| DESCRIPTION |
The instrument was provided by the OSIRIS consortium led by the
principal investigator Dr. Horst Uwe Keller.
The OSIRIS consortium have the following members:
MPS Overall responsibility and project management, system
engineering, interfaces, Focal Plane Assemblies, CCDs
and Readout Boards, HK Boards, integration and
qualification of E-Boxes, harnesses, system
integration, high level software, NAC & WAC system
calibration, QA, mission operations
LAM NAC telescope, camera integration and qualification
WAC optical bench, camera
UPD Integration and qualification, shutter mechanisms and
shutter electronics, Front Door Mechanisms (mechanisms
for NAC and WAC)
IAA Mechanism Controller Board
INTA Filter Wheel Mechanisms, E-Box Power Converter Module,
NAC & WAC CRB Power Converter Modules
RSSD Data Processing Unit
IDA Mass memory, low level software and data compression
DASP NAC & WAC Filters
UPM Thermal and structural analysis, NAC MLI, WAC FPA MLI
For detailed instrument description please see the Space Science
Review Paper (OSIRIS_SSR) included in the dataset.
Instrument Overview
===================
The OSIRIS camera system consists of a narrow angle camera (NAC)
and a wide angle camera (WAC)
==============================
The narrow angle camera (NAC):
==============================
The NAC uses an off axis three mirror optical design. The off
axis design was selected in order to minimize the stray light
reaching the CCD (The NAC has a proven stray light attenuation
of better than 1.0e-9). The optical beam is reflected of the
three mirrors (M1 - M3) before passing through a double filter
wheel, a mechanical shutter mechanism and an anti radiation
plate (ARP) before reaching the CCD.
The NAC optical path:
(target object)
/
Focal Plane ----- /
ARP --- M2 / / / Aperture
Shutter --- ---- /
Filter2 --- /\ /
Filter1 --- / \ /
\ / \ /
\ / \ /
\/ \/
---- ----
M3 M1
Basic NAC parameters:
---------------------------------------------------------------
| Optical design | 3-mirror off-axis |
| Angular resolution | 18.6 urad px-1 |
| Focal length | 717.4 mm |
| Mass | 13.2 kg |
| Field of view | 2.20 x 2.22deg |
| F-number | 8 |
| Spatial scale from 100 km | 1.86 m px-1 |
| Typical filter bandpass | 40 nm |
| Wavelength range | 250nm - 1000nm |
| Number of filters | 12 |
| Estimated detection threshold | 18 mV |
---------------------------------------------------------------
The double filter wheels allows the NAC to place a refocusing
plate together with an optical filter in the optical beam. The
NAC is equipped with two types of refocusing plates allowing
optimum focus at 4km and 1.2km
respectively.
The NAC is equipped with the following optical filters:
-------------------------------------------------------------------
| Name | Wavelength | Bandwidth | Peak | Objective |
| | [nm] | [nm] | [%] | |
-------------------------------------------------------------------
| FFP-UV 600 > 600 > 99 BBAR coated |
| plate to allow |
| use of wheel 2 |
| FFP-IR 600 > 600 > 99 BBAR coated |
| plate to allow |
| use of wheel 1 |
| Neutral 640 520 5.0 Neutral density |
| filter |
| NFP-Vis 600 > 600 > 98 Refocusing lens |
| for near-nucleus |
| imaging, |
| BBAR coated |
| Far-UV 269.3 53.6 37.8 Surface spectral |
| reflectance |
| Near-UV 360.0 51.1 78.2 Surface spectral |
| reflectance |
| Blue 480.7 74.9 74.6 Surface spectral |
| reflectance |
| Green 535.7 62.4 75.8 Surface spectral |
| reflectance |
| FFP-Vis 600 600 >90 Refocusing lens |
| for near-nucleus |
| imaging, |
| BBAR coated |
| Orange 649.2 84.5 92.4 HMC orange |
| filter; |
| surface spectral |
| reflectance |
| Hydra 701.2 22.1 87.4 Water of |
| hydration band |
| Red 743.7 64.1 96.0 Surface spectral |
| reflectance |
| Ortho 805.3 40.5 69.8 Orthopyroxene |
| Near-IR 882.1 65.9 78.4 Surface spectral |
| reflectance |
| Fe2O3 931.9 34.9 81.6 Iron-bearing |
| minerals |
| IR 989.3 38.2 78.1 IR Surface |
| reflectance |
-------------------------------------------------------------------
-------------------------------------------------------------
| Name | Thickness | Wheel | Position | Encoder |
| | centre [mm] | | | [DN] |
-------------------------------------------------------------
| FFP-UV 4.41 1 1 14 |
| |
| |
| FFP-IR 5.15 2 1 14 |
| |
| |
| Neutral 4.64 1 8 11 |
| |
| NFP-Vis 4.18 1 3 4 |
| |
| |
| |
| Far-UV 4.50 2 5 2 |
| |
| Near-UV 4.68 2 6 7 |
| |
| Blue 4.67 2 4 1 |
| |
| Green 4.64 2 3 8 |
| |
| FFP-Vis 5.00 1 2 13 |
| |
| |
| |
| Orange 4.73 2 2 11 |
| |
| |
| |
| Hydra 4.72 2 7 4 |
| |
| Red 4.68 2 8 13 |
| |
| Ortho 4.69 1 5 2 |
| Near-IR 4.75 1 4 7 |
| |
| Fe2O3 4.73 1 6 1 |
| |
| IR 4.74 1 7 8 |
| |
-------------------------------------------------------------
For details on the shutter mechanism see the Shutter section
below.
