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Impact of Eccentricity on East-West Stationkeeping for the GPS Class of Orbits
A strong relationship exists between eccentricity and the potential for an orbit with a mean motion commensurability to the Earth's rotation rate to be chaotic.
Spacecraft Autonomous navigation for Earth Ground Track Repeat Orbits Using GPS
This paper describes a simple empirical stategy for computing manuever times and magnitudes autonomously for Earth orbiting spacecraft with a ground track repeat requirement.
Preliminary TOPEX/Poseidon SLR and GPS Station Coordinate Calibration
TOPEX/Poseidon(T/P) is a joint altimetric mission of U.S. NASA and French CNES design launched August 10, 1992. There are a variety of tracking systems on T/P for both operational and precise orbit determination.
Atmospheric Profiles from Radio Occultation Measurements of GPS Satellites
Atmospheric profiles can be retrieved with techniques utilizing measurements of the propagation delay of signals from Global Positioning System satellites observed by one or more receivers in low earth orbit.
VIGIL--A GPS Based Target-Tracking System
The VIGILANTE project is a planned vision system capable of tracking and recognizing targets in real time, on a small airborne platform.
microGPS: On-orbit Demonstration of a New Approach to GPS to Space Applications
In February 1998 Student Nitric Oxide Explorer (SNOE) was successfully launched and began scientific observations.
Predicting GPS Fidelity in Heavily Forested Areas
There is a compelling need to advance the safety of low altitude flight in forested areas. Signal scattering by trees can interfere with GNSS signal reception and can cause navigation loss within and adjacent to woodlands. An estimate of the signal loss vs. foliage depth is needed to quantify navigational degradation by trees at low altitudes. A previous report described a method which attempts to quantify satellite signal degradation caused by foliage by comparing carrier-to-noise ratio (C/N0) to foliage depth along geometric rays cast from the receiver location to the orbital position of GNSS satellites through a 3D matrix of terrain data. A characteristic curve of attenuation vs. foliage depth was found for both L1 and L2 signals at a single forested site. The current study replicates this result at three additional sites, describes refinements to the method, and explores inherent uncertainties that arise from radiofrequency fading and from receiver limitations for weak signals. For the sites surveyed, 60% and 90% of navigational signal is lost at 10m and 20m of foliage depth, respectively. Since this technique uses low-cost hardware and readily available data collection software, it can allow aviators to estimate GNSS position fidelity in flight ranges near trees.