  The basic constituent of many space-borne gravitational missions, in
particular for interferometric gravitational waves detectors, is the so-called
link made out of a satellite sending an electromagnetic beam to a second
satellite. We illustrate how, by measuring the time derivative of the frequency
of the received beam, the link behaves as a differential, time-delayed
dynamometer in which the effect of gravity is exactly equivalent to an
effective differential force applied to the two satellites. We also show that
this differential force gives an integrated measurement of curvature along the
beam. Finally, we discuss how this approach can be implemented to benefit the
data analysis of gravitational wave detectors.
