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rpayne88

Mothership Propulsion

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I'm currently building a large interplanetary ship in orbit. I want it to be able to go any where. My question is, what engines should I use to propel it and how many? I want it to be able to reach Eelloo and return with out jettisoning any tanks. My goal is to have it get into low orbit and deploy a lander. I already have the lander designed, but I need to know how to get it out there.

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I would suggest about 6-8 LV-N Atomic Rocket Engines. They are highly efficient, but only have 60 kN of thrust. 8 will produce about 480 kN of thrust. Another suggestion is to get your lander up in orbit with a launcher, then dock it to what I call and "Interplanetary Tug" composed of the Large fuel tanks (not the orange ones) and four LV-Ns. I'll put pictures up of the tug later this evening or tomorrow.

Hope this helps you.

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I've heard a lot of people say more than 2 LV-N's is a waste. Not having tried it myself, I can't say for sure if more is good or not.

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I've heard a lot of people say more than 2 LV-N's is a waste. Not having tried it myself, I can't say for sure if more is good or not.

I think you are right. One LV-909 consumes less fuel that 2 LV-N's. LV-909's are also lighter than LV-N's by a lot.

I guess more of a large rocket would do. Or a tug of sorts.

Edited by TinMissileMan
Calculating mistake

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I think you are right. One LV-909 consumes less fuel that 2 LV-N's. LV-909's are also lighter than LV-N's by a lot.

I guess more of a large rocket would do. Or a tug of sorts.

909's may be more effecient with a smaller ammount of fuel, but the more fuel you carry the more the LVN's extra mass doesnt matter.

if you use mods, there are a couple of variants to the LVN you should look at. KSPX has a 2.5m version that has 150kn of thrust, Fatman has a 240kn version that has a higher mass but is also 840 ISP, this higher isp with higher mass is only benificial with more than a large grey tank, otherwise stock engines give better dV.

Novapunch has a 2.5m LVN but i personally prefer the Fatman version better

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I've heard a lot of people say more than 2 LV-N's is a waste. Not having tried it myself, I can't say for sure if more is good or not.

Technically anything more than one is just extra weight which means more fuel required to get around. However, a large ship with only 1 nuclear engine is completely impractical and you will hate yourself if you ever do it. I once sent a huge mothership with two rovers and two spaceplanes to Laythe on only 3 nuclear engines and my burn was estimated at 45 minutes long (at 3x time warp it wound up being about 35 minutes long thanks to some crazy lag) after 6 periapse kicks just to get out of Kerbin's SOI.

So yes, more than 1 of any engine is just extra weight but on a ship that needs it that extra thrust makes the game playable. Just keep your engine mass relatively small compared to your craft mass and you'll be fine.

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This ship here

1k3dOzH.png

has now made trips to Tylo, Eeloo, and Moho while delivering ~50 tons of cargo, and then returned to Kerbin to be refuelled and sent out again. So I guess you could say that it can "go anywhere." It's driven by 12 LV-Ns. I don't put it in low orbits, though, because the mission-specific subships can make the trip from high orbit to orbit or landing fairly easily, once the mothership has delivered them to the destination planetary system, and it would cost oceans of additional fuel to put the whole ship down low and lift it up again for the return trip.

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This ship here

1k3dOzH.png

has now made trips to Tylo, Eeloo, and Moho while delivering ~50 tons of cargo, and then returned to Kerbin to be refuelled and sent out again. So I guess you could say that it can "go anywhere." It's driven by 12 LV-Ns. I don't put it in low orbits, though, because the mission-specific subships can make the trip from high orbit to orbit or landing fairly easily, once the mothership has delivered them to the destination planetary system, and it would cost oceans of additional fuel to put the whole ship down low and lift it up again for the return trip.

Totally WAY beyond my framerate and skill. I'll try a massive, must be constructed in orbit thing tomorrow and post it (if I can even manage it).

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I'd also recommend the Fatman-Series. These look better than the original parts and are still well balanced. Generally speaking, you can reach all planets with very low thrust, you just have to accelerate longer, sometimes up to 30 minutes. It really depends on how much patience you have. It's another matter if you want to travel between moons, this gets tricky with weak engines.

A small trick: If you dock a nuclear driven lander to the back of your mothership, use it's engine to support the main drives. That will save you some heavy engines.

