(ed.). Gravitational waves (IOP, 2001)(422s).

128 LISA: A proposed joint ESA–NASA gravitational-wave missionFigure 10.7. Ultra-low expansion glass housing for the proof (test) mass in the earlyCAESAR design.test mass housing; electrical force on the charge on the test mass; Lorentzforce on the charged test mass from the fluctuating interplanetary magnetic field;residual gas impacts on the test mass; and fluctuating forces due to electrical fielddissipation in the test mass housing. These sources are each allocated an error of1 × 10 −15 ms −2 /rtHz.In view of the performance level desired for the LISA free mass sensors, it isplanned to have a technology demonstration flight for them at the earliest possibledate. Efforts to arrange for such a flight currently are under way both in Europeand the USA. Two sensors would be flown on a thermally isolated optical benchon a small spacecraft, with an interferometer to measure changes in the separationof the two test masses. To keep the rate of charging of the test masses comparablewith what it would be well away from the Earth, and to reduce the effect of theEarth’s gravity gradient, a perigee altitude of 10 000 km or higher is desired. Toreduce the cost, a tentative goal of demonstrating only 3 × 10 −14 ms −2 /rtHzperformance from 1–10 mHz currently is assumed. It is believed that cautious