Engineering topics

Vanmelle, M. J.

Publications and source records attributed to Vanmelle, M. J..

4 records

NASA NTRS1994

Cesium and rubidium frequency standards status and performance on the GPS program

This paper is an update of the on-orbit operational performance of the frequency standards on the Block I GPS 8 to 11 Navstar satellites, the Block II GPS 13 to 21 Navstar satellites and the Block IIA GPS 22 to 40 Navstar satellites. A brief history of the frequency standards depicting improvements incorporated in the GPS Program with corresponding results will be presented. The frequency standards configurations from the start to the present, including the various Block IIA clock configurations will be discussed. Topics such as clock observations and long term trending analysis which could enhance on-orbit performance analysis will be covered.

Vanmelle, M. J.↗

NASA NTRS1977

Temperature reference for microwave radiometer calibration

New temperature reference avoids need to physically remove antenna and replace it with calibrating termination. Device is piece of porous microwave absorber fitted with cap of nonporous plastic foam. Absorbent material is soaked with cryogen. Procedure ensures that temperature at which microwaves are absorbed is exactly that of cryogen.

Love, A. W.↗

NASA NTRS1975

Nondestructive measurement of capillary tube internal diameter

Technique provides nondestructive method of making quick, accurate determination by measuring electrical resistance of capillary tube when it is filled with electrolyte of known conductivity. Apparatus consists of conductivity cell and equipment for measuring resistance and for monitoring and controlling temperature.

Ho, W. W.↗

NASA NTRS1974

Measurements of the dielectric properties of sea water at 1.43 GHz

Salinity and temperature of water surfaces of estuaries and bay regions are determined to accuracies of 1 ppt salinity and 0.3 kelvin surface temperature. L-band and S-band radiometers are used in combination as brightness temperature detectors. The determination of the brightness temperature versus salinity, with the water surface temperature as a parameter for 1.4 GHz, is performed with a capillary tube inserted into a resonance cavity. Detailed analysis of the results indicates that the measured values are accurate to better than 0.2 percent in the electric property epsilon' and 0.4 percent in epsilon''. The calculated brightness temperature as a function of temperature and salinity is better than 0.2 kelvin. Thus it is possible to reduce the measured data obtained with the two-frequency radiometer system with 1 ppt accuracy to values in the salinity range 5 to 40 ppt.

Ho, W. W.↗