The LCROSS Visible Spectrometer (VSP) is designed to measure visible (263-650 nm) emission and reflectance spectrometry of the vapor plume and ejecta cloud resulting from the Centaur impact, measure the grain properties, and measure the emission water vapor dissociation and OH- (308 nm) and H2O+ (619 nm) flourescence. The instrument comprises a dual-scope fore-optic system (shared with the NSP1) providing a 1 degree diameter field of view using a 75 cm, 600-micron core diameter UV/Vis glass optical fiber (NA=0.12+/-0.02) feeding an entrance slit (25 x 1000 microns) to a 1-inch f/4 optical cross Czerny-Turner spectrometer (grating 600 lines/mm, blazed at 350 nm). The spectrum, roughly 263-650 nm, is imaged onto a 1044x64 pixel CCD detector, cooled by a thermal electric cooler, where the data is co-added to give a 16-bit, 1 x 1044 pixel spectra. With the cooler off the power draw is 4.8 W, with a maximum of 11.8 W with the cooler on. Configurable integration time is 8 ms to 65.5 s. The instrument is mounted on the inboard side of the LCROSS R6 radiator panel with its aperture pointing in the +X spacecraft direction.

Instrument Overview
  ===================
 
  The LCROSS visible spectrometer (VSP) is a modified version of
  Ocean Optics Ltd's commercial QE65000 spectrometer.  It has been
  adapted for space use and is similar to a spectrometer developed
  for Mars Science Laboratory (MSL).
 
  The VSP spectrometer design consists of an FC optical fiber input
  (0.11 NA) feeding a 25 micron x 1 mm entrance slit, where light is
  diffracted by a 1-inch f/4 optical cross Czerny-Turner spectrometer
  with an oversized camera mirror.  The 263-650 nm spectrum from the
  slit is imaged onto a 1044x64 pixel Hammamatsu CCD detector.
 
  The data is co-added within the spectrometer, delivering a 16-bit,
  1x1024 pixel spectra to the DHU electronics for telemetry formatting.
 
  The VSP contains no moving parts. The CCD detector is cooled by an
  internal Thermal Electric Cooler (TEC), whose set-points are
  programmable.  The VSP power is 4.8 W (TEC off), and could reach
  11.8 W (at TEC setting -10 C at operating temperature +19-20 C).
 
  Integration time for the VSP is also configurable between 8 ms and 65.5 s.
  Additionally, the VSP supports two operation modes, single and bracket
  spectra.  The former is a single spectra acquisition of the appropriate
  requested integration time. The latter is a three spectra acquisition
  defined by a base integration time and a multiplier that is divided or
  multiplied by the base integration time to yield a shorter or longer
  exposure time, respectively.
 
  The VSP is fed  by 75 cm length 600-micron core-diameter UV/Vis glass fiber
  attached to a fore-optics unit in the Payload Observation Deck (POD).
  This fore-optics unit is a fixed two-mirror and one lens system designed
  to provide a one degree circular field-of-view.
 
  Scientific Objectives
  =====================
 
  The main science objective for the visible spectrometer is to
  provide wavelength dependent information between 250 nm an 650 nm
  with a resolving power (lambda/delta_lambda > 100). The VSP has a
  measured wavelength response of 263nm to 650.25nm,
  pre-flight. Post-flight, the VSP wavelength response was verified
  through fits to several lines from scattered sunlight, from 262.58
  to 650.30 nm, indicating no significant shift during launch.
 
  The LCROSS spacecraft will observe the pre- and
  post-Centaur-impacted lunar regolith in and outside the targeted
  region at a spatial resolution and viewing angle unobtainable from
  Earth. The visible spectrometer will record the sunlit plume
  evolution, and track the evolution of OH- radicals from
  sunlight-dissociated water vapor molecules. Specifically, the
  visible spectrometer will measure the OH- (308 nm) and H2O+ (619
  nm) transitions simultaneously which will assess the water vapor
  production in the ejecta.
 
  The visible spectrometer is also used to provide a UV-visible
  spectra of the shape and evolution of the impact flash event.
 
  The visible spectrometer is also used in a star field calibration
  in the early stages of the mission to check pointing and provide
  health checks on an temporary aperture door covering the two nadir
  fore-optics (one feeds the VSP and one feeds NSP1) and the total
  luminance photometer.
 
  Calibration
  ===========
 
  Spectra generated by the visible spectrometer are initially processed
  by the LCROSS GSEOS (Ground Support Equipment Operating System) which
  extracted the CCSDS files from telemetry, extracted ancillary housekeeping
  data provided by the instrument, and converted them to an ASCII comma-
  separated file with some metadata and with MET-based packet timestamp
  encoded in the filename. Spectra taken in single mode are saved into
  one file. The triplet spectra taken in bracket mode are saved into a single
  file. On-board wavelength calibration is not used, even if available.
 
  Wavelength calibration, mapping pixel to wavelengths in nanometers, is
  provided by cross-checking in-orbit data (using solar spectral lines)
  against lab reference spectra taken on the ground. Wavelength calibration
  is applied only to the 1024 pixels of spectral data.
 
  Conversion from raw data values [DN] to a scene spectral radiance
  [W/m^2 um sr], with errors, is performed using a response curve measured
  by the instrument pre-flight using a NIST-calibrated reference source and
  adjusted for any wavelength shifts post-launch, if appropriate. This
  approach provided a radiance calibration longward of 380 nm. A 'best
  effort' UV calibration for the unit shortward of 380 nm was provided using
  an ETU instrument. The calibration steps are described in the LCROSS
  Instrument Response and Calibration Report in the CALIB directory of this
  archive.
 
  Operational Modes
  =================
 
  The VSP supports two operation modes - single and bracket spectra.
  In bracket mode, the spectrometer takes three spectra in quick
  succession, the first at the commanded exposure time, followed by
  a shorter exposure then a longer one.  The bracketing exposure
  times are computed by dividing and multiplying the commanded time
  by a factor (e.g., 2).  This factor can be set as well. Each
  PDS spectra, a collection of 1044 16-bit numbers (raw) or 1044 32-bit
  PC_REAL numbers (calibrated), is a single spectral acquisition
  regardless whether it was taken in single or bracket mode. The time
  stamp will represent the true time the spectrum was acquired.
 
  The VSP integration time is a configurable parameter. Typical values
  used in the LCROSS mission range from 100 milliseconds to 4 seconds.
 
  The Thermal Electric Cooler (TEC) has a programmable set-point and a
  viable range around the ambient working temperature. The set-point as
  well as the reported temperature the VSP has calculated the TEC is being
  controlled to are labels in the PDS (.lbl) files. The setpoint is
  typically set to -10 C, which is in the middle of the range for a VSP
  operating around +17 to +21 C, the nominal thermal operating environment
  for this instrument.
 
  The integration time is documented with each spectra.

extracted metadata from PDS3 catalog and
                    modified to comply with PDS4 Information Model

LCROSS Visible Spectrometer

Description

Identifier (LID)

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