  Space-based telescopes offer unparalleled opportunities for characterising
exoplanets, Solar System bodies and stellar objects. However, observatories in
low Earth orbits (e.g. Hubble, CHEOPS, Twinkle and an ever increasing number of
cubesats) cannot always be continuously pointed at a target due to Earth
obscuration. For exoplanet observations consisting of transit, or eclipse,
spectroscopy this causes gaps in the light curve, which reduces the information
content and can diminish the science return of the observation. Terminus, a
time-domain simulator, has been developed to model the occurrence of these gaps
to predict the potential impact on future observations. The simulator is
capable of radiometrically modelling exoplanet observations as well as
producing light curves and spectra. Here, Terminus is baselined on the Twinkle
mission but the model can be adapted for any space-based telescope and is
especially applicable to those in a low-Earth orbit. Terminus also has the
capability to model observations of other targets such as asteroids or brown
dwarfs.
