2.0.CO;2, "The Orbital Lifetime of Molniya Satellites", Final evaluation of the Australian Space Research Program, "As the details emerge on Australia's new space agency, we (might) finally have lift-off", "On the Use of Satellites in Molniya Orbits for Meteorological Observation of Middle and High Latitudes", "Systems Engineering of a Terabit Elliptic Orbit Satellite and Phased Array Ground Station for IoT Connectivity and Consumer Internet Access", Models for Propagation of NORAD Element Sets, Illustration of the communication geometry provided by satellites in 12-hour Molniya orbits.

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molniya orbit raan

Its replacement, the Molniya-2, provided both military and civilian broadcasting, and was used to create the Orbita television network, spanning the Soviet Union. is in degrees per day. [23][24] Initially funded by the now defunct Australian Space Research Program, it did not progress beyond initial development.[25][26]. To compensate, the orbital period is adjusted so that the longitude of the apogee changes enough to cancel out this effect. In general, the oblateness of the Earth perturbs the argument of perigee ( is the semimajor axis, and {\displaystyle R_{E}} To install click the Add extension button. The Molniya orbit has a long dwell time over the hemisphere of interest, while moving very quickly over the other. [20][19]:143 An orbit designed in this manner is called a frozen orbit. I use WIKI 2 every day and almost forgot how the original Wikipedia looks like. Create a free website or blog at WordPress.com. = {\displaystyle J_{2}} [2], While satellites in Molniya orbits require considerably less launch energy than those in geostationary orbits (especially launching from high latitudes),[4] their ground stations need steerable antennas to track the spacecraft, links must be switched between satellites in a constellation and range changes cause variations in signal amplitude. That's it. [10][11][12], From 1971, the American Jumpseat and Trumpet military satellites were launched into Molniya orbits (and possibly used to intercept Soviet communications from the Molniya satellites). 2 The Earth completes half a rotation in twelve hours, so the apogees of successive Molniya orbits will alternate between one half of the northern hemisphere and the other. There is some confusion in the existing sources about the naming, with some sources suggesting that all of the satellites on-orbit are of the Molniya-3 type, but referred to as Molniya-1 through -3 depending on their purpose. Geostationary orbits, which are necessarily inclined over the equator, can only view these regions from a low angle, hampering performance. [20], The eccentricity of the orbit is based on the differences in altitudes of its apogee and perigee. Ω It will enhance any encyclopedic page you visit with the magic of the WIKI 2 technology. J

R n The angle measured along the equatorial plane between a vector pointing to a fixed reference point in space and the point on the orbit where the orbital motion …

To broadcast to these latitudes from a geostationary orbit (above the Earth's equator) would require considerable power due to the low elevation angles. ˙

The early Molniya-1 satellites were used for long-range military communications starting in 1968, but the satellites had a short lifespan and had to be constantly replaced. Sites located above 81° latitude are unable to view geostationary satellites at all, and as a rule of thumb, elevation angles of less than 10° can cause problems, depending on the communications frequency. 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. 4 After two launch failures in 1964, the first successful satellite to use this orbit, Molniya 1-01, launched on April 23, 1965. {\displaystyle {\dot {\Omega }}}

Additionally, there is a greater need for station-keeping,[19][20][21] and the spacecraft will pass through the Van Allen radiation belt four times per day. Space debris population in the low Earth orbit (LEO) region, which is defined as a region up to 2000 km altitude, has been extensively studied during the last decades and reasonable models like ESA MASTER model (Wiedemann et al., 2011, Flegel et al., 2011) and NASA ORDEM model (Krisko et al., 2015, Xu et al., 2009) which are covering all size ranges were produced. Ω a The source code for the WIKI 2 extension is being checked by specialists of the Mozilla Foundation, Google, and Apple. {\displaystyle J_{2}} − In the operational part of the orbit (four hours on each side of apogee), the satellite is north of 55.5° N (latitude of, for example, central Scotland, Moscow and southern part of Hudson Bay). However, the perigee needs to be high enough to keep the satellite substantially above the atmosphere to minimize drag (~600km), and the orbital period needs to be kept to approximately half a sidereal day (as above).

[15][16][17], Much of the area of the former Soviet Union, and Russia in particular, is located at high northern latitudes. The primary use of the Molniya orbit was for the communications satellite series of the same name. E [14] A Russian satellite constellation called Tyulpan was designed in 1994 to support communications at high latitudes, but it did not progress past the planning phase. Figure 4: A constellation of three Molniya spacecraft providing service for the Northern hemisphere.

