They should make km the default unit and not miles....
"At 09:00:46 UT Sept. 23, 1999, the orbiter began its Mars orbit insertion burn as planned. The spacecraft was scheduled to re-establish contact after passing behind Mars, but, unfortunately, no signals were received from the spacecraft.
An investigation indicated that the failure resulted from a navigational error due to commands from Earth being sent in English units (in this case, pound-seconds) without being converted into the metric standard (Newton-seconds).
The error caused the orbiter to miss its intended orbit (87 to 93 miles or 140 to 50 kilometers) and to fall into the Martian atmosphere at approximately 35 miles (57 kilometers) in altitude and to disintegrate due to atmospheric stresses."[0]
[0] https://solarsystem.nasa.gov/missions/mars-climate-orbiter/i...
As noted in other comments, NASA (like the rest of the United States [1]) does use the metric system.
But it doesn’t matter. Nothing about the metric system makes it uniquely suitable to landing on Mars. Or space travel in general. What matters is a consistent standard.
Internally NASA could use Armstrongs. Where 1 is the weight or height of Neil Armstrong at KSC on July 16, 1969 at 13:32:00 UTC. It doesn’t matter. As long as it is consistent.
[1]: https://en.m.wikipedia.org/wiki/Metrication_in_the_United_St...
But with the metric system you only really get cm (too coarse) and mm (too fine) but you don't get something like 9/16 so you can't "work in 16ths" and have everything be whole units again.
Adjusting HVAC in degrees-C is infuriating to my Fahrenheit sensibilities. 20C is cold, 22C is hot. 21C is probably ok but really I want something like 20.5C. The comfortable range for a room is 3-5 whole units of F, but requires a bunch of fractions in C that you may not even have available on your thermostat.
Sure, converting between units is easy in the metric system. That doesn't make it the best thing to use all the time. Hell, the idea of thousandths of an inch is used commonly, so even the imperial system is base 1000 in some cases. But I've never seen anyone utilize the fractional scale with metric units, probably because the units are the wrong size for that to be useful.
People who use metric units are perfectly happy rounding to the nearest 0.5cm or 0.25cm if that's what's needed, exactly as people do with inches. Why on earth would you imagine people use mm if something doesn't call for them?
Presumably someone who uses Imperial would say 5/128th inches if they wanted to describe something that's equivalent to 1mm?
25mils ~ 1mm
Or 1/16in as others have said.
1000 mils / 25.4 mm = 39.3
This simple fact still seems wrong to me somehow.
Maybe metric users do use fractions and I just don’t hear about it. Is that table one and a quarter meters high?
If you're cutting it yourself, a precision of 1mm is finer than your saw blade or pencil line anyway, so it's plenty enough.
When I hear anything past about 1/8th of an inch my brain shuts down, and I give up.
In reality I use both systems all the time. It’s situational.
> When I hear anything past about 1/8th of an inch my brain shuts down, and I give up.
Realistically, same. 32nds don’t get used outside of some specialty wrenches. 16ths are a practical limit where other scales start to make more sense. Probably millimeters.
I use both systems.
I do prefer Fahrenheit for HVAC (and weather) because it’s higher resolution and has reasonable values at human scales. Thermostats that lack half-degrees-c are never quite right IMO.
So you are one of those, lol. There is nothing "less human" about 25 C than say 72 F. Nothing, it just happen to be the scale you are used to.Both are arbitrary.
> Fahrenheit for HVAC (and weather) because it’s higher resolution
99.99% of thermostats and thermometer in C had at least 1 decimal place. At usual "human temperatures" the difference in resolution between the scales is less than 2X, so even assuming only integer values, I am willing to bet against you in a double blind test that you cannot differentiate 68F vs 69F in an statistical significant way.
> I find it easier to say that’s three eighths than 9mm
Just because you are used to. Fractions are more complicated than integers, every elementary school program knows it.
So to summarize, the problem is not with the magnitude of the units which is arbitrary (a degree F and inches are not more human, logical or normal that a degree C or cm)the problem is with the convoluted way of the imperial system for multiples and submultiples of the base unit.
I guess 20.5 is nice, 15.5 is cool, 10 is cold, 4.5 is really cold, 26.5 is hot, 32 is really hot and 37.7 is dangerously hot. It’s fine if you are used to it but I don’t really see a benefit.
I was in a hotel room in Japan that only had whole unit adjustments for the A/C. To get 20.5C I had to switch to Fahrenheit. I guess I was unlucky.
