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The fuel highway rough idea (edit: more like hub)


M_Rat13

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So, we all know how difficult traversing the Kerbol system can be. The further you go, the bigger a ship you need. But, what if you could refuel mid flight, all along a journey. Suddenly, ship size would decrease drastically.

Apologies if someone already thought of something like this.

The idea is, to put refuelling platforms on small moons, which would then fly up to meet spacecraft, to refuel them in the moon's orbit. For example:

You want to send a lander to Moho. You deliver it into Kerbin orbit, where a nuclear tug is waiting for it at a refuelling space station also in Kerbin orbit. This one is special becuase it receives it's fuel directly from Kerbin.

Next, you fly to Minmus, where a refuelling rig flies into orbit, filled with mined fuel from Minmus, and feeds the fuel to the tug.

Then, you set a course for Eve. Once in Eve orbit, another refuelling rig, this time from Gilly, comes to greet and refuel you in Eve orbit (as it's easier to do this than intercept Gilly).

Finally, it's off to Moho, and your lander lands, does whatever it needs to, then it's back along the refuel highway with the tug to be delivered back to Kerbin.

Now, in my mind, this could get you as far as Moho, using Gilly, or as far as Dres, using Ike. Jool/Eeloo become the problem, in my mind.

See, with the way orbits work and what each specific moon is like, I don't really know how a refuelling station, as a pathway on to Eeloo or maybe just another Jool moon and back, would be able to work, and I need your help. Granted, you could just build a bigger spacecraft that can work from Ike, but the idea is to not need big spacecraft in the first place, or at least not as big as usual .

So thoughts, ideas, suggestions. Am I a madman? A genius? I really just need feedback to know if I'm on to something, and to see if you can help me overcome hurdles in my plan. I leave the projects fate, in your hands.

Edit: I've started to realize this idea isn't really best as highway, but as a hub with everything in it, fuelled from nearby, with tugs bringing new stuff or new kerbals in, able to refuel for the return journey.

Also, still don't know the best set up for the one in Jool, which would serve all 5 moons at this point

Edited by Starhawk
Added original edit back from dupe thread.
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@M_Rat13 It's an interesting idea, and it's one that would be interesting to play around with. Your ship could indeed be smaller, but perhaps not as much as you might think. Much of the energy required for interplanetary transfers is just the energy spent accelerating out of your starting planet's gravity well. In the case of Kerbin, this would be 1km/s. This plus a bit gets you to Minmus orbit. Now you're currently at 1.3km/s. Getting from there to a Duna transfer can be another 400m/s. Getting into a low Ike orbit is about another 400m/s. Getting from there to a Dres transfer is 1200m/s. Dres is weird. Because it's so small, you need to match velocities with it pretty closely and end up with expensive capture burns. Plus, Dres's orbit is so inclined that you need a lot of Delta-V to match inclinations... Sometimes around 1km/s.

Not counting plane changes, it's another 2.3 kilometers per second to get into an elliptical Jool orbit. From there, transfers to the moons range from 1 to 2 kilometers per second of Delta-V, assuming you don't use gravity assists, which are really easy in the Jool system. In fact, you can practically get anywhere for almost free.

So, if you use the refueling route, the most Delta-V you will need on a single trip is from Dres to elliptical around Jool, at 2.3 kilometers per second plus the plane change, plus getting to whatever moon you want. To be fair, though, Dres is weird, and all things considered, Ike to elliptical Jool orbit is cheaper, at 2 kilometers per second or lower, assuming optimal trajectories are found..

Over your whole trip, including refueling, you would probably be expending 5.6km/s of Delta-V minimum, maybe up to 8 maximum unless you do something crazy, but you will only need 2 at a time.

But, going directly from Low Kerbin Orbit to an elliptical Jool orbit costs about 2.2km/s minus inclination changes, which are usually under 300m/s. Even if you skip Dres, your ship sizes would end up about the same - 2km/s vs 2.2km/s (excluding plane changes).

Is saving 200m/s worth all the time spent waiting for transfer windows, the time spent doing rendezvous and docking, and the mass spent on docking equipment? I'm not sure. If you are doing it for fun, then go ahead, I think it's a cool idea, but if you're looking for maximum time efficiency, I wouldn't bother, as the performance hit going directly from Kerbin to Jool is minimal.

