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If one wants a satellite to fly over some given spot on Earth every day at the same hour, the satellite must complete a whole number of orbits per day. Assuming a circular orbit, this comes down to between 7 and 16 orbits per day, as doing less than 7 orbits would require an altitude above the maximum for a Sun-synchronous orbit, and doing more ...
where is the orbital inclination, is the eccentricity, is mean motion in degrees per day, is the perturbing factor, is the radius of the earth, is the semimajor axis, and ˙ is in degrees per day. To avoid this expenditure of fuel, the Molniya orbit uses an inclination of 63.4°, for which the factor 4 − 5 sin 2 i {\displaystyle 4-5\sin ...
is the dimensionless drag coefficient related to the satellite geometry, and accounting for skin friction and form drag (~2.2 for cube satellites). The orbit decay model has been tested against ~1 year of actual GPS measurements of VELOX-C1 , where the mean decay measured via GPS was 2.566 km across Dec 2015 to Nov 2016, and the orbit decay ...
A satellite in a synchronous orbit that is both equatorial and circular will appear to be suspended motionless above a point on the orbited planet's equator. For synchronous satellites orbiting Earth, this is also known as a geostationary orbit. However, a synchronous orbit need not be equatorial; nor circular.
Animation (not to scale) showing geosynchronous satellite orbiting the Earth. A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day).
Groundtrack of Molniya orbit. In the operational part of the orbit (4 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). A satellite in this orbits spends most of its time in the northern hemisphere and passes quickly over the southern hemisphere.
A spacecraft's attitude must typically be stabilized and controlled for a variety of reasons. It is often needed so that the spacecraft high-gain antenna may be accurately pointed to Earth for communications, so that onboard experiments may accomplish precise pointing for accurate collection and subsequent interpretation of data, so that the heating and cooling effects of sunlight and shadow ...
As a satellite passes 50 or 60 miles overhead, the mascons pull it forward, back, left, right, or down, the exact direction and magnitude of the tugging depends on the satellite's trajectory. Absent any periodic boosts from onboard rockets to correct the orbit, most satellites released into low lunar orbits (under about 60 miles or 100 km) will ...