to deliver optimal power and interoperability options while maintaining GPS accuracy and reliability.

According to the company, while tracking GPS signals, this clock exhibits a frequency accuracy of better than 1×10^-12 and a 1 PPS accuracy of better than 50 nanoseconds, RMS. The proprietary oscillator steering discipline algorithm can enhance the RMS accuracy of either the double oven crystal oscillator, or optional enhanced rubidium oscillator for greater depths of accuracy.

 In order to increase interoperability, the 8835’s 10/100 base-T Ethernet interface can leverage a range of network protocols including network time protocol (NTP), simple network management protocol (SNMP), Telnet, secure shell (SSH), and FTP for status and control. The unit can also accept a variety of power sources including 24 VDC, 48 VDC, or 100–240 VAC with an external AC/DC converter.

Targeting defense, satcom, and wireless applications, this highly compact and configurable device operates from -30oC to +60oC with a terminal node controller (TNC) GPS receiver port.

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The U.S. Air Force Space and Missile Systems Center (SMC) says it continues to work on GPS III ceramic capacitor testing and plans to have an updated launch schedule published late next month.

As Inside GNSS reported, the first GPS III satellite’s delivery, originally scheduled for August, was delayed by four months because of a Lockheed Martin subcontractor’s failure to test a ceramic capacitor.

The U.S. Air Force Space and Missile Systems Center (SMC) says it continues to work on GPS III ceramic capacitor testing and plans to have an updated launch schedule published late next month.

As Inside GNSS reported, the first GPS III satellite’s delivery, originally scheduled for August, was delayed by four months because of a Lockheed Martin subcontractor’s failure to test a ceramic capacitor.

"GPS III-01 remains on track for a spring 2018 launch. The GPS III program office continues to resolve final issues and plans to close on an available-to-launch date around 31 January 2017," said Lt. Gen. Samuel Greaves, SMC commander and Air Force program executive officer for space.

During Lockheed Martin’s navigation payload testing, they discovered a ceramic capacitor that had not been properly qualified per the program’s approved parts control plan, the company said. "Upon discovering the issue, we took immediate corrective action with the payload provider to qualify the capacitor. The capacitor qualification test forecast completion is [in] December," said Chip Eschenfelder, a Lockheed Martin spokesman, in response to an Inside GNSS query in September.

Harris Corporation, which provides the ceramic capacitor part, said it is working with Lockheed Martin and the Air Force to remedy the situation. Ellen Mitchell, a spokeswoman for Harris, said that the capacitor was among more than 28,000 parts used in the payload. "It is part of a legacy Exelis program that Harris acquired last year," she told Inside GNSS.

Colonel Steve Whitney, U.S. Air Force GPS program manager, told Bloomberg that the ceramic capacitor testing should have been completed five years ago.

GPS III is the next generation of GPS satellites, which will introduce new capabilities to meet the higher demands of both military and civilian users, the Air Force said. The satellite is expected to provide improved anti-jamming capabilities as well as improved accuracy for precision navigation and timing.

GPS III will incorporate the common L1C signal, which is compatible with the European Space Agency’s Galileo global navigation satellite system and complements current services with the addition of new civil and military signals.

In April, the Air Force awarded an $82.7-million contract to Space Technologies Corporation (SpaceX) for GPS III Launch Services. The Air Force characterized the launch contract as "the first competitively sourced National Security Space (NSS) launch services contract in more than a decade."

As Inside GNSS reported, President Obama signed the National Defense Authorization Act (NDAA) for Fiscal Year 2017, a $619-billion bill with a number of provisions affecting satellite navigation. The NDAA authorizes all of the spending the White House requested for the various elements in the GPS program, including $141.89 million for GPS III satellite development and $34.06 million for GPS III procurement.

The actual funding for FY17 in the form of an appropriations bill has yet to be approved, however — although that is not a bad thing for the GPS program. Congress passed a continuing resolution, signed into law December 10, which allocates money at FY16 levels through April 28, 2017.

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The U.S. Air Force has approved Lockheed Martin’s current GPS satellite ground control system upgrade to enable it to operate with more powerful and accurate GPS III satellites, the company said.

The Air Force’s Critical Design Review (CDR) for the Contingency Operations (COps) contract, completed on November 17, allows Lockheed Martin to proceed with the modification of the existing Architecture Evolution Plan (AEP) Operational Control Segment. The AEP, maintained by Lockheed Martin, controls the 31 GPS IIR, IIR-M and IIF satellites in orbit.

The U.S. Air Force has approved Lockheed Martin’s current GPS satellite ground control system upgrade to enable it to operate with more powerful and accurate GPS III satellites, the company said.

The Air Force’s Critical Design Review (CDR) for the Contingency Operations (COps) contract, completed on November 17, allows Lockheed Martin to proceed with the modification of the existing Architecture Evolution Plan (AEP) Operational Control Segment. The AEP, maintained by Lockheed Martin, controls the 31 GPS IIR, IIR-M and IIF satellites in orbit.

Lockheed Martin said that the COps modifications allow the AEP to support the new GPS Block III satellites by enabling them to perform their positioning, navigation and timing mission, once they are launched. COps is envisioned as a temporary gap filler prior to the GPS constellation’s transition to the next generation Operational Control System (OCX) Block 1, the company said.

"The GPS constellation is a valuable asset to our warfighters, our nation and the world. This risk-reduction effort ensures the Air Force has the ability to maintain the constellation at full strength," said Mark Stewart, vice president of Lockheed Martin’s Navigation Systems mission area. "We are here to support the Air Force and the GPS III program any way we can."

In February, the Air Force awarded Lockheed Martin the $96 million COps services and supplies contract. The government approved the company’s proposed ground system modification during a Preliminary Design Review on May 11, the company said.

