Duna refueling logistics

[RocketSquid]

So, I'm planning a duna mission that will use ISRU. I have elected to use a mothership-based mission plan, so I will need to efficiently carry fuel to an orbiting mothership. My question is, would it be easier to produce fuel on an unmanned lander on Ike or on a manned base on duna? Duna would have higher dV costs, but I could then use engineers (productivity boost) or the wonderful Phoenix industries atmospheric ISRU MAV base.

[FancyMouse]

Why not do both?

[Snark]

Any particular reason not to use a manned miner on Ike?

dV to get up to orbit from Ike is quite a bit lower than Duna.

[RocketSquid]

13 hours ago, Snark said:

Any particular reason not to use a manned miner on Ike?

dV to get up to orbit from Ike is quite a bit lower than Duna.

I'm making a base on duna, partially because it's easier to land there (atmosphere). The base will be manned, and there will be little crew left for Ike. I may have them land there, if the advantage proves too great to miss it. But on duna I can also make fuel from the atmosphere, without mining.

[merlinux]

3 hours ago, RocketSquid said:

I'm making a base on duna, partially because it's easier to land there (atmosphere). The base will be manned, and there will be little crew left for Ike. I may have them land there, if the advantage proves too great to miss it. But on duna I can also make fuel from the atmosphere, without mining.

It might seem easier to land on duna with parachutes. But making a base would be 100% easier to do on Ike.Pinpointing your landings is the culprit here. And for sure you would want to gather all this ore from Ike if you want to get a reusable lander to land on Duna. Mining ore on duna can also be useful for other purposes. Also have a look at UKS it as a very nice orbital logistics system.

[RocketSquid]

3 hours ago, merlinux said:

It might seem easier to land on duna with parachutes. But making a base would be 100% easier to do on Ike.Pinpointing your landings is the culprit here. And for sure you would want to gather all this ore from Ike if you want to get a reusable lander to land on Duna. Mining ore on duna can also be useful for other purposes. Also have a look at UKS it as a very nice orbital logistics system.

I have UKS, and also pathfinder. Pathfinder means that I can land the entire base in one ship, since the base can just be inflatable. Also, I have the phoenix industries MAV mod, which allows me to make fuel out of duna's atmosphere, no mining required. I have yet to unlock the full orbital logistics portion of UKS, however. It is a science mode save, so cost is not an issue.

[Plusck]

The lower the gravity, the higher the payload fraction, and so the higher volume of fuel and/or ore you can take up to orbit. While Duna's atmosphere reduces the fuel cost of landing on the planet, your fuel/ore carrier will be landing almost empty.

So for me, there isn't the slightest doubt: Ike is far easier to refuel from. And that is without even considering the fuel prospecting process in stock (for which Ike wins hands down).

[RocketSquid]

But we need to consider the dV of the mothership itself. ISRU converters and drills are heavy: the mass of a single small drill and a convert-o-tron 125 is 1.5 t. The mass of the phoenix industries ISRU MAV base is 1 t, and it will generate fuel far faster than the aforementioned combo. To get reasonable efficiency with drills and converters, I'd need to use the larger converter, which would, with a small drill, weigh 3.5 t more than the atmospheric ISRU base, which I can use on duna. So, if I refuel from Ike, I would need more fuel on the ship, since I would be carrying more mass.

[Geschosskopf]

On 3/19/2016 at 6:38 PM, RocketSquid said:

So, I'm planning a duna mission that will use ISRU. I have elected to use a mothership-based mission plan, so I will need to efficiently carry fuel to an orbiting mothership. My question is, would it be easier to produce fuel on an unmanned lander on Ike or on a manned base on duna? Duna would have higher dV costs, but I could then use engineers (productivity boost) or the wonderful Phoenix industries atmospheric ISRU MAV base.

First off, always mine and refine with engineers aboard.  Otherwise, extraction and refining rates are painfully slow, even in high-value ore deposits.

Second, the ISRU infrastructure needed depends entirely on whether you need the fuel in space, on the ground, or both.  In your case, you mostly need fuel in space, to refuel the mothership for its return and perhaps to refuel the Duna lander after it makes a round trip to the surface.  For this application, the only really practical and efficient method is to get the fuel from Ike.  You burn less fuel making the trip from Ike to the mothership than you do from Duna.

The ONLY reason to bother with mining/refining on Duna itself is if you plan to consume a lot of fuel there exploring the whole planet with stuff that won't be going to space along the way.  IOW, rovers and/or airplanes powered by fuelcells or otherwise consuming fuel.  If you're not going to be driving/flying around on Duna, instead just biome-hoppiing with a lander (or even just a single landing), then refuel the lander at the mothership between hops, using fuel coming from Ike.

