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Joe.L

Launching large fuel tank into orbit

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Posted (edited)

Afternoon all,

 

I am trying to launch a large fuel tank into a LKO to then dock with my space station, however, I am really struggling to do so. I tried to break the fuel tanks down to then dock together at the station but that is causing problems in itself. How do you guys launch heavy stuff into space?

Edited by Joe.L

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Is your problem launching the tank, or docking to the station?

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launching the tank, I just don't seem to have enough fuel to into orbit, then I struggle with balance etc when I add more fuel tanks

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Posted (edited)

I usually use the fuel in the tank on the way up, dock it to the station empty, and then send up a fuel on a tanker either from Kerbin or Minmus.

Edited by RoninFrog

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@Joe.L when i need to launch a fuel tank into orbit i tend to disable the tank from being able to allow fuel flow. I then build a large launcher for it with tons of srb as a first stage lifter. If that sort of thing fails you, you could launch the tank dry and put it into a parking orbit then send multiple refueling missions to it before going onto taking it to a station or making one out of it. Good luck!

 

103705232020

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Posted (edited)

 

10 minutes ago, RoninFrog said:

I usually use the fuel in the tank on the way up, dock it to the station empty, and then send up a fuel on a tanker either from Kerbin or Minmus.

but how do you send that fuel up to refill the empty tank?

Edited by Joe.L

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Posted (edited)
4 minutes ago, Joe.L said:

but how do you send that fuel up to refill the empty tank?

Me?  I usually send a fuel tanker from Minmus or the Mun.  It would probably be less complicated to just send up a great big refueling rocket straight from the launchpad, though.

Edited by RoninFrog

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First we need to know the actual problem you're having, with specifics.

Is the problem that you can't get 3400m/s with a decent launch TWR under the tank?

Or is the problem that you don't know anything that I just said?

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24 minutes ago, Superfluous J said:

First we need to know the actual problem you're having, with specifics.

Is the problem that you can't get 3400m/s with a decent launch TWR under the tank?

Or is the problem that you don't know anything that I just said?

yeah no idea what you mean, i'm trying to now send a smaller fuel tank up but still would want to know how to send a bigger one up there for future reference.

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2 hours ago, Joe.L said:

Afternoon all,

 

I am trying to launch a large fuel tank into a LKO to then dock with my space station, however, I am really struggling to do so. I tried to break the fuel tanks down to then dock together at the station but that is causing problems in itself. How do you guys launch heavy stuff into space?

How big is the fuel tank? I'm usually fine launching a 2.5m tank full, but i've never attempted to try and launch a 3.75 m tank, so I would suggest going with the advice above.

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yeah I can get the small tank into orbit, however I wanted to know if there was a way in which to launch the Kerbodyne_S3-7200_Tank and dock.

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Posted (edited)

Not to sound contrite here, but the flowchart works like this:

Step 1:    Do you have enough fuel?   

     If no, add fuel.

Step 2:    Do you now have enough Thrust to go to space today?

    If no, MOAR BOOSTER.

Step 3:   Goto step 1.

 

Overall, it sounds like you are just building too small of a rocket.    Build a bigger rocket.   Put more engines one it.     Overpower the sucker.  Carry too much fuel.   It's a fuel hauler anyways.    Just dock the whole shebang when it gets there.     Do this a couple times and you'll see how ineffecient that design was, and you'll start refining it down to exactly what you need.

Go big or stay home.

Oh, and the thread has been moved to gameplay Questions. 

Edited by Gargamel

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so just go as big as possible with as much engines as possible?

6 minutes ago, Gargamel said:

Not to sound contrite here, but the flowchart works like this:

Step 1:    Do you have enough fuel?   

     If no, add fuel.

Step 2:    Do you now have enough Thrust to go to space today?

    If no, MOAR BOOSTER.

Step 3:   Goto step 1.

 

Overall, it sounds like you are just building too small of a rocket.    Build a bigger rocket.   Put more engines one it.     Overpower the sucker.  Carry too much fuel.   It's a fuel hauler anyways.    Just dock the whole shebang when it gets there.     Do this a couple times and you'll see how ineffecient that design was, and you'll start refining it down to exactly what you need.

Go big or stay home.

Oh, and the thread has been moved to gameplay Questions. 

 

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The trick to launching really heavy stuff is to build a suitably large and powerful rocket. You'll need two key values- TWR, Thrust to Weight Ratio, and delta-V, effectively how much acceleration your rocket has and thus how far it can go.