As Inside GNSS reported, under a separate contract in October, Lockheed Martin completed the Commercial Off-the-Shelf (COTS) Upgrade no. 2 (CUP2) project, which is part of a multi-year plan to refresh the AEP’s technology and enhance the system’s ability to protect data and infrastructure, the company said. Lockheed Martin said CUP2 is now fully operational and managing the current GPS constellation.

In September, Lockheed Martin received a $395 million U.S. Air Force Space and Missile Systems Center contract option to build two additional GPS III satellites. The contract option calls for long-lead and production hardware to manufacture GPS III space vehicles (SVs) 9 and 10.

The government plans to compete future purchases of GPS III satellites beginning with the GPS III SV 11. This future competition will maintain the current technical GPS III baseline, and will add additional hosted payloads to increase system accuracy, search and rescue capability, and universal S-Band compatibility, the Air Force said.

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Unmanned aerial vehicles (UAV) are finding increased application in both domestic and governmental applications. Small UAVs (maximum take off weight less than 20 kilograms) comprise the category of the smallest and lightest platforms that also fly at lower altitudes (under less than 150 meters).

Designs for this class of device have focused on creating UAVs that can operate in urban canyons or even inside buildings, fly along hallways, and carry listening and recording devices, transmitters, or miniature TV cameras.

Unmanned aerial vehicles (UAV) are finding increased application in both domestic and governmental applications. Small UAVs (maximum take off weight less than 20 kilograms) comprise the category of the smallest and lightest platforms that also fly at lower altitudes (under less than 150 meters).

Designs for this class of device have focused on creating UAVs that can operate in urban canyons or even inside buildings, fly along hallways, and carry listening and recording devices, transmitters, or miniature TV cameras.

Operational requirements for these kinds of UAVs typically encompass flying close to the ground and in relatively narrow spaces with a lot of obstacles. This introduces problems for a simplistic application of technologies used in larger UAVs. In particular, the rotary wing UAV platforms used in those scenarios provide vertical takeoff and landing and hovering capability, but they are intrinsically unstable systems requiring high-rate and accurate attitude and position data to be automatically controlled.

Automatic control of the degrees of freedom of such flying robots is the key factor to make them easily usable by a trained but not particularly skilled pilot; therefore, it is essential for such devices if intended for a wide commercial market.

Small, lightweight, power-efficient, and low-cost microelectromechanical system (MEMS) inertial sensors and microcontrollers available in the market today help reduce the instability of such platforms making them easier to fly. Current MEMS inertial measurement units (IMUs) come in many shapes, sizes, and costs — depending on the application and performance required — and are widely used as sensors for relative position estimation.

Although MEMS inertial sensors offer affordable, appropriately scaled units, they are not currently capable of meeting UAV requirements for accurate and precise navigation due to their inherent measurement noise. However, the accuracy of a MEMS-based inertial navigation system (INS) can be improved by integrating them with a GNSS receiver, simultaneously developing appropriate integration mechanisms.

This article describes an integrated multi-GNSS/INS system — developed and tested in both a car and on board a small quadrotor — that has been designed to achieve sufficiently accurate position and attitude control using lightweight and ultra low-cost components so as to be suitable for the technological and commercial aspects of the vehicle.

The architecture combines the advantages of absolute satellite-based positioning with the high dynamic performance and data rates of inertial sensors. The article will describe the system architecture, its carrier phase–based methodology for positioning and attitude determination, and an evaluation of the system’s performance of achieved results during real-time tests.

System Architecture Definition
Figure 1 shows a simplified block diagram of the developed on-board unit. The sensor package is composed of four non-professional, non-dedicated commercial-off-the-shelf (COTS) GNSS chipsets connected to one patch antenna each and attached to the tips of an ad hoc cross-shaped structure fixed to the quadrotor body. A motion-grade COTS MEMS IMU placed near the center of mass of the UAV measures angular rates and accelerations.

The main goal of the final system is to achieve a compact and cost-effective real-time position and attitude estimator, which is the reason why the components employed are relatively inexpensive compared to readily available platforms with costlier and bulkier elements. Therefore, an important investment of effort has been made in the system integration and in the development of specific techniques and algorithms to achieve high performance () with the combination of devices of individually moderate accuracy.

These low-cost receivers provide information to the “Processing Unit” (PU) block shown in Figure 1 in the form of so-called raw measurements, that is, basic GNSS signal-in-space data such as pseudoranges or carrier phase readings, in addition to standard position, velocity, and time (PVT) outputs. These outputs, along with the readings produced by the IMU (and possibly other sensors) are processed in the PU by a real-time microprocessor-based platform, which gathers and synchronizes these data and applies the fusion algorithms to compute the PVT and attitude (PVTA) of the platform. This PVTA estimator works on top of the standard vehicle control unit of the UAV.

The system is designed to provide high-accuracy attitude performance based on precise GNSS carrier phase measurements, reducing the position errors by combining measurements from several receivers. Furthermore, the aid of the IMU allows the high data output rate necessary for active attitude control and increases the reliability of the GNSS based attitude solution when its information is used in the ambiguity resolution process.

In the following sections we present an overview of the main functionalities developed within the processing unit, discussing their design principles and the criticisms associated with their practical implementation.

The PVTA Processing Unit
Figure 2 illustrates the architecture of the proposed navigation system (PVTA estimator) and the custom board hosting it, developed by Acorde Technologies, S.A., which is based on an ARM9 microcontroller.

This works at a clock frequency of 400 megahertz, includes two separate data and instruction cache memories of 32 kilobytes each, and two high performance sets of ROM and RAM memories of 64 and 32 kilobytes, respectively. Additionally, the board includes a SDRAM controller to interface external memory, addressable linearly up to 64 megabytes, and allowing back switching with eight-chip selects. Moreover, QNX has been selected as the real-time operating system that offers specific support for this platform and can be easily run on the board without needing to adapt it to the particular hardware setup.

