New Mexico has special appeal for us with its rich history of
scientific research and development. Marsha and I put
together an 8 day trip with my sister, brother-in-law and their
son, all of which have interest in the sciences, SW culture
During part of my career, I led the development of state-of-the-art high speed signal digitizers at Tektronix for the nuclear industry and worked with these labs for a number of years. One I remember well was the Kirkland AFB "Trestle" project. It was important at the time to study the effects of HEMP (High Altitude Electromagnetic Pulse) from nuclear detonations high in the atmosphere. The early days of testing revealed that something was taking out electronics 100's of miles distant from the tests. One famous example was the partial shutdown of the honolulu telephone system during an atmospheric nuclear test in the mid pacific. Street lights and other electronics were also effected. This was 800 miles away! Researchers realized that so called compton electrons were formed by the gamma radiation and they needed to find ways of shielding from the very strong HEMP that was generated. Atmospheric testing had come to an end by treaty so the scientists decided to build a platform that could allow full size airplanes to be placed upon it but it couldn't contain much metal--no metallic nuts and bolts.... nothing metallic. Hence it became the worlds largest structure made of wood. B-52 shown in the picture is ready for testing. Kirkland AFB generated a 44 minute movie that describes its history and construction. You can view it here. They claimed that they held up testing waiting for our digitizers.
Today, the structure has been inactive since 1995 with no funds available to maintain. The designer, Dr. Carl E. Baum is no longer alive but was the advocate with many of his notes still available. I met him in the 1970's.
New Mexico has a wealth of scientific organizations centered around early development of nuclear weapons, rocketry then later for deep space research using the VLA (Very large Array). I've always wanted to come back and see these and other special places but never had the time. I wanted to see these sites and new ones one last time and look up a few people I knew so many years ago.
Didn't get to all of them but had fun at what we did. All of the people I knew are retired now; the nostalgia was great!
Over the years Kirkland
AFB had a museum devoted to nuclear weapons and early
testing. I use to enjoy visiting it whenever in town but
9-11 changed all that because public access was closed for
security concerns. Kirkland is a key base in the weapons
program where training takes place. The facility was split
into two parts, the "on base" secure facility and the Nuclear Museum
which now resides off base in SE Albuquerque. I do miss some
of the exhibits that the earlier museum had such as the "lady
Godiva" and raw uranium weight and radiation samples but I guess
that's the price you must pay for security.
|"Lady Godiva" facility showing segmented core,
no longer at new museum
On July 16, 1945 the first prototype of the implosion Atomic Bomb (called the 'Gadget') was detonated at Jornada del Muerto (Journey of Death) desert in South Central New Mexico. This was the initial culmination of the Manhattan Project. The Technical Director, Robert Oppenheimer named the test, "Trinity". Many books have been written about the project with some pictures and details found here.
The "Trinity" test site is open to the public only two days a
year. One great way to visit is to arrange a bus trip
through the Nuclear Museum that includes docents that are retired
physicists and engineers from Sandia Labs and related
organizations. Our trip was scheduled so that we could visit
the "Trinity" site while in town. Being able to spend time
with some of the retirees was a real plus as we discussed some
experiments that took place, such as "Trestle". They told me I was
showing my age!
Being a typical engineer and interested in radiation monitoring,
I took my GM (Geiger-Müller) counter along. I knew ahead of
time that the site was cleaned up and radiation levels would be
|McDonald Ranch House, where final assembly of Plutonium pieces and neutron initiator were completed||Only remains left of the tower that held the "gadget"
It vaporized in the explosion
|Docent describing Ground Zero|
|Ever present security hiding behind the bushes
||Docents (yellow hats) giving lecture on the Trinity story
at McDonald. They're retired Sandia Physicists and
||All that remains of "Jumbo". An approach to an
intermediate test that was ruled out as the development
|Fatman, weaponized version of the "gadget"|| Central point outside ground zero
|| Trinitite: fused sand found under "gadget" detonation
-Still radioactive today-
Any visit to a radioactive site always raises the question as to how much exposure am I going to receive? Being a retired engineer, I couldn't resist the opportunity to do some measurements of my own. I carried a RADALERT GM counter which is sensitive to alpha, beta and gamma radiation to various degrees.
