Next-generation cold object radiometer

I. SCIENCE GOALS AND OBJECTIVES The proposed instrument is the next-generation Cold OBject RAdiometer (COBRA) designed for ice giant, icy satellite, and lunar science. Specifically, COBRA will perform measurements of (i) the atmospheric structure of the ice giants through nadir sounding in the far-IR, (ii) the radiative balance of planetary bodies and their satellites, including ice giants, and (iii) the thermophysical properties of satellites and primitive bodies in order to derive information on their surface structure and composition. The instrument we are proposing is an enhancement of JPL’s Mars Climate Sounder (MCS) on MRO and Diviner Lunar Reconnaissance Explorer (Diviner) on LRO which have provided breakthrough science by measuring the thermal infrared properties of the atmospheric limb of Mars and the surface of the Moon, respectively. COBRA is a highly accurate radiometer that measures radiance in a set of bandpass filters spanning 0.3-200 µm and can help answer important questions such as the following: • What is the atmospheric circulation in the upper troposphere of Uranus and Neptune, and how does this circulation interact with other parts of the atmosphere? • Is the internal heat flux from Uranus as low or that from Neptune as high as currently assumed? • What is the small-scale variability of thermal properties, composition, and polar cold-trap distribution of the Moon?

II. METHODOLOGY We are proposing to develop the next-generation (beyond MCS and Diviner) multi-spectral IR/Far-IR remote-sensing imaging radiometer specifically to measure cold bodies with temperatures that reach below 60 K (Neptune, Uranus, their satellites, and the Moon’s poles). The enabling technology for MCS and Diviner is the uncooled thermopile arrays developed at JPL. COBRA extends the capabilities of these thermopile arrays so the pixel pitch (100 um), format size (128 x 64), and spectral response (e.g. optical coating) are designed to make accurate and sensitive radiometric measurements of extremely cold objects. We will build the instrument using a new optical design that has an intermediate focus which allows for the integration of a filter block that is compatible with the new larger arrays. Finally, we will use a compact pointing mirror to replace the bulky actuators flying on MCS and Diviner. This instrument will have nearly 100x more pixels than the state-of-the-art and a sensitivity per pixel that is nearly two times higher. This performance will be achieved with an instrument that is 50% less massive than MCS or Diviner.

III. RELEVANCY The proposed research is directly relevant to NASA’s MatISSE program since this program is to “develop and demonstrate planetary and astrobiology science instruments to the point where they may be proposed in response to future announcements of flight opportunity without additional extensive technology development”. This proposal will develop new technologies that significantly improve instrument measurement capabilities for planetary missions and retire major technological risks prior to science instrument solicitation. The multi-spectral IR/Far-IR remote-sensing imaging radiometer we are proposing to build will be far more capable than MCS and Diviner in terms of spatial/spectral resolution and sensitivity, BUT will be significantly lighter and more compact. The thermal infrared radiometer technology proposed here is applicable to a wide range of Discovery, New Frontiers, and flagship missions identified in the Decadal Survey including Comet Surface Sample Return, Io Observer, Uranus or Neptune orbiter. Because this proposal is relevant to MatISSE, it is intrinsically relevant to NASA PSD and SMD.