Transfer engine discussion

[Rolanvorxariat]

Rune, is that Von Braun's Mars Mission concept?

[Norcalplanner]

It all depends on the mass of the rocket, the delta v requirements, and what you're optimizing for. Optimal delta v will push you towards LV-Ns. Optimizing for cost will push you towards Mainsail and Skippers. Optimizing for part count will push you towards the big Kerbodyne engines.

[Laie]

You also took a page out of Von Braun's book?

I came up with it myself, but I wasn't surprised when I found I wasn't the first to have the idea. I call them tug and tag, because the latter only tags along for a while.

Initially, it was a high-TWR kicker stage to get me underway really quickly; but a) I was sorry for the fuel and often only used them as a tank the high thrust was problematic. See how the exhaust is by no means parallel? That's not perspective, that's the KR-2Ls bending the vessel. So over a few iterations it became ever more nukes and fewer big engines. And much smaller, too.

(click for gallery)

Man, was I ever proud of that design. These days, I think it's way over the top.

Edited December 12, 2014 by Laie

[FleshJeb]

Poodle on an orange tank, with a ring of 4-6 nukes, and asparagus-staged T-800 tanks. Decent average ISP (4=532, 6=572).

Or a nuke with a ring of 6 ions. (ISP=925).

[SkyRender]

Personally I favor the Skipper for speedy transfers. The Mainsail is a delightful engine in its own right, but definitely overpowered for the sort of payloads I tend to push around. You really need a hefty mass to justify the Mainsail over the Skipper, something in the neighborhood of 4 orange tanks' worth of mass.

[Archgeek]

I found myself pushing my giant asparagus-storm Eve-return lander along with a ring of 6 nukes under FL-800 tanks, with fuel lines drawing out of the central Kerbodyne tank fueling a KR-2L. Intent was to use the KR-2L as a kicker motor to add needed TWR for Kerbin escape, then turn it off for the rest of mission. It's not often that one pipes fuel out of central stack, but it worked out surprisingly well, and left the transfer vessel amusingly reusable. The lander actually had an ion-based kerbin return system, so the main transfer stage is still floating out there in case I ever want to bring Gilly home or something. XD

[Xavven]

Personally I favor the Skipper for speedy transfers. The Mainsail is a delightful engine in its own right, but definitely overpowered for the sort of payloads I tend to push around. You really need a hefty mass to justify the Mainsail over the Skipper, something in the neighborhood of 4 orange tanks' worth of mass.

I agree about the Skippers. Usually I use those before my LV-N clusters stage if I need a lot of delta-v, or if I'm going for a no-nukes mission for whatever reason, like early-tech to Moho in career mode.

Oh the topic of Moho visits, my last one was with a 3-man crew + hitchhiker + 2-man lander, and that package required a KR-2L transfer stage. Controlling that thing SUCKED because it was before the Vernor engine was added to the game and I was shy about spamming RCS ports.

[Rune]

Rune's post is the project rho or whatever, a proposed nuclear vessel with radiation shielding for the payload.

Not really, though that is a heck of a good page for nuclear rocket geeks. Mine is a replica of an actual real life proposal by the father of the Saturn V himself!

Yup I know what it is. No cookie for me.

You are going to have to grab one from your own jar... I gave you too little time ago!

Rune, is that Von Braun's Mars Mission concept?

Yes! Well spotted! Von Braun's Mars '69 plan. Sporting three nuclear tugs, and lots of presents for the red planet under those shrouds. Of course I'm building two ships, and of course they have a standard crew of six but can fit all twelve in an emergency. And I plan to follow the mission model, even though those nuclear tugs are SO overkill for the stock system... The rest is more adequately sized (up to and including the Saturns V-25(U) to lift all the pieces up, modified form my Saturn V replica).

Rune. I'm going to have something like ten times the required delta-v for transfers. But it looks so cool!

[Bigbootie]

Great information here everyone! That's what I love about this community, pose a question and the friendly feedback and different points of view come rolling in. I probably will build something ridiculous with a high, high TWR using the KR-2L's (or more likely overbuild and have a low TWR with KR-2L's) in some shape or fashion. I'll post some pics but it will be awhile as I am floating around in the South China Sea right now and it will be weeks before I get back to the space center.

[aleis]

For simpler missions lately I've started using transfer fuel tanks. I build my lander wide with engine sticking out beyond the stage below it and have a fuel tank on a decoupler with fuel lines running up to the lander.

Edited December 12, 2014 by aleis

[Pixel of Life]

I'm surprised nobody posted this:

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I, however, usually use either the LV-N or the LV-909 for light craft, and the Skipper for heavier ones.

Edited December 13, 2014 by CaptainKorhonen

[Remkeau]

Nukes for effeciency, KR-2L for thrust. Like this:

(I actually didn't want to waste delta-v, but got bored of the long burns )

[Rune]

The new prograde autopilot is going to mean low TWR designs are going to actually be bearable to burn! As in, put an alarm and go do something else for 15 minutes, or admire the view. Me likes.

Rune. I was doing that anyway, but now I can do it without ALT+Tabbing all the time.

[RocketPilot573]

The new prograde autopilot is going to mean low TWR designs are going to actually be bearable to burn! As in, put an alarm and go do something else for 15 minutes, or admire the view. Me likes.

Rune. I was doing that anyway, but now I can do it without ALT+Tabbing all the time.

Very true, I don't believe I have ever even done a 20 minute burn without mechjeb pointing at the maneuver node.

[John FX]

I'm surprised nobody posted this:

http://imgur.com/a/iNqmQ

I, however, usually use either the LV-N or the LV-909 for light craft, and the Skipper for heavier ones.

One reason would be because it is out of date, the stats for the engines have changed since it was made. I visited the TWR thread, downloaded the code and I have updated it for the current set of engines (as taken from the WIKI anyway) and the graphs look a bit different now. I will be posting them in the TWR thread.

EDIT 2:

I got rid of some images from my IMGUR account but here is a gallery of all the charts from TWR=0 to TWR=3 for a single engine in vacuum. So to pick the engine for your transfer stage, first pick your TWR and look at that chart then find your payload mass and look across until you are at the amount of Dv you need. Bingo, that is your ideal transfer engine. If it is primary (bright) green then that is not an option for a single engine.

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Edited December 14, 2014 by John FX

[panzer1b]

i like nukes for just about everything that isnt super lightweight.

They are simply unbeated (aside from ions for the ultra patient), and one is plenty for 20 tons (can be 1 for 30 if ur really patient and plan well with ur burns).

of if you really dont give a crap about dV, strap a OP-2L onto any fuel tank combo and you can get absurd TWR with respectable isp (overkill isp for its TWR). The KR-2L is just a little (er alot) overpowered as it combines 2 things that no other engine has, TWR and ISP in one package. Its nowhere near nuke ISP, but considering it has exponentially better thrust (and superior isp to everything but 909s/poodle/nuke/ion/aerospike)