Who refuels and where

[Boris_T_Roach]

I'm another with the re-fueling ships sent ahead of the manned probes, and since everything is built in LKO it makes it doddle for launching say 10 days apart for a Jool mission,

But then the fun starts when trying to get a safe orbit about Vall without getting dropped into Jool by Laythe or fired into solar escape orbit by Tycho

Boris

Or smacking into Vall because the PE changed too much when you hit the SOI and the project PE did not match to the actual PE

[Aragosnat]

Yeah. I know I could do Minmus for a decent fuel depo. But, without the Kethane mod which I don't want to use do to I want to keep my mod use small. Makes such a benifit not that worth while as I would like to just spend time on designing the ships and sending them off to find their dooms. So basicly refuel while in lowish Kerbin Orbit and at the target destionation. That is if it is not a one way ticket to their doom.

[Moon Goddess]

What I've been doing lately is the first transfer window to my destination say Duna, I send a big fuel tank, while it's on the way we prepare the manned duna mission. That way when we're ready to return, simply dock to the return fuel.

[hotmailcompany52]

Well, I usually have a refuel spot at the destination after a few visits and one orbiting Kerbin as part of my orbital ship yard.

[Scotius]

I do a bit of everything. I have big station in LKO, with plenty of fuel and numerous docking ports. I also have one or two orbital tankers (1 Jumbo, big mono tank, some xenon in case a probe will need a drink ) in LKO ready to refuel any craft in trouble. I keep kethane miner in munar orbit so i can easily refuel my ships there, or carry fuel to main station. If i'm sending kerballed interplanetary mission somewhere i make sure there is long range tanker on standby. Duna and Jool sooner or later get their own fuel depot of modest size, plus kethane miner to keep tanks filled.

[AllenM3]

Maybe I do not understand orbital mechanics very well, but why dive down to Kerbin Pe to do your Hoffman transfer? Can't you just do that from Mun or Minimus and use the sum of your orbital speed over them plus their orbital speed over Kerbin to give you a boost to other planets?

If you are in Kerbin orbit 100km Pe x 100km Ap with a full tank its going to take quite a bit of fuel to make a kerbin escape orbit.

But lets say to head out to minimus, refueled via a fuel station then make your orbit Pe around 80km off of kerbin.

Then you roughly have a spacecraft with a full tank of fuel with a orbit of 80km Pe x 47,000km Ap. When you burn at Perikee you are taking advantage of the Oberth effect and it takes a tiny bit more fuel to make a kerbin escape orbit. I find this way the most efficient way to make interplanetary transfers from Kerbin cause it leaves you with almost a full tank.

[M5000]

I don't refuel, but I don't see much point in refueling at Mun or Minmus for an interplanetary trip, as I like to launch my missions from as low of an orbit as possible, usually 70Km, to exploit the Oberth effect, which is why stations are to be constructed in the orbital "tier" of 100Km to 750Km to avoid collisions with departing missions, for general purpose, in my space program. That said, I've only thus far sent single-shot missions containing probes or rovers out there so far, as I don't see much point in manned missions in the first place, so I haven't really had the need for refueling anyhow.

Just design your vehicle to be able to perform at least one single MASSIVE burn from one planet to another, say, Eeloo to Moho. Yeah, really big burns.

If you can handle that massive burn, I say the best place to refuel is a moon on the outer orbit of the planet or system you're to explore.

That is, assuming you're a Kethane user like myself. If you happen to have a fuel station dedicated and in orbit, by all means should you use that. However, for Kethane mining..

Coming in to the Jool system? Refuel at Pol or Bop.

Coming in to Duna? Refuel at Ike.

Coming in to Kerbin /from/ somewhere out there? Refuel at Minmus.

Coming in to Eve? Refuel at Gilly.

I would speculate that if you're performing a mission to a place that /doesn't/ have a teeny-tiny super low-grav moon on its outer orbit, the planet will have low enough gravity to make refueling relatively efficient in the first place. As you can see, all those systems I listed above have a small, low, or very low, gravity world on their outer rims. However, for those that don't, for example Dres, Moho, or Eeloo, you would still be able to refuel with similar but not identical, trouble to that you would have on the Mun. I'm actually in the process of planning a grand tour mission that will be set into motion as soon as I can get SSTO spaceplanes down to an art, but the mission route I have planned goes straight from a 70Km orbit, to Jool's system, and actually hits the Mun and Minmus on the way home.

In short, low gravity worlds where returning Kethane from the surface to the orbital refinery (how I would choose to do it) is a trivial task, so that you can maintain peak efficiency.

