Grand Tour Delta-V

[Chronin]

So ever since mining and resources came out, Grand Tours have become a lot easier, since ships don't need to take their own fuel everywhere. However, I am attempting an old-school Grand Tour, with a single launch and no refueling. The problem is that I haven't been able to find up-to-date info for a few things.

The most important is how much Delta-V something like this needs. I've found maps a few years old, but I haven't seen any 1.0.x info, which, thanks to the new Aero, is very different from the old stuff.

My design will be a mothership that carries a few landers with it, which will land and take off before docking to the mothership again. The landers have plenty Delta-V, but I have no idea how much Delta-V I'm going to need for the mothership. Does anyone have any experience with this? Are the Delta-V maps accurate enough, or do gravity assists make huge differences? 

I guess that's really all I was wondering, so thanks in advance

[Snark]

So what are the parameters you're following? "Land on every body"?  Or is there an actual requirement that the mothership has to orbit?

Just wondering whether it might be possible to save some fuel by not actually orbiting.  Just do a flyby.  When you're going to, say, Moho, separate the lander from the mothership when you're still a few days out, and give it a nudge so that it arrives at Moho a few hours before the mothership does.  Land, grab whatever science, then when the mothership goes flying past, take off again and rendezvous.

[Snark]

The stock planets haven't changed their masses or orbital parameters since forever.  So as long as your mothership doesn't enter atmosphere, any old maps should still be accurate.

[Chronin]

Alright, thanks. I still think I'll try and Aerobrake on Duna, but I'll just go off the maps for the rest.

[Tatonf]

Hello,

For an up-to-date Delta-V map I suggest this one :

I think that the major obtacles are Eve and Moho.

Eve because it will be your first destination since you need to get rid off it's special heavy lander asap, but aerobreaking with the mothership will be hard (if not impossible) so you'll need to spend some large amount of fuel to slow down.

Moho because it requires large amount of delta-V for going to it and coming back. Gravity assist is probably your best friend.

If you want some ideas there's still this old video (pre 1.0) which is kind of awesome :

https://www.youtube.com/watch?v=Q2V6a9-FUHM

Edited December 6, 2015 by Tatonf

[Stratzenblitz75]

Here is the plan I made for my old grand tours: https://www.lucidchart.com/publicSegments/view/53879cc7-c91c-4c57-81a3-61cb0a0090ac

Yes, it is very old, but since the planets haven't changed all that much, it should still be accurate*. Be warned though, I measured planet landing/liftoff values with my crafts. If your lander has a low TWR, then these values could be inaccurate.

If my map doesn't help, then you could easily make your own with the help of this excellent launch window planner: https://alexmoon.github.io/ksp/. I recommend going to Eve first, so that you can dump your heavy Eve lander early on. From there, Moho is a nice target since its close by. Although, it is still expensive to make an Eve->Moho transfer, so you might have to make a minimalist craft just for that transfer. Also, be sure to use hyperedit to test all your crafts and measure Delta V usage for landings/liftoffs. Trust me, you don't want to find out your craft can't make orbit after a lengthy grand tour mission.

 

 

 

[Chronin]

Oh don't worry, I am using Hyperedit quite a lot

However, after watching the videos and going through your old screenshots, I am beginning to realize that I may have imposed to many arbitrary restrictions on myself. We'll see. For now, thanks for all the advice

[Chronin]

Well, I was going to have the mothership orbit, but there's one more big parameter that I never mentioned because it wasn't too important or relevant to the question. 

Rather than have multiple landers for planets, I wanted to use the same lander for every planet or moon. So what lands on Moho is the same one that lands on Laythe or Eve. In other terms, this means that there can only be 1 stage on the lander. I can't drop anything to lose weight. 

Obviously, that wouldn't be possible unless I could somehow design something that is capable of getting off Eve without staging, so I made the lander "modular". The lander is one stage with ~4750 Delta-V, and by itself is able to land and come back from all but 3 of the bodies. For Eve, Laythe, and Tylo, it will be modified by adding more fuel and engines, which will be dropped and decoupled, as they are not the core lander.

I'm beginning to question the logic of that decision after seeing those videos, as they all make use of multiple landers and ships to get everywhere. But oh well, I'll see how it goes

[Snark]

10 minutes ago, Chronin said:

Rather than have multiple landers for planets, I wanted to use the same lander for every planet or moon. So what lands on Moho is the same one that lands on Laythe or Eve. In other terms, this means that there can only be 1 stage on the lander. I can't drop anything to lose weight. 

