Refueling Station

[locustgate]

So what is the best altitude for a refueling station for a reusable tug?

[LethalDose]

So what is the best altitude for a refueling station for a reusable tug?

Where and what for?

[maltesh]

Wherever your tug is going to be departing from most often with something to push or pull. If your tug's going to be moving things from low Kerbin orbit to elsewhere, you want your refueling station as low as you can comfortably rendezvous with, to save on launch costs.

[locustgate]

Where and what for?

Duna, Kerbin, Jool+moons. Prefer have a refuel station in each location, long term goal.

Wherever your tug is going to be departing from most often with something to push or pull. If your tug's going to be moving things from low Kerbin orbit to elsewhere, you want your refueling station as low as you can comfortably rendezvous with, to save on launch costs.

The tug will be returning from another planet/body, the tugged ship will be coming from the surface, from kerbin it has enough fuel+rcs to dock, other bodies, maybe maybe not.

I'm using Karbonite converters to create fuel on other moons.

Edited November 11, 2014 by locustgate

[GoSlash27]

IMO the best altitude is LKO, 70KM.

Least amount of DV required to get supplies to it, excellent harnessing of the Oberth effect, and no guess-work for finding transfer windows for the next mission.

Best,

-Slashy

[locustgate]

IMO the best altitude is LKO, 70KM.

Least amount of DV required to get supplies to it, excellent harnessing of the Oberth effect, and no guess-work for finding transfer windows for the next mission.

Best,

-Slashy

The supplies are coming from Minimus and/or Mun. Depending on the yields.

Edited November 12, 2014 by locustgate

[Wanderfound]

As a general rule, as low as possible. 70km on Kerbin, 8,000m at the Mun, just above the atmosphere at Duna, etc.

[The Yellow Dart]

I prefer mine a bit higher around kerbin, usually 90 or 100k for the following reasons:

1. When launching a ship to rendezvous with your station, you have more options to meet it in one orbit. With a station right at 70k, if you launch a bit too late and end up in orbit behind it, you can't lower your orbit to catch up without entering the atmosphere.

2. At 100k, if you are launching a vessel to somewhere far like Moho or Jool with low thrust to weight, your long burn time is less likely to bring you into the upper atmosphere, which can throw off the accuracy of the maneuver.

3. Also 100k is a nice, easy-to-remember starting point to learn how to deorbit thing and reenter atmo so that you land near KSC. For me I put my Pe at 40k right over KSC when 1/2 an orbit away, a little lower for spaceplanes. From there you can learn to adjust from different altitudes as needed.

4. And last, not too often will you have a craft that can attain orbit but not be able to make it up to a 100k orbit.

TLDR, I vote 100k.

[Zylark]

I like my gas-stations up high. Around Kerbin that is 300km. It might be high for stuff coming from Kerbin, but since the fuel is coming from mining Karbonite on the Mun and most vessels visiting it are incoming from any other place than Kerbin, that do not matter much.

Other advantages include doing the burn to other places when fully fueled from a higher orbit, no need to burn up ~200dV getting from say 100km to +300km. Your Tug probably got plenty of fuel when incoming, so that can just rendezvous with your new payload in LKO, then haul it all to the Gas-Station, top off the tanks and then get to wherever it need be.

If you need to refuel stuff that struggles to get to low orbit, much less high orbit, just have a roaming refueler. This can also siphon off fuel from lifters that is a bit over-dimensioned for the payload. Waste not, want not

[mhoram]

If you intend to optimize the altitude for "lowest Delta-V to target planet", the charts in this thread will help you:

http://forum.kerbalspaceprogram.com/threads/75542-Should-I-build-a-refueling-station-at-the-edge-of-Kerbins-SOI?p=1072850&viewfull=1#post1072850

[locustgate]

If you need to refuel stuff that struggles to get to low orbit, much less high orbit, just have a roaming refueler. This can also siphon off fuel from lifters that is a bit over-dimensioned for the payload. Waste not, want not

Never heard of such thing, I tend to make my orbiters with plenty of dV. Well dV for a short 2 way.

