Well, at least 1 ton = 1 tonne, approximately, so we wouldn't have to worry about metric/imperial.

I think most of us in the UK use a mixture of what we've grown up with and new stuff we've absorbed as adults. For instance, go into a wood yard and they'll know exactly what you mean by "three metres of two by four"
I cook and buy food in metric, I sew and knit in metric, if I'm buying a plant, I measure it in metric, but the height and weight of people always comes in imperial. It's the mental image conveyed, I think. You talk about a person's height, and automatically make a mental comparison with your own height. Weight is different - men tend to be refered to by their weight in imperial. Women, on the other hand, tend to come in dress size - especially among other women.

I work in a company where size matters - small sizes mainly and can safely say that I spent the first three months confused as to what people were talking about. As has been said, people used a mixture. You get comments like:

"the gold plating is 35 microns thick so we'll need a 4 thou stencil."

Thats micrometers and thousandth of an inch. I have no idea how the two numbers relate so I quickly learnt just to memorise them and ignore the mixed units.

Basically, go for whatever the character would say and let the reader go with it. If it's Joe Bloggs on a British street they'll probably talk in feet and stones. If it's a Doctor, they may talk in meters and kilograms.

Or just do what I do - describe them how others see them, which isn't in numbers.

Probably imperial, as everyone else says, but I think you can get a variety of interesting effects (i.e. cold, clinical, military, nerdy, sociopathic etc) - which you may not of course be remotely interested in - by unexpectedly using metric measurements where imperial ones might be considered more 'normal'.

A little like those people who unnerve by telling the time by the 24-hour clock in casual conversation. The time is nineteen thirty seven hours precisely.

A little like those people who unnerve by telling the time by the 24-hour clock in casual conversation. The time is nineteen thirty seven hours precisely.

That's probably because they're reading the time from a watch, PC or phone which is displaying it in 24-hour format.

Perfectly understandable in those circumstances, I agree. I was thinking more in general terms about people who deliberately use offensively modern measurements in order to create a spurious sense of infallible efficiency.

One might also be moved to criticise those who deliberately use archaic measurements in order to create a spurious sense of olde worlde mystique. Must dash - I'm off to be measured up for a brand new pair of seven league boots.

I'm off to be measured up for a brand new pair of seven league boots.

Take care. As Terry Pratchett once pointed out, it's dangerous to wear shoes, the purpose of which is to place one foot 21 miles in front of the other.

It's metre in Europe, not meter unless you're talking about measurement devices e.g. gas meters or electrical meters, as opposed to linear measurements, e.g. 25.4mm per inch x 36 = 1 metre.

(There's been many a disaster caused by getting them mixed up, including the leaking seal on the space shuttle, leaded to an explosion and catastrophic loss of life).

In my novel I refer to feet and inches, even florins and sixpences.

Ps. Should that full stop be inside or outside? . ).

Cheers
Michael




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oops

"leading".

I've just re-read this post and released why proof readers and editors are so important. They'd probably tell me to get a life.

(There's been many a disaster caused by getting them mixed up, including the leaking seal on the space shuttle, leaded to an explosion and catastrophic loss of life).

In fact, that was caused by trying to launch immediately after the said Shuttle had been exposed to overnight temperatures of about -20C, which was way outside of its design parameters. The seal in question relied on the build-up of pressure in the SRB (solid rocket booster), immediately after ignition, to seat it properly and seal the joint. In those temperatures, however, the rubber seal became rigid and unable to flex, meaning that it was unable to do what it was designed to do. The engineers who designed the SRB knew this, and tried to convince the people making the decisions not to launch. They were overruled by people who thought more of the embarrassment of not launching than of the safety of those on the Shuttle.

A better example of a mix-up of units was the Mars Climate Orbiter, which burned up in Mars' atmosphere as a result of trying to go into too low an orbit. This happened (according to reports that I read at the time) because the European collaborators on the project were working in metric, while the Americans were working in Imperial. The Europeans had converted their measurements to Imperial, but the Americans didn't realise this and did their own conversion.

Alex

Is minus 20C way out of the design parameters for a space craft? You're possibly doing your research on the wrong website.

