SSTO Self Launching Mothership. Asking for some opinions.(wip)

[Jakalth]

I now have a fully functioning self launching mothership(freighter). It's name is the Jak-MS03 Clarksen. It is a somewhat finicky monster to get into orbit, but once there, has quite the punch for hauling your cargo to the Mun, Minmus, and planets beyond, Way beyond.

Jak-MS03 Clarksen

The MS03 Clarksen is a product of a need for an orbital transfer freighter, and a bit of simply wanting to make something fairly big. The craft can reach orbit using the first stage alone, but in the process, nearly drains the craft dry of fuel. Once in Orbit, it requires refueling, primarily with liquid fuel for the Nervs, but a little Oxidizer does help if you need to top off the tanks on it's cargo later on. In orbit, it's a little simpler looking but is quite functional.

The stats for the MS03 Clarksen:

Mass: 796.6tons at launch, around 300tons once in orbit.

Parts: 329 parts at launch.

Engines: 12 Nervs, 2 Mammoths, 1 Mainsail

Fuel: 56,870 units of LF, 64,570 units of OX, 1,130 units of monoprop

Delta-V: 3,850 at launch using the Mammoths and Mainsail. about 1,300 left in orbit from the Nervs once the mammoths run dry.

TWR: 1.14 at launch that climbs quickly using the mammoths and mainsail. 0.88 when bone dry on just the Nervs, in orbit.

Docking ports: 2 top mounted inline docking ports, 2 bottom mounted inline docking ports, 2 side mounted shielded docking ports, 1 nose mounted docking port Sr.

Flight data:

On launch, just go full power. It's TWR is a little low for the first thousand meters or so but that changes quickly as it climbs. Keep throttling down as it gains altitude so that it's acceleration is reduced but it also burns less fuel. At 9-11Km, start your gravity turn. Normally that would be done sooner, but its got a bit of a tendency to dive out of control at low altitudes. Keep the gravity turn shallow, aka; keep it more vertical, until it has passed the 20Km mark. From this point on you can start to deepen the gravity turn and nose her down more. You can manually kill the Mainsail at or above 20Km if you wish to save every drop of fuel possible, it's less efficient then the mammoths and won't be needed from this point on except for emergency's. For ease of flight, aim for about a 72-75Km orbit and really watch your fuel burn.

Once in space, use the most efficient orbital insertion you can make to get it into a semi circular orbit. Once the mammoths run out of fuel, stage them and jetteson the external tanks. The Nerv engines can now be used to fine tune your orbit making it more usable for refueling. The Clarksen will need a refueler sent up to it once it reaches a clean orbit. But first, you'll want to jettison the front nose cone so you can make use of the big docking port Sr on its nose.

Once refueled, it should have somewhere between 7000 and 8800 Delta-V for flying its self around the Kerbal system. The actually Delta-V you'll have once fully loaded depends entirely on the weight of the cargo you attach to it. There should be few places in the Kerbal system this freighter can't reach.

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I've got an SSTO mothership currently in development and I've got some questions to figure out for it. Right now, by definition, it is a Single Stage To Orbit rocket. It is self launching, can reach orbit on a single stage, and still has enough delta-V left to change orbits and/or allow for sloppy flying on this first stage alone. It might still need a little more electricity(large solar panels), and some adjustments to it's RCS and reaction wheels. But the main questions are this:

1: Should I make it a full SSTO by removing the decoupler separating the outer engines and fuel tanks from the body of the ssto?

benefits: More fuel and delta-V for the Nerv's(after refueling), looks good, more room for solar panels and reaction wheels.

drawbacks: heavier, much lower TWR from the Nerv rockets which means much longer burn times, slower maneuvering.

2: How much power generation does it really need to keep its self running in space? Is 20 2x3 solar panels enough?(32.0 electric/sec @ optimum alignment to the sun) Would it be safer to add 2-4 of the Large solar panels?(24.0 electric/sec each)

3: Does it really need RCS for maneuvering in orbit and deep space where it will be used solely to transfer freight? If so, occasional use requiring low mono propellant, or frequent use requiring much more mono propellant?

Your honest opinions and suggestions would be appreciated.

Mass: 706 tons

Part count: 303 parts

Delta-V of the Mammoth engines at launch: 4,047m/s

TWR, at launch: 1.16

Engines: 2 Mammoths, 12 Nervs

Number of docking ports: 7(1 large, 6 normal)

Internal storage?: no...

Which side is up?: ummm.... that side-->

Nose cone decouples freeing up the docking port Sr.

Fuel from the central body of the mothership is routed to the mammoth engines/tanks for lift off and orbital achievement.

Orbit is achieved solely by the 2 Mammoth rockets.

Nervs are used for orbital changes and long distance freight transfers after mothership has been refueled with liquid fuel only.

Without the Mammoths and fuel tanks the Nervs have a TWR of 0.32 and 7100 delta-v.

With the Mammoths and fuel tanks the Nervs have a TWR of 0.17 and 8400 delta-v.

Edited May 22, 2015 by Jakalth

[Captain Sierra]

Decouple tanks in space. 1300m/s from that much tankage means you're nearing diminishing returns with it.

For control: replace RCS thrustes with the Vernors. They burn LFO (so keep a bit of Ox on the main ship for maneuvering) and have a LOT more punch. They're advantageous for turning larger craft.

[Jakalth]

Origional post updated with the changes to the craft and a craft file for download if anyone wants to give it a try as well. I added a bit more fuel to the side tanks, and added in a central Mainsail engine for added TWR at launch and for emergency use in space. It has a bit more solar panel use, just in case, and I fiddled with the aerodynamics of it during launch to help stabilize it.

@Captain Sierra;

Though your suggestion to use the Vernors is a very good suggestion, the fact that the Clarksen will not be hauling much if any oxidizer is a limiting factor. I've also decided to simply rely on the reaction wheels for steering the craft. It's rather sluggish to turn, but other then orbital corrections, it won't need to make many course changes. The RCS it already has will suffice for now. If use of the craft shows it still needs more, I'll be adding in the Vernors by your suggestion.

I kept with the Jettisoned fuel tanks instead of the single solid craft. I believe you are correct in that it has reached diminishing returns. I tested it with more tanks and the Delta-V for the Nervs started to decrease instead of increase. Not to mention the mass of the side tanks severely limited the TWR of the Nervs and the freighters total cargo capacity.