I find distances in metric and imperial perfectly usable and use both regularly.
As outlined in detail elsewhere in the thread there are advantages to working in fractions in some situations. Specifically when using a ruler or tape measure with different markings for 1/2, 1/4, 1/8 and 1/16. There’s no reason that has to be unique to inches, it just works out well in some cases.
Or, you know, 20, 15, 5, 30 and 40 instead of the arbitrary decimals you chose to use to prove your point
To the identical 5 degrees range of the Celsius scale ?
If I need to take measurements while boiling water or making ice then I would probably use C.
> How do you divide 7"3/8 by 5?
Same way I divide 4.7625 cm by 5. With a calculator.
25, yes. It's not too hard to do the math.
> Same way I divide 4.7625 cm by 5. With a calculator.
That's roughly 0.95 right by intuition, but (7"3/8) / 5 doesn't come easy to me.
When more precision is needed, so easy to go to the 32nd
That's not realistic, obviously, so we just pick one. The units in the system are arbitrary, really.
In reality regardless of the system you choose every calculation is going to end up with fractions of something. You aren't just going to do it in your head.
For example, you could define mars units where the gravitational acceleration on mars is 1. Now your velocity in freefall is just equal to the time you've been freefalling! You don't even have to do a calculation!
(note: Don't actually do this. Gravitational acceleration isn't a constant when you're doing orbital mechanics.)
My experience with U.S. students is that they are having a much harder time making sense of the imperial system (that they are used to) than doing problems in metric, even though they don’t use it in everyday life.
First off, you linked to a list of english measures which are not used in the US. Nobody uses fathoms or barleycorns.
Here is the list of actual US customary units: https://en.m.wikipedia.org/wiki/United_States_customary_unit...
Second, none of that is relevant to landing on Mars.
The only problem space where metric has an advantage is in converting between meters, kilometers and millimeters.
That’s great, and it’s easy to learn. But it doesn’t suddenly make all problems of distance easier to solve.
If I am traveling toward Mars at 47 meters per second it doesn’t help me to know that is also .047km per second. And converting to kilometers per hour involves using base 60 twice anyway because metric time is unwieldy.
In reality none of your measurements are going to be nice round numbers. Mentally converting from meters to km might be nice sometimes but it’s essentially a party trick.
It won’t help the lander make decisions. The hardware doesn’t inherently work in base 10.
Does NASA mix meters and kilometers? Isn’t that the same problem that destroyed the Mars Climate Orbiter?
The fact is the units are irrelevant beyond just being defined and used consistently.
Also, I can’t think of a situation where I need to convert miles to feet. My bike ride is six miles, I’m never going to express that in feet. If I need to describe the size of a thing in a room I will probably use feet, maybe inches if it is small. Probably not feet and inches. I wouldn’t use miles at all. Easy conversion between those units just isn’t a problem that comes up. It’s more important to me to have reasonably sized units and that the person I am communicating with understands them.
How many pounds does a cubic feet of water have?
How many BTUs do you need to heat 10x10x3 ft water pool 20 degrees F?
How much work in ft-lb is done by gravity when a 10 oz mass drops from 19 yards?
How many HP are needed to rais 2400 lbs 74 inches in 30 sec?
It is obvious you have 0 experience doing back-of-the-envelope calculations for scientific or engineering purposes. It is a no-contest between the metric and the imperial systems.
Yes it does. It means you can immediately sanity-check your numbers even if you don't have a good sense of what meters and kilometers are, because you have that base/kilo relationship.
> My bike ride is six miles, I’m never going to express that in feet.
You can eyeball how fast you're going in feet per second and have a rough idea of how long your ride is going to take. Or rather you could if you had any idea of how long your ride was in feet. There are lots of little everyday things that just become much easier.
I estimate my bike ride progress in landmarks and time. Not feet per second. Did I get to the boat ramp in 20minutes? Better speed up and get to the park by 30.
But you'll have small distances and large distances and pieces from external sources who use measurements on a scale that makes sense to them. You can make your external sources do conversions themselves, but that's just moving the problem around. There will usually end up being a point, or probably several points, where you have to relate a small distance to a large distance, and wherever that happens, a human sanity check is a help.
> I estimate my bike ride progress in landmarks and time. Not feet per second. Did I get to the boat ramp in 20minutes? Better speed up and get to the park by 30.
Precisely - you have no sense of the relation between your speed and how far you can go, because you're using a terrible measurement system, and you don't even notice the how that's robbing you of the ability to develop useful intuitions.
