Why I really appreciate the Kerbal players here

[wumpus]

On 12/21/2015 at 11:50 AM, Sean Mirrsen said:

As an aside to that aside, I consider that the worst article of the entire What If series [what if #58: Orbital Speed]. For the reason that it took one facet of the questions mentioned, and ran with it without answering the actual questions.

Indeed two of the three questions listed imply having to control the speed of reentry, and the first question explicitly proposes slowing down. So naturally the entire article is devoted to saying how going into space means going fast, and no word on whether slowing down would be a valid way of avoiding the need for a heatshield.

The question is landing without a heatshield, by means of firing a retrorocket.  The problem is that such a descent would be worse than a (semi-efficient) Tylo decent (scaled to our solar system, anyway), and vastly worse than an Earth ascent (and the required mass of boosters).  Step one would be a pure sideways burn, the reverse of which what if #58 explained (painfully close to an Earth descent, but with neither gravity nor aero (including non-vac Isp) losses.  You then pick an acceptable speed downward (lets say 500mph, just because the direction this thread has taken.  And also because it is close enough to what [commercial] jets fly at that we can be confidant it doesn't require a heat shield.  Assuming we start at 50 miles up (within the Karman line, but still a thin atmosphere) we will then have to burn a constant 1g thrust for 6 minutes.

To explain all the issues to a non-Kerbalnaut requires first explaining everything what if #58 did, determining the size of the rocket for the final descent burn (really big), and then trying to imagine the size of the rocket that could do such a feat.  If you are lucky, an Apollo booster (the part that took them to orbit) could do the slowdown (obviously) and the command module* could do the 6 minute 1g burn (you might have to soup up the engines, there really isn't any reason for that much thrust in the command module).  You could then finish the whole article with a simple comparison about bringing a heat shield to return to Earth or bringing an Apollo rocket.

* I think the command module might have done some of the orbital burn.  This wouldn't be needed due to the extra delta-v around due to the lack of any gravity losses.

PS.  In the US in the 1970s, students were exclusively taught the metric system in elementary school (at least in Baltimore County, Maryland).  President Carter (a nuclear engineer himself) had made the biggest push for metric since President Jefferson (back when the metric system was new).  The most important thing I learned in high school chemistry was something my teacher called the "factor label method", which was how to convert back and forth between units.  This is critical since nearly all American engineers and similar who have to calculate with imperial measurements convert them to metric before calculation and then convert them back for labels/purchases/whatever (might not be needed for trivial calculations, but it is nearly always the fallback when you have to change units more than once).  The "factor label method" would *still* be critical (even in the metric only world) as it allows you to deal with multiple units (like converting distance to area, and thrust vs. mass) easily.  I was shocked how much trouble this gave other engineering students while I simply did my basic chemistry approach and got the right answer.

PPS.  Is that really where "points" come from, for font size?  If I set things for metric do my word processors show fonts in mm?

Edited March 21, 2016 by wumpus

[Mastikator]

1 hour ago, 5thHorseman said:

In all fairness, every single person on Earth would agree that was a jumbled mess. But those of use who are belabored with the Imperial System actually only use 4 of those 38 terms, making that chart almost 10 times the size it should be.

Nobody but an expert in some field that uses the special terms even considers anything outside of:

Inch -12-> Foot -3-> Yard -1750-> Mile, and for most of us (myself included, I had to look it up) that "1750" is actually just "a lot."

Are the numbers logical? No. Are they the worst thing to befall mankind since the dawn of civilization? Nope, not that either. Are they a minor inconvenience that I'd rather be rid of? You betcha. But so are about 100 other things in life.

The problem with the imperial system isn't that it isn't logical nor natural, it's that it's convoluted. Pretty much everyone knows only of base 10 so having all measurements be measured in base 10 is very practical. 1km = 1000meter, 1 cubic decimeter of water = 1 kg. It's very straightforward and simple. Metric is far from perfect and it's arbitrary but it's still leagues less convoluted than imperial.

[Nathair]

3 minutes ago, Mastikator said:

 Metric is far from perfect and it's arbitrary but it's still leagues less convoluted than imperial.

Arbitrary means either whimsical or dictatorial, neither of which really applies here. The SI system with its decimal multiples was chosen for some very specific (and good) reasons, they didn't just pick a radix out of a hat and run with it. While the base units are somewhat arbitrary in the sense that a metre could have been defined as, say, ten times longer or shorter than it was I don't see how any system could possibly escape that. You have to pick a starting point for any system. As to dictatorial, I just don't think we could call a system that has gradually been voluntarily adopted over a period of centuries "arbitrary" in that sense either.

[Korvath85]

1 hour ago, Waxing_Kibbous said:

*quick correction, it's 1760 yards in a mile, or 5,280'.

Do golf courses in non-USA countries use yards? Hmmm...

Ah yes, I read it wrong.  I interpreted the emoji as poking fun at the metre-meter connundrum.

[Enorats]

Base 10 being more intuitive has nothing to do with being human centric or how many fingers or toes we have. It is intuitive because our entire numeric system is a base 10 system. If our system used some other base then that base would be more intuitive to us because we'd have more practice with it. It also makes conversions quite easy as we can simply add or drop zeroes when the bases match up in this manner.

