  Observations that require large physical instrument dimensions and/or a
considerable amount of cryogens, as it is the case for high spatial resolution
far infrared (FIR) astronomy, currently still face technological limits for
their execution from space. Angular resolution and available observational
capabilities are particularly affected. Balloon-based platforms promise to
complement the existing observational capabilities by offering means to deploy
comparatively large telescopes with comparatively little effort, including
other advantages such as the possibility to regularly refill cryogens and to
change and/or update instruments. The planned European Stratospheric Balloon
Observatory (ESBO) aims at providing these additional large aperture FIR
capabilities, exceeding the spatial resolution of Herschel, in the long term.
The plans focus on reusable platforms performing regular flights and an
operations concept that provides researchers with proposal-based access to
observations. It thereby aims at offering a complement to other airborne,
ground-based and space-based observatories in terms of access to wavelength
regions, spatial resolution capability, and photometric stability. While the
FIR capabilities are a main long-term objective, ESBO will offer benefits in
other wavelength regimes along the way. Within the ESBO Design Study (ESBO DS),
a prototype platform carrying a 0.5 m telescope for ultraviolet and visible
light observations is being built and a platform concept for a next-generation
FIR telescope is being studied. A flight of the UV/VIS prototype platform is
estimated for 2021. In this paper we will outline the scientific and technical
motivation for a large aperture balloon-based FIR observatory and the ESBO DS
approach towards such an infrastructure. Secondly, we will present the
technical motivation, science case, and instrumentation of the 0.5 m UV/VIS
platform.
