Ki-Beom Ahn

Slewing Mirror Telescope optics for the early observation of UV/optical photons from Gamma-Ray Bursts

We report on design, manufacture, and testing of a Slewing Mirror Telescope (SMT), the first of its kind and a part of Ultra-Fast Flash Observatory-pathfinder (UFFO-p) for space-based prompt measurement of early UV/optical light curves from Gamma-Ray Bursts (GRBs). Using a fast slewing mirror of 150 mm diameter mounted on a 2 axis gimbal stage, SMT can deliver the images of GRB optical counterparts to the intensified CCD detector within 1.5~1.8 s over ± 35 degrees in the slewing field of view. Its Ritchey-Chrétien telescope of 100 mm diameter provides a 17 × 17 arcmin² instantaneous field of view. Technical details of design, construction, the laboratory performance tests in space environments for this unique SMT are described in conjunction with the plan for in-orbit operation onboard the Lomonosov satellite in 2013.

Implementation of the readout system in the UFFO Slewing Mirror Telescope

China Center of Advanced Science and Technology (CCAST);Chinese Academy of Sciences (CAS);Institute of High Energy Physics (IHEP);National Natural Science Foundation of China (NSFC)

THE UFFO SLEWING MIRROR TELESCOPE FOR EARLY OPTICAL OBSERVATION FROM GAMMA RAY BURSTS

While some space born observatories, such as SWIFT and FERMI, have been operating, early observation of optical after grow of GRBs is still remained as an unexplored region. The Ultra-Fast Flash Observatory (UFFO) project is a space observatory for optical follow-ups of GRBs, aiming to explore the first 60 seconds of GRBs optical emission. Using fast moving mirrors to redirect our optical path rather than slewing the entire spacecraft, UFFO is utilized to catch early optical emissions from GRB within 1 sec. We have developed the UFFO Pathfinder Telescope which is going to be on board of the Lomonosov satellite and launched in middle of 2012. We will discuss about scientific potentials of the UFFO project and present the payload development status, especially for Slewing Mirror Telescope which is the key instrument of the UFFO-pathfinder mission.

A next generation Ultra-Fast Flash Observatory (UFFO-100) for IR/optical observations of the rise phase of gamma-ray bursts

The Swift Gamma-ray Burst (GRB) observatory responds to GRB triggers with optical observations in ~ 100 s, butcannot respond faster than ~ 60 s. While some rapid-response ground-based telescopes have responded quickly, thenumber of sub-60 s detections remains small. In 2013 June, the Ultra-Fast Flash Observatory-Pathfinder is expected tobe launched on the Lomonosov spacecraft to investigate early optical GRB emission. Though possessing uniquecapability for optical rapid-response, this pathfinder mission is necessarily limited in sensitivity and event rate; here wediscuss the next generation of rapid-response space observatory instruments. We list science topics motivating ourinstruments, those that require rapid optical-IR GRB response, including: A survey of GRB rise shapes/times,measurements of optical bulk Lorentz factors, investigation of magnetic dominated (vs. non-magnetic) jet models,internal vs. external shock origin of prompt optical emission, the use of GRBs for cosmology, and dust evaporation inthe GRB environment. We also address the impacts of the characteristics of GRB observing on our instrument andobservatory design. We describe our instrument designs and choices for a next generation space observatory as a secondinstrument on a low-earth orbit spacecraft, with a 120 kg instrument mass budget. Restricted to relatively modest mass,power, and launch resources, we find that a coded mask X-ray camera with 1024 cm2 of detector area could rapidlylocate about 64 GRB triggers/year. Responding to the locations from the X-ray camera, a 30 cm aperture telescope witha beam-steering system for rapid (~ 1 s) response and a near-IR camera should detect ~ 29 GRB, given Swift GRBproperties. The additional optical camera would permit the measurement of a broadband optical-IR slope, allowingbetter characterization of the emission, and dynamic measurement of dust extinction at the source, for the first time.

A Modulation Transfer Function Compensation for the Geostationary Ocean Color Imager (GOCI) Based on the Wiener Filter

The modulation transfer function (MTF) is a widely used indicator in assessments of remote-sensing image quality. This MTF method is also used to restore information to a standard value to compensate for image degradation caused by atmospheric or satellite jitter effects. In this study, we evaluated MTF values as an image quality indicator for the Geostationary Ocean Color Imager (GOCI). GOCI was launched in 2010 to monitor the ocean and coastal areas of the Korean peninsula. We evaluated in-orbit MTF value based on the GOCI image having a 500-m spatial resolution in the first time. The pulse method was selected to estimate a point spread function (PSF) with an optimal natural target such as a Seamangeum Seawall. Finally, image restoration was performed with a Wiener filter (WF) to calculate the PSF value required for the optimal regularization parameter. After application of the WF to the target image, MTF value is improved 35.06%, and the compensated image shows more sharpness comparing with the original image.