Sensor Synchronization
Low-cost GNSS receivers, IMUs, and other sensors generate data in principle asynchronously with respect to each other. GNSS receivers are expected to be intrinsically synchronized among each other using the internal 1PPS signal (a one-hertz pulse). The GNSS time reference can be considered absolute for sensor synchronization purposes. In our case, this one-hertz reference is also the rate at which the GNSS modules generate observables.

The selected IMU uses its own clock (nominally 100 hertz), providing sensor data samples not aligned with the GNSS time reference or even synchronized, as this internal clock is very low precision. The IMU also generates interrupt requests (IRQ) to notify the PU whenever new inertial measurements are sampled.

Figure 3 depicts the adopted synchronization scheme, which is based on two conceptual modules (the host and the synchronization hardware [SHW]), both residing in the PU. The general time reference is given by the 1PPS signal from the base GNSS receiver, which is followed by all four GNSS modules sending their respective observables to the “host” with a small latency on the order of a few milliseconds. The GNSS data is also used to obtain the integer number of GPS seconds to which the last one-hertz pulse and subsequent carrier/pseudorange measurements belong.

The SHW includes a timer module or counter N_CNT. This timer is aligned with every 1PPS cycle and runs at one megahertz (f_CNT). Consequently the output of this timer is modulo-f_CNT. Between pulses this counter runs using its own reference, but the periodic alignment removes any possible drift as long as GNSS updates are present.

The IMU generates an IRQ with each new set of data, triggering the SHW to immediately store the value of N_CNT, thus allowing a time accuracy on the order of 1/f_CNT. The SHW then reads the data from the IMU and forwards this information to the PU with N_CNT, which serves as the timestamp of the measurements. The combination of the GNSS seconds and the GNSS-synchronized one-megahertz counter allows the tagging of inertial measurements with absolute time values within plus/minus one microsecond.

The misalignment between IMU IRQs and GNSS observables is solved via extrapolation: the microcontroller keeps a 100-hertz timer synchronized with GNSS time to generate an estimation of the inertial inputs using the most up-to-date measurements from the IMU (which runs at nearly 100 hertz). This way there are always exactly 100 inertial samples for every one-hertz pulse.

In practice, both the SHW module and synchronization host are elements of the same microcontroller unit. Several integrated hardware modules within this controller, with their corresponding drivers, take care of the timing tasks to provide an abstraction layer so that the fusion application only sees perfectly aligned 100-hertz and 1-hertz data.

Attitude Estimation by Using GNSS Carrier-Phase Measurements
The problem of accurately estimating the vehicle attitude using low-cost and lightweight sensors is resolved assuming an interferometric approach applied to the four GNSS antennas precisely mounted on the cross-shaped support. Carrier phase measurements are used to produce highly precise relative readings from the GNSS receivers. Indeed, the carrier phase is the most precise positioning resource obtainable from a GNSS signal.

The attitude of the vehicle is determined using the relative positions of the antennas; if the relative position between two antennas is known, yaw angle can be solved. With the relative position of three antennas forming a plane, the 3D attitude can also be determined. In this case, a fourth antenna is used to increase the accuracy of the solution.

Although GNSS receivers can measure the fractional carrier phase with millimetric precision, the number of wavelengths from the receiver to the satellite is unknown, a factor commonly known as integer ambiguity. To resolve the relative position between each pair of antennas, this ambiguity must be fixed.

Once all the phase ambiguities are resolved correctly, accurate relative positioning at the centimeter-level will be readily achievable using at least four satellites.

A common way to solve these ambiguities is the differencing technique, with a single phase difference between receivers expressed as:

ΔΦⁱ_αβ = Δρⁱ_α + Δdρⁱ_α – c · dT_α + λΔΝⁱ_αβ – Δd_ion + Δd_trop + Δε(Φ)    (1)

Assuming an interferometric model as depicted in Figure 4, the single phase difference between receivers α and β (e.g., α = 1 and β = 2) tracking satellite i can be formed in order to eliminate the orbital errors and, in the case of short baselines (0.5 meter baseline here), the spatially correlated ionospheric and troposheric errors as well. The ambiguity term is also differenced (λΔΝⁱ_αβ). In the case of low-cost receivers without a common clock, the receiver clock error needs to be eliminated by double differencing two single differences related to two different satellites.

The remaining error term — containing effects such as multipath or receiver errors — is doubled in the worst of cases as a consequence of double differencing. Multipath errors depend on the reflecting environment and cannot be avoided, although in high-end antennas the use of ground planes. On the other hand, the undifferenced carrier phase receiver noise is usually less than one millimeter, so that the combined receiver error on double differences is usually less than two millimeters in modern GNSS receivers.

Undifferenced phase measurements must be extrapolated to the time of the reference receiver before forming the differences. However, carrier phase measurement is also affected by Doppler shifts, produced by the relative motion of the satellites and the GNSS antennas. Thus, the phase extrapolation scheme employs the Doppler shift information and clock offsets to compensate for errors caused by the Doppler effect (which still remains after double differences as the shift varies from one instant of time to another). Extrapolation solves the lack of a clock steering mechanism in low-cost receivers.

Once the ambiguities are solved, using the approach discussed in the next section, carrier phase double differences are formed to feed a tightly coupled GPS/INS architecture as part of the measurement update.

