| Sunday,
May 11, 2003
Bruce Moomaw, "Explaining Thirty Years Of
Fudge," t (Space Daily, referenced above):
"There was never any thought that those
[RCC] panels would withstand a 20,000 foot-pound kinetic energy strike
[such as Columbia's foam fragment produced]. ... Kinetic energies of a 2
1/2 or 3-pound hunk of foam when it's traveling 700 feet per second --
that's high school physics."
700 feet per second (some 427 mph) would, if the
above figures are accurate, be the difference in speeds between the
orbiter and the foam piece when contact was made. Two factors might
contribute to this difference: continued acceleration of the orbiter after
the foam seperated, and deceleration of the foam. My question: does
everyone agree that that's the speed delta, and that 20,000 foot-pounds is
therefore a good estimate of the strike energy? All this high-school
physics is too complex to make it into popular press articles.
Mike Juergens mjcom99@hotmail.com
A 700 fps speed differential seems high. (30 mph
is 44 fps 30 : 44 as x is to 700, cross multiply the terms 30 times
700 equals 44 x or x = 300*700 / 44 = 477 mph if I haven't done
something backward this early.) That speed differential seems a bit high,
but let's see. Quick assumptions: the foam simply stops in
atmospheric drag when it falls off, shuttle is doing 4 gees = 128
fps/second, v = at, so to get 700 fps you need 700/128 = 5.4 seconds
acceleration, s (distance traveled) = 1/2 * a * t^2 so 1/2 * 5.4 * 5.4 *
128 = more than 1800 feet, and I don't think the Shuttle is 1/4 mile long.
It's also early Sunday morning and I may have got something wrong but I
don't think so.
The fundamental equations are v = at, and s
(distance) = 1/2 a T^2, and the fundamental constant is g = 32 ft/s/s.
But in fact wouldn't 70 feet/second, which isn't
impossible, do a pretty good job with a pound of foam?
>Quick assumptions: the foam simply stops in
atmospheric drag when it falls off
Actually, your assumption seems to be that the foam
keeps going at the speed it had before it separated, and the delta v is
totally due to the shuttle accelerating into it. You solved for distance
for the delta to be 700 fps, and found it to be too long.
If the foam did simply stop, the shuttle would hit
it in a fraction of a second, acceleration would be a minor factor, and
the delta would equal the speed of the shuttle, the foam being at speed 0.
If the foam decelerates sharply, the outcome approaches this case, and the
most important thing to know is the shuttle speed when the foam separated.
If the foam decelerates more gradually, then both
the acceleration rate, which we know, and the deceleration rate, which we
don't know, are factors. But in any case I don't see the delta getting to
700 fps unless the shuttle was going at least that fast, and the foam
decelerated sharply. If the films of the foam strike have been presented
real-time, seperation to impact was less than 1 second. On that basis,
impact energy may well have been as cited. I just wondered if this was a
generally understood and accepted data point. If impact energy was low,
then the analysis while the shuttle was airborne looks better, and we need
to consider other failure mechanisms, such as a colision with orbital
debris.
BTW, my way of converting FPS to MPH was (FPS * 60 *
60) / 5280. And the answer is 477.27, and I made a transcription error in
my last message.
Mike Juergens mjcom99@hotmail.com
===
Jerry,
I'm nowhere near as competent in math as you are -
my math training ended with geometry and trigonometry in high school.
But shouldn't you include the _deceleration_ rate of
the piece of foam (due to drag) - as well as the acceleration rate of the
shuttle - when determining the collision speed?
Sincerely,
Calvin Dodge Certified Linux Bigot (tm) http://www.caldodge.fpcc.net
That will teach me to try to work on this stuff
at 0800 before coffee. Thanks. But I think the mystery is solved:
Hi, Jerry.
The speed of the foam that hit Columbia was about
500 mph, according the video analysis done by the CAIB. The foam took
quite a bit less than a second to strike the wing once it broke off the
tank. The acceleration of the foam wasn't caused they the acceleration of
the shuttle, but by the foam being picked up by the slipstream between the
tank and the shuttle. I don't rememver the exact velocity of the shuttle
at that point - I think it was in excess of 1500 mph, but the airstream
between the tank and the shuttle was moving somewhat slower.
This has been discussed extensively in the CAIB
press briefings and public meetings, transcripts of which are on their web
site.
