Launch strait up to the Mun or get into orbit first: A video demonstration

[Echo__3]

Please pardon my voice as I was recovering from Strep Throat

[Vezbot]

Launching straight up to the Moon never works due to the arcing of your orbit compared to the Muns, and the relative velocity will the the orbital velocity of the Mun going on it's path. The problem with launching straight up is that the Moon is a long distance away from you, and having the rocket pointed where the Mun is won't do much in terms of orbital velocity, and distance. If you point at the Mun and launch straight up the Moon will have moved farther in it's orbit, and you will be in empty space in the Mun's orbital path. To get launching straight up at the Mun, you need to point towards where the Mun would be, nullifying the going straight to the Mun because you will create an orbit as you make your burn and start your ascension regardless. Physics will never allow burning straight towards the Mun. 

If I missed anything or explained improperly I'm open to a discussion. Have a good day!

 

[Echo__3]

9 hours ago, Vezbot said:

If I missed anything or explained improperly I'm open to a discussion. Have a good day!

No, you did not miss anything. The point of the video was to show that getting into orbit, performing an ejection burn, and circularizing around the Mun are better than just trying to go straight for the Mun. This is just a question that I see come up pretty regularly, so I thought I would demonstrate both ways so people could see that getting into orbit is the correct way.

[jimmymcgoochie]

On 9/24/2020 at 3:01 AM, Vezbot said:

Launching straight up to the Moon never works due to the arcing of your orbit compared to the Muns, and the relative velocity will the the orbital velocity of the Mun going on it's path. The problem with launching straight up is that the Moon is a long distance away from you, and having the rocket pointed where the Mun is won't do much in terms of orbital velocity, and distance. If you point at the Mun and launch straight up the Moon will have moved farther in it's orbit, and you will be in empty space in the Mun's orbital path. To get launching straight up at the Mun, you need to point towards where the Mun would be, nullifying the going straight to the Mun because you will create an orbit as you make your burn and start your ascension regardless. Physics will never allow burning straight towards the Mun. 

If I missed anything or explained improperly I'm open to a discussion. Have a good day!

 

Going straight up is the least efficient path for a rocket as you’re fighting directly against gravity the whole time which wastes (on Earth/Kerbin) 9.8m/s of delta-V for each second that you do it. A gravity turn minimises the losses due to gravity and air drag and is a lot more efficient which saves fuel. Likewise, a high angle suicide burn at escape velocity uses more fuel than a low altitude deorbit then a short descent. 

It’s entirely possible to time a direct ascent to intercept the Mun (as demonstrated in the video) while still having a periapsis below the surface of Kerbin, but it’s a lot less efficient to do so and you’ll save fuel doing it the normal, orbit-y way.