Asteroid moving tips

[MagicFireCaster]

Hey guys, i want to build a ship to move a 23.5t asteroid from LKO to gilly orbit, and i need to keep it cheap, and maybe bring a small lander with me, any suggestions so i don't have to spend a lot of funds? 

[steuben]

A few lv-ns, a drill, an isru, and the lander in a puller configuration.

 

[MagicFireCaster]

I've already mined it, so it haves minimun mass, i just want to know if is cheaper to use a big a ship or just a medium ship with nuke engines.

[Snark]

17 hours ago, MagicFireCaster said:

I've already mined it, so it haves minimun mass, i just want to know if is cheaper to use a big a ship or just a medium ship with nuke engines.

Smaller ships are always cheaper, if they can get the job done.

I'd say, use a ship with a single LV-N, and the amount of fuel you need to do the move.  To figure out how much fuel, first tote up how much total dV you'll need, then just Tsiolkovsky it to get the fuel amount.

[Evanitis]

Oooow, math looks so neat... but also intimidating. Some mortals would just build a 23.5t dummy-payload to check a DV readout with it.

Though I'm interested if there's such an equation for determining how many parachutes I'll need for a few hundred tonnes one.

*searches*

Hey there is! Wonder if it's accurate these days.

[Snark]

47 minutes ago, Evanitis said:

Oooow, math looks so neat... but also intimidating. Some mortals would just build a 23.5t dummy-payload to check a DV readout with it.

Oh, c'mon, it's not that bad.  Take the mass of the ship with fuel, divide by the mass without fuel, press the "ln" button on your calculator, multiply by 9.8, multiply by I_sp, and there you are.  I do it all the time, just takes a few seconds.

 

[Evanitis]

I'd hate to alt-tab to access my only calculator.

But I believe I could write a kOS script for that. Ohh, wait...

[Plusck]

19 hours ago, MagicFireCaster said:

I've already mined it, so it haves minimun mass, i just want to know if is cheaper to use a big a ship or just a medium ship with nuke engines.

If you've already mined it, be careful about detaching things then reattaching a tug to it - the "newly discovered" attribute that you need for the asteroid-mining contracts could fail.

[Snark]

42 minutes ago, Evanitis said:

I'd hate to alt-tab to access my only calculator.

That's what your phone is for.  I mean, what else would you do with it? 

[MagicFireCaster]

3300 Delta V with the payload would be enough if i want to get back to kerbin? I don't know how to calculate how much DV will i have for a second trip once i drop the asteroid in gilly's orbit. 

[Snark]

1 hour ago, MagicFireCaster said:

3300 Delta V with the payload would be enough if i want to get back to kerbin? I don't know how to calculate how much DV will i have for a second trip once i drop the asteroid in gilly's orbit. 

From Gilly, the dV you need to get home to Kerbin will vary, based on where it is in its orbit (which is highly elliptical) and whether you use Eve for an Oberth maneuver.  If you have 1000 m/s of dV remaining after dropping the asteroid, you ought to be fairly safe, as long as you use a decent launch window.  There are a lot of planners out there, http://ksp.olex.biz is my favorite.

That's 1000 m/s of dV after you drop the asteroid.  That's a lot of mass, relative to your ship, so you'll need to take that into account-- i.e. when you're figuring out "how much fuel do I need to have in my ship, at Gilly, in order to have 1000 m/s of dV to get home", be sure you're using the mass of your ship without the asteroid.

[MagicFireCaster]

59 minutes ago, Snark said:

From Gilly, the dV you need to get home to Kerbin will vary, based on where it is in its orbit (which is highly elliptical) and whether you use Eve for an Oberth maneuver.  If you have 1000 m/s of dV remaining after dropping the asteroid, you ought to be fairly safe, as long as you use a decent launch window.  There are a lot of planners out there, http://ksp.olex.biz is my favorite.

That's 1000 m/s of dV after you drop the asteroid.  That's a lot of mass, relative to your ship, so you'll need to take that into account-- i.e. when you're figuring out "how much fuel do I need to have in my ship, at Gilly, in order to have 1000 m/s of dV to get home", be sure you're using the mass of your ship without the asteroid.

