At installation time, the beam emitted by the UTM injection system needs to be aligned with the UTM inner axis. The accuracy of this alignment is that needed to keep the beam aligned with the pupil image independent of the inner axis rotation angle: this amounts to a precision of about 0.5mm in shear and 0.2milliradians of tilt. The laxness of this constraint means that this alignment needs to be done only once: thermal drifts in alignment, whether due to the motion of the Nasmyth table itself or of components on the table, are not expected to exceed this magnitude during the course of operation (of course, it would not harm to check this from time to time). A number of techniques can be used for this initial alignment, but manual alignment using a theodolite inserted in the UT output beam looking at both the telescope pupil and the injected light is one option.

The initial coarse alignment of a beam train (requirement 1) takes place using the BCA primary fiducial as before (there exist additional options to use the UTM light injector in addition to or instead of the primary fiducial for this task, but for brevity discussion of these options will be left to a later date).

The start-of-night alignment (requirement 2) is changed from the original scheme. Instead of using the primary fiducial, the UTM light injector is switched on. The location of the spot seen on the FTT camera is set to be the fiducial point to which the FTT servoes starlight; as a result all subsequent starlight beams will have the same tilt as the injected beam. At the same time the shear of the injected beam is measured using BEASST. The tilts of M4 and M5 are adjusted so that the measured shear coincides with a fiducial point on BEASST and does not change when the DL is moved backwards and forwards: this condition means that the injected beam is aligned with the DL axis.

At this point, the primary fiducial can be switched on and the downstream beam aligned with the UTM injected beam, using BEASST to compare the tilt and shear of the two beams. Further alignment of the fringe tracker and piston terms (requirements 4 and 5) can then proceed as in the original system.

To maintain alignment of the optical train in the presence of thermal drifts during the night (requirement 3), BEASST can either be used in its original mode with starlight, or the UTM alignment source can be switched on while slewing between stars (or any other convenient time) and used to check for thermal drift in any of the optics in the beam relay optical train. Any relative drift in tilt of the UTM alignment source with respect to the FTT camera is compensated for by resetting the FTT fiducial point using the spot seen on the FTT camera.