The Augmented Forward Signal (AFS): Defining the Navigation Signal Standard for Future Lunar Missions
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Augmented Forward Signal↗
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Recent Activities in Spaceborne GPS
After years of patient advocacy and paper studies by a diverse corps of enthusiasts, spaceborne GPS has at last become a presence in the world of flight projects. Owing to rapidly declining hardware costs, and the high value of autonomous onboard positioning, timing, and attitude determination, basic navigation receivers are coming to be seen as almost indispensable to future low earth orbiters.
Geodesy Geophysics Global Positioning System↗
British American satellite time transfer experiment
The use of the Timation satellite for navigation purposes is discussed. The advantages of the satellite for navigation and time transfer are defined as: (1) well-known position, (2) line-of-sight signal which allows use of ultrahigh frequency signals, (3) worldwide coverage, and (4) celestial navigation solution similar to the conventional celestial navigation practices. A diagram of range measurement by phase measure is provided. The application of an intercept chart for determining position using the navigation satellite is demonstrated. The results of a ground based time transfer experiment are reported.
EASTON R. L.↗
GPS navigation experiment using high precision GPS timing receivers
Global Positioning System (GPS) Time Transfer receivers were developed by the Naval Research Laboratory (NRL) to provide synchronization for the NASA Global Laser Tracking Network (GLTN). The capabilities of the receiver are being expanded mainly through software modification to: Demonstrate the position location capabilities of a single channel receiver unsign the GPS C/A code; and Demonstrate the time/navigation capability of the receiver onboard a moving platform, by sequential tracking of GPS satellites.
Buisson, J. A.↗
STS-1 operational flight profile. Volume 5: Descent cycle 3. Appendix D: GRTLS six degree of freedom Monte Carlo dispersion analysis
The results of a six degree of freedom (6-DOF) nonlinear Monte Carlo dispersion analysis for the latest glide return to landing site (GRTLS) abort trajectory for the Space Transportation System 1 Flight are presented. For this GRTLS, the number two main engine fails at 262.5 seconds ground elapsed time. Fifty randomly selected simulations, initialized at external tank separation, are analyzed. The initial covariance matrix is a 20 x 20 matrix and includes navigation errors and dispersions in position and velocity, time, accelerometer bias, and inertial platform misalinements. In all 50 samples, speedbrake, rudder, elevon, and body flap hinge moments are acceptable. Transitions to autoland begin before 9,000 feet and there are no tailscrapes. Navigation derived dynamic pressure accuracies exceed the flight control system constraints above Mach 2.5. Three out of 50 landings exceeded tire specification limit speed of 222 knots. Pilot manual landings are expected to reduce landing speed by landing farther downrange.
Montez, M. N.↗
GPS Operations in High Earth Orbit: Recent Experiences and Future Opportunities
Over the past two decades, spacecraft in Low Earth Orbit (LEO) have significantly benefited from real-time reception of navigation and timing signals from the Global Positioning System (GPS). By employing GPS receivers that are specially developed to support reception in space, LEO spacecraft now realize significantly reduced recovery time after trajectory maneuvers, improved operations cadence, increased satellite autonomy, and more precise, real-time navigation and timing performance. Now, despite extremely weak signal reception and less favorable geometry, a number of upcoming HEO missions are poised to benefit from improved navigation, timing, and onboard autonomy thanks to GPS. This paper will describe the results of two recent missions (MMS and GOES-16), provide an understanding of the benefits and limitations of GPS beyond LEO, and outline future missions and opportunities where this capability would result in significant and enabling benefits.
Global Positioning System↗
GPS Operations in High Earth Orbit Recent - Experiences and Future Opportunities
Over the past two decades, spacecraft in Low Earth Orbit (LEO) have significantly benefited from real-time reception of navigation and timing signals from the Global Positioning System (GPS). By employing GPS receivers that are specially developed to support reception in space, LEO spacecraft now realize significantly reduced recovery time after trajectory maneuvers, improved operations cadence, increased satellite autonomy, and more precise, real-time navigation and timing performance. Now, despite extremely weak signal reception and less favorable geometry, a number of upcoming HEO missions are poised to benefit from improved navigation, timing, and onboard autonomy thanks to GPS. This paper will describe the results of two recent missions (MMS and GOES-16), provide an understanding of the benefits and limitations of GPS beyond LEO, and outline future missions and opportunities where this capability would result in significant and enabling benefits.
