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Spacecraft System
The spacecraft module contains computers, communication antennas
and data recorders to transmit and receive information
between the observatory and ground stations.
Onboard computers and sensors, w/ ground-based control
center assistance, command and control the vehicle and
monitor its health during its expected 5 yr. mission.
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 charge
3 nickel-hydrogen batteries that provide backup power.
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 graze off the highly polished mirror surfaces
and are 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 8 mirrors is almost 4 ft. in diameter and 3 ft. 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 w/
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 1/2 arc second.
This is comparable to reading the letters of a stop sign 12 miles away.
The Chandra is not NASA's 1st X-ray observatorie.
'Einstein' orbited the Earth from 1978 to 1981.
Chandra is 20-to-50 times more sensitive than any previous X-ray
telescope.
Science Instruments
Within the instrument section of the observatory,
2 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, of violent,
high-temperature occurrences like the death of stars or colliding galaxies.
The High-Resolution Camera is composed of
2 clusters of 69 million tiny lead-oxide glass tubes.
The tubes are only 1/20 in. long and 1/8th 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.
Charge-Coupled Device Imaging Spectrometer
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,
2 screen-like instruments, called diffraction gratings,
can be inserted into the path of the X-rays
between the telescope and the detectors.
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 the
operations of Chandra 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 3 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 Chandra to the Science Center.
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.
(Propaganda is integral to NASA funding.)
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