Questions about Interplanetary travling

[vildar87]

Hello peoples. I have a goal in mind that i have had since I first started playing KSP about a month ago, and have slowly been working towards it ever since. before I get to my questions, let me outline what I want to do to make it easier to understand;

First, to build a Satellite orbiting kerbin that is also a good sized refueling station. From this, i want to attach several other crafts. once I have it all assembled in orbit, I want to fly the entire station, and the attached crafts, to each and every celestial body, land, refuel using kethane, and then head on to the next. I intend it to be one long trip around the entire solar system, before returning safely to Kerbin, with all Kerbals safe.

so first, question I have; does Center of Mass affect thrust in space? think i worded that right. if not, what i mean is does the station have to be balanced for interplanetary travel?

second question; Not sure if this has been done before, but I have gone through the Delta-V map and figured that the highest Delta-V that the station would need to go from one planet to the next before it could refuel is 9250 m/s. that is figuring about 100m m/s for aerobraking when possible and such. I just calculated this over an hour or two so not sure just how accurate it is, I don't have any experience with interplanetary travel atm, so if someone that has more experience could look over my numbers for me? thanks

so this is the route I figured quickly, and the delta-v for it;

kerbin > Gilly = 3000

Gilly > Moho = 4630

Moho > Duna + Ike = 3500

Ike > Dres = 1500

Dres > Pol = 3400

Pol > Bop = 6800

Bop > Tylo = 6600

Tylo > Vall = 5900

Vall > Laythe = 4500

Laythe > Eeloo = 9250

Eeloo > Kerbin = 3400

so thats what i figure so far, if anyone has any tips or anything to add, it would be appreciated.

Edited September 24, 2013 by vildar87

[Kegereneku]

First, yes it does. A LOT. If it's not aligned with the direction of thrust the rocket will rotate.

Know that the camera is focused on the center of mass. And if its engine are gimbaled they can compensate a little, very little.

Another solution is to move fuel around the different fuel-tank to move the center of mass

Second, this map here is a minimal Dellta-V :

http://forum.kerbalspaceprogram.com/showthread.php/20993-Request-Delta-V-maps?highlight=delta

For maximal DeltaV map you want this launch windows planner and look for the worst time.

http://alexmoon.github.io/ksp/

Worst windows between Kerbin and Jool is 20 000m/s, worst between Moho and Jool is 35 000m/s, you can use gravitational slingshot but i doubt it will be enough.

But I have to warn you, if you didn't knew any of it before you won't succeed. I don't think anybody ever visited all planets with one mothership. (For starter because it would weight 900 tons with over 500 parts)

[capi3101]

Your station does have to be balanced while in flight or it will flip around like nobody's business. Only counter to that is good pod torque and RCS - you really need both, particularly if your ship is massive - and I guarantee you you'd run out of RCS before you finished your grand tour. I should tell you about the very first Hellhound mission...it was unbalanced and I was only going to the Mun that time, let's put it that way......

Just a thought - you might want to crunch the numbers on a Dres to Eeloo run and hit it before heading on to the Jool system - designing a ship for 6800 delta-V would be a lot easier than designing one for 9250 (read: less massive, not as many parts so not as laggy). That's a couple of hard targets to reach...

I'll also advise you to add at least 25% to all the numbers in the delta-V map. If you've never done an interplanetary run before, you're going to want a fatter fuel reserve to account for piloting errors; the maps account for the best case only.

[maltesh]

second question; Not sure if this has been done before, but I have gone through the Delta-V map and figured that the highest Delta-V that the station would need to go from one planet to the next before it could refuel is 9250 m/s. that is figuring about 100m m/s for aerobraking when possible and such. I just calculated this over an hour or two so not sure just how accurate it is, I don't have any experience with interplanetary travel atm, so if someone that has more experience could look over my numbers for me? thanks

Could you link the delta-V map you're using? Every delta-V map I've seen works only for journeying from (and sometimes, returnting to) Kerbin. I haven't seen one that gives information for traveling when neither the origin nor destination is Kerbin.

[capi3101]

@Maltesh: Alexmoon's Launch Window Calculator (which Kegereneku linked to his post) can give you that information - it's a porkchop plot generator that gives you all kinds of information, including phase and ejection angles and total delta-V. Only real beef I have with it is that it can do moon-to-moon and planet-to-planet transfer calculations, but not planet-to-moon (it's not even good for planning to go to Mun or Minmus).

Hey...there's something you could do, vildar - plug your numbers into the calculator and see what pops out (i.e. see if it verifies your math). It'll even give you an idea of how long your grand tour will take. Of course, you do have more than one planet-to-moon transfer there along your route, so that might take some adjusting.

[nhnifong]

Docking Strut should help with the wobbliness.

Refer to Metaphor's grand tour for an example of what the lightest way to do this is. No one has ever come close AFAIK. Of course, since you're not doing it in one launch, you can get off a little easier.

