yee@trident.arc.nasa.gov (Peter E. Yee) (11/30/90)
o Hopkins Ultraviolet Telescope (HUT) uses a spectrograph to examine
faint astronomical objects such as quasars, active galactic nuclei and
normal galaxies in the far ultraviolet.
o Ultraviolet Imaging Telescope (UIT) will take wide-field-of-view
photographs of objects such as hot stars and galaxies in broad ultraviolet
wavelength bands.
o Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) will
study the ultraviolet polarization of hot stars, galactic nuclei and quasars.
These instruments working together will make 200 to 300
observations during the STS-35 mission. The Astro ultraviolet telescopes
are mounted on a common pointing system in the cargo bay of the Space
Shuttle. The grouped telescopes will be pointed in the same direction at
the same time, so simultaneous photographs, spectra and polarization
studies will be available for each object observed. The telescopes will be
operated by Columbia's crew.
A fourth Astro instrument, the Broad Band X-Ray Telescope
(BBXRT), will view high-energy objects such as active galaxies, quasars
and supernovas. This telescope is mounted on a separate pointing system
secured by a support structure in the cargo bay.
For joint observations, BBXRT can be aligned with the ultraviolet
telescopes to see the same objects, but it also can be pointed
independently to view other X-ray sources. BBXRT will be operated
remotely by ground controllers. Since the ultraviolet telescopes and the
X-ray telescope are mounted on different support structures, they can be
reflown together or separately.
The Hopkins Ultraviolet Telescope
The Hopkins Ultraviolet Telescope is the first major telescope
capable of studying far ultraviolet (FUV) and extreme ultraviolet (EUV)
radiation from a wide variety of objects in space. HUT's observations will
provide new information on the evolution of galaxies and quasars, the
physical properties of extremely hot stars and the characteristics of
accretion disks (hot, swirling matter transferred from one star to
another) around white dwarfs, neutron stars and black holes.
HUT will make the first observations of a wide variety of
astronomical objects in the far ultraviolet region below 1,200 Angstroms
(A) and will pioneer the detailed study of stars in the extreme ultraviolet
band. Ultraviolet radiation at wavelengths shorter than 912 A is absorbed
by hydrogen, the most abundant element in the universe. HUT will allow
astronomers, in some instances along unobserved lines of sight, to see
beyond this cutoff, called the Lyman limit, because the radiation from the
most distant and rapidly receding objects, such as very bright quasars, is
shifted toward longer wavelengths.
HUT was designed and built by the Center for Astrophysical
Sciences and the Applied Physics Laboratory of The Johns Hopkins
University in Baltimore, Md. Its 36-inch mirror is coated with the rare
element iridium, a member of the platinum family, capable of reflecting
far and extreme ultraviolet light. The mirror, located at the aft end of the
telescope, focuses incoming light from a celestial source back to a
spectrograph mounted behind the telescope.
A grating within the spectrograph separates the light, like a
rainbow, into its component wavelengths. The strengths of those
wavelengths tell scientists how much of certain elements are present.
The ratio of the spectral lines reveal a source's temperature and density.
The shape of the spectrum shows the physical processes occurring in a
source.
The spectrograph is equipped with a variety of light-admitting slits
or apertures. The science team will use different apertures to
accomplish different goals in their observation. The longest slit has a
field of view of 2 arc minutes, about 1/15th the apparent diameter of the
moon. HUT is fitted with an electronic detector system. Its data
recordings are processed by an onboard computer system and relayed to
the ground for later analysis.
Johns Hopkins scientists conceived HUT to take ultraviolet
astronomy beyond the brief studies previously conducted with rocket-
borne telescopes. A typical rocket flight might gather 300 seconds of
data on a single object. HUT will collect more than 300,000 seconds of
data on nearly 200 objects during the Astro-1 mission, ranging from
objects in the solar system to quasars billions of light-years distant.
HUT Vital Statistics
Sponsoring Institution: The Johns Hopkins University,
Baltimore, Md.