Delta-V varies depending on your rocket's weight, engine efficiency (ISP) and ambient pressure- more atmospheric pressure = less efficiency and so less thrust from your fuel. To get more delta-V, add more fuel or strap on some extra boosters.

TWR is important mostly in the lower stages when you're launching from the surface- it needs to be above 1 or your rocket simply won't produce enough thrust to overcome gravity, and 1.4 is a good number to aim for.

You can see both of these numbers in the stage list at the right side of the screen in the VAB (and SPH) and there's a toggle to switch between surface and vacuum values. In atmosphere, the air gets in the way and reduces your rockets' power, but powerful lifter engines like the Mammoth and Mainsail are designed to produce lots of power even at sea level to haul your rocket off the launch pad. Vacuum-optimised engines like the Terrier and Poodle are nowhere near as good at sea level, but are more efficient when in space; use those on your upper stages. You'll get less delta-V in atmosphere but you should make sure that your TWR on each stage is above 1 and preferably above 1.2 in surface mode to ensure your rocket will make it into space without wasting fuel. Around 3400m/s of delta-V should be enough to make it into a low (80x80km) orbit of Kerbin, but it never hurt to have a bit more than that in case your launch profile isn't particularly efficient.

The best way to launch a rocket is with a gravity turn- launch straight up until you get some speed up (100m/s should do, but it can be less if you have a lot of thrust to spare) and then start gradually turning to the east to gain orbital velocity. Drag in the atmosphere bleeds delta-V so launching up will reduce that loss, but to stay up you'll need to go sideways to pick up orbital velocity and in the upper atmosphere drag is minimal. Check out the Gravity Turn mod which automates this whole progress, you can learn a lot from watching it try (and occasionally fail) and use that information to improve your own technique and your rocket designs.

To build your rocket, start at the top: what size of fuel tank are you trying to put in orbit? Bigger is better for refueling purposes but if you're just using plain stock parts (no mods or DLCs) then 3.75m is as big as it gets, so try using the second-largest Rockomax 2.5m tank and see how you get on with that. One possible design for a dockable fuel tank would be:

Bottom- Clamp-O-Tron Senior port (2.5m version) > large monopropellant tank with 4x RCS thrusters > 2.5m battery > Rockomax 32 fuel tank with some solar panels in the middle (small deployable or just static would do) > large reaction wheel > large RGU (if you have unlocked it) with 4x RCS thrusters > C7 fuel tank adapter (2.5m to 1.25m) > Clamp-O-Tron port (1.25m version) > nose cone on the top. It should be flyable enough to dock to a space station with either docking port and will also have plenty of fuel in it.

Docking ports can be used as decouplers if you right-click them and select 'enable staging' - you might require advanced tweakables to be switched on in the game settings to see this option - so you can stick the top of your final rocket stage straight onto the larger docking port. For a 2.5m fuel tank of that size, you're probably going to need a Skipper engine to make it into orbit and move it around with any kind of acceleration. Don't forget your reaction wheels, but you can skip the RCS and probe core on the rocket stage.

Your first stage will probably have to be a 3.75m one using a Mammoth engine, with some form of additional boosters on the sides. Useful tip: if using solid boosters, set the radial decouplers to enable crossfeed and stick some fuel tanks on top of the SRBs which will provide extra fuel to the core engine and then dumped when they are empty along with the spent SRBs. Struts are required for heavy rockets with big boosters to stop the boosters wobbling themselves loose and causing destruction and when using additional fuel tanks on top of SRBs, use the move tool to slide the boosters down so that they get jettisoned properly; sepratrons with ~1-2 fuel should be enough to throw them clear if they don't drop away on their own.

The biggest rocket I've ever built is below- it launched 610 tons of fuel tanks into a 150x150km orbit around JNSQ's 2.7x larger Kerbin, requiring over 5000m/s of delta-V. Most of the parts were from Near Future Launch Vehicles which adds 5m and 7.5m fuel tanks, and the whole rocket used 7.5m fuel tanks, with eight(!) strap-on liquid fueled boosters that were each 5m wide and had a combined first stage thrust of 87 meganewtons- that's 87,000kN! Monstrously large, hideously expensive and I can still smell the overheated electronics as my (pretty good) PC struggled to cope, but over 600 tons in one launch!

Spoiler

Behold- the Black Hole!

8iBYGJ4.png

And beside the VAB for scale (you don't want to know how I got it there!)

