  We present a 3He / 4He dilution refrigerator designed for cooling
astronomical mm-wave telescope receivers to around 100 mK. Used in combination
with a Gifford-McMahon closed-cycle refrigerator, 4He and 3He sorption-pumped
refrigerators, our cryogen-free system is capable of achieving 2 microW cooling
power at 87 mK. A receiver attached directly to the telescope optics is
required to rotate with respect to the downward direction. This scenario, of
variable tilt, has proved difficult for typical dilution refrigerators, but our
design has a geometry chosen to allow tilt to 45 degrees and beyond.