Ambiguity Resolution Algorithm
As illustrated by Figure 5, the ambiguity resolution algorithm processes data provided by two different sources: the GNSS receivers and the last attitude information provided by the “Kalman Filter” block. From the GNSS receivers, the algorithm uses the following information:

• coordinates of the antenna of the main receiver (latitude, longitude, height) at one hertz
• ephemeris of satellites in view (obtained from the main receiver) when available
• phase, Doppler, GPS time, and clock offsets from the four receivers at one hertz.

Furthermore, it exploits the fact that, considering Figure 4, λΔΝⁱ_αβ can never exceed the number of wavelengths that fit in one baseline. Also, once the algorithm has fixed a solution, it uses the last time-updated attitude information (roll, pitch, and yaw, and their related variances) to define the search space of the ambiguities.

The ambiguity resolution algorithm is divided into several functional parts and two different strategies are envisaged, depending on the operational scenario, to provide a batch solution (when no a priori information of the attitude is known) or an on-the-fly solution (when the Kalman filter outputs are available).

Ephemeris and latitude, longitude, and height (LLH) global coordinates from the reference receiver are used to form the unitary line-of-sight vectors from the reference antenna to the GPS satellites. Previously, this information has been used to exclude low-elevation satellites from the position calculation. Doppler shifts, carrier phases, and clock offsets are used to extrapolate carrier phases to the time of the reference receiver before forming double differences.

The Kalman filter provides the “measurement update” of the roll, pitch, and yaw angles and their estimated residuals. Then the ambiguity search space is defined by using the concept of guessed baselines that will be explained in the following sections.

From the synchronized ambiguous carrier-phase double differences and the search space definition, the baseline computation of all the candidate ambiguity solutions can start. This consists of testing individual (each baseline separately) and combined (combination of three individual baseline candidates, b₁–b₂–b₃ solutions. When only one solution remains after the tests have been accomplished, ambiguities are considered to have been solved on the fly and can be provided at the PVT update rate. When the correct solution cannot be distinguished from the others, the solved carrier phase cannot be provided, thus the batch algorithm must be invoked.

The batch algorithm is based on a test over the accumulated carrier phase residuals instead of the instantaneous ones. Consequently, several epochs are required to reach the solution for the integer ambiguities.

Ambiguity Search Space Definition
The search space definition is made following the concept of “guessed baseline” as described in the article by L. Baroni and H. Koiti listed in the Additional Resources section near the end of this article. The basic idea is to search for integer combinations derived from guessed baselines instead of searching for all the integer combinations. This way, baseline-configuration geometry information can be used as a constraint to reduce the ambiguity search space to a set of ambiguity combinations that produce coherent antenna positions.

If the baseline length is fixed and known, as in the present case, only a maximum number of integer cycles can fit between antennas. This number is reached when the baseline is rotated parallel to the satellite’s line of sight vector. The maximum number of integers is calculated as the baseline length divided by the carrier wavelength, rounded downwards, thus:

Equation (2) (see inset photo, above right)

The baseline can be rotated 180 degrees with the integer being negative, or can be at right angles with the satellite’s line of sight in such a way that the integer could be zero. In this way, the number of ambiguity candidates comes down to 2N_max+1. Not all combinations of integers are possible when combining several satellites, but if a brute force algorithm was used, the number of possible integers would be (2N_max+1)^p with p being the number of ambiguities.

Attitude information from the inertial sensors combined with its predicted accuracy can be used to reduce the three-dimensional search space containing the remote antennas. Figure 6 shows an example of this.

The guessed baselines are generated in such a way that they cover the whole attitude range, while they are equally spaced. The angular step θ between two baselines is the angle that gives, at most, a whole wavelength of phase difference from one baseline to the other for any given satellite direction. To compute the individual baselines a least squares approach has been chosen due to its reliability and the reduced number of ambiguity candidates expected. Equation (3) represents the least squares problem:

Hb = ∇ΔΦ – λ∇ΔN – ε(Δφ)   (3)

where H consists of double-differenced LOS vectors, b is the baseline, ∇ΔΦ represents the carrier phase double differences, and ε(Δφ) is the residual double difference (DD) noise.

To obtain the coordinates of the individual baseline, the over-determined equation system must be solved in the following way:

b = (H^TH)^-1H^T(∇Δφ – λ∇ΔN)   (4)

At this point a sequence of tests must be undertaken to reduce the number of candidates to one for each baseline. First, a test of residuals is executed. The phase residuals are defined as the difference between the carrier phase difference measured by two antennas/receivers forming a baseline and the computed phase difference derived from the baseline vector estimation and satellite line-of-sight vectors. In formulas, the phase residuals can be defined as:

V = —HB + ∇ΔΦ + λ∇ΔN   (5)

where V is the vector containing the phase residuals, H consists of double-differenced line-of-sight vectors, b is the baseline, and ∇ΔΦ represents the carrier phase double differences.

Errors in double-difference carrier phase observations from a multi-antenna system mainly arise from multipath effects and the receiver noise. Under favorable conditions when multipath is low, the double-differenced carrier phase residuals generally exhibit a Chi-square distribution (sum of squares of independent random observations having a standard Gaussian distribution). Based on this observation, the quantification of the agreement between measured and computed observations can be made using the quadratic form of residuals:

V^TC^-1_obsV ≤ x²_ƒ,1-α   (6)

Where x²_ƒ,1-α is the Chi-square percentile corresponding to the degrees of freedom f (equal to the number of satellites minus four) and the confidence level 1 – α. C_obs is the covariance matrix of the observations. When the ambiguity candidate fails a test, the tested solution is discarded and removed from the list of candidates.

At this point the baseline geometry test is invoked. A parameter K, selected by the designer, represents the array size of the surviving candidates (i.e., the ones that provide the best results after the geometry test is executed) with respect to the whole search space.

