[amsat-bb] Re: Since We Are Off Topic Somewhat....
kl7uw at acsalaska.net
Fri Feb 15 07:26:30 PST 2008
Yes, you are referring to the principle called conservation of
energy. The space shuttle gains kinetic energy in gaining orbit and
has to lose it upon return to earth. The kinetic energy is mostly
converted to heat in re-entry. The heat is a function of velocity
and mass. Temperature is a function of how fast kinetic energy is
converted (how fast re-entry), but on difference is that the Shuttle
is fitted with ceramic tiles to survive heat to reentry whereas a
satellite has no protection. The usual reason anything survives
reentry into earth's atmosphere is size or mass. Very large items
(meteors, satellites or space shuttles) may have pieces that impact
earth (this was seen with the Columbia).
At 12:36 AM 2/15/2008, Auke de Jong, VE6PWN wrote:
>This might be excessively basic, but wouldn't the heat energy of the
>friction in re-entry be roughly equivalent to the energy from the engines
>which put the craft up there in the first place? This doesn't include the
>de-orbit burn, obviously, but since the shuttle has a lot of mass, there
>will be more time spent at high velocity dragging against the atmosphere,
>than a relatively small satellite which weighs much less mass, given the
>same descent path because of it's higher intertia(Kinetic Energy).
>Also, since the shuttle enters at a sharp angle, the rate of deceleration
>would be higher since power=forceXdistance. If a satellite enters at a slow
>angle(typical), then the temperature of the heat generated from friction
>would be much lower, for much longer and pieces of the craft might have
>slightly better chances of not vaporizing.
>I like the way that the first paragraph in this page:
>http://en.wikipedia.org/wiki/Kinetic_energy is worded, relative to this
>----- Original Message -----
>From: "Edward Cole" <kl7uw at acsalaska.net>
>To: "Jim Jerzycke" <kq6ea at pacbell.net>; "Joe" <nss at mwt.net>; "'AMSAT-BB'"
><amsat-bb at amsat.org>
>Sent: Friday, February 15, 2008 1:24 AM
>Subject: [amsat-bb] Re: Since We Are Off Topic Somewhat....
> > Also remember that during launch the space shuttle is facing directly
> > into the direction of travel thus presenting the lowest drag (and
> > least friction). During re-entry the space shuttle lifts its nose a
> > bit to expose more area of the underside of the craft to produce more
> > drag. This increases friction. As the shuttle descends, air density
> > increases which increases friction. The shuttle slows due to this
> > friction. The decent path is a smaller rate of decent (lower angle)
> > than launch which is nearly vertical at first. This gives more time
> > for slowing due to atmospheric friction. All this produces very high
> > temperatures. Too steep a decent would increase temperatures beyond
> > what the tiles on the skin of the shuttle can withstand and the
> > shuttle would burn up just like a meteor. Hope this helps understanding.
> > Ed (just an old retired NASA engineer - not quite rocket scientist).
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