That's how I'm seeing it.

-M5K

[Geschosskopf]

Then you roughly have a spacecraft with a full tank of fuel with a orbit of 80km Pe x 47,000km Ap. When you burn at Perikee you are taking advantage of the Oberth effect and it takes a tiny bit more fuel to make a kerbin escape orbit. I find this way the most efficient way to make interplanetary transfers from Kerbin cause it leaves you with almost a full tank.

I disagree that using Minmus as a refueling base is at all efficient. Sure, if you only consider the 1 interplanetary ship you're transferring, then yes, topping off at Minmus will save you about 400-500m/s on average doing the transfer burn. But that's chump change. You also have to consider the delta-V costs of the infrastructure that makes this possible. And that's where the 2nd Law of Thermodynamics bites you on the but.

Take a look at the Delta-V Map. It takes about 5500m/s to achieve Minmus orbit. Thus, if you're just sending stock tanks up to Minmus, you've got that plus maybe a few hundred more to rendezvous with the interplanetary ship. So call it an even 6000m/s to allow for inaccurate burns and such. That's an expenditure of more than 10x what the interplanetary ship "saves" by going to Minmus. And that's each and every time you do it.

It's even worse with Kethane. Due to the mechanics of how Kethane conversion works, the most fuel-efficient system is to have a miner that never moves once landed, a dedicated Kethane ferry, and an orbital refinery. Each of these things has to get to Minmus at 5500m/s each, plus 720m/s for the miner and ferry to land and the ferry to launch again, plus another couple hundred for the ferry to rendezvous with the refinery. So call that 17400m/s as initial cost to set the system up. If that was all there was to it, it would take about 35 interplanetary trips for the savings in transfer delta-V to pay off this sunk cost. But each time the ferry lands, reloads, and comes back, that's another 500-600m/s (including rendezvous), which is a bit more than the "savings" on the transfer of using such a system.

OTOH, if your interplanetary ship stays in LKO, you only have to spend about 4700m/s to send a tanker to it from the ground. And this is all forgetting 1 salient point. If you're able to send heavy fuel tanks or especially a whole Kethane complex to Minmus, you've got launch vehicle design down. You therefore are perfectly capable of launching an interplanetary ship that's got enough delta-V aboard not to need refueling anyway.

EDIT: And note, the supposed savings is bogus anyway. To save 400-500m/s on the transfer burn, you still have to spend 1000m/s to get the interplanetary ship out to Minmus to top it up, plus a bit more to deorbit and get back to Kerbin. So no way around it, going to Minmus costs you fuel over what you'd spend just staying at Kerbin.

Edited September 27, 2013 by Geschosskopf

[Caesar15]

Refueling requires being able to dock...and that is something I have not mastered, even though I have travelled and landed on other planets. It would probably be easier though with the fueling stations I reckon, but what do I know.

[Eric S]

It's even worse with Kethane.

OK, first of all, it's not worth arguing over doing this without Kethane, and I don't think anyone has said it's a good idea if you're not mining kethane.

As for doing it with kethane, you're overlooking a lot here.

First, you're measuring everything in delta-v, which makes sense to an extent for a single craft mission. You're talking multiple launches, probably different size craft, etc, at which point just summing the delta-v is inaccurate to the point of being virtually meaningless. If I lift a 300 ton mining operation in a single lift, the total fuel expended would probably be about the same as if I broke it up into three or four missions, but the summed delta-v is going to be radically different.

Second, you're assuming that your idea of an efficient kethane operation is the same as mine. To be honest, I do my refining on the surface. At the quantities that I mine/refine kethane, the mass of the converter and the solar panels or generator is inconsequential. The fact that you get more mass out of the kethane than you put into it is a minor issue at most, certainly less of an issue than having to launch so many missions to do it your way.

Third, you're assuming that fuel is fuel is fuel. Which for the most part is true now, but when career mode gets a budget, then the fuel you get from Minmus for the cost of infrastructure is going to be far more efficient than the fuel you have to pay for, and then pay for a craft to lift, when you amortize that infrastructure over several missions. For those of us who already play like the budget matters, it's a win now.

Here's how I do it.

Step one: Launch a self-sufficient automated drive section with kethane processing built in. Most of the craft on the launch pad is the processing unit, the craft itself is going to handle it's own circularization and transfer burn.

Step two: Take that craft to Minmus and process fuel.

Step three: Launch the payload on a craft that's just big enough to get the payload to Minmus.

Step four: Pick up the payload with the drive section.

Step five: Use the drive section to take the payload wherever it needs to go.