The same should hold true for going inwards to Moho, I think.

 

TL;DR: From an efficiency standpoint it's slightly better than taking a direct route, but your craft won't end up that much bigger than if you had taken the direct route. If you stop at Dres, which is a bit out of the way, your craft may actually need to be bigger than going directly.

 

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1 hour ago, M_Rat13 said:

So, we all know how difficult traversing the Kerbol system can be. The further you go, the bigger a ship you need. But, what if you could refuel mid flight, all along a journey. Suddenly, ship size would decrease drastically.

And mission complexity would increase drastically...

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@Ultimate Steve Obviously, I'm no expert, but the idea is to always take the shortest hop possible.

If Ike to Jool is the cheapest, go that way. Or not if the gain isn't that great. Is it cheaper to get to Moho from Eve or Kerbin or Minmus? These are things to consider, but the 'highway' gives you more options.

Also consider you can refuel on the return journey too, so non refuelling effectively needs double the fuel, sort of, I know it's not exact.

Oh, and I know Eeloo isn't the most sought after destination, but that's why I'm curious about a Jool refuel spot too, however that would work. It might make Eeloo trips that little more desirable. Well, and also allow easier exploration of the Jool moons.

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16 minutes ago, M_Rat13 said:

@Ultimate Steve Obviously, I'm no expert, but the idea is to always take the shortest hop possible.

If Ike to Jool is the cheapest, go that way. Or not if the gain isn't that great. Is it cheaper to get to Moho from Eve or Kerbin or Minmus? These are things to consider, but the 'highway' gives you more options.

Also consider you can refuel on the return journey too, so non refuelling effectively needs double the fuel, sort of, I know it's not exact.

Oh, and I know Eeloo isn't the most sought after destination, but that's why I'm curious about a Jool refuel spot too, however that would work. It might make Eeloo trips that little more desirable. Well, and also allow easier exploration of the Jool moons.

I would recommend refueling equipment at your destination, for operations there and refueling for the return trip, but along the way it would be a bit extra in my opinion. Another thing is waiting for transfer windows... If you went from Jool to Eeloo, the transfer window may only come every several years, which is a lot of waiting even at maximum time warp.

As far as Kerbin to Moho... Moho needs a large plane change burn, even moreso than Dres. It's cheaper to do the plane change maneuver closer to solar apoapsis and more expensive to do it near periapsis. The higher your apoapsis, the cheaper the plane change. Starting at Eve would mean a lower apoapsis, which would necessitate a much larger plane change burn, even optimally, which would most likely outweigh any Delta-V benefit from starting at Eve.

Usually when going to Moho I completely ignore transfer windows and wait until Kerbin is at Moho's descending or ascending node, so I can do the plane change at apoapsis, then reduce periapsis to Moho's orbit, then reduce Apoapsis so that I get an encounter in 1 or 2 orbits.

Don't underestimate Moho. It is probably the most Delta-V intensive planet to get into orbit of.

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What about having a huge refueling ship in orbit around a planet and having small mining ships to create fuel, to keep it infinitely fueled? Having land bases can be difficult and in only one location it can be hard. That's just my idea, I might actually construct one tonight to see the feasibility of it

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5 minutes ago, Ultimate Steve said:

I would recommend refueling equipment at your destination, for operations there and refueling for the return trip, but along the way it would be a bit extra in my opinion. Another thing is waiting for transfer windows... If you went from Jool to Eeloo, the transfer window may only come every several years, which is a lot of waiting even at maximum time warp.

As far as Kerbin to Moho... Moho needs a large plane change burn, even moreso than Dres. It's cheaper to do the plane change maneuver closer to solar apoapsis and more expensive to do it near periapsis. The higher your apoapsis, the cheaper the plane change. Starting at Eve would mean a lower apoapsis, which would necessitate a much larger plane change burn, even optimally, which would most likely outweigh any Delta-V benefit from starting at Eve.

