Please explain Delta-V for me.

[sadron]

Okay, so I know that thrust from your engines is a factor and Delta-V is based on meters per second, and I at least sort of understand it in terms of in game practice, but could someone please put what Delta-V is into layman's terms for me? Each planet requires a certain Delta-V but because my brain doesn't seem to want to think along certain lines you may as well tell me you've discovered a way to smell the color blue.

This image was posted in another thread which prompted me to try and make this topic to have my question answered. If you can explain it to me, to help my brain finally comprehend it, I'd much appreciate it.

[Tex_NL]

Check out this topic.http://forum.kerbalspaceprogram.com/showthread.php/28301-can-someone-explain-delta-v-to-me IT'S LESS THAN TWO DAYS OLD!

[leax256]

in short delta-v is tech talk for The change(delta) in Velosity(v). So it's a measre of how much your ship can change it's velosity.

[Daze]

The dV is the variation of velocity needed to perform a manuever in orbital mechanics (for example manuever node in KSP is measured in how much dV do you need...)

Taking for example the system Kerbin-Mun on the picture we can see how much dV we need to perform a successfully landing on Mun.

Starting from Kerbin you can see 4500dV, this means that you need about 4500dV to put a spacecraft in LKO (Low Kerbin Orbit), after this we see that on the line which connect Kerbin to Mun there's a "860dV" this dV is the dV that you need to perform a transfer from LKO to a Mun orbit intersection (For example: the velocity when you are in LKO is about 2300-2400 m/s right? Now you have to increase that speed of 860 m/s, so you have to reach about 3160-3260 m/s in LKO to make an intersection with Mun obit.

Now you can see another number on the Mun icon, which indicate how much dV do you need to Land and (next to circle) another number which explain how much dV do you need to make a stable orbit around Mun; so for your lander you will need 640(landing dV)+210(orbit dV)+400-700(for human error and to reach escape velocity)

To know how much dV has you spacecraft you can use mod like MechJeb or Kerbal Engineer Redux

Sorry for bad english, hope you understand

[sjwt]

Delta V is the speed in M/S you need to be going at the split second on launch to get through the gravity wells and atmosphere to your destination..

So think of it as the sum of energy that needs to be spent to get from A to B

[Tokay Gris]

Ok, I'll try.

Delta-V is change in velocity, basically.

So, the more fuel you have, the more you can change your velocity.

And the heavier you are, the more energy (fuel) you need to change your velocity.

If your engine is more fuel efficient, it uses less energy for a specific change in velocity.

So, basically:

- Heavier: Less Delta-V

- More fuel: More Delta-V

- More efficiency (f.e. the nuclear engine): More Delta-V

[rryy]

The numbers in the chart represent how much you need to change your velocity to transfer, land, etc. A change in velocity from 2200 m/s to 3100 m/s would be 900 m/s of delta-v, and if you want to perform that maneuver, your ship would need at least 900 m/s of delta-v.

[SkyRender]

Just to add to the conversation, delta-V is calculated as a function of weight, specific impulse, and a natural logarithm of the difference between the total mass and dry mass (ie. with full fuel tanks vs. empty fuel tanks). What this results in is an inverse exponential curve of effective delta-V as you add more fuel. Generally speaking, if you can, you should seek to improve specific impulse (ISP) as much as possible for a rocket before you try to solve the problem of insufficient delta-V with more fuel. Someone else here recommended Kerbal Engineer Redux, and I second that suggestion. It saves a ton of busywork to have the calculations for delta-V, thrust-to-weight, and engine firing time done for you in real-time as you build your rocket.

[sadron]

The dV is the variation of velocity needed to perform a manuever in orbital mechanics (for example manuever node in KSP is measured in how much dV do you need...)

Taking for example the system Kerbin-Mun on the picture we can see how much dV we need to perform a successfully landing on Mun.

Starting from Kerbin you can see 4500dV, this means that you need about 4500dV to put a spacecraft in LKO (Low Kerbin Orbit), after this we see that on the line which connect Kerbin to Mun there's a "860dV" this dV is the dV that you need to perform a transfer from LKO to a Mun orbit intersection (For example: the velocity when you are in LKO is about 2300-2400 m/s right? Now you have to increase that speed of 860 m/s, so you have to reach about 3160-3260 m/s in LKO to make an intersection with Mun obit.

Now you can see another number on the Mun icon, which indicate how much dV do you need to Land and (next to circle) another number which explain how much dV do you need to make a stable orbit around Mun; so for your lander you will need 640(landing dV)+210(orbit dV)+400-700(for human error and to reach escape velocity)

To know how much dV has you spacecraft you can use mod like MechJeb or Kerbal Engineer Redux

Sorry for bad english, hope you understand

That actually helped me quite a bit. And I think your English was fine.

[Daze]

That actually helped me quite a bit. And I think your English was fine.

Thank You!

[SkyRender]

One caveat if you're using Kerbal Engineer Redux: the atmospheric stats for Kerbin will list your delta-V as lower than the map is designed for. The assumption is that you are working from vacuum delta-V stats, ergo it will be closer to 4000-4100dV looking at the Kerbin tab to get off of Kerbin (using normal engines; nuclear engines are all sorts of hard-to-explain when it comes to atmospheres). Really, that first kick to get into stable orbit is the hardest part of most flights. As long as the drive stage you're sending up has enough delta-V for whatever it is you intend to do (and enough thrust if that something involves landing), you'll generally be fine.

[nyrath]

With an automobile, there is friction. Because of that, we talk about how many miles a car can drive on a fuel tank of gasoline. We can't do that with a rocket. Instead we use delta-V.

There is no friction in space. Here on Terra, if you are driving a car and take your foot off the accelerator, the car will coast to a stop due to the friction of the road. In space, if a spacecraft turns off its engines it will maintain its current velocity for the rest of eternity (unless is crashes into a planet or something). In the movie 2001 A Space Odyssey, you may have noticed that the spacecraft Discovery was traveling to Jupiter with nary a puff coming out of the rocket motors.

This is why it makes no sense to talk about the "range" of a rocket. Any rocket not in orbit around a planet or in the Sun's gravity well has a range of infinity. In theory it can do a burn and travel to, say, the Andromeda Galaxy, it is only that it will take millions of year to get there. Instead of a rocket's range, one should talk about a rocket's delta V capacity.

The important thing is that a mission can be rated according to how much delta V is required. For instance: lift off from Terra, Hohmann orbit to Mars, and Mars landing, is a mission which would take a delta V of about 18,290 m/s. If the spacecraft has equal or more delta V capacity than the mission, it is capable of performing that mission. The sum of all the delta V requirements in a mission is called the delta V budget.