To the human
eye, space appears serene and void. It is neither.
by the Marshall Space Flight Center
To the "eye"
of an X-ray telescope, the Universe is totally different ‚€“ a violent,
vibrant, and ever-changing place. Temperatures can reach millions
of degrees. Objects are accelerated by gravity to nearly the speed
of light and magnetic fields more than a trillion times stronger
than the Earth‚€™s cause some stars to crack and tremble.
space telescope, called the Chandra X-ray Observatory, will allow
scientists from around the world to obtain unprecedented X-ray images
of these and other exotic environments to help understand the structure
and evolution of the Universe. The observatory will not only help
to probe these mysteries, but also will serve as a unique tool to
study detailed physics in a laboratory that cannot be replicated
here on Earth ‚€“ the Universe itself. NASA‚€™s Chandra X-ray Observatory
has every prospect of rewriting textbooks and helping technology
advance in the coming decade.
X-ray Observatory will provide unique and crucial information on
the nature of objects ranging from comets in our Solar System to
quasars at the edge of the observable Universe. The observatory
should provide long-sought answers to some major scientific questions,
such as what and where is the "Dark Matter" in our Universe? The
largest and most massive objects in the Universe are galaxy clusters
- enormous collections of galaxies, some like our own. These galaxies
are bound together into a cluster by gravity. Much of their mass
is in the form of an incredibly hot, X-ray emitting gas that fills
the entire space between the galaxies. Yet, neither the mass of
the galaxies, nor the mass of the hot X-ray gas is enough to provide
the gravity that we know holds the cluster together. X-ray observations
with the Chandra X-ray Observatory will map the location of the
dark matter and help us to identify it.
X-ray image of Eta Carina revealed a surprise - a bright horseshoe
nebula around the star
What is the
powerhouse driving the explosive activity in many distant galaxies?
The centers of many distant galaxies are incredible sources of energy
and radiation ‚€“ especially X-rays. Scientists theorize that massive
black holes are at the center of these active galaxies, gobbling
up any material ‚€“ even a whole star ‚€“ that passes too close. Detailed
studies with the Chandra X-ray Observatory can probe the faintest
of these active galaxies, and study not only how their energy output
changes with time, but also how these objects produce their intense
energy emissions in the first place.
are absorbed by the Earth‚€™s atmosphere, space-based observatories
are necessary to study these phenomena. To meet this scientific
challenge, the Chandra X-ray Observatory, NASA‚€™s most powerful X-ray
telescope, was launched in July 1999. Complementing two other space
observatories now orbiting Earth ‚€“ the Hubble Space Telescope and
the Compton Gamma Ray Observatory ‚€“ this observatory studies X-rays
rather than visible light or gamma rays. By capturing images created
by these invisible rays, the observatory will allow scientists to
analyze some of the greatest mysteries of the Universe.
The launch of the Space
Shuttle Columbia with the Chandra X-ray telescope
Named in honor
of the late Indian-American Nobel Laureate Subrahmanyan Chandrasekhar,
the observatory was formerly known as the Advance X-ray Astrophysics
Facility. The Chandra X-ray Observatory was carried into low Earth
orbit by the Space Shuttle Columbia. The observatory was deployed
from the shuttle‚€™s cargo bay at 155 miles above the Earth. Two firings
of an attached Inertial Upper Stage rocket and several firings of
its own on-board rocket motors after separating from the Inertial
Upper Stage placed the observatory into its working orbit.
Unlike the Hubble
Space Telescope‚€™s circular orbit that is relatively close to the
Earth, the Chandra X-ray Observatory was placed in a highly elliptical
(oval-shaped) orbit. At its closest approach to Earth, the observatory
will be at an altitude of about 6,000 miles. At its farthest, 86,400
miles, it travels almost one-third of the way to the Moon. Due to
this elliptical orbit, the observatory circles the Earth every 64
hours, carrying it far outside the belts of radiation that surround
our planet. This radiation, while harmless to life on Earth, can
overwhelm the observatory‚€™s sensitive instruments. The X-ray observatory
is outside this radiation long enough to take 55 hours of uninterrupted
observations during each orbit. During periods of interference from
Earth‚€™s radiation belts, scientific observations are not taken.
X-ray Observatory has three major elements. They are the spacecraft
system, the telescope system and the science instruments.