 

Some of the earliest counting systems used a base 6 if I recall correctly, and our entire system of timekeeping is a relic of that system, which is why all our time measurements are multiples of 6.

[Mastikator]

2 hours ago, Nathair said:

Arbitrary means either whimsical or dictatorial, neither of which really applies here. The SI system with its decimal multiples was chosen for some very specific (and good) reasons, they didn't just pick a radix out of a hat and run with it. While the base units are somewhat arbitrary in the sense that a metre could have been defined as, say, ten times longer or shorter than it was I don't see how any system could possibly escape that. You have to pick a starting point for any system. As to dictatorial, I just don't think we could call a system that has gradually been voluntarily adopted over a period of centuries "arbitrary" in that sense either.

The meter is currently defined as the length light can travel in 1/299 792 458th of a second. 299 792 458 is not a natural number but at least the meter is defined on a natural constant.

The kilogram on the other hand, a measurement of mass is defined by the weight of this thing on the Earth. Which is not only arbitrary but problematic because weight is a function of gravity and gravity chances based on where you are. It should be something like x number of carbon atoms = 1 kg (83.259 mol to be specific). Or it could be defined as 45 945 114 x Planck mass. That would be objective. (yes I googled planck mass and divided 1kg by it on my spare time, I'm not even ashamed to admit that)

The 1kg = 1000 gram, 1 metric ton = 1000kg thing is certainly straight forward, so metric still beats imperial in terms of convenience.

[pandaman]

Base 12 would have been quite handy as 12 is naturally divisible by 2, 3 and 4.  But I guess we ended up with a 10 digit numerical system because we evolved with 10 easily 'findable' digits.

If we encounter 6 fingered aliens then it will be interesting to compare systems. 

[Enorats]

1 hour ago, Mastikator said:

The meter is currently defined as the length light can travel in 1/299 792 458th of a second. 299 792 458 is not a natural number but at least the meter is defined on a natural constant.

The kilogram on the other hand, a measurement of mass is defined by the weight of this thing on the Earth. Which is not only arbitrary but problematic because weight is a function of gravity and gravity chances based on where you are. It should be something like x number of carbon atoms = 1 kg (83.259 mol to be specific). Or it could be defined as 45 945 114 x Planck mass. That would be objective. (yes I googled planck mass and divided 1kg by it on my spare time, I'm not even ashamed to admit that)

The 1kg = 1000 gram, 1 metric ton = 1000kg thing is certainly straight forward, so metric still beats imperial in terms of convenience.

A milliliter is the same as a cubic centimeter. A milliliter (or cubic centimeter) of water at the melting point of water was the original definition of a gram. So a kilogram was a liter of water at its melting point. This was where the artifact you linked was derived, so measurements of mass are at least indirectly linked to unalterable physical properties too, though they remain the only ones not directly defined by such.

 

What I'll never understand is why we couldn't have aligned the prefixes. Cubic Meters = Liter = Gram makes so much more sense than Cubic Centimeter = Milliliter = Gram. Sure, the "base" unit might not be the most commonly used version that way, but who cares.. we use a wide range of them anyway depending on the application.

[Nathair]

2 hours ago, Mastikator said:

The meter is currently defined as the length light can travel in 1/299 792 458th of a second. 299 792 458 is not a natural number but at least the meter is defined on a natural constant.

The kilogram on the other hand, a measurement of mass is defined by the weight of this thing on the Earth.

You're confusing modern realisation with the original incarnations. The metre was initially defined as one ten millionth of the distance from the equator to the pole on the meridian passing through Paris. That's a decimal realisation of a natural measurement. A gram was then dependently defined as the weight of a cube of water one hundredth of a metre on a side.

[Nathair]

2 hours ago, Enorats said:

Some of the earliest counting systems used a base 6 if I recall correctly, and our entire system of timekeeping is a relic of that system, which is why all our time measurements are multiples of 6

Actually they used base 12 and base 60, probably counting the twelve knuckles on one hand with the five fingers on the other. Hence 60 minutes in an hour and 12 hours on the clock.

[Mastikator]

47 minutes ago, Nathair said:

You're confusing modern realisation with the original incarnations. The metre was initially defined as one ten millionth of the distance from the equator to the pole on the meridian passing through Paris. That's a decimal realisation of a natural measurement. A gram was then dependently defined as the weight of a cube of water one hundredth of a metre on a side.

Not sure what your point is

[Superfluous J]

I am by no means defending Imperial. I'm just saying that using hyperbole to try to make it look even worse than it is makes your argument look flimsy.

Sometimes I wonder, if only long ago they'd decided to ignore those pudgy little "side fingers" when deciding what base to use and we ended up in an octal system, how much quicker we'd have ramped up in computing once we got to that point.

Regarding 12 and 60, I'm pretty sure any usage of "12" comes from the lunar cycles, and wouldn't be surprised if the 360 degree circle is because our year is so close to that many days long.

Also?

10 hours ago, Mastikator said:

it's still leagues less convoluted than imperial.

I see what you did there.

[Nathair]

6 hours ago, Mastikator said:

Not sure what your point is

Then I'll try to make it more clear. No, the metre was not defined by light as you suggested nor was the kilogram defined by some random object. Those are both backwards. You have confused modern realisation with unit origins. Enorats the forum ninja was making the same point.

 

[Vanamonde]

This thread hasn't been anywhere near its topic in quite some time.