The design of the Large Millimeter Telescope (LMT/GTM) relies on an active surface system for the primary
reflector in order to meet its surface accuracy specifications. Each of the 180 segments of the 50m diameter
primary surface is supported by four linear actuators, one for each corner. Currently, while awaiting completion
of the reflector panels needed to populate the outer portion of the surface, the precision reflecting surface is
limited to the inner three rings of segments, which provide a 32.5m diameter primary with 84 segments. The
interim active surface system must provide control for these segments long enough to allow completion of the
rest of the reflecting surface and procurement and installation of the final actuators.
During the LMT/GTM first light program in 2011, the interim active surface system of 336 actuators suffered
from a wide range of problems that prevented useful operation. Following extensive diagnostic testing in 2012, the
project implemented a substantial actuator improvement program in the first half of 2013, including mechanical
modifications and replacement of the control system electronics. Later, each actuator was characterized on
an external test bench, providing demonstration of actuator operation and readiness, as well as calibration
information to further improve absolute accuracy.
In this paper, we present results of the accuracy and repeatability of the refurbished actuators, as well as
results from the accelerated lifetime testing on site. The uniformity of the calibration coefficients is also presented
and discussed. The results demonstrate that the refurbished actuator units are sufficient for the needs of the
interim active surface system.