His path was as follows:

Kerbin to Eve, aerobrake to highly eccentric orbit.

Land and return to orbit using jetpack for final bit.

Small craft to visit Gilly and return.

Eve to kerbin transfer, + 4 kerbin slingshots.

Burn on final slingshot to Jool encounter.

Aerobrake at laythe into most eccentric possible orbit.

Land and return.

Transfer to Tylo, brake into a semi-low orbit depending on the capability of your lander.

Land and return, using jetpack for final bit.

Visit Bop and Pol.

Transfer to Eeloo. Land and return.

Transfer to Dres, Land and return.

Transfer to Duna, Aerobrake to eccentric orbit, land and return.

Visit Ike.

Use a series of Kerbin and Eve slingshots to lower to Moho orbit.

Brake to eccentric orbit. land and return.

Burn direct to Kerbin if you can afford it, or burn to eve and use a slingshot.

Aerobrake at kerbin to eccentric orbit.

Visit mun and minmus.

land at kerbin.

Edited September 17, 2013 by nhnifong

[vildar87]

awsome guys, love all the support here!

Kegereneku and capi3101; thanks for the info about the COM, I will play around with things and add counter weights if needed. worse comes to worse I think adding extra fuel between one craft and the station would off set it.

maltesh; I was just using a normal delta-v map, and calculated all the escape delta v needed from one, to the capture and orbit of another planet. didn't realize that the delta - v maps were just to/from kerbin

I will check out the launch window calc and run my numbers again, thanks for that Idea Capi.

Nhnifong; I do use quantum struts, so that has some strutting capabilities once docked, will check out docking strut as well though. and thanks very much for Metaphor's grand tour, that is exactly what I was looking for. gives me something to go off of.

and so far have gotten the impression that it is a lot more difficult than i think, which is good. to me this kind of trip is kind of the end game of ksp, one of the hardest things possible. so it is definitely something I am going to keep on aiming for.

at the moment I have a design for the station its self that I like for now. weight is 1, 105 tons, with 9312 m/s delta v. of course the delta v will decrease when the ships are added on, but i will be adjusting the designs later. while this thing is massive, not sure if i am going to stick with it for the final design. here are some stats at the moment. this of course is just the station its self, not the launch mechanism.

Parts; 468

Weight; 1,105 tons

ISP; 800s

Thrust; 4200

Delta-V; 9312

Solar Wing Electrical charge; 400/s

Fuel tanks, 20 large orange tanks plus misc smaller ones.

Liquid Fuel; 69120

Oxidizer; 84480

Mono propellant; 15,000

Electric charge capacity; 80205

crew capacity; 3

Engines; 28 LV-NB Atomic rocket motor (large Nuclear rocket, 150 max power, 800 ISP 5 tons)

I am sure i will have some difficulty getting it into space, but I will manage somehow. at the moment one thing I am debating is whether to stay as this, a fuel station time, or trim down most of the fuel and go as minimal as possible.

[capi3101]

Hmm...I'd humbly suggest chunking that up a little (i.e. build a drive stage and a separate supply stage, then dock them together in orbit). My Thunderbolt Superheavy 7 is an interplanetary tug with 25 LV-Ns and I launch it under its own power with eight SRBs to assist. It's only got about 1.5 orange tanks equivalent of fuel and it barely makes orbit (though it does chuck off an X200-32 prior to orbital insertion). After I refuel it, I then add a couple of fuel stages and finally a payload.

Of course, the only real reason to build something with that much thrust is to push really, really heavy loads...

[vildar87]

yeah I am starting to realize that the size of the ship is rather prohibitive, might try to redesign it to be more efficient. but thanks for all your tips and info guys

[Kulebron]

The calculations seem very wrong. You don't need that much delta-v to get from Laythe to Eloo. The delta-v map lacks shortcuts, and jool system there assumes the most stupid ways: descend to Jool and then climb again to another object. If you orbit Laythe, you already have a very good speed. You'll need only 500-700 m/s to escape both Laythe and Jool, and then it depends on the shot direction: you can either shoot it back to Jool's movement and descend to Kerbin (1000 m/s) or shoot higher and get to Eloo.

To lower orbit from Pol to Bop you also need very low delta v.

[vildar87]

yeah i am realizing that, and so i am redoing my calcs and seeing what i can figure out.

[Blaster]

I actually have a challenge for rocketeers to make a ship that is asymmetric but flies straight - The Caldari Challenge

[Kulebron]

How much asymmetric? If I balance the center of mass to be above the engine, will it be symmetric or not?

[Kasuha]

How much asymmetric? If I balance the center of mass to be above the engine, will it be symmetric or not?

The "center of gravity" and "center of thrust" markers are a bit too coarse to allow good enough balancing. I made a slightly asymmetric ship just yesterday, it looked spot on in VAB but in the air it was pretty hard to keep it on course. We are talking about tenths of degree differences.