What are the reasons for KSP not using SI units?

[Brotoro]

Oooo, post #1 by Drillgorg.

Welcome to the forums!

[Vanamonde]

No, the temp scale is in Celsius...

Kerbin's poles and equator are the same temp, and things like that. The numbers make no sense in any scale. It's just a placeholder, and the whole thing is being reworked for 1.0.

[Drillgorg]

Oooo, post #1 by Drillgorg.

Welcome to the forums!

Haha thanks! I've been lurking for a while but felt compelled to post here since I do calculations kinda like these for my job.

[Borsek]

Temperatures of planets are based purely on distance and atmosphere/no atmosphere, however they DO make sense, it's on a Celsius scale, they just aren't made biome-specific, in other words, the thermometer is ok, it's just the world that's not realistically done.

[Baxeg]

What? Are you serious?

3.2 kN ∙ 6.34 km = 20.288 J (your incorrect method)

(3.2 ∙ 10³) N ∙ (6.34 ∙ 10³) m = 20.288 ∙ 10ⶠJ (the correct method)

You're drunk, go home.

why did you ignore the k ∙ k in the 1st solution his method aint incorrect just cause you ignored the "kilo"

[Brotoro]

...the whole thing is being reworked for 1.0.

That is nice the hear.

[Fel]

Kerbin's poles and equator are the same temp, and things like that. The numbers make no sense in any scale. It's just a placeholder, and the whole thing is being reworked for 1.0.

Don't forget that parts are often rated at 3600*C and girders are even upto 5000*C, which would the the point of failure, hence meaning the melting point should be much higher.

[Brotoro]

I thought one of the 1.0 videos said the temperature tolerances of the parts were all getting lowered to 2000° or less.

[Vanamonde]

Temperatures of planets are based purely on distance and atmosphere/no atmosphere, however they DO make sense, it's on a Celsius scale, they just aren't made biome-specific, in other words, the thermometer is ok, it's just the world that's not realistically done.

Watch how those measurements fluctuate as you go in and out of sunlight, graze the surface of the sun, and so on.

[pincushionman]

When I was in college, in the US, (2000-2004) I was taught that while most industries in the States use "American" units (inch, mile, pound), space industries had switched to the metric standard. This included a senior project with a design concept for an air-launched satellite - with the arcraft portion presented in American units and the rocket/satellite design expressed in metric.

So it doesn't seem wrong to me to see kN and tonnes being thrown around in game, even though I use American units in the aircraft I work. I thought that was the modern space standard. Someone who actually works in satellites, feel free to correct me.

Furthermore, getting all up in arms about "kilo"newtons is pretty pedantic, imho. All it does is eliminate a superfluous 10^3. Same with tonne, it's shorthand for 10^3 kg or 10^6 g (this one's weird since the "base unit is the kg, not the g). We do this all the time in engineering - civil calculations use "kips" (kilopounds), material strengths are nearly always quoted in ksi (kilopounds per square inch), and stiffnesses are in Msi (megapounds per square inch). This is because in engineering, the scale of the values is always so huge, and you'd otherwise end up writing a whole lot more zeroes because having precision down to the unit values is, frankly, a waste of everybody's time, effort, and patience.

Also, as a point of reference, a tonne is 1000 kg, which is very close to 2200 lbs., so a tonne is a ton, give or take 10%.

[Fel]

Also, as a point of reference, a tonne is 1000 kg, which is very close to 2200 lbs., so a tonne is a ton, give or take 10%.

10% is all you need to crash a mars lander

Also, the metric ton isn't the only other "ton" short ton (us ton) and the long ton (uk ton)...

http://www.merriam-webster.com/table/dict/weight.htm

[Sandworm]

I get the sense that if the news announced the approach of a 300mm wave that most Americans would head for the hills.

In all seriousness, within the US the distinction is a class issue. Those with science training are fluent in metric. Not being fluent in metric allows people to avoid meaningful scientific discussions, shielding themselves from realities well understood by scientists. The "difficulties" of the metric system are re-enforced by school curricula that focus on ridiculously underused measurements. Canadians do not order beer by the deciliter. It's a separation akin to the old french/latin/english separations within britain.

