Solar Energy now following inverse square law

[hobbsyoyo]

Be aware that solar panels reduce their power generation as they overheat. There's a certain planet that might surprise you *hint hint*

This is realistic, fwiw.

1> Maneuvers are done at nodes. In reality a manned trip to somewhere like Mars could apply a low amount of thrust for the entire transfer, but in KSP the thrust is all done at once and then the vessel coasts until it enters the SOI and has to do an insertion burn. For a renewable resource like electricity, that means your vessel needs enough generation and/or battery capacity to handle the entire burn in a short period.

and more importantly for this discussion,

That's only true if you are using an ion engine to get to Mars. Real missions (and the vast majority to the region of Mars don't use Ion engines) use higher thrust hydrazine thrusters with burn times on the same order as KSP burns.

2> In the real world an ion drive has a ridiculously low thrust (several orders of magnitude below KSP's version), which also means they don't have to use huge amounts of electricity for a burn in the first place.

Ion engines require ridiculous amounts of power at any thrust. They all operate in the multi-kW range, necessitating large solar arrays. They're all power hogs regardless of their thrust levels - it's the nature of the beast.

If you want to make something like an ion-propelled probe that can visit the outer planets using the real world's engineering efficiencies, it wouldn't need to stack a dozen RTGs and/or dozens of solar arrays just to power a single small engine.

Yes it would to be usable at the outer planets. The asteroid belt is about as far as you can push the technology using solar arrays. RTG's cannot provide nearly enough power to do the job under any realistic circumstances IRL.

Primarily thanks to the 0.23 thrust increase (a factor of 4 difference), though, one KSP ion engine now uses about 8.5e/s, while one RTG only produces 0.75 and we've already discussed how ineffective the solar panels are. So, you end up stacking a ton of RTGs (at a ridiculous cost) for each ion engine, or use an appalling number of solar panels.

The fact that you can power any ion probe with RTG's is a concession to enhanced game play over realism.

Anywho, sorry to quibble over real life stuff that's beside the point.

What I would like to say is that I do fully support making ion engines higher thrust and lower power requirement for gameplay reasons. I haven't gotten ion engines in the new career mode yet, but in previous sandbox iterations, you couldn't leave the ion engine thrusting (even without time warp) for hours on it's own - you had to manually tweak the trajectory every few minutes because SAS couldn't keep a lock on the heading. So they need to have more powerful thrust so you can do a good burn in like 45 minutes tops. And also the lower power requirements will let us use them further out and with less RTG's and solar cells.

Yeah, I'm sorry that my reply came out so flippantly. I didn't mean to imply that you don't! Funny, I'm also an astronomer and occasional spacecraft engineer. How many of us are on here, anyway?

I'm an aerospace engineer, I work on satellites.

[Grumman]

There's many, many fundamental reasons why it's not possible. But let give me you just one to consider - how exactly are you going to synchronize your rotation with the trajectory around the sun? You don't realize the amount of precision required. To end this quickly: KSP just wasn't build to allow things like that.

That is trivially easy to answer: when you feel you are going too far off course, drop out of timewarp for a second and adjust your orientation. Being able to skip the hours of sitting around doing nothing makes that one second spent out of timewarp adjusting your course much easier to bear.

Using your Dawn flightpath as an example: Yes, it required a total of 1,000 degrees of incremental trajectory adjustments, but those adjustments took place over five years. Even if you adjusted your course every time you were more than 5 degrees off course and took a full second to turn your ship those 5 degrees, that's still only three minutes of time spent instead of five years.

Anyway, if you want to discuss this further, I started a thread here.

[Laie]

(refinery working off fuel cells)

Actually, it is realistic. If it took more energy to refine the ore, than you could get from the refined fuel, you'd be better off just using your input energy directly, than bother mining at all in the first place. And there would be no oil industry on Earth.

That's comparing pineapples and oranges. First off, how would you use the energy "directly"? It will do you no good if you have nothing to use it on. You need some propellant to toss out of your rocket in order to create thrust.

Second, I don't want to go into the details, but you need a lot more energy to convert stuff into fuel than you eventually gain by burning it. As with all things energy, you can't win or draw even. It's still worthwhile because energy is cheap, especially in this game, while lifting fuel from the motherworld most decidedly isn't.

The "you can't win or draw even" bit should by rights prevent you from running refineries on fuel cells.

[Grumman]

Second, I don't want to go into the details, but you need a lot more energy to convert stuff into fuel than you eventually gain by burning it. As with all things energy, you can't win or draw even. It's still worthwhile because energy is cheap, especially in this game, while lifting fuel from the motherworld most decidedly isn't.

The "you can't win or draw even" bit should by rights prevent you from running refineries on fuel cells.