Materials used in space shuttles are designed and tested across their transition temperature. They must exhibit the desired mechanical properties such as tensile strength(in N/mm sq, not LB/sq inch), hardness (vickers scale not Brunnel), toughness,(stress / strain curve) impact strength (in kilojoules), and fatigue strength (crack opening displacement tests) at a wide range of temperatures differences, much much much way way lower than -20C.

PS - There's no brass monkeys in space because it's so cold... do you know the freezing point of brass? Oh, and electrical heaters don't work cause there's no earth connection!

Yes I hear you - I should get a life.

Michael

I used to work in the space industry, as a systems engineer, so I know considerably more than most people about how spacecraft operate and how they are designed, constructed and tested. There are two main environments that you have to worry about: the launch environment (high levels of vibration and acceleration) and the space environment (big temperature oscillations due to the spacecraft going in and out of the Earth's shadow; high radiation levels; vacuum; outgassing during the initial period in space, etc.)

The issue was with the solid rocket boosters, rather than with the rest of the shuttle or its cargo; in particular with the rubber O-ring seals that sat between the sections of the boosters. In the original design, the O-rings were not seated in the gaps that they were designed to seal. Instead, they were placed nearby, in positions such that they would flex and move into position, in response to the buildup of pressure inside the SRB when it ignited. On the morning of the Challenger launch, the overnight temperatures had been around -20C, and the engineers who had designed the boosters (at Morton Thiokol) were worried about the effect of the low temperatures on the O-ring seals. They tried to voice their concerns to senior Nasa managers, through their company's management, but were ignored. There had already been a number of delays to that particular Shuttle flight, and Nasa were getting a lot of bad press over it. The senior managers took the decision to go for launch, despite the warnings from SRB engineers over the safety of the systems at such low external temperatures. When Challenger launched, one of the Morton Thiokol engineers told one of his colleagues that he reckoned the crew had less than a 50% chance of making it into orbit safely. He was right.

During the subsequent investigation into the Challenger disaster, Richard Feynman famously did an experiment with a sample of the O-ring rubber, which he obtained from people at Morton Thiokol. He clamped the sample in a micrometer, to deform it, and then put the micrometer and rubber into ice water, at around zero degrees centigrade. After a while, he took the micrometer out and discovered that, when he opened it, the O-ring rubber remained deformed. It had lost its resilience at zero centigrade, exactly as the Morton Thiokol engineers said it would do. This lack of resilience meant that, at sub-zero temperatures, the O-rings could not do what the SRB design required them to do; namely, deform into their correct place to seal the gaps between the sections of the SRB.

The above is not a result of research that I've done on any website. I remember following the whole saga in the media, and in space industry magazines such as Spaceflight. I remember the role that Feynman played in bringing out the truth of the matter, partly through his experiment, and partly as a result of actually talking to the SRB engineers (which Nasa tried to steer the committee away from doing). I also remember how Nasa tried to engineer a whitewash of the whole matter, and how Feynman, in response, threatened to publish his own report into what had really been going on inside Nasa. Feynman was a Nobel laureate, and a very highly-regarded physicist (I still have one of his textbooks, from my days as a physics student), so his threat was no small matter; he would have been listened to. In the end, the report was not a whitewash, although it wasn't quite as damning as Feynman had wanted to make it.

Incidentally, before the Space Shuttle, solid-rocket motors were not man-rated (i.e. not considered safe for launching humans into space), because of the fact that, once you've started them, there is no way of shutting them down before they run out of fuel. On the Shuttle, the SRBs produce about 60% of the take-off thrust. Once they are started, the Shuttle has to launch, because they are solid-rocket motors and can't be shut down. If the explosive bolts, which hold the SRBs to the launch pad before launch, were to fail to detach, the SRBs would take the entire launchpad up with them - that's how much power they have. (That last claim is something that I heard from one of the astronauts, Jeff Hoffmann, who used to be a research associate at Leicester University, where I did my MSc, and who gave a lecture there while I was a postgrad student.)

