  Maunakea Spectroscopic Explorer will be a 10-m class highly multiplexed
survey telescope, including a segmented primary mirror and robotic fiber
positioners at the prime focus. MSE will replace the Canada France Hawaii
Telescope (CFHT) on the summit of Mauna Kea, Hawaii. The multiplexing includes
an array of over four thousand fibres feeding banks of spectrographs several
tens of meters away. We present an overview of the requirements flow-down for
MSE, from Science Requirements Document to Observatory Requirements Document.
We have developed the system performance budgets, along with updating the
budget architecture of our evolving project. We have also identified the links
between subsystems and system budgets (and subsequently science requirements)
and included system budget that are unique to MSE as a fiber-fed facility. All
of this has led to a set of Observatory Requirements that is fully consistent
with the Science Requirements.