The laws of thermodynamics you are referring to only apply to a closed system. This is not a closed system - you are importing energy in the form of fuel-containing ore into the system by extracting it from the Earth.

[sal_vager]

Yep, the extra energy is in the ore, just like it's cheaper to extract oil than it is to make fuel with the Fischer–Tropsch process.

[lazarus1024]

I'm perfectly aware of the physics involved, as I'm an astronomer by profession. The thing is, KSP has already changed quite a few other things for the sake of gameplay, primarily due to one single factor: only the active vessel can apply thrust, and only when it's not in time warp. While it sounds simple, in practice this has a couple significant effects:

1> Maneuvers are done at nodes. In reality a manned trip to somewhere like Mars could apply a low amount of thrust for the entire transfer, but in KSP the thrust is all done at once and then the vessel coasts until it enters the SOI and has to do an insertion burn. For a renewable resource like electricity, that means your vessel needs enough generation and/or battery capacity to handle the entire burn in a short period.

and more importantly for this discussion,

2> In the real world an ion drive has a ridiculously low thrust (several orders of magnitude below KSP's version), which also means they don't have to use huge amounts of electricity for a burn in the first place.

If you want to make something like an ion-propelled probe that can visit the outer planets using the real world's engineering efficiencies, it wouldn't need to stack a dozen RTGs and/or dozens of solar arrays just to power a single small engine. Primarily thanks to the 0.23 thrust increase (a factor of 4 difference), though, one KSP ion engine now uses about 8.5e/s, while one RTG only produces 0.75 and we've already discussed how ineffective the solar panels are. So, you end up stacking a ton of RTGs (at a ridiculous cost) for each ion engine, or use an appalling number of solar panels.

The point is, it all depends on what the developers' concept of an ideal unmanned probe is. If it's supposed to be something with an ion engine, one RTG, four small solar arrays, and a few batteries, then you'd get something that'd look approximately like a real-world probe. But, that sort of design can't even produce one quarter of the electricity needed to offset an ion's thrust. Sure, if we could set the probe to 10% throttle and timewarp (or switch to something else) then it'd be different, but we can't, and the developers already made it clear with the new resource scanning system that they're not fans of the "go make a sandwich" type of gameplay. So, for gameplay reasons the current electrical generators need to be boosted substantially just to keep ions viable as a propulsion system.

Errrr, umm, probably not. It is most efficient the burn your fuel low in the gravity well to take advantage of the Oberth effect. You'd only burn at a low thrust constant rate for the duration of the mission, then flip and apply reverse thrust part way through if your only option was a low thrust engine or were limited by something else, like electrical generation (ion/VASMIR).

It would be nice if the equation was tweaked slightly, or failing that give us another couple of options. Like a higher power/density RTG (maybe as a 1.5m size, but thin stack, 5-10e/sec) as a top option and maybe a nuke plant above all of those (but with a lot of mass, like 2-4t, 2.5m size but maybe producing something like 100 e/sec).

[Laie]

This is not a closed system - you are importing energy in the form of fuel-containing ore into the system by extracting it from the Earth.

Some hand-waving required... but yes, for all we know this "Ore" may well be a matching mixture of LF&O that requires nothing but some separation. Makes me wonder what would happen if you held a match to an asteroid, though. Or bumped into it.

[Renegrade]

Seriously? Another thread about this?

http://forum.kerbalspaceprogram.com/threads/118819-PSA-Solar-panels-now-useless-past-Dres-%28as-it-should-be%29

http://forum.kerbalspaceprogram.com/threads/118364-Inverse-square-solar-power-Solar-panels-rebalanced

Forum must be write-only memory.

I notice that I was not getting the solar power I got in previous version out in Jool space. So I checked with a solar escape probe, turns out solar power now follows the inverse square law. So for example the KSP wiki still states that out at Jool you receive 50% the power you receive at kerbin, but now it is 3-4%

Jool and Kerbin share an almost identical distance relationship is Jupiter and Earth, and now have the almost identical solar power available! Imagine that!

This changes game play radically! Solar power is virtually useless out beyond Duna. How is laythe warm enough to be wet?

We actually have power-based gameplay, forcing us to consider the benefits of solar vs fuel cell vs RTG, rather than just spamming #lolmassless #lolstats for any physical destination in the Kerbol system. The old system was clearly #lolsolar.

Here's a counter question by the way: how is Minmus made out of mint ice cream/frozen water?

I'm not saying that they should go back to the old equation, but it does mean that solar panels seem almost useless now for anything that isn't explicitly designed only to go to the inner planets. The base energy production numbers might just need a bit of tweaking to keep solar power viable.

Just like in real life, the outer planets ARE harder to deal with. The Juno spacecraft will be the first Jupiter mission to be powered by solar instead of RTG (and that's likely more due to political pressure and declining Pu-238 stocks, as it's panels produce the same power as the Voyager probes' RTG set, at like three times the mass), and it will be sporting three huge panels that make Gigantors look small.