Usually when going to Moho I completely ignore transfer windows and wait until Kerbin is at Moho's descending or ascending node, so I can do the plane change at apoapsis, then reduce periapsis to Moho's orbit, then reduce Apoapsis so that I get an encounter in 1 or 2 orbits.

Don't underestimate Moho. It is probably the most Delta-V intensive planet to get into orbit of.

This is why I need people like you to explain it to me.

Refuelling at your destination also sounds great if you plan to land on Eve or Duna. Landers could stay in orbit at a space station lets say (refuelled from Gilly/Ike), and you just have to bring the Kerbals in to use them, rather than dragging, mainly in Eves case, a massive lander with you every time, that is only single use.

I also think the Jool 'system' still could take massive advantage of a refuel station somewhere, as it makes inter moon travel much easier, and you can just head straight between them if needs be, with a giant space station housing everything, rather than going constantly back and forth between Kerbin, only needing to bring in new equipment or new recruits.

So, if I understand you, Moho, Dres, and Eeloo are a pain regardless, but Eve, Duna, and the Jool 'system' (and Kerbin), can all benefit with refuelling platforms.

Again, I still don't know where to place the stuff for Jool, but I'm now more seeing a hub, rather than just one thing.

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1 minute ago, M_Rat13 said:

So, if I understand you, Moho, Dres, and Eeloo are a pain regardless, but Eve, Duna, and the Jool 'system' (and Kerbin), can all benefit with refuelling platforms.

Generally, everywhere can benefit from refueling platforms to be used for operations at that body and refueling ships for the return journey, but it's rarely beneficial to stop somewhere along the way to a destination to refuel.

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7 minutes ago, The_Cat_In_Space said:

What about having a huge refueling ship in orbit around a planet and having small mining ships to create fuel, to keep it infinitely fueled? Having land bases can be difficult and in only one location it can be hard. That's just my idea, I might actually construct one tonight to see the feasibility of it

Where would you get the fuel from? Unless you make an asteroid ship. Just going to put that idea aside for a moment...

That's why I point to low gravity moons of planets as mining bases. The low gravity allows the mining rigs to meet craft in orbit, either around the moon or the planet. I can even start to see space stations for planet landers, refuelled from these moons.

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Moho is hard, but captures could go below 2km/s if you're targeting the right spot (from a direct shot from Kerbin orbit), most of you went after the Higher Inclination Intersect, logically, you have to turn your closest distance into furthest distance, moreover, there are some Oberth Effect roles that'll kill efficiency, try taking your Moho Periapsis around 10 Km to be safe and go after the Lower Intersect.

Edited by GRS
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2 minutes ago, M_Rat13 said:

Where would you get the fuel from? Unless you make an asteroid ship. Just going to put that idea aside for a moment...

That's why I point to low gravity moons of planets as mining bases. The low gravity allows the mining rigs to meet craft in orbit, either around the moon or the planet. I can even start to see space stations for planet landers, refuelled from these moons.

Yep, that's what I'm planning to do. I will have several mining ships docked to the fuel vessel, have them land, mine ore, convert it, and then go back and transfer it to the fueling vessel for use by other craft. 

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7 minutes ago, Ultimate Steve said:

Generally, everywhere can benefit from refueling platforms to be used for operations at that body and refueling ships for the return journey, but it's rarely beneficial to stop somewhere along the way to a destination to refuel.

Sounds more like a hub network than highway is needed. Still a cool idea.

Imagine. Kerbals take an SSTO to orbit, where they dock at a space station. They then transfer to an interplanetary shuttle, also docked there. This shuttle goes to Minmus, then gets refuelled. Then, it's off to Eve we go. There, the Kerbals dock at another space station, where a refueller has also arrived from Gilly, to fuel up their lander, also docked there. They take the lander down, do whatever they need to, then back up to the space station. The Gilly refueller goes off to refuel the lander again, and the Kerbals take the trip back to Kerbin via Minmus, where they once again board the SSTO, and land at the Kerbal space center.

Convoluted? Probably. But I like it. It feels an efficient use of fuel.

5 minutes ago, The_Cat_In_Space said:

Yep, that's what I'm planning to do. I will have several mining ships docked to the fuel vessel, have them land, mine ore, convert it, and then go back and transfer it to the fueling vessel for use by other craft. 

