Fuel Lift concepts

[Jouni]

When speaking about efficiency, many people often forget that the most expensive resource in KSP is player time. The longer it takes to build something, the less efficient the result is. As a result, standardized lifters are always more efficient than (but perhaps not as interesting as) lifters customized for the payload.

The second most expensive resource, especially for us with older computers, is part count. The more parts you need to achieve something, the more lag you will experience. With too much lag, flying a ship can become hard and annoying.

Fuel, on the other hand, is just a number. It has no intrinsic value, so it's real price is based on the player time, part count, and other real resources needed to get it where it is required. On launchpad, fuel is really cheap. At LKO, it's still quite cheap. Near Jool, fuel can be really expensive, unless you are using kethane or something similar.

So when speaking about fuel efficiency, the first question should always be, whether the mission can be completed at all with the design at hand. If not, then you'll definitely need something more efficient.

Then comes the margin of error. With less margin of error, you have to plan the mission more carefully, which naturally requires time, and the risk of failure increases. Failures have their price too. If you fail to get a fuel tanker to its destination, you'll have to launch another, possibly changing the design before launch. On the other hand, failed interplanetary missions may require expensive rescue operations.

The third question in fuel efficiency is the need for refueling. Planning and executing refueling operations takes time, but it can also reduce the time required for planning the main mission. The opportunity for refueling during the mission can reduce the risks associated with the mission. On the other hand, the risks can also increase, depending on player skills, as the mission becomes more complex.

So if we want to talk about fuel efficiency, it's better to talk about mission efficiency instead of some arbitrary goals.

[Duxwing]

Why is your station at 600km? Craft there lose the Oberth effect, and every launch thereto requires more dV than a launch to LKO.

-Duxwing

[Jouni]

Why is your station at 600km? Craft there lose the Oberth effect, and every launch thereto requires more dV than a launch to LKO.

Interplanetary launches from a 600 km orbit are generally more efficient than from lower orbits. You lose some Oberth, but you save fuel by being closer to Kerbin escape. Compared to a 100 km orbit, Eve and Duna are cheaper to reach from a 600 km orbit, while the rest of the planets are borderline cases.

In general, it's always cheaper to reach Eve and Duna after refueling at a high orbit than from a low orbit. For the rest of the planets, high orbits are worse than low orbits, but 600 km still counts as a low orbit.

[Himynameisjake]

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Got annoyed with the design I sent you, so here's a much better one.

http://www.fileswap.com/dl/ZEvWWBV6Qz/

Caution, it is a framerate hog, with almost 1500 parts without a payload, this means that (at least on my computer) the first couple stages are a no-go for physics warp. The file I linked here includes a 7 Jumbo tank with asparagus style staging. With that payload it has a whopping 4838 atmo and 5701 vacuum delta-v, you can get the 254T payload to an orbit of 620km without touching the fuel in the payload. It has flight controls (RCS and SAS*6), 6k Battery life and 6 RTG's to keep you powered up until forever. It's also so stable I just launch it from the platform, no Launch Stability Enhancers. Some of the strutting could be prettier, but that's as nice as I'm making it tonight. The center booster is set to 25% thrust limit and has its own RCS pack because it has a tendency to flail about when it pushes that big of a load by itself. The Mainsails are separated from the tanks by an octagonal strut to allow them to cool properly, meaning you never have to reduce thrust on any of the other engines. Zero fails thus far, lifting much more than you were originally looking for.

Edited March 9, 2014 by Himynameisjake
Much improved ship design.

[Himynameisjake]

Bonus shot, any particular place you want your five full jumbo tanks sent op? That wasn't even being as efficient as I could have been, and timed right, you could send 5 tanks almost anywhere.

[Duxwing]

Interplanetary launches from a 600 km orbit are generally more efficient than from lower orbits. You lose some Oberth, but you save fuel by being closer to Kerbin escape. Compared to a 100 km orbit, Eve and Duna are cheaper to reach from a 600 km orbit, while the rest of the planets are borderline cases.

