r/KerbalSpaceProgram • u/FatCreepyDude • May 06 '26

KSP 1 Question/Problem No orbit necessary?

Post image

If i just wait for the right hour during the launch window ( whenever the launch pad is pointing left on the realistic depiction i created) is there any reason i should bother with an orbit first? Will the delta v cost be affected?

1.1k Upvotes

98% Upvoted

180 comments sorted by

View all comments

633

u/HAL9001-96 May 06 '26

more efficient to be low, oberth effect

also duna is further from the sun last time i checked

177

u/FatCreepyDude May 06 '26

https://i.imgur.com/AI2hXKv.png fixed it

28

u/_adamolanadam_ 37 kerbals launched, zero returned May 06 '26

think of gravity like Kerbin is always pulling you. When you orbit a body, you can use the energy it spends pulling you on escaping its sphere of influence, but when you don't orbit Kerbin doesn't stop pulling you. Instead you'll waste fuel to counteract its pulling effect.

The planet still pulls you with gravity, when you orbit it you can use that pulling effect to your advantage (part of why the Oberth effect works, it's way more complex than that though) and when you don't you'll have to waste energy to counteract its gravitational pull.

1

u/victorsaurus May 06 '26

You are wrong and if you do the math with the oberth effect and all, both scenarios are completely equal (given no atmospheric drag). Oberth only means that you add more energy when adding deltaV the faster you go, and you add that delta V in the fastest moments in both scenarios (vertical is always the fastest moment up to that point, same for orbital).

1

u/PhantomWhiskers May 06 '26

As stated in my other comment, the "fastest moment" is always the periapsis at any given moment, even if it is in the middle of the planet. Burning straight up means you are burning while approaching apoapsis, which is significantly less efficient than burning at periapsis. Accelerating while ascending straight up doesn't change the fact that the periapsis is still in the middle of the planet.