UPPER LIMITS ON THE COSMOLOGICAL GRAVITATIONAL-WAVE BACKGROUND AND MASER CLOCKS IN-SPACE

We consider the possibility of detecting gravitational waves through t he measurement of a time varying phase shift using a hydrogen maser do ck on a satellite. Such measurements enable us to put interesting uppe r limits on the contribution of the gravitational-wave background to t he dimensionless density of the Universe. The requirements on residual accelerations and the sensitivity of an accelerometer on the spacecra ft are shown to be realistic and could be achieved using the accelerom eter technology developed by ONERA for the ARISTOTELES mission. Such a n experiment placing upper limits on the cosmological gravitational wa ve background could be conducted using the proposed Russian satellite ''Millimetron''.