LV-909 or LV-N for Interplanetary Travels?

[JiWint]

I'm stuck orbiting Dres with half of lander fuel,because the main fuel ran off when I was making an orbit around Dres.

lander=6 FL-400 tanks with lv-909s,4 heavy landing legs,one-man lander command pod,2 JR docking ports with a small rover.

Lander pictures http://i.imgur.com/RqVPiW7.jpg http://i.imgur.com/JkUUufn.jpg

I have to send refueling craft now - With as much as possible fuel in it when I reach Dres.

And I need to select an engine for this.LV-909 or LV-N? Which would you choose? And why?

Refueling craft:

smallest octo probe + 3 smallest solar panels + Control reactor (lighter one) + docking port + orange tank + 4 FL-T800 + [insert Engine Name Here] ?

Edited August 30, 2013 by JiWint
^^

[UbioZur]

For the gimbal (or vectoring engines), look at that video at about 9.24. I can't explain it better.

For the lander, a screen would be easier than the description.

For interplanetary transfer, usually LV-N are better as they have a better ISP (so less fuel consumption).

[KSK]

Yes - LV-Ns are usually better for interplanetary transfer, although it depends what you're flying. For a fuel tanker though - yeah LV-N.

909s work pretty well for cis-Munar and cis-Minmus travel though.

[Lazro]

*they

For interplanetary travels, it all depends on whether you want speed or efficiency. The LV-N is more efficient in space, but is very inefficient in atmosphere, is heavy, and also has low thrust. The LV-909 (or Rockomax Poodle) is two times less efficient than the LV-N, but they have more thrust. In this case, you will need a large amount of fuel to get to Dres, meaning that, if you have time to spare, you should use the LV-N.

For your next question, a "vectoring engine" consists of a rocket engine on a "gimbal:" basically a set of hinges that allows the engine to rotate around to some extent. This means that your engine thrust can be directed to one side or another, allowing you to steer.

[JiWint]

I can't watch videos for now,because I'm using wireless internet (modem) with slooow gprs connection :/.

I want to transport an orange tank with 4 largest FL tanks attached to it (with decouplers,for little asparagus).

So I'll select the LV-N one. Lander images comming in a few minutes.

[iStickyDuck]

Firstly if you want to send a refueling craft or any craft to another planet you should use Nuclear Engines because they are the most efficient and will leave you with the maximum amount of fuel.

Secondly, Gimbal and Vectoring Engines are... well... they are engines with the ability to direct thrust which allows for rotating in space without reaction control systems (RCS) but only works when throttled up... I find it hard to explain but I've done my best

A Gif demonstrating Gimbal/Thrust Vectoring:

http://upload.wikimedia.org/wikipedia/commons/thumb/6/6e/Gimbaled_thrust_animation.gif/220px-Gimbaled_thrust_animation.gif

(Don't know the code to embed it...)

[JiWint]

Thanks Lazro and IStickyDukck, I was thinking why are engines end moving sometimes ^^.But I notice that when there's a gimbal,rocket controls a way much worse when not thrusting.

[ArmchairGravy]

I'll answer the easy one: vectoring engines use gimbals to slightly adjust the angle of the engine nozzle and thus give you a way to steer. When you lock the gimbals on a vectoring engine, it will just thrust straight.

As for these and those? They are really more indicative of spatial relationships between objects or people. "Give these vectoring engines to those engineers."

The engine? Look at the ISP in vacuum for both. As long as you're using it in vacuum, the LV-N is you're better choice.

[Hannu]

If you try to use one LV-N with a full orange tank, acceleration will be very low. It is possible, but transfer orbit burn will be little complicated (if burn time is about half round around Kerbin). I recommend to put 4 FL-800 tanks around the big orange and use 4 LV-Ns. You should not need decouplers or other fancy stuff. Put yellow fuel lines from orange to small tanks or transfer fuel manually when they become empty.

[Zeroignite]

One thing to note though is that because of the LV-N's high mass, for ships smaller than around 9 tons you can actually get better delta-v out of the 24-77 radial engine, or the 24-77s.

[JiWint]

So which,LV-N,LV-909 or 24-77? O_o

[Lazro]

In this case, with the ultra-heavy payload, definitely the LV-N.

[Tiron]

One thing to note though is that because of the LV-N's high mass, for ships smaller than around 9 tons you can actually get better delta-v out of the 24-77 radial engine, or the 24-77s.

Hmm. I should investigate this for my mapping probe(The one I mapped Kerbin, the Mun, Minmus, Duna, Ike, and Dres with, and am probably going to remap Kerbin again with.) I can see why this would be the case though: The LV-N weighs 2.5 tons, the inline 24-77 is 0.1 tons. My upper stage only weighs 5.21 tons, so literally half the weight of the thing is the bloody engine. And that's such a massive weight reduction, I can see where it COULD have more Delta-V after. Though the prospect of using a tiny engine on a size 1 probe...heh.

