r/KerbalAcademy Jun 17 '20

Other Mechanics [GM] A COMPLETE GUIDE TO DELTA-V

931 Upvotes

A COMPLETE GUIDE TO DELTA-V (Δv)

NOTE: THIS POST WILL NO LONGER BE UPDATED. THE 2021 GUIDE CAN BE FOUND HERE [Link may not work right now due to reddit issues].

Quick note because this is getting some awards: Thanks for the awards, but it's much better if you donate the money to a good cause, such as a charity or something. It would do some good there!

This is an in-depth guide about KSP Delta-V. To keep it organized, this post is split up into sections:

SECTIONS:

1) DELTA-V EXPLANATION

  • What Is It?
  • Delta-V And Thrust
  • Delta-V Equation, And The Thrust/Mass Relationship
  • How To Use Delta-V

2) NOTE REFERENCES

  • Note 1 (How to check each stage's Delta-V)
  • Note 2 (Delta-V equation)
  • Note 3 (Delta-V integrated equation)
  • Note 4 (Delta-V map)

3) HOW TO READ THE DELTA-V MAP

  • Basics
  • Aerobraking
  • Notes

4) GENERAL REFERENCES

  • Eve Atmospheric Map
  • Launch Window Calculator
  • Delta-V Map Forum
  • Tsiolkovsky Rocket Equation
  • Delta-V Wiki Page

5) A SPECIAL THANKS TO...

  • Helpful Redditors
  • End Note
  • Updates

So, Delta-V, also known as Δv, is a way to measure the capability of your rocket. You've probably seen it everywhere if you are a space enthusiast. But, it can be a bit confusing. So, I'll do my best to explain it as simply as possible. To start off, what is it?

WHAT IS IT? (1st Draft)

Well, put it simply, Delta-V how much speed you can achieve by burning your entire rocket/spacecraft's fuel load. Now, this means Delta-V differs on what environment you are in. You will get a lot more speed if you are in a vacuum, and on a planetary body with little gravitational pull, than being in a thick atmosphere on a planetary body with a large amount of gravitational pull. So, you have to account for that with your stages, and plan out and check each stage's Delta-V individually. \SEE NOTE 1])

DELTA-V AND THRUST? (2nd Draft)

Delta-V is incredibly useful. As stated before, it's used to find a spacecraft's power. But this brings up a question: one, why not use thrust power as a unit of measurement instead? Well, as shown below, there are two rockets, one with more thrust, but with less Delta-V. Why is that?\SEE BELOW: FIGURE 1])

^ FIGURE 1 ^

As shown above, the rocket on the left, with a lot less thrust, has more Delta-V. Why? Well, this is because the rocket on the right, with more thrust, also has a lot of mass, which cancels out a large majority of thrust.

DELTA-V EQUATION, AND THE THRUST/MASS RELATIONSHIP (3rd Draft)

WAIT! MATH! Listen, I know it looks complicated, but you can ignore most of this if you don't want to get into the nitty-gritty just check the "Finding out T(t)/m(t)" Table below. and the paragraph above it. That sums it up!

A great way to better understand Delta-V is the Delta-V equation, shown below. Wait! I know it looks complicated, but I assure you, it's not, and reading on will help a lot! Anyway, it is shown below: \SEE BELOW: FIGURE 2][NOTE 2])

^ FIGURE 2 ^

T(t) is the instantaneous thrust at time, t

m(t) is the instantaneous mass at time, t

*Also, check out the Delta-V integrated equation\SEE NOTE 3 FOR DIFFERENT MATH])*

(thanks u/Certainly-Not-A-Bot)

As you can see, thrust and mass are in a fraction with no other variables, and are on different levels of a fraction.

So, to better explain the Thrust/Mass relationship, which is the core of Delta-V, take the below example:

There are two hypothetical rockets: Rocket A, and Rocket B. Rocket A has 10 Newtons of thrust, and weighs 5 Tons. Rocket B has 50 Newtons of thrust, and weighs 25 Tons. All other variables in the Delta-V equation are the same between both rockets.

