Exploring The Invisible Universe:
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To the human eye, space appears serene and
void. It is neither. 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. NASA’s newest 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 |
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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. The Chandra 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:
Since X-rays 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, is scheduled for launch in 1999. Complementing two
other space observatories now orbiting Earth – the Hubble Space Telescope and
the Compton Gamma Ray Observatory – this observatory will study 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. 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
will be carried into low Earth orbit by the Space Shuttle Columbia. The
observatory will be 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 will place 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 will be placed in a highly elliptical (oval-shaped) orbit. At its
closest approach to Earth, the observatory will be at an altitude of about 6,200
miles. At its farthest, 87,000 miles, it will travel almost one-third of the
way to the Moon. Due to this elliptical orbit, the observatory will circle
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 will
be 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 will not be taken. The Chandra X-ray Observatory has three
major elements. They are the spacecraft system, the telescope system and the
science instruments. The Spacecraft System The spacecraft 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. The spacecraft 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. The Telescope System 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 will graze
off the highly polished mirror surfaces and will be funneled to the
instrument section for detection and study. The mirrors of the X-ray observatory are the largest of their kind and the smoothest ever created. If the surface of the state of Colorado were as relatively smooth, Pike’s Peak would be less than one inch tall. 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. |
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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 will assist heating elements inside the unit in
keeping a constant internal temperature. By maintaining a precise
temperature, the mirrors within the telescope will not be subjected to
expansion and contraction – thus ensuring greater accuracy in observations. The assembled mirrors were tested at
NASA’s Marshall Space Flight Center in Huntsville, Ala. 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 will allow 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. The Chandra 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. Science Instruments 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. A High-Resolution 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 will complement
the Charge-Coupled Device Imaging Spectrometer, described below. The Chandra 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. By studying 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. Observatory Operations The Smithsonian 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. The Operations Control Center is
responsible for directing the observatory’s mission as it orbits Earth. A
control center team will interact with the observatory three times a day –
receiving science and housekeeping information from its recorders. The
control center team also will send new instructions to the observatory as
needed, as well as transmit scientific information from the X-ray observatory
to the Science Center. The Science Center is an important
resource for scientists who wish to study X-ray emitting celestial objects
like quasars and colliding galaxies. The Science Center will provide user
support to researchers, including science data processing and a science data
archive. The Science Center will work with NASA and the scientific community
to allow public access to the scientific results. NASA and Partners The Chandra X-ray Observatory program is managed
by the Marshall Center for the Office of Space Science, NASA Headquarters,
Washington, D.C. TRW Space and Electronics Group of Redondo Beach, Calif., is
the prime contractor and has assembled and tested the observatory for NASA.
Using glass purchased from Schott Glaswerke, Mainz, Germany, the telescope’s
mirrors were built by Raytheon Optical Systems Inc., Danbury, Conn. The
mirrors were coated by Optical Coating Laboratory, Inc., Santa Rosa, Calif.,
and assembled by Eastman Kodak Co., Rochester, N.Y. The Chandra X-ray Observatory Charge-Coupled Device Imaging Spectrometer was developed by Pennsylvania State University, University Park, Pa., and the Massachusetts Institute of Technology (MIT), Cambridge. One diffraction grating was developed by MIT, the other by the Space Research Organization Netherlands, Utrecht, Netherlands, in collaboration with the Max Planck Institute, Garching, Germany. The High Resolution Camera was built by the Smithsonian Astrophysical Observatory. Ball Aerospace & Technologies Corporation of Boulder, Colo., developed the aspect camera and the Science Instrument Module. |
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Links to the Chandra
X-ray Observatory:
Links to the Chandra X-ray Observatory can
be found at the following website: http://www1.msfc.nasa.gov/NEWSROOM/chandra/chandra.html
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[ TOP 10 FACTS] ABOUT [CHANDRA X-RAY OBSERVATORY ] AND [MORE ON CHANDRA]
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