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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Code and codeless ionospheric measurements with NASA's Rogue GPS Receiver

The NASA/JPL Rogue Receiver is an 8-satellite, non-multiplexed, highly digital global positioning system (GPS) receiver that can obtain dual frequency data either with or without knowledge of the P-code. In addition to its applications for high accuracy geodesy and orbit determination, the Rogue uses GPS satellite signals to measure the total electron content (TEC) of the ionosphere along the lines of sight from the receiver to the satellites. These measurements are used by JPL's Deep Space Network (DSN) for calibrating radiometric data. This paper will discuss Rogue TEC measurements, emphasizing the advantages of a receiver that can use the P-code, when available, but can also obtain reliable dual frequency data when the code is encrypted.

Srinivasan, Jeff M.↗
NASA NTRS1988

Functional description of signal processing in the Rogue GPS receiver

Over the past year, two Rogue GPS prototype receivers have been assembled and successfully subjected to a variety of laboratory and field tests. A functional description is presented of signal processing in the Rogue receiver, tracing the signal from RF input to the output values of group delay, phase, and data bits. The receiver can track up to eight satellites, without time multiplexing among satellites or channels, simultaneously measuring both group delay and phase for each of three channels (L1-C/A, L1-P, L2-P). The Rogue signal processing described requires generation of the code for all three channels. Receiver functional design, which emphasized accuracy, reliability, flexibility, and dynamic capability, is summarized. A detailed functional description of signal processing is presented, including C/A-channel and P-channel processing, carrier-aided averaging of group delays, checks for cycle slips, acquistion, and distinctive features.

Thomas, J. B.↗
NASA NTRS1996

Performance Assessment of Two GPS Receivers on Space Shuttle

Space Shuttle STS-69 was launched on September 7, 1995, carrying the Wake Shield Facility (WSF-02) among its payloads. The mission included two GPS receivers: a Collins 3M receiver onboard the Endeavour and an Osborne flight TurboRogue, known as the TurboStar, onboard the WSF-02. Two of the WSF-02 GPS Experiment objectives were to: (1) assess the ability to use GPS in a relative satellite positioning mode using the receivers on Endeavour and WSF-02; and (2) assess the performance of the receivers to support high precision orbit determination at the 400 km altitude. Three ground tests of the receivers were conducted in order to characterize the respective receivers. The analysis of the tests utilized the Double Differencing technique. A similar test in orbit was conducted during STS-69 while the WSF-02 was held by the Endeavour robot arm for a one hour period. In these tests, biases were observed in the double difference pseudorange measurements, implying that biases up to 140 m exist which do not cancel in double differencing. These biases appear to exist in the Collins receiver, but their effect can be mitigated by including measurement bias parameters to accommodate them in an estimation process. An additional test was conducted in which the orbit of the combined Endeavour/WSF-02 was determined independently with each receiver. These one hour arcs were based on forming double differences with 13 TurboRogue receivers in the global IGS network and estimating pseudorange biases for the Collins. Various analyses suggest the TurboStar overall orbit accuracy is about one to two meters for this period, based on double differenced phase residuals of 34 cm. These residuals indicate the level of unmodeled forces on Endeavour produced by gravitational and nongravitational effects. The rms differences between the two independently determined orbits are better than 10 meters, thereby demonstrating the accuracy of the Collins-determined orbit at this level as well as the accuracy of the relative positioning using these two receivers.