Alex

Alex, I remember seeing a documentary about that, and wanting to cry for the engineers who knew it was all going to go wrong, and then had to watch. (My ex-husband used to work for one of the companise concerned, when they were building the wobbly Millenium bridge. He said the structural engineers knew what would happen and said so, but neither the architects nor the builders would listen...)

Presumably once the seal has deformed into the right shape and place and sealed things up, it doesn't matter if it gets cold, because now it's the right shape?

Emma

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Duh! Got that anecdote the wrong way round - the builders knew it would wobble, but engineers and architects wouldn't listen. That'll teach me to post in a hurry because I'm not really here...

Presumably once the seal has deformed into the right shape and place and sealed things up, it doesn't matter if it gets cold, because now it's the right shape?

With that original design of the SRBs, it would have been impossible for the seals to get cold once they had been deformed into place by the pressure inside the booster, because by then the booster would be firing and the temperature inside it would get pretty hot.

After the Challenger disaster, the SRBs were redesigned to have two O-ring seals, rather than just one, and for them to be placed into their correct positions during the manufacturing process. This increased costs, but meant that the same mishap that happened to Challenger could not happen again.

Nasa still didn't learn the lessons, though. The Columbia disaster, in 2003, was basically down to the same kind of high-level arrogance as the Challenger disaster. The senior decision-makers at Nasa were quite happy to wave off concerns about foam from the external tank hitting the Shuttle during launch, claiming that it could have no effect on the orbiter. After the disaster, they did experiments in which they fired chunks of the foam, of about the same size as the one that was identified as having damaged Columbia, at a shuttle wing on the ground. They discovered that, far from being of no consequence, the foam punched a sizeable hole in the leading-edge insulation of the wing, rendering it incapable of protecting the spacecraft during reentry.

The two Shuttle disasters were really down to the number of design compromises that were made when the whole system was being designed. In the original designs for a reusable spacecraft, by Werner Von Braun, the spacecraft part of the system sat in front of the external tanks, etc. This made it impossible for anything from those external parts to fall onto the spacecraft and cause damage. The Shuttle, however, was heavily adapted, mainly because the US military wanted something capable of launching large payloads into orbit. That increased the size of the orbiter (the bit that goes into space), and required a much bigger external tank to fuel it. I think the use of solid-rocket motors to boost it also came from that same design compromise. So the whole thing is over-complicated and hence fault-prone (and hence less reliable than the Russian spacecraft that will now take over resupplying the space station).

Alex

Alex

Thanks for the discussion.

To go, boldly, into materials testing arena for the final frontier, technical specifications are critical, including diversity of design and strength in depth, i.e. back-up. I won't give away my engineering background, but materials are required to be tested to their operating parameters with a built in factor of safety. The temperature in space is not a kick in the pants away from absolute zero, >200c, so why would an organisation like NASA accept a design parameter of only -20c?

Regards
Michael

Michael, you're missing the point. The part of the Challenger Shuttle system that failed was not designed to go into space. It was designed to be discarded about 2 minutes or so into the flight (i.e. in the stratosphere), after its fuel was exhausted.

And poor design was identified as part of the problem: the O-ring design that was in use required the build-up of pressure inside the SRBs to correctly seat the rubber seals in place. That was done for cheapness, not for good engineering reasons. When you add into the equation the fact that the rubber used became rigid at temperatures below zero, it was a fact that the joints between the segments of the SRB were likely to remain unsealed if temperatures had been at those sort of levels immediately prior to launch. The real failing, on the day of launch, was on the part of those senior decision makers who absolutely refused to accept the advice of the engineers, and instead took a risk with 7 people's lives. And then spent a lot of time during the enquiry attempting to insist that their decision had not directly led to the disaster. It was only Richard Feynman's ice water experiment - live, during the cross-examination of one of those Nasa decision-makers - that finally 'outed' them and showed the world what a bunch of fools they were. (The joke was that he was only on the panel as a token scientist, to give it credibility; Nasa fully intended the whole thing to be a whitewash. Feynman, though, was a physicist to his core, and an experimentalist first and foremost. He approached the investigation with the same rigour that he would have approached a scientific experiment.)

None of this, by the way, has anything to do with imperial/metric measurements or confusion over units.

Alex