Delta V required to change the inclination of my orbit

[Tazin]

I would like to know how can i calculate this. I have a very tight-budget launch for Duna, a contract came up that requires me to take an orbit with about 30º inclination around ike, how can I estimate the Dv required for that burn before I launch?

[GoSlash27]

Tazin,

I'd calculate it the same way as a standard equatorial orbit for Ike. It doesn't actually take any more DV to set the inclination at Ike if you do it early. Hit up Duna for the aerobrake and prograde/ radial to get the intercept. Once you've got that, the difference between equatorial and polar is trivial.

1100 m/sec for an Ike intercept from LKO using aerobraking at Duna, then another 200 m/sec to circularize at Ike.

Plus whatever percentage safety margin you like.

Good luck!

-Slashy

[FancyMouse]

For a contract where not any inclined orbit works, this becomes a little bit trickier. Theoretically it can be achieved by mid-course correction (thus only a negligible amount of dV), however to get the correct longitude of AN, you need to tweak your trajectory to enter Ike SoI at a correct time. This is harder than just getting the inclination right.

Another way, which should just cost a tiny little more, is to enter Ike SoI with periapsis close to the desired periapsis. Then when circularize, first circularize to an elliptical orbit, then change inclination at apoapsis, then orbit to periapsis and finish circularizing. This literally just split circularization into two parts, and plug in the inclination change in between, so you're really only paying extra inclination change at high apoapsis, which shouldn't be too big.

All I want to say is, if you plan well, going to inclined orbit isn't going to cost you too much dV than equatorial orbits.

And, all these become more complicated if you want to do aerocapture from Duna. I don't have data to evaluate whether it's more efficient to directly go to Ike, or aerocapture enough and then enter Ike.

[panzer1b]

For a contract where not any inclined orbit works, this becomes a little bit trickier. Theoretically it can be achieved by mid-course correction (thus only a negligible amount of dV), however to get the correct longitude of AN, you need to tweak your trajectory to enter Ike SoI at a correct time. This is harder than just getting the inclination right.

Another way, which should just cost a tiny little more, is to enter Ike SoI with periapsis close to the desired periapsis. Then when circularize, first circularize to an elliptical orbit, then change inclination at apoapsis, then orbit to periapsis and finish circularizing. This literally just split circularization into two parts, and plug in the inclination change in between, so you're really only paying extra inclination change at high apoapsis, which shouldn't be too big.

All I want to say is, if you plan well, going to inclined orbit isn't going to cost you too much dV than equatorial orbits.

And, all these become more complicated if you want to do aerocapture from Duna. I don't have data to evaluate whether it's more efficient to directly go to Ike, or aerocapture enough and then enter Ike.

Aerocapture (if you time it 1005 right and execute it such that ur AP is right where ike is) is always going to be most efficient then direct to ike as there will be near 0 braking burns required aside from the circularization burn at ike.

Overall, unless there is some good reason not to, aerobraking is basically free dV that costs you absolutely nothing but a minor 10-20m/s burn to actually set it up properly. Now timing it such that ike is in the right spot, thats hard, but i feel even that could be done if you had the patience and time to actually calculate when its best to leave kerbin to duna so ike is in the right spot after ur arobrake.

As for adive for inclination anything, do it as far away from the planet as possible. if im expecting the need to do inclination change, i never circularize, and always try to get the area where i will burn to change the inclination to be as far away as possible (the slower u fly, the less dV it takes to alter ur vector).

[GoSlash27]

For a contract where not any inclined orbit works, this becomes a little bit trickier. Theoretically it can be achieved by mid-course correction (thus only a negligible amount of dV), however to get the correct longitude of AN, you need to tweak your trajectory to enter Ike SoI at a correct time. This is harder than just getting the inclination right.

Another way, which should just cost a tiny little more, is to enter Ike SoI with periapsis close to the desired periapsis. Then when circularize, first circularize to an elliptical orbit, then change inclination at apoapsis, then orbit to periapsis and finish circularizing. This literally just split circularization into two parts, and plug in the inclination change in between, so you're really only paying extra inclination change at high apoapsis, which shouldn't be too big.