Principal Investigator: Dr. Arthur F. Davidsen
Telescope Optics: 36 in. aperture, f/2 focal ratio, iridium-
coated paraboloid mirror
Instrument: Prime Focus Rowland Circle
Spectrograph with microchannel plate
intensifier and electronic diode array
detector
Field of View
of Guide TV: 10 arc minutes
Spectral Resolution: 3.0 A
Wavelength Range: 850 A to 1,850 A (First Order)
425 A to 925 A (Second Order)
Weight: 1,736 lb
Size: 44 inches in diameter
12.4 ft. in length
Wisconsin Ultraviolet Photo-Polarimeter Experiment
Any star, except for our sun, is so distant that it appears as only a
point of light and surface details cannot be seen. If the light from objects
is polarized, it can tell scientists something about the source's geometry,
the physical conditions at the source and the reflecting properties of tiny
particles in the interstellar medium along the radiation's path.
The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE),
developed by the Space Astronomy Lab at the University of Wisconsin-
Madison, is designed to measure polarization and intensity of ultraviolet
radiation from celestial objects. WUPPE is a 20-inch telescope with a
5.5-arc-minute field of view.
WUPPE is fitted with a spectropolarimeter, an instrument that
records both the spectrum and the polarization of the ultraviolet light
gathered by the telescope. Light will pass through sophisticated filters,
akin to Polaroid sunglasses, before reaching the detector. Measurements
then will be transmitted electronically to the ground.
Photometry is the measurement of the intensity (brightness) of the
light, while polarization is the measurement of the orientation (direction)
of the oscillating light wave. Usually waves of light move randomly -- up,
down, back, forward and diagonally. When light is polarized, all the waves
oscillate in a single plane. Light that is scattered, like sunlight reflecting
off water, is often polarized. Astro-1 astronomers expect to learn about
ultraviolet light that is scattered by dust strewn among stars and galaxies.
They also can learn about the geometry of stars and other objects by
studying their polarization. To date, virtually no observations of
polarization of astronomical sources in the ultraviolet have been carried
out. WUPPE measures the polarization by splitting a beam of radiation
into two perpendicular planes of polarization, passing the beams through
a spectrometer and focusing the beams on two separate array detectors.
In the ultraviolet spectrum, both photometry and polarization are
extremely difficult measurements to achieve with the high degree of
precision required for astronomical studies. To develop an instrument
that could make these delicate measurements required an unusually
innovative and advanced technical effort. Thus, the WUPPE investigation
is a pioneering foray with a new technique.
The targets of WUPPE investigations are primarily in the Milky Way
galaxy and beyond, for which comparative data exist in other wavelengths.
Like the Hopkins Ultraviolet Telescope, WUPPE also makes
spectroscopic observations of hot stars, galactic nuclei and quasars.
Operating at ultraviolet wavelengths that are mostly longer than those
observed by HUT (but with some useful overlap), WUPPE provides
chemical composition and physical information on celestial targets that
that give off a significant amount of radiation in the 1,400 to 3,200 A
range.
WUPPE Vital Statistics
Sponsoring Institution: University of Wisconsin, Madison
Principal Investigator: Dr. Arthur D. Code
Telescope Optics: Cassegrain (two-mirror) system, f/10
focal ratio
Instrument: Spectropolarimeter with dual
electronic diode array detectors
Primary Mirror Size: 20 in. diameter
279 sq.* in. area
Field of View: 3.3 x 4.4 arc minutes
Spectral Resolution: 6 Angstroms
Wavelength Range: 1,400 to 3,200 Angstroms
Magnitude Limit: 16
Weight: 981 lb
Size: 28 inches in diameter
12.4 ft. in length
* This and subsequent changes were made to avoid confusion
since the computer will not create exponents for cm2 or the
circle over the A for Angstrom.
The Ultraviolet ImagingTelescope
In the 20 years that astronomical observations have been made
from space, no high-resolution ultraviolet photographs of objects other
than the sun have been made. Nonetheless, the brief glimpses of the
ultraviolet sky have led to important discoveries in spiral galaxies,
globular clusters, white dwarf stars and other areas.
Deep, wide-field imaging is a primary means by which
fundamentally new phenomena or important examples of known classes
of astrophysical objects will be recognized in the ultraviolet. The
Ultraviolet Imaging Telescope (UIT), developed at NASA's Goddard Space
Flight Center in Greenbelt, Md., is the key instrument for these
investigations.
