Spaceborne GPS Current Status and Future Visions

2019

The importance and application of global navigation satellite systems (GNSS) has never been greater; there is increasing demand for both commercial and government projects; indeed, owning and operating a GNSS facility has become a matter of national esteem. This article reviews some of the history that led up to the USA building its benchmark Global Positioning System (GPS) exploiting electromagnetic waves and reviews the progress being made by other nations in constructing accurate navigation positioning systems.

can be achieved for high-Earth orbiting satellites using a GPS receiver with a very stable oscillator. This accuracy improves to better than 15 meters RMS if the GPS receiver's signal acquisition threshold can be reduced by 5 dB-Hertz to track weaker signals.

Proceedings of the 32nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2019), 2019

is the Head of the Navigation Support Office at ESA's European Space Operations Center (ESOC) in Darmstadt, Germany. Previously, he worked at the European GNSS Authority (GSA) as the Head of System Evolutions for Galileo and EGNOS and he also worked for the European Commission in the Galileo Unit. For over 25 years, he has worked on activities related to the use of GPS/GNSS for space applications. He holds a master and doctoral degree in aerospace engineering from the Technical University of Berlin, Germany. Erik Schönemann has joint the Navigation Support Office at ESA/ESOC in 2006 as a contractor and became permanent staff in 2015. He is involved in Galileo studies since the launch of the first Galileo validation satellite GIOVE-A and is the technical manager of the Galileo Reference Service Provider (GRSP). He is involved in the coordination of ESA's reference frame activities and contribution to International Services like ILRS, IGS and UTC. Erik Schönemann holds a master and a doctoral degree in Geodesy from the Technical University of Darmstadt, Germany. Francesco Gini is a Navigation Engineer at the Navigation Support Office (OPS-GN) at the European Space Operations Center (ESOC) of ESA. He is responsible for the Space Service Volume (SSV) and Precise Orbit Determination (POD) related activities. He received his PhD in Astronautics and Satellite Sciences at the University of Padova, Italy in 2014 and since then he has been working in ESOC. Michiel Otten is a Navigation Engineer at the Navigation Support Office (OPS-GN) at the European Space Operations Center (ESOC) of ESA. He is responsible for the LEO POD activities and the International Doris Service (IDS) Analysis Centre activities. He received his Master degree in Aerospace Engineering at the Delft University of Technology in 2001 and since then he has been working at ESOC. Pietro Giordano holds a Master in Telecommunication Engineering from University of Padua (Italy) and a Second Level specializing Master in Navigation and Related Application from University of Torino (Italy). He worked in Thales Alenia Space (Italy) as GNSS receiver Engineer before joining ESA in 2009, where he worked first as GNSS receiver support to Galileo project and later as GNSS Security Engineer in the Galileo project. Currently he is in charge of multiple activities related with space GNSS receivers and R&D in space GNSS receiver technology such as Technical Officer for POD receiver in Sentinel, Proba3 missions, development of GNSS space borne receivers for real time on-board POD in CubeSats, development of LEO PNT payloads, support for definition of new AGGA chip and development of GNSS space borne receivers for lunar missions.

1999

Vegas, and his Ph.D. degree in Mathematics from Northwestern University. His current work focuses on space surveillance systems. Dr. C. C. (George) Chao is a Senior Engineering Specialist in the Astrodynamics Department at The Aerospace Corporation. He received his B.S. degree in Mechanical Engineering from National Cheng Kung University in Taiwan, his M.S. and Ae.E degrees in aeronautics from Caltech and his Ph.D. in Engineering (astrodynamics) from UCLA. He is a co-author of a book "Orbital Mechanics" and has over 25 years of experience in orbit dynamics, perturbations and GPS applications. Dr. Alison Brown is the President of NAVSYS Corporation, which specializes in developing GPS technology. Dr. Brown received her BA and MA in Engineering from Cambridge University, England, a SM in Aeronautics and Astronautics from MIT, and a Ph.D. in Mechanics and Aerospace from UCLA. She has over 15 years experience in GPS receiver design and has eight GPS related patents. She served as the Space Representative for the Institute of Navigation Council in 1993 and has served as the Technical Chairman and General Chairman for the ION Satellite Division and the ION Annual Meetings. She is a member of the editorial board for GPS World. Randy Silva is a Software Engineer at NAVSYS Corporation. Mr. Silva received his Bachelor's Degree from the University of Colorado. He has worked for the last several years developing software for many GPS applications.

The NAVSTAR Global Positioning System (GPS) is a constellation of 24 satellites that provides users with continuous, worldwide positioning capability using the data transmitted in the GPS navigation message. The receiver uses delay lock loops (DLLs) to correlate incoming bit sequences with identical sequences generated by the receiver (see Fig. 3.1). The bit sequences are Gold codes formed as a product of pseudorandom noise sequences [Spilker, 1978]. By aligning the received and locally generated codes, the receiver determines the pseudorange to each satellite [Getting, 1993]. When the measurement is made, the receiver clock time is compared to the satellite time of transmission to determine the pseudorange. The satellite time of transmission is encoded onto the bit sequence using the navigation data. There are six orbital planes, spaced 60E apart and each containing four satellites. The inclination of the orbital plane with respect to the equator is 55E in order to provide global coverage. At an altitude of 20,200 km, an equatorial orbit would not provide coverage above 72E latitude [Spilker, 1996]. Earlier Block I satellites were inclined at 63E, but this was lowered to 55E for the current Block II satellites. This was done primarily because the space shuttle was planned as the launch vehicle for GPS satellites [Forssell, 1991]. However, the Challenger accident prompted a switch to Delta-II rockets for satellite launches although the orbit inclination remains at 55E. Each orbit is nearly circular with an eccentricity close to zero (< 0.02). The orbital period of 11 hr 58 min allows for the use of Doppler frequency shift which occurs due to