That would be kinda difficult, i can't calculate how much fuel i'm going to have the i get to gilly's orbit, indeed i know how much delta V i will use (more or less) based on Swash's Delta-V Map to get to gilly, so i think i will go with that instead, 3000 DV with the asteroid should be enough then 

[Snark]

31 minutes ago, MagicFireCaster said:

That would be kinda difficult, i can't calculate how much fuel i'm going to have the i get to gilly's orbit, indeed i know how much delta V i will use (more or less) based on Swash's Delta-V Map to get to gilly, so i think i will go with that instead, 3000 DV with the asteroid should be enough then 

3000 with asteroid should be plenty.  Especially since the second half of that will be without the asteroid.

Just make sure you get a good launch window-- going to Eve on a good window is fairly cheap, dV-wise, but it gets expensive in a hurry as you get away from the window.

If you did want to know how much dV coming back:  that's pretty straightforward.  Figure out how much dV to get there.  Then take the amount of fuel you'll burn to get that much dV.  Subtract off that fuel, subtract off the mass of the asteroid, then figure how much dV you get from the fuel that's remaining.

But if you don't feel like doing that-- yeah, 3000 m/s is plenty.  It's considerable overkill, but plenty. 

Edited January 31, 2016 by Snark

[cantab]

Engine clusters are a big help to push off-centre masses around, just reduce the thrust limiter on some of the engines. Trouble is nuclear engines are expensive, so it might be worth looking at a chemical engined design instead. Three Terriers should be enough thrust. The question is whether the extra fuel and tankage for the chemical option, *and* the potentially bigger launcher for it, adds less cost than the 30 grand for three nuclear engines.

[Dunbaratu]

16 hours ago, Snark said:

Oh, c'mon, it's not that bad.  Take the mass of the ship with fuel, divide by the mass without fuel, press the "ln" button on your calculator, multiply by 9.8, multiply by I_sp, and there you are.  I do it all the time, just takes a few seconds.

 

What doesn't take just a few seconds is accessing all that data to plug in to the formula in the first place when your ship is composed of more than one part, and more than one stage, as any non-trivial ship will be.  If the game simply had a dumb summation of the relevant fields it would be nice, and not really be doing any thinking for you - just taking away the tedium of note-taking.

[Snark]

3 hours ago, Steven Mading said:

What doesn't take just a few seconds is accessing all that data to plug in to the formula in the first place when your ship is composed of more than one part, and more than one stage, as any non-trivial ship will be.  If the game simply had a dumb summation of the relevant fields it would be nice, and not really be doing any thinking for you - just taking away the tedium of note-taking.

Point taken, though it depends on the circumstances.  Certainly if multiple stages are involved, then it becomes inconvenient.  But if the ship's already in orbit, it's often the case that all the stages are done and there's just one stage to contend with.  Total mass is an easy readout from the map view's info panel, and fuel mass is trivial to figure out: get the total readout from the resource panel, then multiply by .005 for LF-only ships, or divide the LF by 90 for LFO-fueled ships.

And of course, there's the personal "inconvenience multiplier" of how big a deal one thinks it is to pull out a calculator and punch buttons.  I happen to like doing that once in a while, so for me it's a non-issue.  But I happen to like math, and I consider figuring out that sort of thing to be part of the fun of KSP.  I can see how other folks could be allergic to it. 

[Evanitis]

8 minutes ago, Snark said:

And of course, there's the personal "inconvenience multiplier" of how big a deal one thinks it is to pull out a calculator and punch buttons.

Can't deny that. Even my phone is relic of better ages. I sometimes -call- people with it who has no better things to do to google things for me. My only calculator is a Microsoft software.

Though I barely found it inconvenient to detach stages and empty some tanks to get drymass readouts. I do it too much when making SSTO planes, but I don't find it bothersome enough to get RCS build aid.

Math is cool and amazing.