Monday, November 28, 2011

The Sunday Times

Last week in the Sunday Times there was an article on page 19 which discusses the concept of a 'Space Elevator', which "could use gravity to hold it in orbit".

Well thank God they don't waste money on a Science Editor.


Anonymous said...

you should see their explanation of the Retro Encabulator. Proper old fashioned science.

Anonymous said...

Clearly nobody wasted any money teaching you physics.

The natural tendency of a body is remain at rest, or in uniform motion in a straight line, unless acted upon by some external force. This is Newton's very first law of motion, and he published it in 1687. I'd have hoped most educated people might have got their heads around it by now.

So a satellite, space elevator terminus or the moon would travel in a straight line past the earth, unless gravity (the external force) acted to hold them in orbit.

Or are you one of those people who think satellites are "held up", by something you call "centrifugal force"? If so, you're not really in a position to criticise anyone else's grasp of science.

Jamie 1960 said...

The mistake in the article is to assume that a space elevator would be in orbit. This is not the case as it is simply a very tall tower and anyone stepping off it would fall down to Earth (As Arthur C Clarke pointed out in his 1978 novel The Fountains of Paradise) unlike say, an astronaut stepping off the International Space Station which, like all satellites has sufficient velocity to stay in orbit.

A space elevator would certainly not be 'held up' by gravity.

Anonymous said...

Physics education fail. Come to that, google fail.

Unless you're referring to the original Tsiolkovsky suggestion from over a century ago, space elevators, also known as geostationary orbital tethers, *are* very much in orbit. They are definitely NOT "simply a very tall tower".

Also, whether or not you fall to earth or away from it depends entirely on how far up the tether you choose to step off. The higher up, the longer you would take to fall (duh), but only up to the point that you reach the height of a geostat satellite. If the cable extends beyond this point (and it would, for counterweighting), stepping off the cable higher up puts you on an interplanetary course away from the earth.

Amusingly, you're also completely wrong about the ISS, which is never being more than 250 miles up and therefore barely into space at all (c.f. geostat satellites, which are almost 22 THOUSAND miles further up). As a result, it suffers atmospheric drag which requires it to perform station keeping burns to stay in orbit. Without regular three hour station keeping engine boosts, the ISS would have dropped out of orbit long ago.

Not even geostationary satellites have "sufficient velocity to stay in orbit", however, as there is no such velocity, what with the universe being a complicated place.

While you're googling "orbital station keeping", you might like to also check out the Dunning-Kruger effect.

Anonymous said...

Satellites stay in orbit because they are travelling fast enough to counteract the downward pull of gravity. I can still remember seeing a picture of a man twirling a bucket of water around his head to illustrate the point.

Gravity doesn't hold anything up- it pulls towards the centre of the Earth. That's why we stick to the ground.