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What is 'Ask an Elf'?

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961938.  Thu Jan 10, 2013 7:45 am Reply with quote

Ask an Elf is an idea that we're considering for the new website in which people ask us difficult questions - ones they can't seem to Google - and the Elves post up answers. It's a bit like one of those 'answers' sites you get online, but in our case the answers will be curated rather than crowd-sourced.

So while we're thinking about it, do you have any questions that you've always wanted to know the answer to - such as 'why is there something, rather than nothing' or 'why doesn't the atmosphere fall to earth' or 'why do we not have airport-style moving walkways instead of pavements'? If you do, post them up - one per thread, please. And feel free to try to answer each other's...

961972.  Thu Jan 10, 2013 9:24 am Reply with quote

Did Edgar Allen Poe murder Mary Rogers?

961976.  Thu Jan 10, 2013 9:36 am Reply with quote

What is the fate of all the material that burns up entering the earth's atmosphere? Does it ever become re-usable?

961977.  Thu Jan 10, 2013 9:37 am Reply with quote

Anonymous wrote:
What is the fate of the material that burns up entering the earth's atmosphere? Does it ever become (re-)usable?

961979.  Thu Jan 10, 2013 9:41 am Reply with quote

Well that was odd! Both of those ^^ were me btw, made. by some quirk, whilst not signed in and I don't seem to be able to edit them. The question stands though

What is the fate of the material that burns up entering the earth's atmosphere? Does it ever become (re-)usable?

961995.  Thu Jan 10, 2013 10:25 am Reply with quote

The solid rocket boosters from the space shuttle were recovered from the ocean and reused. They had parachutes to reduce their impact on the water. The strap on* boosters used for the Soyuz rockets are recovered and the metal is recycled but they are not actualy reused. I assume this is because they land on solid ground rather than on the water though I don't know for sure.

Of course, neither of these go above the Earth's atmosphere. Any object falling to Earth from space in an uncontrolled re-entry will be heated to around 1,600 degrees C, which is high enough to melt just about everything unless you build satellites and rockets out of rhodium. The fastenings are going to go and so the thing is going to fall apart. Some bits may survive large enough to please souvenir hunters but not enough to make it worth collecting by the people who launched it.

Am I now an elf? If so, can I get a date with Galadriel?

*Fnarr, fnarr.

962002.  Thu Jan 10, 2013 10:47 am Reply with quote

Cele - when the forum was set up, it was inadvertently left as 'public' rather than 'registered'. I've corrected it now.

962003.  Thu Jan 10, 2013 10:47 am Reply with quote

one per thread, please.

962008.  Thu Jan 10, 2013 10:58 am Reply with quote

Even re-entering objects (that are only shedding oribital velocities) get MUCH hotter than that - right up into plasma temperatures. The Apollo capsule heat shields were subjected to temps of over 2500C by the compression heating, and they were barely doing 10km/sec. The space shuttles usually re-entered from about 7.5kn/sec and their heat shields saw over 2300C .

The temperature is essentially just a function of the speed of the object, so with that in mind...

"Space stuff" that's *entering* (rather than *re-entering*) the atmosphere must (by definition) be going faster than this or it wouldn't be there in the first place. Even a "stationary" object would get to about (from memory) 11km/sec just by being drawn in by the earthj's gravity. An object which is orbitting the sun at the same distance as the earth , but with a different vector, would be doing something like 40km/sec in its own right, so it could hit the atmosphere at nearly 80km/sec if they happen to be heading in opposite directions.

Things from higher orbits will be slower, but they will be accelerated by the earth's gravity on the way in, so they're likely to be in the 11km/sec to 70km/sec region depending on their relative proper motion compared to that of the earth.

But the SERIOUSLY quick ones are objects which aren't even orbitting the sun - the intersteller objects which are passing through the solar system but are going too fast to be captured by the earth's gravity. Theoretically these objects could be doing substantial fractions of the speed of light, but they are very rare so they don't get caught by the speed cameras very often.

To get back to the question - in most cases these objects get hot enough to vapourise (either partially or entirely). The vapour cools and condenses into dust, which then blows around and eventually falls to the ground (probably), most of it ending up on the tops of cupboards or in the air filters of computers until your woman gets off her backside and actually does the dusting. So it adds to the "stuff" that we call Earth, qand therefore could conceivably be recycled. It's highly likely that the sand/cement/aggregate/ballst/hardcore used in building and road construction includes some of this stuff.

Of course some objects don't FULLY vapourise because they're too big for all of the matter to boil off before the drag slows them down and removes the copmpression heating. These objects generally fall to the ground or land in the display counters of specialist shops where they are sold to gullible tourists who think they're rare.


962017.  Thu Jan 10, 2013 11:18 am Reply with quote

Doffcocked within 2.5 hours!

If I think of anything, I will <ahem> start a new thread here.
Is there any likelihood of such questions appearing on the show, if they can be crowbarred into the alphabet scheme?

962088.  Thu Jan 10, 2013 1:44 pm Reply with quote

Trying to think of questions, I'm stumped by the fact that if I think of a question, I can find an answer of sorts.

I note by the suggestion of "why is there something rather than nothing", this is a hobby horse of John's lectures, so I can see where this came from :) This questions has a slightly more philosophical element to it rather than physical.

962093.  Thu Jan 10, 2013 2:24 pm Reply with quote

If there were nothing rather than something, , there would be nothing to question why there was nothing rather than something.

962095.  Thu Jan 10, 2013 2:41 pm Reply with quote

I suppose, CB, you could ask - what are the top 3 unanswerable questions? And then ask your favourite...

962098.  Thu Jan 10, 2013 2:53 pm Reply with quote

I would suggest that nothing cannot "be"; it can only "not be" so the question is a non sequiter (sort of Descartian).


962350.  Fri Jan 11, 2013 1:35 pm Reply with quote

PDR wrote:
A pretty full answer.

That's pretty much what I thought - so this stuff* isn't only getting thrown away, it's being put into a state where it will only be re-usable over geological time if that. Except that is for the organic bits which will be 'recycled' by nature pdq.

Not a brilliant idea if you ask me.

* see the prog for details of schemes to clear up man made space junk

PS Perhaps an elf can tidy this up and put it in a separate thread. Like I should have done in the first place : /


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