FIGURE 3.2 Comparison of the sensitivity of LISA with that of ground-based interferometers such as LIGO for various potential sources. Because of its lower frequency range, LISA is sensitive to the coalescence of massive black holes. It also has the potential to survey the Milky Way for binary systems involving white dwarfs, neutron stars, and stellar mass black holes. Courtesy of W.Folkner, Jet Propulsion Laboratory, California Institute of Technology.

mission, to be flown in 2002, will provide a test at an acceleration level approximately 10⁵ times greater.

The controllers that will be used to make the spacecraft follow the reference mass also need demonstration. Several thruster designs exist that develop proportional ion thrust control at the micronewton force level. The key technical issues are lifetime and reliability.

The laser interferometry in LISA needs to operate at displacement sensitivities of 10⁻¹³ m, which is less sensitive by a factor of 10⁵ than the initial terrestrial interferometers. The technical challenge is to achieve the performance at low frequencies (10⁻¹ to 10⁻⁴ Hz).

The thruster and laser interferometry can be tested on the ground.