In order to adapt to small size and low cost space platform such as mini-satellites, this paper studies the design of optics for compact star sensor. At first, the relationship between limiting magnitude and optical system specifications which includes field of view and entrance pupil diameter is analyzed, based on its Pyramid identification algorithm and signal-to-noise ratio requirement. The specifications corresponding to different limiting magnitude can be obtained after the detector is selected, and both of the complexity of optical lens and the size of baffle can be estimated. Then the range of the limiting magnitude can be determined for the miniaturization of the optical system. Taking STAR1000 CMOS detector as an example, the compact design of the optical system can be realized when the limiting magnitude is in the interval of 4.9Mv~5.5Mv. At last, the lens and baffle of a CMOS compact star sensor is optimally designed, of which length and weight is respectively 124 millimeters and 300 grams.
Advanced optical imaging systems should have high imaging quality and robotic environmental suitability. Such a
near-infrared lens with the Pitzval style is designed and developed. Its operation wavelength is from 0.72μm to 1.0μm
and its relative aperture as high as 1:2. Its passive athermalization design to suit for the wide operation temperature range
from -45°C to 60°C is implemented through optimal selection of its optical glasses and opto-mechamical structure.
Sharp ghost image due to even reflection at optical surfaces is eliminated with our suggested means, and thus stray light
within its image plane is both low and uniform even under backlighting. The Modulation Transfer Function (MTF) of the
designed lens at the Niquest spatial frequency 90 lines/mm of focal plane array detector is higher than 0.6 within its
operation temperature range and its entire field of view. Eighty percent of its diffraction encircled energy is within one
pixel of the detector. Its point source transmittance (PST) when the illuminating off-angle of point source is from 5 to 60
degrees, which is just out of its field of view, is computed through modeling and simulation, and as low as between 10-3
to 10-11. The experimentally measured MTF values and veiling glare index of our developed lens reaches respectively to
0.61 and 0.372% and validates our suggested design in the paper.
Noise equivalent temperature difference (NETD) is the key parameter characterizing the detectivity of infrared systems.
Our developed pushbroom longwave infrared imaging spectrometer works in a waveband between 8μm to 10.5 μm. Its
temperature sensitivity property is not only affected by atmosphere attenuation, transmittance of the optical system and
the characteristics of electric circuit, but also restricted by the self-radiation. The NETD accurate calculation formula is
derived according to its definition. Radiation analysis model of a pushbroom image spectrometer is set up, and its
self-radiation is analyzed and calculated at different temperatures, such as 300K, 150K and 120K. Based on the obtained
accurate formula, the relationships between the NETD of imaging spectrometer and atmospheric attenuation, F-number,
effective pixel area of detector, equivalent noise bandwidth and CCD detectivity are analyzed in detail, and self-radiation
is particularly discussed. The work we have done is to provide the basis for parameters determination in spectrometer
system.
A star tracker optical imaging system is designed for Polaris detection. System parameters determination and its configuration chosen method are given. Based on Macsutov-Cassegrain configuration, the system is designed imagery tele-centric. It works at 0.6μm~1.1μm waveband and the view field is 0.5 degree. The tube length of the system is 80mm, which is only 8 percent of its focal length. Its MTF reaches diffraction limit and the spot diagrams are quit near a circle. About 80% of the energy is encircled in a CCD pixel. And the distortion is less than 1%. Moreover, it has a perfect thermal adaptability from -40℃ to 60℃.
Zoom lens with variable focal length is well fit for researching objectives far and near. Design of zoom lens working at mid-wave infrared wavelength (7.7-10.3_m) and its view field 10 degrees is presented. Determination of the initial configuration of the variable and the compensate groups are discussed according to the mechanism compensate curves. The compensate group is determined with positive power. Its focal length changes during a large scope, which is from 300mm to 100mm. And the corresponding F number variables from 3.75 to 1.25. So the residual aberration needs to be carefully corrected. The optimized zoom lens is composed of four group elements, and its performance reaches diffraction limited at each focal position.
A two-mirror catadioptric system with corrective lens groups is adopted in the remote sensing camera of microsatellite.
Compared with the refractive system, it has the advantage that its performance is hardly influenced by thermal
environment. Stray light results in image blur and the contrast reduction of the camera. It is necessary to analyze and
control it. In traditional way, stray light can be effectively suppressed with a long baffle, which is not suitable for
microsatellites with limited space. And a compact one with high performance is designed. First of all, model of the
camera is set up and its stray light is analyzed with Lighttools. The main and the primary baffles are designed and
optimized. Then the point source transmittance is calculated to evaluate and verify the designs. Its veiling glare index is
also simulated and calculated based on black-patch measurement.
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