Best place to set up a refueling station for interstellar travel?

[Burke112]

Since apparently KSP will include interstellar travel in later versions, I was thinking about setting up a refueling base to act as a stop-off point for interstellar ships. So, in order to reduce the amount of delta-V required to get from the Kerbol system to whatever system(s) will be implemented in future KSP versions, would it be best to set up a refueling station around...

-- Moho, to maximize the Oberth effect by burning close to Kerbol, or...

-- Eeloo, to provide a very high starting orbit (and thus reduce the dV required to leave Kerbol's SOI)

Or would it be better to place it around one of the planets between the two, to provide a combination of the two effects? For example, one could say that Eve might be the best, because you get the second greatest benefit from the Oberth effect, while starting from a slightly higher orbit than Moho. So, which do you think would be the best location for a refueling station/jumping off point -- a planet where the Oberth effect can be maximized, a planet with a high starting orbit, or some combination thereof?

In this case, assume that the method used for interstellar travel is similar to that used for KSP interplanetary travel -- you have to burn all the way to the other star system (in other words, you don't just have to burn to Kerbol escape, then get insta-transported to the other star system via loading screen).

[Sephta]

Where did you get this information? As far as I can read the planned features interstellar travel is not on the agenda. (http://wiki.kerbalspaceprogram.com/wiki/Planned_features)

It is requested quite some time, but it was never confirmed afaik.

Edited June 20, 2013 by Sephta

[UmbralRaptor]

N/A. If star systems are realistically far apart, getting to one in a useful timeframe will require a ÃŽâ€V budget that trivializes interplanetary travel. I suspect that the best place for a fueling station would be near a large resource supply (eg: Kerbin).

[Burke112]

There are actually several times on the forums where the devs have stated that interstellar travel will be a part of KSP at some point. I'll try to post links to the actual threads.

Whether or not such a feature is planned, it would be interesting to know which planet would be the best to place a refueling station around for interstellar travel. Personally, if Squad implemented interstellar travel, a resource gathering system, and a system to actually build things in orbit/on other planets (and not just assemble pre-made pieces with docking nodes), I'd be overjoyed. KSP is already an amazingly fun game; if those features were implemented, it would be downright addicting...

Edit: here's a quote from this (closed) thread -- http://forum.kerbalspaceprogram.com/showthread.php/17209-Interstellar-travel

"Other star systems will be added and they won't be random. The reasoning behind this as stated by HarvesteR is that he wants people to be able to have the ability to share a common achievement. "Hey, I just landed on the 2nd planet in System X!" .. "I remember doing that, it was a blast!""

and

"FTL is planned, the engine is made, it's just no in-game yet, and other systems will be a part of KSP, not just the Kerbol system"

Of course, the devs could change their minds and decide not to implement FTL travel or interstellar travel, due to either not having the time (it seems like they must be pretty busy as-is just working on all of the other improvements that will be made), or issues with lag/time required to get from point A to B. I do hope they actually DO implement interstellar travel, though.

Edited June 20, 2013 by Burke112

[Burke112]

N/A. If star systems are realistically far apart, getting to one in a useful timeframe will require a ÃŽâ€V budget that trivializes interplanetary travel. I suspect that the best place for a fueling station would be near a large resource supply (eg: Kerbin).

Well, whether or not the actual advantage imparted is minimal in comparison to what is required to get to the nearest star system, which planet would require the lowest dV? I guess it could vary -- if the star systems are ridiculously close together, starting from a high orbit would probably be the best, whereas if the stars were reasonably far apart, a low orbit would be better, as the Oberth effect provides a "lasting" benefit to reducing dV use, whereas starting from a high orbit only provides an initial benefit, but nothing beyond that. If the stars were very close (highly unlikely), the initial benefit from starting from a closer location would outweigh the benefit from the Oberth effect, since the trip itself would be too short to fully realize the Oberth effect, but if the stars are placed far apart (much more likely), the benefit from the Oberth effect would outweigh the benefit from starting at an orbit a bit closer to the star. I guess it could be compared to having to walk to a certain location, and being given a choice of either a) starting 750 feet closer to your target than you otherwise would (similar to starting at a high orbit that puts you closer to your target), or being given a bike that tripled your speed. If the target was 1000 feet away, starting 750 feet closer, and thus reducing your traveling distance to one-quarter of its original value, would be a better option, but if you were trying to get to a target ten miles away, the initial boost of 750 feet would be negligible compared to the lasting benefit of traveling at a faster speed.

