characters per second is used for coordinated simultaneous  view time transfer, the

average of the values listed in Table 11 2 can be expected with distances of hundreds

of kilometers between two receivers.

Compared with the uncoordinated simultaneous  view technique described in paragraph

11.4.4, coordinated time transfers with USNO can provide not only more accurate

relative timing in the shorter term, but also better absolute timing and better long  term

stability for setting and rating high  quality clocks.

Figure 11 5.  Coordinated Time Transfer  using GPS

11.5  SATELLITE ORBIT DETERMINATION USING GPS

Precise satellite orbit determination can be done using GPS receivers on a satellite. 

These spaceborne GPS receivers must be specifically qualified for space use, because

of the high temperature extremes and radiation levels.  The space applications would

be limited to low earth orbit satellites in order to receive adequate coverage from the

half geosynchronous orbit of the GPS constellation.  In addition to orbit determination,

the spaceborne GPS receivers could be used to determine the spacecraft attitude. 

Preliminary studies and demonstrations have shown that using GPS for autonomous

spacecraft position and attitude determination can be done cheaper and more

accurately than some of the current methods.

11 15