Fuel to orbital station

[Spingitore]

Hello, this is my first post, so please be nice to a noob

I am on my first career in KPS (well actually my first anything at KPS in general) and I've been able to get to both the Mun and Minmus. Next planned step is a round trip to Duna, but the next transfer window is 230 Kerbal days from present time. So I decided to try and build some orbital stations in the meantime, to fully explore the two Kerbin moons and maximize midgame science.

The question is: what is the most efficient way to bring fuel to the orbital stations? I read somewhere that is better to send big empty tanks and make multiple flights with small tanks to fill the big ones. I made some calcuations, though, and noticed that in many cases (i.e. same brand) there is no difference in the full/empty ratio for liquid fuel tanks. So what's the point of sending many small filled tanks in different flights instead of a minor number of flights with big filled tanks? Consider I can only send FL-T and Rockomax with my present science level...

Second question: since I planned to build orbital stations orbiting both moons, either for the fun of it and to help with ground exploration, is it worth to build an additional 'starting' orbital station over Kerbin?

Thanks

[Scanyland]

I don't think there is a best way to do it but what I like to do is load up the largest tank I can and get it to the station, I always find that the worst case scenario is that I have to tap into the fuel supply if I don't have enough to finish the journey. Then what I do is when send another mission I try to send it with extra fuel and transfer the extra to the station. I would also recommend building a station in orbit of kerbin just to get the hang a building one and to get a technique and design scheme you like.

[FancyMouse]

Welcome to the forum!

You're right. With all fuel coming from launchpad, it really doesn't save anything. Staying up empty is mostly when your fuel source is not from KSC - for example drilling and ISRU. That's when you can reuse your fuel tank, refill the tank with fuel coming from other planet/moon, and then continue the journey. To send fuel to LKO, my preferred way is to drill from Minmus and then send it back via aerobraking. It's going to take a while, but a single roundtrip carries most of the fuel to station.

For LKO space station - it really depends on what you want to do. Having a spare station in orbit never hurts, but I find my LKO station quite useful - one of its primary usage is to refill my SSTO spaceplane so that it can go further. It also has grabbed some asteroids so that my tourists, when going to the station, can see something special without going too far.

[AeroGav]

As well as ISRU, orbital fuel depots are useful because we always build a bit of extra fuel into our designs, therefore most of the time when returning from space we've got a bit of spare fuel left.   If you can be bothered to offload that to the fuel depot before re-entry, you can soon build up quite a stash -.

[Spingitore]

Thanks to both of you for the quick replies.

I don't have the science to drill (actually I wasn't even aware that is possible to 'harvest' fuel out of Kerbin), so that wasn't in my mind, at least for the moment. The reason I wanted to build the stations was: for the moons, to have a refueling station, so that I could use the lander multiple times without the need to get back to Kerbin every time (also adding a science lab); for the one in LKO: to use it as an intermediate place to grab a fuel tank and make moons orbital costruction easier (i.e. adding a lot of DeltaV without the need to launch it fro KSC).

I am pretty sure the ones I planned for the moons are worth it, just not sure it is worth it the one in LKO, at least for the use I described... Maybe it is just easier to send everthing directly from KSC?

[Magzimum]

The reason people may send an empty tank up first and then fill that with smaller tanks is that they may (1) not be comfortable flying large rockets or (2) have a default launcher which works really well but is too small for the big tanks, or (3) they enjoy repetitive work. Assuming you can launch the big tank as efficiently as the small ones, there is no bonus. In fact, the net effect is that your total launch mass has increased by the dry mass of those small tanks.

21 minutes ago, AeroGav said:

[...], orbital fuel depots are useful because we always build a bit of extra fuel into our designs, therefore most of the time when returning from space we've got a bit of spare fuel left.   If you can be bothered to offload that to the fuel depot before re-entry, you can soon build up quite a stash -.

Awesome idea. Gonna build that immediately! I often come home with spare fuel in the tanks... and I am about to launch a big over-dimensioned mission.