Schroeder, Christine A.↗
NASA NTRS2001

Flight Performance Evaluation of Three GPS Receivers for Sounding Rocket Tracking

In preparation for the European Space Agency Maxus-4 mission, a sounding rocket test flight was carried out at Esrange,, near Kiruna, Sweden on February 19, 2001 to validate existing ground facilities and range safety installations. Due to the absence of a dedicated scientific payload, the flight offered the opportunity to test multiple GPS receivers and assess their performance for the tracking of sounding rockets. The receivers included an Ashtech G12 HDMA receiver, a BAE (Canadian Marconi) Allstar receiver and a Mitel Orion receiver. All of them provide CIA code tracking on the L1 frequency to determine the user position and make use of Doppler measurements to derive the instantaneous velocity. Among the receivers, the G12 has been optimized for use under highly dynamic conditions and has earlier been flown successfully on NASA sounding rockets [Bull, ION-GPS-2000]. The Allstar is representative of common single frequency receivers for terrestrial applications and received no particular modification, except for the disabling of the common altitude and velocity constraints that would otherwise inhibit its use for space application. The Orion receiver, finally, employs the same Mitel chipset as the Allstar, but has received various firmware modifications by DLR to safeguard it against signal losses and improve its tracking performance [Montenbruck et al., ION-GPS-2000]. While the two NASA receivers were driven by a common wrap-around antenna, the DLR experiment made use of a switchable antenna system comprising a helical antenna in the tip of the rocket and two blade antennas attached to the body of the vehicle. During the boost a peak acceleration of roughly 17g's was achieved which resulted in a velocity of about 1100 m/s at the end of the burn. At apogee, the rocket reached a maximum altitude of over 80 km. A detailed analysis of the attained flight data will be given in the paper together with a evaluation of different receiver designs and antenna concepts.

Bull, Barton↗
NASA NTRS1990

Application of a novel multi-stage signal parameter estimator to high dynamic GPS receivers

The performance of a novel multistage estimator when applied to the estimation of the position, velocity, and acceleration of high dynamic Global Positioning System (GPS) receivers is discussed. For the present application, a two-stage specialization of the more general estimation scheme is considered, wherein the first-stage algorithm is selected to be a modified least-squares algorithm operating upon the differential signal model and referred to as differential least-squares (DLS) and the second stage is simply an extended Kalman filter (EKF). In terms of the threshold on received carrier power-to-noise power spectral density ratio (CNR), when compared to the single-stage EKF algorithm, the DLS-EKF algorithm is about 1.5-2.0 dB better in terms of threshold and outperforms the crossproduct AFC (automatic frequency control) loop by 2-5 dB. For the case when data modulation is present, the proposed scheme provides an improvement of about 6 dB in terms of CNR compared to an earlier approximate MLE (maximum likelihood estimation) scheme. There are also very significant improvements in terms of other performance measures.

Kumar, R.↗
NASA NTRS1995

Using Unmanned Aerial Vehicles and GPS Receivers

It is proposed that a small fleet of unmanned aerial vehicles (UAVs) be used over a period of years to monitor the rise of pressure surfaces caused by the hypothesized rise in average temperature of the troposphere due to global warming. Global Positioning Satellite System (GPS) receivers would be used for the precise tracking required.

global warming UAV unmanned aerial vehicles GPS↗
NASA NTRS2018

Using GPS Receivers 1PPS Output to Verify Time Stamp Accuracy and Measure Propagation Delay

A simple Pulse Overlay (PO) circuit using a logic OR gate was developed to overlay a precise leading edge 1 Pulse Per Second (1PPS) time reference marker from a GPS receiver onto a Non-Return -to- Zero-Level (NRZ-L) Pulse Code Modulation (PCM) telemetry data stream to validate time stamp accuracy and measure propagation delay (PD) in telemetry equipment.

telemetry↗
NASA NTRS2006

Orbiting GPS Receiver Modified to Track New L2C Signal

The L2C signal is a great step forward for civil applications of GPS, enabling high-accuracy dual-frequency measurements. Engineers from the Jet Propulsion Laboratory and ITT teamed to reprogram FPGA firmware and add tracking software on an orbiting receiver to track the new GPS L2C signal from SAC-C. SAC-C is an Argentinean science satellite and was launched in November 2000 with a BlackJack GPS receiver. This is a dual-frequency digital receiver with 48 tracking channels and four antennas. On SAC-C, it provides precise orbits, atmospheric occultation data, tests of GPS surface reflections, and serves as an orbiting test bed for new GPS development such as the L2C tracking reported here.