No tweaking is needed. The only thing I'd like to see added would be some more RTG options, for part count reduction reasons (or maybe output buffage to the existing RTG for the same reason - maybe double it's output, so it's still sucky close to the sun compared to solar, but more competitive out system and fewer parts).

[Brotoro]

Actually, it is realistic. If it took more energy to refine the ore, than you could get from the refined fuel, you'd be better off just using your input energy directly, than bother mining at all in the first place. And there would be no oil industry on Earth.

No. You are using energy sources (be it solar cells or an RTG) that have a low power (energy per second) output and no reaction mass to turn some feedstock into an energy source that is very concentrated and includes reaction mass...just the sort of thing needed to run a rocket engine.

And people keep using the oil industry on Earth as an example of why ISRU works...but this is also faulty thinking. The oil industry works on Earth only because we have an atmosphere with lots of oxygen in it, so we have a source of free oxidizer that you don't have in almost all places out in space in KSP. The oil would be useless as a propellant without the oxidizer. Both the oil AND the oxidizer were provided to us by photosynthetic lifeforms, which used sunlight over long periods of time to perform the chemical separation to create the useable propellants for us. All the oil industry does is separate a fraction of the oil that is useful (for a particular purpose) from the rest, and bring it to us.

Ore is just goofy. Unless it is an explosive mixture of fuel and oxidizer, which is also goofy since any meteor strike would start a chemical reaction that would explode the crust of your planet (but which would explain why Danny can destroy a whole planet by hitting it with a kerbal). And even then, how can you have the option of turning one tonne of ore into either one tonne of liquid fuel OR one tonne of oxidizer?

Edited May 12, 2015 by Brotoro

[TheMoonRover]

<snip> I don't actually see that - for one thing I can't think of any mission that has used (or has proposed using) ion engines beyond about Mars. <another snip>

I can think of one: Dawn. That uses ion propulsion and is exploring the asteroid belt. It's currently somewhere around the dwarf planet Ceres (RL equivalent of Dres), which has just under twice the semi-major axis of Mars IIRC.

<big snip> Ore is just goofy. Unless it is an explosive mixture of fuel and oxidizer, which is also goofy since any meteor strike would start a chemical reaction that would explode the crust of your planet (but which would explain why Danny can destroy a whole planet by hitting it with a kerbal). And even then, how can you have the option of turning one tonne of ore into either one tonne of liquid fuel OR one tonne of oxidizer?

I agree that the Chemistry is extremely dubious, however it DOES obey the laws of themodynamics, as it is not a closed system. Ore is being mined from the ground, and the energy comes from it. Consider the implications of a more (or less) power-efficient drill.

[lazarus1024]

No. You are using energy sources (be it solar cells or an RTG) that have a low power (energy per second) output and no reaction mass to turn some feedstock into an energy source that is very concentrated and includes reaction mass...just the sort of thing needed to run a rocket engine.

And people keep using the oil industry on Earth as an example of why ISRU works...but this is also faulty thinking. The oil industry works on Earth only because we have an atmosphere with lots of oxygen in it, so we have a source of free oxidizer that you don't have in almost all places out in space in KSP. The oil would be useless as a propellant without the oxidizer. Both the oil AND the oxidizer were provided to us by photosynthetic lifeforms, which used sunlight over long periods of time to perform the chemical separation to create the useable propellants for us. All the oil industry does is separate a fraction of the oil that is useful (for a particular purpose) from the rest, and bring it to us.

Ore is just goofy. Unless it is an explosive mixture of fuel and oxidizer, which is also goofy since any meteor strike would start a chemical reaction that would explode the crust of your planet (but which would explain why Danny can destroy a whole planet by hitting it with a kerbal). And even then, how can you have the option of turning one tonne of ore into either one tonne of liquid fuel OR one tonne of oxidizer?

If Ore were actually ice, all you'd need is electricity to melt it and then hydrolize it. Then you'd be 1:1 with rocket fuel/oxidizer and starting feed stock.

Frankly I think calling it ore is silly, it should just be called ice.

[Fel]

If Ore were actually ice, all you'd need is electricity to melt it and then hydrolize it. Then you'd be 1:1 with rocket fuel/oxidizer and starting feed stock.

Frankly I think calling it ore is silly, it should just be called ice.

So...

A) You have a magical ice detection system...

You heat up the water to 0~1 degrees Celsius.

C) You put some ions in the water to make separation easier

D) You run an electric current through the water slowly, and with much waste, converting it into H2 and O2

E) You cool down the gas past the boiling point of O2 but before the boiling point of H2

F) You separate out the O2 from the H2 (it should be the liquid that remains)

G) You now cool down the H2 to form liquid H2.

