Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Titanscape on 26/01/2008 19:15:01
-
Satellites over London and Toronto, off the equator ideal, how is it that they stay there and are not pulled down to the equator?
How far up can they orbit, surely not over the arctic circle?
Do they survive less long?
Eventually the moon gets them right, they are pulled into an elliptical orbit?
-
There are a great many satellites in polar orbit I have been receiving cloud cover pictures from them since 1965.
-
The Earth is a sphere (almost, but as far as this is concerned, it may as well be regarded so), so it matters not what orbital plane a satellite takes, the sphere still looks the same. The fact that the Earth is spinning on an axis along running through its poles makes no difference to the gravitational pull of the Earth for orbiting satellites.
Where an equatorial orbit is of benefit is for geostationary satellites, but the benefits is not because the satellite cannot stay in orbit in another plane, it is just that the satellite, when it is in orbit, cannot remain fixed over a single point over the Earth; whereas a satellite taking a polar orbit will only transit over the poles, while taking an orbit that passes north to south, then south back up to north, passing over the equator before heading over the pole, then back around the other side over the equator, and back up to the other pole.
The other advantage with equatorial orbits is that it is easier to launch a satellite from the equator since you can use the Earth's rotation to save a bit of energy; but once in orbit, if you have the energy to change to a different orbit, the satellite can take any orbit it wishes.
-
The fact that the Earth is spinning on an axis along running through its poles makes no difference to the gravitational pull of the Earth for orbiting satellites.
Although it has no practical affect on the orbit of polar satellites there is an interesting effect due to the rotation of the Earth beneath the satellite that can be considered as the dragging of space-time by its rotation.
An experiment is underway with the Gravity probe B satellite to investigate this effect which has required engineering of unprecedented precision and took over 40 years in gestation.
http://einstein.stanford.edu/content/story_of_gpb/gpbsty3.html
-
LEO (low Earth orbit) satellites are often put in a polar orbit because they will go round the Earth several times per day. As the Earth spins, daily, below them, they get to see every part of the Earth's surface, eventually. This is great for surveying, weather etc. etc.
-
What I was really asking was about geostationary orbits, such as permanently over London, so far from the equator.
-
No it can,t be done, if you tried it would oscillate between 51° north and 51° south in a figure of eight fashion.
The Russians do the best they can by putting them into a very elliptical polar orbit
Circular orbit: An orbit that has an eccentricity of 0 and whose path traces a circle.
Hohmann transfer orbit: An orbital maneuver that moves a spacecraft from one circular orbit to another using two engine impulses. This maneuver was named after Walter Hohmann.
Elliptic orbit: An orbit with an eccentricity greater than 0 and less than 1 whose orbit traces the path of an ellipse.
Geosynchronous transfer orbit: An elliptic orbit where the perigee is at the altitude of a Low Earth Orbit (LEO) and the apogee at the altitude of a geosynchronous orbit.
Geostationary transfer orbit: An elliptic orbit where the perigee is at the altitude of a Low Earth Orbit (LEO) and the apogee at the altitude of a geostationary orbit.
Molniya orbit: A highly elliptic orbit with inclination of 63.4° and orbital period of half of a sidereal day (roughly 12 hours). Such a satellite spends most of its time over a designated area of the planet.
Tundra orbit: A highly elliptic orbit with inclination of 63.4° and orbital period of one sidereal day (roughly 24 hours). Such a satellite spends most of its time over a designated area of the planet.
Hyperbolic orbit: An orbit with the eccentricity greater than 1. Such an orbit also has a velocity in excess of the escape velocity and as such, will escape the gravitational pull of the planet and continue to travel infinitely.
Parabolic orbit: An orbit with the eccentricity equal to 1. Such an orbit also has a velocity equal to the escape velocity and therefore will escape the gravitational pull of the planet and travel until its velocity relative to the planet is 0. If the speed of such an orbit is increased it will become a hyperbolic orbit.
Escape orbit (EO): A high-speed parabolic orbit where the object has escape velocity and is moving away from the planet.
Capture orbit: A high-speed parabolic orbit where the object has escape velocity and is moving toward the planet.
-
What I was really asking was about geostationary orbits, such as permanently over London, so far from the equator.
Any orbit will always be in a plane, with includes the centre of the Earth. If you set up an orbit at a tilt from the equator but with a 24hr period, it would appear to move, vertically, up and down in the sky as it passed above and below the equator each day; not much use for fixed receiving antennas!