Of course, I'm nowhere close to being an expert on orbital mechanics, so that's why I'm asking you guys for advice -- after all, I could easily be completely wrong.

[UmbralRaptor]

For the purposes of starting out a journey to another star, I'd go with Dres or Eeloo (Low mass worlds somewhat far out). From there, do a stardive, with a large burn at peristron periastron for the purposes of maximizing my hyperbolic excess velocity. What to do when entering a star system seems like a rather harder problem (aerobrake? Ha!)

Edited June 20, 2013 by UmbralRaptor
I'm not good at Greek.

[Sephta]

Edit: here's a quote from this (closed) thread -- http://forum.kerbalspaceprogram.com/showthread.php/17209-Interstellar-travel

"Other star systems will be added and they won't be random. The reasoning behind this as stated by HarvesteR is that he wants people to be able to have the ability to share a common achievement. "Hey, I just landed on the 2nd planet in System X!" .. "I remember doing that, it was a blast!""

and

"FTL is planned, the engine is made, it's just no in-game yet, and other systems will be a part of KSP, not just the Kerbol system"

I did make a suggestion in that area as well - nevertheless: it's not the case, that we will be flying to that other system. So there is no need to have a base set up... (for game mechanics anyway)

If you'd like to know, where the best place is to set up such a station: in the orbit of the planet with the best infrastructure and most resources - in our case Kerbin. In comparison to the needed dV for interstellar travel any fuel used to go "further out" is wasted. For that distances to point to it and start your engine...

[CaptainKipard]

...with a large burn at peristron ...

For the sake of clarity I think he means periastron, as in "astron"; the greek for "star".

[willow]

For interplanetary burns the most usefull setup is a fuel depot on the edge of the sphere of influence of kerbin. Because it's easily reachable from kerbin (you need to be able to conveniently get to it to refuel it and for IP ships to refuel) and it has low delta-v requirements to get you out to every planet.

So in interstellar travel assuming it works via similar "point and burn" mechanism, the most useful setup would be a fuel depot on the edge of kerbols sphere of influence so you'll require little delta-v to get to interstellar space and can still reach it from within the kerbol system.

[Jod]

I don't know what the FTL engine will be, but it will probably not work with liquid fuel and not be efficient within kerbol SOI to avoid huge balancing issues. Hence - making fuel depots now is shooting blind.

Depending on the stats of FTL drive there are several plausible locations(including Eeloo orbit in case FTL has ungodly weight that I have to drag with me across kerbol system), but I would probably go for Duna orbit. It is at the same inclination as Kerbin, allows aerobraking to save a bit of liquid fuel, has low escape velocity and can easily be resupplied. Even if FTL works only outside kerbol SOI, it is easy to calculate how much you need to slow down before entering the system to end up in Duna orbit. I don't think using a gravity slingshot effect to slow down will be useful, but if it will then Kerbin orbit is the way to go, maybe even Eve.

Jool is a gamble, currently it has too low gravity for a gas giant but if it gets increased(or there will be a larger gas giant in another system) then it will be the planet to go to slingshot some speed down and then aerobrake the rest.

It will heavily rely on resources too. If mining will be implemented then outer rim planets like Eeloo and Jool are the more likely targets. The decision whether to make the station in Kerbol orbit or near the planets should be based on craft fuel reserves, remember that you need to transport fuel to the refueling station too so making a fuel depot that can easily refuel ships but can't be easily refueled itself is still inefficient.

Edited June 20, 2013 by Jod

[Umlüx]

jool would be ideal for a fuelstation. if there ever will be a working FTL drive, chances are high you'll need hydrogen as fuel. you could mine jool for it.

[JelloTickles]

jool would be ideal for a fuelstation. if there ever will be a working FTL drive, chances are high you'll need hydrogen as fuel. you could mine jool for it.

You don't simply "mine" Jool.

[Akalaël]

If ever other stars are implemented,

see the point 12 of this thread.