In real conditions, K best solutions for each baseline should be considered to avoid discarding the correct solutions, i.e., retaining only the K solutions of each list of baseline candidates {b₁^(K),b₂^(K),b₃^(K)} with smaller baseline length errors obtained in the test of residuals. Then, these K best solutions are combined by means of the baseline geometry test which generates a list of baseline combinations rank-ordered by an associated error, which is obtained as a function of baseline length and known distances between baselines.

The geometry test takes advantage of the knowledge of not only the baseline lengths but also the relative position and orientation of the baselines. As mentioned earlier, the baseline geometry test exploits the fact that the baselines are not actually independent of each other, as their body coordinates are considered fixed and accurately known. The list of baseline-combination candidates is shortened depending on the obtained error value, which keeps the lower-error candidates on top of the list. Finally, the first- and second-best candidates are used to compute an error ratio in order to ensure that the selected solution can be trusted:

Equation (7) (see inset photo, above right, for equations)

Once the baselines are computed, attitude can be solved for by minimizing the function

Equation (8)

where I_i is the actual i baseline coordinates in the body frame and b_i represents the corresponding vector coordinates in the local frame. The a_i terms are weight factors, and c is the unknown rotation matrix, which transforms vector coordinates from the local to the body frame. The c matrix that minimizes L(C) can be found using Davenport’s q-method.

Batch Solution
The batch solution is based on the accumulated phase residuals test, which calls for storing the phase residuals that belong to the more likely solutions from several epochs. This test is accomplished after a configurable amount of seconds of processing and storing of data. This accumulation phase is required to observe GNSS signals within a different geometric environment in an attempt to reduce the influence of multipath.

In the following example, the angular search space has been defined as a ±30-degree search for roll and pitch (whose initial values are provided by the MEMS INS) and a full (0–360-degree) search for the yaw angle. In these conditions, the latter angle is completely unknown for a low-cost IMU. The angular steps chosen are 10, 10, and 7 degrees for baselines 1, 2, and 3, respectively. The number of possible baseline solutions is reduced after residuals and baseline length tests, as detailed in Table 1.

After completion of the geometry test, the candidate that shows the lowest error is selected as the “correct” solution and the algorithm can switch into “On-the- Fly” mode.

On-the-Fly Solution & Attitude Results
The algorithm for on-the-fly (OTF) ambiguity resolution is intended for use under dynamic conditions and is initiated with fixed ambiguities obtained from the “batch algorithm.” Its goal is to determine the correct set of ambiguities in the shortest period of time and with a minimum of computations, using single-epoch phase measurements.

Figure 7 shows an example of the effect of solved ambiguities for a static data collection for each baseline. In particular, it shows roll, pitch, and yaw angles computed from solved baseline vectors during a static data collection and by means of the batch solution, accumulating residuals during 10 epochs and using six satellites for the computation (so that five ambiguities are obtained: N1, N2, N3, N4, N5). The computed solution is compared with the one obtained from a GNSS reference receiver.

From Figure 7 we can appreciate how our solution in the attitude estimation is quite good, in particular for the heading angle, and differs by only a few degrees for the pitch and roll angles with respect to the reference solution.

On the other hand, Figure 7 shows the roll, pitch, and yaw angles computed from solved baseline vectors, during a static data collection and by means of the OTF solution, using again six satellites and one epoch. As expected, we can see that the OTF solution generates a more noisy solution compared with the results obtained with the batch solution. The attitude data computed through the multi-GNSS antenna platform are then integrated with the INS according to a tightly coupled technique. Details will be explained in the next section.

Navigation Solution Determination
Figure 8 reports the complete block diagram of the proposed navigation system, hosted in the PU. Even if only three GPS receivers are in principle sufficient to have attitude estimation, our choice to use four GNSS devices is made to provide additional redundancy and robustness against partial GPS outage or physical failure of one of the receivers. Double difference measurements, ephemeris, and estimated attitude are fed into the Tightly-Coupled Algorithm at a rate equal to 1 Hz.

The selected low-cost IMU provides three accelerometers and three gyro measurements at a nominal rate of 100 Hz. They are low-pass filtered to mitigate the mechanical vibrations of the UAV, then are used to compute the INS navigation solution according to strapdown mechanization equations described in the article by D. H. Titterton and J. L. Weston cited in Additional Resources.

An efficient real-time implementation of the strapdown inertial navigation algorithm requires the splitting of the computing processes into low- and high-speed segments. The low-speed calculations are designed to take into account low-frequency, large-amplitude body motions arising from vehicle maneuvers. These are used to determine attitude, velocity, and position, whilst the high-speed section involves a relatively simple algorithm designed to keep track of the high-frequency, low-amplitude motions of the vehicle (i.e., coning and sculling computations). See the articles by P. G. Savage in Additional Resources for more details. We have chosen a computation rate for the high-speed segment equal to 100 hertz while the low-speed portion has a rate that can range from 10 to 20 hertz.

The INS solution is blended with the GPS information in an extended Kalman filter (EKF) according to a tightly-coupled method. This filter estimates the navigation solution and the INS errors by using the following parameters as input:

• ranges, attitude, and Doppler outputs computed by the INS device
• Doppler frequency estimated by the GPS base receiver
• satellites’ position and velocity
• double-difference carrier-phase measurements
• estimated attitude from the four GNSS receivers.

The EKF incorporates a 17-state error model that includes position error, velocity error, and attitude error, accelerometer bias, gyroscope bias, clock bias, and clock drift errors, represented as follows:

Equation (9)

Equation (10)

Equation (11)

where:

• H[n] is the Jacobian matrix of the non-linear relationship between the user position and clock and the N_sat pseudoranges ρ₁, …, ρ_Nsat. A detailed explanation of H[n] can be found in the Ph.D. thesis by M. Petovello (Additional Resources).
• H_yaw[n] is the measurement design matrix for external heading measurements and can thus be written as given in G. Falco et alia 2013;.
• H_DD[n] is the design matrix related to the DD carrier-phase measurement for each baseline, which depends on H[n] and the lever-arm effect. (For a complete formulation, see the article by Y. Yang et alia in Additional Resources).