Space Service Volume↗
Carrier synchronization techniques for unbalanced QPSK signals. I
This paper uses MAP estimation techniques to obtain carrier reconstruction circuits for unbalanced QPSK signals. In addition, the performance analysis of these circuits is carried out to the extent that a loop design can proceed. Numerical results are presented in order to demonstrate the utility of the theory developed. This signal design will be used in the development of the Tracking and Data Relay Satellite System (TDRSS) and the Navigation Satellite Timing and Ranging Global Positioning System (NAVSTAR GPS).
Braun, W. R.↗
Discovery: Under the Microscope at Kennedy Space Center
The National Aeronautics & Space Administration (NASA) is known for discovery, exploration, and advancement of knowledge. Since the days of Leeuwenhoek, microscopy has been at the forefront of discovery and knowledge. No truer is that statement than today at Kennedy Space Center (KSC), where microscopy plays a major role in contamination identification and is an integral part of failure analysis. Space exploration involves flight hardware undergoing rigorous "visually clean" inspections at every step of processing. The unknown contaminants that are discovered on these inspections can directly impact the mission by decreasing performance of sensors and scientific detectors on spacecraft and satellites, acting as micrometeorites, damaging critical sealing surfaces, and causing hazards to the crew of manned missions. This talk will discuss how microscopy has played a major role in all aspects of space port operations at KSC. Case studies will highlight years of analysis at the Materials Science Division including facility and payload contamination for the Navigation Signal Timing and Ranging Global Positioning Satellites (NA VST AR GPS) missions, quality control monitoring of monomethyl hydrazine fuel procurement for launch vehicle operations, Shuttle Solids Rocket Booster (SRB) foam processing failure analysis, and Space Shuttle Main Engine Cut-off (ECO) flight sensor anomaly analysis. What I hope to share with my fellow microscopists is some of the excitement of microscopy and how its discoveries has led to hardware processing, that has helped enable the successful launch of vehicles and space flight missions here at Kennedy Space Center.
Howard, Philip M.↗
The role of time-frequency in satellite position determination systems.
Tests were conducted by NASA on radio navigation satellite systems that employ the use of time-frequency determination. The satellites used for this purpose were the ATS 1 and 3, and the Nimbus 3 and 4. Several systems were tested in order to examine the feasibility of three satellite navigation concepts: (1) multiple satellite range measurements, (2) satellite range rate, or range and range rate measurements and (3) satellite angle measurements. Test results indicate that locations of ships and aircraft can be determined to within 3-5 km, one sigma, by these satellite methods, and that location accuracy is both a function of the RF employed and of the extent of knowledge of the satellite orbit.
Ehrlich, E.↗
27th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting
This document is a compilation of technical papers presented at the 27th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting, held November 29 - December 1, 1995 at San Diego, CA. Papers are in the following categories: Recent developments in rubidium, cesium, and hydrogen-based frequency standards; and in cryogenic and trapped-ion technology; International and transnational applications of PTTI technology with emphasis on satellite laser tracking, GLONASS timing, intercomparison of national time scales and international telecommunications; Applications of PTTI technology to the telecommunications, power distribution, platform positioning, and geophysical survey industries; Applications of PTTI technology to evolving military communications and navigation systems; and Dissemination of precise time and frequency by means of Global Positioning System (GPS), Global Satellite Navigation System (GLONASS), MILSTAR, LORAN, and synchronous communications satellites.
Sydnor, Richard L.↗
Sensitivity of Mars surface navigation to timing errors
This study will show that the surface asset positioning process is robust and relatively insensitive to these errors. Indeed, the combination of in-situ and MN orbiter to Earth Doppler data is capable of simultaneously resolving surface asset and MN orbiter positions to an accuracy of 10 m, and clock errors to levels better than 3 msec.
