  The Single Aperture Large Telescope for Universe Studies (SALTUS) is a
mission concept for a far-infrared observatory developed under the recent
Astrophysics Probe Explorer opportunity from NASA. The enabling element of the
program is a 14 m diameter inflatable primary mirror, M1. Due to its importance
to SALTUS and potentially other space observatories, this paper focuses
entirely on M1. We present a historical overview of inflatable systems,
illustrating that M1 is the logical next step in the evolution of such systems.
The process of design and manufacture is addressed. We examine how M1 performs
in its environment in terms of operating temperature, interaction with the
solar wind, and shape change due to non-penetrating particles. We investigate
the longevity of the inflatant in detail and show it meets mission lifetime
requirements with ample margin and discuss the development and testing to
realize the flight M1.