Obviously, that wouldn't be possible unless I could somehow design something that is capable of getting off Eve without staging, so I made the lander "modular". The lander is one stage with ~4750 Delta-V, and by itself is able to land and come back from all but 3 of the bodies. For Eve, Laythe, and Tylo, it will be modified by adding more fuel and engines, which will be dropped and decoupled, as they are not the core lander.

I'm beginning to question the logic of that decision after seeing those videos, as they all make use of multiple landers and ships to get everywhere. But oh well, I'll see how it goes

Yeah, the issue there is if you pack that much dV into a single-stage lander, it's far over-designed for most places, which means you're lugging around a lot of mass you don't need.  Tylo, Eve, and Laythe are special cases and probably would do better to have separate landers.

In any case, best of luck, and let us know how it went!

[Chronin]

While you are definitely correct in stating that it's over-engineered for most places, it is "only" 25 tons, which is quite small when compared to the 750 ton mothership.

[Stratzenblitz75]

A reusable lander with modular fuel tanks/engines seems like a perfectly viable option. Sure, you are lugging around extra mass to many of the planets, but I think that's a good trade off for lower part counts, and reduced complexity. You might have some challenges making a modular Eve stage, but if you think you can do it, go for it!

Also, what are you trying to land on each planet? Are you using a command chair? Command pod? Are you bringing science equipment or rovers?

[Chronin]

I've been having more trouble with the Tylo modifications that with Eve's tbh. The lander itself, because of weight, has extremely poor TWR, and so I end up losing a lot of Delta V landing on Tylo. 

Being able to use parachutes on Eve greatly helps, as well as the fact that I have allocated a lot more room for the Eve addons on the mothership than for Tylo's. 

The Lander itself is a lander can (Mk. I) with a bit of mono prop, few solar panels, ~1700 Liquid fuel, and some docking ports. It flies using a single Aerospike, which I found to be the best compromise on power, weight, and size. I could have put some small experiments on it, but because I'm doing this in Sandbox, I figured they'd just raise part count 

Edited December 6, 2015 by Chronin

[fourfa]

Interesting thread.  Anyone ever seen a delta-V map that addresses direct transfers (ie Dres-Jool, Jool-Eeloo, Moho-Eve) rather than to and from Kerbin?

[Tatonf]

2 hours ago, fourfa said:

Interesting thread.  Anyone ever seen a delta-V map that addresses direct transfers (ie Dres-Jool, Jool-Eeloo, Moho-Eve) rather than to and from Kerbin?

Such a thing would require making a map for each celestial body, like the one we're used to that start from Kerbin. This is because each body will give you different Oberth effect and have different gravity, and thus each transfer will require a different amount of delta-V. For exemple, a Dres-Jool transfer would require a 150 m/s (escape) + 300 m/s (interplanetary travel) = 450 m/s ; while a Jool-Dres transfer would require 2800 m/s (escape) + 20 m/s (interplanetray travel) = 2820 m/s.

 

[fourfa]

Good point - I suppose there's no need for a full map from everywhere to everywhere else, just neighbor to neighbor in both directions.  Stratzenblitz's mission flowchart is a good start, I guess I'll start making something like that for myself.

[Snark]

If you're looking to save dV and don't care about getting every possible science result:  you can save a crapload of fuel by making a very lightweight lander for worlds with no atmosphere (this is a big deal in particular for Tylo).  Just mount a command chair on top of a probe core and give it a very small LFO tank with a tiny engine (say, a Spark).  You can build something with a few thousand m/s of dV that's only a ton or so.  Can put a kerbal down on just about any vacuum world.  And it's lightweight enough that you can have, for example, a disposable lander for Tylo that has drop-tanks to jettison.

 

25 tons is huge for a lander on anything other than Eve.

[Chronin]

While the approach of going uber-lightweight is definitely a very efficient and valid one, my plans for this mission was to have everything be huge. In the past, I generally always stayed in the middle in terms of craft size, weight, and D-v, but I want to experiment with both huge and tiny projects. This is my huge project

In a normal mission that weighs, say, 200 tons, a 25 ton lander is gargantuan. It would make up 1/8 of the entire mission weight. But for this mission, 25 tons is only 1.666% of the mission weight, an so I won't put too much effort in to changing it. 

Edited December 7, 2015 by Chronin

[sdj64]

In my grand tour the mothership had somewhere around 7000 - 8000 delta V.  The booster stage pushed it to Eve for another 1300 delta V so you should probably aim for 9 to 10 thousand if you use the same mission plan as I had.  Using a smaller ship to fly to Moho and back to Eve saves lots of delta V for your mothership, and you can also do that with Dres and Eeloo and between Jool's moons if you want for even more fuel saving.