Observing the expression of H[n], it appears that the DD phase measurements are used to improve the attitude resolution only, not the position accuracy. This is by no means a conceptual limitation, and DD measurements could be similarly added as observations to the current tightly coupled position solution algorithm.

Nevertheless, the main innovation of the new tight-coupling algorithm implemented in our navigation solution is in the use of the DD measurements that are given as input to improve the estimation of the attitude.

Field Tests Results
Our algorithm design took computational complexity into consideration to allow real-time operation in a low-cost, low-power microcontroller. The code has been implemented in C language and is able to run in real time with room for further optimization. It also permits the option of running additional firmware on top of the navigation core, such as a possible integration of control algorithms in the same platform. More details about the firmware design can be found in G. Falco et alia 2014.

We first tested and validated the hardware and software of the developed navigation system on a car and then mounted on board the target UAV. We used two antenna arrays for the land applications two antenna arrays: The first consists of four low-cost GNSS antennas with a relative distance of 50 centimeters, while the second set is formed by professional-grade antennas with stable phase centers and connected to a professional reference receiver. Figure 9 shows the test equipment and the various settings of the GNSS antennas.

Attitude accuracy tests were conducted first in an open-sky situation, then in a challenging urban scenario. Hereafter, we show the results obtained during a drive in downtown Santander, Spain, the whole trace of which is shown in Figure 10. Narrow streets, boulevards, and the presence of high buildings characterize that urban environment, which affected the correct reception of the satellite signals. Moreover, in such a scenario, the DD carrier phase resolution becomes very difficult to achieve, and often attitude must be estimated by using only the IMU information.

Figure 11 depicts the three Euler angles for yaw, pitch, and roll during the test drive. As reflected in the figure, we can only compare the two attitude estimations at a limited number of points because the receiver often experienced time instants where the three Euler angles were not available. In the part of the trajectory where we can measure such angles, we can observe the error in the INS output of pitch and roll with mean errors of 0.5 and 0.8 degrees, respectively. In comparison, the yaw has a mean error that is slightly bigger the one degree.

After having validated the performance of the system on a land vehicle, we further tested it on board the target UAV. The selected end-user application is a four-rotor rotary wing UAV named Anteos (See Figure 12).

The integration within the UAV required three different integration activities board electrical/mechanical, GNSS antennas mechanical, and software integration.

The mechanical integration of the navigation system processor required the board to be free of most of the vibration that a UAV can generate. For this reason, the board was mounted on the payload docking bay of the UAV. The board is aligned with the UAV INS (namely, an attitude/heading reference system, or AHRS) to obtain directly comparable measurements.

The electrical integration consisted of providing the main batteries voltage to a switching power supply.

The integration of the GNSS antenna required a specific carbon fiber structure prototype to be mounted on top of the UAV, allowing the required 50-centimeter baseline between the antennas. Special care was taken to decrease vibration and the flexion of the structure as much as possible during UAV flights. Moreover compared to other low cost antennas, the chosen unit presents an excellent trade-off between minimization of phase center variation and antenna compactness.

On the UAV side, a serial line has been dedicated to communication with the platform. The purpose of this communication is to gather real time measurements from the navigation system and incorporate them on the UAV real-time telemetry daemon, a portion of the UAV control code dedicated to logging telemetries both for instantaneous use within the UAV control law, and for the logging and post-processing of the mission data.

The flight tests compared the measures taken from the new navigation platform and the on-board INS alone, allowing a real-time comparison of the position/attitude solutions taken from the two independent units. As an example, in Figure 13 the latitude and longitude for both units have been converted in the planar displacement with respect to a common point in order to compare the results in terms of meters. The depicted test was taken from motors power on (i.e., around 40 seconds on ground with UAV motors on) and then about 200 seconds of flight.

In Figure 14 we have plotted the attitude solution obtained with our navigation system compared with the reference one.

The integration showed the capability of the system components to be easily combined and to provide accurate measurements on a demanding platform such as a rotary-wing UAV (no preferred directions, no clamping on ground, side movements, strong electromagnetic fields induced by the four electric motors, vibrations, high dynamics). Once the UAV is in flight the general trend of the measurements follows those of the UAV’s INS, even though at some points the reported attitude differs by some degrees from that of the UAV, which would lead the attitude controller onboard the UAV to overreact.

Conclusions
We designed a sophisticated real-time navigation solution that exploits information coming from multiple GPS receivers and a low-cost MEMS IMU. We were able to estimate the attitude of a UAV platform by forming double-difference carrier-phase measurements to feed a tightly coupled GPS/INS integration architecture. In this way, we demonstrated the technical feasibility of an accurate, low-cost navigation system using non-dedicated hardware and its potential application for UAV navigation.

Acknowledgment
The presented results have been achieved within the LOGAM project which has been funded by the European Union’s Seventh Framework Programme (FP7/2007-2013) under grant agreement #277663.