UIT is a powerful combination of telescope, image intensifier and
camera. It is a 15.2-inch Ritchey Chretien telescope with two selectable
cameras mounted behind the primary mirror. Each camera has a six-
position filter wheel, a two-stage magnetically focused image tube and a
70-mm film transport, fiber optically coupled to each image tube. One
camera is designed to operate in the 1200 - 1700 Angstrom region and
the other in the 1250-3200 Angstrom region.
Unlike data from the other Astro instruments, which will be
electronically transmitted to the ground, UIT images will be recorded
directly onto a very sensitive astronomical film for later development
after Columbia lands. UIT has enough film to make 2,000 exposures. A
series of 11 different filters allows specific regions of the ultraviolet
spectrum to be isolated for energy-distribution studies. After
development, each image frame will be electronically digitized to form
2,048 x 2,048 picture elements, or pixels, then analyzed further with
computers.
UIT has a 15-inch diameter mirror with a 40-arc-minute field of
view -- about 25 percent wider than the apparent diameter of the full
moon. UIT has the largest field of view of any
sensitive UV imaging instrument planned for flight in the 1990s. It will
photograph nearby galaxies, large clusters of stars and distant clusters of
galaxies.
A 30-minute exposure (the length of one orbital night) will record a
blue star of 25th magnitude, a star about 100 million times fainter than
the faintest star visible to the naked eye on a dark, clear night. Since
UIT makes longer exposures than previous instruments, fainter objects
will be visible in the images.
The instrument favors the detection of hot objects which emit most
of their energy in the ultraviolet. Common examples span the
evolutionary history of stars -- massive stars and stars in the final stages of
stellar evolution (white dwarfs). Images of numerous relatively cool stars
that do not radiate much in the ultraviolet are suppressed, and UV
sources stand out clearly.
The UIT's field of view is wide enough to encompass entire
galaxies, star clusters and distant clusters of galaxies. This deep survey
mode will reveal many new, exciting objects to be studied further by
NASA's Hubble Space Telescope. Although the Hubble Space Telescope
will have a much higher magnification and record much fainter stars, the
UIT will photograph much larger regions all at once. In addition, the
UIT will suffer much less interference from visible light, since it is
provided with "solar blind" detectors. For certain classes of targets, such
as diffuse, ultraviolet-emitting or ultraviolet-scattering nebulae, UIT may
be a more sensitive imager.
A wide selection of astronomical objects will be studied in this first
deep survey of cosmic phenomena in the ultraviolet. The UIT is
expected to target hot stars in globular clusters to help explain how stars
evolve. Another experiment may help astronomers learn whether
properties and distribution of interstellar dust are the same in all
galaxies. High-priority objects are Supernova 1987A and vicinity, star
clusters, planetary nebulae and supernova remnants, spiral and "normal"
galaxies, the interstellar medium of other galaxies and clusters of
galaxies.
UIT Vital Statistics
Sponsoring Institution: NASA Goddard Space Flight Center
(GSFC), Greenbelt, Md.
Principal Investigator: Theodore P. Stecher (NASA GSFC)
Telescope Optics: Ritchey-Chretien (variation of
Cassegrain two-mirror system with
correction over wide field of view)
Aperture: 15 in.
Focal Ratio: f/9
Field of View: 40 arc minutes
Angular Resolution: 2 arc seconds
Wavelength Range: 1,200 A to 3,200 A
Magnitude Limit: 25
Filters: 2 filter wheels, 6 filters each
Detectors: Two image intensifiers with 70-mm
film, 1,000 frames each; IIaO
astronomical film
Exposure Time: Up to 30 minutes
Weight: 1,043 lb
Size: 32 inches in diameter
12.4 ft. in length
THE BROAD BAND X-RAY TELESCOPE
The Broad Band X-Ray Telescope (BBXRT) will provide astronomers
with the first high-quality spectra of many of the X-ray sources discovered
with the High Energy Astronomy Observatory 2, better known as the
Einstein Observatory, launched in the late 1970s. BBXRT, developed at
NASA's Goddard Space Flight Center in Greenbelt, Md., uses mirrors and
advanced solid-state detectors as spectrometers to measure the energy of
individual X-ray photons. These energies produce a spectrum that
reveals the chemistry, structure and dynamics of a source.
