ETTC'2003 - SEE

decreases near to zero, then PDOP is very large. If there is an air-station, VDOP will be less than 10
when the target below 1km.
3
4
2
3
1
4
Y
Y
1
Target track
2
X
Target track
Fig 2. 4-stations system
X
Fig 3. rearranged 4-stations system
Fig.2 and fig.3 show that by rearranging the ground stations the locating accuracy can be improved
greatly.
CONCLUSION
The ground station synchronization is the major error source in 3∆t passive locating system. The high
precision time synchronization among the ground stations is the key technology in 3∆t system. Using
the GPS common-view technology in the existing PPK telemetry system, the 3∆t passive locating
system used to measure the track and the point of fall of the reentry vehicle is feasible. If the accuracy
of the ground stations coordinates is very high, the system range error is about 10m. When the PDOP is
about 2 to 8, the location error of 3∆t passive locating system is about 20m to 80m.
REFERENCES
1. Mingsun Xie, “The technology of the reentry telemetry system”, National Defence
Industry Press, 1992
2. Lewandowski, W., Thomas, C “GPS time transfer”, Proceedings of the IEEE, VOL.79,
NO.7, JULY 1991
3. Zhongkang Sun, “Active and Passive locating technology based on one or more bases”,
National Defence Industry Press, 1996