Growing Importance of Satellite Navigation. On Earth and in the Outer Space [Analysis]

PUBLISHED AT: Monday, 04 December 2017, 12:17
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GNSS systems are becoming more and more important. Not only are they being relevant for the economy, as they also have a huge impact on everyday lives of the human beings. The aforesaid solutions serve a number of purposes related to transportation or positioning. Globally they also act as a synchronizing system for perfect time measurement. Throughout the recent period satellite navigation has also been used, more and more frequently, with regards to the satellites themselves. Knowing the exact position of the satellite remaining in the outer space bears a great degree of significance, when it comes to the services offered by the said platforms.

GNSS stands for Global Navigation Satellite System. Contrary to the seemingly simple meaning of the acronym, the GNSS systems do not carry out navigational tasks directly. For instance, their role is not to define the route, to provide clues, directions, allowing the recipient to reach the specific location. The purpose of such hardware is solely to define the position of the recipient within a specific coordinate system at a specific point in time.

The market related to such services enjoys constant growth. According to the 2017 GNSS Market Report  issued by GSA, the value of the market solely for the EU would go up from EUR 21.9 billion (2015) to EUR 59.4 billion in 2025. According to the aforesaid report it is estimated that almost 8 billion satellite navigation receivers would remain use by 2020. Globally, this translates into a single device per single person, on average. Smartphones are going to constitute a vast majority of the said hardware. Today they form 80% of the GNSS receivers.

Among the GNSS satellite constellations, four offer worldwide coverage. These are: Russian GLONASS, US GPS, European Galileo and Chinese BeiDou systems. The first two are fully operational, while the remaining ones are still being implemented, with full operational capabilities expected to be reached by 2020.

Alongside the above global systems, SBAS – Satellite Based Augmentation Systems are also being used to augment the navigation capabilities regionally. This type of services is used for the purpose of adjusting and enhancing the accuracy and credibility of the positioning data provided by the GNSS global solutions. European EGNOS or US WAAS systems are the best examples of SBAS.

The existing global systems, such as GPS or GLONASS, do not provide real time signal reliability, momentary accuracy or functioning data in real time. However, this piece of data remains critical, e.g. for an aircraft on finals, using the GNSS receiver. Considering the above, satellite augmentation systems have been created delivering the information in real time, also transmitting proper adjustments that allow for heightening the positioning accuracy.

prof. Paweł Wielgosz, University Of Warmia And Mazury In Olsztyn

SBAS Systems Coverage. Image Credit: ESA

Utilizing GNSS on Earth and in the Air

Logistics are a field in which satellite positioning is frequently employed. This concerns vehicle localization and fleet management services, allowing for rational management of the vehicle fleet of a single entity. Moreover, traffic within the given space may also be monitored by the authorized organs, thanks to the navigation services. This type of activities are applied in cases of car, train, naval or air traffic.

GNSS systems also have a track-proven record of being used for agricultural purposes in so called precision agriculture. There, they are used, for instance, to automatically control the agricultural machinery. Mapping and research conducted with the use of satellite navigation may be used in geodesy or civil engineering, when creating roads or in case of mining activities.

Location Based Services - LBS, are yet another important segment of GNSS capabilities. The aforesaid services include personalized marketing offers delivered to the user of the smartphone. The said offers are based both on the personal preferences of the user (e.g. within the scope of selecting restaurants offering regional cuisine) as well as on location where the potential customer finds himself, at the moment when the offer is placed. LBSs also include the navigation proper - selecting routes towards the given location along with suggestions as to how one could reach the given place.

Finally, satellite navigation systems are a great tool used to precisely measure time and synchronize the ground-based clocks. This feature is useful e.g. in the area of bank transactions. GNSS time measurement is also useful for the energy companies who remain able, thanks to the said service, to monitor the energy flow within own power grids.

The signals provided by the navigation satellites may also be utilized to measure the changes occurring in the Earth’s magnetic field caused by the ionosphere storms. The research concerning the impact of the ionosphere storms greatly expands human knowledge on ionosphere dynamics related to activity of the Sun. The said initiative will also make it possible to perfect the GPS receivers sent into the orbit, so that loss of positioning signal would be less probable.

Utilizing Satellite Positioning in Space Missions

GNSS receivers have been, since many years, a component of numerous objects sent into the orbit. Such instruments fitted onto the launch vehicles allow for accurate tracking of its trajectory, required to place the satellite in the proper target orbit. The same type of receivers is also used in case of other satellites, and here the purpose is similar: high accuracy tracking, allowing for confirmation of satellite’s position at any given moment.

The basic application for the space GNSS receivers is to set the orbit parameters of the satellites carrying the receiver. This is required to ensure proper functioning of most of the satellites, such as SAR or altimetry satellites. Furthermore, satellite-borne GNSS receivers are also used to carry out radio occultation, for the purpose of researching the space weather and atmosphere temperatures.

prof. Paweł Wielgosz, University Of Warmia And Mazury In Olsztyn

It remains quite obvious that the signal sent by the navigation satellites in the MEO orbits, at altitudes of around 20 thousand kilometres, may be used for the purpose of positioning the instruments placed in the LEO orbits.

