over the past
decades we've struggled to see beyond
the atmosphere lying between earth and
space
even from mountaintop observatories the
atmosphere has blurred our view of the
universe
and because the atmosphere absorbs
certain forms of energy
our knowledge of celestial phenomena has
been limited
one answer has been to go beyond the
atmosphere
in fact between the late 60s and the
late 70s nasa launched a series of
special purpose observatories
revealing ultraviolet sources such as
very hot stars and very young
stars these satellites made tremendous
breakthroughs
and encouraged astronomers to move on to
larger observatories
seeking answers about more distant
galaxies mysterious pulsars
and quasars and the universe
itself astronomers envisioned the next
step
a multi-purpose observatory in space
one that could image farther and more
clearly than its predecessors
uncovering phenomena in ultraviolet
visible and near infrared regions of the
spectrum
an observatory that could expand our
perception to the outer reaches of the
universe
that next step was hst nasa's hubble
space telescope
with its precision optics and diverse
array of scientific instruments
nasa is responsible for developing
operating and maintaining this
ground-sized space observatory
with its unparalleled goals the hubble
space telescope
poses a much greater challenge to
operate than ground-based observatories
or the satellites that came before it
so
led by nasa engineers scientists and
researchers from universities
industries and the european space agency
have combined
efforts to meet the challenge of
operating hubble space telescope
the result is one of the most complex
operations and maintenance systems in
the world
one that ensures quality observations
and spacecraft performance
into the next century
to take a closer look we started the
space telescope science institute in
baltimore maryland
aura a consortium of american
universities operates the institute for
nasa
the space telescope science institute is
the international center for science
activities with hst
it plans the day-to-day observations and
sets up the long-term
science program astronomers first come
in contact with the institute when they
submit their proposed science program
as with any major observatory the demand
for the telescope
exceeds the time available we expect to
receive
over a thousand proposals a year and
only 200 can be conducted
a committee of international astronomers
selects the proposals based on their
scientific merit
because the hst offers several hundred
instrument configurations
our scientists work with the selected
researchers to detail their observations
next numerous proposals are incorporated
into a week-long
observing schedule that ensures the
efficient use of every telescope minute
there are many many factors involved in
scheduling observations with the space
telescope
there are many instruments onboard a
space telescope within the same
instrument
there are several observing modes even
the simplest
observation requires using different
filters
we may also have to revisit the same
target at different times of the year
we want to maximize the time spent
observing with the space telescope
and minimize the time wasted moving the
telescope around
therefore we will group the observations
to happen in the same area of the sky
we also want to use the same instrument
for
long periods of time even weeks at a
time to minimize
switching instruments on and off
unnecessarily
before the telescope schedule can be
completed another essential factor is
entered
the guide stars to establish guide stars
for operations
the institute has converted 1500
photographic plates of the sky
into a catalog of 15 million stars
using the catalog the institute's
computer selects
guide stars for each target hst
stabilizes on a target by finding and
locking onto
two guide stars with its precision
guidance sensors
the sensors detect any minor drift from
the guide stars
and correct the spacecraft's position
through the onboard computers
with the guide stars and other system
factors incorporated
the institute produces a week-long
schedule which specifies
when where and how hst science
instruments will be used
from the institute the science schedule
is transmitted to the space
telescope operations control center
located at goddard space flight center
in greenbelt maryland
this is the nerve center of hst's ground
system
the science schedule automatically goes
into one of the control center computer
systems
which adds commands for operating and
maintaining the observatory
these new commands cover such operations
as moving the telescope
or pointing its communications antennas
the system also schedules links to
nasa's communications satellites
merging both the science and spacecraft
commands
the computer generates a master schedule
for the week
if this second by second schedule
printed out the stack would be one to
two feet high
commands are sent to hst's two on-board
computers
which on an average day carry out over
12 000 commands
the spacecraft's safety is also
monitored at the control center
a typical satellite has about a thousand
parameters that must be monitored
hst has about six thousand
these parameters include specific
spacecraft temperatures
voltages electrical currents and the
condition of its computers
our engineers must instantly recognize
the codes for each function
interpret their measurements and take
immediate action if something is unusual
because the engineers are overrun with
data we became concerned about the
potential for human error
to minimize this possibility we are
developing an artificial intelligence
system
that automates much of the analysis
if the system finds something amiss it
tells the operator
eventually it will also prescribe a
solution
for the irregularity
before the actual observations begin
nasa must calibrate hst's various
systems
during a crucial seven-month period
