# [LINK] Finally up to date on the Shuttle

Antony Barry tony@tony-barry.emu.id.au
Fri, 14 Feb 2003 17:17:17 +1100

```On Friday, February 14, 2003, at 02:01 PM, Chirgwin, Richard wrote:

> There seems, to someone whose physics needs work, to be a contradiction
> here. Anyone good enough at aerospace to sort me out?

IWAPLO (I was a physicist long ago) but I'm pretty rusty. Gravitational
attraction between two bodies is GmM/r^2 where m and M are the masses
of the bodies, G is the universal gravitational constant and r is the
distance between them. "^" is just there to indicate a superscript for
exponentiation). As they approach the force gets rapidly greater,
inversely proportional to the square of the distance to the centre of
the earth in the case of an orbiting body. For the moon the force is
small. For something in a 200km orbit much greater. (384000/6400)^2 =
2500 times less for instance. So the moon takes a month to go round the
earth and the shuttle 90 minutes. The acceleration to sustain circular
motion is (v^2)/r where v is the velocity so you can derive v^2 = GmM/r.

Thence when the retrorocket brakes the shuttle it starts to drop which
increases it's speed. The more you slow it the faster it ends up going
and it hits the atmosphere at about 5 miles per second. Friction does
the rest. The trick is to convert the energy of motion into hot air
without breaking the shuttle and frying the occupants. Remember that
the speed of the shuttle is the gravitationally and kinetically stored
energy of the 100 tonnes of fuel that put it into orbit. It didn't all
just disappear when the shuttle got to orbit. It's represented by it's
height and velocity and has has to go someplace when the shuttle comes
down. Sadly this time some of it went into destroying the shuttle and
killing it's occupants.

Tony

phone : +61 2 6241 7659 | mailto:me@Tony-Barry.emu.id.au
mobile: +61 4 1242 0397 | http://tony-barry.emu.id.au

```