After two launch failures, and one satellite failure in 1964, the first successful satellite to use this orbit, Molniya 1-1, launched on 23 April 1965. Note that the two spacecraft at the time of switch-over are separated by about 1,500 kilometres (930 mi), so that the ground stations only have to move their antennas a few degrees to acquire the new spacecraft.[28]. Post was not sent - check your email addresses! Satellites placed in Molniya orbits have been used for television broadcasting, telecommunications, military communications, relaying, weather monitoring, early-warning systems and some classified purposes. [2][27] Since each satellite has an operational period of approximately eight hours, when one spacecraft travels four hours after its apogee passage (see figure 8 or figure 11), then the next satellite will enter its operational period, with the view of the earth shown in figure 6 (or figure 9), and the switch-over can take place. % Earth’s gravitational parameter [km^3/s^2], % Using fourth-order Runge–Kutta method to solve fundamental equation. The 12-h Molniya orbit requires about 4 mm of aluminum shielding for selected TID level. where Figure 3: Groundtrack of a Molniya orbit.

To maximise the amount of time that the satellite spends over the apogee, the eccentricity should be set as high as possible. As the apogee altitude is as high as 40,000 km, it will therefore, for a considerable period around apogee, have an excellent visibility from the Northern Hemisphere, from the Russian Federation but also from northern Europe, Greenland and Canada. The rotational period of the Earth relative to the node (i.e. The J2 term of the gravitational field of the Earth causes secular perturbations of both the right ascension of the ascending node and the argument of perigee , the formulas giving the change per orbital revolution (in radians) being. [19] The coverage from a satellite in a Molniya orbit over Russia is shown in figures 6 to 8, and over North America in figures 9 to 11. [4][6] The early Molniya-1 satellites were used for civilian television, telecommunication and long-range military communications, but they were also fitted with cameras used for weather monitoring, and possibly for assessing clear areas for Zenit spy satellites. At apogee, the green illumination zone applies. P is the orbital period. In general, the oblateness of the Earth perturbs the argument of perigee, so that even if the apogee started near the north pole, it would gradually move unless constantly corrected with station-keeping thruster burns. Said next spacecraft has the visibility displayed in figure 3 (or figure 6) and the switch-over can take place. This page was last modified on 28 December 2015, at 22:54. Molniya Orbit. ω

[3][7] The original Molniya satellites had a lifespan of approximately 1.5 years, as their orbits were disrupted by perturbations, and they had to be constantly replaced. is in degrees per day. A Molniya orbit has two (2) twelve (12) hour daily orbits. These two factors constrain the eccentricity, which becomes approximately 0.737.

2(0)= 1(0)+ Ω1−Ω2 (ref. After two launch failures in 1964, the first successful satellite to use this orbit was Molniya 1-01 launched on April 23, 1965. If three spacecraft are used, then each spacecraft will be active for a period of eight hours per orbit, centered around apogee,[2] as illustrated in figure 4. Disadvantages are that, as opposed to a spacecraft in a geostationary orbit, the ground station needs a steerable antenna to track the spacecraft and that the spacecraft will pass the Van Allen radiation belt four times per day. American Institute of Aeronautics and Astronautics, Preliminary Analysis of the First Successful Soviet Communications Satellite, "A History of Soviet/Russian Meteorological Satellites", Journal of the British Interplanetary Society, "Soyuz 2-1a launches with Russian Meridian 4 military satellite", "Reducing a Common Danger: Improving Russia's Early-Warning System", "History and the Current Status of the Russian Early-Warning System", "Russia blinded by loss of missile detection satellite", "Russian Soyuz-2.1b rocket successfully launches Tundra satellite", "Soyuz rocket successfully delivers EKS-2 early-warning satellite to rare orbit", "Russia sends military satellite into orbit for missile warnings – Spaceflight Now", "Determination of Look Angles To Geostationary Communication Satellites", "On the Use of Satellites in Molniya Orbits of Meteorological Observation of Middle and High Latitudes", 10.1175/1520-0426(1990)007<0517:OTUOSI>2.0.CO;2, "The Orbital Lifetime of Molniya Satellites", Final evaluation of the Australian Space Research Program, "As the details emerge on Australia's new space agency, we (might) finally have lift-off", "On the Use of Satellites in Molniya Orbits for Meteorological Observation of Middle and High Latitudes", "Systems Engineering of a Terabit Elliptic Orbit Satellite and Phased Array Ground Station for IoT Connectivity and Consumer Internet Access", Models for Propagation of NORAD Element Sets, Illustration of the communication geometry provided by satellites in 12-hour Molniya orbits.

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