Step six: The payload section does it's business.

Step seven: Use the drive section to take the payload back to Kerbin.

Step eight: Do just enough of an aerobrake to capture, drop the payload so that it continues to aerobrake and then reenters, and take the drive section back to rendezvous with Minmus.

Step nine: Refuel at minmus.

Step ten: Plan a new mission and repeat steps three through nine until you start feeling that this makes the game TOO easy.

I used the same drive section for 1) a kerbal'ed eve landing/ascent mission. 2) a kerbal'ed Laythe landing/ascent mission. 3) a grand tour, landing everywhere but eve and laythe. 4) another eve landing/ascent mission when I wanted to try it a different way.

If you're only doing a single mission that doesn't involve kethane processing, then yes, the amount of work necessary for the infrastructure isn't going to make up for anything.

EDIT: And note, the supposed savings is bogus anyway. To save 400-500m/s on the transfer burn, you still have to spend 1000m/s to get the interplanetary ship out to Minmus to top it up, plus a bit more to deorbit and get back to Kerbin. So no way around it, going to Minmus costs you fuel over what you'd spend just staying at Kerbin.

And if delta-v is your currency, you're right. I can't imagine a situation where that's really the case though. Just changing the mass of the payload changes the delta-v you get out of the same amount of fuel. Redesigning the craft moving fuel from one stage to another can alter the delta-v of the overall craft even if the fuel stays the same.

[Boris_T_Roach]

Here's how I do it.

Step one: Launch a self-sufficient automated drive section with kethane processing built in. Most of the craft on the launch pad is the processing unit, the craft itself is going to handle it's own circularization and transfer burn.

Step two: Take that craft to Minmus and process fuel.

Step three: Launch the payload on a craft that's just big enough to get the payload to Minmus.

Step four: Pick up the payload with the drive section.

Step five: Use the drive section to take the payload wherever it needs to go.

Step six: The payload section does it's business.

Step seven: Use the drive section to take the payload back to Kerbin.

Step eight: Do just enough of an aerobrake to capture, drop the payload so that it continues to aerobrake and then reenters, and take the drive section back to rendezvous with Minmus.

Step nine: Refuel at minmus.

Step ten: Plan a new mission and repeat steps three through nine until you start feeling that this makes the game TOO easy.

I used the same drive section for 1) a kerbal'ed eve landing/ascent mission. 2) a kerbal'ed Laythe landing/ascent mission. 3) a grand tour, landing everywhere but eve and laythe. 4) another eve landing/ascent mission when I wanted to try it a different way.

If you're only doing a single mission that doesn't involve kethane processing, then yes, the amount of work necessary for the infrastructure isn't going to make up for anything.

And if delta-v is your currency, you're right. I can't imagine a situation where that's really the case though. Just changing the mass of the payload changes the delta-v you get out of the same amount of fuel. Redesigning the craft moving fuel from one stage to another can alter the delta-v of the overall craft even if the fuel stays the same.

I use rather the same system where I can re-use the drive units and/or the whole core ship for any mission

Eg. my SEKI reciever station in solar orbit was driven there by my un manned probe drive section.... which came back to Kerbin to pick up the Eve communications relay , a bit of aero braking and manuvering to get a 130km orbit being cheaper than sending up a whole drive section, the same goes for my manned Jool probes, the same core section that comes back after docking with the Vall lander gets re used for another mission.

The only parts to get dumped usually are the X32 fuel tanks and the fuel tanks and engines of the landers after they get back into orbit.

But then my space program is built along the lines of 'mission to Duna complete..... now what do we do?"

Boris

Current mission : 2nd manned mission to Eeloo. objective : To find out how big an impact crater the first mission made

[Geschosskopf]

First, you're measuring everything in delta-v, which makes sense to an extent for a single craft mission. You're talking multiple launches, probably different size craft, etc, at which point just summing the delta-v is inaccurate to the point of being virtually meaningless. If I lift a 300 ton mining operation in a single lift, the total fuel expended would probably be about the same as if I broke it up into three or four missions, but the summed delta-v is going to be radically different.

Actually, 1 big ship will expend considerably more fuel than the same mass divided into several launches. The more the payload weighs, the slower the rocket accelerates for a given amount of thrust, so the engines have to burn longer to achieve the same final velocity, which means you need proportionally more fuel and/or more engines. This adds more rocket mass for the same size payload, which again increases burn time, and so on in a snowball effect. And all the while your ratio of payload to total mass is shrinking.