I see what you mean now. At that point you're having to transport two crafts though, one of which will have to be huge, which is what I'm trying to avoid.

Also I'm sort of disappointed you aren't at least going to be lugging around a giant asteroid...

Actually, how fast is mining equipment? You may have given me another crazy idea...

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20 minutes ago, M_Rat13 said:

Also I'm sort of disappointed you aren't at least going to be lugging around a giant asteroid...

I can always make a frame and put engines on the back and grip it with claws....

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2 minutes ago, The_Cat_In_Space said:

I can always make a frame and put engines on the back and grip it with claws....

See, now I'm just wondering if you can mine fuel faster than you use it, or at least store enough for a burn and refill when not burning.

If so, you effectively have a mobile version of my rough idea, especially if you have multiple.

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Might be an interesting idea just for the fun of it. However, stock KSP doesn't really have a need to move big craft or products around the planets, it's not like a 4X game, so there really is not much if anything to be gained from it.

From a practical point of view it is more useful to learn to make smaller and more efficient craft so that you don't need to refuel a couple of times for a longer trip. 

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Something I like to do a lot is, to send the craft itself up to LKO empty of fuel on a launcher.

This makes the most inefficient part of the trip easier, and then it's a simple matter of using a refueler in LKO to top it off, or just send a second launch with a fuel payload to dock and fill her up.

They say once you are in LKO you are "half way to anywhere" so to me at least, it makes the most sense to refuel there and then head out to your destination. It's also easy and convenient, as setting up infrastructure there is simple and close.

Edited by Rocket In My Pocket
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In my career game I put big mining landers on Ike, Gilly, Mun and Minimus.  In some cases they also carry a lab or something like that to satisfy a mission, but even without that they are very heavy. 

The big convertatron is fast.  It can keep up with 4 big drills going simultaneously.  For this I use the fuel cell array and 2 medium extendable radiators.  Works great on Gilly and Miniums, but on the Mun and Ike it wastes a great deal of fuel to reach orbit, rendezvous, and land again.  So it's worth it to use rovers to fill on the surface and leave the tonnage of ISRU on the surface.  

The little convertatron and little drill I put onboard little vessels to hypothetically refill themselves, but they are actually really bad and take forever.  I never understood the point of big ore tanks.  The small radial ore tank seems the most practical for all fuel making purposes.  The big ore tanks are just for weight lifting competitions.

I don't do giant fuel stations anymore.  Rather re purpose every transfer stage used for real missions, by leaving them in stable orbits with a core, coms, and docking port.

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10 hours ago, Foxster said:

Might be an interesting idea just for the fun of it. However, stock KSP doesn't really have a need to move big craft or products around the planets, it's not like a 4X game, so there really is not much if anything to be gained from it.

From a practical point of view it is more useful to learn to make smaller and more efficient craft so that you don't need to refuel a couple of times for a longer trip. 

I was about to mention landers, that you could refuel from nearby, rather than bringing it back to Kerbin to ditch and building another one (think using Gilly to refuel Eve lander). Then I realized you'd need the lander to be an SSTO....

That'd be interesting on certain planets....

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Refueling can be a benefit for many missions, but to answer your question specifically about mid-flight refueling I'd say that's almost always a bad idea. Let's say you're going to Jool

Going from LKO to a flyby of Jool costs just under 2000DV - you accelerate once and then you coast the rest of the way. Circularizing around Jool costs another 3000DV - you coast in and decelerate one time. You're spending 0 DV during the coast phase.

If you have to "stop" at a refueling station along the way you have to spend DV to match orbits with your fueling station and then spend more DV to accelerate back on course for Jool. This is all wasted DV

There may be some ideal situation where you have a refueling depot in exactly the right place at exactly the right time, but everything in the solar system is moving, so lining that up would be extremely difficult if it's even possible.

 

Edited by Tyko
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44 minutes ago, Atkara said:

@Tyko, I don't think he wants to place refueling infrastructure in interplanetary space. He's talking about hopping from planet to planet.

Other than the benefit of the Oberth Effect, the two are the same.

Is there a mass savings? Yes. Is it worth the effort? Well, that's up to the player.

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