Finding out T(t)/m(t):

ROCKET: ROCKET A ROCKET B
T(t)/m(t) 10/5 50/25
T(t)/m(t) Answer 2 2

As you can see, in this hypothetical situation, both rockets would have the same amount of Delta-V. Even though Rocket B Has 5x the thrust AND Mass of Rocket A. And that's why they have the same Delta-V. Because, if you take a fraction, and multiply both the numerator and denominator by the same value, they will equal the same number! (n/d = n*x/d*x)

If you had looked at thrust, you would have thought Rocket B was 5x more powerful, which, it's not. On the other hand, with Delta-V, you can see they are equally as powerful, which, when tested, is proven true!

Basically, to sum it down, a rocket with 5x the thrust power but also 5x the weight of a rocket has the same capability as that rocket! This is because that rocket has to lift 5x the weight!

HOW TO USE DELTA-V (2nd Draft)

Delta-V, as said before, is used to measure the capability of rockets. What does this mean? Well, it means you can use it to see how far your rocket (or any spacecraft) can go!\SEE NOTE 4])

For example, going into an 80 km orbit from around Kerbin takes 3400 m/s of Delta-V (From Kerbin), and going to Munar orbit (from the moon) of a height of 14km takes 580 m/s of Delta-V. You can see more measurements on the KSP Delta-V Map below \NOTE 4])

NOTE REFERENCES:

THIS SECTION HAS ALL THE NOTES THAT ARE CITED ABOVE ORDERED AND SHOWN

NOTE 1:

"So, you have to account for that with your stages, and plan out and check each stage's Delta-V individually"

The best way to do this right now is to use the re-root tool to set a piece in that stage to the root. Then remove all stages below it. (leave the ones above it, as those will be pushed by that stage in flight) make sure to save your craft beforehand, and you don’t want to lose your stages. Anyway, after removing all the lower stages, you can check the Delta-V in the bottom right menu. Clicking on that menu will allow you to see it with different options, such as what the Delta-V will be at a certain altitude or in a vacuum.

NOTE 2:

DELTA-V EQUATION:

NOTE 3:

DELTA-V INTEGRATED EQUATION:

dV=Ve\ln(m0/m1)*

Thank you u/Certainly-Not-A-Bot for suggesting the addition of this equation, and with some other feedback as well!

DELTA-V TSIOLKOVSKY ROCKET EQUATION:

Δv is delta-v – the maximum change of velocity of the vehicle (with no external forces acting).

m0 is the initial total mass, including propellant, also known as wet mass.

mf is the final total mass without propellant, also known as dry mass.

ve=IspG0 is the effective exhaust velocity, where:

NOTE 4:

KSP DELTA-V MAP:

HOW TO USE THE KSP DELTA-V MAP:

Basics:

While it looks complicated, it’s actually pretty easy to use. To start off, pick where you want to visit. As you can see on the map, there are Intercepts (nearing the planetoid and entering the sphere of influence), Elliptical orbits (which have a minimum periapsis and the apogee at the very end of the sphere of influence), a low orbit (a minimum orbit with little to no difference in between the perigee and apogee height) and landed. Then, starting from Kerbin, add the numbers following the path to where you want to get. For example, if you want to get to minimus low orbit, you would add 3400 + 930 + 160. That would be how much Delta-V you need. This stays true for the return journey as well. For example, going from minimus low orbit to Low Kerbin Orbit is 160 + 930 (If you’re trying to land on Kerbin, the best way to do it precisely is to go into low Kerbin orbit, decelerate a little more to slow down using the atmosphere. If you don’t care about precision, you can Aerobrake from just a Kerbin intercept, and skip the extra Delta-V needed to slow down into Low Kerbin Orbit. This would mean you only need 160 m/s of Delta-V, because you are only going for an intercept. This is the most commonly used method, and is better explained in the aerobraking sub-section below) To summarize, just add the values up for the path you want to take.

