  The Maunakea Spectroscopic Explorer (MSE) will each year obtain millions of
spectra in the optical to near-infrared, at low (R ~ 3,000) to high (R ~
40,000) spectral resolution by observing >4,000 spectra per pointing via a
highly multiplexed fiber-fed system. Key science programs for MSE include black
hole reverberation mapping, stellar population analysis of faint galaxies at
high redshift, and sub-km/s velocity accuracy for stellar astrophysics. One key
metric of the success of MSE will be its survey speed, i.e. how many spectra of
good signal-to-noise ratio will MSE be able to obtain every night and every
year. The survey speed is directly linked to the allocation efficiency - how
many fibers in the focal surface can be allocated to targets - and to the
injection efficiency - what fraction of light from a target can enter the fiber
at the focal surface. In this paper we focus on the injection efficiency and
how to optimize it to increase the signal-to-noise ratio of targets observed in
sky dominated conditions. The injection efficiency depends on the size of the
fiber and requires highly precise, repeatable and stable positioning of the
fiber in the focal surface. We present the allocation budget used for
Conceptual Design Review and the modeling that allows to estimate the injection
efficiency, which is just one part necessary to meet the science requirements
on sensitivities.