The background radiation well outside the test site was averaging about 15 CPM (counts per minute). The hottest spot I could find inside the inner fence was 300 CPM which was maybe 75 yards from ground zero on the north side at waist height. When the counter was held next to the few remaining pieces of Trinitite on the ground, only modest increase in the count was noted. My conclusion was that most of the radiation was gamma plus cosmic background. No wind was blowing this day so I really don't think that the count had much contribution from alpha and beta emissions. Of course, the site has been cleaned up by removing the top layer of Trinitite and soil particularly around ground zero.
It should be noted that I have
recorded well over 300 CPM using this same counter when
flying at 39,000 feet. Most people will only be at
Ground Zero for maybe 1 hour maximum. In short, you
get 5 times more exposure flying cross country than you
would at a visit to the Trinity site. Few people
realize this! My counter calibration referencing
Cesium 137 source gives: 0.31 mR/Hr for the hot spot noted
above. To convert to mrem you need a QF (quality
factor) that depends upon the type of radiation
detected. Ballpark estimates show that my readings
are very consistant with the numbers represented in
the picture at left.
|Official statement regarding radiation levels
click on image to see larger copy
Nearly all modern design of nuclear weapons now use some form of the implosion principle. "Trinity" proved the concept.
Many books have been written about the program. A consensus from the Sandia folks is: The Making of the Atomic Bomb, written by Richard Rhodes is the best. It won the 1988 Pulitzer Prize.
The nuclear museum also included a visit to EMRTC (Energetic Materials Research and Testing Center) in Socorro, NM. This was a fun trip for retired engineers and those that have survived their explosives building years. Many engineers have experimented with explosives in their teens and I was no exception. Once I accidently set off an Ammonia and Iodine mixture which was very shock sensitive and I decided then that I should take up less dangerous hobby such as electronics.
It should be no surprize that EMRTC is in New Mexico and reasonably close to the Los Alamos labs. Building nuclear weapons involves the precise detonation of energetic materials. Today most of the testing takes place at the labs themselves often using simulators. Much has been learned over the years. Exploding bridgewires was an early technique tested at Trinity.
|Technician describing "det" cord
||Learning about ANFO
EMRTC has a number of roles for both private and government
interests. One is to teach "first responders" how to deal
with explosives which are becoming more frequent in encounters
with society. Particulary, "home brew" concoctions.
"Pipe bombs" have always been a hazard but now we have such nasty
componds as TATP (triacetone triperoxide) or HTMD (Hexamethylene
triperoxide diamine) both of which can easily be produced in the
home or garage and are extremely dangerous because they're
unstable and shock sensitive. They are often found with
terrorists activities. These two bad guys can also be made
into homemade caps to set off less sensitive explosives.
Professional explosive handlers want nothing to do with them
because of the hazards.
Erythritol Tetranitrate (ETN) is a most interesting explosive for
the amateur experimentor as it's easy to make from an artificial
sweetener and has burn characteristics that make it attractive
even as a cap.
We were treated to a lecture on modern explosives, their
application, how they are detonated plus characteristics of
each. We also were shown from the safety of an observing
bunker, four explosions; a blasting cap, 'det' cord, plastic
explosive and 4 lbs of ANFO (Ammonium Nitrate and Fuel Oil).
The biggest explosion and least expensive was the ANFO but it
required a cap to set off plus a small plastic explosive which in
turn set off the ANFO. The plastic is called a 'booster'
because normal ANFO is very insensitive. It was amazing how
powerful only four pounds can be. Explosive use is all about
"speed of burn". The most powerful are not necessarily the
fastest; gasoline releases more energy than most high
explosives. They all have applications.
For many years, the common way to set off explosives was using an
electric blasting cap. With all the use of the radio spectrum
nowadays such as cell phones, two way radios, etc. They're
starting to move away from that approach because transmitters can
induce a current in the blasting cap wires which can accidently
detonate the primary explosive prematurely. The new way is
using "shock cord" which is much safer. They can still be
set off electrically but much shorter lead wires and no
significant explosive on the personnel end.
Det Cord (Detonating Cord) is an explosive that you can
shape. We witnessed cutting a hole in the top of a table but
in practice a heavier version could be used to open a wall for
military or law enforement quick access. Det cord is also
used to connect multiple secondary explosives. Jokingly, Det
Cord is an expensive but quick way to cut trees down.
EMRTC has even tested very small explosives used to inflate air bags in your automobile.
