The HTRDLS instrument is an infrared limb-scanning radiometer designed to sound the upper troposphere, stratosphere, and the mesosphere as part of the Chemistry Platform for NASA's Earth Observing System (EOS) Program. The instrument performs limb scans at multiple azimuth angles, measuring CO2. 03, H20, aerosols and other significant greenhouse trace gases in 21 channels ranging from 6. 12 to 17.76pm. The Detector Subsystem (DSS) focal plane assembly (FPA) contains the 2 1 detectors for the science measurements and a set of alignment detectors to be used for instrument integration. All detector elements are Photoconductive HgCdTe operating in the 60-65K range and each channel has a separate cold ifiter. The FPA is mounted in a customized vacuum dewar which couples to a Stirling-cycle mechanical cryocooler via a sapphire rod.Lockheed Martin has designed, fabricated and tested detectors covering the entire HIRDLS spectral range. All the n-type HgCdTe starting material was grown at Lockheed Martin. The vacuum dewar and the preamplifier designs were done at Lockheed Man.In this paper, we will discuss the key features of and design drivers for the DSS design and the design validation activities. The details of the DSS to instrument interfaces will be discussed. We will consider the solutions found for design and packaging issues with the DSS, and the design trades made at the subsystem level to optimize the instrument performance and increase the ease of assembly and instrument integration.