the gravity recovery and climate experiment (grace), twin satellites launched in march 2002, are making detailed measurements of the earth's gravity field. it will yield discoveries about gravity and the earth's natural systems. different sensors and instruments have been placed in the grace satellites to fulfill the primary scientific objective of the mission in mapping the earth’s g...

the space environment consists mainly of high-energy charged particles, such as protons, electrons and heavy ions. they are originating from several sources including galactic cosmic radiation, solar flares and van allen belts. high energy electromagnetic radiation and neutrons have also been measured on spacecraft. although shielding can reduce the effect of space radiation it cannot be elimin...

This study focuses on the development of a precise attitude control system for small satellites. In general, conventional methods used for attitude control in standard-sized satellites are not applicable to small satellites because of constraints of power consumption, space requirements, and mass. In addition, small satellites are more greatly affected than standard-sized satellites by attitude...

Geometric Dilution of Precision (GDOP) is a coefficient for constellations of Global Positioning System (GPS) satellites. These satellites are organized geometrically. Traditionally, GPS GDOP computation is based on the inversion matrix with complicated measurement equations. A new strategy for calculation of GPS GDOP is construction of time series problem; it employs machine learning and artif...

Plant viruses often contain parasites of their own, referred to as satellites. Satellite RNAs are dependent on their associated (helper) virus for both replication and encapsidation. Satellite RNAs vary from 194 to approximately 1,500 nucleotides (nt). The larger satellites (900 to 1,500 nt) contain open reading frames and express proteins in vitro and in vivo, whereas the smaller satellites (1...