May I see how you calculated the dV? I want to learn!

In general, it's always cheaper to reach Eve and Duna after refueling at a high orbit than from a low orbit. For the rest of the planets, high orbits are worse than low orbits, but 600 km still counts as a low orbit.

Could putting your fuel dump a sneeze from Kerbin escape and letting your crew cabin desperately aerobrake to Kerbin on inbound flights further reduce your interplanetary crafts' necessary size?

-Duxwing

[Camacha]

When speaking about efficiency, many people often forget that the most expensive resource in KSP is player time. The longer it takes to build something, the less efficient the result is. As a result, standardized lifters are always more efficient than (but perhaps not as interesting as) lifters customized for the payload.

Seeing as I do not get paid to play KSP, that does not matter at all. For me, the fun of KSP is actually figuring out how I can do something the most efficient way - just like in real life. Just slapping on boosters and engines is only fun the first time, when engineering decisions come into play things become interesting. Trying to match realistic goals is not arbitrary at all - while the lack of specific game mechanics are.

Talking about player time, I have just spent months developing just proper vertical thrust control in kOS - and I love it I do not care that it is a slow process or has taken longer than doing 50 missions by hand, I can fly them to perfection with my own software now.

[Jouni]

Seeing as I do not get paid to play KSP, that does not matter at all. For me, the fun of KSP is actually figuring out how I can do something the most efficient way - just like in real life. Just slapping on boosters and engines is only fun the first time, when engineering decisions come into play things become interesting. Trying to match realistic goals is not arbitrary at all - while the lack of specific game mechanics are.

Fun is one thing, efficiency is another. Nothing in this world is free, because every action has at least opportunity cost. If you choose to play KSP, you can't use that time to do other things.

Fuel efficiency is currently an arbitrary goal, because fuel has no in-game cost. The only relevant cost is the player effort required to get the fuel where it is needed. This has some strange consequences. For example, the bigger ships you use, the cheaper fuel becomes.

[psyper]

that's a nice concept you have there psyper even if it doesn't quite solve my problem. I haven't played around with kethane mining as I'm still pretty new to Kerbal but I might use this technique for my next station.

How do you setup auto-fuel transfer, can you do that without any mods? Manually refueling can get quite annoying with several tanks, a way to automate it would help alot

unfortunately its a mod - http://kerbalspaceprogram.com/goodspeed-automatic-pump/

I lifted up the middle section first and then had a lifter which was able to lift 4 empty tanks each time - it had a little bit of fuel left over which I drained in to the tanks as I dropped them off - I could probably fill up the rest of the tanks once its completed by sending up the lifter without a payload and just draining the remaining fuel in to the station. - not sure how many lifts that would take!! If you need the craft files let me know.

[Jouni]

May I see how you calculated the dV? I want to learn!

I'm just using the Launch Window Planner.

Could putting your fuel dump a sneeze from Kerbin escape and letting your crew cabin desperately aerobrake to Kerbin on inbound flights further reduce your interplanetary crafts' necessary size?

People have different opinions on where the refueling station should be. I used to have a station orbiting Minmus, but when I started having multiple simultaneous interplanetary missions going on, sending everything to Minmus for refueling would have been dull and repetitive. Now I refuel small ships at my LKO stations, while larger ships wait for the nearest fuel tanker or kethane miner.

[milosh]

Why is your station at 600km? Craft there lose the Oberth effect, and every launch thereto requires more dV than a launch to LKO.

The station is the starting point for my interplanetary colonization efforts. Although Jouni gave a good and correct physical explaination, my real reason was KSP limit in warp speed below 600km orbit. Depending on which planet I want to reach I need to warp through several years for an optimal transfer - doing that without maximum warp speed is not a fun thing to do

@Himynameisjake: I really like how thoughtfull you have structured your lifter as seen on your last pic, now that's a clean design and not cheap-strutted as mine on Page 2 - I will certainly take this as an inspiration for improving my lifter Only missing thing: the tanks should be able to manoveur by themselfs, as each of them needs to dock on a docking port at my station and they should also each cary an RCS tank for refueling my ships RCS tanks. That's someting I'd have to consider when adapting your structure.