Additional Resources
[1] Acorde Technologies, S.A., website
[2] Aermatica SPA, website
[3] Baroni, L., and H. Koiti, “Analysis of Attitude Determination Methods Using GPS Carrier Phase Measurements,” in Mathematical Problems in Engineering, Vol. 2012, Hindawi Publishing Corporation, Article ID 596396, p. 10, doi:10.1155/2012/596396, 2012
[4] Falco, G., and M. Campo-Cossío Gutiérrez, E. López Serna, F. Zacchello, and S. Bories, “Low-cost Real-time Tightly-coupled GNSS/INS Navigation System Based on Carrier Phase Double Differences for UAV Applications,” Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+2014), Tampa, Florida USA, pp:841-857, doi: 10.13140/2.1.4638.4642, 2014
[5] Falco, G., and M-C. Cossio and A.Puras, “MULTIGNSS Receivers/IMU System Aimed at the Design of a Heading-Constrained Tightly-Coupled Algorithm,” Proceedings of the International Conference on Localization and GNSS (ICL-GNSS 2013), Turin, Italy, doi: 10.1109/ICL-GNSS.2013.6577263, 2013
[6] Mehut. Y., and C. Delaveaud and S. Bories, “Low-Cost GNSS Antennas Phase Center Variations Characterization for UAV Attitude Determination Application,” Proceedings of AMTA 2013 35th Symposium, Colombus, Ohio USA, October 7–10, 2013
[7] Petovello, M., Real-time Integration of a Tactical-Grade IMU and GPS for High-Accuracy Positioning and Navigation, Ph.D. Thesis, Department of Geomatics Engineering, University of Calgary, Canada, UCGE Report No. 20173
[8] Savage, P. G., “Strapdown Inertial Navigation Integration Algorithm Design Part 1: Attitude Algorithms,” Journal of Guidance, Control and Dynamics, Volume: 21, Number: 1, pp. 19 – 28, 1998
[9] Savage, P. G., “Strapdown Inertial Navigation Integration Algorithm Design Part 2: Velocity and Position Algorithms,” Journal of Guidance, Control and Dynamics, Volume: 21, Number: 2, pp. 208- 221, 1998
[10] Strang, G., and K. Borre, Linear Algebra, Geodesy and GPS, Willesley-Cambridge Press, ISBN-10: 0961408863
[11] Titterton, D. H., and J. L. Weston, Strapdown Inertial Navigation Technology, 2nd ed., Paul Zarchan, Editor, ISBN:1-56347-693-, 1997
[12] Wei, Z., “Positioning with NAVSTAR, the Global Positioning System,” Report No. 370, Department of Geodetic Science and Surveying, The Ohio State University, Columbus, Ohio USA, 1986
[13] Yang, Y., and A. Farrel, “Two Antennas GPSAided INS for Attitude Determination,” IEEE Transactions On Control Systems Technology, Volume: 11, Number: 6, pp. 905-918, doi: 10.1109/ TCST.2003.815545, 2003

The post Thinking Small appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

The European Frequency and Time Forum (EFTF) will take place at The University of Neuchâtel, Neuchâtel, Switzerland from June 23 – 26, 2014. A technical exhibition will also be held during the conference.

Online registration is available.

The European Frequency and Time Forum (EFTF) will take place at The University of Neuchâtel, Neuchâtel, Switzerland from June 23 – 26, 2014. A technical exhibition will also be held during the conference.

Online registration is available.

The European Frequency and Time Forum (EFTF) is a technical conference for time and frequency products and related technologies. It brings together researchers and technologists from manufacturers, service providers, operators, application developers, National Metrology laboratories, defence timing, and standards bodies to share the latest information and promote the development of precise time and frequency systems and components.

Tutorials will be held on Monday, June 23, followed by the conference and exhibition on June 24-26.

Tutorials include both the fundamental topics of frequency and timing at a level suitable for practitioners new to the field, and more advanced and specialized topics related to specific areas.

The EFTF plenary presentation takes place on  Wednesday, July 25. The speakers will be Professor Serge Haroche, ENS and Collège de France (Nobel Prize for Physics 2012), and Dr. John Kitching, NIST (USA).

Among the sessions for the EFTF working group, Group 5 is of particular interest to readers of Inside GNSS. The session topics are:

• Group 1: Materials, Resonators, & Resonator Circuits
• Group 2: Oscillators, Synthesizers, Noise, & Circuit Techniques
• Group 3: Microwave Frequency Standards
• Group 4: Sensors & Transducers
• Group 5: Timekeeping, T&F Transfer, Telecom and GNSS applications
• Group 6: Optical Frequency Standards and Applications

A number of social activities, including a trip to the International Watch Museum, are offered during the conference.

The post EFTF 2014: European Frequency and Time Forum appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

An emphasis on quality assurance in system engineering and components in the first GPS III satellite now under development has driven projected costs up in the program above the budgeted amount, leading the U.S. Air Force to deny a $70 million incentive fee to prime contractor Lockheed Martin.

An emphasis on quality assurance in system engineering and components in the first GPS III satellite now under development has driven projected costs up in the program above the budgeted amount, leading the U.S. Air Force to deny a $70 million incentive fee to prime contractor Lockheed Martin.

Nearly four years ago, a team lead by Lockheed Martin won a cost-plus contract worth more than $1.46 billion contract to build two GPS III research & development satellites. However, a recent General Accountability Office (GAO) report and subsequent confirmation by the GPS program office indicates that additional testing of key components planned for GPS III spacecraft has been the main cost driver.

Projected expenditures on the first two GPS III satellites are at least 18 percent higher than first estimated, up to $1.6 billion today, according to the GAO. The foregone Lockheed Martin incentive fee, which represents about five percent of the program’s targeted budget, would offset about half of the cost increase.

The GAO report, titled “Space Acquisition: DOD Faces Challenges in Fully Realizing Benefits of Satellite Acquisition Improvements,” was discussed at a March 21 hearing conducted by the Subcommittee on Strategic Forces of the U.S. Senate Committee on Armed Services.

Over the last several years, the Air Force Space and Missile Systems Center (SMC) at Los Angeles Air Force Base “has taken action aimed at preventing parts quality problems by issuing policy relating to specifications and standards,” according to the written statement given by Cristina Chaplain, GAO director of acquisition and Sourcing Management. “According to officials, [SMC] is requiring the GPS III program development contractor to meet these specifications and standards.”