If your objective is to save on fuel, therefore, you're better off launching in small pieces. In fact, you're better off doing everything in small pieces. Have an interplanetary flotilla instead of 1 big ship, have each part of the Kethane operation be a separate ship, etc. I've found that doing things this way, for some reason most payloads have a tendency to weigh between 20-30 tons so all can use the same launch vehicle and transfer tugs. Thus, they can all be treated as equals for discussions like this and delta-V is a perfectly useable metric.

Now, if you do things differently, that's fine, but you'll consume more fuel doing it. In any case, though, if your interplanetary payload and your Kethane equipment payloads weigh about the same, you can also use delta-V as the metric.

Second, you're assuming that your idea of an efficient kethane operation is the same as mine. To be honest, I do my refining on the surface. At the quantities that I mine/refine kethane, the mass of the converter and the solar panels or generator is inconsequential. The fact that you get more mass out of the kethane than you put into it is a minor issue at most, certainly less of an issue than having to launch so many missions to do it your way.

If you can fly 1 ship, you can fly a flotilla, especially if just going to Minmus where you can launch them all at your own pace any day you want, avoiding the rush of trying to fit them all into the same launch window.

Now, the overall objective is to save fuel. The Kethane operation's part in this is providing the most net fuel in orbit for the amount of Kethane mined, less the fuel consumed in moving stuff up and down. Refining on the ground provides less fuel in orbit than if you lifted the raw Kethane and refined in orbit, for 2 reasons: the inefficiency in the conversion process and the fact that LOF is heavier than Kethane so requires more fuel to get into orbit than raw Kethane. And the net fuel provided in orbit gets worse if you're also moving the refinery, drill, and their required electrical parts up and down each time, too. Especially if you're having to move multiple orange tanks to fuel some huge, gas-guzzling monster of an interplanetary ship.

Note that I usually don't do Kethane this way myself. I'm just pointing out the most efficient way to do it.

Third, you're assuming that fuel is fuel is fuel. Which for the most part is true now, but when career mode gets a budget, then the fuel you get from Minmus for the cost of infrastructure is going to be far more efficient than the fuel you have to pay for, and then pay for a craft to lift, when you amortize that infrastructure over several missions. For those of us who already play like the budget matters, it's a win now.

If you're not flying small ships, you're not playing like a budget matters . And you're also assuming that we'll be able to use mods in career mode. I rather doubt we will. First, mod parts won't be in the tech tree, as such circumventing the whole raison d'être of career mode. Second, I figure the whole point of career mode is to provide a level playing field, which will eventually lead to player rankings and whatnot.

[regex]

First, mod parts won't be in the tech tree

Off-topic, but that is incorrect, Harvester has already stated that a few empty tech tree leaves were added specifically to cater to mod-makers.

[Geschosskopf]

Off-topic, but that is incorrect, Harvester has already stated that a few empty tech tree leaves were added specifically to cater to mod-makers.

How many is "a few"? For instance, Kethane introduces at least 5 fuel tanks, 2 drills, 2 refiners, 2 scanners, a generator, a jet engine, and the WAITNONOSTOP: at least 14 parts.

In any case, "a few" means "not very many", so the ability to use mods will be sharply curtailed. Think B9 with its 179 or however many parts would fit?

[regex]

How many is "a few"? For instance, Kethane introduces at least 5 fuel tanks, 2 drills, 2 refiners, 2 scanners, a generator, a jet engine, and the WAITNONOSTOP: at least 14 parts.

In any case, "a few" means "not very many", so the ability to use mods will be sharply curtailed. Think B9 with its 179 or however many parts would fit?

What's wrong with adding parts to an existing tech tree leaf? It's not like they're going to get over-crowded... Anyway, sorry for straying off-topic but mod parts are most definitely going to able to slide into career mode.

E: just look how many parts are already in the game, it's not like SQUAD is going to shoot themselves in the foot and not ever add any more parts.

E2: It's also been stated that there are a bit less than 50 tech tree nodes, including a few empties, and probably including future tech that don't have parts yet.

Edited September 27, 2013 by regex

[Hodo]

I rarely refuel at all.

The reason is I like making SSTO's, and it kinda goes against my playstyle to refuel them with fuel dragged up by non-reusable spacecraft.

I've thought about bringing 2 of my bigger SSTO's into Kerbin orbit and then using one to refuel the other, but my plane already has enough range to get to Eeloo and back. It seems like a bit of a cop-out to start refueling when I'm pretty close to building an SSTO that can return from pretty much everywhere except Moho Eve and Tylo.