For details on the CCD please see the CCD section below.
============================
The wide angle camera (WAC):
============================
The WAC uses an off axis two mirror optical design. The off axis
design was selected in order to minimize the strayligh reaching
the CCD (The NAC has a proven strayligh attenuation of better
than 1.0e-8). The optical beam is reflected of the two mirrors
(M1 & M2)before passing through a double filter wheel, a
mechanical shutter mechanism, an anti radiation plate (ARP)
before reaching the CCD.
The WAC optical path:
---------------------
(target object)
/
/
M2 / / / Aperture
---- /
/\ /
/ \ /
Filter1 --- \ /
Filter2 --- \ /
Shutter --- \/
ARP --- ----
Focal Plan ----- M1
Basic WAC parameters:
---------------------
---------------------------------------------------------------
| Optical design | 2-mirror off-axis |
| Angular resolution | 101 urad px-1 |
| Focal length | 140(sag)/131(tan) |
| Mass | 9.48 kg |
| Field of view | 11.34 x 12.11deg |
| F-number | 5.6 |
| Spatial scale from 100 km | 10.1 m px-1 |
| Typical filter bandpass | 5 nm |
| Wavelength range | 240nm - 720nm |
| Number of filters | 14 |
| Estimated detection threshold | 13 mV |
---------------------------------------------------------------
The WAC camera does not have refocusing plates so the two WAC
filter wheels each have a filter position with no filter mounted.
So the typical WAC observation uses either the filter combination
(empty + filter) or filter + empty)
The WAC is equipped with the following optical filters:
--------------------------------------------------------------------
| Name | Wavelength | Bandwidth | Peak | Objective |
| | [nm] | [nm] | [%] | |
--------------------------------------------------------------------
| Empty Empty position |
| to allow |
| the use of |
| filter wheel 2 |
| Empty Empty position |
| to allow |
| the use of |
| filter wheel 1 |
| UV245 246.2 14.1 31.8 Continuum |
| surface spectral|
| reflectance |
| CS 259.0 5.6 29.8 CS gas emission |
| UV295 295.9 10.9 30.4 Continuum for OH|
| OH-WAC 309.7 4.1 26.0 OH emission from|
| the vicinity of |
| the nucleus |
| UV325 325.8 10.7 31.6 Continuum for OH|
| surface spectral|
| reflectance |
| NH 335.9 4.1 23.6 NH gas emission |
| UV375 375.6 9.8 57.3 Continuum for CN|
| surface spectral|
| reflectance |
| CN 388.4 5.2 37.4 CN gas emission |
| Green 537.2 63.2 76.8 Dust continuum |
| NH2 572.1 11.5 60.9 NH2 gas emission|
| Na 590.7 4.7 59.0 Sodium gas |
| emission |
| VIS610 612.6 9.8 83.4 Continuum for OI|
| surface spectral|
| reflectance |
| OI 631.6 4.0 52.4 O (1D) gas |
| emission |
| for dissociation|
| of H2O |
| R 629.8 156.8 95.7 Broadband filter|
| for nucleus and |
| asteroid |
| detection |
| (NAC redundancy)|
--------------------------------------------------------------------
------------------------------------------------------------
| Name | Thickness | Wheel | Position | Encoder |
| | centre [mm] | | | [DN] |
------------------------------------------------------------
| Empty 1 1 14 |
| |
| |
| |
| Empty 2 1 14 |
| |
| |
| |
| UV245 4.51 1 3 4 |
| |
| |
| CS 4.60 1 4 7 |
| UV295 4.75 1 5 2 |
| OH-WAC 4.82 1 6 1 |
| |
| |
| UV325 4.85 1 7 8 |
| |
| |
| NH 4.86 1 8 11 |
| UV375 4.60 2 3 8 |
| |
| |
| CN 4.61 2 4 1 |
| Green 4.71 1 2 13 |
| NH2 4.74 2 5 2 |
| Na 4.75 2 6 7 |
| |
| VIS610 4.65 2 8 13 |
| |
| |
| OI 4.66 2 7 4 |
| |
| |
| |
| R 4.67 2 2 11 |
------------------------------------------------------------
=============================
The OSIRIS mechanical shutter
=============================
Both the NAC and the WAC cameras are equipped with a mechanical
shutter mechanism for controlling the exposure time. The
shutter mechanism uses two blades to control the exposure.