I gess we will travel to those other stars with FTL.

I'm sad about it but seems the way the dev's are thinking right now.

[UmbralRaptor]

I suppose Jool could be interesting for entering the system, but how much aerobraking would be possible/survivable? Even without reentry heat, the force differences on parts at hundreds (or thousands) of km/s would be... substantial.

For the sake of clarity I think he means periastron, as in "astron"; the greek for "star".

Yep.

[Burke112]

For the purposes of starting out a journey to another star, I'd go with Dres or Eeloo (Low mass worlds somewhat far out). From there, do a stardive, with a large burn at peristron periastron for the purposes of maximizing my hyperbolic excess velocity. What to do when entering a star system seems like a rather harder problem (aerobrake? Ha!)

Do you think you'd be able to set up such a trajectory so you could get a gravity assist from Jool during your eccentric orbit around Kerbol, assuming you started from Eeloo? That would probably help somewhat...

Now, if interplanetary travel was implemented in a 100% realistic manner, where the stars themselves are in orbits, it would be possible to get a massive gravity assist from Kerbol, but due to issues with data usage and lag, I believe they will simply have the stars be at fixed locations (if I remember correctly). Not completely realistic, but then again, compromises have to be made due to the limitations of the users' personal computers.

[Mr Shifty]

It would depend on the distance to the other systems. There is an optimal altitude for interplanetary Hohmann transfers; as you surmise the Oberth effect at low altitudes competes with a gentler gravitational well at higher altitudes, and there is a minimum Hohmann energy altitude (tabluated here for in system transfers.) The same should be true for interstellar transfers, but the optimum altitude will depend on the galactic orbits of and distances to the other stars.

[UmbralRaptor]

Do you think you'd be able to set up such a trajectory so you could get a gravity assist from Jool during your eccentric orbit around Kerbol, assuming you started from Eeloo? That would probably help somewhat...

Just the Oberth Effect.

[Burke112]

Just the Oberth Effect.

Ah. So it wouldn't be possible to get both the Oberth effect and a Jool slingshot? I remember watching one of Scott Manley's videos where he mentioned that you can't utilize both the Oberth effect from Kerbin and a Mun slingshot, but I didn't know if that same principle applied to a Kerbol Oberth effect and a Jool slingshot.

[UmbralRaptor]

Sort of. In principle, you could get both, but the level of precision required is impractical in KSP. And like skipping a Mun slingshot for interplanetary missions, skipping a Jool slingshot for interstellar missions costs comparatively little ÃŽâ€V. (My assumption is that you're burning >>20 km/s at periastron. Possibly hundreds or even thousands of km/s, if we assume new engines.)

[haltux]

-- Moho, to maximize the Oberth effect by burning close to Kerbol, or...

-- Eeloo, to provide a very high starting orbit (and thus reduce the dV required to leave Kerbol's SOI)

Both advantages would be unsignificant, unless you are happy with spending thousands of years travelling.

[Burke112]

Sort of. In principle, you could get both, but the level of precision required is impractical in KSP. And like skipping a Mun slingshot for interplanetary missions, skipping a Jool slingshot for interstellar missions costs comparatively little ÃŽâ€V. (My assumption is that you're burning >>20 km/s at periastron. Possibly hundreds or even thousands of km/s, if we assume new engines.)

If I recall correctly, don't gravity assists become less effective the faster you are traveling when you swing by? Since an interstellar trip would have to start with hundreds or thousands of km/s of velocity, as you said, wouldn't that make the effect almost unnoticeable, even before it is compared to the massive amount of dV required for interstellar travel?

[Mr Shifty]

If I recall correctly, don't gravity assists become less effective the faster you are traveling when you swing by?

Precisely the opposite. The faster you're going, the more effective going a little bit faster is. You can see this when you do long burns. Your apoapsis will change very slowly for about 3/4 of the burn, then start to increase faster and faster near the end. That's the Oberth effect.

[Burke112]

Precisely the opposite. The faster you're going, the more effective going a little bit faster is. You can see this when you do long burns. Your apoapsis will change very slowly for about 3/4 of the burn, then start to increase faster and faster near the end. That's the Oberth effect.

Ah. So I got it switched around -- thanks for clarifying!