Bright Perseids 2007-2012 statistics. Estimation of collision risks in circumterrestrial space
Abstract
Bright meteors are of serious hazard for space vehicles. In the Persieds shower these are the meteors brighter than 0m [2]. During 2007-2012 we conducted wide-angle CCD observations of bright Perseids [3-5]. Observations were performed near Ryazan, Russia, (= 54.467 N, λ=39.750 E, H=200 m) using a Watec 902H camera and a Computar T2314FICS lens with the effective FOV of 140×100 arc degrees directed towards the local zenith. The sky control and meteor detection were provided using a Pinnacle Media Center EN or the Contrast as a grabber and an Intel Core.2 CPU processor, 1.83GHz, 500Mb RAM. Our results as compared to the visual meteors total number (IMO) are shown in Fig. 1. The averaged Perseids maximum lies within the solar longitudes 140.00-140.25 and here the average total shower spatial density is (80±6)·10-9km-3. The bright Perseids average spatial density maximum is about (6±2) 10-9km-3. The bright Perseids average percentage in the shower is calculated as the integrals ratio under the curves in Fig. 1 and is equal to 5% for the presented range of solar longitudes. It is natural to expect that the space densities of meteoroids decrease exponentially from the maximum [1]: D = D0exp{-B|λ-λ0|}, (1) where: D0 is the maximum meteor spatial density near the solar longitude λ0 and B - the factor determined empirically from observations. The meteoroid flux F is equal to the number of particles passing through the elementary area per time unit: F(λ) = D(λ)·v, (2) where: v - is the meteor shower velocity. During the Perseids' maximum (D0=6·10-9km-3 and v=59km/s) the bright meteoroid flux was equal to F (3.8±1.1)10-7km-2s-1, which corresponds to the hour rate HR15 for our camera FOV. The collision risk R here amounted to one collision per month on average with a 1 sq. km plane located normal to the meteor shower. An artificial space object rotating around the Earth constantly changes its orientation relative to the meteor shower, the Sun, and a ground-based observer. From time to time, the Earth occults the satellite from meteoroids. The number of collisions between this meteor shower's dangerous meteoroids and the satellite during the time Т of its flight around the Earth is 6]: N = K1·K2·K3·S·F (λ)·T. (3) Here К1 accounts for the Earth's geliocentric position in the current season relative to the meteor shower radiant. К2 accounts for the satellite's plane surfaces relative to the meteor shower radiant. К3 is defined by the satellite's orbit parameters. Calculations are done in the ecliptic reference system (Fig. 2), wherein a satellite can be considered located in the ecliptic plane. In this figure: N is the normal to the satellite's surface; , , Е - directions to the vernal equinoctial point, the Sun and the Earth; λR, λ, - ecliptic longitudes of the meteor radiant and the Sun; λE - the ecliptic satellitecentric Earth longitude; bR and bE - consequent ecliptic latitudes of meteor shower radiant and the Earth.
- Publication:
-
European Planetary Science Congress
- Pub Date:
- September 2013
- Bibcode:
- 2013EPSC....8..346M