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.
We describe the space project of Ultra-Fast Flash Observatory (UFFO) which will observe early optical photons from
gamma-ray bursts (GRBs) with a sub-second optical response, for the first time. The UFFO will probe the early optical
rise of GRBs, opening a completely new frontier in GRB and transient studies, using a fast response Slewing Mirror
Telescope (SMT) that redirects optical path to telescope instead of slewing of telescopes or spacecraft. In our small
UFFO-Pathfinder experiment, scheduled to launch aboard the Lomonosov satellite in 2012, we use a motorized mirror in
our Slewing Mirror Telescope instrument to achieve less than one second optical response after X-ray trigger. We
describe the science and the mission of the UFFO project, including a next version called UFFO-100. With our program
of ultra-fast optical response GRB observatories, we aim to gain a deeper understanding of GRB mechanisms, and
potentially open up the z<10 universe to study via GRB as point source emission probes.
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.
Since the launch of the SWIFT, Gamma-Ray Bursts (GRBs) science has been much progressed. Especially supporting
many measurements of GRB events and sharing them with other telescopes by the Gamma-ray Coordinate Network
(GCN) have resulted the richness of GRB events, however, only a few of GRB events have been measured within a
minute after the gamma ray signal. This lack of sub-minute data limits the study for the characteristics of the UV-optical
light curve of the short-hard type GRB and the fast-rising GRB. Therefore, we have developed the telescope named the
Ultra-Fast Flash Observatory (UFFO) Pathfinder, to take the sub-minute data for the early photons from GRB. The
UFFO Pathfinder has a coded-mask X-ray camera to search the GRB location by the UBAT trigger algorithm. To
determine the direction of GRB as soon as possible it requires the fast processing. We have ultimately implemented all
algorithms in field programmable gate arrays (FPGA) without microprocessor. Although FPGA, when compared with
microprocessor, is generally estimated to support the fast processing rather than the complex processing, we have
developed the implementation to overcome the disadvantage and to maximize the advantage. That is to measure the
location as accurate as possible and to determine the location within the sub-second timescale. In the particular case for a
accuracy of the X-ray trigger, it requires special information from the satellite based on the UFFO central control system.
We present the implementation of the UBAT trigger algorithm as well as the readout system of the UFFO Pathfinder.
The Ultra Fast Flash Observatory pathfinder (UFFO-p) is a telescope system designed for the detection of the prompt optical/UV photons from Gamma-Ray Bursts (GRBs), and it will be launched onboard the Lomonosov spacecraft in 2012. The UFFO-p consists of two instruments: the UFFO Burst Alert and Trigger telescope (UBAT) for the detection and location of GRBs, and the Slewing Mirror Telescope (SMT) for measurement of the UV/optical afterglow. The UBAT isa coded-mask aperture X-ray camera with a wide field of view (FOV) of 1.8 sr. The detector module consists of the YSO(Yttrium Oxyorthosilicate) scintillator crystal array, a grid of 36 multi-anode photomultipliers (MAPMTs), and analog and digital readout electronics. When the γ /X-ray photons hit the YSO scintillator crystal array, it produces UV photons by scintillation in proportion to the energy of the incident γ /X-ray photons. The UBAT detects X-ray source of GRB inthe 5 ~ 100 keV energy range, localizes the GRB within 10 arcmin, and sends the SMT this information as well as drift correction in real time. All the process is controlled by a Field Programmable Gates Arrays (FPGA) to reduce the processing time. We are in the final stages of the development and expect to deliver the instrument for the integration with the spacecraft. In what follows we present the design, fabrication and performance test of the UBAT.
Geostationary Ocean Color Imager(GOCI) is one of three payloads on board the Communication, Ocean, and
Meteorological Satellite(COMS) launched 27th, June, 2010. For understanding GOCI imaging performance, we
constructed the Integrated Ray Tracing model consisting of the Sun model as a light source, a target Earth model,
and the GOCI optical system model. We then combined them in Monte Carlo based ray tracing computation.
Light travels from the Sun and it is then reflected from the Earth section of roughly 2500km * 2500km in
size around the Korea peninsula with 40km in spatial resolution. It is then fed into the instrument before reaching to the detector plane. Trial simulation runs for the GOCI imaging performance were focused on the combined slot images and MTF. First, we used modified pointing mirror mechanism to acquire the slot images, and then mosaiced them. Their image performance from the GOCI measurement were compared to the ray tracing simulation results. Second, we investigated GOCI in-orbit MTF performance with the slanted knife edge method applied to an East coastline image of the Korea peninsula covering from 38.04N, 128.40E to 38.01N, 128.43E. The ray tracing simulation results showed 0.34 in MTF mean for near IR band image while the GOCI image obtained 9th Sep, 2010 and 15th Sep, 2010, were used to produce 0.34 at Nyquist frequency in MTF. This study results prove that the GOCI image performance is well within the target performance requirement, and that the IRT end-to-end simulation technique introduced here can be applicable for high accuracy simulation of in-orbit performances of GOCI and of other earth observing satellite instruments.
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.
Accurate identification and understanding of spectral bio-signatures from possible extra terrestrial planets have received
an ever increasing attention from both astronomy and space science communities in recent years. In pursuance of this
subject, one of the most important scientific breakthroughs would be to obtain the detailed understanding on spectral biosignatures
of the Earth, as it serves as a reference datum for accurate interpretation of collapsed (in temporal and spatial
domains) information from the spectral measurement using TPF instruments. We report a new Integrated Ray Tracing
(IRT) model capable of computing various spectral bio-signatures as they are observed from the Earth surface. The
model includes the Sun, the full 3-D Earth, and an optical instrument, all combined into single ray tracing environment in
real scale. In particular, the full 3-D Earth surface is constructed from high resolution coastal line data and defined with
realistic reflectance and BSDF characteristics depending on wavelength, vegetation types and their distributions. We first
examined the model validity by confirming the imaging and radiometric performance of the AmonRa visible channel
camera, simulating the Earth observation from the L1 halo orbit. We then computed disk averaged spectra, light curves
and NDVI indexes, leading to the construction of the observed disk averaged spectra at the AmonRa instrument detector
plane. The model, computational procedure and the simulation results are presented. The future plan for the detailed
spectral signature simulation runs for various input conditions including seasonal vegetation changes and variable cloud
covers is discussed.
The Geostationary Ocean Colour Imager (GOCI) is a visible band ocean colour instrument onboard the
Communication, Ocean, and Meteorological Satellite (COMS) scheduled to be in operation from early 2010. The
instrument is designed to monitor ocean water environments around the Korean peninsula in high spatial and temporal
resolutions. We report a new imaging and radiometric performance prediction model specifically designed for GOCI.
The model incorporates the Sun as light source, about 4000km x 4000km section of the Earth surrounding the Korean
peninsula and the GOCI optical system into a single ray tracing environment in real scale. Specially, the target Earth
section is constructed using high resolution coastal line data, and consists of land and ocean surfaces with reflectivity
data representing their constituents including vegetation and chlorophyll concentration. The GOCI instrument in the IRT
model is constructed as an optical system with realistic surface characteristics including wave front error, reflectivity,
absorption, transmission and scattering properties. We then used Monte Carlo based ray tracing computation along the
whole optical path starting from the Sun to the final detector plane, for simultaneous imaging and radiometric
performance verification for a fixed solar zenith angle. This was then followed by simulation of red-tide evolution
detection and their radiance estimation, in accordance with the in-orbit operation sequence. The simulation results prove
that the GOCI flight model is capable of detecting both image and radiance originated from the key ocean phenomena
including red tide. The model details and computational process are discussed with implications to other earth