Engineering topics
Wu, S. C.
Publications and source records attributed to Wu, S. C..
Design and validation of a high-voltage levitation circuit for electrostatic accelerometers
A simple high-voltage circuit with a voltage range of 0 to 900 V and an open-loop bandwidth of 11 kHz is realized by using an operational amplifier and a MOSFET combination. The circuit is used for the levitation of a test mass of 71 g, suspended below the top-electrodes with a gap distance of 57 μm, so that the performance of an electrostatic accelerometer can be tested on the ground. The translation noise of the accelerometer, limited by seismic noise, is about 4 × 10{sup −8} m/s{sup 2}/Hz{sup 1/2} at 0.1 Hz, while the high-voltage coupling noise is one-order of magnitude lower.
Scientific applications of GNSS: could Galileo really make a difference
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GRACE level-1 data processing
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Expected performance of the NetLander geodesy experiment
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Constellation Design for a Mars-orbiting Satellite Communication
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Martian Geodesy from Viking, Pathfinder, and Netlander
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A Novel GPS-Based Sensor for Ocean Altimetry
A technique for a novel application of GPS signals to ocean altimetry is described. The entire Earth surface is divided into a triangular grid of points nearly-uniformly spaced.
Autonomous Formation Flyer (AFF) Sensor Technology Development
This paper proposes an implementation of AFF that borrows technology from the Global Positioning System (GPS), using measurements of both r-f carrier phase and a ranging code.
Demonstration of microGPS for Low Cost Orbit Determination
The capability of low-cost orbit determination with a microGPS space receiver for a low earth satellite, SNOE, is demonstrated using actual GPS data from the GPS/MET satellite.
A Prototype Real-Time Area Differential GPS System
In this paper we describe the system architecture, algorithms, and preliminary results from an operating prototype Wide Area Differential GPS (WADGPS) system spanning the continetal US (CONUS).
The Potential Use of GPS Signals as Ocean Altimetry Observables
This paper investigates a potential application of GPS signals for ocean altimetry. The altimetry information is derived from dual-frequency GPS signals reflected from the ocean surface and received at a low-altitude satellite.
A Prototype WADGPS System for Real Time Sub-Meter Positioning Worldwide
Many planned and proposed NASA science activities will benefit from precise real time positioning with wide area differential GPS (WADGPS). Future NASA users include orbital remote sensing instruments (altimeters, SARs, imagers) and a variety of airborne and Earth based investigations. Real time positioning requirements and goals range from a few meters to a few centimeters. Direct benefits will include the enabling of missions that are not now possible (such as precision remote sensing from the space shuttle and space station) and dramatic reduction of analysis costs for a diversity of current investigations.
First assessment of GPS-based reduced dynamic orbit determination on TOPEX/Poseidon
The reduced dynamic Global Positioning System (GPS) tracking technique has been applied for the first time as part of the GPS experiment on TOPEX/Poseidon. This technique employs local geometric position corrections to reduce orbit errors caused by the mismodeling of satellite forces. Results for a 29-day interval in early 1993 are evaluated through postfit residuals and formal errors, comparison with GPS and laser/DORIS dynamic solutions, comparisons on 6-hr overlaps of adjacent 30-hr data arcs, altimetry closure and crossover analysis. Reduced dynamic orbits yield slightly better crossover agreement than other techniques and appear to be accurate in altitude to about 3 cm RMS.
Automated Precision Orbit Determination for TOPEX/Poseidon with GPS
A highly automated GPS data processing system for the orbit determination of TOPEX/Poseidon is described. The orbit is recovered to an estimated accuracy of better than 4 cm in altitude, 6 cm crosstrack, and 11 cm down track. The RMS postfit residuals on the ionospherically calibrated carrier phase observable are less than 5 mm. The RMS difference over a 4.5-hour overlap period between two 30-hour data arcs is 1 cm in altitude, 5 cm cross track, and 4 cm down track. These results can be obtained within two days of onboard GPS data collection. Most of the data processing for a 30-hour arc of GPS data can be performed on a single workstation in less than 6 hours of CPU time. The estimation scenarios are explained, the automated data processing steps are described, and means to assess solution quality are discussed.
Geocenter location and variations in earth orientation using global positioning system measurements
We have studied the use of GPS ground and flight tracking data to measure short-period earth orientation variations and changes in geocenter location. Comparisons between GPS-estimated earth rotation variations and those calculated from ocean tide models suggest that observed subdaily variations in earth rotation are dominated by oceanic tidal effects. Our preliminary GPS estimates for geocenter location agree with an independent satellite laser ranging estimates to 10-15 cm. Covariance analysis predicts that temporal resolution of GPS estimates for earth orientation and geocenter improves significantly when data collected from low earth-orbiting satellites as well as from ground sites are combined. The low-earth GPS tracking data enhance the accuracy and resolution for measuring high-frequency global geodynamical signals over time scales less than 1 day.