1998

Technology currently is available to support real-time onboard knowledge of the position of a low Earth orbiter at the 5-to 15-m level using the civilian broadcast Global Positioning System (GPS) signal with sophisticated models and filtering techniques onboard the spacecraft. Without these techniques, the standard positioning service yields 50 to 100 m with the current level of selective availability (SA). Proposed augmentations and/or enhancements to the GPS system will make rms accuracies of from 10 centimeters to a few decimeters available to the real-time onboard user.

1999

Technology currently is available to support real-time onboard knowledge of the position of a low Earth orbiter at the 5-to 15-m level using the civilian broadcast Global Positioning System (GPS) signal with sophisticated models and filtering techniques onboard the spacecraft. Without these techniques, the standard positioning service yields 50 to 100 m with the current level of selective availability (SA). Proposed augmentations and/or enhancements to the GPS system will make rms accuracies of from 10 centimeters to a few decimeters available to the real-time onboard user.

Journal of science Education and Technology, 2002

Early in the race to space in the 1950s, the US Department of Defense found that tracking the position of satellites could be used to track fixed bodies on the surface of the Earth. No one realized that the NAVSTAR GPS satellite constellation program, that began its research and ...

ESA Publications Division, 2006

The European Space Agency’s (ESA) main mission is to shape the development of Europe’s space capability and to ensure that investment in space continues to deliver maximum benefit to the citizens of Europe. The European Geostationary Navigation Overlay System (EGNOS) is yet another European success story of cooperation in space science and technology. In line with the ESA practice of “Shape and Share,” the Agency is proud to have shaped, together with the European Industry, the EGNOS technology and to share it now with the GNSS user community. EGNOS is the main European contribution to GNSS-1 to serve the needs of maritime, land transport, time and aeronautical applications in the European and neighbouring regions. EGNOS is the first-generation European GNSS System, and a first step towards Galileo, the second generation, based upon an independent European navigation-satellite constellation. EGNOS will be interoperable with equivalent US (WAAS) and Japanese (MSAS) SBAS systems, in addition to other emerging initiatives – as India’s GAGAN and China’s SNAS systems – aiming at contributing to a truly global navigation system. The EGNOS measured performances are excellent, providing the best SBAS performances worldwide today. Accuracies of the order of 1-2 metres and availabilities of better than 99% for APV are frequently measured in most of Europe. EGNOS services will start in 2007 with the declaration of the EGNOS Open Service, and the transfer of EGNOS ownership from ESA to the recently created GNSS Supervisory Authority (GSA) in 2007. This book is technical in nature and presents a complete overview of the EGNOS mission, system and architecture. It has been written for those GNSS engineering professionals, applications developers, satellite-navigation users and university students wishing to have a complete picture of the EGNOS and Satellite-Based Augmentation System (SBAS) technologies, principles and related applications.

Use of GNSS for space navigation is relatively cheap solution that provides a possibility to find your own position, improved recovery time after manoeuvres for spacecraft and satellites, etc. Medium Earth orbits are not that interesting for business; but they still have their own use. The research provides information about availability of different satellite constellations and some data on accuracy of navigation solution for the medium Earth orbits. How GNSS works for space users. Determination of the coordinates of a space vehicle is important for different operations in space (docking, movement to desired orbit, recovery after manoeuvres, etc), or that would be relevant in the near future (with the removal of large orbit space debris and other operations). Even though satellite navigation systems are most effective on the Earth's surface so far, the question arises – how effective are they when moving away from Earth's surface to the space service volume? As stated in interface control documents of GPS and GLONASS, these systems provide full coverage only up to 3000 km for GPS and up to 2000 km for GLONASS above Earth surface. According to the same document, the GPS space service volume (SSV) lies between 3000 km and 36000 km. There is no performance standard for it as of yet, but the possibility for navigation is actively researched upon. The coordinates, velocity and time of satellite navigation systems in the medium Earth orbits is performed in the radio navigation field, which is formed by radio signals emitted by satellites. To determine the coordinates in three-dimensional space it is necessary to simultaneously receive signals from at least four satellites (the use of multiple constellations might require more satellites for position fix). The navigation satellites are located at the height of about 20 000 kilometers above Earth that is within the limits of the investigated area. Therefore, we can only see limited amount of navigation satellites in direct view on the altitudes below 20 000 km and actually no satellites above. To allow the space navigation the so-called off-nadir satellites can be used. They broadcast signal from beyond the Earth's limb. The details are given in Fig. 1. Fig. 1 depicts how the off-nadir satellites broadcast their signals into space and has several important regions. First is the main lobe region, it corresponds to the signals that are broadcast through the main lobe of the satellite antenna radiation pattern and contain most of the signal strength. They are between the ± 13.8° to ± 23°, as a part of the signal is shadowed by the Earth. The side lobes region corresponds to the signals broadcast through the side lobes. They feature weak feed and initially were considered parasitic. Their use actually allowed to obtain passable results on higher orbits. They lie between ± 30° and ± 60°, though the signal strength is not guaranteed.