X-ray telescope will travel one-third of the way to the Moon
in its orbit
module contains computers, communication antennas and data recorders
to transmit and receive information between the observatory and
ground stations. The onboard computers and sensors, with ground-based
control center assistance, command and control the vehicle and monitor
its health during its expected five-year lifetime.
module also provides rocket propulsion to move and aim the entire
observatory, an aspect camera that tells the observatory its position
relative to the stars, and a Sun sensor that protects it from excessive
light. Electrical power is provided by solar arrays that also charge
three nickel-hydrogen batteries that provide backup power.
At the heart
of the telescope system is the High-Resolution Mirror Assembly.
Since high-energy X-rays would penetrate a normal mirror, special
cylindrical mirrors were created. The two sets of four nested mirrors
resemble tubes within tubes. Incoming X-rays graze off the highly
polished mirror surfaces and are funneled to the instrument section
for detection and study.
of the X-ray observatory are the largest of their kind and the smoothest
ever created. The largest of the eight mirrors is almost 4 feet
in diameter and 3 feet long. Assembled, the mirror group weighs
more than 1 ton. The High-Resolution Mirror Assembly is contained
in the cylindrical "telescope" portion of the observatory. The entire
length of the telescope is covered with reflective multi-layer insulation
that assists heating elements inside the unit in keeping a constant
internal temperature. By maintaining a precise temperature, the
mirrors within the telescope are not subjected to expansion and
contraction ‚€“ thus ensuring greater accuracy in observations.
mirrors were tested at NASA‚€™s Marshall Space Flight Center in Huntsville,
Alabama Marshall‚€™s world-class X-ray Calibration Facility verified
the mirrors‚€™ exceptional accuracy ‚€“ comparable to the accuracy required
to hit a hole-in-one from Los Angeles to San Diego. This achievement
allows the observatory to detect objects separated by one-half arc
second. This is comparable to reading the letters of a stop sign
12 miles away.
X-ray Observatory represents a scientific leap in ability over previous
X-ray observatories like NASA‚€™s Einstein, which orbited the Earth
from 1978 to 1981. With its combination of large mirror area, accurate
alignment and efficient X-ray detectors, the Chandra X-ray Observatory
has eight times greater resolution and is 20-to-50 times more sensitive
than any previous X-ray telescope.
Within the instrument
section of the observatory, two instruments at the narrow end of
the telescope cylinder will collect X-rays and study them in various
ways. Each of the instruments can serve as an imager or spectrometer.
Camera will record X-ray images, giving scientists an unequaled
look at violent, high-temperature occurrences like the death of
stars or colliding galaxies. The High-Resolution Camera is composed
of two clusters of 69 million tiny lead-oxide glass tubes. The tubes
are only one-twentieth of an inch long and just one-eighth the thickness
of a human hair. When X-rays strike the tubes, particles called
electrons are released. As the electrons are accelerated down the
tubes by high voltage, they cause an avalanche of about 30 million
more electrons. A grid of electrically charged wires at the end
of the tube detects this flood of particles and allows the position
of the original X-ray to be precisely determined. The High-Resolution
Camera also complements the Charge-Coupled Device Imaging Spectrometer,
Imaging Spectrometer shows the remnant of a supernova
X-ray Observatory‚€™s Imaging Spectrometer is also located at the
narrow end of the observatory. This detector is capable of recording
not only the position, but also the color (energy) of the X-rays.
The imaging spectrometer is made up of 10 charge-coupled device
arrays. These detectors are similar to those used in home video
recorders and digital cameras but are designed to detect X-rays.
Commands from the ground allow astronomers to select which of the
various detectors to use. The imaging spectrometer can distinguish
up to 50 different energies within the range the observatory operates.
In order to gain even more energy information, two screen-like instruments,
called diffraction gratings, can be inserted into the path of the
X-rays between the telescope and the detectors. The gratings change
the path of the X-ray depending on its color (energy) and the X-ray
cameras record the color and position. One grating concentrates
on the higher and medium energies and uses the imaging spectrometer
as a detector ‚€“ the other grating disperses low energies and is
used in conjunction with the High Resolution Camera.
these X-ray rainbows, or spectra, and recognizing signatures of
known elements, scientists can determine the composition of the
X-ray producing objects, and learn how the X-rays are produced.
Astrophysical Observatory controls science and flight operations
of the Chandra X-ray Observatory for NASA from Cambridge, Mass.
The Smithsonian manages two electronically linked facilities ‚€“ the
Operations Control Center and the Science Center.