Meteors are light phenomena resulting from the entry of dust particles (meteoroids) of millimeter to centimeter in size, into the Earth’s atmosphere. Meteor showers occur when the Earth passes through stream of dusts which are derived from specific comets or asteroids. These small bodies dynamically linked with dust stream of meteor showers are called meteor parent bodies. Annual meteor showers occur during the same period every year. Major annual meteor showers and their parent bodies are listed in Table 1.As the velocity of meteoroids of each meteor shower is known (Table 1), the size of the meteoroid can be estimated based on its brightness and light curve. Chemical composition of the meteoroid can be determined by the emission spectra. Thus, optical observation of meteor showers is important in understanding physical and chemical properties of meteoroids and their parent bodies. The International Space Station (ISS) is an ideal platform for continuous meteor observation without distortion caused by weather and atmospheric disturbances.
We conduct two-year long meteor observation project (named METEOR) onboard ISS, using a super sensitive, color high definition TV (HDTV) camera (Fig. 1) equipped with a wide-angle,bright lens (F 0.95, f=10.5mm, diagonal FOV 57.8 deg). The camera is installed in front of window of the Window Observational Research Facility (WORF) of the pressurized US Lab module (Destiny). Antares rocket for the first launch and Falcon 9 rocket for the second both failed in October 2014 and June 2015. METEOR was succesffuly launched with Atlas V rocket on March 22, 2016 for the third time luck. The observation started on July 7th, 2016 and is currently underway (Fig.2). Table 1. List of majot anual meteor showers Photometric observation is done in visible wavelength. Reflective coating on the window absorbs UV radiation, but transmittance rises rapidly after 304 nm to > 90% in the visible and into the near infrared. The Meteor camera is equipped with IR cut filer, which provides visible light only, up to 700 nm. A transmitted blazed diffraction grating is installed in front of the lens for the spectral observation to estimate meteors’ elemental abundance. The atomic emission lines of major elements are located within the visible wavelength; Fe I (370nm), Ca I (393nm), Mg I (518nm), Na I (589nm). The flux data collected will allow better comparison of physical and chemical data among major meteor showers and their parent bodies.
Operation and System configuraion
The ISS orbits the Earth for 90 minutes at an altitude of 400 km with an orbital inclination of 51.6 deg. The ISS night time where the Sun is beneath the horizon viewed from the ISS is about 35 minute in a single orbit. With the ISS orbiting the Earth 16 times in a single day, total night time for tmeteor observation is about 560 minutes.Except aperture adjustment and HDD swap which needbcrew support, all the operation of METEOR is remotely conducted from the operation center resided in our institute. Recording schedule is uploaded to the onboard PC in advance of observation. The onboard software on the PC performs on/off of the camera and the encoder, and processing/analyse of the observation data, based on the uploaded batch files. The shutter for the window is open while no visiting vehicle is docked to Node2 Nadir. With a visiting vehicle docked on Node2, the shutter open time is limited for 5-6 hours per day, according to the flight rule.
Data analyses & handling
With allowable data downlink rate (max. 4 Mbps) and with available command window of 9 hours per day, maximum downlinkable data volume per day is 6-9 GB. A single night pass data of about 35 minutes with 20 Mbps is 5.5 GB. Thus, all the acquired data can not be downlinked. All the recorded data are stored in a 750 GB HDD installed in the onboard PC. Software is being developed for autonomous detection of meteors in the acquired image data, and extraction of the data including meteor images, so that the image with meteors can only be downlinked in future The downlinked data is used for scientific interests, and is openly distributed by internet for the purpose of education and public outreach.
Initial results and upcoming study
Table 2 summarizes meteors captured on July 30 during a peak of Southern Delta Aquarids meteor shower. Due to the high beta angle of ISS till July 28, observation could be done only on July 29-31. In order to estimate physical properties from luminosity of the meteoroid, we will determine the luminosity of each data based on the ground calibration test data, using light sources.
 T. Arai (2014). LPSC 45th abstract #1610.  D. Jewitt & L. Jing (2010) Astronomical Journal, 140:1519–1527.  D. Jewitt et al. (2013) Astrophysical Journal Letters, 771:L36 (5pp),doi:10.1088/2041-8205/771/2/L36