The high mass X-ray binary pulsar 4U 1538-52 was observed between July 31 and August 7 , 2003 .
Using these observations , we determined new orbital epochs for both circular and elliptical orbit models .
The orbital epochs for both orbit solutions agreed with each other and yielded an orbital period derivative \dot { P } / P = ( 0.4 \pm 1.8 ) \times 10 ^ { -6 } yr ^ { -1 } .
This value is consistent with the earlier measurement of \dot { P } / P = ( 2.9 \pm 2.1 ) \times 10 ^ { -6 } yr ^ { -1 } at the 1 \sigma level and gives only an upper limit to the orbital period decay .
Our determination of the pulse frequency showed that the source spun up at an average rate of 2.76 \times 10 ^ { -14 } Hz sec ^ { -1 } between 1991 and 2003 .