BBXRT is actually two 8-inch telescopes each with a 17 arc-minute
field of view (more than half the angular width of the moon). The two
identical telescopes are used to focus X-rays onto solid-state
spectrometers which measure photon energy in electron volts in the
"soft" X-ray region, from 380 to 12,000 eV. The use of two telescopes
doubles the number of photons that are detected and also provides
redundancy in case of a failure.
X-ray telescopes are difficult to construct because X-ray photons are
so energetic that they penetrate mirrors and are absorbed. A mirror
surface reflects X-rays only if it is very smooth and the photons strike it
at a very shallow angle. Because such small grazing angles are needed,
the reflectors must be very long to intercept many of the incident X-rays.
Since even shallower angles are required to detect higher-energy X-rays,
telescopes effective at high energies need very large reflecting surfaces.
Traditionally, X-ray telescopes have used massive, finely polished
reflectors that were expensive to construct and did not efficiently use the
available aperture. The mirror technology developed for BBXRT consists
of very thin pieces of gold-coated aluminum foil that require no polishing
and can be nested very closely together to reflect a large fraction of the
X-rays entering the telescope.
Because its reflecting surfaces can be made so easily, BBXRT can
afford to have mirrors using the very shallow grazing angles necessary to
reflect high-energy photons. In fact, BBXRT is one of the first telescopes
to observe astronomical targets that emit X-rays above approximately
4,000 electron volts.
The telescope will provide information on the chemistry,
temperature and structure of some of the most unusual and interesting
objects in the universe. BBXRT can see fainter and more energetic
objects than any yet studied. It will look for signs of heavy elements such
as iron, oxygen, silicon and calcium. These elements usually are formed
in exploding stars and during mysterious events occurring at the core of
galaxies and other exotic objects.
BBXRT will be used to study a variety of sources, but a major goal is
to increase our understanding of active galactic nuclei and quasars. Many
astronomers believe that the two are very similar objects that contain an
extremely luminous source at the nucleus of an otherwise relatively
normal galaxy. The central source in quasars is so luminous that the host
galaxy is difficult to detect. X-rays are expected to be emitted near the
central engine of these objects, and astronomers will examine X-ray
spectra and their variations to understand the phenomena at the heart of
quasars.
Investigators are interested in clusters of galaxies, congregations of
tens or thousands of galaxies grouped together within a few million light-
years of each other. When viewed in visible light, emissions from
individual galaxies are dominant, but X-rays are emitted primarily from
hot gas between the galaxies.
In fact, theories and observations indicate that there should be
about as much matter in the hot gas as in the galaxies, but all this
material has not been seen yet. BBXRT observations will enable scientists
to calculate the total mass of a cluster and deduce the amount of "dark"
matter.
A star's death, a supernova, heats the region of the galaxy near the
explosion so that it glows in X-rays. Scientists believe that heavy
elements such as iron are manufactured and dispersed into the
interstellar medium by supernovas. The blast or shock wave may produce
energetic cosmic ray particles that travel on endless journeys throughout
the universe and instigate the formation of new stars. BBXRT detects
young supernova remnants (less than 10,000 years old) which are still
relatively hot. Elements will be identified, and the shock wave's
movement and structure will be examined.
BBXRT was not part of the originally selected ASTRO payload. It
was added to the mission after the appearance of Supernova 1987A in
February 1987, to obtain vital scientific information about the supernova.
In addition, data gathered by BBXRT on other objects will enhance
studies that would otherwise be limited to data gathered with the three
ultraviolet
telescopes.
BBXRT Vital Statistics
Sponsoring Institution: NASA Goddard Space Flight Center,
Greenbelt, Md.
