  The Institute for Astronomy and Astrophysics in T\"ubingen (IAAT) has a
long-term experience in developing and building space-qualified imaging and
photon counting microchannel-plate (MCP) detectors, which are sensitive in the
ultraviolet wavelength range. Our goal is to achieve high quantum efficiency
and spatial resolution, while maintaining solar blindness and low-noise
characteristics. Our flexible detector design is currently tailored to the
specific needs of three missions: For the ESBO DS (European Stratospheric
Balloon Observatory Design Study) we provide a sealed detector to the STUDIO
instrument (Stratospheric Ultraviolet Demonstrator of an Imaging Observatory),
a 50 cm telescope with a UV imager for operation at an altitude of 37-41 km. In
collaboration with the Indian Institute of Astrophysics we plan a space mission
with a CubeSat-sized far-ultraviolet spectroscopic imaging instrument,
featuring an open version of our detector. A Chinese mission, led by the Purple
Mountain Observatory, comprises a multi-channel imager using open and sealed
detector versions. Our MCP detector has a cesium activated p-doped
gallium-nitride photocathode. Other photocathode materials like
cesium-telluride or potassium-bromide could be used as an alternative. For the
sealed version, the photocathode is operated in semi-transparent mode on a
MgF$_2$ window with a cut-off wavelength of about 118 nm. For missions
requiring sensitivity below this cut-off, we are planning an open version. We
employ a coplanar cross-strip anode and advanced low-power readout electronics
with a 128-channel charge-amplifier chip. This publication focuses on the
progress concerning the main development challenges: the optimization of the
photocathode parameters and the sophisticated detector electronics.