Regards, Keith
-- Keith Soltys
Well that ought to be good enough. Now what
did it weigh? If 500 mph then that's probably rounded from 477, which
means the 700 fps number is about right, and the mv^2 energy would be
considerable.
and:
I suspect that the foam might have been accompanied
with several pounds of ice accumulation because of the incomplete coverage
of the tank
Gene
Indeed
===============
Airport Security
I ran into a TSA employee, still in uniform, while
at the post office. While standing in line we got into a conversation. The
nice young woman joked that TSA stands for "takes scissors away"
and implicitly made it clear that she & most of her fellow employees
were there because the work was easy, the money decent & the commute
not too bad. A deep committment to making us all more secure was clearly
not on her agenda. I guess the others are there 'cause they like the
power. Luckily my lifestyle & work make it possible for me to drive or
sail on the few occaisons I need to leave my neighborhood.
Dick peace, freedom & keep your word
Would it matter a lot if they were sincerely
dedicated to security? Nothing they can do would prevent a suicide bomber
from waiting until there is a huge jam of people at the security line,
then blowing himself and all the TSA people and all the machinery to
kingdom come; which would shut down at least one major airport and
probably more than one.
====
Google doesn't block searches for air rifles. They
don't, however, accept paid advertisements for them.
When you do a google search, companies pay to have
ads appear in a slightly different type face and background color along
the top and to the right of the main Google results.
The nice thing is that the paid ads are
"outside" the search area. The search area results are purely a
function of Google's algorithm (and webmasters' attempts to spoof it).
So, the user can make a choice as to whether to
consider paid advertising or not.
In the air rifle case, Google is making a choice
about the advertising they will accept. It's their right, but that choice
causes me to have contempt for them. The only way to get them to change is
to switch to another search engine and send Google a letter/email telling
them why you're switching. Get enough people to do that and their numbers
will drop. "Money talks".
Steve Setzer
===
Jerry,
I believe you missed the point made by your recent
correspondent who sent you the link about air guns advertising being
banned on Google.
It's not the PageRank system of finding links that
has changed, it's the policy for paid advertising accepted by Google that
has changed.
If you "google" for "air guns"
at this moment, there will be only one paid advertisement (at least a few
seconds ago when I did so that was the result).
That is what the purveyor of air guns in the linked
page is complaining about, and perhaps he indeed has a point. I suppose
the question is: at what point does a company's services become so
pervasive and/or influential as to enter the realm of utility and/or
monopoly?
Norman Ferguson
It's certainly their right. I never pay attention
to paid placements anyway -- in fact I tend to avoid them and look for the
first hits that were not paid for. Particularly when some of the paid
placements tell me I can get Jerry Pournelle cheaper at their
establishment. Some of the paid placements are just plain silly.
I already have my air rifle from the days when I
was an editor at Survive Magazine...
I don't know for sure about "Air Guns",
but they took my advertisement for the "FloridaGuns.com" website
a few months ago. A search of "Gun Training" returned one add
for a firearm training program at the top of the page. A search for
"Air Gun" pulled up adds (one for the airgunstore.com site).
Al Lipscomb.
Maybe they've changed policies?
=================
subject: Persistance
is admirable, but . . .
Dear Jerry:
This is
ridiculous. The FBI has decided that Dr. Steven Hatfill definitely
was behind the anthrax letters, but don't ask to see the proof, because
they don't have it. Just a "highly circumstanial case"
that apparently isn't strong enough to take to trial.
Hmm,
instead of "ridiculous," maybe I should have said "Unamerican,
unjust, and frightening" ?
Best,
Stephen
DELENDAM ESSE SAUDI ARABIA!
I thought the Constitution was intended to
prevent that kind of arbitrary power in the government, what with having
to be confronted with accusers, and a speedy trial and all, but apparently
things have changed a lot.
Subject: Recovered.
http://www.cnn.com/2003/WORLD/meast/05/07/
sprj.nilaw.iraqi.artifacts/index.html
Roland Dobbins
And more will be, over time.
Subject: Confessions of a spammer.
http://www.oregonlive.com/business/oregonian/
index.ssf?/base/business/105256787116000.xml
Roland Dobbins
The path to spamming success requires
expensive investments in software and the agility to adjust to the
technological warfare between spammers and companies that try to block
their messages. It also requires the stamina to withstand daily hate mail
and even death threats.
Shiels decided a spamming career wasn't worth
the personal cost.
...
He spent about $10,000 on software to harvest
e-mail addresses, to disguise his online identity and to send millions of
messages a day.
The Poor Man got death threats. Awww....
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