I had an ion lander with excess delta V around 7000, a liquid fueled lander with 2300 delta V, and separate additions for Tylo and Laythe.  I did use seats on all the landers and it would have been a lot bigger with real pods, probably at least twice the size.  You can see my mission report with the link in my signature, maybe that will help you plan things.  As some people have said above the 1.0 aero really only changes Eve (easier), Laythe (harder with jets), and Duna (harder to parachute).  Transfers and other things will take the same dV as before.  Aerobraking will be difficult but possible if you make sure to enter at good speeds and angles and design your ship with a good heat shield.

If your whole mothership goes into orbit around every planet and moon without any aerobraking it takes at least 20000 dV, probably aim for 25000 or more to make sure.

[Chronin]

I had seen your Origin Grand Tour before, and it's very useful to determine my route. I am actually thinking of copying you and making an ion tug for Moho, but that depends on how much Delta-V it can have when towing 15 tons. 

As for the mothership, I was planning on giving it 15,000 Delta-V, as the lander would be able to reach Eeloo, Dres, and most of the Jool moons alone. But your ion lander has insipid me. I'm going to go change some stuff now, see if I can fit a tug in a Mk. III cargo bay

Also, I'm not quite sure it's possible to get 25,000 m/s of Delta-V without ion engines. Unless you asparagus hundreds of Nervs

[fourfa]

Just to be clear, 25,000m/s delta-V is for a non-ISRU mission?  With ISRU, it would just be the biggest single stretch of launch-escape-capture-land in the whole mission?  Something closer to 6000m/s for ideal transfers? (Assume zero time constraints)

For that matter, where is the biggest single stretch of launch-escape-capture-land in the whole mission? Eve-Moho?

(not including Eve ascent)

Edited December 7, 2015 by fourfa

[technion]

I'm very interested in how anyone would complete a grand tour with Eve in the picture in 1.05. The type of craft needed to ascend now is much, much more difficult to simply attach to an existing rocket and bring along. The mothership will be rediculously long and bendy with it attached.

[Red Iron Crown]

On 12/6/2015, 7:11:53, fourfa said:

Interesting thread.  Anyone ever seen a delta-V map that addresses direct transfers (ie Dres-Jool, Jool-Eeloo, Moho-Eve) rather than to and from Kerbin?

Don't bother with a map for that, use a transfer calculator. There's a couple of web ones, like olex's (simpler) or alexmoon's (more complex), or you can get a planner in game with Transfer Window Planner.

If you absolutely must have a map, check out jellycubes' maps for other planets, they'll give better figures for non-Kerbin-centric maneuvers (though the atmospheric landing/ascent values are from the old aero model).

[fourfa]

thanks.  I've been using the transfer calculators.  Not hard to get the ejection burn, but have found it hard to get accurate numbers on the capture burn

[Snark]

8 hours ago, fourfa said:

thanks.  I've been using the transfer calculators.  Not hard to get the ejection burn, but have found it hard to get accurate numbers on the capture burn

Unless you're aerobraking or something, numbers for the capture burn are easy.  Just use the transfer calculator in reverse.

For example, let's say you're using http://ksp.olex.biz to take a trip from Kerbin to Moho.  You need two burns:  one to leave Kerbin, and one to capture at Moho.  (Well, and likely a correction burn in between to deal with inclination and what-not, but you get the idea.)

To get the ejection burn from Kerbin, you tell it:  "Depart Kerbin, here's my parking orbit altitude, arrive Moho" and it gives you the dV for that.

To get the capture burn at Moho, use it backwards.  You tell it:  "Depart Moho, here's my parking orbit altitude, arrive Kerbin" and it gives you the dV for that.

It's not totally perfect (the reverse-burn estimate will only be correct if you actually did a perfect Hohmann transfer from the origin planet), but it's pretty good.

[fourfa]

ah! brilliant

[Empiro]

I don't know if this would be acceptable for a "true" Grand Tour, but it seems to me that as soon as you make LKO, you'd want to split off your ship and send fuel tanks off separately.

You don't want to be hauling fuel for exploring all of Jool while you're messing around Eve and Moho, so just send that fuel off to Jool from Kerbin.

You'd naturally want to go to Eve first to get that out of the way, and then at every step of the way you dock with fuel tanks sent from LKO, each of which has just enough fuel to refill your lander to land on whatever body you're around and transfer you to the next destination. This way, you're not carrying fuel around that you won't immediately use, and you won't run into the worst parts of the rocket equation.

You'd still need a huge launch craft, but it won't be nearly as big as trying to get 20+km/s worth of delta-V.

Edited December 8, 2015 by Empiro