Jump to content

Retrograde

quarthinos

By quarthinos
in KSP1 Discussion

 Share

Recommended Posts

phoenix_ca

phoenix_ca

Posted
Posted (edited)

The former. If you're going to head for the inner planets, it's better to go with an orbit with an inclination of 180º, ascending directly to it (I use inclination because prograde/retrograde still leaves some room for ambiguity; the direction you are travelling in is always referred to as "prograde" for the purpose of navigation, but the orbit itself is called "retrograde" if the inclination is between 90º and -90º. Bah.). Make sure you plan for a much more difficult launch; it takes a quite of extra delta v, because you'll have to cancel-out the current rotation around an inclination of 0º (imparted by the rotation of Kerbin) and then expend the usual amount to get into a stable orbit.

Plane changes are generally very costly in terms of delta-v, and are best avoided (in some cases, it may be even less expensive to slingshot yourself around some nearby object to help with a plane change).

Edited by phoenix_ca
Link to comment
Share on other sites
RoboRay

RoboRay

Posted
Posted (edited)

Why do people keep saying you have to be in a retrograde orbit to head to an inner planet? YOU DO NOT. You only have to make your injection burn retrograde in respect to Kerbin's orbit around the sun, which you can do just as easily in an easterly prograde as in a westerly retrograde orbit.

dHRDt.png

All you are accomplishing by launching on any heading other than 090 or by other ways of getting into a retrograde orbit is wasting an awful lot of fuel.

Please stop telling people "this is how it's done." That is not how it's done. Example: the real-world Venus probes did it... they all injected from easterly, prograde orbits.

Edited by RoboRay
Link to comment
Share on other sites
Vanamonde

Vanamonde

Posted
Posted
but the IRL venus probes could use n-body physics
What other bodies are you concerned about? In this vicinity there's only the moon, and the real probes never got anywhere near it. If the N other bodies are not close by (in relative terms), then it's essentially a 1 body problem, which KSP simulates just fine.

Is the confusion perhaps about the word "retrograde" itself? Retrograde with respect to Kerbin's orbit is a good thing for reaching inner planets. Launching retrograde with respect to Kerbin's rotation is NEVER a good idea.

Link to comment
Share on other sites
RoboRay

RoboRay

Posted
Posted (edited)
Yes, but the IRL venus probes could use n-body physics, not patched conics.

What difference are you expecting, in regards to the launch? Even the pull of our moon will not have an appreciable affect on the launch.

Can you get to Eve launching into a prograde orbit using less delta V than launching retrograde?

The injection burn will require the same Delta V either way. It's the launch where you save fuel by going east. The speed required to attain orbit is the same regardless of how the body is rotating. If you do launch in the direction it is rotating, you get its rotation speed as your starting velocity. If you go west, you have to burn additional fuel to equal a Delta V double it's rotational speed...

For no benefit at all, once you do get into orbit.

Edited by RoboRay
Link to comment
Share on other sites
Stromgol23

Stromgol23

Posted
Posted

Taken from http://ksp.olex.biz/ :

The ejection angle is the angle, at which you want to start your transfer burn in your origin planet's or moon's orbit. You want to get this angle right in order to escape the sphere of influence of your origin parallel to its own orbital prograde (shown) or retrograde heading.
4.Timewarp some more, until your ship is properly positioned for the transfer burn in the parking orbit. You need to put yourself at the ejection angle before your origin's prograde (for a higher destination orbit) or retrograde (for a lower destination) orbital heading.

Retrograde orbital heading not retrograde orbit.

Link to comment
Share on other sites
EndlessWaves

EndlessWaves

Posted
Posted
So, let me make that right : If I plan to get into a retrograde orbit, I fly up in Kerbin's orbit, then I get at 90° on the Navball and WOOOSH here I go?

No, 90° will put you in a kerbin orbit that's prograde with respect to kerbin's rotation and to get into a solar retrograde orbit the direction of burn will depend on your position around kerbin.

Link to comment
Share on other sites
Person012345

Person012345

Posted
Posted (edited)
Taken from http://ksp.olex.biz/ :

Retrograde orbital heading not retrograde orbit.

Select kerbin to eve. Which way does the illustration appear to show the ship orbiting?

If the burn angles given to you are in fact for a prograde orbit, that could explain why people are having such difficulty getting to eve using it, because it appears to show the ship heading in a retrograde orbit in the illustration. Could you clear up whether the angle given is for a retrograde or prograde orbit?

Edited by Person012345
Link to comment
Share on other sites
Ascensiam

Ascensiam

Posted
Posted (edited)

As for me, i think the right idea has already been posted. If you want to go further out, try slingshotting from the mun, that's efficient and fun at the same time.

I'm sure this can be made efficient though, there's some sort of line between the 70,000 point and using slower speeds further out on an orbit to achieve bigger effect.

Edited by Ascensiam
Link to comment
Share on other sites
phoenix_ca

phoenix_ca

Posted
Posted
As for me, i think the right idea has already been posted. If you want to go further out, try slingshotting from the mun, that's efficient and fun at the same time.

I'm sure this can be made efficient though, there's some sort of line between the 70,000 point and using slower speeds further out on an orbit to achieve bigger effect.

That's the Oberth effect. Not so much a line in the sand, but an asymptotic curve.

Link to comment
Share on other sites
Ascensiam

Ascensiam

Posted
Posted
That's the Oberth effect. Not so much a line in the sand, but an asymptotic curve.

Yes. Adding these effects and making them useful factors in the game (And there is quite a lot to begin with) is going to take it's time, but i am sure it's going to be worth it, some nerds want to live their dreams on this game.

Link to comment
Share on other sites
Ziff

Ziff

Posted
Posted
Yes. Adding these effects and making them useful factors in the game (And there is quite a lot to begin with) is going to take it's time, but i am sure it's going to be worth it, some nerds want to live their dreams on this game.

You make it sound as if the Oberth effect doesn't work in KSP. You realize it does , right ?

Link to comment
Share on other sites
Peppe

Peppe

Posted
Posted
Taken from http://ksp.olex.biz/ :

Retrograde orbital heading not retrograde orbit.

What is the heading talk in the first line of the how to use section:

How to use these values?

Using these values for interplanetary flight is no more complicated than obtaining them:

Place your ship in a circular, 0° inclination parking orbit around your planet/moon of origin. For a destination in a higher orbit, make this orbit at a 90° heading; for a lower destination, go for 270°.

-----------------

270 heading orbit is a retograde orbit, is it not?

When do you burn in a prograde orbit to get to eve?

The only real question that matters is how to get there in the lowest delta v.

Link to comment
Share on other sites
This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
 Share
Go to topic listing
×
×
  • Create New...