Anyone doing his DeltaV calcs themselves?!

[maculator]

If yes how do you do it. I don't mean how to calculate it, but more how to do it the easy way.

[andylaugel]

When I need or want to do a dV calculation myself, I just reach for my old TI-85 graphing calculator. It's not that hard to plug in something like 9.81*350*LN(8.31/(8.31-5*(210+171)/1000)) and get the answer back. I suppose I could write a program on it to make things easier if I wanted to though.

[Acevy]

Originally posted by andylaugel:

When I need or want to do a dV calculation myself, I just reach for my old TI-85 graphing calculator. It's not that hard to plug in something like 9.81*350*LN(8.31/(8.31-5*(210+171)/1000)) and get the answer back. I suppose I could write a program on it to make things easier if I wanted to though.

same

[RoofCat]

My mobile phone calculator has ln in scientific mode. And it is always by my side. That's my choice.
MS Excel is very convenient to do stage based automated calculations (it also allows a lot of code) and I suppose its open source counterparts too. But my old 2007 Office DVD got damaged.
I have been thinking about writing a simple app for android or Windows to reduce typing in calculator, but in the end nothing of that makes sense, because there already is KER and not just that. So it could be fun project for some student, but not much value on the market.

[Jupiter3927]

I do it manually but I use a different formula.
((Engine Force)*(# of Engines)*(Fuel per Tank)*(# of Tanks))/((Payload Mass+Average Mass per Tank*# of Tanks) *Fuel Consumption)

It gives the same answer but doesn't ask for engine ISP or G.
It gives a pretty graph when you plug X in for # of tanks in a graphing calculator.

[maculator]

Thats interresting. I always just used the normal Tsiolkovsky rocket equation. I was thinking about playing ksp in a seperate career without any mods just for fun. But whenever I think about it I come to the conclusion that there are mods I can't live without. KER beeing one of them. It's one of those mods that really make the game unnecessary complicatd if you don't use it.

[RoofCat]

simple weight proportions are enough to build rockets.

You google delta v maps and then consider you need delta v calculator. Don't google delta v in the first place and you won't need calculator. Use test launches.

BTW I have considered googling delta v kind of cheating when I started. You are a kerbal explorer. Do kerbals have google at all?

[Manwith Noname]

No, they have kookle.

[RoofCat]

Originally posted by Manwith Noname:

No, they have kookle.

...and their internet is kinkynet?

[andylaugel]

Here are a few silly but practical examples of when I've used my calculator and the formulas to do dV math in KSP--times when KER was not enough. I've placed the answers in spoiler tags, so you'll have to hover your mouse over them to see them.

Example 1

http://steamcommunity.com/sharedfiles/filedetails/?id=783692376
M-181a Mun Relay is an example of a communications relay satellite I use. Another craft tows it mostly into place, whereupon it undocks and circularizes its orbit using RCS thrusters. The RCS thrusters have a Isp of 240, the satellite masses 2.3t full and 1.3t empty. KER won't tell me it's dV, so I need to compute it myself. I find it has 1,343.3 m/s dV--more than enough to handle circularizing an orbit over most celestial bodies. I might even opt to launch them with less fuel, so the delivery system doesn't need to be as heavy.

Example 2

http://steamcommunity.com/sharedfiles/filedetails/?id=1096300591
M-235 Nosecone (not pictured, but similar to the pod on top of the assembly in the photo above) is in orbit around Vall, having captured Asra's Craft in its "Klaw." It's a handy passenger pod too, able to hold up to 5 kerbals. No engines though--it's a pod that usually relies on a tugboat for transportation. We know it masses 5.46 tons, has 265 units of monopropellant (4 kg/unit), and RCS thrusters with an Isp of 240. Wouldn't it be nice to know how much dV does it has to play with? KER won't tell us. But using the dV equation, we can determine the nosecone has 508 m/s dV.

We can use maneuver nodes to estimate how much dV it will take to transfer between different known orbits, which is about all I'd be using this pod for. Can it reach another piece of space debris containing a stranded astronaut? Can it return to the tug under its own power? My tugs are easily x30 larger than this pod, so the fuel savings could be significant.

Example 3

http://steamcommunity.com/sharedfiles/filedetails/?id=855749345
Can M-085 Cloud Dragon (centered in photo above) return to Kerbin under its own power? It is currently parked on Ike. It's a mining ship that's been patched to have an antenna it originally lacked. It masses 213.84t, has Poodle engines, 8100 units of liquid fuel (5 kg/unit), 9900 units of oxidizer (5 kg/unit), and 6000 units of ore (10 kg/unit). KER tells me it has 1,664 m/s of dV, but its large ISRU can convert all that ore into usable fuel. So doing the math manually, we find that it has total dV of 4,164 m/s.

I started to work on my own return dV estimates using in-game tools, but KAC and my orbiting craft at 50 km over Ike told me it would require at least 2,340 clicks to advance the node far ahead enough in time to the ideal transfer window. But I could have taken notes though when I was flying out to Duna, recording how much it took to get into Duna orbit without aerobraking though--effectively building my own dV map. My gut though is telling me that returning to Kerbin orbit would require some aerobraking--a somewhat risky proposition for a craft without parachutes.

