How to get a rocket with an LV-N “Nerv� to orbit (not as my first stage!)

[uofitorn]

Hey everyone.

I just started playing KSP a few weeks ago and I'm not very good yet. In fact, I'm pretty awful I'm just starting to explore beyond Kerbin & its moons but I'm finding my rockets just aren't up to snuff. I've ready plenty of posts on the forums about making sure I have the right dV by using MJ, etc, and indeed I do use that. But that's not my problem. I'm terrible at actually constructing the rockets.

Right now, I've been looking into using the LV-N Nerv as my second stage for interplanetary transfer. As I understand it, the LV-N is best used when provided with a lot of fuel so that its initially high cost in weight is offset compared to lighter but slightly less efficient engines. My problem, however, is that I can't seem to create a design that will actually put a rocket with LV-N(s) to orbit!

If I use a single LV-N below 2 or 3 LF tanks in the 2nd stage my rocket is too skinny in the middle and has some stability problems, but I can make it to space ok most times. However, I've been relying some on my 2nd stage to fully reach Kerbin escape velocity because I guess my first stage is not that great either (6 orange tanks mounted radially around another orange atop mainsails) and the LV-N simply isn't powerful enough to finish the job.

So my other idea was to use a Mk1 Stack Tri-Coupler just below my third stage, 3 LF tanks x 2 (or 3) down, followed by 3 LV-Ns and finally a TVR-300L Stack Tri-Adapter to couple the 3 LV-Ns to my first stage (and orange tank). But this rocket is even worse than the last because it wobbles at the start and falls apart shortly after liftoff. It's very unstable at the connection points between the tri-coupler/tri-adapter. It seems the tri-coupler/tri-adapter does not bind itself well to what it's attached to on the other side (not sure how to explain that better).

Can anyone link some pictures of rockets they've designed that have successfully used a LV-N in their second stage or provide some advice on how I can best use them structurally?

Thanks!

[Yuriznikov]

I usually make 3 stage rockets when going interplanetary,and only use the LV-N's for when i am close to full orbit.

My first stage would boost me trough the thickest part of the atmosphere, up into the higher atmosphere where you begin to pick up speed (usually around 1000 m/s is where it depletes). Then my second mid-stage comes in which usually has something along the lines of a skipper engine (depending on payload). I use a quite small tank for this engine as it only has to get me into a near-full orbit.

I cut it off at about 70km x 15km orbit so it would fall back to earth and not litter space. Only above 70km i then fire my LV-N and complete the orbit.

The LV-N's are best used above 70km obviously, as they are more efficient there. They dont really pack a punch but last a long time.

Also don't forget that they only require liquid fuel, and no oxidizer.

If you would want to build a 2 stage rocket i would suggest trying to make a first stage that will last you a long time to get your apoaps up above 70km only to use the second stage after that.

[nigelvn]

Hopefully you can find some usefull tips:

- try not to use the LV-Ns to get your transfer stage in orbit, instead make sure your lifter can get the transfer stage in orbit. Once in orbit you should use the LV-Ns to go interplanetary, but not earlier as the trust is simply not enough.

- Try to use asparagus staging and use extra boosters (SRBs or just LF + O) on the outside if it is not sufficient by itself.

- use enough struts, if a craft wobbles it is possibly due to a lack of struts.

- I do have this picture lying around:

As you can see it has 4 LV-Ns as 1 is not enough, as lifter I built asparagus staging, but as it was not sufficient I added LF + O boosters. The row closest to the Main rocket is in asparagus, the rows more outside feed the one more to the middle till the last one which puts everything in the beginning of the asparagus staging

You can also see the great amount of struts I used

[Sharpy]

As I understand it, the LV-N is best used when provided with a lot of fuel so that its initially high cost in weight is offset compared to lighter but slightly less efficient engines.

I think you're only seeing one side of the problem. The NERV is weak. Three tanks? And I guess you mean LF Fuselage Long, the huge ones? That's good for a retrograde solar orbit rescue mission, not plain interplanetary travel; a definite overkill. It's not *that* heavy. Seriously, make a craft consisting of a probe core, one small (1.25m) LF fuselage tank and one LV-N. You'll have something of order of 5000m/s of delta-V.

If you plan interplanetary travel, one LF Fuselage Long is a plenty. And if you want more - stick 3 side-to-side with the flat sides, then attach (through a decoupler) one with one Nerv on top, then one consisting of several thin LF fuselages with a Nerv on top of that. I think I got some 30,000 dV out of such a contraption.

Also: asteroid of minmus mining, launch empty(ish) tanks, refuel in orbit.

[Coga19000]

First of all, what kind of fuel are you using? Normal rocket tanks hold both fuel and Oxidiser - the combination needed for all rocket engines... Except for the Nerv, which only needs Liquid Fuel. Therefore, hauling Oxidiser on your interplanetary stage is basically empty weight.

Secondly, the tricoupler has a serious problem when used like that ; when you attach an upside down tricoupler to four fuel tanks the way you described, it will only attach to one node, not all four of them. The oscillations (wobbling) are caused by the other three tanks swaying free.

Thirdly, stick with 2.5m tanks. A 1.25 Nerv stage that can compare to a Terrier has to be absurdly long ; 2.5m can be much shorter before the Nerv is more efficient.

[Foxster]

You say you have MJ? Good, that will make things easy.

Here's one easy way to build a rocket...

Build your top stage that has the nuke(s) as you like it. The only advantage in more than one nuke for a transfer stage is how long the burns will take. The downside of more being more mass and so less dV available.

Now slap on a separator and whatever you think looks good for the next stage down. Check what MJ says about TWR for this stage. Aim for between 1.2 and 2.0. Adjust the design until you get that.

