The usefullness of deep-space re-fueling

[lextacy]

Im gonna be blunt. What is the point of re-fueling on another planet? Are you really getting more dV per distance ratio? Here is some situations people have been known to do.

1. Go to Jool and re-fuel at Minmus - I honestly think this produces a negative net value of fuel consumption. By the time you have retro-captured , rendezvous or aero braked to your re-fueling point, and then to break that orbit all over again, you have wasted more fuel than you have gained overall.

2. Land at the Mun , then land again, and again to explore more - This one seems really efficient as your using 0 dV to arrive at a re-fueling point. Providing you landed at a rich drilling area.

3. Refueling at a LEO station to then go interstellar - Im not totally sure on this. If you can brute force rendezvous from the surface with pin point accuracy , topping off fuel can actually give you a pretty chunky net gain of fuel. If your rendezvous are sloppy and use like 6 burns, well not so much.

Feel free to discuss, add your unique situations, and tell us did it give you the results you were looking for. I voted that interplanetary re-fueling using planets as checkpoints is far detrimental to your dV.

Edited March 13, 2015 by lextacy

[Snarfster]

I have a Karbonite scoop with fuel conversion in Jool orbit, that has helped immensely with solving my long range logistical issues.

Refuelling at Minmus could have its benefits. Your kerbin escape burn from Minmus is minimal.

[Cebi]

I would refuel on planet only if my lander could separate for ascent from the "refueling rig". It is costly thou and realy depend on the weight of the refueling contraption. My prefered solution is to make infrastructure on strategic places in star system and then refuel multiple missions there.

Edit: Or did i misinterpereted and you mean landing on planet without mining and refuel from some tank that has been droped there earlyer?

Edited March 13, 2015 by Cebi

[Superfluous J]

Im gonna be blunt. What is the point of re-fueling on another planet? Are you really getting more dV per distance ratio? Here is some situations people have been known to do.

1. Go to Jool and re-fuel at Minmus - I honestly think this produces a negative net value of fuel consumption. By the time you have retro-captured , rendezvous or aero braked to your re-fueling point, and then to break that orbit all over again, you have wasted more fuel than you have gained overall.

Untrue. If you build your ship to just have enough dV to get to Minmus orbit with nearly dry tanks, it will cost you about 4500+1100 (orbit + everything else to end up in Minmus orbit, ready to refuel). If instead you went to Jool, that would cost 4500+1930. Going to Minmus to refuel saves you having to put enough fuel to get 820 more dV, which is a lot of fuel you don't have to lift off of Kerbin.

And Jool's a bad case because you slow down for free so don't need as much dV total. When making a Moho, Dres, or Eeloo ship the savings is astonishing.

2. Land at the Mun , then land again, and again to explore more - This one seems really efficient as your using 0 dV to arrive at a re-fueling point. Providing you landed at a rich drilling area.

I never do this because you're wasting fuel lifting all that drilling and processing equipment everywhere. Better to make a ship that can hop 3-5 times and just make sure your last hop lands at your drilling/refueling base.

3. Refueling at a LEO station to then go interstellar - Im not totally sure on this. If you can brute force rendezvous from the surface with pin point accuracy , topping off fuel can actually give you a pretty chunky net gain of fuel. If your rendezvous are sloppy and use like 6 burns, well not so much.

I can rendezvous with an orbiting station with just a few dozen dV. However, bringing all that fuel way down the gravity well only to push it back up seems counterproductive to me. Better in my mind to bring the near-empty (and therefore much lighter) ship to Minmus to refuel.

Feel free to discuss, add your unique situations, and tell us did it give you the results you were looking for. I voted that interplanetary re-fueling using planets as checkpoints is far detrimental to your dV.

Planets? I agree with you. I would never even consider going to - say - Dres on my way to Jool.

Certain Moons? I totally disagree. If you do it smart the savings are massive.

[lextacy]

I would refuel on planet only if my lander could separate for ascent from the "refueling rig". It is costly thou and realy depend on the weight of the refueling contraption. My prefered solution is to make infrastructure on strategic places in star system and then refuel multiple missions there.

Edit: Or did i misinterpereted and you mean landing on planet without mining and refuel from some tank that has been droped there earlyer?

nope! ONe thing you said that I should have brought up is a #4

4. Land on Mun, refuel the ascent - Basically a LEM style landing, but only 1 stage. Hence the entire lander comes up and docks with CSM. The old LOK lander Russia was working on used a similar 1-stage setup.

[DocMoriarty]

Refueling IMO makes most sense in orbit around a moon so that the interplanetary space ship itself doesn't need too much fuel to launch from KSC. Actually I use tugs and very modular 'space trains' assembled in orbit so refueling at Minmus would always save a lot of dv. Alone launching all the fuel necessary for a space train from KSC is a massive undertaking which takes a lot less when done at Minmus. Another occasion where refuelling would make sense is landing on a fairly heavy gravity planet such as EVE so that the lander can land nearly dry and get refuelled. Limits landings though to sites with resource extraction.

