Nozomi Mars Imaging Camera
Introduction and Description
The Mars Imaging Camera (MIC) is a visual wavelength camera to be launched with the Planet-B spacecraft. It was built by NEC of Japan using 3 Kodak line array CCD's operating in a pushbroom (forward sweeping) mode to acquire color images of Mars.
The size of the MIC is approximately 92 mm x 150 mm x 235 mm and a sketch appears in Figure 1. It weighs about 2.5 kg and consumes about 14 W of power while imaging. A complete list of specifications is also presented in Table 1.
| Hardware Specifications | ||
|---|---|---|
| Optics | Aperture | 21.4 mm |
| Focal length | 30 mm | |
| F number | F1.4 | |
| CCD | linear 3 color CCD (Kodak KLI_4103) | |
| 4104 pixels (only 2560 pixels are used) | ||
| RED | 9V/ µ J/cm2@ 650nm | |
| GREEN | 8V/ µ J/cm2 @ 550nm | |
| BLUE | 4V/ µ J/cm2 @ 450nm | |
| Pixel Pitch | 12 µ m | |
| Integration Time | 0.512 ms | |
| Total Field Of View |
Azimuth | 360 deg |
| Elevation | 54.2 deg | |
| Pixel Resolution |
Azimuth | 82.9 arcsec@7.5 rpm |
| Elevation | 82.5 arcsec@ceter of FOV | |
| 65.4 arcsec@edge of FOV | ||
| A/D Conversion | 8 bit, 6 MHz | |
| Image Memory | 1 Mbyte | |
| Image Compression Module |
JPEG revision 5 algorithm | |
| range | 3 to 100 | |
| speed | 3.4 Mpixels/s @ 12 MHz | |
The optics consist of a radiation hardened lens system with an aperture of 21.4 mm and a focal length of 30 mm giving an F number of 1.4 and guiding light to 3 linear CCD sensors. Color images are produced by using each of the three color filters, centered on 450, 550, and 650 nm, respectively, in succession.
The CCD sensors consist of 1 x 2560 pixel arrays. The individual pixels of the CCD sensors are 12 µ m wide with an individual resolution of about 74"(arc seconds) along the array and approximately 82.9" in the direction of rotation, given a rotation speed of 7.5 RPM and 0.51 ms integration time. The field-of-view along the array is 54.2° and effectively 360° in the perpendicular direction due to the spin of the spacecraft, although actual size is limited by the memory of the camera system. A/D conversion of the CCD elements is done at 6 MHz and is stored in the camera's 1 Mbyte on-board memory. Image compression uses a JPEG standard algorithm to compress images from 3 to 100 times at 3.4 Mpixels/sec at 12 MHz.
The camera has 4 possible gain settings, one for dark Martian surfaces, two for bright surface areas and Phobos & Deimos, and one for the polar caps.
During the mission, MIC can operate in two modes: command and auto. Command mode is when command are sent directly to the camera to begin imaging until an image of the pre-selected size is completed. This is the normal operating mode. Only one shot is available per rotation, so when to start imaging has to been selected carefully. Auto mode was designed primarily for observations of Phobos and Deimos. The camera continuously images until a pixel registers a value higher than a preset threshold value, at which point it begins building an image of pre-selected size.