Edit: Oh dur, it's only 2/3rds [Half (specifically 53%)] full...because I used it to get from Duna to Dres...But still. That's a huge fraction of the weight for the engine.

Edited August 30, 2013 by Tiron

[Anton P. Nym]

If you're just sending a lightweight probe, the lightweight LV-909 or the Rockomax 24-77 can make sense as a planetary transfer stage. (Weight savings making up for the lower fuel efficiency.)

For a big tanker (or any other interplanetary craft with lots of mass) LV-N will always be the way to go; the fuel efficiency is so much greater than any other engine in the game.

-- Steve

[halbert5150]

Sometime when you get to the point you want to start adding mods to the game you might be interested in the novapunch part add-on. it will double the number of engines in the game for you and gives some more options. Even though the advice you have gotten in this thread is the right advice it just sounds to me like you would be interested in novapunch.

As far as the lv-n I dont now if anyone else suggested this but I lie to radial mount three or four lv-n at the bottom. Its still very efficient but it gives you more thrust and therefore shorter burn times. Im not the best pilot in the world and so the shorter burn times seam to be easier to get right. Especially on those planetary transfers.

Edited August 30, 2013 by halbert5150

[MrPopcup]

If you have a small probe 3 tons or less then put 909 engine, now to be honest I only put 909 engine for only the Kerbin system, and for the rest of planets I usually put LV-N engine no matter what.

[RadHazard]

I made a chart comparing fuel efficiency of the most commonly used engines, and I found that the total weight of the craft isn't important when it comes to fuel efficiency, but rather the TWR. If your TWR is <1, LVNs are the way to go, but beyond that the other engines win out. The chart was made with the basic assumption that the craft consists of nothing but one engine and as much fuel as it could carry while still achieving the given TWR.

While that is obviously a simplification, using MechJeb's dV readout, I was able to confirm that replacing the LV-Ns with LV-909s on a 4-engine craft with a TWR close to one did not change the dV significantly, which matches what my chart predicts. This is valid because A) both engines have similar thrust values, and the payload/fuel ratio did not change significantly. The only change was the ISP and the weight of the engines, as well as a small change in thrust (60 for the LV-N vs 50 for the LV-909).

For small craft in which even a single LV-N provides >1 TWR, I recommend an LV-909 or one of the radial engines (not graphed). If TWR is important, I recommend using LV-T30s or Mainsails. Otherwise, for the most extreme range, use as few LV-Ns as you can get away with. 1 would obviously be best, but sometimes impatience wins out over fuel efficiency.

If anyone is interested, I also wrote a simple java program that calculates how many engines and how much fuel is necessary to propel a given payload at a given TWR, while still having at least as much dV as you specify, assuming the combination of numbers you gave is achievable, of course.

Edited August 30, 2013 by RadHazard
Edited for clarity

[Dispatcher]

It depends on the mission. I prefer the atomic in general for orbit to orbit transfers due to its iSP. However, the 909 is more fuel efficient in low orbit. From testing, I find that the 909 ranks well as an engine which can move payload while being kind to the fuel supply. And most of that payload is not in engine mass. Nice chart, RadHazard!

[tavert]

I made a chart comparing fuel efficiency of the most commonly used engines, and I found that the total weight of the craft isn't important when it comes to fuel efficiency, but rather the TWR. If your TWR is <1, LVNs are the way to go, but beyond that the other engines win out. The chart was made with the basic assumption that the craft consists of nothing but one engine and as much fuel as it could carry while still achieving the given TWR.

While that is obviously a simplification, using MechJeb's dV readout, I was able to confirm that replacing the LV-Ns with LV-909s on a 4-engine craft with a TWR close to one did not change the dV significantly, which matches what my chart predicts. This is valid because A) both engines have similar thrust values, and the payload/fuel ratio did not change significantly. The only change was the ISP and the weight of the engines, as well as a small change in thrust (60 for the LV-N vs 50 for the LV-909).

<snip image>

For small craft in which even a single LV-N provides >1 TWR, I recommend an LV-909 or one of the radial engines (not graphed). If TWR is important, I recommend using LV-T30s or Mainsails. Otherwise, for the most extreme range, use as few LV-Ns as you can get away with. 1 would obviously be best, but sometimes impatience wins out over fuel efficiency.

If anyone is interested, I also wrote a simple java program that calculates how many engines and how much fuel is necessary to propel a given payload at a given TWR, while still having at least as much dV as you specify, assuming the combination of numbers you gave is achievable, of course.

