the grace mission has substantiated the low–low satellite-to-satellite tracking (ll-sst) concept. the ll-sst configuration can be combined with the previously realized high–low sst concept in the champ mission to provide a much higher accuracy. the line of sight (los) acceleration difference between the grace satellite pair is the most frequently used observable for mapping the global gravity f...

gravity recovery and climate experiment (grace) satellite gravimetry mission launched in march 2002 based on its twin gravimetric satellites makes application of both high-low (hl) and law-low (ll) gravimetric techniques possible. the ll is based on satellite-to-satellite tracking (sst) via the one way two frequencies k-band-ranging between the two grace satellites. as a result of combination o...

the recent dedicated satellite gravimetry missions have provided huge amount of high quality gravity data with global coverage. from computational point of view, estimation of the unknown gravity field parameters is a highly demanding task due to the sheer number of observations and the unknown coefficients. different computational schemes have been proposed to tackle the problem. since the ear...

one of the most valuable and important application of artificial satellites in geodetic sciences is recovery of the earth's gravity field. orbits of satellites either gravimetric or nongravimetric are analyzed to improve the earth's gravity field. gravimetric satellites are launched at low altitudes to observe gravity field in more detail. grace twin satellites are the second spacecra...

Navigation using GPS generally requires that the user track four satellites to resolve his 3-D spatial position and time bias. There are several reasons why it is desirable to navigate while tracking only three satellites: -The proposed 18 satellite GPS constellation will exhibit substantial periods of poor four satellite geometry over large geographic areas several times a day. -Failure of a G...

The Silicon Tracker/Converter of the Gamma-ray Large Area Space Telescope (GLAST) will have an active area of 80 m2, representing one of the largest planned applications of the silicon-strip detector technology. The large number of channels (1.3 million) to read out, together with the requirement that the tracker provide the trigger to the data acquisition, force the readout electronics to be o...