  We present an Environmental Control System (ECS) designed to achieve
milliKelvin (mK) level temperature stability for small-scale astronomical
instruments. This ECS is inexpensive and is primarily built from commercially
available components. The primary application for our ECS is the high-precision
Doppler spectrometer MINERVA-Red, where the thermal variations of the optical
components within the instrument represent a major source of systematic error.
We demonstrate $\pm 2$ mK temperature stability within a 0.5 m$^{3}$ Thermal
Enclosure using resistive heaters in conjunction with a commercially available
PID controller and off-the-shelf thermal sensors. The enclosure is maintained
above ambient temperature, enabling rapid cooling through heat dissipation into
the surrounding environment. We demonstrate peak-to-valley (PV) temperature
stability of better than 5 mK within the MINERVA-Red vacuum chamber, which is
located inside the Thermal Enclosure, despite large temperature swings in the
ambient laboratory environment. During periods of stable laboratory conditions,
the PV variations within the vacuum chamber are less than 3 mK. This
temperature stability is comparable to the best stability demonstrated for
Doppler spectrometers currently achieving 1 m s$^{-1}$ radial velocity
precision. We discuss the challenges of using commercially available
thermoelectrically cooled CCD cameras in a temperature-stabilized environment,
and demonstrate that the effects of variable heat output from the CCD camera
body can be mitigated using PID-controlled chilled water systems. The ECS
presented here could potentially provide the stable operating environment
required for future compact, "astro-photonic" precise radial velocity (PRV)
spectrometers to achieve high Doppler measurement precision with a modest
budget.
