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# ISRU is less more?

## Question

Weight, heat, and power not withstanding, is it better to have a drilling rig with only 2 drills (for weight balance) or to spam as many drills as possible around the hull?

I have a drilling rig with as many as I could fit, but I wonder if I'm "saturating" the extraction rate?

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I just checked this out with an 80-drill rig hyperedited to an 8.4% ore patch on Minmus, with level 3 engineer.

Unfortunately I scrimped on cooling, so it was only possible to see it for a second as the drills hit 100% efficiency...

Spoiler

Still, the numbers all tally. "Ore rate" is given as 0.021577. That is 0.015 (small drill rate) x 17 (3-star engineer) x 8.46% ore concentration. Total ore production with all 80 drills active is 1.73 ore/s.

The small ISRU, meanwhile, consumes 2.5 ore/s for an LFO mix of 0.5 total (0.22+0.28).

That means you'd need 116 small drills (+ 3-star engineer) to keep up with one small ISRU.

Meanwhile, next door, my single large drill produces 0.11 ore/sec and the ISRU uses 0.5/sec to produce 0.45+0.55 LFO, so a fifth of the consumption for twice the output.
Therefore I'd need 4-5 large drills to maximise production for this ore concentration with my 3-star engineer. Or 23 drills if I used the small ISRU...

There is, however, a difference between "surface harvesting" and "asteroid harvesting". A large drill will mine 0.25 ore/sec from an asteroid (without an engineer on board). Therefore you only need 2 drills for 1 large ISRU on an asteroid.

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9 hours ago, tg626 said:

So 8 large drills saturate 1 (which one?) ISRU, and right now I have 12 small drills which would equal 2.4 large drills.

Right?

When people talk about drills and ISRU, they generally are only talking about the large versions of each. The small ones are really only good if you have a severe space/weight restriction (such as landing on Tylo, then refuelling before returning to orbit, or making an SSTO that can refuel itself... just because).

The small drills are terribly slow (1/5th the speed of the large ones).
Using the small ISRU instead of the large ones basically amounts to throwing away 9/10ths of the ore that you've mined; while this is not really a problem on celestial bodies (it just takes more time to mine) it is disastrous for asteroids since the ore supply is finite. However, it does seem that the small ISRU produces half the output of the large one; since it is 1/10th as efficient, that means that it actually consumes 5x the quantity of ore per second.

Therefore, if you need 8 drills to saturate a large ISRU (this would seem to imply about 8% ore concentration and a level-3 engineer on board), you'd need 8x5x5= 200 small drills to saturate a small ISRU converter, for half the fuel output...

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6 minutes ago, tg626 said:

I think I have like 16....

Oh... well that might have a chance to bottleneck it.  Depends if you're using an engineer - a high-level engineer can boost drill output a huge amount.  This thread has some math, but not positive if still current.

But it really does not take that long to top up a tank with just 2-4 drills.  So even if there is excess ISRU capacity, I generally don't see it as worth the weight / cost / space etc. to add more.  That said, I usually have my mining ships go back to orbit to refuel other craft.  If you have a base that's not going to move, there's less of a downside to adding a ton of drills.

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4 hours ago, John Kermin said:

I have heard this one multiple times.

1. Does everybody has to plant flags or just one guy for the whole mission ?

2. What does it take to "Hop out of Kerbin SOI"? What is the Ap so it gets recognized ? (I never went further than Minmus)

1. In 1.1, yes. However I've read someone saying that in 1.2 only one person has to actually plant the flag, as long as the others are inside physics range. They may all have to step out of the craft, though.

2. You just need to escape the Kerbin system. As soon as you escape, aim for Kerbin (it's still pretty visible) and burn back. Unfortunately, because you are leaving the SOI with whatever speed you had at the boundary, the burn back is a bit more expensive than if you had avoided leaving the SOI in the first place. I generally set a maneuvre node just before leaving the SOI, then burn back on that heading plus 100m/s or so... but you'd need a lot more if you exit quickly.

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It takes a ton of drills to bottleneck the ISRU, so I'd not worry about that.  How many drills you want comes down to mining time vs weight, electricity consumption and heat output.  I usually either go with 2 or 4 drills on a mining ship.

