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Destination Tomorrow - DT11 - Charters of Freedom

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Subido el 28 de mayo de 2007 por EducaMadrid

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NASA Destination Tomorrow Segment describing how NASA atmospheric scientists contributed to the conservation of the Declaration of Independence, the Constitution, and the Bill of Rights.

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In the late 1700s, three of the world's most important documents were written here in the 00:00:00
United States. 00:00:08
Now called the Charters of Freedom, the Declaration of Independence, the Constitution, and the 00:00:10
Bill of Rights were conceived and written by early Americans who believed that tyrannical 00:00:15
rule and oppression should be replaced by individual liberties and freedom. 00:00:20
Until the mid-20th century, these documents were proudly displayed for the general public, 00:00:25
but the years of inadequate preservation left them a bit faded and brittle. 00:00:30
This all changed in 1951 when the documents were placed in specially adapted encasements 00:00:35
which were designed to slow down the deterioration process. 00:00:41
These glass encasements were filled with inner helium, which would protect the documents 00:00:45
from the harmful chemically corrosive effects of air, keeping them safe for generations 00:00:49
to come. 00:00:54
But in the late 1990s, conservators began noticing that the documents were, in fact, 00:00:55
still showing signs of deterioration. 00:01:00
Mysterious small white spots were appearing inside the encasements and on the documents. 00:01:03
To help determine the cause of the deterioration and how to fix the problem, the National Archives 00:01:08
asked researchers at NASA to perform a series of tests on the atmosphere inside the encasements. 00:01:13
I spoke with Dr. Joel Levine at NASA Langley Research Center to find out more. 00:01:19
In 1951, the National Bureau of Standards, which is now NIST, the National Institute 00:01:25
of Standards and Technology, was asked by the National Archives to preserve these very 00:01:30
important documents, the Declaration of Independence, the U.S. Constitution, and the Bill of Rights. 00:01:37
It became apparent several years prior to 1998 that some mysterious white spots appeared 00:01:43
in all encasements, and over time, over several years, they increased in number. 00:01:51
The National Archives conservators wanted to know if we had technology that could determine 00:01:57
the chemical composition of the encasements noninvasively. 00:02:03
Noninvasively means without extracting air. 00:02:07
We didn't want to touch the air. 00:02:10
We didn't want to touch the encasement. 00:02:12
We wanted to come up with some technique that could tell us the answer without disturbing 00:02:14
the contents of the encasement, both the documents and the atmosphere. 00:02:20
After considerable discussion, we decided we should use a technique called laser spectroscopy. 00:02:24
What the laser did is provide energy at the very wavelength that water vapor absorbs, 00:02:31
and as we looked at the absorption, we could determine what the background gas was. 00:02:38
We're interested in not the document, but the atmosphere in the encasement that's protecting 00:02:43
the document. 00:02:49
What we found is that the gas that was sealed 50 years ago was still there. 00:02:50
When the laser studies were done, NASA researchers conclusively determined that helium in the 00:02:55
encasements had not leaked out. 00:03:00
This determination only increased concerns over the origin of the mysterious white spots. 00:03:03
Most conservators believed that chemically corrosive air had leaked into the encasements, 00:03:09
causing the damage. 00:03:13
With this belief dispelled, the puzzle only intensified. 00:03:14
So in some instance, we actually went back to step one because we still had the problem. 00:03:18
The problem is what is responsible for these white spots. 00:03:23
We eliminated air as a corrosive agent, and the next thing the National Archives asked 00:03:27
us is could we tell them noninvasively how much water vapor was in the encasement. 00:03:33
Because the documents were written on sheepskin, which requires a small amount of water vapor 00:03:40
for stability, the relative humidity inside the encasements was originally set between 00:03:45
25 and 35 percent. 00:03:49
To determine if the humidity levels had changed, the NASA researchers needed to measure the 00:03:51
relative humidity inside the sealed encasement. 00:03:56
The first technique considered involved placing the encasements in a freezer to cause the 00:03:59
condensation of gaseous water vapor to liquid water droplets. 00:04:03
This idea was rejected due to the distinct possibility that the documents inside could 00:04:07
be damaged by the condensed water. 00:04:12
It was later decided that the humidity could be checked by using a very inexpensive device 00:04:14
called a thermal electro-cooler. 00:04:20
This device would sample only a small area of the encasements, keeping the documents 00:04:22
inside safe. 00:04:26
I called up the archives and I said we just have to freeze a small part of it at the edge 00:04:27
where there is no document, no ink, and we can solve your problem. 00:04:32
When the humidity levels were checked, it was found that the levels inside the encasement 00:04:36
were 60 to 65 percent, twice the expected relative humidity. 00:04:40
This is because when the documents were originally sealed in 1951, the relative humidity in Washington, 00:04:45
D.C. was very high. 00:04:52
The backing paper that the documents were laid upon had actually soaked up water vapor 00:04:54
like a sponge. 00:04:58
Once the documents were encased, the water vapor inside the backing paper could not escape, 00:05:00
so it remained in the encasement's atmosphere, causing the humidity to rise. 00:05:05
The white spots were basic or alkaline chemicals that were pulled out of the glass because 00:05:09
of the presence of high levels of water vapor. 00:05:16
And now, when the National Archives opens with its new encasements, we are all sure 00:05:20
that the documents will be stable for many centuries, and in some small part, NASA scientists 00:05:26
and NASA technology help preserve these documents for many generations to come. 00:05:33
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Idioma/s:
en
Niveles educativos:
▼ Mostrar / ocultar niveles
      • Nivel Intermedio
Autor/es:
NASA LaRC Office of Education
Subido por:
EducaMadrid
Licencia:
Reconocimiento - No comercial - Sin obra derivada
Visualizaciones:
544
Fecha:
28 de mayo de 2007 - 17:05
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
05′ 39″
Relación de aspecto:
4:3 Hasta 2009 fue el estándar utilizado en la televisión PAL; muchas pantallas de ordenador y televisores usan este estándar, erróneamente llamado cuadrado, cuando en la realidad es rectangular o wide.
Resolución:
480x360 píxeles
Tamaño:
32.95 MBytes

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