Mars Network navigation timing errors↗
High-Altitude MMIC Sounding Radiometer for the Global Hawk Unmanned Aerial Vehicle
Microwave imaging radiometers operating in the 50-183 GHz range for retrieving atmospheric temperature and water vapor profiles from airborne platforms have been limited in the spatial scales of atmospheric structures that are resolved not because of antenna aperture size, but because of high receiver noise masking the small variations that occur on small spatial scales. Atmospheric variability on short spatial and temporal scales (second/ km scale) is completely unresolved by existing microwave profilers. The solution was to integrate JPL-designed, high-frequency, low-noise-amplifier (LNA) technology into the High-Altitude MMIC Sounding Radiometer (HAMSR), which is an airborne microwave sounding radiometer, to lower the system noise by an order of magnitude to enable the instrument to resolve atmospheric variability on small spatial and temporal scales. HAMSR has eight sounding channels near the 60-GHz oxygen line complex, ten channels near the 118.75-GHz oxygen line, and seven channels near the 183.31-GHz water vapor line. The HAMSR receiver system consists of three heterodyne spectrometers covering the three bands. The antenna system consists of two back-to-back reflectors that rotate together at a programmable scan rate via a stepper motor. A single full rotation includes the swath below the aircraft followed by observations of ambient (roughly 0 C in flight) and heated (70 C) blackbody calibration targets located at the top of the rotation. A field-programmable gate array (FPGA) is used to read the digitized radiometer counts and receive the reflector position from the scan motor encoder, which are then sent to a microprocessor and packed into data files. The microprocessor additionally reads telemetry data from 40 onboard housekeeping channels (containing instrument temperatures), and receives packets from an onboard navigation unit, which provides GPS time and position as well as independent attitude information (e.g., heading, roll, pitch, and yaw). The raw data files are accessed through an Ethernet port. The HAMSR data rate is relatively low at 75 kbps, allowing for real-time access over the Global Hawk high-data-rate downlink. Once on the ground, the raw data are unpacked and processed through two levels of processing. The Level 1 product contains geo-located, time-stamped, calibrated brightness temperatures for the Earth scan. These data are then input to a lD variational retrieval algorithm to produce temperature, water vapor, and cloud liquid water profiles, as well as several derived products such as potential temperature and relative humidity.
Brown, Shannon T.↗
Precise time and time interval (PTTI), an overview
Present applications of precise time and frequency (T/F) technology can be grouped as follows: (1) Communications systems which require T/F for time division multiplexing and for using spread spectrum techniques. (2) Navigation systems which need T/F for position fixing using a timed signal. (3) Scientific-Metrological applications which use T/F as the most precisely reproducible standard of measurement. (4) Astronomical-Space applications which cover a variety of the most demanding applications such as pulsar research, Very Long Baseline Interferometry (VLBI) and laser/radar ranging. In particular, pulsar time-of-arrival measurements require submicrosecond precision over a period of one-half year referred to an extraterrestrial inertial system, and constitute the most stringent requirements for uniform timekeeping to date.
Winkler, G. M. R.↗
A microcomputer-based position updating system for general aviation utilizing Loran-C
Modern digital electronic technology is used to produce a device to convert LORAN C to useful pilot information using a simple software algebra and low cost microprocessor devices. Results indicate that the processor based LORAN C navigator has an accuracy of 1.0 nm or less over an area typically covered by a triad of Loran C stations and can execute a position update in less than 0.2 seconds. The system was tested in 30 hours of flight and proved that it can give reliable and accurate navigation information. Methods of converting time differences to position, design considerations for the microcomputer system, and the system for coordinate conversion are discussed. Testing with predetermined points and possible fixes for errors are also considered.