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I think I have like 16....

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It's a base.  I have a clawed tanker Rover that moves the fuel between a lander fuel shuttle and the base.

It has an engineer aboard.  Guess I could experiment a bit and try different numbers of drill actove, noting the results.

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When I've done the math (not since pre-release), on the typical rich planetary ore patch (10-11%) and a high level engineer, it takes roughly 8 drills to saturate one ISRU, with sufficient power and cooling.  If you're going to move a heavy permanent mining base, sure why not, max it out.  Or start small and make it expandable with additional drills.  As long as it's connected as one ship or base, doesn't matter where they are.

If you don't have a high level engineer, it's worth your time to do a quick training mission to plant flags on Mun, Minmus, and hop briefly out of Kerbin SOI.

For self-fueling ships, the rocket equation rewards efficiency.  I like large ISRU, 2 drills, 3 large fuel cell arrays, and a pair of medium thermal control systems.  That can be carried almost anywhere without growing into a capital ship.  If that's just too much, then the small ISRU and a single drill, and downscale the power and cooling accordingly.

Regardless of ship or base, the only cost to sub-optimal refining is mission elapsed time (game time, not play time).  Whether that matters at all, or a lot, is up to the individual player.

Edited by fourfa

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Here's the base.  Interestingly, all drills on can't seem to exceed the processing of ONE convert-o-tron (no ore accumulates) and one convert-o-tron will over heat (LF+O) with no drills running...

Edit: I dashed off this image in a hurry, I forgot to spec that 2 modules have ore tanks under them.

I should also add that 3 upper stages were brought into orbit and assembled into a fueling platform. While a fourth launch brought a CSM life boat to the orbiting platform and delivered the Fuel Shuttle.

Edited by tg626

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I should have specified in my answer - I meant 8 large drills.  The small drills pull 1/5 the ore of the large drills.  Bring up another drill module with the big ones, why not?

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So 8 large drills saturate 1 (which one?) ISRU, and right now I have 12 small drills which would equal 2.4 large drills.

Right?

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Good info, thanks!!

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On 8.10.2016 at 7:35 PM, tg626 said:

Weight, heat, and power not withstanding, is it better to have a drilling rig with only 2 drills (for weight balance) or to spam as many drills as possible around the hull?

I have a drilling rig with as many as I could fit, but I wonder if I'm "saturating" the extraction rate?

That strictly depends on your time requirements, and *WHERE* you drill.

If you mine asteroids, 2 drills and a good engineer will saturate your ISRU easily.

If you mine planets, you may consider more drills... but do you actually need them? You'd be hard-pressed to come up with a tanker that requires more if you allow a week for mining.

OTOH: definitely consider the big ISRU. It has exactly the same ore consumption as the small ones - but it produces several times as much fuel.

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The number of drills to saturate an ISRU depends on the skill of the engineeer and the ore rate. The number of drills (assuming adequate cooling) is proportional to ore extraction rate. If you mine faster than you can convert, its not such a problem. My designs typically go to orbit with both fuel and ore,so being able to fill up the ore and fuel tanks simultaneously is nice (my fuel tanks fill up, then the ore tanks).

Taking ore to orbit is nice because its 3 types of fuel in one, and allows the orbital depot to have some flexibility. If a LV-N craft docks and takes just LF, then I use ore to replace just the LF. If a SSTO docks that used only had LFO tanks with a lot of Oxidizer emptied (for example, a rapier design that just aims to get to a fuel depot, and then fill up on LFO to maximize the dV it has operating in closed cycle after a refill with no other engines for space propulsion), then you'll need to replenish the Oxidizer. Maybe you've got a monoprop tug for moving modules around. Normally my monoprop needs are so low that my tankers don't bother with a large monoprop tank, and just take up ore.

Taking up ore works really well with an all-in-one design rather than a surface rendevous. You'll need ore tanks anyway as a buffer tank from the drills to the ISRU to the fuel tanks.

This has 12 large ore tanks... I wouldn't mind a bit of saturation of the ISRU so that the ore tanks and fuel tanks fill up simultaneously:

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I tend to focus on convenience rather than productivity,   one thing I really hate is my drill shutting down overnight from lack of power and having to be manually restarted each morning.