Principal Investigator: Dr. Peter J. Serlemitsos
Telescope Optics: Two co-aligned X-ray telescopes
with cooled segmented lithium-
drifted silicon solid-state detectors in
the focal planes
Focal Length: 12.5 ft. each, detection area 0.16 in.
diameter pixel
Focal Plane Scale: 0.9 arc minutes per mm
Field of View: 4.5 arc minutes (central element);
17 arc minutes (overall)
Energy Band: 0.3 to 12 keV
Effective Area: 765 cm2 at 1.5 keV, 300 cm2 at 7 keV
Energy Resolution: 0.09 keV at 1 keV, 0.15 keV at 6 keV
Weight: 1,500 lb (680.4 kg)
Size: 40 inches in diameter
166 inches in length
ASTRO CARRIER SYSTEMS
The Astro observatory is made up of three co-aligned ultraviolet
telescopes carried by Spacelab and one X-ray telescope mounted on the
Two-Axis Pointing System (TAPS) and a special structure.
Each telescope was independently designed, but all work together
as elements of a single observatory. The carriers provide stable platforms
and pointing systems that allow the ultraviolet and X-ray telescopes to
observe the same target. However, having two separate pointing systems
gives investigators the flexibility to point the ultraviolet telescopes at one
target while the X-ray telescope is aimed at another.
Spacelab
The three ultraviolet telescopes are supported by Spacelab
hardware. Spacelab is a set of modular components developed by the
European Space Agency and managed by the NASA Marshall Space Flight
Center, Hunstville, Ala. For each Spacelab payload, specific standardized
parts are combined to create a unique design. Elements are anchored
within the cargo bay, transforming it into a short-term laboratory in
space.
Spacelab elements used to support the Astro observatory include
two pallets, a pressurized igloo to house subsystem equipment and the
Instrument Pointing System. The pressurized Spacelab laboratory
module will not be used for Astro. Rather, astronauts and payload
specialists will operate the payload from the aft flight deck of the orbiter
Columbia.
Pallets
The ultraviolet telescopes and the Instrument Pointing System are
mounted on two Spacelab pallets -- large, uncovered, unpressurized
platforms designed to support scientific instruments that require direct
exposure to space.
Each individual pallet is 10 feet long and 13 feet wide. The basic
pallet structure is made up of five parallel U-shaped frames. Twenty-four
inner and 24 outer panels, made of aluminum alloy honeycomb, cover the
frame. The inner panels are equipped with threaded inserts so that
payload and subsystem equipment can be attached. Twenty-four standard
hard points, made of chromium-plated titanium casting, are provided for
payloads which exceed acceptable loading of the inner pallets.
Pallets are more than a platform for mounting instrumentation. With
an igloo attached, they also can cool equipment, provide electrical power
and furnish connections for commanding and acquiring data from
experiments. Cable ducts and cable support trays can be bolted to the
forward and aft frame of each pallet to support and route electrical cables
to and from the experiments and the subsystem equipment mounted on
the pallet. The ducts are made of aluminum alloy sheet metal. In
addition to basic utilities, some special accommodations are available for
pallet-mounted experiments.
For Astro-1, two pallets are connected together to form a single
rigid structure called a pallet train. Twelve joints are used to connect the
two pallets.
Igloo
Normally Spacelab subsystem equipment is housed in the core
segment of the pressurized laboratory module. However, in "pallet only"
configurations such as Astro, the subsystems are located in a supply
module called the igloo. It provides a pressurized compartment in which
Spacelab subsystem equipment can be mounted in a dry-air environment
at normal Earth atmospheric pressure, as required by their design. The
subsystems provide such services as cooling, electrical power and
connections for commanding and acquiring data from the instruments.
The igloo is attached vertically to the forward end frame of the first
pallet. Its outer dimensions are approximately 7.9 feet in height and 3.6
feet in diameter. The igloo is a closed cylindrical shell made of aluminum
alloy and covered with multi-layer insulation. A removable cover allows
full access to the interior.
The igloo consists of two parts. The primary structure -- an
exterior cannister -- is a cylindrical, locally stiffened shell made of forged
aluminum alloy rings and closed at one end. The other end has a
mounting flange for the cover. A seal is inserted when the two structures
are joined together mechanically to form a pressure-tight assembly.