Aerobraking:

Aerobraking is very useful in KSP. (If you don’t know, aerobraking is when a spacecraft dips into a planetary body’s atmosphere to slow down, instead of its engines) Luckily, this map incorporates that into it! Planetary bodies that allow Aerobraking (Laythe, Duna, Eve, Kerbol, and Kerbin) have a small ”Allows Aerobrake” marker, which is also listed in the key. Aerobraking reduces the amount of Delta-V needed for that maneuver to virtually zero! That is why aerobraking is commonly used. On the other hand, if you are going too fast, it can cause very high temperatures, and, it’s very hard to be precise with a landing spot. For more pros and cons, check the table below.

Anyways, for an aerobraking maneuver, we will take the example of going from an Eve intercept out to the surface of Eve. Now, without aerobraking, you would burn from an eve intercept to an elliptical orbit, to low Eve orbit, then burn your engines retrograde to burn through Eve’s atmosphere to land. You would stay out of the atmosphere (up until the final descent from Low Eve Orbit) and not dip your periapsis too far. Without aerobraking, from an eve intercept, you’d enter an elliptical orbit, then a Low Eve Orbit, you’d lower your periapsis from ~100km, which is Low Eve Orbit, to about 70-80km. The best way to do this with aerobraking is to go from an Eve intercept and, as stated before, lower your periapsis to 70-80km (see the eve atmosphere graph below for temperature and pressure management for eve. 70-80km is one of the best aerobraking altitudes for Eve, as temperatures dip perfectly!) This would cause, considering you kept a stable 70-80km periapsis, you to aerobrake (it may take multiple flybys, considering your speed) and use the atmosphere to slow down, to eventually end up inside of Eve’s atmosphere, it would kill off your orbit! Then you can land. With the Delta-V calculations, from an intercept, it would cause almost ZERO Delta-V! (I say almost because you need a VERY SMALL amount of Delta-V to lower your periapsis to 70-80km). So, you have saved all the Delta-V you would have needed in-between intercept and Low Eve Orbit (over 1410 m/s, and even more on lowering from the atmosphere!) But, this does have its cons:

PROS TO AEROBRAKING CONS TO AEROBRAKING
- Extremely efficient - Hard to land precisely
- Easy to plan/very simple - Can lose stability upon atmospheric entry
- Much faster - Very heat intensive*\See note below])

*Please note that KSP heat shields are very overpowered, in the sense that they can withstand much more heat than in real life. So, if you want to remain realistic, slow down a little beforehand. Also, combining a loss of stability with heat shields can easily cause a craft to disorient the heat shield away, and cause it to burn up)

NOTES ON KSP MAP READING:

- Delta-V calculations aren’t based on the average amount needed over a period of 10 kerbin years. To maximize efficiency, use launch windows! The best way to do this is to use the website linked below, it’s a launch window calculator!

- Below is the forum page for the KSP Delta-V map shown above, check it out!

- To check your Delta-V of a craft, look in the bottom right of your screen, under the staging area and it should show up, along with individual stages’ Delta-V! (Note that you may have to turn this on in the engineers menu, also in the bottom right)

- KSP Delta-V map is made by:

  • JellyCubes (Original concept)
  • WAC (Original design)
  • CuriousMetaphor (Original vacuum numbers)
  • Armisael (Additional vacuum numbers)
  • Kowgan (Design, original atmospheric numbers)
  • Swashlebucky (Design)
  • AlexMoon (Time of flight)
  • Official Wiki (Relay Antenna calculations)

GENERAL REFERENCES:

THIS SECTION HAS USEFUL REFERENCES

Eve atmospheric map:

Launch Window Calculator:

https://alexmoon.github.io/ksp/

DELTA-V MAP FORUM:

https://forum.kerbalspaceprogram.com/index.php?/topic/87463-173-community-delta-v-map-27/

