h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: Man-made Satellites - Update - A37762158
Author: Gnomon - U151503

This is an update of A248591. The only part I've changed is the bit I've highlighted in red. This was completely wrong in the original so it has to be updated.

It would be great if somebody who understands physics checks that I've got the science right. The rest of you can check that it reads OK and is understandable.

Thanks.

<>
=
*then* the gravity

I understand what you've written, thanks Gnomon

GB

Orcus pointed out that what the entry said about diamond was wrong as well, so I've changed that paragraph (2nd from the end) and marked it in red.

A satellite in orbit around the Earth (or any other body) is actually doing almost exactly what Douglas Adams described as "How to Fly", that is falling towards the ground but always missing.

<>

Not sure I'd say <> I'd have said "Carbon is also found in the human body, and all other life on this planet"

Hi Gnomon

Great entry. Since you speak of Arthur C. Clarke would it worth a footnote mentioning his Novel 'The Fountains of Paradise' in the Space Elevator section? (From that other encyclopaedia - http://en.wikipedia.org/wiki/The_Fountains_of_Paradise ).

t.

I'm really just trying to make this entry correct.

The other entry on the Space Elevator mentions the Fountains of Paradise. I really ought to combine those two entries together, or make one about satellites and one about the space elevator. But I'm not going to do that just now.

Hmm. I don't think this entry really covers the subject matter implied by the title. It's a nice introduction to geostationary communications satellites and space elevators, but most satellites aren't geostationary - it's only a special case. It should at least mention Sputnik 1, GPS, spy satellites, earth observation etc etc. Or change the title to cover only the Clarke orbit.

Also a few inaccuracies:

The first bit implies Clarke patented the idea of an orbit, which is clearly wrong.

Geosynchronous and geostationary are not the same thing. The former merely has a 24 hour orbit, but not necessarily circular and over the equator.

I thought ion engines were fairly new. I'd be very surprised if *all* satellites use them.

Not all communications satellites are in geostationary orbits.

The Clarke orbit is 36,000km away, I think, to the nearest thousand.

IIRC, when NASA tried to release that cable they were researching the potential for power generation, nothing to do with space elevators.

Buckminster fullerenes are balls (C60). We're talking about carbon nanotubes here, cylindrical fullerenes.

It might be an idea to double-check all the facts in the original entry. The updates look fine though

*nudges Gnomon*

Oi! Don't forget about li'l ol' update here.

So many things have been pointed out wrong with this entry, and so much of it is duplicated in the other entry, the one I wrote about the Space Elevator, that I am unsure how I should proceed.

I know one thing for sure, it's going to be a lot of work.

roll your sleeves up then, I'll getcha a spade and a pint of something cold and black for when your finished

The one thing that I noticed that seemed scientifically inaccurate was the sentence:
The trick is to get the centre of gravity into the right place and that will take care of the rest, no matter how large or odd-shaped the satellite.

In this instance, it wouldn't be the "centre of gravity", a term normally associated with balance and tipping points, but "centre of its mass".

Actually, the phrase was used more than once.

Ref this para:

"The hardest known substance, diamond, is not actually the strongest - it's very resistant to scratching, but not so good for making a cable under tension. Diamond is a form of carbon. Carbon has another form, graphite, which is extremely soft and usually used to make pencil 'lead'. Carbon is also found in the human body, and all other life on this planet, plus it is one of the primary ingredients of oil."


Diamond is the hardestknown natural substance. There are synthetic 'super-hard' materials such as beta-carbon nitride and borazon (which is also a carbon nitride) which are harder than diamond.

The relationship between diamond and graphite is that they are both allotropes of carbon.

Perhaps (taking into account GB's earlier comment) one should say that
carbon is integral to all life on this planet (and probably anywhere else in the Universe).

A

Hi B-A!

I agree with everything you wrote, but the potential is still there for life to be based on some other element or elements than just Carbon.

There are groups that are trying to construct what how they would be alive, but they also seem to be stuck on defining life!

If we should actually be successful in building life around copper or silicon, how would we explain our bias to them!

Strangely, I have an entry on a marine species that comes pretty close to being largely silica, my entry on the Glass Sponge. Granted it is using the silica mostly to build it's skeletal structure and provide energy through light transmission, but it's still using a lot of silica!

Well, silicon is Group IV, same as carbon, and so it does have the ability to catenate (form chains). But carbon's ability to form long chains is unique, and this is considered essential for life forms (e.g. cnstructing globular enzymes with 'induced fit' mechanism for active sites etc.etc. Also the oxide(s) of carbon are gaseous (for respiration) whereas that of silicon is solid (sand!).

I believe I understand, but we aren't limited to chains formed by only one element. Some salts create rather long chains by sharing the load.

That might be really interesting, a form of life created from salt!

I wonder whether it could survive a good rain, and what it would mean to the story of Sodom and Gamorha?

OK, folks. It appears that people are happy with the paragraphs I put in, and not happy with the rest. I don't have the knowledge of the history of satellites to bring it fully up to scratch, so I think I will just put those paragraphs into the original entry, remove this from Peer Review (thank you, my peers ) and add the whole shebang to my list of stuff that badly needs updating.

You take on an awful lot, my friend; more power to you.

The best of luck with the whole general mish-mash of work!