A Question About Delta V

[Semnae]

So first off, the delta v for your craft is different numbers at the VAB and the launch pad. I'm assuming that's a bug to be fixed at a later date, but for now I'm using the delta v shown on the launch pad because that's what counts down when I'm actually flying. I wanted to know the minimum amount of delta v needed to get to space and circularize separately so I could better plan my first two stages. I tried to determine this by trial and error. I built the smallest craft I could get to space, and recorded the delta v. My plan failed when I tried to use that delta v for a circularization stage. The larger the circularization stage, the more delta v it actually took to get to space, rendering the first part of my experiment useless. Is it supposed to work like this, or is this another bug? I thought the delta v required to get from place to place was supposed to remain consistent between space craft of different design and sizes. Otherwise, there's no point in having a delta v map like the trip planner.

[Max]

I usually count around 3500-4000 m/s of deltaV to get to a low orbit. The deltaV will actually vary depending on your launch profile and the drag of the rocket. If you launch straight up then turn sideways and circularize once into space, that's not efficient. The most efficient should be to push sideways as much as possible and burn prograde the whole way, without needing almost any cicularization, but by doing this you will loose all this efficiency to drag so that's not good either. The key is to make a nice profile in between those two.
Some key values that help me decide if the profile is good enough :
- start with a slight angle (5°) when in the first layers of the atmosphere
- keep acceleration around 2g-3g (not too high not too low)
- be at 45° angle when you get to 8000 - 20000 meters
- try to stay under 1400 m/s when under 35 000 meters
- you have almost no drag when over 55 000 - 60 000 meters.

The profile has to be the smoothest without you needing to pilot the rocket except for the initial turn.

Hope that helps

[Max]

Originally posted by Max:

I usually count around 3500-4000 m/s of deltaV to get to a low orbit. The deltaV will actually vary depending on your launch profile and the drag of the rocket. If you launch straight up then turn sideways and circularize once into space, that's not efficient. The most efficient should be to push sideways as much as possible and burn prograde the whole way, without needing almost any cicularization, but by doing this you will loose all this efficiency to drag so that's not good either. The key is to make a nice profile in between those two.
Some key values that help me decide if the profile is good enough :
- start with a slight angle (5°) when in the first layers of the atmosphere
- keep acceleration around 2g-3g (not too high not too low)
- be at 45° angle when you get to 8000 - 20000 meters
- try to stay under 1400 m/s when under 35 000 meters
- you have almost no drag when over 55 000 - 60 000 meters.

The profile has to be the smoothest without you needing to pilot the rocket except for the initial turn.

Hope that helps

Oh and since you like to experiment here's one : clamp your rocket at a 5° angle on the pad, launch it and tell SAS to follow prograde and see how it goes without touching anything. Modify the stages until you get a nice ascent profile.

[Exsilium Games]

there is a mod out there that will show you delta-v per stage

[alohl669]

Originally posted by Max:

Oh and since you like to experiment here's one : clamp your rocket at a 5° angle on the pad, launch it and tell SAS to follow prograde and see how it goes without touching anything. Modify the stages until you get a nice ascent profile.

Awesome, you have saved me hours of testing. Now I have so many things I want to ask you that I don't know where to start.

[alohl669]

Ok ok, I have the first question. While I'm designing a rocket and I test it, I have the same problem every time. "ok I arrived at the mun/minmus(whatever), but I can't back home. I need more power... more fuel... oh ♥♥♥♥ I have tons of mass and I've just improved my rocket a bit".

I need to learn how to read correctly the engine's parameters. When to use them and learn the main differences among the list of fuels. But mainly, I want to get rid of some bad habits, because is hard for me when I need to duplicate my ship size to get some new achievement.

Have you any tips to build rockets? or maybe do you know any place where I can learn it?

[Max]

Originally posted by alohl669:

Ok ok, I have the first question. While I'm designing a rocket and I test it, I have the same problem every time. "ok I arrived at the mun/minmus(whatever), but I can't back home. I need more power... more fuel... oh ♥♥♥♥ I have tons of mass and I've just improved my rocket a bit".

I need to learn how to read correctly the engine's parameters. When to use them and learn the main differences among the list of fuels. But mainly, I want to get rid of some bad habits, because is hard for me when I need to duplicate my ship size to get some new achievement.

Have you any tips to build rockets? or maybe do you know any place where I can learn it?

Well i think a good tip to start is to understand orbital mechanics :
- Prograde/Retrograde burns are more efficient the closer you are to the body you orbit around (planet/moon)
- Change of inclination is best performed far from the body you orbit around
- When leaving the sphere of influence of a body, you will get part of its own orbiting speed, so leaving the sphere of influence of a moon in the same direction it's orbiting will result in a larger orbit around the planet. Leaving the moon in the opposite direction it's orbiting around the planet will result in a smaller orbit around the planet.
- Using the atmosphere of a planet can save you from spending the energy of slowing down your craft, abuse this.

It will definitely get easier for you to learn by yourself when the trajectories will be fixed in the next patch
As for guessing the size of the rockets you build, you can use a ksp deltaV chart (have a look on google) the numbers are the same for ksp 1 and 2. A few figures to remember:
- go to kerbin orbit : 3300-3500 m/s
- go to mun, minmus or leave kerbin : 800-1000 m/s
- go to duna, eve : 1100-1400 m/s
- when you orbit an atmosphereless body at say 600m/s, you're likely to spend 800-1000 m/s to land and the same to get back to orbit.

[Max]

Oh and of course, split the rocket into at least 2 stages. three stages if you want to land on something.

[ulzgoroth]

Originally posted by alohl669:

I need more power... more fuel... oh ♥♥♥♥ I have tons of mass and I've just improved my rocket a bit".

Note that that isn't you making a mistake, that's just the tyranny of the rocket equation getting you. (You might also be making a mistake, sure, but the basic problem is universal.)

Every bit of weight you add to a stage makes every stage below that need to be larger in proportion. Getting more delta-V out of the same technology makes your rocket expand exponentially - and I mean that like a mathematician, not somebody who just thinks 'exponentially' is an intensifier.

[Unbearable Pain]

Same bug encountered, and this is a reason why i delete game. Unfortunatelly, community patch doesn't fix that. :(

No any fixes for now?