 

[Spingitore]

Actually I feel more comfortable with big rockets than smaller ones . Probably because I have spent quite a few time balancing and learning to pilot the ones for a round trip to the Mun. Usually a central body with a couple of Rockomax X200-32, sorrounded by 8 Kickback solid fuel boosters . Well that's what I intend for 'big' right now... I guess that may be VERY relative...

[Spingitore]

"Scanyland--I don't think there is a best way to do it but what I like to do is load up the largest tank I can and get it to the station, I always find that the worst case scenario is that I have to tap into the fuel supply if I don't have enough to finish the journey. Then what I do is when send another mission I try to send it with extra fuel and transfer the extra to the station. I would also recommend building a station in orbit of kerbin just to get the hang a building one and to get a technique and design scheme you like."

Ok then I will first for the LKO space station, at least for the sake of training, if anything, and, as suggested by you and Aerogav, to rescue fuel from other missions.

Edited January 2, 2017 by Spingitore
Forgot the quote

[Carl]

Also depending on where you are in your career you can be running into limits in terms of getting enough payload up on a single launch. Try building a design that can get 120 tons to orbit without using any of the 160 science techs, not easy, (in fact i gave up and rushed mainsails and twin boars).

[Spingitore]

16 minutes ago, Carl said:

Also depending on where you are in your career you can be running into limits in terms of getting enough payload up on a single launch. Try building a design that can get 120 tons to orbit without using any of the 160 science techs, not easy, (in fact i gave up and rushed mainsails and twin boars).

I've completed about half of the 160 techs. The heaviest rocket I've successfully launched (to land on the Mun and back) is roughly 260 tons, fuel and engines included. I hope you don't mean 120 tons of 'tools', in that case not even in my wettest dreams 

[HebaruSan]

Unrelated to your actual question...

6 hours ago, Spingitore said:

Next planned step is a round trip to Duna, but the next transfer window is 230 Kerbal days from present time. So I decided to try and build some orbital stations in the meantime, to fully explore the two Kerbin moons and maximize midgame science.

My advice is to not scrape all the science you can out of Mun and Minmus. Your original ambition to go to Duna will be more exciting and interesting than doing the same things over and over. And unless you're prepared to time warp for long periods, you risk never actually getting to Duna (or any other new planet!); you will never find 1380 hours of real-time stuff to occupy yourself until the window comes around naturally, and the game tends to feel "done" once you finish the tech tree (which Mun and Minmus can do).

Making orbital stations is tremendous fun, so by all means go for that. But once you've had your fill, consider time warping to your Duna window. It can feel weird to some of us to do "nothing" for that long. But it's also weird that Kerbals are able to design, build, and launch huge, complex ships instantaneously and have them work flawlessly on the first try. If you told NASA they only had 230 days to launch a manned Mars mission, they'd panic and tell you it's fifteen years too late to plan anything. So you can role-play that they spend the next 230 days designing the Duna ship and working out all the kinks.

 

Edited January 2, 2017 by HebaruSan

[Carl]

Quote

2 hours ago, Carl said:

Also depending on where you are in your career you can be running into limits in terms of getting enough payload up on a single launch. Try building a design that can get 120 tons to orbit without using any of the 160 science techs, not easy, (in fact i gave up and rushed mainsails and twin boars).

I've completed about half of the 160 techs. The heaviest rocket I've successfully launched (to land on the Mun and back) is roughly 260 tons, fuel and engines included. I hope you don't mean 120 tons of 'tools', in that case not even in my wettest dreams

I mean 120 tons delivered to orbit after lifter burn out. Takes a nearly 1400 ton at launch rocket to do it. But i had 160 techs to do that. heaviest before that was 91 tons to orbit, you can find that here (spacecraft exchange thread with pics and craft file).

Edited January 2, 2017 by Carl

[Spingitore]

2 hours ago, HebaruSan said:

Unrelated to your actual question...

My advice is to not scrape all the science you can out of Mun and Minmus. Your original ambition to go to Duna will be more exciting and interesting than doing the same things over and over. And unless you're prepared to time warp for long periods, you risk never actually getting to Duna (or any other new planet!); you will never find 1380 hours of real-time stuff to occupy yourself until the window comes around naturally, and the game tends to feel "done" once you finish the tech tree (which Mun and Minmus can do).