I use SSTOs, but mainly as cargo haulers. As I have yet made a rocket that can haul as much as my Spaceplane SSTOs into orbit. But if I want to go to another world, it is easier for me to launch all the things I don't want to pack in the space plane due to issues with the game mechanics. (Landing legs lowering while in the cargo bay when I raise the gear on the space plane.) So for my landers I usually launch them up on the end of a rocket, and dock them with my station, and then send up the space plane, and dock it at the station and refuel it while I am there, then head to where ever I want to go.

My space planes are my every use craft, unless its just launching light weight parts to orbit I use my SSTO space planes.

[Spatzimaus]

I've got three space stations orbiting Kerbin, full of fuel. These are just straight depots, no refineries, refueled by vessels launched from Kerbin.

I've got three depots (consisting of a 400-ton tanker and a 50-ton lander with kethane refinery for on-site refills) around Mun, and another three around Minmus. These are generally older models, since those moons were my test sites, but are still perfectly capable of refilling outbound vessels. They also help with INBOUND vessels (I've had ships re-enter Kerbin's SOI without enough fuel to safely land back home), as well as pass-throughs. When I did my Grand Tour, my ship needed to go from Eeloo down to Eve, so it stopped at Mun for a refill on the way.

I've got another depot around Duna, with the tanker in low Duna orbit and the lander around Ike. Likewise, I've got a depot around Eve with its lander around Gilly. These make interplanetary trips fairly easy, since you'll have plenty of ways to refill. The 50-ton landers still have more than enough fuel to fill my usual vessels, so I use them as recovery vessels (flying to meet ships that can't make it to where the tankers are).

And finally, I've got two Tankers in the Jool system; one is between the outer two moons, with its lander orbiting Pol (where it refuels), and the other's near the inner Jool moons with its lander currently around Vall. I've actually got a third depot around Jool, but its tanker is currently stranded far in the outer system and the lander goes wherever I need emergency fuel (generally Laythe).

Most interplanetary missions require just one refueling, before returning, with spaceplanes requiring an additional refill in LKO before departing. Yes, it's possible to make designs that don't need any refueling at all, but those stripped-down designs just aren't as FUN.

[Eric S]

Actually, 1 big ship will expend considerably more fuel than the same mass divided into several launches. The more the payload weighs, the slower the rocket accelerates for a given amount of thrust

Why would you have the same amount of thrust? My large rockets tend to have similar TWR and payload percentages compared to my smaller ones (once they're large enough to use mainsails that is). The only time I've got a lower TWR is if the payload is fragile.

Now, the overall objective is to save fuel.

No, that's your goal, not mine. Mine is to minimize the cost of the operation. Since we don't have maintenance costs, the cost of a kethane mining operation amortized over it's lifetime does nothing but go down as you get more use out of it.

Note that I usually don't do Kethane this way myself. I'm just pointing out the most efficient way to do it.

True, but I don't think the difference is that great. You gain 3% on liquid fuel conversion, and the large converter weighs 4 tons, which is a drop in the bucket on a large kethane processing rig. An all-in-one kethane processing vehicle saves you a docking operation, though I'll admit that's more an issue of convenience/time than fuel.

If you're not flying small ships, you're not playing like a budget matters . And you're also assuming that we'll be able to use mods in career mode. I rather doubt we will.

If you're lifting a payload with an interplanetary transfer stage that either goes somewhere other than Eve/Duna or returns, and I'm lifting a payload without an interplanetary transfer stage, my launches will be smaller, so sooner or later, I'll not only catch up with you, but pass you. The large ship is a one time cost, which just like a general kethane mining operation, the amortized cost approaches zero per mission as you use it for more missions.

As for career mode, as others have pointed out, we already know that mods can work in career mode, and just the stock game won't work if they limit the tech tree to one part per node, as the number of nodes that they've discussed are fewer than the number of parts in just the stock game.

All that said, I'm not saying you're wrong, but more that you're evaluating this from a different point of view. I'm pretty sure that we both agree on the following:

If you're not using kethane, none of this makes sense. If you need to refuel, you'll do at some point along your trip where you're going to stop anyway, at which point LKO is much more likely than Minmus.

If you're doing this for a single mission and that mission doesn't involve taking a kethane processing rig with you, it's just adding a lot of parts and work. You need to use something like this over multiple missions (or in the case of a mobile refinery, multiple places within a single mission) for it to be of benefit.

And to get back to the point of the OPs question, while it can be a fuel-lifted-from-kerbin saving maneuver, you'd doing it more because Minmus is where you get your kethane than because of the savings of the one specific maneuver.