All I want to say is, if you plan well, going to inclined orbit isn't going to cost you too much dV than equatorial orbits.

And, all these become more complicated if you want to do aerocapture from Duna. I don't have data to evaluate whether it's more efficient to directly go to Ike, or aerocapture enough and then enter Ike.

FancyMouse,

IME it's possible to hit any orbit cheaply, even if the desired orbit is perpendicular at the start. Just burn at the intercept to get a CPA at the An or Dn, then burn retro at Pe just enough to get capture. Once you're slung out to Ap, the burn required to match the plane is peanuts.

Best,

-Slashy

[FancyMouse]

IME it's possible to hit any orbit cheaply, even if the desired orbit is perpendicular at the start. Just burn at the intercept to get a CPA at the An or Dn, then burn retro at Pe just enough to get capture. Once you're slung out to Ap, the burn required to match the plane is peanuts.

That is actually my "Another way" paragraph:wink:

- - - Updated - - -

Aerocapture (if you time it 1005 right and execute it such that ur AP is right where ike is) is always going to be most efficient then direct to ike as there will be near 0 braking burns required aside from the circularization burn at ike.

Yeah agree in that case it will cost less, but it's much harder to achieve. Maybe I should've said I was concerning in a reasonable average case which one is better. I don't find it too easy doing a proper aerocapture (with neither not-capturing nor capturing to surface) without quicksaves, which kind of concerns me, and in average case you may need some more dV to correct post-aerocapture orbit which potentially can cost some more.

But of course maybe I'm just dumb for aerocapture - at least I probably should fix controllability of my ship during aerocapturing (I play with RT), so I can control my airbrakes for the purpose - though I don't know whether I can really control my apoapsis by doing this.

[Wolf Baginski]

It can be hard getting an exact number for inclination, but it takes little delta-V to miss the target at about the right angle. You can eveball it while you adjust the burn, the exit trajectory shows the orbital plane. Then, when you get in the SOI, you can do a burn to get the correct periapsis, burn at periapsis to get the initial elliptical orbit, and burn at apoapsis to fine-tune the inclination and timing. Because you're going so slowly at the apoapsis of a highly elliptical orbit you don't need a lot of delta-V.

It depends a little on the aerodynamics model, but you can change the amount of braking by adjusting attitude. Pure prograde with a spaceplane produces less braking than going into the radial SAS setting, and you can do that in very thin air. Eventually the attitude can't be maintained by the reaction wheels you have. This sort of manouver can certainly shift the location of the periapsis a little. It's a fine-tuning though, not such a big change.

This is the general sort of thing that was done by the Apollo capsule and the Space Shuttle on re-entry, Apollo for the landing point and the Shuttle for losing velocity as high as possible.

[Renegrade]

I would like to know how can i calculate this. I have a very tight-budget launch for Duna, a contract came up that requires me to take an orbit with about 30º inclination around ike, how can I estimate the Dv required for that burn before I launch?

A lot of people seem to be ignoring the question here (while offering some good advice).

The cost is 2*orbital_velocity*sin(inclination_change/2), for a circular orbit, where orbital_velocity is the speed of the given orbit, and inclination is the change in degrees or radians or whatever (doesn't matter which, so long as the sin() function used is using the same unit - most programming languages use radians, and Windohs calc has a sind() and sinr() function for degrees and radians respectively).

For example, the orbital speed of a 20km orbit around Ike is about 352.8, so:

cost = 2*352.8*sin(30/2)

or 182.6 and change delta-v cost.

Non-circular orbits are a bit more involved (the principles are the same though; lower speed = cheaper).

[OhioBob]

The following web page discusses the mathematics:

http://www.braeunig.us/space/orbmech.htm#maneuver

Equation 4.73 is used for simple plane changes, while equation 4.74 is used for combination burns, such as when a plane change is incorporated into an orbit insertion burn.