50 miles West of Socorro and EMRTC in an isolated valley is a
unique Radio Astronomy facility. Called the VLA for Very Large Array.
It was the first major attempt in the US to use multiple large
parabolic dish antenas to synthesize an even bigger one by using
spacial separation of smaller antennas and applying interferometry
techniques. Now a worldwide effort is underway with the VLBI
(Very Long Baseline Interferometry) but the VLA facility is still
very active and is being upgraded to the EVLA (Extended VLA) which
will have modernized electronic equipment.
|Many of the 27 antennas
||Antenna being serviced
Interferometry measures the correlation between signals from antennas at different locations. This is a measure of how similar two signals are. The idea is a very powerful one that has led to medical imaging such as CAT scanners. Mapping of the planet Venus surface used synthetic aperture radar which is related. The concept can be applied to radio signals. Modern computing power has opened up many fields of science that are just beginning to yield untold results.
How does it work?
For example, if the two antennas do not see a common source of signal, there will be no similarity between their signals, because the signals will come from independent sources (mostly LNA noise), and the correlation will be zero.
On the other hand, if the antennas see a common source, their signals will have a common part in addition to the independent part caused by preamplifier noise etc. The common part will in general arrive at different times to the two antenas (because of the geometry - different path lengths from the source to each antenna) and will therefore have a relative delay (time offset) between the two antennas, This delay is also measured by the interferometer and is partly reflected in that the correlation is a complex number.
Obviously, the amount of correlation depends on the power of the source: a brighter source will produce a bigger common component (compared to receiver noise) so the correlation will be higher. In this way an interferometer is similar to a radiometer (total power) telescope.
But the correlation also depends on the angular brightness distribution of the source and the antenna spacing (baseline). By recording the correlation with many different baselines, its possible to reconstruct an image of the source.
The most popular output of an interferometer are the "fringes". They are just the real (or imaginary) part of the correlation, plotted versus time. As the Earth rotates, the delays change and the phase of the correlation rotates, so its real and imaginary parts change periodically.
Radio Interferometry and Aperture Synthesis
The angular resolution, or ability of a radio telescope to distinguish fine detail in the sky, depends on the wavelength of observations divided by the size of the instrument. Yet, even the largest antennas, when used at their shortest operating wavelength, have an angular resolution only a little better than one arc minute, which is comparable to that of the unaided human eye at optical wavelengths. Because radio telescopes operate at much longer wavelengths than do optical telescopes, radio telescopes must be much larger than optical telescopes to achieve the same angular resolution.
At radio wavelengths, the distortions introduced by the atmosphere are less important than at optical wavelengths, and so the theoretical angular resolution of a radio telescope can in practice be achieved even for the largest dimensions. Also, because radio signals are easy to distribute over large distances without distortion, it is possible to build radio telescopes of essentially unlimited dimensions. In fact, the history of radio astronomy has been one of solving engineering problems to construct radio telescopes of continually increasing angular resolution.
The high angular resolution of radio telescopes is achieved by using the principles of interferometry to synthesize a very large effective aperture from a number of small elements. In a simple two-element radio interferometer, the signals from an unresolved, or "point," source alternately arrive in phase and out of phase as the Earth rotates and causes a change in the difference in path from the radio source to the two elements of the interferometer. This produces interference fringes in a manner similar to that in an optical interferometer. If the radio source has finite angular size, then the difference in path length to the elements of the interferometer varies across the source. The measured interference fringes from each interferometer pair thus depend on the detailed nature of the radio "brightness" distribution in the sky.
Each interferometer pair measures one "Fourier component" of the brightness distribution of the radio source. Work by Australian and British radio astronomers in the 1950s and 1960s showed that movable antenna elements combined with the rotation of the Earth can sample a sufficient number of Fourier components with which to synthesize the effect of a large aperture and thereby reconstruct high-resolution images of the radio sky. The laborious computational task of doing Fourier transforms to obtain images from the interferometer data is accomplished with high-speed computers and the fast Fourier transform (FFT), a mathematical technique that is especially suited for computing discrete Fourier transforms.