following launch marshall space flight
center located in huntsville alabama
was responsible for building hst
early in the calibration process
marshall personnel managed the
spacecraft's initial checkout
from goddard's control center
at the beginning of deployment the
shuttle bay doors open
and the arbiter applies power to hst
communication is then established
between the ground control center
and the spacecraft to verify proper
configuration
and to activate basic systems for
thermal safety
next the arbiter's arm lifts hst out of
the bay
so the telescope's solar arrays and
antennas can be extended
the arm releases the observatory into
orbit some 300 miles above the earth
hst's solar arrays are oriented properly
to convert the sun's energy into
electrical power for the observatory
the arbiter stays nearby for about two
days after release
in case hst needs further assistance
during this early critical period
once we establish that the spacecraft
can operate on its own
the arbiter returns to earth meanwhile
ground control engineers continue to
verify
that major components are up and running
and that the telescope is pointing
properly
next through a long series of
calibrations the telescope
mirrors star trackers fine guidance
sensors and rate gyros are aligned
at approximately the end of the first
month marshall officially turns
responsibility for hst operations over
to goddard
during the second month goddard conducts
further telescope calibrations
and early checkout of the science
instruments
subsequent checkout of the optics and
the instruments occurs during the
remaining five months
only then can the long-awaited
observations begin
to make these observations hst's
commands
must travel an intricate path the
science commands from the institute are
integrated with
spacecraft commands at goddard's control
center
ultimately the signals are relayed to a
nasa
tracking and data relay satellite
orbiting 23 000 miles above earth
the commands then go into hst's onboard
computers to be implemented
this path reverses when data gathered by
an observation is sent back to earth
with commands loaded into its computers
the telescope automatically proceeds
with observations
in this case hst pivots slowly to its
new target
light from the target goes down the
telescope and hits the primary mirror
it reflects back to the secondary mirror
reduced to a narrow beam the light is
aimed back to the focal plane just
behind it
the image is directed to hst's fine
guidance sensors
which locate and lock onto guide stars
on either side of the target
with hst now centered on its target the
light travels into the science
instruments which will make the
observation
the instrument shutters open the correct
filter is selected and hst begins its
exposure
while most observations are pre-planned
10 percent require real-time interaction
at the institute by scientists
real-time observations with the space
telescope defy pre-programming
for example we want to observe the red
spots
on jupiter this is a complicated
operation because the planet moves
and it also rotates in order to be able
to do this we have to take an early
picture of the planet
send information down to the ground and
then
have an operator make a very quick
decision as to exactly
where the instrument that is being used
has to be pointed
this is a very challenging operation
indeed
within 24 hours of an observation the
observer can obtain the data from the
science institute's data
archive and distribution service the
investigator who submitted the proposal
has exclusive rights to this information
for one year
after this period the data is available
to scientists around the world serving
as an hst library
the archive will distribute an
equivalent of 500 million pages of
information
over a single year the observations are
distributed through worldwide
astronomical computer networks
are through optical disks magnetic tapes
and photographs astronomers can use this
information at their home institution
to further their own research
from this data who can say what great
discoveries will be made
astronomers hope for answers about black
holes
the evolution of galaxies and the size
of our universe
looking to the future to ensure the
continuous flow of such exciting data
nasa has created contingency plans
in contrast to the unexpected repair of
the solar maximum mission spacecraft in
1984
nasa has prepared for hst's on orbit
servicing
hst is designed and developed by nasa
for on-orbit servicing by astronauts
consequently hst instruments and various
components were developed to be modular
this allows the astronauts to replace
degradable parts such as solar arrays
and batteries during routine servicing
missions
the modular design also makes it
possible to update the observatory with
new instruments
during the first planned maintenance
mission for the hst
we expect to remove one of the original
scientific instruments and replace it
with a near-infrared instrument
the first scientific instruments on the
hst are sensitive to the ultraviolet
and visible portions of the
electromagnetic spectrum
when we add an infrared capability we
will be able to examine regions such as
this
where stars are in the process of
formation today
and we'll also be able to probe still
further back
into the early history of our universe
hubble space telescope operations can be
compared to the complexity and challenge
of the operations necessary to send
astronauts to the moon the expertise of
thousands of individuals has contributed
to the innovative
science instruments computer systems
information systems and maintenance
hardware that constitute hst's
operations network
this elaborate system supporting hubble
space telescope
promises long-sought answers to
universal questions
exciting discoveries to ponder and
possibly
a new understanding of our universe
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