“The GPS III program has cited multiple reasons for the projected cost increases including reductions in the program’s production rate; test equipment delays; and inefficiencies in the development of both the navigation and communication payload and satellite bus,” the GAO’s written statement indicates. “The contractor is also behind in completing some tasks on schedule, but the program does not expect these delays to affect the launch of the first satellite [scheduled for 2014],” the reported indicated.

Gen. William Shelton, commander of Air Force Space Command, told a press conference last month that he saw no reason for concern in the GPS III program, which he characterized as "going extremely well." According to a Space News report from the press conference, Shelton said, "We are on schedule, on target with that program," adding that the unit costs for the first two development satellites had not been finalized.

Lockheed’s GPS III contract includes an additional five options of two space vehicles (SVs) each. However, the Air Force appears likely to purchase fewer than that. In January, Lockheed Martin announced that the Air Force had awarded it a $238 million contract for production of the third and fourth GPS III satellites, as well as a $21.5 million contract to provide a Launch and Checkout Capability (LCC) for the next-generation ground segment (OCX) to command and control GPS III satellites from launch through early on-orbit testing.

However, the GAO report says that it is “unclear at this time when this [LCC] capability will be delivered. This gap-filler capability will not enable the new capabilities offered by GPS III satellites, such as a jam resistant military signal and three new civil signals, so most of these capabilities will be unused until OCX Block 2 is delivered in 2016.”

The cost-risk for the development phase of the GPS III program remains with the Department of Defense, but will be converted to a fixed-price basis with most of the production SVs. Last month, Gil Klinger, deputy assistant secretary of defense for space and intelligence, told members of a House subcommittee that the U.S. Air Force will be shifting the GPS III program to a fixed-price contract as part of an effort to control costs.  The Air Force Space Command (AFSPC) later told Inside GNSS that this could occur as soon as SV5.

The testing regime reflects the “back to basics” emphasis of the GPS Directorate and Air Force acquisition officials that stresses “rigorous system engineering” and “high confidence in initial capability” of new platforms and systems.

Keoki Jackson, Lockheed Martin’s navigation systems vice president, told Aviation Week that the Air Force’s requirement for additional testing was based on a recommendation from The Aerospace Corporation. The testing on the engineering “pathfinder” satellite should be a “one-time thing,” Jackson added.

Lockheed Martin believes that by helping the contractor avoid defective components the test results will help save tens of millions of dollars in reduced costs for parts and associated labor on the production version of the GPS III, beginning with SV3.

That emphasis stems in part from the Air Force’s experience with the previous generation of GPS satellites, Block IIF, designed and built by Boeing.

“According to the GPS directorate, the cost of the GPS IIF program, as of April 2011, was at $2.6 billion — more than triple the original cost estimate of $729 million,” the GAO report stated, adding that the IIF satellites’ development challenges were mostly responsible for the 4.5-year delay in the launch of the first GPS IIF satellite to May 2010.

“Approximately one month after they were enabled, the second IIF satellite’s Cesium clock — one of three atomic frequency standard clocks onboard that provide GPS accuracy through redundancy — failed,” the GAO official pointed out. An investigation identified “design and manufacturing issues.” According to a Special Acquisition Report (SAR) released recently by the Department of Defense (DoD),  Boeing has initiated the rework of all cesium units for SVs 3–12. “The cost and schedule impacts are as yet undetermined,” the GAO report stated.

In 2009, interface compatibility issues were identified between the IIFs’ navigation data unit (NDU) and the government-provided Nuclear Detonation (NUDET) Detection System (USNDS) units. The contractor-proposed solution met requirements, according to the GPS SAR, but limited the amount of operational flexibility to support the USNDS mission. This led the Air Force to pursue interface modifications in a successful redesign efforts that resulted in an additional $21.2 million payment to Boeing.

Earlier in the program, an investigation into a factory test anomaly determined that the IIF’s L1 transmitter signal power would have to be reduced from previous settings to “maximize hardware reliability,” which would cause an approximate 40 percent reduction in operational signal power. The GPS program invested $4.6 million and developed a hardware solution restoring L1 power levels for three SVs.

The space acquisitions report can be downloaded from the GAO website.

The post Parts Testing Drives Up GPS III Program Costs, Forces Prime to Forego $70 Million Incentive Fee appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Topcon Positioning Systems (TPS) announced the company’s new CR-G5 high-performance, GNSS choke ring antenna.

Based on the company’s new TA-5 full-spectrum GNSS antenna element, the CR-G5 geodetic antenna offers excellent vertical phase center stability over the GNSS frequency band superior performance in tracking low elevation satellite signals, according to the company.

Topcon Positioning Systems (TPS) announced the company’s new CR-G5 high-performance, GNSS choke ring antenna.

Based on the company’s new TA-5 full-spectrum GNSS antenna element, the CR-G5 geodetic antenna offers excellent vertical phase center stability over the GNSS frequency band superior performance in tracking low elevation satellite signals, according to the company.

The TA-5 technology utilizes an array of vertical convex dipoles to provide “full wave” tracking for all existing and future GNSS signals. A “white paper” on the TA-5 can be found on-line in Inside GNSS’s eLibrary here. The antenna element possesses a relative bandwidth that more than covers the entire GNSS band from 1160 up to 1615 MHz.

The CR-G5 is designed for the long-term installations required for reference network and monitoring applications. The unit is shock tested to withstand repeated one-meter drops onto concrete, and meets environmental ratings for IPX7 (waterproof) and IP6X (dustproof), Topcon sources say.

The post Topcon Introduces Full-Spectrum GNSS Geodetic Antenna appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.