The state of the art technology used today also makes it possible to utilize the GNSS network to position the satellites orbiting much higher, e.g. on the geostationary orbit - 35,768 kilometres above the Earth. This is quite complicated, as the navigation satellites emit their signals directionally, towards the Earth. Hence, to position the GEO orbit satellites, medium orbit GNSS systems are used, as they are “looking” towards the planet. Hence, to determine its position, a satellite in the geostationary orbit must intercept weak signals emitted by satellite navigations placed on the other side of the Earth, at distances of up to 50 thousand kilometres.

A typical GNSS receiver designed for space applications weighs 6 kilograms and has dimensions of around 30×30×15 cm. Thus, it is significantly larger than a chip serving the very same purpose in a smartphone. A receiver as such is a sophisticated and complex electronic device which, additionally, needs to be highly resistant to conditions of the outer space. Furthermore, it should also withstand acceleration and shock emerging during a lift-off of a launch vehicle. The receivers are also travelling at velocities much faster (3-8 kilometres per second) than their counterparts on Earth.

The GNSS units must also comply with strict reliability requirements. This is a typical condition set for the space systems where no chances exist to conduct repairs, with some minor exceptions from that rule. Thus such receiver is often doubled (with another redundant device available) onboard the satellite, as in case of most hardware sent into the outer space. Once one instrument fails, the other takes over its role. A major emphasis is also placed on the rigorous test procedures. The GNSS receiver undergo thorough testing on Earth, before they are launched into space.

Testing of the Space Receivers - Important Market Niche

Back in 2014 Astri Polska company got very interested in the activities based around ground testing of GNSS signal receivers designed for space applications. Lion receiver was introduced into production at roughly the same time, by the German branch of the Airbus Defence and Space company. Representatives of the Astri Polska entity managed to successfully finalize a transfer of technology concerning the testing equipment for the Lion receiver, from Ottobrunn to Poland. The operation was approved by ESA. The project was being then continued for two years, as a part of the ESA Polish Industry Incentive Scheme. It lasted 2 years.

By transferring the Lion receiver testing to Poland, not only did Airbus diminish the cost of the procedures, but the company also relieved some of the highly qualified employees who could get involved in implementation of other tasks.

The domestic industry and engineers, on the other hand, have been acquiring entirely new expertise. The incentive resulted in creation of GNSS Lion receiver testing software at the Astri Polska company. Testing of an instrument as such remains fairly complicated. Moreover, the whole procedure must be carried out in conditions similar to the actual ones, that would be experienced by the system in the outer space. Procedures as such are carried out at a laboratory that remains in possession of GNSS signal emulators, simulating the signal profile available in the outer space, during the specific mission.

In our project Lion underwent laboratory testing procedure during a thoroughly planned scenario, as if the receiver was placed on the actual weather satellite remaining in low orbit, to work within the MetOP-SG mission. For the sake of the test an assumption was made that both GPS as well as the Galileo constellations are 100% completed and in working order. Astri Polska was responsible primarily for preparing software controlling the test environment and the Lion receiver. Furthermore, the software also read the results and carried out the preliminary analysis. The results of our tests were then passed on to Airbus.

Karol Brzostowski, Head of the Satellite Applications and Services Department of Astri Polska

Following the success of the FLIRT-PL project, the employees of the Astri Polska company came to a conclusion that creation of a flexible testbed that could accommodate a wide range of space GNSS receivers is a relevant, yet forgotten gap in the market. No obstacles exist to utilize the Airbus’s testing software for the purpose of testing instruments delivered by other manufacturers. The experts working at the Astri Polska company decided to take steps in this direction, convincing other manufacturers of receivers, including Ruag, Thales Alenia Space or ESA, to participate in the effort.

The GNSS receiver that remains operable on Earth does not necessarily have to be in working condition in the outer space. This is related to the higher level of radiation, as well as to the huge variations of temperature. Receivers destined to be used in case of satellites need to go undergo testing in chambers that can simulate the space conditions. They also need to be shock- and g-load-proof, to withstand the forces accompanying the launch procedure. Furthermore, the circuitry of the receiver should remain compatible with other systems installed on the given satellite - any mutual interference remains undesirable.

prof. Paweł Wielgosz, University Of Warmia And Mazury In Olsztyn

ESA approved the concept of creating a universal GNSS space receivers test bed for laboratory applications. In this way, FLIGhT project was born. Currently Astri is in process of creating software that would remain capable of testing three different receivers, including two designed exclusively for space applications: Airbus Lion and Ruag Podrix systems.

Lion GNSS

GNSS Lion space receiver. Image Credit: Airbus Defence and Space

FLIGhT project began in September 2017, it is going to last 15 months. Ultimately the initiative is going to become a valuable product. The first implementation of the software would take place at the European Navigation Laboratory of the ESA ESTEC facility based in Noordwijk. It is probable that in the future the solution could also be applied at Universities. The system could be utilized for the purpose of testing military-grade navigation receivers too.

