Fordham Experiment

Representation of the orientation of a heliosynchronous orbit (in green) throughout the year. As a , the orientation of a non-synchronous orbit (in magenta) is shown at the same time. This article is about a kind of orbit around the Earth. For the orbital class around the sun, see solar orbit. A sun-synchronous orbit (sometimes incorrectly called a heliosynchronous orbit) is a geocentric orbit combining altitude and inclination to make an object in that orbit pass over a given land latitude at the same local solar time. The obliquity of the ecliptic (or angle of illumination) will be close to the same each time. This consistent illumination is a useful feature for satellites that impress the Earth's surface at visible and / or infrared wavelengths (eg meteorology, espionage, remote sensing). For example, a satellite in this type of synchronous orbit in the sun can cross the equator twelve times a day at approximately 3 pm local time. This is achieved by having the orbital plane of the orbit precession (rotating) about one degree each day, to the east, to be adjusted with the revolution of the Earth around the sun.

The uniformity of the sun angle is achieved by natural adjustment of the orbit precession to a full circle per year. Due to the earth's rotation, it will be slightly spheroidal, as the equator is slightly longer than the polar to be a perfect sphere, and that extra-material near the equator causes defects which forces the orbits to tilt in precession: the orbit plane does not is fixed spatially in relation to distant stars, but rotates slightly on the Earth's axis. The speed of precession depends both on the inclination of the orbit and the altitude of the satellite; balancing both effects, it is possible to develop relations of precession ranges. Typical synchronous orbits to the sun are about 600-800 km in altitude, with periods of 96-100 min of range, and inclinations of about 98 ° (ie slightly retrograde compared to the direction of the terrestrial rotation: 0 ° represents an equatorial orbit, and 90 ° a polar orbit).

It is possible to vary in this type of orbit; so a satellite could have a highly eccentric orbit synchronous to the sun, in which case the "fixed solar time of passage" is only maintained for a chosen point of the orbit (typically the perigee). The chosen orbital period depends on the desired revisit rate; the satellite crosses the equator at the same solar time in each passage, but usually at different lengths due to the terrestrial rotation below it. For example, in an orbital period of 96 min, divided into a Terran solar day (of 15 times), it means that the satellite will cross for 15 different lengths in consecutive orbits, at the same time local solar, for each locality, and will begin again on the same first length every 15 th passage, once per day.

Special cases of a synchronous solar orbit are the noon / midnight orbits, where the local solar time of passage by equatorial lengths around noon or midnight; and, the sunrise / sunset orbit, where the local solar time of passage by equatorial lengths is around dawn and dusk, so it fulfills its cycle between day and night. These orbit modes are useful for radar active satellites, such as for satellite solar panels that can always be watching the sun, without shading the Earth. It is also useful for some satellites with passive instruments that need to limit the solar influence in their measurements, to the point of allowing these instruments to point to the dark side of the Earth. The sunrise / dusk orbit has been used for solar observations of such scientific satellites

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