Mothership fuel

[aaaaaaaaaaaaaa]

How much fuel should I bring to Duna if I an powering the craft with 2 nerv neucular engines

[kbmodigity]

You cant realy ask how much fuel should you bring but rather how much Delta-V do you need. The amount of Delta-V takes into the account of the weight of all the parts and fuel that you are bringing along with how efficient your engines are burning the amount of fuel you have. Programs like Kerbal Engineer Redux (KER) do these calculations for you.

FOr a trip to Duna from a low Kerbin orbit you need about 1100 delta-v to make the trasfer and around 500 delta-v to get into orbit without aerobraking. You will also need some delta-v to make the landing as well if you plan on going to the surface as the atmosphere is too thin to give you a safe landing by chutes alone.

To get back into orbit you need around 1500 delta-v and then around 1100 to get back into a transfer with Kerbin again.

All these numbers too are assuming everything you are doing is the most efficient such as you are going to Duna when Kerbin and Duna are at optimal phase angles and then again for the return trip.

You have to remember too that if you are doing a mothership+lander type craft that when you detach the lander its own delta-v will be much different as the mothership and lander combines. This is because as stated above the weight of the lander will be much less than the 2 togther. It will also have most likely different engines and a different amount of fuel.

I hope this makes sense as I am not that good at explaining things but I'm sure there are others in the community that can help you out better than me if this doesnt make sense.

[Gamer]

8000 dV minimum. 10,000 dV if you don't want to be paranoid about your fuel.

[aaaaaaaaaaaaaa]

Diposting pertama kali oleh Lord Gaben:

8000 dV minimum. 10,000 dV if you don't want to be paranoid about your fuel.

So how much fuel is that because my ship is just a Duna and Ike orbiter

[dnrob7]

Diposting pertama kali oleh Modern dimetrodon:

Diposting pertama kali oleh Lord Gaben:

8000 dV minimum. 10,000 dV if you don't want to be paranoid about your fuel.

So how much fuel is that because my ship is just a Duna and Ike orbiter

How long is a piece of string?

The question doesn't make sense.

[=BB= Misophist]

Diposting pertama kali oleh Modern dimetrodon:

Diposting pertama kali oleh Lord Gaben:

8000 dV minimum. 10,000 dV if you don't want to be paranoid about your fuel.

So how much fuel is that because my ship is just a Duna and Ike orbiter

Enough that I would advise using drop tanks

[andylaugel]

Well, my M-113 Centaur mission to Duna has the capacity to store 29,870 LiquidFuel, 11,770 Oxidizer, and 6,000 ore (ISRU can convert ore into fuel).
http://steamcommunity.com/sharedfiles/filedetails/?id=753306790
But yeah, dV is a better question to ask. For any single-stage craft, dV = engine Isp * 9.81 * ln( start mass / end mass ). You can also look at the subway map[wiki.kerbalspaceprogram.com] to estimate dV requirements. Looks like a bit over 3 km/s for a one-way trip to Duna from low Kerbin orbit.

[andylaugel]

Assuming you use "Nerv" engines and have a desired dV of 4,000 m/s:
4,000 m/s = 800 * 9.81 * ln (wet/dry)
0.50968... = ln( wet / dry )
e^0.50968... = wet / dry
1.664765 = wet / dry mass
So your craft with all the tanks full should mass 166.5% or more what it does when the tanks are empty.

[kbmodigity]

You have to look at it this way. Lets say you wanted to travel 1 km/s in space. The amount of delta-V is the same amount on a 2000 ton ship or a 1 pound ship. The difference is that the 1 pound ship will need far less fuel than the 2000 ton ship as it needs to spend much less energy to achieve that speed. Also, if one ships engines are less efficient than the others that will determine how much fuel is needed too to reach the required amount od delta-v.

This is why mods like kerbal engineer redux are a must have in my opinion when trying to figure out what a craft is capable of. If a craft weighs a ton and has massive amounts of fuel doesnt mean it will even make it to orbit.

[andylaugel]

The other factor to consider is thrust. A "Nerv" engine produces 13.875 kN (kilonewtons) in atmosphere, or 60.0 kN in vacuum. Thrust is a force, and force = mass * acceleration. We'll use the following units of measure: kN = metric tons * m/s/s. F = ma also means that m = F/a, or a = F/m.

Your 2 "Nerv" engine lander will have 120 kN of thrust in vaccum, or 27.75 kN in atmosphere.

Ike has no atmosphere, and a surface gravity of 1.10 m/s/s. F = ma, so m = F/a. Plugging in the numbers, we find that 2 Nervs can support 109 tons on Ike. But if it wants it to move, we want to accelerate faster than surface gravity pulls us down. If we want a thrust to weight ratio of 1.5, we'll want to mass less than 72.7 tons.

