Interferometry for the LISA technology package (LTP) aboard SMART-2

The interferometer of the LISA technology package (LTP) on SMART-2 is needed to verify the performance of the gravitational sensors by monitoring the distance between two test masses with a noise level of 10 pm Hz-1/2 between 3 mHz and 30 mHz. It must continuously track the motion of the test mass distance while that distance changes by many (mu)m with a speed of up to 20 (mu)m s-1, without losing track of the sign of the motion and without exerting any influence on the test masses that might lead to a motion above that level. As a result of a detailed comparison study, a heterodyne Mach-Zehnder interferometer was selected as the baseline for the SMART-2 mission. Its design and expected performance are described in this paper.