The satellites used highly eccentric elliptical orbits of 63.4 degrees inclination and orbital period of about 12 hours. Set of highly elliptical orbits (HEO) for continuous Arctic observation was described. Comparison of spatial coverage from three-satellite 16-h TAP HEO constellation in three orbital planes (120° apart in RAAN; P3) as shown in (a) and (b) vs constellation in one orbital plane P1 as shown in (c): (a) Earth views for a minimum latitude of continuous observations, (b) Earth views from satellites ±60° in MAA around the apogee direction (two-satellite viewing), and (c) as in (b), but for HEO constellation in one orbital plane. Figure 12 also shows results for 14-, 15-, and 16-h HEO systems. Corresponding altitude scaling factors are 0.97 and 1.01. The thickness of slab aluminum shielding required to keep the annual TID below 10, 5 and 3.33 krad (i.e. The radiation models for the trapped protons AP8 and electrons AE8 (Sawyer and Vette 1976; Vette 1991) have been utilized for conditions of a solar maximum for consistency with our previous analysis providing conservative estimates. Chobotov (2002) applies the MEO category to any small eccentricity orbit with period ranging between 2 and 18 h. The constellation of MEO satellites on circular orbits with inclination 90° (i.e., going over the North and South Poles) is of interest for our purpose of continuous polar coverage. Daily zonal mean coverage from three-, four-, five-, and six-satellite 24-h MEO systems for various VZA limits: (a) 70°, (b) 62°, and (c) 55°. The main conclusion that can be drawn from Fig. The low boundary latitude of continuous coverage zone for 24-h MEO constellations with three, four, five, and six satellites as a function of the VZA limit. It demonstrates that significant areas of the globe in the midlatitude and tropical zones can be observed for more than 50% of the time. A baseline HEO configuration should include at least two satellites to achieve continuous coverage of the polar zone. The Molniya Orbit Russia and its neighboring countries up in the north frequently use the Molniya orbit. Molniya Orbit. 9. The question now is how to meet this requirement for VZA and coverage zone from a HEO or MEO system? To avoid this expenditure of fuel, the Tundra orbit uses an inclination of 63.4°, for which the factor In conclusion, continuous meteorological imaging of polar regions can be achieved from either MEO or HEO constellations. 2 Trishchenko et al. The vulnerability to the Single Event Effect (SEE) was compared for all orbits by modeling the Linear Energy Transfer (LET) for long-term conditions and for the 5 min “worst case” scenario. The selection of 24-h MEO system ensures the most favorable space radiation environment among other MEO systems with periods of ≤24 h. The thickness of aluminum slab to keep the annual TID at 3.33 krad yr−1, i.e., 15 years of mission lifetime for a total mission dose of 50 krad. An argument of perigee of 270° places apogee at the northernmost point of the orbit. Point S denotes the satellite position, point O corresponds to the center of Earth, and P1 and P2 denote the position of subsatellite point and the intersection of line of sight with the surface. (A11) and (A12) and recalling that cos2x = cos2x − sin2x leads to the relationship between angles δ, ε, and φ: The condition of overlap should be fulfilled, which leads to, The pixel growth factor FPGF as a function of VZA can be computed as, Atmospheric Imaging Mission for Northern Regions, European Organisation for the Exploi tation of Meteorological Satellites, Geostationary Environmental Moni toring Spectrometer, Geostationary Coastal and Air Pollu tion Events, Infrared Atmospheric Sounding Interferometer, Infrared Fourier-Transform Spectrometer—Geostationary, National Aeronautics and Space Administration, National Oceanic and Atmospheric Administration, Notation for configuration with one (three) orbital plane(s), Television and Infrared Observation Satellite, Half of the angular spacing between two MEO satellites, Minimum (the southmost) latitude observed at the apogee point in the Northern Hemisphere by the HEO satellite looking across the North Pole. An argument of perigee of 90° would likewise serve the high southern latitudes. Molniya orbit is a highly elliptical orbit with an inclination of 63.4 degrees, an argument of perigee of -90 degrees and an orbital period of one half of a sidereal day. We are interested in the relation between angle φ (or latitude span), scan angle β, and VZA θ as a function of satellite altitude h and Earth’s radius Re. [20], The Japanese Quasi-Zenith Satellite System uses a geosynchronous orbit similar to a Tundra orbit, but with an inclination of only 43°. "spy satellites". These LEO sounding systems can provide global sounding information several times per day (Trishchenko and Garand 2012). The constellation was developed to better reach consumers in far northern latitudes, reduce the impact of urban canyons and required only 130 repeaters compared to 800 for a geostationary system. The multiple-apogee systems, as shown in Figs. This capability is beneficial for the MEO–GEO and MEO–LEO satellite intercalibration, as well as for potential use in improved retrievals of scene anisotropy (bidirectional reflectance/emission function), cloud height and AMV among others, from multiview (stereo) observations. This is beneficial for satellite intercalibration and for creating the backup imaging capacity in this zone, as well as for improved retrievals due to multiview capacity. ... Abbreviated as RAAN. On the other hand, no fewer than six satellites are required to achieve continuous coverage at the VZA limit of 55° for the latitude zone above 55° with lowest altitudes starting at 24 000 km (period ≥ 14.6 h). Stationary orbitsare a special kind of synchronous orbit. Points O1, C, and O2 lie along the equator for the case of GEO satellites. 5a–c. It's also used to observe two off-equator regions of Earth, 180 degrees of longitude apart. A well-established HEO is the Molniya (‘‘lightning’’ in Russian) orbit used intensively by the Soviet Union and the Russian Federation for communication purposes since 1965. (A15) defined in appendix A. Figure 9b shows that four MEO satellites in constellation can also achieve continuous coverage within VZA limit of 62° but the latitudinal boundary cannot be lower than ~55° and satellite altitudes should be ≥38 000 km (period ≥ 25.8 h). Spatial coverage from a one-satellite HEO system is also shown in Fig. In-depth analysis of the space environment showed that the 12-h Molniya orbit exposes the spacecraft to a challenging ionizing environment due to the high energy protons of the inner radiation belt ( Trichtchenko, 2012 ).
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