What is delta V?

[Dcseal]

Now, i'm a KSP noob. I know how to get to mun,/mimmus, but only with unlimited fuel. Don't know how to get to it without. I constantly hear about something called Delta V? What is it?

[Guest]

"delta" - change

"V" - velocity

"delta-V" - Change in velocity

Tsiolkovsky's your bro, learn his equation.

E: Here is a good place to start for KSP tutorials.

Edited April 11, 2016 by regex

[JedTech]

Delta-V is displayed in KSP when you create a maneuver node. It is displayed as the m/s (meters per second) you have left to burn in order to accomplish the maneuver.

Mods like Kerbal Engineer Redux allow you to see the Total Delta-V that your stages have both in flight and in the VAB. This can help you to better plan your missions.

Use a Delta-V map like this to learn how much Delta-V it takes to get to certain places.

Edited April 11, 2016 by JedTech

[Empiro]

3 hours ago, Dcseal said:

Now, i'm a KSP noob. I know how to get to mun,/mimmus, but only with unlimited fuel. Don't know how to get to it without. I constantly hear about something called Delta V? What is it?

Basically it says how fast your rocket can go if you burn all of your fuel, starting from a complete stop, and assuming no other forces like air drag or gravity.

It's very helpful in your rocket design to understand why the delta-V is calculated the way it is, but if you get a mod, you won't need to do any of the math yourself.

How much delta-V you have is the fundamental way to measure where you can go and what you can do. A delta-V map like the ones linked above are like subway fare maps. You add up the total cost to go from point A to point B, and your delta-V is essentially how much money you have.

[Foxster]

dV=range

(Purists save the vitriol please). 

[Jovus]

Delta V is, as other have said, the sum total of the change in velocity your rocket can make; i.e. how fast your rocket can go.

This can be unintuitive at first. After all, you want to get to what you think of as a place, e.g. the Mun, Duna

However, it starts to make sense when you realize that all the parts of the solar systems are moving , and in order to get to them, you have to match their velocity.

It's a bit more complicated than that; e.g. if you want to orbit a body you obviously don't want to  move exactly like it is (that's landing), but that's the basic idea.

Delta-V maps will tell you how much velocity you need to gain or lose to do the various things on them (e.g. orbit Eve, land on the Mun) from wherever else you would like to start (usually the surface of Kerbin). Of course, you need to gain the velocity in the correct way (if you burn directly away from the Mun you usually won't get there), and delta-V maps usually are based on some minimum or close-to-minimum value.

[mhoram]

This question pops up time and again.

Here is a nice thread explaining different ways to understand Delta-V:

It is probably best to read that thread sorted by date, since it was from before the forum change.

[wumpus]

http://smbc-comics.com/index.php?id=4040

Note: I think I've commented that the stuff is probably RP-1 (and it isn't "delta-v" without an oxidizer as well).  The yellow "0" just doesn't belong in rocket fuels (expect maximum "evilness" in your rocket chemicals).

[KocLobster]

There are already some fantastic answers here. But to simplify it as much as possible if you're still having trouble understanding dV, you can look at it like dV is how far your rocket is able to go. It's how efficient your engine is with the mass it has to lug around, and how much fuel it has to do it with.

[Gojira1000]

dV (as measured in KSP) is the meters per second of potential velocity change for a craft, based on mass, fuel and ISP. There are a host of factors that can alter or affect it.

You can either use a spreadsheet to do the math for a given craft, or use a mod like Kerbal Engineer Redux.

Comparing the dV of a craft with a dV map of the Kerbol system, you can get an idea as to whether or not a ship can make a given trip. Subject to other concerns like TWR, of course.

[Redshift OTF]

I'll post my interpretation. It's roughly like how much fuel you've got in your rocket. Your craft has a certain amount of DeltaV and when it runs out you can't change were you're going because you can't use your engines any more.

Have you used manoeuvre nodes yet? When you create one it shows a DeltaV bar and that's how much DeltaV you need, (how much thrust), to carry out that manoeuvre.

If you want to relate that to what others have said above, if you want to change your orbit in any way you need to change your speed at certain positions and you use that by firing your engines and that uses fuel. It probably doesn't help that the stock game doesn't show how much DeltaV your craft has when you are building or flying something so the concept is a little alien to new players although there are mods that let you see this number and it is very useful for planning out what your craft can do.

[mrclucks]

First of all, welcome to KSP!!

Second of all, you should know that all of us were once noobs and couldn't even launch a rocket even remotely straight, so you are encouraged to ask questions about even the most minor things(as long as you try to use the search function to see if your question has been answered before).  

Delta v, or DV as many people shorten it to, stands for difference in velocity.  If you're in a stationary car with 10 miles per gallon and you have 10 gallons of fuel, then you basically have 100 miles of DV if you ignore gravity and friction and all.  To translate it to rockets, if you're in orbit around an object going 100 meters per second(m/s) and you have 50 m/s dv, then you can burn all your fuel prograde(the direction you are going in) and go 150 m/s, or burn your fuel retrograde(the opposite direction you're going in) and go 50m/s.  

The speed you're going changes if you go normal or antinornal(basically North or South) or radial and anti radial( basically rotate the orbit anticlockwise around the point of the burn, or clockwise around the point of burn), but it gets easier to understand and alot more intuitive once you do more burns in space.  

 

I highly suggest you go with regex's link to learn more about orbital mechanics.  KSP is a hard game with a high learning curve and the fun and satisfaction is from trying this and that to learn what works and what doesn't work.  

I suggest you install kerbal engineer redux(KER for short) which will give you the total burn time and DV of each stage you build, as well as mechjeb.l that only gives you alot of information, while mechjeb is a mod which will plot and execute burns for you.  You can learn alot from mechjeb on how to do many things, however it is not very efficient and by doing manuvers and such by your self will show you different ways to do the manuvers and how to do them more efficiently.  

