[amsat-bb] Since We Are Off Topic Somewhat....

Alan Sieg WB5RMG wb5rmg at somenet.net
Thu Feb 14 20:04:20 PST 2008

> Time to come down,, the de-orbit burn happens to slow it down just a bit
> to cause the orbit to more or less decay..

I don't think orbital decay would be a good descriptor.
Orbiter does the de-orbit burn about half-a-rev away, then a nose dive.
The de-orbit burn puts the brakes on big time, then after it turns
nose forward, a slight push towards the earth brings it on down fast.

An orbital decay is very gradual, and takes many orbits...

> So in actuality it comes down from space even slower than going up.
> Yes?  45 min vs 10.

Right, as others have said - going up through the dense atmosphere is
the slowest part of the trip. They even hold back throttle until it
has passed maxQ, or maximum dynamic shake, just before passing the
'sound-barrier'. After that, the air is much thinner and with less
fuel on board - and the acceleration increases very rapidly.

> Ok,  same goes with any satellite,,

Not really. Launch may be the same - but a de-orbiting satellite can
take weeks/months/years of slowing/losing altitude enough to encounter
the upper atmosphere. That's when the trouble starts.

> coming down,,  17K MPh  to 0  unless it has protection
> it will  burn up in the atmosphere from friction with the air.

You hit the nail on the head. Orbiter has protection. Major protection.
Reinforced carbon-carbon leading edge treatment on the wings and nose.
Ceramic tiles on the belly provide the required capacity to shed all
that kinetic energy as heat. The thermal padding over the rest of the
orbiter is to protect the vehicle structure from the heat passing by.
The shock wave just millimeters out in front of the orbiter is hotter
than the surface of the sun... I remember seeing Wayne Hales describing
this on NASA-TV after the TPS repair job a few flights back in 2007...

De-orbiting satellites have no TPS, and as soon as they encounter
atmospheric ionization - it cooks off pretty quickly. Only major
chunks survive, and then only as really hot blobs.   Think of the
bright meteors during a storm like the Leonids - most of those are
no bigger than a grain of sand - but come in around 70 km/sec ...

It should be interesting to see what the media does with this story.
Personally, I suspect the fuel would cook off before impact with
some large body of water. But if we let it do that, we couldn't flex
THE muscle. It would take to long to program an EKV target model for
one of the big mid-course interceptors... so perhaps this approach
will score some points. We gotta catch up you know. We've never
destroyed a satellite 'on purpose' . .  All you gotta do is get right
in front of it, and let it hit you. An explosive just adds to the show.

Waiting for Atlantis to get back is good idea .!. I think I heard
that they did extend joint-ops for one day. Maybe early next week
they'll let the Navy have a crack or two at "Shoot-Sat".

  Thanks  (this wasn't supposed to get this long)   /;^)
  <- WB5RMG is Alan Sieg  *  http://wb5rmg.somenet.net ->

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