Miles per hour is literally a measure of distance over time. If I wanted to use my GPS I could very easily determine how far I can go in a given amount of time. I can do this equally well in the metric or imperial systems, without converting to feet or meters.
The hardware doesn’t think in base 10, but having more than that in imperial makes it better?
Your document lists 12 mass units alone. I rest my case, what could possibly be more logical, convenient, and need less conversion.
If communication was your major goal, then the system that is used by 7.3 billion people on this planet would be your choice.
Great, we agree.
> Metric on the other hand sucks because none of my measurements will ever be nice round numbers.
Depends on the situation. Metric units can be useful.
> The hardware doesn’t think in base 10, but having more than that in imperial makes it better?
No, it means neither system has an advantage so just pick one. Or invent a new one that allows better hardware utilization.
> Your document lists 12 mass units alone. I rest my case, what could possibly be more logical, convenient, and need less conversion.
I don’t convert, I just pick the unit that fits the problem.
> If communication was your major goal, then the system that is used by 7.3 billion people on this planet would be your choice.
Yeah I use the metric system all the time. Just like NASA.
But one of the systems does have an advantage because it stays in base 10, whereas the other doesn't.
>> Your document lists 12 mass units alone. I rest my case, what could possibly be more logical, convenient, and need less conversion. >I don’t convert, I just pick the unit that fits the problem
But you can't if you just use the `intuitive unit', and that's the whole problem. How would you measure the amount of liquid fuel in, say, the small tank for an attitude control thruster of some probe? How does that add to the overall mass of the whole probe? Or to the force you then need to accelerate it by a certain amount? And now compared to the whole launcher?
In which units do you measure everything going on in a small wind tunnel model, and how do you compare that with the real thing?
Under which conditions do you go from fluid ounces to ounces to cups to pints to quarts to gallons (also note that, again, you not only switch units but bases)?
>Yeah I use the metric system all the time. Just like NASA.
Good for you, it solves all the problems.
That's a benefit to humans, not to hardware, which was the context in which I was speaking.
> But you can't if you just use the `intuitive unit', and that's the whole problem. How would you measure the amount of liquid fuel in, say, the small tank for an attitude control thruster of some probe? How does that add to the overall mass of the whole probe? Or to the force you then need to accelerate it by a certain amount? And now compared to the whole launcher?
Honestly? I'd probably measure it in volts. That's what the hardware is doing after all. That's my point, it doesn't help the computer to convert to base 10 and do calculations that way. Fuel level is measured in volts using binary. For a human something like grams probably makes more sense so sure, display it in those units. But that's a conversion.
> In which units do you measure everything going on in a small wind tunnel model, and how do you compare that with the real thing?
Again, volts on strain sensors. Maybe analog or maybe binary, in newtons. Again, the hardware doesn't think in units humans prefer. There has to be a conversion that doesn't use simple in-your-head math.
> Under which conditions do you go from fluid ounces to ounces to cups to pints to quarts to gallons (also note that, again, you not only switch units but bases)?
Cups, pints, quarts and gallons are all based on the ounce and powers of two. A gallon is 128oz, a half gallon is 64oz, a quart is 1/2 of a half gallon (or a quarter gallon) or 32oz (also, approximately a liter). A pint is half a quart or 1/8th of a gallon or 16oz, a cup is half a pint or 1/16th of a gallon or 8 oz. These fractional scales are really handy for converting between units in some situations. The unit fits the task at hand or you can trivially double or halve the size of the unit if needed. It's the same fractional scale and math used with the inch.
I have gone much farther here than I normally would. I don't think I can constructively explain this to you any further.
Using one universally accepted system is core idea behind metric system. Now, it looks like it is competition between two equal systems, but historically it is competition between ideas 'we should have one universal system' and 'every country/area can stay on their local systems'. Just all other legacy local systems (outside u.s. customary) disappeared.
With metric it's a matter of shifting the decimal.
How much is a sixteenth inch anyways.
A 16th is half an 8th. Twice as much as a 32nd. AKA 2^4, 2^3 and 2^5, respectively.
Do you think kids find it sexy to talk about meters, kilograms and degrees Celcius rather than feet, miles, pounds and Fahrenheit?
I can't fault for choosing what is more understandable to the target audience.
During the stream, you can hear the various teams giving measurements in metric, whilst the media gave coverage in imperial.
It's a pretty interesting video from that perspective, as you can hear the two "realities" being translated for the intended audience.