GPS receiver↗
NASA NTRS2002

Flight Performance Evaluation of Three GPS Receivers for Sounding Rocket Tracking

In preparation for the European Space Agency Maxus-4 mission, a sounding rocket test flight was carried out at Esrange, near Kiruna, Sweden on February 19, 2001 to validate existing ground facilities and range safety installations. Due to the absence of a dedicated scientific payload, the flight offered the opportunity to test multiple GPS receivers and assess their performance for the tracking of sounding rockets. The receivers included an Ashtech G12 HDMA receiver, a BAE (Canadian Marconi) Allstar receiver and a Mitel Orion receiver. All of them provide C/A code tracking on the L1 frequency to determine the user position and make use of Doppler measurements to derive the instantaneous velocity. Among the receivers, the G12 has been optimized for use under highly dynamic conditions and has earlier been flown successfully on NASA sounding rockets. The Allstar is representative of common single frequency receivers for terrestrial applications and received no particular modification, except for the disabling of the common altitude and velocity constraints that would otherwise inhibit its use for space application. The Orion receiver, finally, employs the same Mitel chipset as the Allstar, but has received various firmware modifications by DLR to safeguard it against signal losses and improve its tracking performance. While the two NASA receivers were driven by a common wrap-around antenna, the DLR experiment made use of a switchable antenna system comprising a helical antenna in the tip of the rocket and two blade antennas attached to the body of the vehicle. During the boost a peak acceleration of roughly l7g's was achieved which resulted in a velocity of about 1100 m/s at the end of the burn. At apogee, the rocket reached an altitude of over 80 km. A detailed analysis of the attained flight data is given together with a evaluation of different receiver designs and antenna concepts.

Bull, Barton↗
NASA NTRS1989

Chip Advancer For GPS Receiver

Instrument errors made negligible. For each integration interval, both delay and rate of change of delay initialized to small fraction of chip - for example, to order of 10 to the negative 7th power - thereby making feedback control and extraction of delay highly accurate and flexible. With appropriate selection of sampling rate relative to chip rate, commensurability errors reduced to extremely small levels. In Global Positioning System (GPS) receiver, pseudorandom code sequence generated by simple digital logic incorporating effects of time, delay, and rate of change of delay. Flexibility in starting time and sum interval very useful in aligning correlation interval with beginnings and endings of data bits.

Meehan, Thomas K.↗
NASA NTRS1988

Efficient detection and signal parameter estimation with applications to high dynamic GPS receivers

A novel technique for simultaneously detecting data and estimating the parameters of a received carrier signal phase modulated by unknown data and experiencing very high Doppler, Doppler rate, etc. is discussed. Such a situation arises, for example, in the case of Global Positioning Systems (DPS) where the signal parameters are directly related to the position, velocity and acceleration of the GPS receiver. The proposed scheme is based upon first estimating the received signal local (data dependent) parameters over two consecutive bit periods, followed by the detection of a possible jump in these parameters. The presence of a detected jump signifies a data transition which is then removed from the received signal. This effectively demodulated signal is then processed to provide the estimates of global (data independent) parameters of the signal related to the position, velocity, etc. of the receiver. One of the key features of the proposed algorithm is the introduction of two different schemes which can provide an improvement of up to 3 dB over the conventional implementation of Kalman filter as applied to phase and frequency estimation, under low to medium signal-to-noise ratio conditions.