Edited November 12, 2014 by locustgate

[Alshain]

I prefer mine a bit higher around kerbin, usually 90 or 100k for the following reasons:

1. When launching a ship to rendezvous with your station, you have more options to meet it in one orbit. With a station right at 70k, if you launch a bit too late and end up in orbit behind it, you can't lower your orbit to catch up without entering the atmosphere.

2. At 100k, if you are launching a vessel to somewhere far like Moho or Jool with low thrust to weight, your long burn time is less likely to bring you into the upper atmosphere, which can throw off the accuracy of the maneuver.

3. Also 100k is a nice, easy-to-remember starting point to learn how to deorbit thing and reenter atmo so that you land near KSC. For me I put my Pe at 40k right over KSC when 1/2 an orbit away, a little lower for spaceplanes. From there you can learn to adjust from different altitudes as needed.

4. And last, not too often will you have a craft that can attain orbit but not be able to make it up to a 100k orbit.

TLDR, I vote 100k.

This, especially #1. I usually have one at 150km.

- - - Updated - - -

I prefer mine a bit higher around kerbin, usually 90 or 100k for the following reasons:

1. When launching a ship to rendezvous with your station, you have more options to meet it in one orbit. With a station right at 70k, if you launch a bit too late and end up in orbit behind it, you can't lower your orbit to catch up without entering the atmosphere.

2. At 100k, if you are launching a vessel to somewhere far like Moho or Jool with low thrust to weight, your long burn time is less likely to bring you into the upper atmosphere, which can throw off the accuracy of the maneuver.

3. Also 100k is a nice, easy-to-remember starting point to learn how to deorbit thing and reenter atmo so that you land near KSC. For me I put my Pe at 40k right over KSC when 1/2 an orbit away, a little lower for spaceplanes. From there you can learn to adjust from different altitudes as needed.

4. And last, not too often will you have a craft that can attain orbit but not be able to make it up to a 100k orbit.

TLDR, I vote 100k.

This, especially #1. I usually have one at 150km.

[LethalDose]

Like Alshain and The Yellow Dart, I prefer to place refueling stations in LKO at around 80-100 km so you have some wiggle room for rendezvous.

If you have fuel supplies coming from Minmus, tho, I would just place the refueling station at Minmus. You can launch IP vessels from Minmus for less dV than from LKO. If you don't want to launch vessels from Kerbin with enough dV to get to Minmus, you can create a tug to move vessels from LKO to Minmus.

[psyper]

I have mine around 80km from Kerbin - that way if I come up a little behind it I can drop down to 70km to catch up with it. For Minmus transfers I have a small station which has the same inclination as minmus so I can just launch straight from it and make a normal Hohmann transfer without any inclination change.

For other planets I would personally keep it pretty close to kerbin - around 70km - to make good use of the oberth effect - also makes transfer from the ground to the station on a delta-v budget.

[Tokay Gris]

So what is the best altitude for a refueling station for a reusable tug?

Depends very much what you use it for and what vessels you intend to refuel.

If you are like me and your vessels heading for - say - Jool are massive monsters with abysmal TWR and need an incredible ejection burn (on the order of 15 min or more), then a good orbit for a fuel station would be in fact LKO. 70 - 80 km.

This because the launching orbit of your interplanetary vessel will most likely be somewhere above 100 km. With such a difference in orbits, you will get Hohmann-orbits often enough that it is worth it.

On the plus side, you need less delta-V to refuel your refueling station....

If your vessels are small and have a descent TWR, they can actually start of from LKO. But if you have a fuel station in LKO and the to-be-refueled vessel also in LKO, you need a phasing orbit first to actually rendezvous.

So in that case, an orbit for the station is better at about 180 km. Then, you get a Hohman-tranfer about every fifth orbit.

So, depending what your tug is supposed to do, you can set the orbit accordingly.

If it is "just" for orbital maneuvers around the Kerbin system, then you need to change orbits often anyways. And LKO has the benefit of needing less delta-V.