Slap on the next stage and repeat.

Have a look at the dV now for just these lifter stages. Does it add up to more than 4000? Then you are good to go.

Slap some fins on the bottom and you might need some small ones on the 2nd stage too.

Go fly your kite rocket!

One last tip: Try to keep your rocket skinny, don't make it too wide with lots of stuff bolted on the side and stick nosecones on the top of exposed horizontal tank tops.

[cantab]

All craft in KSP are built like trees - when you place a part you attach it to one, and only one, existing part. That's why you can't use the tricoupler to join three stacks back together. So if you have an upper stage that needs more than one engine you need one part centrally that you can build the lower stages down from - maybe an engine, maybe some other part. Then the other engines need to be attached however you like.

[Jouni]

If your payload is very tall, it's usually a good idea to attach it between two (or more) rocket stacks. This is how I launched my interplanetary transfer stage in my 1.0.x career mode game:

[Mastikator]

Hopefully you can find some usefull tips:

- try not to use the LV-Ns to get your transfer stage in orbit, instead make sure your lifter can get the transfer stage in orbit. Once in orbit you should use the LV-Ns to go interplanetary, but not earlier as the trust is simply not enough.

- Try to use asparagus staging and use extra boosters (SRBs or just LF + O) on the outside if it is not sufficient by itself.

- use enough struts, if a craft wobbles it is possibly due to a lack of struts.

- I do have this picture lying around:

http://i.imgur.com/ehWIsYL.jpg

As you can see it has 4 LV-Ns as 1 is not enough, as lifter I built asparagus staging, but as it was not sufficient I added LF + O boosters. The row closest to the Main rocket is in asparagus, the rows more outside feed the one more to the middle till the last one which puts everything in the beginning of the asparagus staging

You can also see the great amount of struts I used

I don't think this has enough boosters though, this thing can at most land and launch on the Mun 10 times before running out

[Scarecrow88]

Personally I gave up using LV-Ns some time ago, as the weak thrust made the burns take too long. The nearby planets - Eve, Duna and Jool - are all easily reached without having to resort to using the LV-N, and I find that executing the interplanetary burn is a lot easier with the shorter burns that other engines give you.

[Randazzo]

Just my two or three cents here...

First cent, I hate wobbly rockets. It's not a feature, it's the result of multiple rigid bodies being glued together to approximate a single rigid body. Kerbal Joint Reinforcement puts an end to all that. I also prefer to use a 2.5m nuclear engine (NovaPunch, Modular Rocket Systems, Atomic Age... and some others) to avoid the weird skinny profile. Otherwise, use struts to prevent disintegration and endure the wobble.

Second cent, assuming you're using three 2.5m fuel tanks on top of that Nerv, you're over-engineering a bit for your first ventures out of local Kerbin space. A round trip to Duna can be safely and easily done with ~4000 dV (Less if you're confident in your skills). Building big is tempting, but it really just complicates things if you don't need the extra girth.

Edited July 28, 2015 by Randazzo

[radonek]

Use nerva onto separate tug. Simple design is one LV-N, two fuel tanks paralel to it (to maintain CoM thru fuel depletion) and some decent torque (to manipulate cargo without reaction wheels of its own) plus necesities (cooling, power, docking, control…).

Typical interplanetary mission then work like this:

1) mission ship lift on its own power (expendable) and dock with tug on LKO

2) do transfer burn using mission ship expendable stage (doing transfer burn with nervas tiny thrust would take forever)

3) inclination changes, breaking burn or whatever maneuvring is then done by tug

4) (do something interresting)

5) return trip is powered by tug again, either refueled at destination or supllied from mission ship (empty tanks, lander etc. is ditched)

6) on arrival, you either use tug to maneuver whole thing to LKO and wait for descent module or simply aim your ship to descent trajectory, detach and move tug to LKO

7) tug is serviced and refueled for next mission at LKO fuel depot/station.

Of course, such a tug is also handy for moving cargo around kerbin orbits and hauling stuff to mun/minmus. You don't need to have big fuel capacity on tug itself - spare fuel can be part of mission ship. Key part is Nerva engine itself - its heavy and expensive, so you'd better reuse it. You can also attach anything thats worth reusing (reaction wheels, spare RCS fuel, RTG power…). And since you are only bringing tug up from the well once, and without any cargo, it should be much easier to desing a booster.

[Evanitis]

I don't think this has enough boosters though, this thing can at most land and launch on the Mun 10 times before running out

You are evil. You know that adding moar boosters is a completely viable startegy... in sandbox and science modes. Though makes me wonder how much is the payload of that 3500 tonnes...

Damn, I'm evil too.

[Pecan]

This example probe/launcher has almost 7km/s in LKO and can visit any planet or moon in the system:

1.25m LV-N probe payload

• structural - payload bay (Z-200 battery, 2 x RTGs and deployable solar panels), RGU
  
• fuel - 3 x LF fuselage
  
• engine - LV-N
  

2.5m launch vehicle

• structural - stack decoupler, rocomax converter (2 x radial decouplers on main fuel tank)
  
• fuel - orange tube, 2 x boosters of 2 x TL-800 tanks each
  
• engines - Skipper, 2 x boosters of T-30s
  

It is all an easy combination to build and fly but I set an action group to open the payload bay and solar panels.

[ajburges]

A single LV-N craft?

I have a Mk2 space plane designed around delivering a tug with 800 units fuel. If I get a mission and no tugs are available in LKO, it's time to launch a new tug.

Space plane has a 4 turbo, 2 Swivel/spike power plant.

Quad LV-N?

Mine weighs about the same per meter length as an orange tank. Queue the Mk3 lifters.