Kumar, R.↗
NASA NTRS2004

Relative Attitude Determination of Earth Orbiting Formations Using GPS Receivers

Satellite formation missions require the precise determination of both the position and attitude of multiple vehicles to achieve the desired objectives. In order to support the mission requirements for these applications, it is necessary to develop techniques for representing and controlling the attitude of formations of vehicles. A generalized method for representing the attitude of a formation of vehicles has been developed. The representation may be applied to both absolute and relative formation attitude control problems. The technique is able to accommodate formations of arbitrarily large number of vehicles. To demonstrate the formation attitude problem, the method is applied to the attitude determination of a simple leader-follower along-track orbit formation. A multiplicative extended Kalman filter is employed to estimate vehicle attitude. In a simulation study using GPS receivers as the attitude sensors, the relative attitude between vehicles in the formation is determined 3 times more accurately than the absolute attitude.

Lightsey, E. Glenn↗
NASA NTRS1989

Counterrotator And Correlator For GPS Receivers

Accurate, all-digital, high-speed processor comprising correlator and down-converter developed for receivers in Global Positioning System (GPS). Processor reduces roundoff and commensurability errors to extremely small values. Use of digital chip and phase advancers provides outstanding control and accuracy in phase and feedback. Great flexibility imparted by provision for arbitrary starting time and integration length. Minimum-bit design requires minimum number of logical elements, thereby reducing size, power, and cost.

Thomas, J. Brooks↗
NASA NTRS1989

Digital Signal Processor For GPS Receivers

Three innovative components combined to produce all-digital signal processor with superior characteristics: outstanding accuracy, high-dynamics tracking, versatile integration times, lower loss-of-lock signal strengths, and infrequent cycle slips. Three components are digital chip advancer, digital carrier downconverter and code correlator, and digital tracking processor. All-digital signal processor intended for use in receivers of Global Positioning System (GPS) for geodesy, geodynamics, high-dynamics tracking, and ionospheric calibration.

Thomas, J. B.↗
NASA NTRS2000

Pre-Launch Testing of GPS Receivers for Geodetic Space Missions

The methodology used and the results obtained in the pre-flight testing of the Blackjack Global Positioning System (GPS) space receiver for the Vegetation Canopy Lidar Mission (VCL) and the Ice, Cloud, and Land Elevation Satellite (ICESat) spacecraft is described. Both real and simulated signals were used to: (1) assess the accuracy and coverage of the navigation solutions, (2) assess the accuracy and stability of the 1-PPS timing signal, (3) assess the precision of the carrier phase observable, and (4) measure the cold-start time to first fix. In addition, an anechoic chamber was used to measure the antenna phase centers with millimeter-level precision. While the test results have generally been excellent and are discussed in this paper, emphasis is placed on describing the test methodology. It is anticipated that future geodetic satellite missions using GPS for navigation, timing, and precise orbit determination (POD) can employ the same tests for pre-launch performance assessment of their particular receiver.

Davis, George↗
NASA NTRS1989

Digital signal processor and processing method for GPS receivers

A digital signal processor and processing method therefor for use in receivers of the NAVSTAR/GLOBAL POSITIONING SYSTEM (GPS) employs a digital carrier down-converter, digital code correlator and digital tracking processor. The digital carrier down-converter and code correlator consists of an all-digital, minimum bit implementation that utilizes digital chip and phase advancers, providing exceptional control and accuracy in feedback phase and in feedback delay. Roundoff and commensurability errors can be reduced to extremely small values (e.g., less than 100 nanochips and 100 nanocycles roundoff errors and 0.1 millichip and 1 millicycle commensurability errors). The digital tracking processor bases the fast feedback for phase and for group delay in the C/A, P.sub.1, and P.sub.2 channels on the L.sub.1 C/A carrier phase thereby maintaining lock at lower signal-to-noise ratios, reducing errors in feedback delays, reducing the frequency of cycle slips and in some cases obviating the need for quadrature processing in the P channels. Simple and reliable methods are employed for data bit synchronization, data bit removal and cycle counting. Improved precision in averaged output delay values is provided by carrier-aided data-compression techniques. The signal processor employs purely digital operations in the sense that exactly the same carrier phase and group delay measurements are obtained, to the last decimal place, every time the same sampled data (i.e., exactly the same bits) are processed.

Thomas, Jr., Jess B.↗