Note that precision landings on Duna are very difficult to do, which makes it problematic to put a conventional lander close enough to connect to any fixed mining/refining facility.  This means it's usually a better idea to do your exploring with airplanes or rovers that can taxi/drive up to the fixed ISRU thing.  Because these vehicles have very long range and don't need to refuel themselves, they can explore areas with slim-to-none ore.  If you instead make a biome-hopper that carries the ISRU stuff around with it, you'll likely have problems in the ore-weak areas.

So my advice is first to plan on a high-capacity ISRU operation based on Ike.  Next decide how thoroughly you want to explore Duna and what type of vehicles that will require.  If necessary, then design any ISRU system they need.  A central ISRU base on the "best" ore you can find on Duna, from which fuelcell vehicles fan out over the whole planet, is probably the best way to do that.

[RocketSquid]

12 minutes ago, Geschosskopf said:

First off, always mine and refine with engineers aboard.  Otherwise, extraction and refining rates are painfully slow, even in high-value ore deposits.

Once again, the advantage of Duna is that I do not have to mine for fuel there. I can produce it from the atmosphere.

[Geschosskopf]

2 minutes ago, RocketSquid said:

Once again, the advantage of Duna is that I do not have to mine for fuel there. I can produce it from the atmosphere.

Which is just another form of mining that goes very slowly because there's less good stuff in the air than in the dirt.  It trades planetwide availability for subsisting on trace amounts.  But it doesn't matter in the least HOW you acquire fuel on Duna, what matters is WHY you need to bother in the 1st place.  As I said, there is zero need or desirability to acquire fuel on the surface of any planet unless you're going to consume it on that planet.

[RocketSquid]

1 hour ago, Geschosskopf said:

Which is just another form of mining that goes very slowly because there's less good stuff in the air than in the dirt.  It trades planetwide availability for subsisting on trace amounts.  But it doesn't matter in the least HOW you acquire fuel on Duna, what matters is WHY you need to bother in the 1st place.  As I said, there is zero need or desirability to acquire fuel on the surface of any planet unless you're going to consume it on that planet.

Actually, duna has a primarily-CO2 atmosphere, and the MAV base uses CO2 to make LF+OX, quickly, with or without an engineer. Additionally, its mass is a fraction of the mass of an equivalent mining setup. Even if I modify it to be a full, realistic Sabatier+RWGS reaction, I can still make fuel with less additional equipment. Essentially, fuel is cheap to make on duna, but easy to transport from Ike.

[Warzouz]

Duna space station refueled from Ike : tested and appoved.

[Geschosskopf]

22 minutes ago, RocketSquid said:

Actually, duna has a primarily-CO2 atmosphere, and the MAV base uses CO2 to make LF+OX, quickly, with or without an engineer. Additionally, its mass is a fraction of the mass of an equivalent mining setup. Even if I modify it to be a full, realistic Sabatier+RWGS reaction, I can still make fuel with less additional equipment. Essentially, fuel is cheap to make on duna, but easy to transport from Ike.

Why not just use HyperEdit to magic fuel into your tanks?  Sounds about the same at the bottom line.

Still, you're missing the entire point.  There is no reason to make fuel on the surface of any reasonably large planet unless you intend to consume the fuel there down there, or need it to return to space from the surface.   If you only need fuel for something that will never touch the ground, it will always be way more efficient to get the fuel from a convenient low-gravity moon.  

[RocketSquid]

Just now, Geschosskopf said:

Why not just use HyperEdit to magic fuel into your tanks?  Sounds about the same at the bottom line.

Still, you're missing the entire point.  There is no reason to make fuel on the surface of any reasonably large planet unless you intend to consume the fuel there down there, or need it to return to space from the surface.   If you only need fuel for something that will never touch the ground, it will always be way more efficient to get the fuel from a convenient low-gravity moon.  

I do need to return from the surface, so I will need ISRU there (or just more fuel). And I do intend to make the MAV base consume hydrogen, which I can get from water... from mining duna's surface. However, it still amounts to less hardware if I do it on duna. I just need to know whether the lower mass is worth the increased delta-v cost, a difference of probably about 1100 m/s of delta-v.

However, at this point, I'll probably just make the mothership bigger, and do the mission without ISRU. It seems a lot easier than flying lots of refueling missions.

[Geschosskopf]

1 minute ago, RocketSquid said:

I do need to return from the surface, so I will need ISRU there (or just more fuel). And I do intend to make the MAV base consume hydrogen, which I can get from water... from mining duna's surface. However, it still amounts to less hardware if I do it on duna. I just need to know whether the lower mass is worth the increased delta-v cost, a difference of probably about 1100 m/s of delta-v.

Like I've been saying, if you need the fuel for the mothership, then you want to get it from Ike.  That's always going to be way more efficient than fighting both the atmosphere and higher gravity of Duna.

Think about it.  If the lander can't even get itself back to space without refueling, then it simply will not work as a tanker for the mothership.  This is because it only has fuel for a 1-way trip.  So it can't carry much extra fuel back up with it, and then it will need refueling in space before it can return.  Therefore, a tanker lander always needs enough fuel of its own for a round trip, ascending with its payload and descending without.  Otherwise, it's a net drain on the mothership's fuel.