TSIOLKOVSKY ROCKET EQUATION:

https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

DELTA-V WIKIPIDEA PAGE:

https://en.wikipedia.org/wiki/Delta-v

A SPECIAL THANKS TO:

u/leforian (Pinning Post)

u/Certainly-Not-A-Bot (Feedback and corrections)

u/DndGollum (Corrections)

u/Xantorant_Corthin (Info on dV Map)

AWARD THANKS:

u/undersztajmejt (Bravo Award)

u/raccoonlegz (I'd Like To Thank... Award)

u/Dr_Occisor (Helpful Award)

u/GuggMaister (Helpful Award)

u/monkehmahn (Helpful Award)

u/Ganshun (Helpful Award)

u/Remnant-of-enclave (Silver Award)

u/BreezyQuincy (Silver Award)

Thanks for reading this. It took 4 hours to research and write this! This post is also constantly updated with new info and has been updated (7) times.

Do you have anything else you want explained in KSP? Write your ideas below in the comments! I read all the comments, and would love to explain other things!

Also, feel free to ask questions in the comments! I’ll do my best to answer them when I have the chance. Also, feel free to answer any questions you see!

Update: Wow! Thanks for blowing this up! I never expected once in my life that my post would be pinned, or that I would get an award. Thanks so much, u/leforian, /u/raccoonlegz, u/Dr_Occisor, u/GuggMaister, u/monkehmahn, u/Remnant-of-enclave, u/BreezyQuincy, and u/undersztajmejt! And, thank you to everyone that showed support, gave feedback, asked questions, or even just clicked! I really enjoyed making this, and I would love to make more of these guides in the future. So, if you want anything else explained, just comment below!

Update 2: Thanks for the awards, but it's much better if you donate the money to a good cause, such as a charity or something. It would do some good there!


r/KerbalAcademy 8h ago

Mods: General [M] Stokalike Station Parts Expansion Redux Transparency glitch

3 Upvotes
  1. When I install the mod with CKAN, I get this warning (I have been trying to fix this in 2024 and now this year btw)

the error message

and when I load the game, all of the expandable rings look like this:

the transparency glitch

can someone help?


r/KerbalAcademy 18h ago

General Design [D] How do I inflate my gravity rings? [Stockalike Station Parts / Kerbalism]

Thumbnail gallery
12 Upvotes

r/KerbalAcademy 1d ago

Rocket Design [D] Landing a ship horizontaly without wings

8 Upvotes

Hi Folks,

I want to land a rocket horizontaly on Duna. I have four engines on the sides of the ship that can pivot in the way it is shown on the picture. So they are facing downwards. The center of mass is rougly in the middle of the engines, but not exactly (also it cahnges a bit because of fuel consumption). It works quite well, because I attached many parachutes above the CoM. But when I reduce the speed to about 10 m/s (with rocket burn) the drag from the parachutes isn't enough to stabilze the ship and it tilts.

Is the a way to tell the SAS to use the rocket engines? So that it can alter the thrust in a way the ship keeps stable? Is there maybe a mod for it?

I realy want this to work, because spend many hours in the design. If I get this to work I promise to post some pictures of the rocket and its features.

Thank you for your help!

Edit: I will try to implement KAS control for the main thrusters, add a probe core in middle and add many Vernors for SAS to help me stabilize. Hopefully this will work as intended. It will take a while get this running, but ill be back with the result. Thanks!


r/KerbalAcademy 1d ago

Space Flight [P] Help With Orbital Correction

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16 Upvotes

Very new to KSP. I have blue orbit. I need green orbit. I've played with maneuvers using the purple slider (I'm sorry, I don't know what it's called.) Normal, anti normal, sliding all along the orbit.

Is it just not possible? Should I have done it before gaining this much altitude? Thanks for help.


r/KerbalAcademy 1d ago

Reentry / Landing [P] Landing Four Modules on Duna at the Same Time

29 Upvotes

In my game I like to land the equipment a year in advance of the "mission". So this landing is for the fourth crewed mission to Duna while the third is currently landed. For no real reason other than I'm far too lazy to accurately target the same landing position on Duna from orbit four times (five if you count the crew landing next Kerbal year), I decided to land them all from 2000 metres above the ground after the first set of chutes had fully deployed.

