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Setting up RemoteTech satellite relay network - Molniya question


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Problem: How to set up a com-relay network that will need little/no attention and maintain line of sight comms with KSC at equator. Geostationary orbits need repositioning frequently when using time warp.

Solution: Please discuss your solutions

For those who don't know, a Molniya orbit is a highly elliptical orbit where the satellite spends most of its time at or near apoapsis. Molniya's have an orbital inclination of 63.4 degrees on Earth so they can look down upon the Northern Hemisphere and because the Earth is oblate (fat in the middle) and would otherwise pull it out of that orbital plane with each pass (like a sun-synchronous orbit). Kerbin is spherical so the angle doesn't matter. The KSC is equatorial so selecting to look at either North or South hemisphere doesn't matter.

My Partial Solution: I elected to place four satellites around Kerbin; two at 45 degrees with their apoapsis opposite one another and two at -45 with their apoapsis opposite one another.

My question: Why would I want to synchronize my orbits and why make them 1/2 sidereal day (3 hrs on Kerbin)? Why not just make my orbits as eccentric as possible so the satellite spends more time covering that side? FYI, a 3 hr orbital period can be had by Pe=75km, Ap=3095.352km.

Edited by Oinker
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There is no real point to making orbits half a sidereal day. In the real world, this is helpful because it means that at a certain time, the satellite will be at a predictable point in the sky over a predictable location and thus it can synchronize with ground stations easily. This is not a factor in RemoteTech.

For your approach, you should make the orbits as eccentric as possible, like you said. This allows the satellites to spend most of their orbit on one side. I'm not sure what you perceive to be the advantage over a geosynchronous orbit, though; surely the two opposite satellites in the same orbit will drift apart just as much as your geosynchronous constellation will? Unless, for some reason, you are placing these more accurately than your geosynchronous satellites.

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The reason the Molniya goes for half a sidereal day is to keep the ground track stable over the high-latitude region you want to service. Since the period is an integer fraction of the fraction of the sidereal day, the path of the satellite across the rotating surface always remains the same, and spends large amonunts of time over the region

http://en.wikipedia.org/wiki/File:Molniya.jpg

An actual Molniya constellation uses three satellites in three arrayed Molniya orbits, phased so they reach apoapasis a third of a day apart, and arrayed with the longitudes of their ascending nodes 120 degrees apart from one another, which results in the satellites being visually near each other from the ground viewpoint when the time comes to handoff from one satellite to the next as the planet rotates.

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