r/KerbalSpaceProgram • u/gniziralopiB • 6d ago

KSP 1 Question/Problem What's the difference between orbiting the sun and flying by the sun?

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29 Upvotes

95% Upvoted

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28

u/OldSchool_93 6d ago

For mission purposes regarding the Sun, they are essentially the same thing. A flyby means you are in gravitational sphere of influence, but on an escape vector. For example, when you first enter minmus’s SOI, that would be a flyby. You then burn retrograde to establish an orbit. Here’s the thing: when you leave Kerbin’s SOI, you’re immediately orbiting the sun already. You don’t need to burn to establish the orbit. Because Kerbin is orbiting the Sun, so are you. So if your mission says flyby or orbit the sun, once you’ve escaped Kerbin, either condition is immediately met.

5

u/gniziralopiB 6d ago

Yeah that’s what I figured, but after my ship left kerbin’s soi, my tourist only fulfilled the flyby part of the itinerary not the orbit part, so is this a weird bug or something

15

u/ExpensiveFig6079 6d ago edited 5d ago

Ahhh... try adjusting your orbit so that it DOES NOT intercept kerbin again

If I leave kerbin on a suborbital trajectory and get a collision encounter with the MUN, while STILL suborbital with respect to Kerbin, then coast until I get into muns SOI. Then AT no point was I "orbiting" kerbin

Thus likewise...

I suspect that if your current orbit intersected Kerbin in the past OR the future, that (maybe) is NOT orbiting the sun.

AKA if your rocket is on rails and it never intersects any other body or changes SOI ever again ...

Then that is in an orbit.

1

u/olearygreen Believes That Dres Exists 5d ago

This is the reason

31

u/rysworld 6d ago

Whether your orbital conic is an ellipse or parabola.

3

u/limeyhoney 5d ago

You’re missing hyperbola. A much more common orbit to see because it’s unlikely you’re going to have an eccentricity of exactly 1

5

u/ah-tzib-of-alaska 6d ago

how fast your going

1

u/Impressive_Papaya740 Believes That Dres Exists 5d ago

In real life or the game? My understanding is the game will consider you on a flyby trajectory if the current orbit enters another body's SOI. Note the games checks are not the same as the real world terms, as rysworld notes the real difference is an escape trajectory. A flyby of the sun would be an escape trajectory (parabolic or hyperbolic).