How do I know if I have enough fuel and engine power to reach orbit?

[Scuka]

Simple question, how do I know if my rocket has have enough fuel and engine power to reach orbit on a certain planet/moon?

And in general, how do you know the amount of fuel you need to get from A to B with given weight and engines used?

Edited August 17, 2014 by Scuka

[UmbralRaptor]

The way to tell is if your craft as sufficient ÃŽâ€V and TWR (thrust to weight ratio). ÃŽâ€V (pronounced delta-vee and measured in m/s) comes from the rocket equation, and is literally much much your craft can change its velocity. This is straightforward to calculate it for simpler ships (just Isp*9.82*ln(wet_mass/dry_mass)). You'll also want a ÃŽâ€V map to make sure you have enough. TWR is thrust/(mass * local_gravity). Values for the gravity at the surface of various bodies are on the wiki, though the amount actually required is more complex.

If you want more general information about flying,

has an extensive set of tutorials. Mod-wise, I would consider something like MechJeb/Kerbal Engineer Redux/VOID if only for their ÃŽâ€V displays. (Though other information that they add may be useful)

If you want a theoretical background so you can find out where these numbers come from (and just how much they approximate), intros to orbital mechanics are available on the web. Particularly important are the Vis-viva equation, and Kepler's 3rd law. For interplanetary missions, check out Hohmann transfers and phase angle calculators.

And if you want a textbook on the subject, I am partial to Fundamentals of Astrodynamics

[Volcanix]

First of all, welcome to the forums!

If you want to know if your rocket has got enough fuel to reach orbit or other planets, you should use an information mod like MechJeb or Kerbal Engineer Redux.

Here are the links:

MechJeb

MechJeb is a mixture between an information mod for telling you some interesting stats about your ship and an autopilot mod. It can, for example, fly your ship into orbit without having you doing anything (if I understood it correctly) or other things like docking. I don't use the mod myself so I haven't got any experience of it.

KER - Kerbal Engineer Redux

I use this mod for information about my ship. You just attach a computer chip - like thing on your ship and a window appears telling you the stats about your ship. It shows the ∆V (delta V) and TWR (thrust weight ratio, see UmbralRaptor's post for further details). The TWR is also really important because it gives you information about how quickly your ship can get up into the air. If you got a TWR of 1, your ship can hover. Nothing more, nothing less. With a TWR under 1, it won't be able to lift or hover, because the weight is to high for the thrust provided by the engines in your stage. A TWR over 1 gives your ship the ability to liftoff, at around 1,6 you get kind of a comfortable liftoff.

One personal "rule" I've got for my ships:

The stages I use to get in orbit (the stages that lift the rocket in the atmosphere) must have a high TWR, goal is 2, but under 1,4 it gets really uncomfortable when you fly upwards. You should find that out yourself! A rocket with a huge engine and tiny tank for example has a high TWR, which means that it will accelerate really quickly BUT if the TWR is too high, the atmospheric drag will slow you down so your rocket will become ineffective. Experiment around with that a little.

The first tutorial in my signature shows some good ships that also helped me with ship design. Try it out!

If you've still got questions, just ask them. The forum is the right place for it!

Volcanix

[Scuka]

I belive those Delta-V maps are what I need.

Thanks to both for your awesome answers.

[SRV Ron]

While the mods and aids will help you greatly in designing rockets to fulfill those missions, you are missing out on the fun and learning experience of doing it the Kerbal way. Go to the Kerbal School of Hard Knocks. Just build something and see how it works. If it doesn't work, try something else. When it does work, tweak the design to see if it will work better. Build simple. Simple smaller designs are easier to upgrade to fly better then big complex expensive ones.

Example of an early career design, the first basic rocket;

As is, it will reach 5,000 meters with lots of aerodynamic heating and blow up with the pod surviving upon landing. But, it will also, with proper tweaking and flying, reach well over 33,000 meters and land intact in the ocean just offshore of the launch facility for nearly 100% recovery.

[Cat Biscuits]

the very unprofessional way I always test If I have the delta-v because up to now Ive only played vanilla is ah, Il always send an unmanned probe or two out to my target first before attempting manned missions. even though manned missions are heavier its pretty easy to "eyeball" the weight after a while.

