  The Thermal Management Integrated System (TheMIS) is a key element of the
Australia-Italy Space Industry Responsive Intelligent Thermal (SpIRIT) mission,
launched in a 510km Polar Sun-Synchronous orbit in December 2023. SpIRIT is a
6U CubeSat led by The University of Melbourne in cooperation with ASI, with
support from ASA and with contributions from Australian space industry and
international research organizations. The TheMIS subsystem actively cools and
controls the temperature of sensitive instruments, increasing the potential
range of payloads supported on small spacecraft systems. TheMIS core
functionality is based on a commercial Stirling Cycle Cryocooler in-principle
capable of reaching cold-tip temperatures below T=100K. The cooler is operated
by customized control electronics and is connected to deployable radiators
through pyrolytic graphite sheet thermal straps, all developed by the
University of Melbourne. Until now, this level of thermal control has been
relatively uncommon in nanosatellites. TheMIS aims to validate the design and
performance by controlling the thermal environment of SpIRIT's HERMES payload,
an X-ray instrument provided by ASI which has a noise background strongly
sensitive to temperature. Beyond SpIRIT, TheMIS has the potential to support a
broad range of applications, including holding infrared focal plane arrays at
cryogenic temperatures, and increasing resilience of electronics to space
weather. This paper provides an overview of TheMIS's design, implementation,
and operational performance, detailing the commissioning phase and the early
results obtained from its operations in orbit, with comparison to the thermal
model developed during the mission environmental testing campaign. Finally, the
paper discusses ongoing challenges for thermal management of payloads in small
satellite systems and potential future strategies for continuous improvement