Edited April 27, 2015 by Sandworm

[Vanamonde]

We're talking about the units in the game, guys. Again, let's please not get into the pros and cons of Imperial, or anything else not game-related.

[Renegrade]

Also, as a point of reference, a tonne is 1000 kg, which is very close to 2200 lbs., so a tonne is a ton, give or take 10%.

Um, that's a long ton (ah.. 2240 lbs I think), not a ton (short ton or 2000 lbs). At least in North America. Still, they're all rather close, with the long ton and metric ton (tonne) being almost identical...

How do I know such thing? I made a study of volumes, density and masses of existing vessels in order to start work on my own spacy game, which I started sometime in like.. '89 or something. Some idiot keeps on re-writing my design document, so it'll never be done at this rate. Anyhow, various references use the different sorts of tons with reckless malice.

[SAI Peregrinus]

The SI base units are the metre, kilogram, second, ampere, kelvin, mole, and candela.

The SI derived units are the radian, steradian, hertz, newton, pascal, joule, watt, coulomb, volt, farad, ohm, siemens, weber, tesla, henry, degree Celsius, lumen, lux, becquerel, gray, sievert, and katal.

The officially sanctioned non-SI units accepted for use with the SI are the minute, hour, day, degree, minute (of arc), second (of arc), hectare, litre, tonne (or metric ton), neper, bel, decibel, electron volt, unified atomic mass unit, dalton, astronomical unit, natural unit of speed (speed of light in a vacuum), n.u. of action (reduced Planck constant), n.u. of mass (electron mass), n.u. of time, atomic unit of charge (elementary charge), a.u. of mass (electron mass), a.u. of action (reduced Planck constant), a.u. of length (Bohr radius), a.u. of energy (Hartree energy), and a.u. of time.

The prefixes are yocto, zepto, atto, femto, pico, nano, micro, milli, centi, deci, deca, hecto, kilo, mega, giga, tera, peta, exa, zetta, and yotta.

The angstrom, are, barn, bar, millibar, atmosphere, bayre, mmHg, and torr are commonly used but not officially sanctioned.

The kilonewton IS an SI unit. The tonne is not an SI unit, but is accepted for use within the SI.

The SI is officially defined in the SI brochure: http://www.bipm.org/utils/common/pdf/si_brochure_8.pdf

You want Section 3, English, page 121.

Edited April 27, 2015 by SAI Peregrinus

[Nobody_1707]

When I was in college, in the US, (2000-2004) I was taught that while most industries in the States use "American" units (inch, mile, pound), space industries had switched to the metric standard. This included a senior project with a design concept for an air-launched satellite - with the arcraft portion presented in American units and the rocket/satellite design expressed in metric.

Yeah, metric is currently standard for space applications to prevent problems when we work with foreign space agencies. We were definitely still using US Customary units until, at the very earliest, they canceled the Apollo program.

[Chyort]

I vote for the ever classic FFF System. What could possibly be better for kerbals?

[Starwhip]

I thought one of the 1.0 videos said the temperature tolerances of the parts were all getting lowered to 2000° or less.

Except the heatshields, probably.

[Temeter]

KSP is not using SI units because it's a game simplifying complex concepts far enough to make it understandable for normal players without the respective scientific background, with the aim of creating a fun game.

So it's perfectly logical to use common systems instead of scientific correct ones. Makes the whole thing more intuitive and easier to relate to.

[pincushionman]

10% is all you need to crash a mars lander

Also, the metric ton isn't the only other "ton" short ton (us ton) and the long ton (uk ton)...

Um, that's a long ton (ah.. 2240 lbs I think), not a ton (short ton or 2000 lbs). At least in North America. Still, they're all rather close, with the long ton and metric ton (tonne) being almost identical...

