Adventures in Satspotting: Why Are Different Orbits Needed for Satellites?

universetoday.com ^ | David Dickinson

[BenLurkin]

Congratulations: perhaps you’re a new space-faring nation, looking to place a shiny new payload around the planet Earth. You’ve assembled the technical know-how, and seek to break the surly bonds and join an exclusive club that thus far, only contains 14 nations capable of indigenous spaceflight. Now for the big question: which orbit should you choose?

Welcome to the wonderful world of orbital mechanics. Sure, satellites in orbit have to follow Newton’s laws of motion, as they perpetually ‘fall’ around the Earth without hitting it. But it’ll cost you in fuel expended and technical complexity to achieve different types of orbits. Different types of orbits can, however, be used to accomplish different goals.

The first artificial moon to be placed in low-Earth orbit was Sputnik 1 launched on October 4th, 1957. But even before the dawn of the Space Age, visionaries such as futurist and science fiction author Arthur C. Clarke realized the value of placing a satellite in a geosynchronous orbit about 35,786 kilometres above the Earth’s surface. Placing a satellite in such an orbit keeps it in ‘lockstep’ with the Earth rotating below it once every twenty four hours.

[rjsimmon]

Different orbits are for different missions. Molniya, LEO, need for longer loiter times, larger coverage, the list goes on and on...

[bigbob]

Kepler’s Fault.

[DannyTN]

Mount rail guns on the satellites so that they can follow any orbit they want.

[TexasGator]

“Mount rail guns on the satellites so that they can follow any orbit they want”

You might have to reconsider due to the size of the energy source required.

[freedomlover]

Placing a satellite in such an orbit keeps it in ‘lockstep’ with the Earth rotating below it once every twenty four hours.

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Clarity FAIL

Yeah the Earth rotates below it once every twenty four hours, but it ROTATES ALONG WITH THE EARTH so that (at least in the case of true geostationary orbit) it preferably stays in the same position in the sky to an observer on the ground. Makes antenna focusing a bit easier that way.

[dainbramaged]

I have seen something more than once that looks like a satellite, way faster than a jet aircraft and traveling from south to north.
Is that a possible orbit path?

[T-Bird45]

Thanks for posting the article. I’m an amateur radio operator and have always been interested in satellites used for amateur radio communications. This article is very informative so I posted it to my amateur radio club’s Facebook page.

[BenLurkin]

I think so. But there are probably people here who know for sure.

[Boogieman]

Yep:

http://en.wikipedia.org/wiki/Polar_orbit

[jagusafr]

All I remember from my 45-minute lecture in orbital mechanics at the Executive Space Course at Space Command: successful orbit is moving forward faster than you fall. Made sense to this non-science lawyer...

[gr8eman]

Low Earth Orbits, North to south (Polar), rotate erf 2 times a day, albeit at different longitudes. Weather satellites (Imagery), GPS (I think), and comms sats such as Iridium on which INMARSAT operates uses this orbit.

[Conan the Librarian]

I suggest http://www.heavens-above.com/ for desktop use and
Sat-Track for your hand held devices.

Easy to use (as long as you know your Lat-Lon) and you can actually name what you are seeing up there.

Very useful for Space Station passes.

[MikeD]

Polar orbits are often used for reconnaissance satellites, as the Earth turns underneath them as they travel along their north-south path. Polar orbits are also often used for geomagnetic research satellites, as that orbital path allows the spacecraft to pass over the magnetic poles.

MD, who has built UV instruments for a spacecraft in Lunar polar orbit and one about to enter Jovian polar orbit.

[publius911]

bookmark

[dainbramaged]

Thanks for the information - my brother and I used to sleep out in the back yard on clear nights waiting for the Echo One satellite to pass over in the early 60’s, listening to short wave radio on Dad’s Zenith Transoceanic.