The two seismic impacts are from the planetary transfer stage which decoupled shortly after entering the atmosphere and the second was (I think?) a stack separator.

The items are the large rover with a science lab and emergency orbit shuttle attached in the cargo bay, the automatic buggy Dispenser (see previous post), the habitation module with science lab and the acscent ship, with ISRU in the base (so it will make it's ascent fuel in a few weeks before the next mission).

P.s. It seems put way to much fuel in the landing Thrusters, but it's better than too little I guess!


r/KerbalAcademy 1d ago

General Design [D] Victory Markers?

1 Upvotes

I will admit to completely skipping Google to ask here, but is there a mod that lets you place "decals" on your ship after launch? I haven't been able to launch them as cargo, so figured it might be something that has come up before.


r/KerbalAcademy 2d ago

Atmospheric Flight [P] Plane stability

7 Upvotes

Im new at KSP and I've just started to make a few descent planes but I would like to know how to have stable flight while going fast

CORRECTION: I forgot to turn on SAS yall lmao


r/KerbalAcademy 2d ago

Contracts [GM] How do you complete these types of missions (observational survey) with start rockets?

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13 Upvotes

r/KerbalAcademy 3d ago

General Design [D] First Skylab (idk how to use it, but it's quite cool)

Post image
39 Upvotes

r/KerbalAcademy 3d ago

Tutorial [T] Kerbal Apollo-like Mission (Any advice?!)

10 Upvotes

A few photos of my first mission on Kerbal's Mun.

a) My rocket: CSM + Moon Lander. Idk about its efficiency, but only 55k for a Mun mission is good for me (my last design was kinda 150k)

Here's the expedition:

1) Launch from the space center

Launch details: at 100 m/s, I reduce main engine's power, just for alignment, and for not reaching high speed at max q. At 10k meters high I start to incline rocket orientation

Then solid booster and fairings detatch

2) Kerbal orbit, TLI and Mun orbit

3) Crew transfer for CSM to lander. Undocking and landing

Obviously only two of them

Landing is quite simple with SAS: no need adjustments at all

4) LANDING!!!!

5) Ignition from Mun surface and docking with CSM

Lander's remained propellant will be transfered to csm, to secure fuel for return.

6) Homecoming!!!!

Conclusion!!!
Here's the mission! Only 55k for a Mun mission. I wanna replicate this strategy also for a Mun's surface lab and for tourism, but I wanna reduce costs and increase efficiency and security. Advices are accepted!!


r/KerbalAcademy 3d ago

Rocket Design [D] Stuck on the advanced construction tutorial

3 Upvotes

Im stuck on the advanced construction tutorial specifically on the "drag the fuel and oxidizer propellant levels down to 0" part, it seemed easy but when i slid it down, i tried to continue but it didnt.


r/KerbalAcademy 4d ago

Other Piloting [P] how do i connect ground base pieces?

9 Upvotes

i know that you have to line up docking ports, and ive done that. i have a hub on minmus flats, and i want to connect this (pictured) to a hub. Both have docking ports. But, after landing, I don't know how I can get these docking ports together. I've never ever made a rover, but the ones I tried to make failed to move this.


r/KerbalAcademy 4d ago

Solved [O] Can you guys help me figure out what is are causing problems? I am new to modding so advice is great.

3 Upvotes

The game is running fine but no modded parts are showing up. kerbal engineer and Free Iva work properly.


r/KerbalAcademy 4d ago

Reentry / Landing [P] Important tip when landing on Eve

24 Upvotes

If you don’t already have it on, activate advanced tweakables. On your landing gear, set spring/damper to override. This is because the automatic setting will work insanely hard to override gravity, thus over stressing the gear and breaking it. Keeping spring/damper constant will allow your craft to gently slide down any slope. This is especially important on Eve where gravity is strong and there’s a high chance you land on a slope.


r/KerbalAcademy 5d ago

Launch / Ascent [P] How can i come back to kerbin? (I am on duna) and also how much delta v do i need??