Example 4

http://steamcommunity.com/sharedfiles/filedetails/?id=844223577
M-086 Gold is a fuel depot on Vall. It uses Poodle engines (Isp 350), masses 290.76 tons fully fueled, and contains 25,920 units of Liquid fuel and 21,120 units of Oxidizer. It wants to deliver fuel to my Tylo lander and tug in orbit at 130 km moving at 695 m/s, which need at least 4 orange tanks of fuel. How much fuel does it need to reserve for itself if it wants 1,100 m/s dV after delivery for landing?
We can compute all fuel masses 235.2 tons. Subtracting that from the total mass, we find the ship should mass 55.560 empty (still contains monopropellant).
dV = g * Isp * ln((desired fuel mass 'x' + dry mass)/ dry mass)
1,100 = 9.81 * 350 * ln ((x + 55.56)/55.56)
x = 55.56 * e ^ (1,100 / ( 9.81 * 350 )) - 55.56 = x
x = 20.98 tons of fuel, or 4196 units, or 9% of the tanker's total capacity.
Knowing there are 9 units of Liquid Fuel for every 11 units of Oxidizer, we can determine we need 1888 units of Liquid Fuel and 2308 units of Oxidizer. A little more than half an orange tank of fuel.

[maculator]

^Interesting, those occasions are the only ones I did it myself too. And when I watched the scott manley series back when I was a noob, but that was for fun.
When you got some crazy stacked rockets KER can actually get confused.
To avoid doing it myself I came up with a solution:
Build the satelite, check DeltaV and mass, note it.
Build the rocket but instead of using the satelite use a fuel tank you fill up until it has the mass of the satelite and get the correct deltaV for the rocket, switch the dummy for the real payload, done.
Now that I think about it: KER can't actulally do DeltaV calcs for RCS.

[RoofCat]

issues, that come to my mind:

• engines dropped without tanks may be problematic (slow solar burns left with single nuke);
  
• RCS is problematic. I don't use it anyway due to very low Isp and rather ruining delta v;
  
• stages, that keep working while some other smaller ones are dropped (some 50% SRB, liquid, tanks) aren't accurate;
  
• solutions, that include Lf+Ox and pure LF - the real delta v is a range and depends on order of use;
  
• ore.

And then Elon had all the math and supercomputers in the world and yet he built multiple test rockets. Because that's the way we do. And it works great in KSP too. Have your R&D budget building and testing new ones. I'm pretty sure it will add to rpg factor and otherwise quite shallow business simulation.

[maculator]

Of course I do testing. But totally without DeltaV isn't that much fun. The fun is to eyball it and then in the test you actually see how much you're getting out of it.
No calcs would work just fine for simple trips in kerbins soi I guess, but if you plan a mission with mulziple stops you don't want to have it fail because your 6. landing proofs to be impossible due to too less fuel. So knowing that you probably have enough is a nice thing to have.

For me the fun is to start with an overengineered rocket and then from use to use ditch more and more fuel, get cheaper fins, smaller batteries until I reach the point where I can't save any more of anythhing.

[RoofCat]

you can have test node in LKO at any time. You can add test node to test node to see how much it takes to slow down at target as well. You can make 3..4 of them chained. And while at NavBall it will show only the delta v for first node, hovering with mouse you will also see the values for the rest. Return is roughly the same except for Kerbin moons.
With conventional vacuum stage if your payload is less than 1/10 and engine roughly the same, you will have ~5000m/s delta v.
With nukes that number grows closer to ~11ooom/s. Most nuke designs have closer to just 8ooo m/s though. Heavy engines, lazy designing...

So basically you have to do the math once for a few dry mass proportions (1/6; 1/8; 1/10;... 1/20...) for a Terrier (all Lf+Ox vacuum engines have almost the same Isp so the results are very close) to be able to accurately guess your stage delta v without any ln() later on.
And the same for Nukes.

Ancient scientists were calculating a lot of things with drawings in "sand". You have education, math and supercomputer in mobile phone, but have forgotten the ways of Archimedes :)

It's all about VERY simple proportions.

[maculator]

I always got the feeling you just use these forums to tell everyone how you think the game should be played and how wrong everyone else is.

I mean this was about the way people do or don't calc there DeltaV. Then it somewhat turned into how necessary it is/isn't to have DeltaV readings and now you turned it into "look folks I'm doing it this way, this is the right way! The rest is cheesy!"

There is nothing wrong with knowing that it takes about 3.4km/s to go to orbit and based on this knowledge and DeltaV readings you construct a rocket that possible can do it. Then you just trim it down after each test flight and you'll end up with a pretty accurat number for your construction.

Maneuver nodes won't help you with that.

[RoofCat]

no, I'm just saying you make it complicated in the first place to solve 5 min later with calculator.

Lets say your upper stage is 6t. Which is common 0.5t Terrier - 4.5t tank - 1t MK1 command pod stage+chute+decoupler. (there is info icon bottom right for basic ship info where you can track mass all the time)
So 6t payload.
~6t launch engine? Mainsail it is. Now add roughly 10 times that fuel - 60t. 72t full mass.
Mainsail has 1379kN ASL. Optimal 2/3 from that for TWR 1.5 means roughly 90t (900kN) full mass. Which means you can add 18t fuel more and it will be fine and just increase delta v.

I bet it will reach LKO easily and not just that. It will rather do the most part of the transfer burn too because of those extra 18t fuel. Did you need calculator so far?

1-1-10 is approximate LKO formula for Lf+Ox engines. 3400 or 3600m/s, couldn't care less.
SRBs are much heavier of course and offer different dynamics. Another example - single stage orbiter: 1t MK1 command pod+chute+decoupler, 1t Dart engine, 10t fuel. Guaranteed LKO.
Reliant has more kN, that's how you build 25 science LKO ship with ~14..15t early on.

Lf+Ox vacuum stages are more efficient and you can have even more fuel - that's how you reach ~5000m/s for them.
That Terrier stage mentioned above has ~3700m/s. As a simple rule double fuel amount for vacuum stages to keep it comfortable when more delta v is needed. Add another 4.5t tank and have 4850m/s. Drop one of the tanks as it is emptied and get ~5000m/s.

There are cases when more math may be needed - low solar rescue and Eve launch for example. But the rest is rather simple.