Kerbal Space Program is wall-to-wall metric. That is great!

[MetricKerbalist]

Hi everyone,

I am so glad that Kerbal Space Program uses the metric system exclusively.  The metric system -- that is, the International System of Units (SI), as the modern metric system is known -- is a precondition for doing any kind of serious science, including space science.

Hooray for KSP.

Stanley

[MetricKerbalist]

Hi everyone,

I will also point out that I have already learned a lot about astrophysics from KSP.  I have now spent a lot of time looking at the KSP Wiki.  Looking at the specifications of the seven plants in the Kerbol System has got me to examining or reexamining orbital mechanics.  I know a very little bit about the subject, and thinking about it in the context of the Kerbol system has led me to ponder old things -- that is, subjects which I already knew but have not thought about in a long time -- and discover new ones.

I am very enthused about KSP.

Stanley

[Vanamonde]

Howdy, and glad you're enjoying your metric practice. 

[Starhelperdude]

I have flashbacks from a thread that was created, and closed, long ago...

but yeah, I like metric

welcome to the forums!

[MetricKerbalist]

Hi Starhelperdue,

Looking at your description, apparently you are involved with the European Space Agency, which of course is highly impressive.   Regarding the metric system, Germany and the entire European continent is way ahead of the United States.  In my considered opinion, full metrication is one of the biggest reforms needed in the United States.  That is why I was so enthused to see just how metricated -- that is to say, completely metricated -- Kerbal Space Program is.

Stanley

[Spaceman.Spiff]

Hi @MetricKerbalist

Welcome to the forums!

 

[Zhetaan]

Well, I wouldn't say exclusively.  Electric charge still ... well, I don't know what it is.  It's not in coulombs, that's for certain.  It's not convertible to joules, ampere-seconds, watts, or any other unit I can tell, either.

Other than that, though, yes, it's pretty exclusively metric--which is pretty funny if you think about it, because astronomy in general is about the least metric of the physical sciences.

In any case, welcome to the happy little family.

Edited June 2, 2021 by Zhetaan

[MetricKerbalist]

3 minutes ago, Zhetaan said:

Well, I wouldn't say exclusively.  Electric charge still ... well, I don't know what it is.  It's not in coulombs, that's for certain.  It's not convertible to joules, ampere-seconds, watts, or any other unit I can tell, either.

Other than that, though, yes, it's pretty exclusively metric--which is pretty funny if you think about it, because astronomy in general is about the least metric of the physical sciences.

In any case, welcome to the happy little family.

Hi Zhetaan,

Thank you for your response.

So first -- and this is a genuine question -- what units does Kerbal Space Program use for electrical measurements?  I honestly don't know, so could you kindly inform us.

Second, why do you say that astronomy is so non-metric?  Here I assume you refer to the fact that astronomers and astrophysicists often use astronomical units and parsecs to measure distance.  But the BIPM (that is, the International Bureau of Weights and Measures, which has day-to-day responsibility for administering SI) specifically allows these non-metric units to be used because they are so useful in space science.  However, if space scientists were to translate astronomical units and parsecs to metric units, then these non-metric units would be converted to metres or to some sub-unit or super-unit of metres (for example, kilometres).  They would not be translated to -- heaven forbid -- miles or feet.

Stanley

[Zhetaan]

12 hours ago, MetricKerbalist said:

So first -- and this is a genuine question -- what units does Kerbal Space Program use for electrical measurements?  I honestly don't know, so could you kindly inform us.

It doesn't have a name:  it's just an EC unit.  The reason for it is because the other things that are measured on a rocket, such as Fuel or Ore or even IntakeAir, have mass and volume, so (although this was not always the case) the developers decided to standardise the massive things to metric or metric-derived masses, volumes, and densities.  EC doesn't have any of these properties, and more to the point, the way it is used in the game is definitely a departure from real-world physics, so even if it were to be standardised, it wouldn't be realistic.  For example, batteries in KSP function a lot more like capacitors.  A number of rocket engines have 'alternators', which would be a very short-lived experiment if one tried it in real life.  Aside from that, something that takes energy from the exhaust, such as a turbocharger, would be seriously detrimental to the rocket's function:  taking energy out of the exhaust is the very last thing that one would want to do, because chemical rocket engines are inefficient enough as it is.

12 hours ago, MetricKerbalist said:

Second, why do you say that astronomy is so non-metric?  Here I assume you refer to the fact that astronomers and astrophysicists often use astronomical units and parsecs to measure distance.  But the BIPM (that is, the International Bureau of Weights and Measures, which has day-to-day responsibility for administering SI) specifically allows these non-metric units to be used because they are so useful in space science.

I didn't; I said that it was the least metric.  It's still very metric, but a lot of the units used in astronomy stand apart from the metric system.