I'm wondering if a few RTGs  will keep the drills alive overnight (albeit running at a very slow rate) so I don't have to keep doing that.   That way I can go into a high rate of time warp to my next launch window and not have to micromanage the extraction hardware.

Apart from the RTG question,  my next mining operation will be a

• self refuelling spaceplane.  Because docking and rendezvous are incredibly time consuming and inconvenient !
• only one small drill.   Out at Duna or beyond, electrical power for the converter is the limiting factor. More drills would get you more ore but you wouldn't have the power to turn it into fuel anyway.
• Large converter because it generates 10x the fuel for the same input of electrical power.
• try to land on tidally locked bodies with no day/night cycle.  Minmus is bugged and gives solar power in the dark too.

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5 hours ago, AeroGav said:

I tend to focus on convenience rather than productivity,   one thing I really hate is my drill shutting down overnight from lack of power and having to be manually restarted each morning.

I'm wondering if a few RTGs  will keep the drills alive overnight (albeit running at a very slow rate) so I don't have to keep doing that.   That way I can go into a high rate of time warp to my next launch window and not have to micromanage the extraction hardware.

Apart from the RTG question,  my next mining operation will be a

• self refuelling spaceplane.  Because docking and rendezvous are incredibly time consuming and inconvenient !
• only one small drill.   Out at Duna or beyond, electrical power for the converter is the limiting factor. More drills would get you more ore but you wouldn't have the power to turn it into fuel anyway.
• Large converter because it generates 10x the fuel for the same input of electrical power.
• try to land on tidally locked bodies with no day/night cycle.  Minmus is bugged and gives solar power in the dark too.

I don't know if 1.2 changes anything, but to date:

Drills appear to be purely on-off things. Either they have the power to run, or they don't. An ISRU converter will happily soak up any remaining power and run at decreased load, but the drill will shut off.

I don't think that the RTGs will help really, since the devourer of energy is the ISRU. Fuel cells are the obvious answer, since they supposedly only run when there is a need for power, but I really haven't explored their use so I can't say much about them.

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5 hours ago, Plusck said:

I don't know if 1.2 changes anything, but to date:

Drills appear to be purely on-off things. Either they have the power to run, or they don't. An ISRU converter will happily soak up any remaining power and run at decreased load, but the drill will shut off.

I don't think that the RTGs will help really, since the devourer of energy is the ISRU. Fuel cells are the obvious answer, since they supposedly only run when there is a need for power, but I really haven't explored their use so I can't say much about them.

Did a quick test on the runway,  6 RTGs are enough to power a small drill and run the converter.  With 4, the batteries drain and as you say, the drill turns off first.       That's with an engineer onboard.  It's possible that on a super high ore concentration the converter would use more electricity to keep up with the incoming ore.

A brief test with a fuel cell stack appears to indicate that the fuel cell perpetual motion machine appears to tbe the way to go.  Over unity and all that...

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At least in 1.1 as soon as you start time warping above X1000, you enter "on rails"  electricity, and the isru and drills doesn't use much. I've powered my entire Big Trip with just two Rtgs. You just need to ensure that you have enough batteries to power the rig while accelerating to 1000x

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On 8.10.2016 at 10:59 PM, fourfa said:

If you don't have a high level engineer, it's worth your time to do a quick training mission to plant flags on Mun, Minmus, and hop briefly out of Kerbin SOI.

I have heard this one multiple times.

1. Does everybody has to plant flags or just one guy for the whole mission ?

2. What does it take to "Hop out of Kerbin SOI"? What is the Ap so it gets recognized ? (I never went further than Minmus)

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A patch to 1.2 made it only one guy in physics range of the others (they don't have to get out of the ship). For older versions, everyone needs to plant a flag, but you can immediately recover them to reduce clutter if you want.

You're looking for an 'escape from Kerbin' marker after a maneuver node. You can test the variation with direction and so on without making the maneuver, just drag the node around and see what happens. To leave and quickly return, there's a best direction, but I can't figure it out clearly yet and I don't remember where on the forums I read it. Try searching for something about kerbal xp.