Making orbital stations is tremendous fun, so by all means go for that. But once you've had your fill, consider time warping to your Duna window. It can feel weird to some of us to do "nothing" for that long. But it's also weird that Kerbals are able to design, build, and launch huge, complex ships instantaneously and have them work flawlessly on the first try. If you told NASA they only had 230 days to launch a manned Mars mission, they'd panic and tell you it's fifteen years too late to plan anything. So you can role-play that they spend the next 230 days designing the Duna ship and working out all the kinks.

 

In my ideal world, the entire humanity should be enslaved for the only purpose of advancement of science, with exploration as the main practical goal. This means that, as of today, at least a billion people would be working 16-18 hours per day with the only final aim of explore, exploit and colonize the Solar System. 230 days to get to Mars would be overwhelmingly enough, also considering that the preservation of human life and health of astronauts would be number 2139485902375 in the list of worries. I would say, given these conditions, that not 230, but  more than 23 days to prepare and launch a spaceship to Mars would be considered high treason and sentenced with death.

Back to the real word(?), I will take your suggestion, meaning that building 2-3 orbital stations, starting from scratch, and not following any tutorial (I like trial and error) will be quite challenging and time consuming, even in Kerbal time, and possibly I will not have either the time and more importantly the will to grind much science on the moons thereafter. Also consider that one of the aims of building those stations was to minimize the repetition of science missions to Mun and Minmus.

1 hour ago, Carl said:

I mean 120 tons delivered to orbit after lifter burn out. Takes a nearly 1400 ton at launch rocket to do it. But i had 160 techs to do that. heaviest before that was 91 tons to orbit, you can find that here (spacecraft exchange thread with pics and craft file).

 Ok I was afraid you would say that. No actually I've never even thought of sending up such huge tonnages, as I always tried to design and build the smallest and lightest ship able to do the desired job. I can't even figure out what to do with such a huge spaceship right now (don't want to open the link because I'm trying to take my own path, however wrong and limited it may be, at least for now) 

[Carl]

Eh don't worry, it's a tourist shipping design, meant to send 22 tourist on mun tours or deliver them plus fuel to an orbital station for landings. Thats why it's so big, 5 hitchhikers and a command pod. Probably very different from what your building.

[Srpadget]

You're asking what's most "efficient".  From the rest of the discussion in your post, I assume that by "efficient" you mean either "most fuel delivered to station per ton of vehicle on the launch pad" or "most fuel delivered to station per Funds spend on launch".  I would respectfully suggest that this may not be the most relevant measure of efficiency.  If you pick and choose contracts well, cash is ridiculously abundant in KSP, and if you are reasonably proficient at craft design and piloting, mass fractions to orbit are pretty respectable even without spaceplanes.

So I would suggest that the most "efficient" design is the one that gives you the most FUN PER HOUR OF PLAYING TIME.  So, if your idea of a fun time is flying lots of fuel resupply missions in Kerbin local space, then the best design for you will be a relatively small vehicle that requires several missions to completely refill your station's storage tanks.  But since you are talking about going to Duna, it seems to me that you are signaling "I think interplanetary exploration would be fun".  Thus, the appropriate definition of "efficient" would seem to me to be "whatever it takes to completely refuel your space station in ONE LAUNCH"... so that you can dispose of the "boring" refueling mission quickly, and get on with interplanetary exploration.

And if that's the case, the "most efficient" approach is to go big.  Because lots of little refueling missions just eats playing time, and delays your next major goal, which is going to Duna.

[GoSlash27]

In general, big launchers are more economical than small launchers, both in playing time and $/ tonne. The only reason I can think of to go with multiple smaller launch vehicles is if you don't have the tech, upgrades, or cash for a single big launch.

 Best,
-Slashy

An alternative to Carl's suggestion:

The large "CheepLifter" does 140 tonnes very economically.

Best,
-Slashy

[Wanderfound]

This is likely beyond your abilities at the moment, but if you can pull it off: SSTO spaceplane tanker. Get one of those up and running, and you can deliver fuel to orbit for less than √1/unit.