4a is the region of high-density proton flux in the equatorial zone. It is assumed that the argument of perigee ω for the elliptical orbit is equal to 270° in order to place the apogee at the highest latitude, such that the true anomaly v for the satellite crossing the equatorial plane is equal to ±90°. orbit, but at the particular inclination of the Molniya orbits, this effect is zero and the apogee stays where its put. Choosing an inclination of 63.3 or 116.6 degrees allows the satellite to have a constant argument of perigee of 90 or 270 degrees because the orbits are not perturbed by the gravitational field of Earth (J2 term of the Geopotential Model). The Meridian communications payload covers frequencies in VHF, UHF and S-Band frequencies. It should be understood that any HEO orbit can still be subject to impacts by high-energy solar and cosmic particles resulting from open magnetic lines in the polar region. Meridian 2 successfully deployed its solar arrays and antennas following orbital insertion and initiated communications with the ground. It may lead to a reduction of coverage by nearly 6%, that is, close to 90-min gaps in data over a specific area. where E is the eccentric anomaly. The Molniya orbit was discovered by Soviet scientists in the 1960s as a high-latitude communications alternative to geostationary orbits, which require large launch energies to achieve a high perigee and to change inclination to orbit over the equator (especially when launched from Russian latitudes). Figure 6 shows this new function overlaid on top of Fig. The graphical representation of expression (3) is displayed in Fig. An important feature of HEO orbits is the diversity of viewing geometry, in contrast to polar-orbiting low Earth observing (LEO) and GEO satellites. Amer. This allows the spacecraft to stay above the peak density–trapped proton region. For example, the satellite on orbit with e > 0.50 spends >50% time above 45°N. Together, both relations expressed by Eqs. The analysis of the two-line element (TLE) orbital data for the Sirius XM satellites on the 24-h Tundra at critical inclination also reveals the existence of a perigee drift <1° yr−1. The arrays can be rotated to provide optimized sun tracking and power generation. (8) that the ΔV budget is driven by two factors: the shape of the orbit (coefficient C) and the angular difference Δω in argument of perigee. The above condition can be expressed in terms of the length of the semilatus rectum for the elliptical orbit as. For the circular orbit, this time will be below 25%, that is, at least twice smaller. Semi-major axis: 26600 km 2. Unlike GEO, the HEO system allows observations of the same point at different VZA. It is slightly above 30 m s−1 at the apogee, reaches 200 m s−1 at ±3 h, 300 m s−1 at ±4 h, >400 m s−1 at ±5 h, and exceeds 700 m s−1 at ±6 h. The ground speeds for the orbits with inclination 66° and 70° are higher, on average, by about 15 and 40 m s−1, respectively. Other factors that can influence the final selection of orbit inclination include launch vehicle capacity, spacecraft mass, expected mission lifetime, and the efficiency and amount of available fuel for orbital maneuvers. The 100% (continuous) coverage is achieved for a latitude range from the pole (90°) to slightly below 60°, while coverage of 50% is still achieved at 10° latitude, providing a valuable backup to all GEOs. Meteor. The impact of data reception is much more significant for the 24-h HEO system. The 16-h imaging per satellite for (a) two-satellite constellation and (b) with a restriction of antenna elevation at Yellowknife >5°. Results were computed for the 16-h imaging scenario for each satellite and condition VZA < 70°, which is considered a practical limit for quantitative data processing. Several other parameters of the MAP HEO orbits are presented in Table 1. SPENVIS Web-based tool was used to generate results.