Duna has an atmosphere and a surface gravity of 2.94 m/s/s. Plugging in the numbers again, we find our 2 Nerv lander craft needs to mass less than 9.44 tons. Or 6.29 tons if we want a TWR of 1.5. This might be a little conservative, as Duna's atmosphere is much thinner than Kerbins. But it's a starting point. Oh, and the 2 Nervs mass 6 tons by themselves, so... yeah.

Nervs are efficient, but lack thrust. Designing landers based on them is challenging. This is why my Nerv powered movers and asteroid catchers are designed to stay in orbit. A lander can stay docked for the interplanetary voyage, and seperate when it needs to land.

[tkraftson]

Use Kerbal Engineer Redux (KER) and it will calculate the delta V that your fuel and ship will deliver.

Also there is trial and error experiments that are part of the appeal of KSP.

[kbmodigity]

Diposting pertama kali oleh andylaugel:

The other factor to consider is thrust. A "Nerv" engine produces 13.875 kN (kilonewtons) in atmosphere, or 60.0 kN in vacuum. Thrust is a force, and force = mass * acceleration. We'll use the following units of measure: kN = metric tons * m/s/s. F = ma also means that m = F/a, or a = F/m.

Your 2 "Nerv" engine lander will have 120 kN of thrust in vaccum, or 27.75 kN in atmosphere.

Ike has no atmosphere, and a surface gravity of 1.10 m/s/s. F = ma, so m = F/a. Plugging in the numbers, we find that 2 Nervs can support 109 tons on Ike. But if it wants it to move, we want to accelerate faster than surface gravity pulls us down. If we want a thrust to weight ratio of 1.5, we'll want to mass less than 72.7 tons.

Duna has an atmosphere and a surface gravity of 2.94 m/s/s. Plugging in the numbers again, we find our 2 Nerv lander craft needs to mass less than 9.44 tons. Or 6.29 tons if we want a TWR of 1.5. This might be a little conservative, as Duna's atmosphere is much thinner than Kerbins. But it's a starting point. Oh, and the 2 Nervs mass 6 tons by themselves, so... yeah.

Nervs are efficient, but lack thrust. Designing landers based on them is challenging. This is why my Nerv powered movers and asteroid catchers are designed to stay in orbit. A lander can stay docked for the interplanetary voyage, and seperate when it needs to land.

I am not going to do the math but assume you are correct, but I think you are a little off on what this thread is about. The OP seems to not understand the difference between fuel and D/V. He also made no statement about landing on Duna, just getting there. Yes what you say is correct, but honestly I think its a little over his head after reading his response.

I was in his shoes at my early days of KSP too. Thank god for Scott Manley and this awsome community.

My point is I think we need to try to help simplify and explain what they are not understanding, not give calculations and numbers that even I, a seasoned KSP player, dont understand. If they dont understand what D/V is compared to just how much fuel then I highly doubt they will understand things like "1.10 m/s/s. F = ma, so m = F/a"

Edit : I also assumed before he responded that he was trying to land as well, along with a return trip.

[andylaugel]

Fair enough, kbmodigity. I just got to thinking about the design constraints of a Duna lander, and overlooked that he was just talking about an orbiter.

Modern dimetrodon had also sucked me into his earlier "infinity starship chalenge" thread, where he was asking us to capture an asteroid, mine it, and without nuclear engines and only an orange-fuel tank of fuel, get it and your craft into Laythe orbit. I thought he might like to hear some of the math involved in this sort of thing.

[kbmodigity]

Diposting pertama kali oleh andylaugel:

Fair enough, kbmodigity. I just got to thinking about the design constraints of a Duna lander, and overlooked that he was just talking about an orbiter.

Modern dimetrodon had also sucked me into his earlier "infinity starship chalenge" thread, where he was asking us to capture an asteroid, mine it, and without nuclear engines and only an orange-fuel tank of fuel, get it and your craft into Laythe orbit. I thought he might like to hear some of the math involved in this sort of thing.

Oh wasnt aware of this. You would think someone who issues a challange like that would know the difference between fuel and d/v. I can see where you are coming from with the math point of view.

I hope the OP is not a troll, he has enough hours in the game to where he would be right around the point for extraplanetary exploration. I just hope we all arent being taken for a ride as I try to help people who seem to realy want to learn.

EDIT : so far he doesnt seem to read but only keeps asking the same question. Hopefully he will read and look some stuff up. How hard can it be? Its only rocket science,lol

PS I hope i didnt sound harsh to you. Sometimes I come across that way and i guess its due to lack of my verbal skills. No ill intent was meant.

[aaaaaaaaaaaaaa]

Right now I'm planning to bring 2 rokomax jumbo fuel tanks worth of fuel

[Anonymous Captain]

To everyone who is confused/not bothered reading all the super serious maths, here's a tl;dr:
Add more fuel and engines, gravity is your best friend and SAVE YOUR ♥♥♥♥♥♥ FUEL