There are external fittings on the cannister for fastening it to the
pallet, handling and transportation on the ground, and thermal control
insulation. Two feed-through plates accommodate utility lines and a
pressure relief valve. Facilities on the inside of the cannister are
provided for mounting subsystem equipment and the interior igloo
structure. The cover is also a cylindrical shell, made of welded aluminum
alloy and closed at one end. The igloo has about 77.7 cubic feet of
interior space for subsystems.
Subsystem equipment is mounted on an interior or secondary
structure which also acts as a guide for the removal or replacement of the
cover. The secondary structure is hinge-fastened to the primary
structure, allowing access to the bottom of the secondary structure and to
equipment mounted within the primary structure.
Instrument Pointing System
Telescopes such as those aboard Astro-1 must be pointed with very
high accuracy and stability at the objects which they are to view. The
Spacelab Instrument Pointing System provides precision pointing for a
wide range of payloads, including large single instruments or clusters of
instruments. The pointing mechanism can accommodate instruments
weighing up to 15,432 pounds and can point them to within 2 arc
seconds and hold them on target to within 1.2 arc seconds. The
combined weight of the ultraviolet telescopes and the structure which
holds them together is 9,131 pounds.
The Instrument Pointing System consists of a three-axis gimbal
system mounted on a gimbal support structure connected to the pallet at
one end and the aft end of the payload at the other, a payload clamping
system for support of the mounted experiment during launch and landing
and a control system based on the inertial reference of a three-axis gyro
package and operated by a gimbal-mounted microcomputer.
Three bearing-drive units on the gimbal system allow the payload to
be pointed on three axes: elevation (back and forth), cross-elevation
(side to side) and azimuth (roll), allowing it to point in a 22-degree circle
around a its straight-up position. The pointing system may be
maneuvered at a rate of up to one degree per second, which is five times
as fast as the Shuttle orbiter's maneuvering rate. The operating modes of
the different scientific investigations vary considerably. Some require
manual control capability, others slow scan mapping, still others high
angular rates and accelerations. Performance in all these modes requires
flexibility achieved with computer software.
The Instrument Pointing System is controlled through the Spacelab
subsystem computer and a data-display unit and keyboard. It can be
operated either automatically or by the Spacelab crew from the module
(when used) and also from the payload station in the orbiter aft flight
deck.
In addition to the drive units, Instrument Pointing System
structural hardware includes a payload/gimbal separation mechanism,
replaceable extension column, emergency jettisoning device, support
structure and rails and a thermal control system. The gimbal structure
itself is minimal, consisting only of a yoke and inner and outer gimbals to
which the payload is attached by the payload-mounted integration ring.
An optical sensor package is used for attitude correction and also
for configuring the instrument for solar, stellar or Earth viewing. The
Astro-1 mission marks the first time the Instrument Pointing System has
been used for stellar astronomy. Three star trackers locate guide stars.
The boresite tracker is in the middle, and two other trackers are angled
12 degrees from each side of the boresite. By keeping stars of known
locations centered in each tracker, a stable position can be maintained.
The three ultraviolet telescopes are mounted and precisely co-
aligned on a common structure, called the cruciform, that is attached to
the pointing system.
Image Motion Compensation System
An image motion compensation system was developed by the
Marshall Space Flight Center to provide additional pointing stability for
two of the ultraviolet instruments.
When the Shuttle thrusters fire to control orbiter attitude, there is
a noticeable disturbance of the pointing system. The telescopes are also
affected by crew motion in the orbiter. A gyro stabilizer senses the
motion of the cruciform which could disrupt UIT and WUPPE pointing
stability. It sends information to the image motion compensation
electronics system where pointing commands are computed and sent to
the telescopes' secondary mirrors which make automatic adjustments to
improve stability to less than 1 arc second.
The Astro-1's star tracker, designed by the NASA Jet Propulsion
Laboratory, Pasadena, Calif., fixes on bright stars with well-known and
sends this information to the electronics system which corrects errors
caused by gyro drift and sends new commands to the telescopes' mirrors.
The mirrors automatically adjust to keep pointed at the target.
Broad Band X-ray Telescope and the Two-Axis Pointing System (TAPS)
Developed at the NASA Goddard Space Flight Center, these
pointing systems were designed to be flown together on multiple
missions. This payload will be anchored in a support structure placed
just behind the ultraviolet telescopes in the Shuttle payload bay. BBXRT
is attached directly to the TAPS inner gimbal frame.