You can do all of this... but it isn't "free energy", even if it isn't a closed system.

Actually, it is realistic. If it took more energy to refine the ore, than you could get from the refined fuel, you'd be better off just using your input energy directly, than bother mining at all in the first place. And there would be no oil industry on Earth.

Oil is usable in its pure form; but the "extraction process" also isn't very destructive on the oil itself. Oil, basically, is energy in a very pure form.

The "space equivalent" would be having raw deposits of H2 and O2 just lying around. Of course, impurities can do some pretty nasty things and purifying raw chemicals like that takes a fair amount of energy as well. Let alone how you somehow manage to detect them without even testing to see what the chemicals are.

"gameplay" vs "reality"

Edited May 12, 2015 by Fel

[CorBlimey]

You've also got fuel cells, but yeah, RTGs are your only choice at that point. Also, a tip for power usage: "locked" batteries can be re-enabled even when your probe is out of power, so they're really useful as emergency or long-term energy storage. Took me way too long to figure this out...

tip of my hat to you sir. I did not know that. That is damn damn useful (hopefully it works with remotetech, but I doubt it, will have to see)

[Renegrade]

If Ore were actually ice, all you'd need is electricity to melt it and then hydrolize it. Then you'd be 1:1 with rocket fuel/oxidizer and starting feed stock.

Frankly I think calling it ore is silly, it should just be called ice.

This entire Ore thing is off-topic, but what the heck? We've got enough of these solar threads already~

Ice is the output from H2/LOX burning - or to be more exact, water. There's no way you'd be able to justify using fuel cells from water (that's the infamous water-powered car), as it would take at least as much energy for electrolysis to convert it into hydrogen and oxygen as it would get back from burning (significantly more so in fact).

Ice powered car:

Problem, science?

With Ore, you can't be certain as to what it is (although I agree that the 1:1 ratio was a mistake), it could very well basically be a LiquidFuel/Oxidizer slurry that could indeed very well explode if you heated it too much..

[quasarrgames]

It's funny how nobody's even thought of the other side of the scale. Now solar panels are even more useful near eve and moho.

FINALLY I CAN DRAIN THEM DRY WITH MY SOLAR DRILL OF AWESOME! > : )

[xtoro]

Guys, remember, Squad has said that KSP is a game first, a simulator second. So things that are unrealistic are designed for gameplay/playability, and not based on reality. No sense getting all upset over these things or comparing KSP to real life... It's just to have fun. Remember, the solar system isn't that small, and there are no little green kerbals running around in real life either

[Renegrade]

It's funny how nobody's even thought of the other side of the scale. Now solar panels are even more useful near eve and moho.

FINALLY I CAN DRAIN THEM DRY WITH MY SOLAR DRILL OF AWESOME! > : )

>.<

I think that's always been the case~

(although as was mentioned before, they're negatively impacted by heat, so not sure how an Eve or Moho installation would fare when it's in the sunlight)

[architeuthis]

This entire Ore thing is off-topic, but what the heck? We've got enough of these solar threads already~

Ice is the output from H2/LOX burning - or to be more exact, water. There's no way you'd be able to justify using fuel cells from water (that's the infamous water-powered car), as it would take at least as much energy for electrolysis to convert it into hydrogen and oxygen as it would get back from burning (significantly more so in fact).

Ice powered car:

http://alpha.renegrade.net/images/KSP_Science.jpg

Problem, science?

With Ore, you can't be certain as to what it is (although I agree that the 1:1 ratio was a mistake), it could very well basically be a LiquidFuel/Oxidizer slurry that could indeed very well explode if you heated it too much..

It does seem bad for gameplay balance, not to mention straining physically incredulity that you can more than break even powering your ISRU plant with just fuel cells. IMO it makes things far too easy past Duna's orbit.

For comparisons sake, the most recent NASA manned Mars DRM called for predeployed ISRU plants that would produce LOX (via solid oxide CO2 electrolyzers) for the ascent vehicle and ECLSS consumables. Since they are mission critical complex systems two redundant sets of ISRU plants are would be predeployed. Power would be supplied by a 30 kWe fission reactor. Cryocoolers could potentially condense CH4 processesed via the Sabatier process/electrolysis from the martian regolith as well but would require far more power (close to 1MWe if nuclear). If solar PV is substituted for the reactor the ISRU power requirements increase again by a factor of three to four because propellant production could only be done during the day, which requires a greater processing rate (and even moreso if there is an unplanned 1-2 month long martian dust storm). The ISRU plant would chug away for a minimum of 300 days to produce enough oxygen for the ascent vehicle. With a bigger system and even more power the process could potentially be sped up.

...1 MWe is alot of power! About 10 ISS arrays worth!