In recognition of their contributions to the development of the Fourier synthesis technique, more commonly known as aperture synthesis, or earth-rotation synthesis, Martin Ryle and Antony Hewish were awarded the 1974 Nobel Prize for Physics. During the 1960s the Swedish radio astronomer, Jan Hogbom developed a technique called "CLEAN," which is used to remove the spurious responses from a celestial radio image caused by the use of discrete, rather than continuous, spacings in deriving the radio image. Further developments, based on a technique introduced in the early 1950s by the British scientists Roger Jennison and Francis Graham Smith, led to the concept of self-calibration, which is used to remove errors in a radio image due to uncertainties in the response of individual antennas as well as small errors introduced by the propagation of radio signals through the terrestrial atmosphere. In this way radio telescopes are able to achieve extraordinary angular resolution and image quality, not possible in any other wavelength band.
Very Long Baseline Interferometry (VLBI)
In conventional interferometers and arrays, coaxial-cable, waveguide, or even fiber-optic links are used to distribute a common local oscillator reference signal to each antenna and also to return the received signal from an individual antenna to a central laboratory where it is correlated with the signals from other antennas. In cases in which antennas are spaced more than a few tens of kilometers apart, however, it becomes prohibitively expensive to employ real physical links to distribute the signals. Very high frequency (VHF) or ultrahigh frequency (UHF) radio links can be used, but the need for a large number of repeater stations makes this impractical for spacings greater than a few hundred kilometers.
Interferometer systems of essentially unlimited element separation are formed by using the technique of very long baseline interferometry, or VLBI. In a VLBI system the signals received at each element are recorded by broad-bandwidth videotape recorders located at each element. The recorded tapes are then transported to a common location where they are replayed and the signals combined to form interference fringes. The successful operation of a VLBI system requires that the tape recordings be synchronized within a few millionths of a second and that the local oscillator reference signal be stable to better than one part in a trillion. A single magnetic tape capable of recording for several hours can contain one trillion bits of information, which is roughly equivalent to storing the entire contents of a modest-sized library. Hydrogen maser frequency standards are used to give a timing accuracy of only a few billionths of a second and a frequency stability of one part in a billion billion.
Needless to say, some of the greatest advances in computerized computational techniques has come from radio astronomy. In time, VLBI will be deployed between planets to gain resolution.
Located in the SE corner of New Mexico, these caves are some of
the most impressive in the world. We have been here before
but its still impressive after many years. It takes a full
day just to explore the portion thats open to the public.
Miles of passageways have been found since the early part of the
20th century. Many unexplored sections still exist. Carlsbad
is famous for its bat flights every evening and morning in the
warmer months. It was the bats that first gave its location
|Gathering place, 750' underground
||The Chapas plus Marsha
Lechuguilla cave has currently over 120 miles of passages
identified to a depth of 1,600 feet and is located only 4 miles
from Carlsbad Caverns. It will probably never be opened to
the public for protection. So far no connection between the
two has been found but it would be naive to think that one doesn't
White Sands covers a large area in South Central New Mexico and in active use by the US Army, Air Force and NASA. The central hub is Alamogordo in which Holoman AFB is located. Many military and space exploration rocket engines are tested, first, in this area. We made a visit to the New Mexico Museum of Space History.
|Used V2 tail fin from early flights
New Mexico Museum of Space History
|Nike rocket over Alamogordo
||Early tracking system|
|Typical sand dunes
White Sands National Monument
|Eric & Donavan
White Sands National Monument
|Neil & Marsha
White Sands National Monument
White Sands National Monument
is located within the missile test range and may be closed for
a few hours now and then when a test is underway. Its a very
unusual type sand in that its made of gypsum; the same stuff as in
"sheetrock". Not the place to be on a hot summer day!
By a stroke of luck our trip coincided with the annual balloon festival that
Albuquerque is famous for. It draws a crowd of 100,000 from
around the world and lasts a week.
|Getting ready||Inflation||Just after sunrise|
|Petroglyph National Monument
|New Mexico Museum of Natural History
||Dinosaur with feathers
Days can be spent here exploring. Just to the West is Petroglyph National Monument and in the heart of town are several first class museums.
This was the final destination on our eighth day. Its known
as an artsy city in Northern New Mexico. Many retirees end
up here as it has a pleasant climate and rich culture. Lots
of shops and museums.
|Old Town, Santa Fe
||Museum of Indian Arts
|Downtown Santa Fe
Museum of Indian Arts
|Museum of Indian Arts
We intended to drive to Los Alamos and visit the Bradbury museum but ran out of time.