The TAPS will move BBXRT in a forward/aft direction (pitch)
relative to the cargo bay or from side to side (roll) relative to the cargo
bay. A star tracker uses bright stars as a reference to position the TAPS
for an observation, and gyros keep the TAPS on a target. As the gyros
drift, the star tracker periodically recalculates and resets the TAPS
position.
ASTRO OPERATIONS
Operation of the Astro-1 telescopes will be a cooperative effort
between the science crew in orbit and their colleagues in a control
facility at the Marshall Space Flight Center and a support control center
at Goddard Space Flight Center. Though the crew and the instrument
science teams will be separated by many miles, they will interact with
one another to evaluate observations and solve problems in much the
same way as they would when working side by side.
On-Orbit Science Crew Activities
The Astro science crew will operate the ultraviolet telescopes and
Instrument Pointing System from the Shuttle orbiter's aft flight deck,
located to the rear of the cockpit. Windows overlooking the cargo bay
allow the payload specialist and mission specialist to keep an eye on the
instruments as they command them into precise position. The aft flight
deck is equipped with two Spacelab keyboard and display units, one for
controlling the pointing system and the other for operating the scientific
instruments. To aid in target identification, this work area also includes
two closed-circuit television monitors. With the monitors, crew
members will be able to see the star fields being viewed by HUT and
WUPPE and monitor the data being transmitted from the instruments.
The Astro-1 crew will work around the clock to allow the maximum
number of observations to be made during their mission. The STS-35
commander will have a flexible schedule, while two teams of crew
members will work in 12-hour shifts. Each team consists of the pilot or
flight mission specialist, a science mission specialist and a payload
specialist. The crew and the ground controllers will follow an observation
schedule detailed in a carefully planned timeline.
In a typical Astro-1 ultraviolet observation, the flight crew member
on duty maneuvers the Shuttle to point the cargo bay in the general
direction of the astronomical object to be observed. The mission
specialist commands the pointing system to aim the telescopes toward
the target. He also locks on to guide stars to help the pointing system
remain stable despite orbiter thruster firings. The payload specialist sets
up each instrument for the upcoming observation, identifies the celestial
target on the guide television and provides any necessary pointing
corrections for placing the object precisely in the telescope's field of
view. He then starts the instrument observation sequences and monitors
the data being recorded. Because the many observations planned create a
heavy workload, the payload and mission specialists work together to
perform these complicated operations and evaluate the quality of
observations. Each observation will take between 10 minutes to a little
over an hour.
The X-ray telescope requires little attention from the crew. A crew
member will turn on the BBXRT and the TAPS at the beginning of
operations and then turn them off when the operations conclude. The
telescope is controlled from the ground. After the telescope is activated,
researchers at Goddard can "talk" to the telescope via computer. Before
science operations begin, stored commands are loaded into the BBXRT
computer system. Then, when the astronauts position the Shuttle in the
general direction of the source, the TAPS automatically points the BBXRT
at the object. Since the Shuttle can be oriented in only one direction at a
time, X-ray observations must be coordinated carefully with ultraviolet
observations.
GROUND CONTROL
Astro-1 science operations will be directed from a new Spacelab
Mission Operations Control facility at the Marshall Space Flight Center.
BBXRT will be controlled by commands from a supporting payload
operations control facility at Goddard.
Spacelab Mission Operations Control
Beginning with the Astro-1 flight, all Spacelab science activities will
be controlled from Marshall's Spacelab Mission Operations Control
Center. It will replace the payload operations control center at the
Johnson Space Center from which previous Spacelab missions have been
operated. The Spacelab Mission Operations Control team is under the
overall direction of the mission manager.
The Spacelab Mission Operations Control team will support the
science crew in much the same way that Houston Mission Control
supports the flight crew. Teams of controllers and researchers at the
Marshall facility will direct all NASA science operations, send commands
directly to the spacecraft, receive and analyze data from experiments
aboard the vehicle, adjust mission schedules to take advantage of
unexpected science opportunities or unexpected results, and work with
crew members to resolve problems with their experiments.