Part of that is due to the use of the arbitrary--but situationally appropriate--units of measure you described.  The simple fact is that astronomical measurement is so far off the scale that SI doesn't have the range to properly accommodate it.  In addition to the AU and parsec (and this is hardly an exhaustive list), there is the gee, which is technically a unit of acceleration, and also a selection of masses and distances that derive from astronomical objects and not SI base units.  Black holes, for example, are described in terms of solar masses--which, on the one hand, I understand, but on the other, I'd really, really like to hear someone use the word yottagram in a sentence.  In fairness, though, one solar mass is beyond the limits of even the newly-proposed SI prefix definitions at 1,989 queccagrams, and compounding the prefix, i.e., 'kilo-queccagram', is not allowed.  I could go with 1.989 ronnatonnes, but I consider that to blur the line between systematic measurement and just making stuff up to sound cool.  There's a reason that astronomers tend to use scientific notation for everything:  1.989 x 10³⁰ kg is sterile, but it won't make anyone burst into fits of giggles.  At the other end of the scale, I once saw a paper describe the gas pressure in a nebula in terms of particles and kelvin per cubic light year.  It's a perfectly valid unit (it's even pseudo-SI if you consider that, since the speed of light defines the metre, a light year is a valid derived unit), albeit it is an odd construction.   It makes sense because the density and temperature of a nebula are relatively easy to measure at a distance, and it's all related through the Ideal Gas Law, so it should be apparent that astronomers know how to use SI ... it's just that often, they can't.

Another part of it is that many, many of the quantities used in astronomy are technically outside of the metric system's purview because they lack dimension.  Of the six Keplerian elements, only semi-major axis is an SI unit.  Eccentricity is a dimensionless ratio; longitude of ascending node, argument of periapsis, inclination, and true anomaly at epoch are all angles (and therefore also dimensionless ratios, albeit with extra conversion factors).  I'll grant that orbital state vectors are typically metric, but they are not used in KSP.  Angles do deserve a special mention:  obviously, the radian can be derived by dividing the length of arc in metres by the radius, also in metres, and I'm certain you're aware that's how it's defined for use in SI.  I'd be willing to accept that for the same reason that I'm willing to accept the temporal second's adoption by SI (the unit saw utility in a number of prior systems before SI gave it a specific definition), but the problem is that astronomers tend to measure angles in degrees (and its subdivisions:  a parsec is one arcsecond of parallax, after all).   Degrees and angular seconds are accepted for use with SI, but they're not SI.  They aren't even coherent units; they require conversion factors.

Not to leave rocketry out of it, either, but in rocketry, we get a lot of ratios:  thrust-to-weight for determining a rocket's lifting ability against the local gravity, mass ratio for calculating its available delta-V, and payload fraction for determining its capacity (and therefore efficiency).  There is lift-to-drag ratio, too, although that is arguably more appropriate to aeroplanes (and spaceplanes) than to rockets in KSP.

None of this, of course, is to argue either for or against the use of the metric system.  I'm not arguing at all:  I am merely pointing out that any system designed for broad applicability is going to run into edge case trouble when confronted with highly technical, highly complex fields such as rocketry and astronomy, and especially so when it operates at the extremes of scale.  As such, you'll find that there are a lot of situations that require either non-standard units or a lot of powers of ten.  However, just as with measuring gas pressure in a nebula, the metric system is often perfectly valid for deriving those units or counting those powers of ten.

12 hours ago, MetricKerbalist said:

They would not be translated to -- heaven forbid -- miles or feet.

Oh, certainly not.  I'm perfectly happy knowing that when I need to convert astronomical units, I can rely on my beloved 327.2 gigacubits.

 

 

 

... I hope that made you laugh, rather than cringe.  Seriously, welcome to the forum.  I hope you have fun here.

Edited June 3, 2021 by Zhetaan

[Kerbart]

21 minutes ago, Zhetaan said:

(...)

Not to leave rocketry out of it, either, but in rocketry, we get a lot of ratios:  thrust-to-weight for determining a rocket's lifting ability against the local gravity, mass ratio for calculating its available delta-V, and payload fraction for determining its capacity (and therefore efficiency).  There is lift-to-drag ratio, too, although that is arguably more appropriate to aeroplanes (and spaceplanes) than to rockets in KSP.

(...)

Well, speaking of rocketry, the main reason we divide effective exhaust velocity with one standard g in order to get an I_sp is because it delivers a number that's measured in a unit everyone agrees on: seconds, so nobody has to wonder what 2000 m/s is when expressed in furlongs per fortnight.

[MetricKerbalist]

Hi Zhetaan and Kerbart,

Thank you very much for your interesting and informative posts.  They offer much food for thought.

Stanley

[kerbonautkazoo]

hello and welcome to the KSP forums! 

[Zhetaan]

11 hours ago, Kerbart said:

Well, speaking of rocketry, the main reason we divide effective exhaust velocity with one standard g in order to get an I_sp is because it delivers a number that's measured in a unit everyone agrees on: seconds, so nobody has to wonder what 2000 m/s is when expressed in furlongs per fortnight.

