  Two way ranging data for spacecraft tracking of China's first Martian mission
Tianwen-I is analysed. Shortly before the spacecraft entered the Mars parking
orbit, the two way coherent microwave link between the spacecraft and the Earth
resembles a long arm gravitational wave interferometer, with both the
spacecraft and the Earth regarded as in an approximate free falling state. By
carefully selecting and analysing data segments of the time series of the two
way ranging data during this time span, a parametric statistical model is built
for the data segments and an upper limit for the stochastic gravitational waves
background (SGWB) is then estimated within the frequency window 0.1Hz to 0.1
mHz. The upper bound improves considerably on those obtained before. In
particular, around the deci-Hz band, there is a three orders improvement on the
bound obtained previously by the two way ranging data of the Chang e 3 mission.
Scientific applications of the upper bound is then considered and a weak upper
bound is worked out for axions which is a promising candidate for ultra light
dark matter.
