3,251 research outputs found
Autonomous satellite orbit determination during the development phases of the global positioning system
An onboard navigation system was developed to aid the design and evaluation of algorithms used in autonomous satellite navigation with Global Positioning System (GPS) data. The performance of the algorithms designed for a GPS Receiver/Processor Assembly (R/PA) intended for LANDSAT-D was investigated during the development phases of the GPS (four to six satellites in the constellation). This evaluation emphasized the effects on the orbit determination accuracy of the expected user clock errors, GPS satellite visibility, force model approximations, and state and covariance propagation approximations. Results are presented giving the sensitivity of orbit determination accuracy to these constraints
Eclipse radius measurements
Methods for predicting the path edges and reducing observations of total solar eclipses for determining variations of the solar radius are described. Analyzed observations of the 1925 January eclipse show a 0.7 (arc second) decrease in the solar radius during the past fifty years
Mathematical specifications of the Onboard Navigation Package (ONPAC) simulator (revision 1)
The mathematical theory of the computational algorithms employed in the onboard navigation package system is described. This system, which simulates an onboard navigation processor, was developed to aid in the design and evaluation of onboard navigation software. The mathematical formulations presented include the factorized UDU(T) form of the extended Kalman filter, the equations of motion of the user satellite, the user clock equations, the observation equations and their partial derivatives, the coodinate transformations, and the matrix decomposition algorithms
Alien Registration- Dunham, Charles B. (Limestone, Aroostook County)
https://digitalmaine.com/alien_docs/35136/thumbnail.jp
Cold electron beams from cryo-cooled, alkali antimonide photocathodes
In this letter we report on the generation of cold electron beams using a
Cs3Sb photocathode grown by co-deposition of Sb and Cs. By cooling the
photocathode to 90 K we demonstrate a significant reduction in the mean
transverse energy validating the long standing speculation that the lattice
temperature contribution limits the mean transverse energy or thermal emittance
near the photoemission threshold, opening new frontiers in generating
ultra-bright beams. At 90 K, we achieve a record low thermal emittance of 0.2
m (rms) per mm of laser spot diameter from an ultrafast (sub-picosecond)
photocathode with quantum efficiency greater than using a
visible laser wavelength of 690 nm
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