What is Delta-V?

[kaio37k]

What is Delta-V?

I know a few things about physics but can never seem to wrap my head around that...

any help appreciated! Happy Flying!

[Rhomphaia]

Delta-V is quite literally "change of velocity"

Any maneuver requires a spacecraft to change it's velocity along a particular vector. delta-V is the amount of velocity change a space craft is capable of.

[dave4002000]

To expand on that a little more: The amount of delta-v a spacecraft has is a function of mass, fuel quantity, and the efficiency of the engine(called specific impulse or ISP) that's using said fuel.

A fixed amount of fuel with a fixed ISP will generate a certain amount of delta-v; which is usually expressed in meters per second. As you add more mass to the vehicle, the amount of delta-v available will be lower. Higher thrust engines will give you a better thrust-to-weight ratio (TWR) but will suffer from a lower ISP. So you have to play a balancing act between a useful TWR and the amount of delta-v you need for your mission.

I have no doubts that someone who is much more adept with math will come in here and post to relevant equations for you, if you so desire.

[Superfluous J]

More "simply put" here from me, but I'm a simple guy so that's what you get

If you have a huge rocket with a lot of fuel, and a tiny rocket with less fuel, and you start them out floating in space together, burn their engines at full until they run out of fuel, and they are both now going 10,000 m/s, they both have a delta-v of 10,000 m/s. It doesn't matter what the ship is like, just how fast it can go with all of its fuel. Both of those ships could launch from the pad and orbit Kirbin. Actually I think they could escape it but I don't pay that much attention to the numbers.

It gets tricky when you're fighting gravity (and atmosphere) because those take delta v but you're not actually gaining velocity. That's why not every rocket can get into orbit even if they have the same delta-v. If you're too slow off the launchpad, you're going to spend more time near the surface which saps delta-v. If you speed up too fast, though, you'll start to slow down in the thick atmosphere, which saps delta-v. I honestly don't know the details, just try to design my rockets to hit 10,000m at 200m/s and hope I'm doing it right!

[capi3101]

Delta-V is, as Rhomphaia mentioned, change in velocity. In rocketry, it's used as a measure of how many changes a rocket can make to its velocity under its own power before it runs out of fuel (velocity being the dot product of speed and direction; changing either speed or heading counts as delta-V).

As dave4002000 mentioned, it is a function of your rocket's mass and the efficiency of the engine. It's specifically measured via the Tsiolkovsky Rocket Equation, which says:

delta-V = ln (total mass / dry mass) * Isp * 9.81 m/s^2

where delta-V is in units of meters per second, ln is the natural logarithm, total mass is the mass of your rocket when its fuel tanks are full, dry mass is the mass of the rocket when its fuel tanks are empty, and Isp is the specific impulse of the engine (i.e. its efficiency). The wiki lists the specific impulses of the engines in the game.

[rpayne88]

Delta-V is, as Rhomphaia mentioned, change in velocity. In rocketry, it's used as a measure of how many changes a rocket can make to its velocity under its own power before it runs out of fuel (velocity being the dot product of speed and direction; changing either speed or heading counts as delta-V).

As dave4002000 mentioned, it is a function of your rocket's mass and the efficiency of the engine. It's specifically measured via the Tsiolkovsky Rocket Equation, which says:

delta-V = ln (total mass / dry mass) * Isp * 9.81 m/s^2

where delta-V is in units of meters per second, ln is the natural logarithm, total mass is the mass of your rocket when its fuel tanks are full, dry mass is the mass of the rocket when its fuel tanks are empty, and Isp is the specific impulse of the engine (i.e. its efficiency). The wiki lists the specific impulses of the engines in the game.

And in space velocity is critical. Dv can be seen as the "range" your rocket has. The more dv you have, the farther you can go. Zero dv means you will not be completing any maneuvers what so ever. Also, take into accout that it is the TOTAL change in velocity. For example, to go from 0m/s to 1000m/s (negleting outside influences such as drag,) you would need 1000 m/s dv. But to go from 0 m/s to 1000 m/s back to 0 m/s, you would need 2000 m/s dv. That is because you need 1000 m/s to accelerate to 1000m/s and another 1000 m/s to decelerate.

[Tank Buddy]

Delta V is change in velocity (m/s), just like Delta T is change in time and Delta L is change in length and so on. Delta V in KSP is used to determine what the limit (Delta V Budget) of the change in velocity is. Knowing Delta V can help you determine what bodies in the Kerbol system you can reach.

I just used the Delta V equation to determine if an engine with less mass and a lower Isp had more Delta V than a motor with more mass and a higher Isp. It turned out that using the .1 Ton engine would grant me an additional 300m/s of Delta V just for shedding .4 tons.

If you are just doing a routine Mun landing or rendezvous, you should not need to calculate it, but if you are transporting a large payload, going to other planets, or finding out if you have enough fuel to make it home, you could find the Delta V of you craft.

Delta V can be found by multiplying the exhaust velocity (Isp x Gravitational constant) by the internal log of original mass/final mass. (The fuel burned)

[BunTiggly]

I'll just rattle it off quickly. It's the amount of velocity (delta-V) that the spacecraft can pump out total. You need to manage how much you build into your ship in order to get into orbit, to Jool, etc and back.