  At present, there is a great worldwide interest in the development of
technologies that allow information about the X-ray emission from pulsating
cosmic sources to be used to obtain navigation solutions for deep-space
spacecraft. In this paper, we illustrate the technique for determining the
spatial position of a spacecraft based on the already existing data from the
RXTE X-ray space observatory. We show that the spacecraft position toward the
Crab pulsar can be determined using an X-ray detector with an effective area of
about 0.6 sq.m in the energy range 3-15 keV with an accuracy up to 730 m in a
signal integration time of 1000 s. Extending the energy range to 1 keV (the
efficiency of the RXTE/PCA spectrometer decreases dramatically at energies
below 3 keV) will allow a spacecraft position accuracy of 400-450 m to be
achieved at the same effective area and up to 300-350 m when using detectors
with an effective area of ~1 sq.m in the energy range 1-10 keV.