It's interesting that you should mention that, because there's a deeper history there.  Specific X is simply a measurement of some quantity divided by the mass to give the amount of that quantity per unit mass.  It's particularly useful when comparing things such as different-mass objects in orbit (or the same object that changes mass, such as a rocket).  Impulse is a quantity of force multiplied by its duration (time), and it takes units equivalent to momentum (newton-seconds in SI, which simplifies to units of mass times displacement divided by time).  Specific impulse, therefore, technically takes units equivalent to velocity (displacement divided by time).

How, then, do we get 'specific impulse' measured in seconds?

The newton (the current SI unit of force) was not standardised until 1946--it wasn't even officially named until 1948.  What, then, did a German rocket scientist in the early to mid-1940s use as a unit of force?

Kilograms.  Oh, yes.

Kilogram-force is a unit equivalent to one kilogram in a one-gee acceleration, so in other words, it equates to 9.80665 newtons.  This technically means that washroom scales ought to be calibrated in newtons and not kilograms (maybe dekanewtons for the sake of close-to-familiar numbers), because unless that scale is a mass balance, it is measuring weight--i.e., force--and not mass, and will, for example, show a reduced value if used on the moon where the force is less because the gravity is less.

Under the German system then in place, mass was a derived unit, not a base unit, so kilograms-force were more fundamental than the kilograms we know today.  It is true that this unit had a proper name, kilopond, though the word kilogram was often used interchangeably with it.  In any case, the point is that aside from the ambiguities that arise when people use the same name interchangeably for units of mass and units of force, when you take units of force multiplied by time and divide, not by units of mass, but by units of force, it leaves only time.

It is true that the U.S. customary system has the same problem with pounds-force and pounds-mass, and the correct unit of mass, the slug, has not seen widespread use.  However, those expatriated German rocket scientists would have seen that as a feature of the U.S. system because it made things easier and more familiar.  Yes, measuring specific impulse in seconds made for easy unit conversion (by obviating the need for it), but that was an emergent property of the systems in use at the time, not a deliberate effort to ease conversion between metric and U.S. units.  Keep in mind that we're discussing actual rocket scientists; being good with numbers and with unit conversion is pretty much a requirement.

Although sometimes, they do get it wrong.  I'm looking at you, Mars Climate Orbiter.

 

P.S.:  Picking obscure or non-standard units doesn't really demonstrate difficulty so much as it does unfamiliarity.  There's a valid point in there, but I don't think it's the one that you were trying to make.  On the one hand, it doesn't take a lot of effort to find out that 2,000 metres per second is 1.203 x 10⁷ furlongs per fortnight.  On the other, I can do the same thing with metric and say that it's 41.30 megacalories per newton-day.

[MetricKerbalist]

15 hours ago, Zhetaan said:

I'm perfectly happy knowing that when I need to convert astronomical units, I can rely on my beloved 327.2 gigacubits.

... I hope that made you laugh, rather than cringe.  Seriously, welcome to the forum.  I hope you have fun here.

Hi Zhetaan,

First, both of your posts were scholarly and instructive.  I enjoyed reading them, and I learned by reading from them.

Second, your conversion of astronomical units to cubits made me chuckle and intrigued me.  Given that dispute exists as to the exact length of a cubit, your conversion is correct!

Stanley

[Ben J. Kerman]

Welcome, @MetricKerbalist! I wish the US used the metric system. Besides 2 other countries that I don't remember, we are the only country that doesn't use the metric system.

Spoiler

Especially for things like cranes, since many equipment manufacturers are outside of the US (Liebherr, a German brand of crane, construction equipment, fridges, hotels, gear cutting machines, aerospace components, the list goes on), you need to make sure to convert the maximum capacity of the crane in a certain configuration on the load chart to US tons from tonnes (I am sure Liebherr probably has imperial load charts available), unless you know the weight of the load in tonnes. Sorry, when I get to ranting about cranes I just can't shut up! I might be talking gibberish anyway, since I am not a crane operator. Yet. At least not in real life, but I am ok at operating computer simulated and Lego cranes.

I hope you find these forums helpful, humorous, and a place to share your stuff with other Kerbonauts.

[MetricKerbalist]

Hi Ben J. Kerman,

You are referring to Myanmar (Burma) and Liberia.  But I believe that even they use degrees Celsius.

Thank you for your post, which was interesting.

Stanley

[Arecibo Kerman]

But it is all still intermingled between imperial and metric.

In the UK miles per hour is still a standard measurement.

Anyway welcome to the forum @MetricKerbalist

[MetricKerbalist]

Hi Arecibo,

Right.  The UK still does use miles per hour.  Ireland and especially continental Europe is wall-to-wall metric, but the UK refuses to go along.

Stanley