Interplanetary ship help

[Redjoker]

I am about to begin sending the pieces of my interplanetary ship into orbit for assembly and wanted some input. First I know that TWR isn't as important in space as it is on the ground but this is a 480 ton ship and I am trying to decide on skipper vs nerva. With 5 Nervas the ship only has a TWR of 0.05 which I am worried that burns may take to long do accurately while the skippers would have a TWR of 0.29.

Secondly I have the question of how to assemble it. I can dock so the linear parts are no problem but the dock on the side while being coplanar with the engine as in the pictures below. I was wondering how in the world would you dock it since all your nav ball markers would be showing as if your were docking with the front of it?

this is where the engines and the main body connect

and here is the whole ship. note: its not going in one piece this is just to show how it will look.

[Psycho0124]

Nervas are your only real choice for interplanetary travel. No other engine offers reasonably efficient use of your fuel. I routinely do massive station deployments using a single NERVA pushing more than 4 jumbo-64 tanks (TWR of 0.04) and have never had a problem with burn time. Do incremental burns, start burning early, be patient. Use alt+> to do physical time acceleration and you'll be set. Patience with low thrust-to-weight ratios pays massive dividends in delta-v.

As for the docking maneuver; just eye-ball it. Set your camera to 'chase' with the v key. Keep your view moving; checking different planes and relative velocities. It looks like you should have more than enough mono-propellant to go slow and take your time with the docking.

Edited June 18, 2013 by Psycho0124

[SDIR]

Actually, for docking you can right click on the docking port you want to dock to and select "set as target." Then the target on your nav ball will be in the same position as the docking port you are aiming for. When I dock, all I do is stare at the nav ball, since that gives me my velocity relative to the target, the way I'm facing, the position of the target relative to the docking port and the direction I'm heading relative to the target.

[arq]

Also, you can select a docking port on your ship and 'Control From Here' to set your navball relative to that port. And I agree, NERVAs are really the only good option for interplanetary travel, even if it means having a lot of them (I used 12 to move a 300t ship to Duna, though it did require a small bit of patience on the burns). It's easy to attach FL800 fuel tanks to the sides of your ship and put NERVAs on the bottom, if having trouble finding places for them.

[Redjoker]

Thanks for all your help, Im thinking im going to need more than 5 nervas for a 500 ton ship since with one nerva and an 80 ton ship took 15 min to do a 800m/s maneuver

[Vanamonde]

My interplanetary burns commonly take 20 minutes to an hour. That's partially due to part-count lag, but also an unavoidable ramification of fuel efficiency.

[capi3101]

Hmm...lesseeeee.....from the screenshot, your finished ship has got 9 Jumbos, right?

Working on that assumption, your liquid fuel mass is going to be right at 288 tonnes. Now you say the ship weighs 500 tonnes...so, the mass ratio is about 1.736.

Skippers in vacuum have an Isp of 350. So that works out to about 1894 m/s of delta-V. You wouldn't be able to return from the Mun on that; you'd be better off using a Poodle.

LV-Ns have a vacuum Isp of 800. So that works out to about 4,329 m/s of delta-V. That'd get you to Duna/Ike/Dres and back.

For interplanetary flights, thrust doesn't matter as much as efficiency.

If you don't think five LV-Ns will cut it, add more; you could easily slip 25 on the design you've got (assuming I've missed a central set of tanks). Just take an LV-N, attach it to the bottom of the tanks, then attach four BZ-52 Radial Attachment Points to the bottom of the tank right next to them, and slap LV-Ns on those too. Poof: you suddenly have as much thrust as a single Mainsail and about 3 m/s^2 of available acceleration given your mass. Still ain't much, but then again you're pushing 500 tonnes around...