How to decrease the minor axis but increase the major axis

[Neywiny]

I was wondering if there was a way to decrease the minor axis, but still have the same major axis. (I need this in the most laymen way possible).

[LethalDose]

Huh, interesting question. Why would you need to do this?

I don't think it's possible to affect one axis and not the other in a single maneuver.

[EtherDragon]

Nope, it's not possible. Here is as simple as I can describe why:

All orbits are ellipses. Basically, you want to change one ellipse into a different ellipse - one that has a skinnier minor axis. In order to do so, you have to change its eccentricity - but one of the defining characteristics of eccentricity is the location of the foci. Essentially, you are trying to change eccentricity (make the orbit/ellipse more skinny) without moving the foci - it can't be done.

http://www.mathopenref.com/ellipseaxes.html <- Here is a fun little math thing you can use to play with ellipses. Try changing the minor axis - see the foci moving around? You can change your orbit with respect to the foci, but you can't change the foci with respect to your orbit (unless you're God, if so I have a few questions you might be able to answer about life, the universe, and everything.) =p

Hope that helps!

EDIT:

It's possible to do this with more than one burn - actually, it only takes two.

(In any order) thrust prograde at Periapsis to raise your Apoapsis, thrust retrograde at Apoapsis to lower your Periapsis. Your last burn should be done such that it changes altitude of that node exactly the same as the altitude change for the other node. In the end, you've increased eccentricity of your orbit, which also decreases the minor axis.

Edited November 25, 2013 by EtherDragon

[Sirrobert]

You probably could, but it would take multiple burns

[Smidge204]

You need a more eccentric orbit; your Periapsis (lowest point) needs to be as low as possible while your Apoapsis (highest point) needs to be as high as possible.

The problem comes in that the body you are orbiting is always at one focus of the ellipse, so if your major:minor axis ratio is too high one of two things will happen:

1) Your highest point will be too high, and you will be on an escape trajectory

2) The lowest point too low: either will be inside the atmosphere of the orbiting body (if it has one) and/or below the surface of the body (meaning you'll crash into it.)

So this fundamentally limits how eccentric your orbit can be. However, if you don't mind an impending crash you can burn retrograde at your apoapsis and collapse your orbit practically into a single vertical line!

=Smidge=

[Neywiny]

Not that laymen smidge, but I just wanted to know if it was possible. I wanted to know how to make an orbit have a perigee at like a 90^ angle to the apogee.

[Smidge204]

Not that laymen smidge, but I just wanted to know if it was possible. I wanted to know how to make an orbit have a perigee at like a 90^ angle to the apogee.

No, because perigee and apogee are the lowest and highest point in the orbit, respectively, and since the body you're orbiting is always at one focus of the ellipse, these points will always be 180 degrees apart and on the line formed by the major axis.

=Smidge=

[Neywiny]

Just a 14 year old's thoughts.

[robot256]

Just a 14 year old's thoughts.

Keep those thoughts coming! And pay attention in your Geometry and Algebra 2 classes--that's what all this math is based on. When your friends ask why they need to know the equation for an ellipse, show them how to calculate an orbit with it. :-D

[Vanamonde]

Just a 14 year old's thoughts.

Typical 14-year-old; all they think about is orbital mechanics.

[Vector]

Not possible? Bah!

If you are only wanting to shrink the minor axis while keeping the same apoapsis, then it is much simpler, just burn retrograde at apoapsis.

If you truly want to keep the same major axis (meaning keep the same orbital period) then that means you want to increase the apoapsis while decreasing the periapsis by an equal amount.

So suppose you want to go from the brown curve to the blue curve:

This is possible like this:

Assuming you are traveling east (counter-clockwise) you can perform a single burn in the direction of the black arrow. This is a combination of radial and retrograde, and if you experiment with a maneuver node you can raise your apoapsis and lower your periapsis by the same amount at the same time. It is not a simple maneuver because it is at an odd angle, but it is possible if you take your time with a maneuver node.

[Neywiny]

all they think about is orbital mechanics.

LOL I've been playing kerbal since 0.13. My friend once asked me for relationship advice, stupid move on his part, and I said "I hear you need help. Have you tried increasing you inclination by 16 degrees?" He didn't laugh and just walked away. but yeah, and I even got science teacher approval last year to play the game in my work only study hall. Surprised the teacher (and everyone else) that such a silent boy could get his way. wow this thread is off topic. Thanks vector for bringing us back.

Only problem with above, the terms raise and lower. although the major axis would stay the same, the periapsis would be in the atmosphere , since it is still the lowest point and if I wanted an 80Km semi-minor axis, the periapsis would be well to far into either the planet or the atmosphere.

Edited November 26, 2013 by Specialist290
Merging sequential posts

[Vector]

Ah, if your periapsis is already near the atmosphere then you can't narrow the minor axis without re-entering. If you burn prograde at periapsis then your major axis will increase more than the minor axis and you will have higher eccentricity, but your minor axis will be increasing too, not decreasing.

Inclination is an important factor to insertion, but 16 degrees is very expensive -- probably why he just walked away.

[Smidge204]

Not possible? Bah!

Well, when I read "perigee at like a 90^ angle to the apogee" I immediately thought of this:

Because that's the only way I could imagine the Ap and Pe being at 90 degrees... and if I understood the question properly, then no that's not possible.

=Smidge=

[Neywiny]

That was 100% what I meant by 90^. Thanks anyways though.