Hello, and welcome to a peak inside the Space
Vault at the New Mexico Museum of Space History.
I’m education director Dave Dooling, and
today I’m going take you from pinholes to
black holes.
Hidden among the boxes and artifacts at the
New Mexico Museum of Space History’s support
center is the ancestor of one of the most
successful telescopes ever built.
It’s easy to overlook—just a bundle of
old electronics and a metal plate full of
holes.
And that’s the key to locating mysterious
gamma-ray bursts, black holes, and other deep
space beasts.
It’s a multiple pinhole camera, known as
the Uniformly Redundant Array, or U-R-A, built
at Los Alamos National Laboratory.
But the pinhole cameras you might know have
just one opening.
Pinhole cameras have been used by artists
for centuries.
Camera obscura means darkened box, which is
all a camera is: a box with a hole in one
side.
Because light travels in straight lines, it
will pass through a pinhole and form an upside-down
mirror image on the other side.
Many primitive animals, like the chambered
Nautilus, have pinhole eyes that evolved from
light-sensitive skin that grew inward.
More advanced eyes, like our own, have lenses
that focus light.
Telescopes use even more complex sets of lenses
and mirrors to focus light into stunning images
of the heavens.
So why take a step backwards?
It’s because electromagnetic radiation doesn’t
react the same with all materials.
Gamma rays are so energetic that they will
pass right through the optics that focus light.
But metal can block gamma rays, and this is
where the pinhole camera comes back into play.
Like most solutions, pinhole cameras have
advantages and disadvantages.
On the plus side, they are simple and form
images that sharply outline everything, near
and far.
On the minus side, that sharpness requires
a tiny opening, meaning a decent image will
take minutes or hours to make.
Larger apertures mean shorter exposures and
blurrier images.
But, a thousand pinholes will produce a thousand
sharp images overlaid on each other.
So, the next step is a computer with special
software to deconvolve the images — that
is, to unfold everything.
The U-R-A pinhole pattern looks random ,but
has an almost eerie mathematical property
that allow the thousands of overlapping images
to be uniquely unfolded.
But why is such a camera needed in the first
place?
We have to step back almost 60 years to a
treaty that led to a startling discovery.
In 1963 the United States and the Soviet Union
signed a treaty to ban nuclear bomb tests
in the atmosphere, oceans, and outer space.
To ensure that the Soviets did not cheat,
Los Alamos developed the Vela Hotel satellites
carrying nuclear flash detectors.
This engineering model is another artifact—and
future story—“in the vault.”
Twelve Vela Hotel satellites were launched,
starting in October 1963.
Things were pretty routine until July 2nd,
1967, when something rang the bell on Velas
3 and 4.
No one remotely suspected that stars could
change over seconds or, for that matter, produce
gamma rays.
So no one had looked to see if there were
non-nuclear flashes in the data.
When gamma rays bursts were found, it was
very puzzling.
More bursts followed, and eventually, Los
Alamos scientists determined that these were
natural, powerful events from far outside
our solar system.
From this was born the new field of gamma-ray
astronomy, and satellites soon started carrying
better detectors.
Scientists now faced a new challenge.
Bursts appeared and disappeared faster than
detectors could pin down their locations.
Not until December 14, 1997, did a coordinated
network help the Apache Point Observatory
above Alamogordo capture the first visible
component of a gamma-ray burst.
So, how best to catch them in the act?
The answer started emerging in the 1970s as
Los Alamos worked on advanced pinhole cameras.
The Los Alamos team included a graduate student
named Ed Fenimore.
Using Aerobee 150 sounding rockets at White
Sands Missile Range, they tested pinhole cameras
by observing the Sun.
Fenimore’s work led him and Thomas Cannon
to file for a patent in 1978, granted in 1980,
for “A system utilizing uniformly redundant
arrays to image non-focusable radiation.”
It promised a strong, clear signal with very
little noise.
Sounding rockets still are a great way to
test new concepts.
But what goes up doesn’t always go up when
bursts go off, and must come down.
The opportunity for a longer test soon emerged
— NASA’s Space Shuttle.
Through the Air Force’s Space Test Program,
Fenimore proposed flying a larger version
of his pinhole camera.
Originally it was scheduled to fly on the
first Shuttle mission out of Vandenberg Air
Force Base in California.
The crew had started training when Space Shuttle
Challenger was lost in early 1986.
In the changes that followed, the payload
was assigned to the STS-39 Shuttle mission.
That payload—Air Force Project 675—included
instruments for studying the Earth’s northern
lights and the space background.
U-R-A itself was, well, mostly just a box.
Only a hexagonal bit of foil to block visible
light really showed its business end, staring
over the starboard side of the Shuttle.
Ten feet behind that was a complex set of
detectors coupled to one of the most sophisticated
computers flown on Shuttle.
It launched on Space Shuttle Discovery on
April 28, 1991, and soon ran into trouble.
Data recorders refused to work, so the crew
did an emergency electrical bypass so data
could be sent directly to Earth.
U-R-A observed the usual suspects—like the
Crab Nebula, the center of our galaxy, and
Centaurus X-3—to compare with earlier X-ray
images.
U-R-A worked well, helping Fenimore and his
team earn a spot on NASA’s High-Energy Transient
Explorer, or HETE.
The Los Alamos team supplied a Wide Field
X-ray Monitor that gave the X and Y coordinates
of a burst.
HETE-1 was lost during launch, but HETE-2,
launched in 2000, was highly successful.
Over the next four years, HETE-2 observed
more than 80 gamma-ray flashes and sent precise
locations within tens of seconds.
It helped pin down the location of short gamma-ray
bursts and implied they were the result of
the collision of two neutron stars.
Bigger things were in the works.
The Los Alamos team won a key spot aboard
the Neil Gehrels Swift Observatory, launched
in 2004 and still operating.
Swift isn’t an acronym.
It describes the spacecraft’s agility as
it swings into position to observe gamma-ray
bursts before they fade.
Knowing which way to point the spacecraft
is the job of the Burst Alert Telescope, or
BAT.
This is U-R-A on a grand scale.
At four-by-eight feet, it’s the largest
pinhole array ever flown, 20,000 times larger
than the first to fly on the Aerobee rockets.
The mask at the front has 54,000 lead tiles—each
thinner and four times smaller than a penny—outlining
54,000 holes.
Combined with 33,000 tiny detectors, BAT observes
a chunk of sky 200 times the apparent width
of the Moon.
Most of the time BAT slowly maps the heavens
in X-rays about as energetic as what you might
get at a hospital.
When a burst is detected it switches into
high gear, quickly telling the satellite which
way to point.
It does this with a computer far slower than
your desktop or cell phone, but resistant
to space radiation, and powered by a genius-level
program developed by David Palmer of Los Alamos.
In nearly 16 years, BAT has detected more
than a thousand gamma-ray bursts—including
four on one day—powerful X-ray flares from
a red dwarf star, and a new black hole hear
the center of our galaxy.
It has helped Swift become NASA’s second
most productive scientific observatory, leading
to more than sixteen-hundred scientific papers.
And the sources of the gamma-ray bursts that
started this long quest?
Some are caused by starquakes on highly magnetized
neutron stars.
Others likely are neutron stars swallowing
each other to become a black hole, or super-massive
stars hammering their cores into black holes.
The only certainty is more questions as we
peer deeper into the heart of the universe.
Not bad for a pinhole camera.
Thanks for tuning in, and keep watching for
another peek inside the Space Vault.
