In this paper, a development approach is proposed for micro-camera systems that are dedicated to constellation operations of satellites. It is to take a regular practice and design the system based on traditional, professional optical layouts rather than simplifying configuration. LIBERO-1 and LIBERO-2 are the cameras under development to study whether the approach is feasible. LIBERO-1 is designed to have better than 1-m resolution in panchromatic spectral channel at the altitude of 500 km. It can support up to 6 multispectral channels and 12000 active pixels in swathwidth. The dimension is estimated to be within 20 cm x 20 cm x 30 cm, which is almost half the length of 1-m resolution cameras available in market. LIBERO-2 has better than 2-m resolution at 500 km altitude. It can also support up to 6 multispectral channels and 8000 active pixels in swathwidth. LIBERO-2 has a similar size to star sensors so that its dimension is 10 cm x 10 cm x 20 cm.
Funded by the Ministry of Commerce, Industry, and Energy of Korea, SI initiated the development of the prototype model of TMA-based electro-optical system as part of the national space research and development program. Its optical aperture diameter is 120 mm, the effective focal length is 462 mm, and its full field-of-view is 5.08 degrees. The dimension is of about 600 mm × 400 mm × 400 mm and the weight is less than 15 kg.
To demonstrate its performance, hyper-spectral imaging based on linear spectral filter is selected for the application of the prototype. The spectral resolution will be less than 10 nm and the number of channels will be more than 40 in visible and nearinfrared region.
In this paper, the progress made so far on the prototype development will be presented
Satrec Initiative and ATSB have been developing a medium-sized aperture camera (MAC) for an earth observation payload on a small satellite. Developed as a push-broom type high-resolution camera, the camera has one panchromatic and four multispectral channels. The panchromatic channel has 2.5m, and multispectral channels have 5m of ground sampling distances at a nominal altitude of 685km. The 300mm-aperture Cassegrain telescope contains two aspheric mirrors and two spherical correction lenses. With a philosophy of building a simple and cost-effective camera, the mirrors incorporate no light-weighting, and the linear CCDs are mounted on a single PCB with no beam splitters. MAC is the main payload of RazakSAT to be launched in 2005. RazakSAT is a 180kg satellite including MAC, designed to provide high-resolution imagery of 20km swath width on a near equatorial orbit (NEqO). The mission objective is to demonstrate the capability of a high-resolution remote sensing satellite system on a near equatorial orbit. This paper describes the overview of the MAC and RarakSAT programmes, and presents the current development status of MAC focusing on key optical aspects of Qualification Model.
The MTF (modulation transfer function) has been used to evaluate the performance of optical systems. More accurate
access to on-orbit MTF opens the way to enhance images so that we can deduce more information from the images of
IKONOS, OrbView, or SPOT. Generally, the MTF was assessed using various methods such as the point source method
and the knife-edge method etc. In this paper, the value of the slanted-edge method is investigated as a tool to assess the
on-orbit MTF. The slanted-edge method is the ISO 12233 standard for the MTF measurement of electronic still-picture
cameras. The method is adapted to estimate the MTF values of line-scanning telescopes. We applied the method to
measure the MTF of high resolution satellite images and also, we compared the MTF measurement with that of the
knife-edge method applied to EOS-C test images to increase the confidence on MTF measurement on EOS-C. EOS-C is
a 2.5m resolution satellite sensor for SI-200 satellite which is under the development by Satrec Initiative. The MTF
measured from this method is used for the MTF compensation of satellite images by generating the MTF convolution
kernel based on the PSF (point spread function).
Pre-launch performance has been characterized on the EOS-C camera: capable of Earth observation at 2.5 m resolution
and 20 km swath width. Topics discussed in this paper include measurements of system modulation transfer function
(MTF) and pixel lines-of-sight (LOS); radiometric and spectral calibration; end-to-end imaging.
Funded by the Ministry of Commerce, Industry, and Energy of Korea, Satrec Initiative has initiated the development of
the prototype model of a TMA-based electro-optical system as part of the national space research and development
program. Its optical aperture diameter is 120 mm, the effective focal length is 462 mm, and its full field-of-view is 5.08
degrees. The dimension is about 600 mm × 400 mm × 400 mm and its weight is less than 15 kg.
To demonstrate its performance and versatility, multi-spectral imaging in visible and near-infrared region was chosen as
the application of the prototype.
In this paper, the progress made so far on the prototype development and the future plan will be presented.
The mission of DIOS program is to provide the function of large-swathwidth or in-track stereo imaging with compact
electro-optical cameras. Optimized from its predecessor SAC (Small-sized Aperture Camera), DIOS consists of two
cameras, each with an aperture of 120 mm diameter, 10 m GSD, and 50 km swath width in the spectral range of 520 ~
890 nm. DIOS is developed to produce high quality images: MTF of more than 12 %; SNR of more than 100. DIOS can
be configured to have cameras side-by-side, providing a swathwidth up to 100 km for a mission of large swathwidth.