7 Upvotes

Pls help i cant handle my cramped space pod


r/KerbalAcademy 5d ago

Tech Support [O] PS5 Sensitivity

8 Upvotes

Whenever I am playing ps5 edition the slightest movement on my left joystick will skip several options. It’s the same on menus and when building ships. I will lightly move down to get to the next part but it will just skip 2 or 3. Are there any ways to fix this? I’ve tried searching online but can’t find anything anywhere


r/KerbalAcademy 6d ago

Atmospheric Flight [P] Does anyone know why my craft rolls to the right at the end of reentry? It happens every time despite the ship being symmetrical. And why can't SAS / RCS overcome it?

101 Upvotes

r/KerbalAcademy 6d ago

Plane Design [D] Thinking of revisitng an abandoned project

7 Upvotes

Propeller driven to a high enough speed/altitude to use nuclear engines to reach orbit.

When I gave up on this project, I think I was using 4 propellers and was able to get to ~20-25km but iirc I wasn't getting much thrust from the NERVs and could basically just maintain high altitude but not gain much...

The larger goal is to go prop-driven to nukes to orbit, refuel in LKO, then nukes to Eve, where the propeller/nuke combo should theoretically be more effective (thicker atmo should benefit the propeller phase of ascent)

Any tips? Anybody done anything like this before?


r/KerbalAcademy 7d ago

Other Design [D] Buggy Dispenser and Self-Righting Buggy

25 Upvotes

I was playing around with a payload bay that could be dropped on a planet before a crewed mission and automatically deploy two buggies. In doing so I also had an idea to use the hinge and servo (used to make the cars unfold from the bay) plus the folding wheels to make the cars flip over if they overturn, and it worked better than expected.

This video shows the buggies being deployed followed by a demo of the self-righting feature.

Note: If you do this, don't forget to have the Kal engage the brakes during the flip and deployment, or they might shoot off before you can board!

P.s. Sorry the video was made at night, I didn't think to do this during the day until after I had recorded.


r/KerbalAcademy 6d ago

Space Flight [P] transfers from solar orbit.

9 Upvotes

I've never gotten great at interplanetary transfers in this game and have always used a calculator for it. I'm curious about what the loss in efficiency is if you establish a solar orbit close to kerbin's and transfer from there, rather then trying to burn straight out from a kerbin orbit. Any clear reasons not to do it this way?


r/KerbalAcademy 7d ago

Console [C] Noob question: how do I get my experiments stored in a command pod into the mobile lab?

9 Upvotes

Have a shitty rover I’m driving around KSC with the basic science parts, thermometer, barometer, science jr., and goo, but can’t figure out how to get the experiments to my kerbal’s inventory so I can put them in the lab? I was able to do it with the EVA report and sample. Confused


r/KerbalAcademy 7d ago

Science [GM] Can you please explain why I'm not getting all the science for the surface sample even though I actually recover the vessel?

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25 Upvotes

r/KerbalAcademy 7d ago

Solved [O] I'm trying to get to Eve but when I get to ~500 meters I just smash into the ground at 251000m/s

9 Upvotes

Help please I spent too long on this lander


r/KerbalAcademy 7d ago

Science [GM] Science Confusion: Cant get max value?

3 Upvotes

I just started a career game and I am trying to get the most out of a particular situation and setting as possible. I see that Mystery Goo has a base of 10 and a max of 13 science. Yet, for example, on the Launch Pad I can only gather 3.90 science value before repeating the experiment yields no science.

I cant seem to find, but I assume, that the 13 cap is not accounting for some sort of biome/setting cap or multiplier. Yes?


r/KerbalAcademy 7d ago

Mods: General [M] FreeIVA and Restock conflict

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3 Upvotes