CCSD3ZF0000100000001NJPL3IF0PDS200000001 = SFDU_LABEL RECORD_TYPE = STREAM SPACECRAFT_NAME = GALILEO_ORBITER INSTRUMENT_NAME = "NEAR INFRARED MAPPING SPECTROMETER" INSTRUMENT_ID = NIMS OBJECT = TEXT NOTE = "Description of the NIMS instrument referenced by EDR and cube labels" PUBLICATION_DATE = 1995-03-15 END_OBJECT = TEXT END Instrument Overview =================== The Galileo Near-Infrared Mapping Spectrometer is described by Carlson et al, 1992 [Reference]. A somewhat earlier version of this paper appears on all NIMS CD-ROMs in the [DOCUMENT.NIMSINST] directory. NIMS is an imaging spectrometer capable of obtaining measurements in the 0.7 to 5.2 micron region. The spectral resolution is .0125 microns at wavelengths below 1 micron, and .0250 micron at wavelengths above 1 micron. The instantaneous field of view is approximately 0.5 x 0.5 milliradians. Instrument cycle times vary from about 1/60 second to 8 2/3 seconds. The instrument has 17 detectors, permitting 17 near-simultaneous measurements which are spaced approximately evenly across the wavelength region. The dispersion element is a dual-blaze grating which may be stepped to obtain additional 17 wavelength sets, with small wavelength offsets from previous measurements. Various grating step sizes and initial grating offsets are possible. For a nominal instrument grating cycle (12 steps), the instrument can measure 204 wavelengths across the 0.7-5.2 micron region in 4 1/3 seconds. There are four commandable gain ranges for all detectors except the last three, which have automatic gain ranging with two gains. The instrument acquires spatial information by utilizing motions of the spacecraft scan platform, 'pushbroom imaging', and motions of a secondary mirror. The secondary mirror moves in a direction perpendicular to the mounting plate and sweeps out 20 pixels yielding an effective field of view of 10 milliradians over the mirror sweep time (1/3 second). The order of acquisition is detector (17 at a time), mirror position (20, alternately down and up), grating position (0 to 24 steps). Scientific Objectives ===================== Measurement of the composition of the Jovian atmosphere and the composition of the surfaces of the Galilean satellites. Calibration =========== Flight calibrations ------------------- Flatfield radiometric calibration target operated at about 300 K. Solar illuminated photometric calibration target of sandblasted aluminum. Dark Levels. Stars. Ground calibrations ------------------- Wavelength calibration based on Hg 5461 angstrom line (in multiple orders) and a laboratory grating spectrometer. Detector spatial response (two-dimensional) based on knife-edge sources. Blackbody calibration. NIST FEL lamp calibration. Measurement of instrument response sensitivity to temperature. Operational Considerations ========================== Rate of motion of target body through field of view must be carefully coordinated with instrument mode. Target motion in spacecraft cone direction preferred. Focal plane must be operated at temperatures below 88K. Radiator must be kept clean, and cannot view warm sources for any length of time. Boresight must not be pointed closer than 12 degrees to sun. Detectors ========= Seventeen individual photovoltaic diodes, tantalum shield. 2 Silicon 0.7 - 1.0 microns. 15 InSb 1.0 - 5.2 microns. Electronics =========== Seventeen channel signal chain. Multilayer circuit boards. Ten-bit digitization. RCA 1802-based control processor with 1.5K of RAM, 1.5K of ROM. Filters ======= Order blocking interference filters, placed on focal plane array. Optics ====== Ritchey-Chretien telescope, 22.8 cm diameter, f/3.5, 800 mm focal length. Operating temperature about 150 K. Etendue 1.1 x 10^-4 cm^2 steradian. Spectrometer ============ 39 lines per mm plane grating spectrometer. 400 mm focal length, f/3.5, Dall-Kirkham collimator. 200 mm focal length, f/1.8, flat-field camera. Bipartite diffraction grating, 30% blazed for 1.9 u, 70% blazed for 3.8 u. Operating temperature about 150 K. Mounting Offsets ================ Co-aligned with SSI, UVS and PPR instruments. Offset from imaging instrument (SSI) 0.25 x 0.25 mrad (see I-kernel). Field of View ============= IFOV = 0.5x0.5 milliradians. Nominal FOV = 10x0.5 milliradians (in 1/3 second). Data Rates ========== 11.52 kbits/second (nominal, from instrument). Data modes ========== Instrument modes ---------------- mode cycle_time wavelengths_per_cycle Long 8 2/3 sec 408 Full 4 1/3 sec 204 Short 2 1/3 sec 102 Bandedge 1 1/3 sec 34 Fixed 1/3 sec 17 During Jupiter operations, any combination of sampled wavelengths may be returned. Telemetry modes (Jupiter operations) ------------------------------------ MPW 11.520 kbits/sec to tape LPU 6.168 kbits/sec to tape LNR 2.592 kbits/sec to tape Actual downlink rate of recorded data depends on on-board compression and editing of data but will probably not exceed 60-80 bits/sec. RT8 10 bits/sec to ground for occasional realtime data return REFERENCE R. W. Carlson, P. R. Weissman, W. E. Smythe, J. C. Mahoney, and the NIMS Science and Engineering Teams, "Near-Infrared Mapping Spectrometer Experiment on Galileo", Space Science Reviews 60, 457-502, 1992. [This volume also contains papers describing the other Galileo instruments.] [Prepared by R. W. Carlson, W. D. Smythe, R. Mehlman, 09 March 1995]