Pre-Phase A Report - Lisa - Nasa

124 Chapter 5 Payload Design
the payload thermal shield. This too is 20 mm in diameter, 3 mm wall thickness. Across
the top of the Y-strut is a cross-member of the same dimensions.
Due to the limited mounting area on the plate, and to the height restriction imposed on
components by the presence of the Y-tube arms above, only three laser control electronics
units measuring 200 mm×200 mm×100 mm are accommodated (rather than the original
four). The redundancy provided by only three units should be acceptable, but it is likely
that the dimensions of the boxes can be reduced, thus allowing all four.
5.3 Structural design – Future work
Further improvements to the payload structure may be obtained by reassessing the design
of the radiator plate (the cause of modal vibrations just above 60 Hz), and in particular its
attachment to the underside of the payload. Moving the lasers and associated components
to a radiator connected to the spacecraft structure would increase the modal frequencies
of the payload, and reduce the loads induced in the payload structure. It would also
increase their separation from the proof masses, and hence reduce their influence on the
gravitational potentials within the instrument. This is currently dominated by the close
proximity of the lasers and control units to the proof masses.
In addition, the launch-lock concept and telescope mounting structure must be developed
in more detail.
3-3-1999 9:33 Corrected version 2.08