Delta-v Budgets | KSP Let's Do The Math

[@MikeAben]

Up Next: Combining ISP Formula - kzbin.info/www/bejne/m6jFh2ObZtiYg9E

[@josephjones2834]

Thank you for this tutorial, I have been looking for a way to calculate delta v without mods for a while now. Awesome video!!

[@MikeAben]

Thanks. One of the first things I did when I started KSP is set up a spreadsheet with this kind of stuff. Although I use Kerbal Engineer, there are always situations where I'm pulling these formulas out again.

[@Warriorking.1963]

Great video. I've been looking for a clear explanation of how to calculate the Delta V of multi-engined stages for quite some time, and now I've found this one... EXCELLENT!

[@MikeAben]

Glad it helped.

[@uglyduckling81]

Kerbal Engineer (KER) is my friend.

[@MikeAben]

Oh, yeah, but I still find it interesting to know this stuff.

[@simpson6700]

it took me a while to realize that m/s makes perfect sense to calculate distance in space, since there is no drag.

[@InfoDav]

Brilliant video series.

[@MikeAben]

Thanks. I hope to get back to this series fairly soon.

[@mickolesmana5899]

I Have orbital mechanic exam tomorrow, thank you for explanation

[@mauricethrun6115]

isnt it necessary to calculate the delta v of the stage which will return the craft to kerbin after landing (on the mun for example) with the gravitation on that particular planet/moon? or this already taken into account by the delta v map?

[@MikeAben]

Actually, the dV of a rocket is independent of the gravitational field. It's dependent upon the masses of the rocket and propellant, and the exit velocity of the propellant, and that's it. Isp is exit velocity divided by the acceleration due to gravity on Earth (g_0). The g_0 only appears in the formula, because KSP uses Isp instead of exit velocity to measure engine efficiency.

[@mashhoodahmed8256]

I want to calculate the velocity budget to send a launch vehicle to an altitude of 500 km. As the velocity budget is calculated like V_leo + V_drag +V_gravity + V_steering. Assuming it to be a circular orbit V_leo = sqrt(u/r) so V_leo is lower for higher altitude giving me a lower velocity budget and if I intend to use a parking orbit I would be increasing velocity budget by introducing a lower orbit and some impulsive maneuvers. Can I directly launch into 500 km orbit and if I can do it why ever use a parking orbit that increase my velocity budget ?

[@MikeAben]

You certainly can insert straight into a 500 km orbit. I do it all the time, but for budgeting such a mission I just take my insertion cost for an 80 km orbit and add the transfer from 80 km to 500 km, even if that is not what I do. It's just simpler. Here's my video on calculating ascents when an atmosphere is involved. It get's into different inclinations, but it would be easy to adapt for different altitudes. kzbin.info/www/bejne/ZnPXk4yMqb9sl8U

[@nickelpickle1134]

I'm still trying to understand this concept, if Kerbin had more gravity, would you lose m/s or is that a different calculation?

[@MikeAben]

If Kerbin had a higher gravitational field, the dV cost of the transfer out to Minmus (if it were still in the same orbit) would be more, if that is what you are asking. I think the capture at Minmus would be more as well, but I would have to look at the math on that one to be sure.

[@ryantran8800]

Hey! I got a question, what did you mean by swivels for the 215 thing?

[@MikeAben]

Sorry, I'm not sure what you're referring to, but Swivel is the name of one of the engines in the game if that helps.

[@cheeki3998]

greetings from 2019! is there a way, perhaps some formula, that you know of -OTHER THAN trial and error of building entire ships and then doing all of this math just to possibly figure out that you don't have nearly enough delta V for your desired journey- to calculate the exact amount of delta V needed in order to lift an already set amount of weight (like a crew compartment with a science bay and antennas for example) to a certain destination? i mean i'm sure there must be because like.... NASA and stuff lol because i have only ever just completely guessed (more like hoped) that i would have enough delta V to get anywhere currently watching your LDTM series and i'm trying to soak as much of it in as i can! thank you for explaining everything as idiot-proof as you do; it honestly does help a lot. :)

[@cheeki3998]

didn't mean to strikethrough that part! apparently the command to let youtube know you want a strikethrough is to put hyphens before and after! lol

[@MikeAben]

You absolutely can calculate the delta-v requirements for most missions. You can see how the delta-v map is used in this episode, but most of these numbers are calculated using the vis-viva equations derived in episode 2. In episode 6, I calculate the costs of ascent off Minmus and a Minmus-Kerbin transfer. The same technique applies to interplanetary transfers, though I never got around to doing an episode on that. I am planning on getting back to this series. Keep watching, and please, keep asking questions when things aren't clear. It really helps me in planning future episodes.

[@ryantran8800]

Oh yeah can you also tell me how you got the ISP and rocket equation answers?

[@MikeAben]

Are you asking where the formulas come from? If so, the links under the info tabs address that. If your asking how to put the numbers through a calculator, then I'm not sure I can help. Calculators are set up differently.

[@hamidbnd]

Great video. But one question; For calculating the mf, shouldn't we also subtract the mass of the side booster's body? you just subtracted the fuel mass.

[@MikeAben]

Good question, but it is just the fuel mass you subtract off. The expelled fuel mass creates thrust, not the ejected stage. Now, the stage mass is subtracted off when calculating the starting of the next stage. It is a good thing to remember, and perhaps I should have emphasized it more, but when using the rocket equation, it is only the loss of propellant mass that affects delta-v.

[@dydunyatv4286]

My brain:*start die*

[@salockingaming6246]

what does the ln mean?

[@MikeAben]

It stands for the natural logarithm, a topic typical covered in senior high school math. I put a link in the description with more on what a logarithm is.

[@mariusj34]

Is drag not calculated?

[@MikeAben]

If you're referring to the 3400 m/s for low Kerbin orbit, drag losses are already factored into that number.

[@graysav]

I don't understand why you calculated it like this when it appears all of the engines are cross feeding fuel and you didn't include the mass of fuel burned by the mainsail.

[@MikeAben]

+Grayson Savage The fuel lines keep the main booster tanks full until all the radial boosters are gone. Until the mainsail is on it's own, it is running off the radial tanks.