Hohman orbit transfer

[JRF2k]

I am a complete ignorant idjit when it comes to this advanced orbital mechanics stuff, but I am trying, I am trying.

So I am looking at this graphic: http://en.wikipedia.org/wiki/File:Hohmann_transfer_orbit.svg and I read that a Hohmann transfer requires two velocity changes.

So, 1 represents the current orbit. And then where the first Delta-V is, the first burn is made, right? This expands the orbit so that 2 is now the orbit. And 1 is perfectly circular in this graphics and this is probably not so in reality, maybe, hmm, in a perfectly circular orbit how do you find out a apoapsis and periapsis? Sorry tangent....

So we get to Delta-V^1, is this the second burn or is this showing that if you want an even more circular orbit you would do another burn there to get orbit 3?

So from going from orbit 1 to 2, I see only one burn that would need to be made. And so, I know, I must be not seeing it right or understanding it correctly.

Are there any good resources for a lay person like myself with an enormous curiosity for it to get a better grasp on these things? I figure the more I know the more enjoyment I'll get from KSP.

Thanks,

JRF2k

[Nibb31]

The Hohmann transfer orbit is simply an eccentric orbit whose apoapsis intersects with your target orbit and the periapsis intersects with your original orbit.

You need to burn at the apoapsis (the Delta-v' point in your example) to circularize into orbit 3. If you don't, your trajectory will stay in orbit 2 and follow the yellow dashed line back down to orbit 1.

It's exactly the same as a launch trajectory really. You have to burn at the apoapsis or else you will fall back down.

Edited June 13, 2013 by Nibb31

[Awaras]

I am a complete ignorant idjit when it comes to this advanced orbital mechanics stuff, but I am trying, I am trying.

So I am looking at this graphic: http://en.wikipedia.org/wiki/File:Hohmann_transfer_orbit.svg and I read that a Hohmann transfer requires two velocity changes.

So, 1 represents the current orbit. And then where the first Delta-V is, the first burn is made, right? This expands the orbit so that 2 is now the orbit. And 1 is perfectly circular in this graphics and this is probably not so in reality, maybe, hmm, in a perfectly circular orbit how do you find out a apoapsis and periapsis? Sorry tangent....

Yes, the first burn is made at the first Delta-V. In a perfectly circular orbit there is no apoapsis or periapsis, or if you want to look at it that way, ANY point of the orbit is the apoapsis AND periapsis simultaneously.

So we get to Delta-V^1, is this the second burn or is this showing that if you want an even more circular orbit you would do another burn there to get orbit 3?

So from going from orbit 1 to 2, I see only one burn that would need to be made. And so, I know, I must be not seeing it right or understanding it correctly.

Yes, this is the second burn that circularizes your orbit to match the red line. If you do not perform that second burn, your ship will continue to follow the yellow dashed line of the elliptical transfer orbit and fall back towards the fist, green orbit...

[SiliconPyro]

In that graphic, orbit 1 is your starting orbit, say, Low Kerbin Orbit. Orbit 2 is the transfer orbit created by your first burn with a PE the same as your first orbit and an AP the same as your destination orbit. Orbit 3 on that graphic is your destination orbit, which is circularized by your second burn.

[JRF2k]

The Hohmann transfer orbit is simply an eccentric orbit whose apoapsis intersects with your target orbit and the periapsis intersects with your original orbit.

You need to burn at the apoapsis (the Delta-v' point in your example) to circularize into orbit 3. If you don't, your trajectory will stay in orbit 2 and follow the yellow dashed line back down to orbit 1.

It's exactly the same as a launch trajectory really. You have to burn at the apoapsis or else you will fall back down.

It seems like I have over-complicated this in my mind. Thanks for responding!

[JRF2k]

In that graphic, orbit 1 is your starting orbit, say, Low Kerbin Orbit. Orbit 2 is the transfer orbit created by your first burn with a PE the same as your first orbit and an AP the same as your destination orbit. Orbit 3 on that graphic is your destination orbit, which is circularized by your second burn.

Thanks. I get it now!

[JRF2k]

Yes, the first burn is made at the first Delta-V. In a perfectly circular orbit there is no apoapsis or periapsis, or if you want to look at it that way, ANY point of the orbit is the apoapsis AND periapsis simultaneously.

Yes, this is the second burn that circularizes your orbit to match the red line. If you do not perform that second burn, your ship will continue to follow the yellow dashed line of the elliptical transfer orbit and fall back towards the fist, green orbit...

Thank you for responding. I understand it better now.