  Two key areas of emphasis in contemporary experimental exoplanet science are
the detailed characterization of transiting terrestrial planets, and the search
for Earth analog planets to be targeted by future imaging missions. Both of
these pursuits are dependent on an order-of-magnitude improvement in the
measurement of stellar radial velocities (RV), setting a requirement on
single-measurement instrumental uncertainty of order 10 cm/s. Achieving such
extraordinary precision on a high-resolution spectrometer requires
thermo-mechanically stabilizing the instrument to unprecedented levels. Here,
we describe the Environment Control System (ECS) of the NEID Spectrometer,
which will be commissioned on the 3.5 m WIYN Telescope at Kitt Peak National
Observatory in 2019, and has a performance specification of on-sky RV precision
< 50 cm/s. Because NEID's optical table and mounts are made from aluminum,
which has a high coefficient of thermal expansion, sub-milliKelvin temperature
control is especially critical. NEID inherits its ECS from that of the
Habitable-zone Planet Finder (HPF), but with modifications for improved
performance and operation near room temperature. Our full-system stability test
shows the NEID system exceeds the already impressive performance of HPF,
maintaining vacuum pressures below $10^{-6}$ Torr and an RMS temperature
stability better than 0.4 mK over 30 days. Our ECS design is fully open-source;
the design of our temperature-controlled vacuum chamber has already been made
public, and here we release the electrical schematics for our custom
Temperature Monitoring and Control (TMC) system.