 

[FyunchClick]

On ‎13‎-‎4‎-‎2016 at 4:59 PM, wumpus said:

http://smbc-comics.com/index.php?id=4040

Aw you didn't include the red button encore:

[cubinator]

Here's my equation that I use when I want to find the delta-V of the current stage. I use it a lot during interplanetary missions with lots of burns. It works anytime, and is easy to put into a calculator:

ΔV = 9.81 * I_sp * ln(M_current / M_current - (.005(LF + OX)))

ΔV: How much the stage can accelerate before it runs out of fuel.

9.81: Kerbin's surface gravity (always use this value even on/around other planets)

I_sp: Basically how fast your ship consumes fuel (higher I_sp means more ΔV for the same amount of fuel)

ln: Natural log, basically inverse of exponent.

M_current: The current mass of your ship. You can find this in map view, with the little button that shows info about your ship.

.005: Each unit of LF weighs .005 tons. I came up with this equation because there's not an easy way to know your dry mass (which is necessary to calculate delta-V) in-flight.

LF: The total number of Liquidfuel units in the current stage.

OX: The total number of Oxidizer units in the current stage.

For more on the delta-V equation, google "delta v" or "Rocket equation" or "Tsiolkovsky rocket equation" or something like that. To figure out how much your rocket can accelerate in m/s, just use the equation above (and make sure you put in the right number of parentheses in the calculator!).

Edited April 14, 2016 by cubinator
extra square

[OhioBob]

"Delta v" is the currency of rocketry.

Traveling anywhere in space is accomplished by making changes in your spacecraft's orbit.  Each change in orbit, or maneuver, requires an engine burn, the "cost" of which is measured in Δv.  Your spacecraft is like your wallet, in which you have a finite amount of money (i.e. Δv) to use to buy maneuvers.  When you plan a trip, you have to make sure you have enough cash in your wallet to cover your costs.  If you run out of money before reaching your destination, you're stranded.

[mcirish3]

12 hours ago, mrclucks said:

you should know that all of us were once noobs and couldn't even launch a rocket even remotely straight,

Thank goodness we did not launch straight we would still be trying to get into orbit if we did.

[mrclucks]

2 hours ago, mcirish3 said:

Thank goodness we did not launch straight we would still be trying to get into orbit if we did.

Sometimes I'll just pack on DV and will in fact launch directly away from the planet just to see how my orbit ends up looking.  I've gotten a periapsis inside the sun and a kerbol escape more than once and it is pretty satisfying that I can build these absurd rockets which are still aerodynamic and still quite simple

[rodrigoelp]

On 4/11/2016 at 8:45 AM, Dcseal said:

Now, i'm a KSP noob. I know how to get to mun,/mimmus, but only with unlimited fuel. Don't know how to get to it without. I constantly hear about something called Delta V? What is it?

Hi @Dcseal, as many others have point out. Delta V or Δv is the difference of your current speed to the final one you want to get. For instance, if you are moving forward on a bicycle at 16kph and a car in front of you is moving at 100kph then you need a Δv of 84kph to keep the same distance between you and the car or a greater amount to catch up to with it. Obviously this is an over simplification that applies to linear motion (which is not the case for orbital motion or radial motion).

There is a fantastic video made by Scott Manley that helped me explain a friend why and how he needed to do his burn to get to mun

Enjoy

[jedensuscg]

And to add to everyone else explaining how Delta-v is essentially the sum of "how fast your Rocket can go", slowing down is stil. A change in velocity. So it's not only hope fast you can go, but also can you slow down again. This is an important distinction, because even if you plan enough delta-v to get to low Kerbin orbit... You need Delta-v to get back to the ground. Same with going to the mun. You have to slow down once you get there, that needs to be calculated into your delta v requirements, otherwise you just fly right by. 

[Wemb]

Yes, what Jedensusch says. It's not really helpful to describe it as a measure of speed at all. It's related of course, but that's about as far as you can say.

The nearest analogue in normal experience might be the 'range' measure found on modern car computers that will recalculate how far you can go on the available amount of current fuel in the vehicle and the speed at which you're moving.  

The situation, in space, is of course completely different - you won't slow down due to friction and gravity may be changing depending on where you go - but because changing _any_ aspect of your trajectory requires you to change your velocity and because the amount needed to do this is not dependant on your total mass, you can describe_any_ journey of _any_ rocket as a the sum of the velocity changes needed to perform the various maneouvers needed (e..g this much velocity ot get into orbit, this much to circularise, this much to transfer to the Mun, this much to circularise around the Mun, this much to come back, etc. and use the value to plan a 'budget' for building your rocket. 

It also means you can use charts like this to also help plan your mission, and associated tools (mods) for KSP to tell you how much dV your rocket has.

Good luck!
Wemb

On 14/04/2016 at 3:09 PM, mrclucks said:

First of all, welcome to KSP!!

Second of all, you should know that all of us were once noobs and couldn't even launch a rocket even remotely straight, so you are encouraged to ask questions about even the most minor things(as long as you try to use the search function to see if your question has been answered before).  

What he said!  Also:

Wemb

Edited April 24, 2016 by Wemb

[marcushouse]

I've done a video up for you to explain just that (it also demonstrates it in action with KSP). Enjoy!

 

[Dcseal]

Thanks guys! I'll try to figure this out and work with it.

[RW-1]

Run! I think you guys got his head spinning or smoking, one of the two ....  

 

OP, we've all been there.

[KroShan]

Well explained!

I just found a good answer provided by ESA

http://lunarexploration.esa.int/#/explore/technology/229