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20120016986.Pdf CIRS AND CIRS-LITE AS DESIGNED FOR THE OUTER PLANETS: TSSM, EJSM, JUICE J. Brasunas\ M. Abbas2, V. Bly!, M. Edgerton!, J. Hagopian\ W. Mamakos\ A. Morell\ B. Pasquale\ W. Smith!; !NASA God­ dard, Greenbelt, MD; 2NASA Marshall, Huntsville, AL; 3Design Interface, Finksburg, MD. Introduction: Passive spectroscopic remote sensing of mid infrared, a rich source of molecular lines in the outer planetary atmospheres and surfaces in the thermal infrared is solar system. The FTS approach is a workhorse compared a powerful tool for obtaining information about surface and with more specialized instruments such as heterodyne mi­ atmospheric temperatures, composition, and dynamics (via crowave spectrometers which are more limited in wavelength the thermal wind equation). Due to its broad spectral cover­ range and thus the molecular constituents detectable. As age, the Fourier transform spectrometer (FTS) is particularly such it is well adapted to map temperatures, composition, suited to the exploration and discovery of molecular species. aerosols, and condensates in Titan's atmosphere and surface NASA Goddard's Cassini CIRS FTS [I] (Fig. I) has given temperatures on Enceladus. Additionally, a lighter, more us important new insights into stratospheric composition and sensitive version ofCIRS can be used to advantage in other jets on Jupiter and Saturn, the cryo-vo1cano and thermal planetary missions, and for orbital and surface lunar mis­ stripes on Enceladus, and the polar vortex on Titan. We sions. have designed a lightweight successor to CIRS - called CIRS-lite - with improved spectral resolution (Table I) to Details of the four key components for CIRS-lite are: separate blended spectral lines (such as occur with isotopes). • high Tc superconducting bolometers (Fig. 2) for long CIRS-lite includes four key components: wavelengths, about five time more sensitive than the thermo­ • high Tc superconductor bolometer/carbon nano-tube 'pile detectors on Cassini CIRS [2], combined with a CNT (CNT) absorber (- 87K, YBCO) absorber. • synthetic diamond beam splitter (- 140K) • chemical vapor deposited diamond beam splitter [3] for 7 • moving mirror mechanism with crossed-roller bearings ( - to 300 microns wavelength (1000 possible), whereas CIRS 11 OK) needs two beam splitters and two FTS's to cover this spectral • single crystal silicon for the input telescope primary range • FTS moving mirror mechanism (double-passed), with less mass than CIRS yet with four times the spectral resolution. Fig. 1 CIRS The increased sensitivity of the long-wavelength detectors g measures Titan C,H, enables CIRS-lite to employ a smaller telescope and smaller I'~G FTS optics while maintaining signal-to-noise (SIN), leading to mass reduction. Further mass reduction comes from re­ placing two FTS's with one, due to the diamond beamsplitter (Fig. 3). Replacing CIRS' flexure-supported moving-mirror It: H• mechanism with double-passed, crossed-roller bearings ena­ ., rji'~ bles us to achieve a four-fold increase in spectral resolution ,. with no increase in mass or volume (Fig. 4). With this dou­ l) 100 l(l(J J(I(.) "00 sao 600 ?Of) 800 90Q H;¢O 1'00 l;ro.o 1·$00 141lO l~OO W.,.,number (em·', ble passing from the FTS optics architecture, we achieve 0.06 cm·! resolution (Rayleigh, unapodized). We have demonstrated the operation of this mechanism under labora­ tory conditions' and Puameter ems CIRS-lite IKISMars TES PFS near IIOK. baRil-pass (um) 1to 1000 1to 333 5taS()' 6t050 0.9t045 • A fourth compo­ resolutioll (em-1) apodized 0.5 0.125 2.4 5 1.5 nent helpful for teie.sOO]l4! diam.eter (em) 50 15 4- lSi 5/4 cryogenic operation detectors HgCdTe HgCdTe themtistOf DTGS JPbSe,PbS is the use of silicon thermopile highTc ool~!lf pjToe1oo. LiTa03 detector tem.ptlRtlire (K) 75 and 110 15 and 89 250 Unoooled 210 and 290 optics [4] (Fig. 5). optics t4!Dlperature (K) 170 -150 250 lIDcooled 290 Silicon can be fab­ poiDt-able miirror no TBD U::g lI10 )'es yes ricated in an excep­ footprilllt (km @:l250klll) 1&0.05 1&0.4 16 2 1&14 tionally pure and m.ass (kg) 43 15 to 20 14 14 31 spatially uniform state, lessening Table 1: Comparison of planetary FTS's figure distortion during a temperature change. The majority of the CIRS-lite optics are aluminum alloy CIRS-lite as a remote sounder operates in both limb and (mirrors, mounts, and bench) to maintain alignment at cryo­ nadir modes. CIRS-lite has better spectral resolution and genic temperature (- 150K). These mirrors are diamond­ higher sensitivity (due to larger telescope and more sensitive, turned in-house at Goddard, as shown in Fig. 6. Table 2 cryogenic detectors) compared with non-Goddard FTS's summarizes CIRS-lite as envisaged for planetary missions. such as TES and ESA's Planetary Fourier Spectrometer (Ta­ The range of wavelength coverage, telescope diameter, etc. ble I). CIRS/CIRS-lite uniquely monitors both the far and will depend on the mission chosen. Fig. 3 uw T.!Ji$ m~gia'!!ihIJlYS!h!