ESTEC

ESA ESTEC seat in Noordwijk, located in the Netherlands. Image Credit: ESA/Anneke Le Floc'h

Here one should also note that Astri Polska is involved in one more ESA-financed project. We are referring to radiation testing of the AGGA-4 ASIC. The said circuit is responsible for GNSS signal processing within the Lion receiver. ASIC (Application Specific Integrated Circuit) is a type of advanced electronic integrated circuitry designed for specific purposes. ASICs may replace larger general purpose integrated circuits. This is often presented as their main advantage. The ASIC type circuits are smaller and lighter, they also are infinitely more functional, reliable and energy-saving.

AGGA-4 Integrated Circuit. Image Credit: Astri Polska

Astri is to verify the operation of the AGGA-4 circuit onboard the MetOp-SG satellite. Not only is the company going to work on simulating the operation of the satellite in the orbit, but also on representation of the space conditions, where the electronics remain exposed to cosmic rays.

The tests are taking place with the device being exposed to space radiation. Two tests are taking place, one involving heavy ions at the UCL facility in Belgium, and the second one, involving protons, at the PSI facility in Switzerland.

Karol Brzostowski, Head of the Satellite Applications and Services Department of Astri Polska

Proper testing and implementation of the AGGA-4 ASIC is an urgent and relevant matter, since the said component is being widely applied in numerous space missions pursued by the European Space Agency. Ultimately the product would be commercialized, thus it remains incredibly important to certify its resistance to space radiation. AGGA-4 is the largest ASIC designed primarily for space applications.

Verification of the Capabilities Offered by a Receiver Designed for Hybrid Purposes

Alongside a number of advantages, positioning on the basis of satellite signals has one major disadvantage. It cannot be utilized indoors, where roofs or floors block the access to the satellite signal. This problem may be solved through application of so called hybrid positioning. Not only does this method make use of GNSS, as ground-based cellphone infrastructure is also used within the process.

Hybrid positioning principle assumes that the position is determined on the basis of two discriminate systems. One is the GNSS conventional satellite navigation, while the second is based upon the LTE technology.

Karol Brzostowski, Head of the Satellite Applications and Services Department of Astri Polska

Therefore, Astri Polska is working on another ESA programme, within the framework of the Polish Industry Incentive Scheme, known as TEcHNO (Test Environment for Hybrid NavigatiOn). The goal of this project is to prepare a software platform that could be used to conduct laboratory testing of GNSS+LTE hybrid solutions. Not only would the said platform make it possible to control the laboratory equipment, as it may also be used to generate simulation scenarios.

Astri has been given two years to complete the task. The final and tangible result of the undertaking is going to take on a form of a technology demonstrator. The first implementation is also planned to happen at the ESTEC facility.

Growing Importance of the GNSS Solutions. Promotion and Awareness.

E-Knot project was very important for the process of promoting the GNSS-based applications and capabilities in Europe, with a major emphasis placed on Poland. The project was aimed at reinforcement of integration between science, education and industry, with regards to the European GNSS domain. The programme in question, financed with the use of the Horizon 2020 fund, was supervised by GSA, the European GNSS agency based in Prague. The task was scheduled to be completed in three years between 2015 and 2017. Astri Polska was involved in the E-Knot programme as a part of consortium formed by numerous European entities working in the field. The consortium members were, throughout the process of implementing the project, organizing trainings, meetings or internships. Finally, recommendations for the decision makers would be prepared, with regards to wide prospective application of the GNSS solutions in Europe.

Undoubtedly, the role satellite positioning plays in case of Earth applications will be continuously becoming more and more significant. GNSS use in case of satellites is also going to bear increasingly higher relevance. One of the factors suggesting so is seen in the unstoppable increment of the number of satellites in space placed in low Earth orbit, as well as in geostationary orbit.

Companies such as SpaceX or OneWeb expect and claim that constellations including hundreds, or even thousands systems that, remaining in orbit, could provide Internet access globally, would be created. Concerning the aforesaid “satellite crowd”, data concerning the location and direction of movement assigned to the specific systems would be very important. In any other case, the quantity of space debris would be multiplied, in line with the pessimistic scenario known as the Kessler syndrome (also called the Kessler effect, collisional cascading or ablation cascade).

Knowledge of accurate position of the research satellites is often required for the sake of correct interpretation of data gathered by their sensors. All of the above remains possible on one condition. The GNSS receiver needs to work correctly and in a reliable manner.

So far, concepts and technologies related to servicing the satellites in space have been in their infancy. Time is required to make such solutions common. This translates into the situation in which GNSS receivers need to be always in good shape. Testing should take place before hardware of this class is sent into the outer space, on Earth. Thus, it shall be interpreted as a good symptom that entities such as Astri Polska or ESA recognize the urgent need to create proper software and laboratory infrastructure that would replicate the space conditions with a high degree of fidelity, for the purposes of testing the space GNSS receivers. Maybe the above area is one of the gaps where the Polish industry could excel, within the framework of Polish ESA membership?

 

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