The first blade covers the CCD at the start of the exposure.
when the exposure is started the first blade is accelerated
to 1.3 m/s before the edge of the blade reaches the edge of
the CCD. the blade edge then passes over the CCD at constant
velocity before being decelerated to standstill after passing
the far edge of the CCD. The end of the exposure is controlled
by performing the same motion with a second blade that initially
is outside the CCD surface. The second blade motion starts after
the exposure time has passed from the start of the first blade
motion. The full blade travel lasts 53ms. For exposure times
shorter than 53 ms the blade motion of the two blades overlap.
In this case the exposure is controlled by a moving slit
(same principle as a SLR camera).
During the blade motions the position is measured using a
position encoder mounted on the drive shaft of the shutter
motors.
The minimum allowed exposure time is 10 ms and accuracy of the
exposure is better than 5us
==============
The OSIRIS CCD
==============
The OSIRIS camera system uses 2048x2048 pixel backside
illuminated CCD's. The CCD's are equipped with anti reflection
coatings optimized for the UV spectral range. The CCD's are
equipped with shielded anti-blooming control. The CCD's are
UV sensitive down to 240nm (50% QE) and IR sensitive up to
1000nm (6% QE). The system gain is set to ~3e- in normal
operational mode. The readout electronics is using a dual
14 bit ADC configuration giving an effective 16 bit system.
The CCD's uses two readout channels (channel A and B) which
can be used in parallel for fast readout. The CCD's can be
read out using hardware windowing and hardware binning (1x1,
2x2, 4x4 and 8x8). The fastest readout of a 1x1 binned fullframe
image is 3.4s. By using windowing and binning modes this time
can be reduced to less than 1s.
OSIRIS CCD specification:
--------------------------------------------------------------------
| Item | Specification |
--------------------------------------------------------------------
| Source detector type | E2V CCD42-40, non-MPP, backside |
| | illuminated,|Hafnium oxide AR |
| | coated |
| Array size | Full frame, 2048 x 2048 pixels |
| Serial register size | 50 + 2k + 50; 50 extra pixel |
| | at both ends |
| | 48 + 2k + 48 transmitted |
| Pixel size | 13.5 um x 13.5 um |
| No. of outputs | 2; either 1 sufficient |
| Overexposure | Shielded anti-blooming control |
| Operation modes | Clock dithering for dark |
| | current reduction for |
| | operations at > 220 K |
| | (optional), windowing, binning |
| Full well | > 100 000 e- px-1 |
| System gain | ~ 3 e- / DU |
| Readout noise (CCD) | < 7 e- rms |
| Dark charge generation | ~0.6 e- s-1 px-1 @ 180 K |
| | ~200 e- s-1 px-1 @ 293 K |
| | (with dithering) |
| QE | 250 nm: 50 %, 400 nm: 60 %, |
| | 600 nm: 80 %, |
| | 800 nm: 60 %, 1000 nm: 6 % |
| Readout rate | 1.3 Mpx s-1; 650 kpx s-1 per channel |
| Readout time (full frame)| 3.4 s (2 channels) |
| Vertical clock rate | 25 us per line |
| Operating temperature | 160 K < T < 300 K |
--------------------------------------------------------------------
|
.png)
.png)