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As a final project before the big update breaks the saves, I decided to dismantle my Kerbin-orbital refueling station and use it to build an interplanetary mission to Laythe. I ended up using lots of the atomic engines on the fuel delivery ship, and the small 50-thrust engines on the lander itself (whcih was launched as a seperate ship. I sent two ships - one containing nothing but fuel, and the other containing the lander and boat for laythe:

Original space station before breaking it apart and adding other modules to it:

08A3AB64E4B3FCD2DD5DA6D0EB4207D05DE62F2F

The lander/boat ship to send:

A17C93A62EEE23DF92E1B98129E8DDB2577FA31C

The refueler ship to send:

BC3B39E0174BDB28807F002B7DEF7684DB0060F0

Them re-united around Jool:

8D03BA27D6AF3B4017A01AA1FABC91D9036F986F

And after the fuel was transferred, the middle bit was removed and the lander/returner ship was ready to use:

F2C0FB3AD397F160317DE5D30F7EBDE6FBA22E02

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Because of the Oberth effect, it is likely that there is some regime where multiple LVNs are actually more efficient since a shorter burn spends more time at lower altitudes (you can perikick to get around some of this, but for further planets you spend half the burn on an escape trajectory, and you can't perikick once you hit an escape traj). That said, it's a whole lot of math (numeric simulations are probably easier) to discover that regime precisely. Mostly for the sake of my finite patience, I try to have roughly 1 LVN per 50t of vessel.

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This is my interplanetary workhorse. Has a Sr. docking port on top, a standard size on the bottom and a Jr. size on the side. Carries 6 drops tanks for extra fuel and room for 2 orbital or lander probes. Also has load of lighting on all docking ports. This has carried my Eve return-lander to its destination with enough fuel to return and an entire modular base to Duna. Even with the 6 nukes, burns are looooooong with heavy payload.

photo.jpg

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As a final project before the big update breaks the saves, I decided to dismantle my Kerbin-orbital refueling station and use it to build an interplanetary mission to Laythe. I ended up using lots of the atomic engines on the fuel delivery ship, and the small 50-thrust engines on the lander itself (whcih was launched as a seperate ship. I sent two ships - one containing nothing but fuel, and the other containing the lander and boat for laythe:

*snip*

Although off topic, this gives me an idea. Do you think it is possible for the governments currently involved in the ISS program could reconfigure the station in orbit for a manned mission to Mars and beyond once we've found a way to make it totally self-sufficient?

Temeter, thanks for the suggestions. According to Kerbal Engineer, I've got 9K Dv using 4 large fat men. I'm still building it, but the fully completed model (in the VAB) not only has sufficient Dv, but looks somewhat pleasing.

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You can start small like I did. This is my first Laythe exploration ship. One man lander ( with smallest possible rover ) attached to command module, strapped on single orange tank tug, powered by one atomic engine.

screenshot3_zps4349743b.png

screenshot17_zps0737aaf5.png

It uses single atomic LVN 240 kN. If you dont want to use mods just use a number of stock LVNs. Its all about TWR ( Thrust to weight ratio ). Well, its all about available delta V, TWR is 2nd of importance. if it is bellow 0.3 your burns will take forever. If it is bellow 0.1 its hard to make a burn in one PE pass. Ideally the higher you can keep your TWR WHILE keeping desired delta V the better. On my 2nd trip I added two boosters powered by 4x 200kN chemical rockets. It was wasteful but bumped my TWR close to 1.0 for initial burn.

screenshot78_zps15e0505c.png

Stack shown with docked refueling shuttle

screenshot80_zpsea47e612.png

...during Kerbal escape burn ( took only 3 min )

screenshot85_zps2049896a.png

detaching used up boosters, finishing the burn with LVN with just 200 m/s to go.

All my screenshots contain MechJeb windows so its easy to find out what is my available delta V, thrust, TWR and mass of the ship.

Hi, Its my first post on the forums, I absolutely love the game!!!! I want to say thank you to developers, modders, and the community.

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909's may be more effecient with a smaller ammount of fuel, but the more fuel you carry the more the LVN's extra mass doesnt matter.

if you use mods, there are a couple of variants to the LVN you should look at. KSPX has a 2.5m version that has 150kn of thrust, Fatman has a 240kn version that has a higher mass but is also 840 ISP, this higher isp with higher mass is only benificial with more than a large grey tank, otherwise stock engines give better dV.

Novapunch has a 2.5m LVN but i personally prefer the Fatman version better

Yes if you use more than 360 liter of fuel the LV-N give more dV, if you use 90 or below the small orange radial engines are best. for 180 liter the 909 is best.

And yes the larger moded nerva engines is an must as it reduces part count a lot, also realistic as an nerva engine would have decent twr.

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