RSS Build Guidelines

[Navy2k]

Hi,

I struggle a bit with RSS and i think its mainly because i carry to much dead weight.

MY specifications today are as following: I have a package of a Command and a Service Module with an attached Lander and a 3rd Stage with 3900 delta-v for the whole package and a weight of around 200.000kg (wet inclusive the ressources for tac life support). This should bring my 3 brave Kerbals to the Moon and back.

My Problem is that i can't get that thing in orbit. Every lifter i build gets only heavier at around 8.000 delta-v if i want to boost it to 10.000 delta-v. (Adding and extra 20% fuel to the first stage brought me only from ~8300 to ~8400 delta-v and adding to the 2nd stage brings down my delta-v on the first of course and negates my efforts)

What TWR Start and endpoints are optimal for an Vehicle like this? I can't for the heck of it figure it out.

Also, could it be that there is a lack of engines around 3.000-6.000 thrust? RftS has many low thrust engines and a few high thrust ones but not many medium ones.

So, lets start a little brainstorming, thanks!

Greetings

Ben

[Taki117]

You could install Novapunch or KW rocketry (if you haven't already) NP has 5m parts that would work well for a heavy lifter stage. You could also add SRBs to the sides of your main lifter stage. (The one that sits on the pad)

[Navy2k]

Ok, im not that novice

I have installed both + b9 (only non Plane parts) + aies + the Russian engines pack + gemini/mercury/apollo pack (don't want to use the Saturn provided and i think it wouldnt work because my Lunar Injection Stage + CSM + LEM are about 25% heavier than stock Apollo) and i build only with procedural tanks. So size isn't the problem but it isn't the solution too

My Problem is i have for exaple an TWR of 1.8 + 3.4 relative to Kerbin for my fist stage. Now i grow my tank from 20m length to 25m and i have a TWR of 1.3 - 3.1 but my delta-v just went up from 4000 to 4100.

Greetings

Ben

Edited June 13, 2014 by Navy2k
typo

[Jimbimbibble]

You want to shoot for an initial TWR of about 1.2-1.5 and start your turn when you are between 50-100m/s vertical speed. You should be at about 45 degrees when you hit 1000m/s. Second stage TWR is typically less than 1, maybe around 0.6. You won't really coast to apoapsis if you have your TWR and turn profile correct because you burn at 100% all the way up. It takes about 9km/s to make orbit in rss. Orbital velocity is about 7.7km/s for a low orbit. If you need moar thrust, you can place engines on the bottom of your rocket in symmetry to create your own engine cluster.

[Navy2k]

Wouldn't a 0,6 TWR in the second stage result in only 0,3 vertical at 45°? But on the other hand i don't need the vertical speed in orbit =)

[Jimbimbibble]

Once you get high enough and your apoapsis is several minutes away, you don't need a whole lot of TWR to keep going. Also, it's ok if you circularize a little bit after apoapsis. The space shuttle actually did that and so did other real spacecraft.

[Hodo]

This is my light lifter for RSS, it is based on the Ares I rocket, it is a SRB first stage that burns for 120 seconds then a second stage with a .7:1 TWR.

First stage has a starting TWR of 1.3-1.4:1 but ends at 6:1.

[Heagar]

Are you building a Apollo alike spacecraft or a - for kerbals normal - a "Asparagus"-launcher?

In any case:

Not only the TWR is the criteria you should care about, but also the burntime.

• If you build Apollo-style your first stage should include the strongest engines. But for the second (you are already in the gravity turn) and third stage the weaker engines are preferable, since they are at liftoff dead weight only.
  
• If you use an asparagus-launcher (for the mun a two-stage rocket is enough [Asparagus plus TMI-stage&payload]) you can build it in a way, that the second pair of the outer tanks are without engines. Witch means, the fuel-consumption in a given period of time is lower.
  
• If your TWR is too low: Use additional solid boosters for liftoff or build an second Asparagus-layer with shorter tanks around the first one witch feed the engines, witch are the first to stage in the first layer.
  
• 
  

In either way: You have to build a gigantic rocket since you want to get 200 t into orbit. Presumly for a long term mission, i suppose. Otherwise the crafts mass (CM, LM, TMI-stage) would exeed only 60-70 t max (without life-support).

But there are other options too:

• If the hole thing can't be liftet, you can use orbital construction for your advantage (putting together the modules like a space station, the manned section at last). Witch can be achieved with launchers you have build already.
  
• If you have installed the KAS-mod (there are solutions for it, but in stock it is difficult): You can deploy most of the life-support with a seperate launch on the mun where it's waiting for your kerbalnouts - witch are coming with the second launch and are landing aside the life-support module.
  
• 
  

BTW: In case you need a engine with 3000 to 6000 KN you can set up a cluster of weaker engines to resolve that problem (Mouting four of the small girders at the bottom of the tank and then mounting the engines to/on them).