[ExI] De-Orbiting Gold

spike spike66 at att.net
Mon May 21 22:48:05 UTC 2012

-----Original Message-----
From: extropy-chat-bounces at lists.extropy.org
[mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of Kelly Anderson
> In order to get high angles of reentry (which go with high G 
> decelerations, the kind you would need if you wanted to drop your 
> payload in a specific
> place) you need a lot of delta V delivered in a short span with a good 
> sturdy competent control system.  If on the other hand, you use 
> minimal control aerobraking, you will likely drop your payload into 
> the sea...

>...So you're saying that I couldn't predict where it would come down
without rapid deceleration? That seems a little hard to believe...Spike, I
have tremendous respect for your knowledge in this area...-Kelly


Thanks Kelly, I didn't explain that very well.  If we go for aerobraking, we
are talking about very shallow reentry angles.  That means high uncertainty
on the reentry path.  Small uncertainties in atmospheric density mean large
uncertainties in landing spot.  Recall the event burning into my brain from
my childhood, the reentry of the ill-fated Apollo 13.  That was a case where
one of the biggest dangers was avoided when mission control realized the
reentry vehicle was about 300 pounds light, since it was not carrying the
moon rocks it had planned to return.  Had that not been found
(understandable under the circumstances) that alone would have caused the
landing site to be off far enough the astronauts would likely have perished
out at sea before they were found.

The reason is that the density of the upper atmosphere is difficult to
predict with the precision that we know the density of the air down here: it
varies by time of day, by F10.7 radiation from the sun up to a factor of 3
at very high altitude, by position of the moon (the atmosphere has tides way
bigger than the seas), by geomagnetic index and a handful of smaller
effects.  Add to all this the fact that the upper atmosphere has waves and
surges, like the ocean only thousands of times bigger.  

If the reentry angle is too shallow, the reentry body (RB) might actually
start to go back out, a skip-off event a little like a flat stone skipping
off the surface of a lake.  Even a small event like that has enormous
consequences when you realize an RB has a velocity of 11 km per second.  You
can have a piece break off, which changes the ballistic coefficient, which
again adds to unpredictability of the landing spot.

So in a very shallow reentry event is difficult to predict exactly where a
payload will reenter.  So back in the Mercury days when we were trying to
work out atmospheric reentry, the trick was to have the RB come in as
steeply as practical (steeper means higher G decelerations, which means
greater heat load and structural load on the shield as well as more
discomfort for the apes aboard) for if they went for shallower angles (less
delta V needed) there was increased risk of losing the capsule to some
unknown location never to be found.

All that being said, there probably is some way to reenter high value
payloads without the shuttle, but all I have seen so far is a number of
approaches which will not work for known reasons or are very high risk.


ps Since I am running over the five a day posting limit, do let me make a
short comment with respect to Brent's commentary on the immorality of
hoarding gold.  On the contrary sir, gold hoarders do a service: they keep
governments honest.  We are a planet awash in fiat currencies that various
governments claim have value.  The test of these claims is in how much gold
(or other predicable-supply substance) the market will give for that
currency.  This is how we know that Monopoly money and anything minted by
the government of Zimbabwe is worthless: no one will give you gold for it.
But they will cheerfully trade you these currencies for gold, plenty of it.
Any fiat currency can be converted to gold if it has actual value.  So gold
hoarding is not immoral, gold traders keep governments honest.


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