[Deutherius]

3. Refueling at a LEO station to then go interstellar - Im not totally sure on this. If you can brute force rendezvous from the surface with pin point accuracy , topping off fuel can actually give you a pretty chunky net gain of fuel. If your rendezvous are sloppy and use like 6 burns, well not so much.

If you meant Low Eve Orbit, then I agree, aerobraking is free, but getting away is costly. Better to just exploit Eve for gravitational slingshots.

If you, however, meant Low Earth Kerbin Orbit (which would make more sense considering the "randezvous from the surface" part), I'll have to disagree on that one. I'm horrible at eyeballing launch windows for optimal randezvous, so I usually end up on the other side of Kerbin than the station I want to dock with (usually flying SSTOs). But even then I'm already at a similar orbit (because I was planning to dock with it), so it's just a tradeoff between deltaV spent and time I can wait. And I can usually way a few orbits, so it's pretty cheap (<100 dV) and the gain should be considerable.

[Xavven]

I can see it being very useful for a Jool-5 mission. I'm in the middle of doing one right now, and hauling as much fuel as I needed out there is a big deal. If I had a mining operation on Pol, it would have reduced my interplanetary transfer mass by a huge amount.

But if you're just going to land a probe on Ike to get some science points and complete an exploration contract, I agree, it's probably not worth bringing along the heavy drilling equipment.

[Wjolcz]

Being able to refuel is going to be amazing. I will finally visit the Joolian system without sending ridiculous sets of fuel tanks back and forth. If it doesnt end up being OP, of course. I really want it to take a LOT of electricity to make fuel.

Just a small outpost with a hab module, generator and a rig with a drill.

Edited March 13, 2015 by Veeltch

[Nansuchao]

A great positive thing about refueling in Minmus Orbit, if you escape to a LKO and you burn at your periapsis you would save a great amount of delta V, thanks to Oberth Effect...

[tntristan12]

I wrote an entire paper detailing the consumption of fuel, and mass targets for how much fuel you will need to get out your delta-v AND still turn a profit on your fuel. It's posted on these forums somewhere. I will see if I can dig it up.

[FlyingPete]

I think that mining Minmus will be a great advantage. You can assemble your interplanetary ship in LKO with just enough fuel to make it to Minmus. Refuel at Minmus (using fuel lifted from the surface at minimal cost). With a low-dV burn, you have a Kerbin orbit with a Pe very close to Kerbin. From here, relatively low dV is needed to get anywhere in the system.

Similarly, fuel mining around Jool removes the need to bring fuel for the return trip, and burn more fuel just to carry that fuel around with you.

[magnemoe]

Im gonna be blunt. What is the point of re-fueling on another planet? Are you really getting more dV per distance ratio? Here is some situations people have been known to do.

1. Go to Jool and re-fuel at Minmus - I honestly think this produces a negative net value of fuel consumption. By the time you have retro-captured , rendezvous or aero braked to your re-fueling point, and then to break that orbit all over again, you have wasted more fuel than you have gained overall.

2. Land at the Mun , then land again, and again to explore more - This one seems really efficient as your using 0 dV to arrive at a re-fueling point. Providing you landed at a rich drilling area.

3. Refueling at a LEO station to then go interstellar - Im not totally sure on this. If you can brute force rendezvous from the surface with pin point accuracy , topping off fuel can actually give you a pretty chunky net gain of fuel. If your rendezvous are sloppy and use like 6 burns, well not so much.

Feel free to discuss, add your unique situations, and tell us did it give you the results you were looking for. I voted that interplanetary re-fueling using planets as checkpoints is far detrimental to your dV.

3 has the benefit that you only have to launch the dry mass, you might save more fuel by using an disposable booster and do the last 600 m/s with the LV-N on the interplanetary ship.

Rendezvous is always less than 200 m/s as long as you are in the plane of target, if you are on the opposite side of target you can spend time or dV.

1 this has an benefit if combined with 3 if you have a long time to the launch window, refuel in LKO so you have 1200 m/s, go to Minmus orbit top up the tanks, do an 80 m/s burn to get into Kerbin orbit, drop Pe to 100-200 km so Pe fits with the burn point, you will save more than 1 km/s, the 1200 m/s to Minmus is free. This is perfect for Moho, for Jool, Dress and Eeloo you has to get into retrograde, not economical for Eve and Duna, NB watch out for Mun, it like to spoil your plan.

Anyway, in the kerbal mythology Mun was the god of violent death, Seth or Mars for us, then the space age began this was shown as accurate, more kerbals has died on Mun than other places combined. Yes the attitude, its only an trip to the Mun and how much airtime can we get on this crater edge is part of the reason

2 works even better in the Jool system, the dV cost of doing all the moons is higher than going to Jool.