So, your lander will have enough fuel for a round trip anyway.  Given that, it has no actual need to refuel on Duna, then you're back to the question of where you need the fuel.  If it's the mothership that needs the fuel, then get it from Ike.  It's way simpler and way more efficient, so you can probably do it in 1 trip.

1 minute ago, RocketSquid said:

However, at this point, I'll probably just make the mothership bigger, and do the mission without ISRU. It seems a lot easier than flying lots of refueling missions.

The number of tanker runs required is a function of tanker size and the efficiency of its trip.  The bigger its tanks, and the less the gravity it has to fight, the more it can deliver per trip, so the fewer trips it has to make.  And the lower the gravity, the bigger the tanker can be.  Because the tanker needs its own fuel to move, a 1-trip tanker will be bigger than its customer, making it the real "mothership".  Even a 2-trip tanker will likely be about the same size as its customer.  But the smaller the tanker, the more sensitive it is to gravity losses, making Ike even more of a better choice than Duna.

Of course, a better alternative to having a mothership is to do a flotilla.  That way, everything can be just big enough to do its own job, you don't waste fuel lugging stuff you need only at Point X to Point Y, you don't have all your eggs in 1 basket, and you don't need a monster tanker to refuel a monster mothership.  Plus, much less lag along the way.

 

 

 

[Plusck]

I don't know about this "fuel from the atmosphere" mod, but then I'm most definitely not an expert on mods.

Still, the point about wasting fuel lifting it from a high-g body is very, very important.

I discovered this the hard way with Moho: I had a decent standardised miner, worked perfectly fine on the Mun, Ike, and Jool's smaller moons. So I thought it would work fine (with a bit of tweaking) on Moho. This was a huge mistake.

Getting up to orbit from Moho, my relatively efficient mining craft had about 2% of its fuel load available for the craft in orbit. Virtually everything it took up had to go back down with it to be able to land again. This was an instructive experience, since I had to try several times to get down with only a few m/s more than the absolute minimum just to kill orbital velocity. I was proud of achieving this, but my very next launch was a stripped-down fuel carrier designed specifically for Moho.

So no, mining on Duna for Duna orbit just doesn't make sense IMO. Maybe the mod makes it worthwhile, but I find that hard to believe.

[Geschosskopf]

4 minutes ago, Plusck said:

I don't know about this "fuel from the atmosphere" mod, but then I'm most definitely not an expert on mods.

It's an old idea in new form. Way back in the day, there was another mod  (Bobcat I think) that did this, based on Kethane IIRC.  And of course Karbonite is present in some atmospheres as well.  But it really doesn't matter, it's just mining in another form.  Instead of drills, you have air scoops, and you don't have to prospect because the air is assumed to be equally productive everywhere.  Then it's just a question of the rates of resource conversion.  In this case, the rates sound quite high.  But all that means is that it doesn't take as long to make a given quantity of fuel.  The real question is how much fuel the lander can deliver per trip.

4 minutes ago, Plusck said:

Getting up to orbit from Moho, my relatively efficient mining craft had about 2% of its fuel load available for the craft in orbit. Virtually everything it took up had to go back down with it to be able to land again. This was an instructive experience, since I had to try several times to get down with only a few m/s more than the absolute minimum just to kill orbital velocity. I was proud of achieving this, but my very next launch was a stripped-down fuel carrier designed specifically for Moho.

That's a familiar story

Here is the tanker and mothership currently working in my Sarnus expedition.  I'm using Eeloo (which is the 3rd moon of Sarnus) as the refueling base, which is the best place available at Sarnus but it's got pretty high gravity (jetpacks don't work there).  

The mothership is docked to the end of a small, uncrewed station, the joint between them being adjacent to the central RCS tank.  The mothership requires 1.5 orange tanks worth of liquid fuel.,  The tanker is on the side 1.25m port.  It can carry 1 orange tanks as payload (the 2.5m radial tanks) and requires the central 3.75m stack for its own use (powering 5x aerospikes)..  It is thus a 2-trip tanker and is somewhat bigger than the mothership.  Both were launched on the same lifter but the tanker needed some extra SRBs on the lifer core.

[Warzouz]

Ah, Moho refueling...

My space station design with Ore Miner was designed to retrieve ore and refine it in orbit. I had to tweak a lot to be able to refuel nearly half an orange tank. from a 60T (loaded with ore) Miner. With that refuel, I would be able to land the science lander (7T, 3000m/s) 4 times.

The efficiency of a Moho refuelling is 46%

• 3200 unit of liquid fuel to power the miner (for the next mining cycle)
• 2752 unit of additional fuel/Oxidizer in the tank.

 

Edited March 22, 2016 by Warzouz