If you have an interplanetary tug that needs to start burning above 100km (i.e. abysmal TWR) so not to dip into the atmosphere on ejection, the station - in my opinion - would be best at about 150 to 200 km to get Hohmann-tranfers more often.

Well, thats the way if you have a hugh refueling station that cannot leave its orbit easily once it is up and are using a refueling tanker to shuttle fuel between the Tug and the station.

If you want to dock the tug to the refueling station directly, then the orbit you are aiming for is the lowest orbit your tug can do an ejection burn and not dip into the atmosphere.

Which with interplanetary vessels is usually not just above atmosphere. At least with my designs.... Usually I start with the "smaller" ones at about 100km. And I did a few ejection burns that got pretty close to getting too low with 150km.

[LethalDose]

For Minmus transfers I have a small station which has the same inclination as minmus so I can just launch straight from it and make a normal Hohmann transfer without any inclination change.

This is so simple its freaking genius.

You, good sir or madam, deserve some rep.

[KerikBalm]

I'm using Karbonite converters to create fuel on other moons.

Then I would say a station at Minmus.... It should be easy enough to get to minmus from LKO, from there, the dV requirements to get to your next destination are reduced by a lot.

However, I don't use any ISRU mods yet, so I simply put my fuel depot at 80km - for much the same reason as has already been stated for 90-150 km orbits.

If I need to catch up to the station, I can orbit at 69.5 km, and be 10.5km lower than the station to catch up. A station at 70km really limits your options for a quick rendevous if you don't launch at the right time.

I do 80 instead of something like 150, because it takes less dV to get there (for 150 km, if you are ahead of it, you need to get your Apoapsis even higher ....)

[DerekL1963]

I prefer mine a bit higher around kerbin, usually 90 or 100k for the following reasons:

1. When launching a ship to rendezvous with your station, you have more options to meet it in one orbit. With a station right at 70k, if you launch a bit too late and end up in orbit behind it, you can't lower your orbit to catch up without entering the atmosphere.

While I agree with the idea that 100k is better than 70k... going lower than your target to catch up with it is only one option - you can also go higher than your target and let it catch up to you. I wouldn't necessarily use this for a station in LKO that you're trying to reach from KSC (though, unless you're going very high, you don't use that much d/v), it's how I rendezvous craft inbound to a SOI with a station or craft already in orbit in that SOI. (Such as a replenishment craft launched from Kerbin and bound for my Munar station.)

[StormKat]

Put it above 120k Kerbin. You get an extra warp level above 120k.

[psyper]

This is so simple its freaking genius.

You, good sir or madam, deserve some rep.

Thanks for the Rep - if you're clever enough you can always wait for a launch window when your refuel station is close to or going directly over KSC and launch at that angle - theres not much difference in delta-v and you can meet up with the station refuel and will be leaving LKO will a full tank of fuel. they do a similar think IRL with the ISS which is why you get strange launch windows (I never knew why until I started playing KSP).

Put it above 120k Kerbin. You get an extra warp level above 120k.

I have a beacon at the end of the runway at the KSC - if I need to warp a lot I change focus to that as it gives you as much warping as you need. Its a bit of a pain switching back and forth but it solves having to sit there waiting for everything to spin round!

[tsotha]

Mathematically, the lower it is the less fuel you're going to be using in the long run. As others have pointed out, though, at 70km Kerbin you're always going to be doing your rendezvous from ahead of your fueling station, since you can't be in a lower orbit.

Ultimately it depends on how tight your dV budget is. If you don't need that last ounce of fuel putting it at 100km or so will save you a lot of aggravation.

[mhoram]

Mathematically, the lower it is the less fuel you're going to be using in the long run.

This is correct under the assumption that you do only a single departure burn.

If you allow two burns, then higher orbits can be Delta-V wise more efficient (in the meaning you need in total less Delta-V for getting to an intercept-course with the target planet)

Starstrider42 made some calculations on the fuel consumption for two-burn departures:

http://forum.kerbalspaceprogram.com/threads/75542-Should-I-build-a-refueling-station-at-the-edge-of-Kerbins-SOI?p=1074426&viewfull=1#post1074426