How Sovek Launches Rockets In A Scaled Up Solar Systems and RF

[Sovek]

Earlier this year I took the plunge and started playing around with RO, however crashing every 15 minutes wasnt fun and wasnt willing (at the time) to try and get 64 bit working, so I decided to play around with KScale 2 in 1.04. This was kind of fun. However in 1.05 I did move to 64 bit and decided to play with an even bigger system, 3x

The challenges in a 3x system are easier than in RO or RSS, but its far greater than in stock. In stock you can get to orbit in about 2-3 minutes, and you will often just coast to your AP before another burn. Getting into orbit costs 3.5km/s of delta V, and getting to the moon is another 800m/s. In 3x, even 4.4km/s of dV isn't enough dV to get into orbit. No, more like 5.5km/s and a further 1.6km/s just to get a flyby of the Mun. Yeah, things scale up pretty quickly.

In a 3x and up system you'll quickly find your going to run into the Tyranny of Rockets. The heavier your payload, the more fuel you need, and you need more fuel to get that fuel up, ect ect. Things get even trickier with Real Fuels and other difficulty mods. Add in a "no Reaction Wheels except for certain satellites" and this makes things even harder because you need more fuel just in order to point your ship in the right direction (although this can be negated in several ways)

So lets bring out my first rocket capable of reaching orbit in my latest Career Mode game, the RB-3 Booster. It can lift 1.9t into orbit and weighs 18.9t at launch.

The RB-3 Booster is powered by 4 88-M6 Spinnaker engines (RLA Stock-A-Like look into SXT for early engines that provide the same thrust at lower tech levels with the Vangaurd engines) burning RP-1/LOX and have a thrust of 53 Kn at the pad with an ISP of 262s. You'll also note the lack of fins. Fins add weight, and therefor less dV. Clustering engines works just as well as any fin but still allows for steering at high speed, More so in the trans-sonic and super-sonic speeds. I Also tend to keep my TWR at launch to somewhere around 1.15-1.3 and pack fuel into the stages. This can allow me have SRB's on launch burning for 1:30-2m while I burn off enough fuel so that when the SRB's burnout, the rocket isn't falling back to Kerbin.

Engines are brought up to thrust and the clamps are released, it takes 4 seconds to clear the tower.

At T+20s the roll should be complete and you should probably start pitching by about 5 degrees.

At T+1:13 the rocket breaks the sound barrier and is now Supersonic, and is past MaxQ

Its also burned about half its fuel, just for the first 10km. Welcome to scaled launches. IIRC the Saturn V was much the same way.

 

Because a majority of the weight is in the first stage, The #1 & #4 engines cut out at T+ 2m, this drops the T:WR from 3+ to a more manageable 1.5.

The reason for this is to keep the time to AP from raising too fast. This leads to a "coasting and less efficient launch. Also note that in scaled system you'll find you'll have to play with your launch profile depending on how much mass the first stage is. In this case the majority of the mass is in the first stage so its acceleration can get as high as 4 G's with all four engines running. This is also uncomfortable for the passengers. Shouldn't do that.

Ok... so its a gratuitous shot of Stock Visual Enhancements... sue me. (what, I need info for this.... fiiine) At T+3m the stage depletes the fuel, By this time I like to have about 1:30 till AP. This allows for a lower thrust engine to be selected and I can adjust my time to AP accordingly. This can allow for an initial orbit eccentricity of 0.001.

 

By the T+4:15 mark, I'm usually burning at the horizon to bring my time to AP down even though I have a 1.4 T:WR. It would probably be more efficient to use a lower thrust engine or reduce the TWR. This is the 105-7P (Vens Stock Revamp) that puts out a whopping 45kn of thrust with a vacuum ISP of 303s.

 

Nearing the end of the burn, the time to AP is nearly gone, this is a good thing.

 

At T+6:25 the hypergolic engine is ignited for the final push into orbit.

At this point, T:WR is pretty pointless so find your most efficient engine (that you are willing to use) and go with that. You shouldn't need a very high TWR to get anywhere.

Edited January 23, 2016 by Sovek

[Norcalplanner]

Glad to see another 3X aficionado out there.  It seems to be the right mix of challenge and fun.  I'm still using mostly stock parts, with a few stockalike mods (MRS, SpaceY) that give a few more options in the size department.  Definitely makes reentry a bit harder - nearly everything ends up with a heat shield.