The OSIRIS-REx Visible and IR Spectrometer (OVIRS) is a spectrometer, which measures light to provide mineral and organic spectral maps and local spectral information of candidate sample sites. It also provides full-disk asteroid spectral data, global spectral maps and spectra of the sample site.
More Information: Detailed Specifications and Instrument Operations
The OSIRIS-REx Visible and IR Spectrometer (OVIRS) is a point spectrometer that provides mineral and organic spectral maps and local spectral information of candidate sample sites. It also provides full-disk asteroid spectral data, global spectral maps (20-m resolution), and spectra of the sample site (0.08–2-m resolution). It provides at least two spectral samples per resolution element taking full advantage of the spectral resolution. OVIRS spectra will be used to identify volatile and organic-rich regions. These data will be used in concert with OTES spectra to guide sample-site selection. These spectral ranges and resolving powers are sufficient to provide surface maps of mineralogical and molecular components including carbonates, silicates, sulfates, oxides, adsorbed water and a wide range of organic species.
The entire hemisphere can be observed at phase angles of 3º or less during the survey phase. Spectral data obtained at different local times and phase angles, mostly during Phase 4 (Survey), will be combined with surface temperatures measured using OTES and the longer wavelength OVIRS channels to determine the actual albedo change from the OVIRS spectra; observations at high phase angles will emphasize the thermal contribution.
The OVIRS design is inexpensive, compact, has no moving parts and allows for straightforward operation. The camera operates in a scanning mode, in which the rotational motion of the asteroid is combined with a rotation of the spacecraft about the OVIRS scan axis to sample a region of interest. Typical observation scenarios will provide global sampling of the surface with a spatial resolution of 20 meters at a fixed phase angle for measurements from 5-km altitude. In addition, very high spatial resolution (= 2m spectral) measurements of proposed sample sites will be obtained at lower altitudes.
The thermal design is such that the measurement noise is dominated by source photon noise. For very low signal, the primary noise term is read noise, which is the optimum design from a noise standpoint. The detector array is thermally coupled to a two-stage passive radiator, which reduces the dark current sufficiently that dark current noise is never louder with more than a factor of two margin. The camera enclosure shields its contents from radiation and contaminants and mounts to the OSIRIS-REx science deck. A cold baffle in the optical path limits the thermal background signal from the instrument enclosure. In addition, small radiators will reduce the temperature of the optics enclosure itself to less than 160 K, further reducing thermal background noise.
Two types of contamination might possibly affect OVIRS measurements. Molecular contaminants, and water in particular, can condense on the cold focal plane. To mitigate this, a nitrogen purge is used until launch. After launch, the detector is heated with decontamination heaters to bake off any remaining water or other molecular contaminant before cooling. Any residual throughput effect can be calibrated out. It is designed to survive the expected 20 krad radiation environment with a factor of 2 RDM. The effect of spurious signals in the spectrum caused by high energy radiation is significantly reduced by the array substrate removal.
The OVIRS team is led by Dennis Reuter (IS, GSFC), Amy Simon-Miller (DIS, GSFC), and Sridhar Manthripragada (IM, GSFC).