[Scuka]

Yeah, testing for take-off from Kerbal is fine, but I'd be a really unhappy person if I landed on some planet and then realised I don't have enough fuel to get back.

[GoSlash27]

I do it the opposite way; I design the craft to have the required delta v and thrust/ weight ratio with as little overall mass as I can manage. *Then* I build it.

I find it's much more fun to complete missions than it is to tinker and adjust, but that's just me.

Best,

-Slashy

[rkman]

Tinkering and adjusting, trying and failing, certainly has its charm while staying within Kerbin SOI.

But that magic quickly fades when one starts trying and failing at various stages of multi year missions to other planets. I'm genuinly curious how Falanghe goes about that.

[Volcanix]

Yesterday, I did a mun landing. The rocket should have gotten enough ∆V for LKO, Transfer to mun, landing and return to Kerbin with only a couple m/s of ∆V left, so I risked Jeb's life to try out. Guess what? I landed on mun, returned to Kerbin and had about 4 Liquid Fuel left. That was close

The important thing about Delta V with those mods is that they calculate The delta v Of your rocket assuming that you Stage it perfect. For example, you decouple The boosters in The same Moment as they run out Of fuel. Try to always have a couple hundreds Of delta v over what you might need according to The delta v map because you can always make a mistake^^

Wargh.. Writing this was horror xD why doesn't Android simply switch The keyboard language when typing english? #justmacuserproblems

Volcanix

[Wanderfound]

Yesterday, I did a mun landing. The rocket should have gotten enough ∆V for LKO, Transfer to mun, landing and return to Kerbin with only a couple m/s of ∆V left, so I risked Jeb's life to try out. Guess what? I landed on mun, returned to Kerbin and had about 4 Liquid Fuel left. That was close

Did a spaceplane to Minmus return trip a few days ago. I used a bit too much fuel playing with the VTOL Vernors while landing, and wasn't sure if I had enough to get back off Minmus (hooray for low gravity!), let alone return home.

I set a 20,000m Kerbin periapsis as I left Minmus orbit; 6 units of oxidiser to spare. Thank Kod for aerobraking...

[dzikakulka]

I thought it would be helpful and more user-friendly: http://i.imgur.com/Vi8H41I.jpg

Not mine. I do not know the author unfortunately

[NecroBones]

Yesterday, I did a mun landing. The rocket should have gotten enough ∆V for LKO, Transfer to mun, landing and return to Kerbin with only a couple m/s of ∆V left, so I risked Jeb's life to try out. Guess what? I landed on mun, returned to Kerbin and had about 4 Liquid Fuel left. That was close

I love those close-calls. My first trip to Duna was kinda like that (just a lot less close, technically speaking, but still made me sweat).

Edited August 18, 2014 by NecroBones

[Pecan]

I thought it would be helpful and more user-friendly: http://i.imgur.com/Vi8H41I.jpg

Not mine. I do not know the author unfortunately

Woo! I haven't seen that one before. It has everything.

[Volcanix]

I thought it would be helpful and more user-friendly: http://i.imgur.com/Vi8H41I.jpg

Not mine. I do not know the author unfortunately

Woah.. That's by far the best I've seen around, from simple tables to huge pictures. But to be honest, I do not know what the symbols of some things mean?

Oh wait. There they are explained. Consider me being blind sometimes. <.<

I love those close-calls. My first trip to Duna was kinda like that (just a lot less close, technically speaking, but still made me sweat).

Haha... After doing a successful mun landing yesterday in my sandbox save I decided to accept the "Explore Mun" contract in my career save game and done it. I thought "ohmergawd that yesterday was SOOO close I need MOAAAAAR ∆V!!" so after landing on and setting a collision course on Kerbin I still got about 1.300m/s of ∆V left. I'm sure I could've gotten to Minmus... My rocket wasn't really cheap, it costed about 75.000 funds. I still made a lot of profit

But I'm drifting away from the topic. Sorry.

If someone's interested in the trip beginning from short-before-mun-landing, here's a little imgur album:

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