[wilt57]

You have to remember to include the fuel burned to lift the re-fueling fuel from 80 km to 600 km. It's the cost of the entire space program, not just any individual ship.

[FREEFALL1984]

Jets, Jets and more Jets, have a single turbojet attached to the bottom of a single FLT100 and a single radial intake attached to the "outside" then fix these with TT-70 couplers to the outside of your rocket, each of these "modules" can lift a shade under 20 tonnes at peak airflow. Use these to either increase the efficiency of your main rocket or to deadlift it half way into orbit, once your airflow is too weak to maintain any reasonable acceleration or once you're concerned about flameouts should happen around 15000m (depending on your T/W and drag) throttle back a little then jettison the turbojet modules and ignite your main boosters, but you NEED to be travelling vertically when this happens because your turbojet modules will fly off in all directions thankfully the careful placement of the radial intakes forces them away from you. Then as soon as you are clear of the debris, starts a steep gravity turn. Your basically raising your launchpad up to 15km, meaning you're not wasting your main fuel reserves on atmosphere Of course the drawback is the effect this has on part count, for 180t of orange tanks you'd need at least 10 jet modules just to get just your cargo of the ground, assuming a 700t lifter and your looking at 880t of total deadlift which makes 44 of these jet modules, each requiring 4 parts and now you've made and additional 176 parts... Which on top of your main rocket is enough to cripple most computers

My current career mode lifter uses the same principle (only much smaller) with 12 basic jets and allows me to get a lifter comprised of 10 FLT800 tanks and 5 LV-T30s (asparagus) into a stable LKO with almost half of my total fuel remaining and with almost 16 tons of cargo.

[Himynameisjake]

@Himynameisjake: I really like how thoughtfull you have structured your lifter as seen on your last pic, now that's a clean design and not cheap-strutted as mine on Page 2 - I will certainly take this as an inspiration for improving my lifter Only missing thing: the tanks should be able to manoveur by themselfs, as each of them needs to dock on a docking port at my station and they should also each cary an RCS tank for refueling my ships RCS tanks. That's someting I'd have to consider when adapting your structure.

I'll private message you as well, but I wanted to ask here as well in case anyone had anything to add.

Adding a RC-LO1 Remote guidance unit, an ASAS unit, a FL-R1 RCS tank, two clamp-o-tron sr.'s, and twelve RCS thrusters to each tank would not affect the launch parameters in any way for a five tank launch to 600km orbit. I'm not sure you could do seven tanks with all that added to a stable orbit with that lifter, but it would be close. I'll update my craft file to meet your requests and get back to you after I try both designs. Any other requests before I start tinkering? For example, would you like the tanks to have independent thrust production capabilities (engines directly mounted to them) and if so, what are your minimum acceptable parameters for delta-v and TWR?

[Skorpychan]

The station is the starting point for my interplanetary colonization efforts. Although Jouni gave a good and correct physical explaination, my real reason was KSP limit in warp speed below 600km orbit. Depending on which planet I want to reach I need to warp through several years for an optimal transfer - doing that without maximum warp speed is not a fun thing to do

You can always switch to a flag for the timewarp while your mission craft occupies a nice low orbit.

As for the original topic, I've got good mileage out of sending tanks up mostly empty, and topping them up from tankers later. Especially when using one orange tank as payload, and not decoupling the main lifter stage.

Instead, I can simply undock the mainsail I've been using for lift, along with the pancake tank it's attached to. That leaves a docking port on the back end of the craft for further expansion.

[Amaroq]

May I see how you calculated the dV? I want to learn!

I installed Kerbal Engineer Redux mod.