Jared L. May, Alexandre E. Adler, Jason E. Austermann, Steven J. Benton, Rick Bihary, Shannon Duff, Malcolm Durkin, Jeffrey P. Filippini, Aurelien A. Fraisse, Thomas Gascard, Sho M. Gibbs, Suren Gourapura, Jon E. Gudmundsson, Johannes Hubmayr, William C. Jones, Ashesh Khatua, Darby McCauley, Johanna M. Nagy, Ivan Padilla, Ricardo R. Rodriguez, John E. Ruhl, M. Shaaf Sarwar, Simon Tartakovsky, Joseph van der List, Michael R. Vissers, Philippe Voyer

Taurus is a balloon-borne cosmic microwave background (CMB) experiment designed to operate more than 10,000 transition-edge sensor bolometers at a base temperature near 100 mK during a multi-week stratospheric balloon flight. This platform provides near-space observing conditions while imposing stringent constraints on mass, power, and system robustness, driving the need for a lightweight and highly reliable cryogenic system. To meet these requirements, Taurus employs a multi-stage cryogenic architecture. A 660 L liquid helium tank provides a stable 4 K reservoir, with vapor-cooled shields establishing intermediate stages at approximately 40 K and 80 K. A superfluid helium tank provides an approximately 1.5 K takeoff point for the sub-Kelvin cooling systems. Each of the instrument's three receivers is supported by an independent sub-Kelvin cooling chain that includes closed-cycle 3He sorption refrigerators that cool to 300 mK. These provide the thermal intercept and takeoff for a Chase Research Cryogenics miniature dilution refrigerator that cools the detectors to approximately 100 mK. Here we discuss the requirements and challenges of the Taurus sub-Kelvin cryogenic system and present results of early performance tests.