DIOS will be configured with installation of slanted two cameras for the mission of in-track stereo imaging to produce
digital elevation model. In this paper, Dual Imaging Optical Sensor (DIOS) will be introduced with design approach and
performance measure. Even though developed for micro satellites, the presentation of development status and test
results will demonstrate the potential capability that DISO can provide for world-wide remote sensing groups: short
development period, cost-effectiveness, wide application ranges, and high performance.
Medium-sized Aperture Camera (MAC) is the main payload for Earth observation satellite RazakSAT to be launched at the end of 2005. The flight model has been recently assembled and tested. The 300 mm diameter Cassegrain telescope optics and the focal plane assembly for a space camera have been aligned. Topics discussed in this paper include the lessons learned from the optics alignment and assembly of the telescope and the focal plane. A computer-aided alignment method was used for the alignment of the relatively wide field of view (+/-1 deg) telescope. RMS wavefront error measurement environment was found to be more critical than previously experienced, and the importance of the initial alignment is discussed. System modulation transfer function (MTF) was used as the figure-of-merit for the alignment of the focal plane assembly with linear CCD detectors. MTF was measured by a knife-edge scanning technique using a dedicated 450 mm diameter collimator with diffraction-limited performance.
Pre-flight performance has been characterized on the Medium-sized Aperture Camera (MAC) of the RazakSAT: capable of Earth observation at 2.5 m resolution and 20 km swath width. Topics discussed in this paper include measurements of system modulation transfer function (MTF) and pixel lines-of-sight (LOS); characterization of focal plane assembly (FPA) and signal processing electronics; end-to-end imaging. The MTF was obtained with knife-edge scanning technique, which is also used to align the FPA. For band-to-band registration, relative pixel LOS was measured using theodolite and effective focal length of the telescope was derived from the measurement. For the FPA and signal processing module, dark reference, pixel-to-pixel response variation and response linearity have been quantified. The end-to-end imaging tests were done to check the imaging function before the launch, by scanning a slide target at the focus of the collimator.
Medium-sized Aperture Camera (MAC) for earth observation on a small satellite is being developed by Satrec Initiative and ATSB. Designed as a cost-effective high-resolution camera, this push-broom type camera has 1 panchromatic and 4 multispectral channels using all-CCDs-in-one focal plane, and it does not split the channels by prisms. The panchromatic channel has 2.5m, and multispectral channels have 5m of ground sampling distance at a nominal altitude of 685km. The 300mm modified Ritchey-Chretien telescope contains two aspheric mirrors and two spherical correction lenses. MAC is the main payload of RazakSAT (formerly known as MACSAT) to be launched in 2005. RazakSAT is a 180kg (including MAC) small satellite, designed to provide high-resolution imagery of 20km swath width on a near equatorial orbit (NEqO). The mission objective is to demonstrate the capability of a high-resolution small remote sensing satellite system on a near equatorial orbit. This paper describes the status report on the development of the MAC Qualification Model and technical issues.
SAC is a compact camera for imaging in visible-NIR spectral ranges. SAC provides high-resolution images over the wide geometric and spectral ranges: 10 m GSD and 50 km swath-width in the spectral ranges of 520 ~ 890 nm. The missions incorporate various imaging operations: multi-spectral imaging; super swath-width imaging with cameras in parallel; along-track stereo imaging with slanted 2 cameras. In this paper, SAC is introduced with design and performance. Though developed for small satellites, presenting development status and test results will demonstrate the potential capability for worldwide remote sensing groups: short development period, cost-effectiveness, and high performance.
Ritchey-Chretien type or Cassegrain type has been widely used for earth-observing space camera. As most earth-observing cameras are required to scan the wide area in a single path, they generally have a wider field of view, compared to the ground-based telescope. However, the alignment of Cassegrain or RC telescope with a wide-field of view is not easy. One reason is that it has a central hole in the primary mirror so that it is difficult to find an optical axis. Another reason is that it can introduce much off-axis aberration such as coma and astigmatism, when it is aligned at on-axis with zero-coma condition. In this paper, we calculate the alignment accuracy using a conventional method for a RC type telescope of which diameter is 300 mm and field of view is 2.08 degrees. We suggest that the most effective alignment method for wide field of view system is a computer-aided alignment. With this method, it was found that the variation of rms wavefront error of the telescope over the entire field of view was less than 10 %.
The ground test model of a high-resolution camera for small satellites was developed. It is a Cassegrain system with field correction lenses. Except for lenses, all optical and structural components are made of the same Aluminum material. This scheme has its advantages in cost, development period, and athermalization. In addition, the deformation of mirrors occurred during assembly could be corrected by using simple clamps. After assembly, the final MTF was measured about 19%. The Aluminum-based test model was found to be a cost-effective tool for ground test.
A method for measuring the wave front errors and the modulation transfer function (MTF) of the large aperture optics is presented. The large aperture Fizeau interferometer with long optical path difference by using a (phi) 400 mm off-axis parabolic mirror is made. The MTF is measured at the wavelength of the interferometer by changing the laser into the partially incoherent light. A bidirectional shearing interferometer is used for collimation testing. The test results of a (phi) 300 mm Cassegrain type satellite telescope made in Korea are presented.