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Shi et al. Satell Navig (2021) 2:5 Page 12 of 13

SSTO

Doppler shift (kHz) Height

12-28 T00 12-28 T02 12-28 T04 12-28 T06 12-28 T08 12-28 T10 12-28 T12
Time
SSTO

Doppler shift (kHz) Height

12-28 T11 12-28 T13 12-28 T15 12-28 T17 12-28 T29 12-28 T21 12-28 T22:31
Time

GEO at 0°

Doppler shift (kHz) Height

Time
Fig. 13 The Doppler shift during the diferent process

to BDS GEO/IGSO satellites. Compared with GEO at Doppler shift decreases to within 25 kHz. In order to
125°, although SSTO is difcult to obtain enough satel- reduce the signal acquisition time caused by large Dop-
lite signals for position calculation at high altitude, BDS pler shift, the receiver should store the Doppler value
GEO/IGSO satellites can still improve its overall position estimated in advance. For the spacecraft in GEO, the
accuracy. Doppler shift is less than 6 kHz, except for some cases
reaching 8 kHz.
Doppler shift
As shown in Fig. 13, the spacecraft in SSTO can obtain
up to 50 kHz Doppler shift because of its high speed
(10.5 km/s) at low altitude. As the altitude rises, the