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

132 LISA: A proposed joint ESA–NASA gravitational-wave missionfrequencies of a few hundred hertz to 1 kHz. Also, the amplitude of the phasenoise at frequencies near 1 Hz and below will be large. To avoid aliasing thehigher frequency noise into the band of interest, below perhaps 3 Hz, it may bedesirable to make the phase measurements at a rate approaching a kilohertz, andthen filter the data in software. For low-frequency noise, it is planned to combineall the signals at a single spacecraft and perform the algorithm for correcting forlaser phase noise there. The resulting signals then can be compressed before beingsent to the ground.The number and amplitude of mechanical motions aboard the spacecraft arekept as small as possible to reduce gravitational attraction changes and excitationof vibrations. Roughly 30 cm diameter X-band antennae probably will be used tosend data down to 34 m Deep Space Network antennae on the ground, and willhave to be repointed about once a week. Step changes in the angle between theaxes of the two optical assemblies probably will be made at the same time withcoarse adjustment mechanisms, but smooth adjustments over roughly a range of5 arcmin are required between the steps. It is expected that offsets in the position,velocity, and dc acceleration of the test masses will have to be solved for at thetimes of the steps.The nominal mission lifetime after the antenna geometry is establishedprobably will be three years. However, there are no expendables required exceptfor the In or Cs fuel for the micronewton thrusters, and that will be made adequatefor a ten year or longer lifetime. Thus, a rolling three year approval periodhopefully can be established, provided that the antenna continues to operateproperly.10.2 Expected gravitational-wave results from LISA10.2.1 LISA sensitivity and galactic sourcesThe two types of noise sources for the LISA antenna have been discussedearlier. The one that dominates at frequencies below about 3 mHz is spuriousaccelerations of the test masses, and the level of error allocated for frequenciesf between 0.1 and 30 mHz is 3 × 10 −15 ms −2 /rtHz for each free mass sensor.Considering only two arms of the antenna for simplicity, and adding the errorsfrom the four sensors quadratically, the resulting noise level for the difference in(one-way) length of the two arms is(L2 − L1) = 1.520 × 10 −16 (1Hz/f ) 2 m/rtHz.This should be combined quadratically with the error allocation of 2 ×10 −11 m/rtHz for measuring the difference in the distances between the testmasses along the two arms.For low frequencies, where the wavelength is long compared with the armlength, the response of the antenna to a gravitational wave [24] can be given