The slewing mirror telescope of the Ultra Fast Flash Observatory Pathfinder

The Slewing Mirror Telescope (SMT) is a key telescope of Ultra-Fast Flash Observatory (UFFO) space project to explore the first sub-minute or sub-seconds early photons from the Gamma Ray Bursts (GRBs) afterglows. As the realization of UFFO, 20kg of UFFO-Pathfinder (UFFO-P) is going to be on board the Russian Lomonosov satellite in November 2012 by Soyuz-2 rocket. Once the UFFO Burst Alert & Trigger Telescope (UBAT) detects the GRBs, Slewing mirror (SM) will slew to bring new GRB into the SMT’s field of view rather than slewing the entire spacecraft. SMT can give a UV/Optical counterpart position rather moderated 4arcsec accuracy. However it will provide a important understanding of the GRB mechanism by measuring the sub-minute optical photons from GRBs. SMT can respond to the trigger over 35 degree x 35 degree wide field of view within 1 sec by using Slewing Mirror Stage (SMS). SMT is the reflecting telescope with 10cm Ritchey-Chretien type and 256 x 256 pixilated Intensified Charge-Coupled Device (ICCD). In this paper, we discuss the overall design of UFFO-P SMT instrument and payloads development status.

Data Acquisition System for the UFFO Pathfinder

The Ultra-Fast Flash Observatory (UFFO) Pathfinder is a payload on the Russian Lomonosov satellite, scheduled to be launched in November 2011. The Observatory is designed to detect early UV/Optical photons from Gamma-Ray Bursts (GRBs). There are two telescopes and one main data acquisition system: the UFFO Burst Alert & Trigger Telescope (UBAT), the Slewing Mirror Telescope (SMT), and the UFFO Data Acquisition (UDAQ) system. The UDAQ controls and manages the operation and communication of each telescope, and is also in charge of the in- terface with the satellite. It will write the data taken by each telescope to the NOR flash memory and sends them to the satellite via the Bus-Interface system (BI). It also receives data from the satellite including the coordinates and time of an external trigger from another payload, and distributes them to two telescopes. These functions are imple- mented in field programmable gates arrays (FPGA) for low power consumption and fast processing without a micro- processor. The UDAQ architecture, control of the system, and data flow will be presented.

Effects of ocean products variability from PSF blurring in NIR band

Development and operational planning for ocean color satellite requires lots of careful consideration of the spatial and radiometric performance, which are represented by modulation transfer function (MTF) and signal-to-noise ratio (SNR) respectively. Those representative values are crucial indicator of sensor performance so that small changes of ocean properties (e.g., remote sensed reflectance (Rrs), surface chlorophyll-a concentrations (Chl-a), and so on) can be quantified and directly related with those values. MTF is affected from a performance of instrument itself and environmental conditions, and its variation leads to change the final products. The goal of this study is to simulate and to analyze the relationship between MTF parameter and ocean product variations, and then to provide a reference for the design of future ocean color sensors. In this study, we used the Geostationary Ocean Color Imager (GOCI) data to generate the simulated atmospheric correction band image. And then Rrs data and ocean products were generated with imagery from two different locations and acquisition times, and we analyzed and compared the statistical results with study area having different characteristics. For ocean products relationships, we notify the linear variation of the absolute percentage difference (APD) according to the changeable MTF value. Especially, Case-II water (turbid water) area shows more sensitive variation than Case-I water (clear water) area. Even though the same area was applied in the simulation, it was 1-2 times higher sensitivity of variation when a specific ocean phenomena such as red tide. The suggested simulation can be confirmed the relationship between blurred NIR band image and ocean products. And statistical results with MTF values were able to help estimating ocean product precision and designing a future mission such as the Geostationary Ocean Color Imager-II (GOCI-II) mission currently being progressed.

Experimental Sensitivity Table Method for Precision Alignment of Amon-Ra Instrument

Corresponding AuthorE-mail: skim@csa.yonsei.ac.krTel: +82 2 362 7891, Fax: +82-2-362-7891 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Opto-mechanical performances of slewing mirror space telescope for GRB detection

The UFFO (Ultra-Fast Flash Observatory) Pathfinder is a space instrument onboard the Lomonosov satellite scheduled to be launched in November 2011. It is designed for extremely fast observation of optical counterparts of Gamma Ray Bursts (GRBs). It consists of two subsystems; i) UBAT (UFFO Burst Alert & Trigger Telescope) and ii) SMT (Slewing Mirror Telescope). This study is concerned with SMT opto-mechanical subsystem design and optical performance test. SMT is a F/11.4 Ritchey-Chretien type telescope benefited from compact design with a short optical tube assembly for the given focal length of 1,140 mm. SMT is designed to operate over a wide range of wavelength between 200 nm and 650 nm and has 17 arcmin FOV (Field of View), providing 4 arcsec in detector pixel resolution. The main detector is 256 x 256 ICCD (Intensified Charge-Coupled Device) of 22.2μm in pixel size. This SMT design offers good imaging performance including 0.77 in MTF at Nyquist frequency of 22.52 /mm and 2.7 μm in RMS spot radius. The primary (M1) and secondary (M2) mirror are hyperbolic surfaces and were manufactured within 1/50 waves (He-Ne, 632.8nm) in RMS surface error. After completion of the initial integration, the SMT opto-mechanical subsystem reached to the system wavefront error better than 1/10 waves in room temperature. We then tested the opto-mechanical performances under thermal cycling and vibration. In this study, we report the SMT subsystem design solution and integration together with thermal and vibration test results.