Fischer, J. P.↗
ATS C-2 satellite VLBI experiment
A proposal is presented to conduct a satellite VLBI experiment using the ATS C-2 spacecraft. The main objectives of the experiment are: (1) precision spacecraft position determination with the VLBI technique and comparison of the L-band interferometric technique with the L-band R and R technique from the viewpoint of operational simplicity and precision, (2) comparison of the single differential Doppler and the wideband VLBI technique for such uses as tracking, geodesy, etc., (3) derivation of real time ionospheric corrections and phase scintillation effects utilizing simultaneous two-frequency (L- and C-band) tracking of the spacecraft in both time delay and Doppler interferometry, (4) development of techniques for precise time dissemination, particularly to marine users, through wideband time-delay interferometry, (5) development of techniques to use synchronous satellites as stable platforms in space in the area of marine geodesy, (6) station location and calibration, and (7) aid to L-band navigation experiments which utilize precise spacecraft position and time in deriving the user's position.
Ramasastry, J.↗
An Introduction to High-Altitude Space Use of GNSS (For Timing People)
The Global Positioning System (GPS) and other global navigation satellite systems (GNSS) are used routinely in low Earth orbit for a variety of applications, including spacecraft navigation, radio occultation remote sensing, and time synchronization. High-altitude use of these systems, near to and above the constellations themselves, are an emerging operational capability. This talk provides an overview of such high-altitude space use of GNSS, specifically related to spacecraft navigation and time synchronization and estimation for members of the Civil GPS Service Interface Committee (CGSIC) Timing Subcommittee.
Parker, Joel J. K.↗
Development of a Real-Time GPS/Seismic Displacement Meter: Applications to Civilian Infrastructure in Orange and Western Riverside Counties, California
We propose a three-year applications project that will develop an Integrated Real-Time GPS/Seismic System and deploy it in Orange and Western Riverside Counties, spanning three major strike-slip faults in southern California (San Andreas, San Jacinto, and Elsinore) and significant populations and civilian infrastructure. The system relying on existing GPS and seismic networks will collect and analyze GPS and seismic data for the purpose of estimating and disseminating real-time positions and total ground displacements (dynamic, as well as static) during all phases of the seismic cycle, from fractions of seconds to years. Besides its intrinsic scientific use as a real-time displacement meter (transducer), the GPS/Seismic System will be a powerful tool for local and state decision makers for risk mitigation, disaster management, and structural monitoring (dams, bridges, and buildings). Furthermore, the GPS/Seismic System will become an integral part of California's spatial referencing and positioning infrastructure, which is complicated by tectonic motion, seismic displacements, and land subsidence. Finally, the GPS/Seismic system will also be applicable to navigation in any environment (land, sea, or air) by combining precise real-time instantaneous GPS positioning with inertial navigation systems. This development will take place under the umbrella of the California Spatial Reference Center, in partnership with local (Counties, Riverside County Flood and Water Conservation District, Metropolitan Water District), state (Caltrans), and Federal agencies (NGS, NASA, USGS), the geophysics community (SCIGN/SCEC2), and the private sector (RBF Consulting). The project will leverage considerable funding, resources, and R&D from SCIGN, CSRC and two NSF-funded IT projects at UCSD and SDSU: RoadNet (Real-Time Observatories, Applications and Data Management Network) and the High Performance Wireless Research and Education Network (HPWREN). These two projects are funded to develop both the wireless networks and the integrated, seamless, and transparent information management system that will deliver seismic, geodetic, oceanographic, hydrological, ecological, and physical data to a variety of end users in real-time in the San Diego region. CSRC is interested in providing users access to real-time, accurate GPS data for a wide variety of applications including RTK surveying/GIS and positioning of moving platforms such as aircraft and emergency vehicles. SCIGN is interested in upgrading sites to high-frequency real-time operations for rapid earthquake response and GPS seismology. The successful outcome of the project will allow the implementation of similar systems elsewhere, particularly in plate boundary zones with significant populations and civilian infrastructure. CSRC would like to deploy the GPS/Seismic System in other parts of California, in particular San Diego, Los Angeles County and the San Francisco Bay Area.
Bock, Yehuda↗