Delta-V for an Interplanetary Tug

[Liudeius]

I'm trying to build an interplanetary tug which can make a round trip from low orbit around Kerbin (fully fueled), to low parking orbit around any other planet or moon, and back to Kerbin for refueling.

How much delta-v should I aim for to do this?

I know it's more complex than that, depending on gravity assists (which I don't expect to use much since they seem to require in-game years patience), but does anyone at least know the absolute most expensive delta-v round trip to achieve so I can use that as a goal?

Answer: Moho, with 8-10k delta-v (round trip) in the interplanetary stage.

Edited August 14, 2013 by Liudeius

[annallia]

I am not sure how much delta V mine has. It does however run off a single X200-32 tank and two FL-T400 tanks (radially mounted) then it has dual LV-N engines on each side. Gets anywhere in the system without refueling.... May need more few depending on what it is pushing though.

Edit- highest delta-v orbit around kerbin would be skirting the edge of its SOI.

[Liudeius]

I am not sure how much delta V mine has. It does however run off a single X200-32 tank and two FL-T400 tanks (radially mounted) then it has dual LV-N engines on each side. Gets anywhere in the system without refueling.... May need more few depending on what it is pushing though.

If only. I'm planning to use it for a universal lander, so I'm expecting to haul at least 100 tons (ignoring its own mass and fuel).

highest delta-v orbit around kerbin would be skirting the edge of its SOI.

I meant the highest delta-v for starting from low Kerbin orbit, transferring to another planet or moon, establishing a parking orbit around it, then returning to Kerbin and reestablishing a low parking orbit.

(So basically everything but going from ground to orbit.)

[rryy]

The most difficult planet to get to is Moho, which takes about 5000 m/s of delta-v to get to, so around 5500 m/s is what you should aim for.

[annallia]

In that case it would be Jool for highest DV to reach for planets and Tylo for moons unless I am reading this wrong:

[TomcatMVD]

What do you use for knowing your ship's Delta V? I used to use the MJ thingy but now it doesn't work.

[Liudeius]

In that case it would be Jool for highest DV to reach for planets and Tylo for moons unless I am reading this wrong:

I have one of those too (slightly less detailed though, thanks, I'll take that).

But I am a bit confused on how to calculate from it.

Firstly, is it the same both ways?

And secondly, do I really have to put 2630 into a low Jool orbit if I'm headed to Pol, then another 2630 to get back? Can't I just go straight from Pol to interplanetary space to get back?

And it seems to me any Jool orbit would be better to sit in until you could find a favorable intersect with Pol while you're headed there, rather than burning retrograde to Jool just to burn prograde again. (Though I'm not very knowledgable on optimizing orbital transfer.

[Liudeius]

What do you use for knowing your ship's Delta V? I used to use the MJ thingy but now it doesn't work.

For Delta V you need the Isp of your engine, mass fully fueled, and mass empty.

Then I've been using this http://www.strout.net/info/science/delta-v/ to do the calculation. (though the formula is Delta-v = Isp * 9.81 * ln(mass full/mass empty). It is 9.8 no matter where you are going.)

Delta V is basically "How efficient is your engine and what percentage of your ship is fuel." (Though if you know the shape of the graph of ln, you can see adding more fuel has diminishing returns.)

You can find the mass of your ship by pressing "m" on the launch pad the mousing over the "I" icon on the right of the map.

Edited August 13, 2013 by Liudeius

[TomcatMVD]

For Delta V you need the Isp of your engine, mass fully fueled, and mass empty.

Then I've been using this http://www.strout.net/info/science/delta-v/ to do the calculation. (though the formula is Delta-v = Isp * 9.81 * ln(mass full/mass empty). It is 9.8 no matter where you are going.)

Delta V is basically "How efficient is your engine and what percentage of your ship is fuel."

You can find the mass of your ship by pressing "m" on the launch pad the mousing over the "I" icon on the right of the map.

Thanks, I was looking for an automated way of knowing it. IIRC it was MJ that had this little part you could attach to your ship as you were building it and it'd tell you the Delta V for each stage. Oh well... I can always do the math I guess

Thanks.

[capi3101]

Kerbal Engineer Redux will do the same thing, though I've had issues with it in 0.21 (it'll report X amount of delta-V in the VAB, Y amount on the launch pad...the Y amount is usually the correct amount).

[Liudeius]

The most difficult planet to get to is Moho, which takes about 5000 m/s of delta-v to get to, so around 5500 m/s is what you should aim for.

Oh, I didn't notice you before. Is that one way or two ways? And is it only the hardest planet to get to, or is it harder than moons too? (According to the chart, Pol looks like more delta-v.)

[rryy]

Kerbal Engineer Redux will do the same thing, though I've had issues with it in 0.21 (it'll report X amount of delta-V in the VAB, Y amount on the launch pad...the Y amount is usually the correct amount).

That's because it calculates delta-v using the vacuum Isp in the VAB, but uses the current atmospheric Isp on the launch pad.

Oh, I didn't notice you before. Is that one way or two ways? And is it only the hardest planet to get to, or is it harder than moons too? (According to the chart, Pol looks like more delta-v.)

It is only one way, but returning to Kerbin should take much less because you can aerobrake. It is also harder than the Joolian moons to get to because with Jool, you can aerobrake so your apoapsis crosses your target moon's orbit. You don't need to use engines to get into a low circular orbit around Jool and then burn back out to get an encounter.

[sgt_flyer]

Yup, for joolian moons, you just need to plan an aerobrake that would lower your apoapsis near your target´s orbit. (And that's free delta-v to aerobrake ) - if you aim to go to laythe, and it's in a good position, you can even skip the jool aerobraking and directly aerobrake into layhte's atmosphere - saving even more delta-v.

[Crater]

AlexMoon's Launch Window Calculator at http://alexmoon.github.io/ksp/ is very useful for this kind of thing. If you tell it where you're going from and to, it'll tell you when to do, and how much it'll take to get there.

As was mentioned above, Moho is the most difficult target, with Eeloo second. You'll need somewhere over 10,000 delta-V for a round trip to Moho.

Also, Mechjeb 2.0.9 works fine with 0.21 and still has the VAB delta-V calculator, which seems to give pretty accurate results from what I've used it for.

Edit : for the Moho trip, you can only aerobrake for the kerbin return insertion, which at best will save you less than 2k delta-V, so you're still going to need upwards of 8k.

Oh..... are you bringing the lander back, or are you leaving it there? Dropping 100t off at the target will give you a lot more delta-V from your fuel load on the way back.

Edited August 14, 2013 by Crater

[Liudeius]

It is only one way, but returning to Kerbin should take much less because you can aerobrake. It is also harder than the Joolian moons to get to because with Jool, you can aerobrake so your apoapsis crosses your target moon's orbit. You don't need to use engines to get into a low circular orbit around Jool and then burn back out to get an encounter.

You'll need somewhere over 10,000 delta-V for a round trip to Moho.

Edit : for the Moho trip, you can only aerobrake for the kerbin return insertion, which at best will save you less than 2k delta-V, so you're still going to need upwards of 8k.

Oh..... are you bringing the lander back, or are you leaving it there? Dropping 100t off at the target will give you a lot more delta-V from your fuel load on the way back.

Nice, my preliminary tug design has about 8-9k delta-V fully loaded, I think it was 16k without the lander (much of which I won't be taking back),

Saving 1-2k delta-v with Kerbin aerobreaking will be very nice too.

Thanks for your help. Onward to Moho!