VKnN8YT.png

(Ignore the magic floating second stage, it's a dodgy shroud on that part)

 

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5 hours ago, Joe.L said:

so just go as big as possible with as much engines as possible?

For your first couple tries, maybe.  But you have a much higher chance of success with too much fuel/power rather than too little.

Follow your Dv Meter and TWr readouts in the editor to make sure you're on the right path.   Others here have already listed the numbers you should be shooting for. 

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On 5/23/2020 at 10:37 AM, Joe.L said:

How do you guys launch heavy stuff into space?

A stock rocket called  Krakatoa.  Built with 88 of the finest parts. 

Spoiler

HLRMGmM.jpg

                                                                

FLIGHT PROFILE:

1.(wait 5s after loading. Physics load cause a small oscilation that may ruin the launch)

2.Launch with SAS on, precision controls mode, Throttle 100%

3.At 42m/s SAS Prograde hold

4.Stage when side boosters run out of fuel.

5.The Core Mammoth will bring it to 2km/s with 74km apoapsis before running out of fuel. Coast.

6.Stage again 15s before apoapsis to circularize, cut the engines just after that.

 

= 6x Kerbodyne S3-14400 plus a MK3 to 3,75m Adapter (444t of LFO) in a 74km x 74km orbit.

 

I don't dock it with my refueling station, it is my refueling station. 

 

On 5/23/2020 at 1:41 PM, Joe.L said:

yeah I can get the small tank into orbit, however I wanted to know if there was a way in which to launch the Kerbodyne_S3-7200_Tank and dock.

 I'd rather design a tanker to send a single Rockomax_Jumbo-64_Fuel_Tank  than a single S3-7200.  IMHO a single S3-7200 its just not big enough to compensate for the added hassle.

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29 minutes ago, Spricigo said:

I'd rather design a tanker to send a single Rockomax_Jumbo-64_Fuel_Tank  than a single S3-7200.  IMHO a single S3-7200 its just not big enough to compensate for the added hassle.

This just reminded me, way back in the mists of time I had ship named OTTO, which stood for "Orange Tank To Orbit." That was back when the only orange tank in the game was the Jumbo-64. It may have even been before 1.0 so it probably wouldn't work anymore, even if I had a copy of the ship which I don't.

But I agree, if you're going to send fuel up make it at least a Jumbo-64.

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12 minutes ago, Superfluous J said:

This just reminded me, way back in the mists of time I had ship named OTTO

Quite popular and iconic concept I guess.

13 minutes ago, Superfluous J said:

But I agree, if you're going to send fuel up make it at least a Jumbo-64.

Well that  was not exactly the point. The S3-7200 carry about11% more fuel. However is an extra large tank, which means using adapters to fit to the large engines. I'd rather stick another large diameter tank or just the conveniently sized single Jumbo-64 for simplicity sake.

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On 5/23/2020 at 9:37 AM, Joe.L said:

Afternoon all,

 

I am trying to launch a large fuel tank into a LKO to then dock with my space station, however, I am really struggling to do so. I tried to break the fuel tanks down to then dock together at the station but that is causing problems in itself. How do you guys launch heavy stuff into space?

The smart guys are gonna want to know your build.  I. E what your stages look like and what rockets you are using. 

 

FWIW - I'm at a mid-high tech atm and have a very easy lifter for @ 40 ton stuff.  Starts off with a mainsail flanked by two Polluxes.  Plenty of juice for the mainsail, btw - and with the Polluxes I often have to throttle the mainsail down when the drag gets high (which just means more fuel later).  About the time I get to space I drop the mainsail and light off a Skipper (I think.. It's the big bell shaped rocket that starts with a S).  Depending on the weight that stage is either still helping me get to altitude or doing the circularization burn & part of the destination burn.

After that... My FuelTruck uses the Poodle and is very handy 

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4 hours ago, Spricigo said:

The S3-7200 carry about11% more fuel.

Oops I feel into the trap of looking at the tank and assuming it was size 2 :o

 

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On 5/23/2020 at 6:41 PM, Joe.L said:

I wanted to know if there was a way in which to launch the Kerbodyne_S3-7200_Tank and dock.

https://kerbalx.com/swjr-swis/MassFraction-Rocket-D1b

With a recoverable rocket:

https://kerbalx.com/swjr-swis/MassFraction-Rocket-D2

But why stick to just one...

https://kerbalx.com/swjr-swis/500t-LKO-Lifter

 

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