[lextacy]

good points everyone....someone mentioned the Jool-5. This would be in-line with a good drilling setup somewhere on one of the moons. This was we could use just use 1 rocket and 1 lander to pound all 5 moons. As for LEO , I meant low earth. But the EVE idea I can agree with.

[Wanderfound]

Refuelling stations at Kerbin and Laythe:

* Send up a gigantic Mk3 passenger liner packed full o'Kerbals. Refuel it in LKO.

* Use all of its fuel getting to Laythe.

* Refuel before descent, drop off a hundred Kerbals at your new Laythe beach resort.

* Burn all your fuel getting back to Laythe orbit.

* Refuel, return to KSC.

[Slam_Jones]

Well, using strategic fuel depots, I can do a round trip mission to Mun with an SSTO and 5 tons max at any point.

If I got really efficient, I could take that SSTO to Jool.

[helaeon]

My experience with my Mun-base is more about re-fueling returning ships than outgoing ones so I don't have to re-launch the whole thing from Kerbin again, or launch from Kerbin generally except for crews. Much easier to mine fuel and lift it from the Mun than from Kerbin, same for Minmus, but I usually find the Mun more convenient.

[Torquemadus]

I'm expecting to use ISRU as a means of producing fuel for return trips. I would arrive at my destination with nearly empty tanks, and then fill them for the return trip. This would mean that I not only don't have to haul the return fuel from Kerbin, but I also don't have to expend fuel pushing the fuel to my destination. This, in turn, should greatly reduce the size, and therefore cost of my interplanetary missions.

[Northstar1989]

Im gonna be blunt. What is the point of re-fueling on another planet? Are you really getting more dV per distance ratio?

You're not the first player to ask this question lextacy. I strongly recommend you check out the Guide to Off-World Refueling I wrote up last year, and have linked in my signature, to answer precisely these kinds of questions...

Regards,

Northstar

[Frank_G]

It proofed much use when exploring Duna. I had a permanent refueling base installed on the surface that provided fuel for the various craft on the surface. I was able to perform suborbital hops to places far from the base with all the option to either return or to ascend to the orbital station at will. This will have a massive impact on stock gaming.

[Foxster]

Not forgetting that it doesn't have to be fantastically efficient or even totally practical. A lot of folks are going to get a big kick out of just setting up the infrastructure.

[RoverDude]

The biggest benefit I get from mining is survey contracts.

This little hopper stays landed next to a surface mining rig and refinery on Minmus (and a matching one on the Mun). Rack up a few survey contracts, go exploring, then land back at the depot (which has been making fuel in the background), fill up, rinse and repeat.

My Minmus one has closed at least twenty survey contracts and has paid for a good chunk of my space program, and could easily redo this on any of the low-gravity planets and moons.

(edit)

...and it has over 8,000 delta v

[cantab]

Refuelling at the Mun or Minmus helps because your interplanetary transfer then requires less delta-V than going from Low Kerbin Orbit. For how much less we can use the Kerbin chart here:

http://www.reddit.com/r/KerbalAcademy/comments/1qu5jv/deltav_charts/

If you consider the type of transfer where you have a low periapsis over Kerbin to exploit the Oberth effect then whatever our destination we have to go through the Kerbin-Mun Transfer and/or Kerbin-Minmus Transfer nodes as appropriate. The saving is then the difference in delta-V needed to reach that node. That's 760 m/s for refuelling at Minmus orbit and 590 m/s at Mun orbit. A good saving on a typical interplanetary departure of 1000-2000 m/s.

Of course that delta-V has to be made up for and more to get to Mun or Minmus orbit to begin with, but by requiring less delta-V on the spacecraft at once you require less fuel storage which makes the ship lighter, and then you can potentially reduce the number of engines and keep the same TWR making it lighter still.

The drawback to refuelling at the Mun or Minmus is you need to time your departure burn from their correctly to put your Kerbin periapsis in the right place for your interplanetary transfer burn. This can then constrain your departure burn date to be away from the optimum date in the transfer window. The effect is worse for a Minmus refuel than a Munar one, and either way it's generally bad for Moho which has short transfer windows but tolerable for other destinations.

As for refuelling in Low Kerbin Orbit, well while it's a reasonable place to refuel I don't much see the point of a fuel station. Ships small enough that the station could top up many of them are probably small enough to launch fully fuelled, while ships large enough that you can't launch them fully fuelled are probably large enough to drink all the station's fuel in one go and therefore you're just better off sending up a simple refueller to fill just that ship than running a station with all its extra complexity.

Edited March 14, 2015 by cantab

[Caelib]

I can sum it up in one word: OPTIONS.

[Van Disaster]

Helps even more when you build the ship offworld

As people have said, only lifting fuel for one direction of a return trip is a total gamechanger. The other thing is, you don't have to base your space program just around trips to and from KSC anymore, which your original post didn't consider.