I've already calculated exactly what you describe: http://forum.kerbalspaceprogram.com/showthread.php/45155-Mass-optimal-engine-type-vs-delta-V-payload-and-min-TWR

This only shows you which engine type to use to obtain minimum total craft mass for a combination of parameters, but you can work out how much fuel and how many engines are needed at each point iteratively. If you go to the last page, there's also a mixed-integer optimization method for evaluating whether you can save even more mass using a combination of different engine types.

Edited August 30, 2013 by tavert

[magnemoe]

So which,LV-N,LV-909 or 24-77? O_o

I have done some testing of this, and it depend on how much fuel and payload you have.

With light 200 kg payload like an probe core, solar panels, some science and an kethane mapper, the LV-N is actually not an good candidate.

With 90 liter fuel the 909 gives you 3000m/s while the LV-N only 2575 m/s, you can not send this to Moho or Eeloo but pretty much any other places.

With 180 liter fuel they come out even at 4300 m/s and any more fuel and the LV-N wins.

With an real payload of a ton or more the LV-N wins all the time. 1.3 ton payload, 90 liter fuel, LV-N 1880 m/s 909 1500 m/s.

However we have overlooked the new 48-S7 who is the inline 24-77, its the new wonder engine for light loads, not quite as good ISP as 909, 20 kN versus 50 but only 0.1 ton against 0.5

1715 on the 1.3 ton challenge, almost as much as the LV-N while the total weight is 2.3 against 4.69 for the LN-N stage, twr is down from 1.5 to 0.8.

This makes the 48-S7 better than the 909 in all relevant settings except TWR however you can easy use multiple 48-S7 on struts.

The 24-77 has the same weight and trust as the 48-S7 but far worse TWR, its only benefit is that its radial so it might be good for some skycrane settings, you can also use 48-S7 on struts however this is more work and increase part and not really worth the bother for landing rovers on light body worlds or the final braking after aerobrake.

This leaves one of the small engines, the ant, then to use it?

Tested an ockto2 core with an extra one as an 40 kg payload.

The ant gives more dV with 30 liter fuel or less, the 48-S7 win with more fuel. With an higher payload like 140 kg the 48-S7 win earlier all the way down to 20 liter fuel.

If you have to use two or more radial ants because of twr restrictions then landing the 48-S7 wins even with only an oscar tank.

---

Conclusion, for small engines use the 48-S7 unless you just want to put an probe into correct orbit after dropping from carrier, her the ant is nice.

For heavier payloads than probes going longer than Minmus, use the LV-N. The LV-N is also nice for sending massive payloads like bases to Mun if you don't mind the long burn time.

[RadHazard]

That's a very thorough series of graphs. Certainly more impressive than my simple java program. Looks like I'll have to bookmark it. Great job!

[JiWint]

Looks like I'll select the LV-N one ^^ thank you everyone,and a nice graph

[halbert5150]

That's a very thorough series of graphs. Certainly more impressive than my simple java program. Looks like I'll have to bookmark it. Great job!

I would still be much interested in your program RadHazard.

[Tank Buddy]

The LV-N has higher thrust and Isp, so the only advantage of the LV-909 is that it is compact and lighter.

[RadHazard]

Here's a basic copy of my program. It takes input from the console, so you'll need to run it through the command prompt using the "java -jar <filename>" command.

it takes three inputs: The T/W ratio you want, the minimum vacuum dV that you want, and the mass of your payload in tons. It will output a table of the more popular engines (I'll eventually add all the engines) along with stats on each.

The important numbers are the last ones on the table, Engines Required and Fuel Mass. Engines Required is the number of engines your ship must have, and Fuel Mass is the amount of fuel you need to have, in tons (including the tank, assumes the 8/9 fuel ratio of the large tanks). If either of these numbers is negative, that means that engine physically cannot provide that T/W ratio and dV, so you'll want to reduce one parameter or the other. The best engine for the job is either the one with the least Engines Required (if you're shooting for low part count) or the least Fuel Mass (If you're shooting for smallest mass).

My program works in three steps:

1) Figure out how much mass each engine can lift while still maintaining the given T/W ratio. This depends only on engine thrust, engine mass, and target T/W.

2) Use the inverted rocket equation to figure out how much mass can be payload while still meeting the dV requirement (that is, the payload fraction). This changes depending on the above max load and the given dV

3) Divide the payload mass by the payload mass/engine to figure out how many engines and how much fuel is required to lift your given payload. This uses the previously calculated payload fraction and the given payload mass.

This approach is analytic, so it should be perfectly correct (barring any rounding errors). If you build your ship with the given instructions, it should meet or exceed both the given T/W and dV you provided. Also note that this program is meant for designing interplanetary stages only. The difference in engine ISP in-atmosphere means that your ship will have less dV than what my program predicts, so if you try to design a launcher with it you'll need to pack extra dV.

I'll probably throw together a thread for it tomorrow, along with a version with a proper GUI.