The interferometer of the LISA mission is realized with V-formations of drag-free spacecraft in heliocentric orbit. Each spacecraft will have at its centre a cubic proof mass made in gold-platinum alloy, that defines one end of the 5 x 10(6) ion interferometer arms. These masses are also those of the inertial reference sensors used for the drag compensation control of the satellites. The goal of the LISA sensor is to obtain a proof mass free of any parasitic forces, at a level of 10(-15) m s(-2) Hz(-1/2) in the very low frequency domain from 10(-4) Hz up to several 10(-3) Hz. Furthermore, the compensation of the satellite drag must limit its relative motion to less than 10(-9) mHz(-1/2), thus reducing the disturbances that may be induced as variations of the satellite self-gravity effects. The sensor proposed by ONERA is derived from the space electrostatic accelerometer GRADIO and ASTRE, the last one hew in Spacelab during a shuttle mission in June 1996. The challenge of the LISA inertial sensor is to exploit the existing concept and technologies with the best care in order to preserve the capacitive sensor resolution while limiting to a minimum the disturbing electrical effects and measurement backactions. The non-direct demonstration of the expected flight performances of such a sensor should be considered in detail in the future.