I apologize for my statement causing confusion. I did not mean to imply they were the same, only that they were close* in an off-the-cuff, back-of-the-napkin sense. I understood the "why do they use this tonne business" question as a statement of "I don't understand what this unit represents." In fact, as long as you have an idea of how big something is that weighs a ton, you have a pretty good idea of how big something is that has a mass of one tonne.

Not exact enough to make real engineering claims, but close enough to say "oh, it's about as big as X," or "I need about Y of thisthatortheitherthing to handle this." If you need to actually run the numbers, you need the actual measurements. But the scale of things where "tons" and "tonnes" apply are not actually that different.

*in standard Earth gravity, 1 tonne mass weighs 2204 lbs., or approximately 1.1 [short] tons - that's the 10%

[Archgeek]

Oooh, I smell meat confusion. kN are blatantly SI units. So are grams, km, MW. Entities confuse SI units with SI base units. Strangely, the SI base unit for mass is the kg, not just the gram.

KSP goes with a higher order of magnitude than the base unit due to the base unit being nigh-unto useless for the application at hand.

[blu3wolf]

Also, a kilonewton is 1000 kilogram meters per second per second. That sounds metric to me.

I think you just never played a game which used pounds of force, feet for altitude, and feet per minute or knots (nautical mile per hour) for speed. Flight simulators are the worst when it comes to units.

Be thankful SQUAD uses convenient-yet-perfectly-metric units.

feet of altitude, meters of visibility, nautical miles of distance... How did anyone let ICAO get away with this??? Three different units to measure lengths???

[HelmyJune]

Also, a kilonewton is 1000 kilogram meters per second per second. That sounds metric to me.

I think you just never played a game which used pounds of force, feet for altitude, and feet per minute or knots (nautical mile per hour) for speed. Flight simulators are the worst when it comes to units.

Be thankful SQUAD uses convenient-yet-perfectly-metric units.

Obviously you have never flown a real plane. Those are all standard in aviation, as far as I know even in Europe. It is supposed to be a flight simulator after all.

To require a change would literally destroy general aviation in particular. Considering a new avionics panel cost as much as your average economy car. (In a small plane, I have no idea what a commercial panel costs)

Now if you were flying something built in Russia or China and it was in imperial units then that would be a little strange.

Experience: US Private Pilot

But more on topic to the actual thread. As far as I've seen everything in KSP is in SI units. Considering nearly all rocket science is done in SI units it makes sense. Especially after NASA crashed their Mars orbiter because they were using a mix of metric / imperial units.

[Mr. Boncrete]

If you are doing many calculations, just plug in numbers and get a totally unrealistic result, you "Oh, something is not in SI units" and you must go back and control all numbers again... That's quite irritating.

There's a lesson in this... You always need to double check your numbers to verify that you're calculating things correctly. If you plan on pursuing further education in a STEM field, get used to this. The sooner the better. Believe me, I know from personal experience. One thing that would be helpful for you is to get a good understanding of scientific notation and working with several numbers with exponents simultaneously.

It can seem daunting at first, but it's nothing more than learning a few small rules, and applying basic arithmetic to the exponents. It's nothing to get flustered over.

Also, you could go ahead and write out the long version of whatever it is you're doing... Soon enough you'll understand clearly why scientific notation is even a thing - Dealing with very large numbers is much simpler when you just account for the exponent rather than checking if you've counted the number of zeros correctly.

And I won't even get into the debate over whether SI units with prefixes are still SI units.

[AlexinTokyo]

The only non-standard units in KSP as far as I can recall right now are electric charge (which might as well be magic points for all the relationship they bear to any real-life quantities) and fuel.

EC I can forgive as an abstraction or simplification for gameplay reasons. I don't think that having to consider the details of power, voltage, current, etc. would add to the KSP experience.

What gets my goat, though, is the use of 'units' of fuel. Why, oh why, can't we get fuel capacities and mass rates in kilograms (kg.s^-1 for flow rate) or tonnes, instead of some arbitrary 'unit' which has a different mass for different types of fuel?