  The Canada France Hawaii Telescope Corporation (CFHT) plans to repurpose its
observatory on the summit of Maunakea and operate a new wide field
spectroscopic survey telescope, the Maunakea Spectroscopic Explorer (MSE). MSE
will upgrade the observatory with a larger 11.25m aperture telescope and equip
it with dedicated instrumentation to capitalize on the site, which has some of
the best seeing in the northern hemisphere, and offer its user community the
ability to do transformative science. The knowledge and experience of the
current CFHT staff will contribute greatly to the engineering of this new
facility. MSE will reuse the same building and telescope pier as CFHT. However,
it will be necessary to upgrade the support pier to accommodate a bigger
telescope and replace the current dome since a wider slit opening of 12.5
meters in diameter is needed. Once the project is completed the new facility
will be almost indistinguishable on the outside from the current CFHT
observatory. MSE will build upon CFHT's pioneering work in remote operations,
with no staff at the observatory during the night, and use modern technologies
to reduce daytime maintenance work. This paper describes the design approach
for redeveloping the CFHT facility for MSE including the infrastructure and
equipment considerations required to support and facilitate nighttime
observations. The building will be designed so existing equipment and
infrastructure can be reused wherever possible while meeting new requirement
demands. Past experience and lessons learned will be used to create a modern,
optimized, and logical layout of the facility. The purpose of this paper is to
provide information to readers involved in the MSE project or organizations
involved with the redevelopment of an existing observatory facility for a new
mission.
