  This paper presents the thermo-mechanical design of the quantum light source
on board SpooQy-1, a 3U CubeSat that was deployed from the International Space
Station on 17th June 2019. SpooQy-1 is a technology demonstrator for
space-based quantum networks. The on-board light source generates and detects
polarization-entangled photon pairs to validate its in-orbit performance.
Entangled photons are generated using spontaneous parametric down-conversion
(SPDC) necessitating stringent dimensional stability and temperature
requirements. Under laboratory conditions these requirements are routinely met
using off-the-shelf laboratory mounts and alignment mechanisms. However, when
facing harsh environments such as the vibration during rocket launch or
temperature changes due to fluctuating illumination conditions, custom
thermo-mechanical solutions are required. In this work, the development and
in-orbit demonstration of an isostatic payload mount is discussed. This
mounting approach enables future space missions with quantum instruments on
resource-constrained CubeSat platforms with limited thermal control
capabilities.