\N."liCSf sncS'aFS::sJi1gte­ a'-,f tlO'"S1eJ siifCGfI' mJiTar' ~the ligllWaightsd. •'1IIIIitfiB ' ...... __ ----1 hmeymmbed bSJ:;;1I:s.irk: . Fig. 5: Fabricating the silicon telescope FigA erRS-lite ray­ trace Fig. 6: Diamond turning one of the aluminum mir­ rors ronment of Venus to under­ 'ClRS-li"te nominal design (pl1lndary) stand the formation and evo­ • s:pecbal resolution 0.1.25 em-I apodized (FTS is d'ouble-p assed; physK:altr:!vel is 1 inch) lution of the planet and its • sp,ectIal cO'i'e:ragl! is 7 to 333 pm, oneFrS with 60 mm diamondbeamspDtteI, no comIJI,ematol' atmosphere. IdetectoraHays TYl'E WAVELENGTH (IJID) PIXEl. lmIllldllJIDl EXTENT Venera D contemplates a mHghTc 16+ to 333 43x43130(]lx 300 1x4 PFS-type instrument on the PC HgCdl'e 9+to 16+ 1.5 x 1.5/20QuOO lx30 orbiter, as shown below. PV HgCdTe 7 to 9+ sameasPC • telesoop.e prinlary di:mwt,eris 15 em • there may be a point-able mmol in front ofthe telescope; similar to the TES de,si:gn .opUcs temperature is 140K(same as VoyagerMIRIS) • aD detectoIsnear 70 to 90K, >'11th passive cooler • colfimatediFTS beam-3.5 em -- need- :5 em dear ap,ertm;e forll'eaJDsplltt,ent 45 degrees. Table 2. Looking beyond the outer solar system: Mars and the role of an orbiting FTS From the Concepts and Approaches for Mars Exploration meeting, June 12-14,2012, Houston, TX (near term: 2018-2024, and midterm: 2024-2030) Challenge Area I: Instrumentation and Investigation Ap­ proaches- Near-term examples include, but are not limited to: Item 3: Orbital measurements of surface characteristics such as composition and morphology Mid- to longer-term examples include, but are not limited to: Item 6: Concepts for measurements of lower atmosphere winds and densities, either globally or at specific sites to support future landing systems. And From MEPAG 2010 Goal II: Understanding the processes and history of climate on Mars (Climate) Objective A: Characterize Mars' atmosphere, present cli­ CIRS-lite for Earth's moon (surface ice deposits) mate, and climate processes under current orbital configura­ Previous lunar missions (Clementine radar and Lunar Pro­ tion spector neutron spectrometer) have respectively seen indica­ CIRS-lite is well-placed to characterize global methane dis­ tions of water ice or hydrogen deposits in permanently shad­ tribution and to support orbital measurements of atmosphere owed areas near the south pole on the lunar far side. The in general. neutron spectrometer hydrogen signal may indicate water, or it may indicate hydrogen deposited by the solar wind (pre­ Venus PFS (Formisano) 0.9 to 45 um, 2 cm·l dominantly hydrogen), as has the LRO LEND instrument. PFS is designed to measure the chemical composition and LROILCROSS apparently identified a plume of water re­ temperature ofthe atmosphere of Venus. It is also able to leased by an impactor, however it is the hydroxyl group that measure surface temperature, and so search for signs of vol­ has been measured, and this may be indicative of hydrates canic activity. rather than water ice. The identification of possible water ice deposits at the lunar south pole is clearly a pacing issue for The PFS scanner - the mirror needed by the instrument for the lunar exploration program. Spectroscopy may be able to pointing - is currently blocked in a closed position, prevent­ identifY the nature of the heterogeneous ice / regolith mix­ ing the instrument spectrometer from 'seeing' its targets. tures that could be present on the moon, with enough quanti­ tative information to specifY the concentration (perhaps ~ 1% Thus there continues to be a need for a PFS-like instrument by mass) of the ice in the regolith and thus the economic at Venus, perhaps CIRS-lite? viability of extracting it. Given the presence of impurities, such an understanding may require high spectral resolution; Future Venus mission possibility - Venera D, whose goal is we will need to distinguish between water ice and hydrated investigation of the surface, atmosphere and plasma envi- non-ice constituents. shell, where water is the dominant grain constituent. The The presence of ice would be an important resource for on­ FIR bands are produced by translational modes in the lattice going lunar habitation, supplying water, oxygen and hydro­ and is thus a sensitive function ofthe deposition mode. gen. In addition to the usefulness of ice as a resource, study Crystalline ice has two peaks in absorptivity; in amorphous of the ice/regolith mixture will make important science con­ ice, the longer wavelength peak is suppressed. tributions. Unknown are the polar regolith grain size distri­ bution and agglutinate physical properties. We do not know It is not assured that the FIR features will be present even if whether the polar regolith is finer grained compared with water ice is present.
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