urn:nasa:pds:context:instrument:vega1.iks 1.0 1.11.0.0 Product_Context urn:nasa:pds:context:instrument:iks.vega1 2021-02-24 1.0 Changed inst LIDs from u:n:p:c:i:instID.scID to u:n:p:c:i:scID.instID And per "Guide toPDS4 Context Products" v1.7, changed all lidvid_reference to lid_reference urn:nasa:pds:context:instrument_host:spacecraft.vega1 instrument_to_instrument_host Reinhard, R and B. Battrick (eds), 'Space Missions to Halley's Comet', European Space Agency ESA SP-1066, ESA Pub Div, Moordwijk, Netherlands, 1986. reference.ESA-SP1066 'Encounters with Comet Halley, The first results', Nature, Volume 321, No. 6067, 15 May 1986. reference.NATURE321 INFRARED SPECTROMETER Spectrometer not applicable not applicable Instrument Overview =================== The infrared spectrometer was designed to study the radiation from the inner coma, in the wavelength range 2.5-12 micro m. The instrument included two high-resolution spectral channels for the chemical analysis of the cometary matter, gas and dust, and an image modulation channel for determination of the size of and thermal emission from the nucleus. The light that exits from the telescope wass divided into three beams by means of two beam splitters. The secondary beams were then focussed on a wheel that rotated at the rate of 8 rev/sec and carried three rings, namely two circular variable filters and one image modulator. Behind the encoding wheel, the beams entered a cryostat which cooled the three detectors. The two filters covered the ranges 2.5-5 micro m and 6-12 micro m, which included the emission bands of the parent molecules. The long-wave channel could detect water ice and the short-wave channel could be used to identify a number of minerals, such as silicates. The imaging channel did not resolve details of the nucleus, the objective being to derive its most important parameters: size, shape, temperature and optical properties in the infrared. To accommodate the nucleus pointing uncertainties, a field of view of 1deg was judged necessary and an angular resolution of 1 arcmin satisfactory. More instrument characteristics are given in the table below. Since the sensitivity of the instruments was degraded by four to five orders of magnitude between 77 K and room temperature, it appeared mandatory to cool the detectors during the two measuring sequences using the Joule-Thomson expansion of nitrogen. For that purpose, 2 l of nitrogen were stored in four tanks at a pressure of 350 atm. The detector temperatures reached stability within 25 min (to +/- 0.1deg) and could be maintained so for 3 h. ------------------------------------------------ Table. Infrared Spectrometer characteristics Objective Ritchey-Chretien Primary mirror aperture 140 mm Secondary mirror aperture 56 mm Focal distance 538.1 mm Field of view 1deg Resolution Diffraction limited ------------------------------------------------- Channel Imaging Short Long wavelength wavelength -------------------------------------------------------------------------- Wavelength. micro m 7-14 2.5-5 6-12 Spectral resolution, 2.5 50 50 lambda/delta lambda M Optical transmission 0.10 0.39 0.33 Detector HgCdTe In Sb HgCdTe Chip area, mm**2 2x2 2x2 2x2 Geometrical factor, cm**2 sr 0.046 0.045 0.038 IR background, W 1.2x10**-4 3.5x10**-6 9.7x10**-5 Photon noise, W 1.3x10**-12 4x10**-13 1.4x10**-12 Nominal NEP, WHz**-1/2 4x10**-12 2x10**-12 1x10**-11 at 6 kHz at 200 Hz at 200 Hz -------------------------------------------------------------------------- Problems: (1) No useful data were obtained by the Vega 2 IKS instrument due to a failure of the cryogenic system. (2) On Vega 1 the instrument operated before the flyby at distances between 250,000 km and 40,000 km and after the flyby at distances more than 100,000 km. The data flux was erroneously interrupted for 30m near the closest approach. (3) The internal background signal was about 10**4 times the cometary signal. Separation of the cometary signal was done assuming its variation as r**-1 (where r is the distance to the nucleus) and interpolating the background measured at approximately 250,000 km before and after the closest approach.