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On 10/12/2016 at 10:07 PM, John Kermin said:

I have heard this one multiple times.

1. Does everybody has to plant flags or just one guy for the whole mission ?

2. What does it take to "Hop out of Kerbin SOI"? What is the Ap so it gets recognized ? (I never went further than Minmus)

@chrisb2244 is correct, only one kerbal has to plant a flag(all other kerbals in physics range will also get flag-planting xp)...i am unsure whether they have to be unboarded, standing outside the lander on the Mun surface. Maybe it works for all Kerbals, even those withing craft?

2. Open map view.
Click Kerbin -> Focus view...or just double-click like a madman on Kerbin
On the right hand side is some button that opens up extra info of the selected planet/moon
Read through the details(atmopheric height, mass, etc.) until you get to SOI (Sphere of influence)...thats the Ap you are looking for.
It's like 86 000 000m, or about twice as far out as Minmus.

I would suggest burning for an elliptical orbit of about that height. A tiny bit of RCS thrust should push the Ap outside of the SOI. You will instantly see this as the Ap disappears and turn into an escape icon. Once you pass that marker, just burn 100m/s back towards kerbin(ignore the navball if the solar reference confuses you, just point the rocket visualy towards kerbin). Wait 5minutes and you should be entering the SOI again

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in 1.2 everybody get the flag planting bonus even if in craft.

I has 12 drills on my minmus miner, overkill even with an level 2 engineer as it mine faster than the rsru can convert unless you do multiple resources at once.

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On 14-10-2016 at 9:36 AM, Blaarkies said:

@chrisb2244 is correct, only one kerbal has to plant a flag(all other kerbals in physics range will also get flag-planting xp)...i am unsure whether they have to be unboarded, standing outside the lander on the Mun surface. Maybe it works for all Kerbals, even those withing craft?

2. Open map view.
Click Kerbin -> Focus view...or just double-click like a madman on Kerbin
On the right hand side is some button that opens up extra info of the selected planet/moon
Read through the details(atmopheric height, mass, etc.) until you get to SOI (Sphere of influence)...thats the Ap you are looking for.
It's like 86 000 000m, or about twice as far out as Minmus.

I would suggest burning for an elliptical orbit of about that height. A tiny bit of RCS thrust should push the Ap outside of the SOI. You will instantly see this as the Ap disappears and turn into an escape icon. Once you pass that marker, just burn 100m/s back towards kerbin(ignore the navball if the solar reference confuses you, just point the rocket visualy towards kerbin). Wait 5minutes and you should be entering the SOI again

If you exit Kerbin's SOI ahead of Kerbin (prograde in Kerbol orbit), Kerbin will catch up and you will get back into the planet's gravity, you only need a tiny burn at periapis to make it back into an elliptical orbit. "Higher is slower", so if your Kerbol apoapsis is just slightly higher than Kerbin's, you will end up back in Kerbin's SOI only a few days later.

Edited by Stoney3K

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Personally, I found the tank volume to be the worst roadblock.

Made a tanker: 175 tons of liquid fuel (35190 units), 215 tons of oxidizer (43010 units).

Kerbin-Minmus travel of the tanker: 4 days.

Fueling up: 1 day.

Minmus-Kerbin travel: 7 days.

Fueling up one big craft - and back to Minmus.

The problem is the amount of tanks needed uses up about half the fuel it carries. So - drills, ISRUs - that's all moot. A decent engineer, a pair of drills and a single standard ISRU will get you all the fuel you need in a week. It's the storage space for the fuel that suffers.

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8 hours ago, Stoney3K said:

If you exit Kerbin's SOI ahead of Kerbin (prograde in Kerbol orbit), Kerbin will catch up and you will get back into the planet's gravity, you only need a tiny burn at periapis to make it back into an elliptical orbit. "Higher is slower", so if your Kerbol apoapsis is just slightly higher than Kerbin's, you will end up back in Kerbin's SOI only a few days later.

I've done all of my "Sun SOI visits" behind and below Kerbin because the ship would always catch up with Kerbin. Same theory. Is higher better than lower for any reason?

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