basking in its warm rays nature seeks
out the sun's inexhaustible power
this nuclear reactor burns four million
tons of hydrogen every second creating
an unmatched source of energy
ancient observers worship the
life-giving rays of this day star
modern science has taught us to harness
its power
this superstar is essential to life on
earth as well as to one of man's boldest
ventures
space station freedom
196 000
cells will collect energy to power this
laboratory and indeed become the solar
connection
the united states
canada
japan
and the european space agency have come
together to build freedom
responsibility for the entire electric
power system known as work package 4
rests in cleveland ohio at the nasa
lewis research center
the power collection system is being
developed by the solar array branch of
the photovoltaic power module division
design of space station began in 1984.
now its pencils down
time to build and test the actual flight
hardware
in the summer of 1991 for the first time
anywhere in the world
an array of cells and structural
components were tested together in the
simulated low earth orbit environment of
tank 5 in the electric propulsion
laboratory
funding from nasa's office of safety and
mission quality and the work package 4
project office
allowed engineers to develop and design
a high-fidelity plasma generation and
diagnostic system the intent
to test the electrodynamic reaction
between the photovoltaic system the
structure and the plasma
a nitrogen cold wall was attached to a
test fixture to regulate temperature of
the test article
the cage design allowed for quick
installation and removal of hardware
from the vacuum tank
a light bank of 252 ded lamps was built
to provide illumination equal to
one-third of the sun's intensity
spherical probes measured the current
voltage profile to determine plasma
density
in preparation for the test an engineer
checks to ensure that illumination is
falling evenly on each solar cell
the cells eight millimeters thick and
eight centimeters square are the largest
ever used in space
the cells are welded to a flexible
printed circuit which is insulated from
the outside environment the cell edges
remain exposed
sixteen thousand four hundred individual
cells are grouped into blankets one
hundred ten feet long by fifteen feet
wide
each blanket is protected by and
deployed from a blanket box
underwater testing was conducted by
lockheed corporation aiding engineers in
improving deployment techniques of the
blanket box
from the beginning of life on earth and
now in space
nature has relied on the sun
these sunflower seedlings track the sun
morning till night
technology imitates nature
once freedom's wings are attached to the
truss alpha and beta gimbals will enable
them to track the sun during orbit
60 minutes in sunlight and 30 minutes in
eclipse
while in sunlight the six wings will
collect light and convert it directly to
electric current
at the same time 304 nickel hydrogen
battery cells will be charged to provide
power while freedom is in earth shade
up and energized the solar arrays will
supply more than 56 kilowatts of
condition power to the user
the most power ever used in space
solar energy will supply power for
experiments
research projects
housekeeping functions
and life support systems
however these can come crashing to a
halt in the harsh environment of space
micrometeors can damage freedom
structure
contamination can degrade its power
and an invisible gas known as plasma can
cause
arcing why is that a threat
the potential effects of such arcing was
studied by the photovoltaic power module
division
project manager marion felder
the threat that plasma poses to the
space station freedom was examined here
in tank 5 during the plasma interactions
test the objectives of this test were to
investigate on a systems level the
possibly detrimental effects of the
space plasma on the photovoltaic system
as well as on the structures that make
up space station freedom
we also wanted to investigate the
effectiveness of a possible mitigation
strategy that is a plasma contactor for
hardware we used two fully populated
photovoltaic panels in combination with
a variety of anodized aluminum
structures which were there to simulate
various structures on the space station
freedom
the solar ray circuit that we had was
capable of generating 160 volts at
almost one amp under test illumination
conditions we used the voltage that was
generated on the solar array to drive
the potential of the aluminum piece to a
voltage that would be quite close to
what it would be seeing when on orbit
the combination of the largest aluminum
panels and the photovoltaic circuit was
approximately one four hundred ninety
the scale of the space station freedom
and therefore allowed us to get the very
first large-scale test of plasma
environment interactions with space
station type hardware
our data capture system was designed to
return information in three specific
areas current collection floating
potential and arc transients as well as
to give us information on key
environmental parameters like
temperatures and the plasma potential
concern for the possible detrimental
effects of arcing on the space station
freedom led us to plan and conduct this
plasma interactions test
so that the program office could assess
the risks and develop engineering
solutions
we look to the space environment's
effects branch here at lewis for a more
detailed description of the low-earth
orbit plasma environment and its
potential impacts
contrary to popular belief space station
freedom will be orbiting not in empty
space but in the upper reaches of the
earth's atmosphere the upper reaches of
the atmosphere are mainly atomic oxygen
and this atomic oxygen gets ionized by
the ultraviolet radiation from the sun
ultraviolet radiation splits the atomic
oxygen atoms up into an ion and electron
and in the altitudes the space station
will be flying there will be something
like a million electrons and ions per
cubic centimeter
that is flying through
this space plasma as we call it is is
going to be important in terms of
interactions between the space station
and its surroundings
first of all what what will happen if
the arcing does occur
one of the things is it can
cause tiny holes in the anodized surface
and change its properties in particular
could change the thermal properties of
the surface so that it wouldn't maintain
the right temperature
in addition the material that comes off
during these arcs
will deposit somewhere else on the space
station the solution to the possible
arcing problem on space station we think
is a device called the plasma contactor
mike patterson of the space propulsion
technology division explains his group's
involvement with the test here at nasa
lewis at the epl facility tank 5 our
organization provided support for the
plasma interactions test for the space
station freedom solar array one of the
critical aspects of conducting that
experiment was to provide a simulation
of the low earth orbit space plasma
environment and to do that we provided
holic acid plasma sources to generate a
quiescent low density low electron
temperature space plasma environment we
used a number of hollow cathode plasma
source devices
optimized for operation to provide a low
electron temperature and a very uniform
plasma to engulf the solar array to
simulate the low earth orbit environment
the plasma contactors have been
developed previously for specific
mission applications on specific
spacecraft primarily for science this is
really the first time that the plasma
contactor is going to be used as a
utility as a technology to ensure that
the spacecraft can perform its function
as it turns out it's a vital component
it will be a vital component of the
power system aboard space station and
it's critical for space station
operations
so in that in that context it's the
first time that the technology has
really been utilized and it's not a
demonstration of the technology it's
there to perform a specific function the
demanding requirements for the plasma
contactor system for space station
freedom uh require us to uh
do everything we can to push the
holocaustic technology that we presently
have
and uh that's a a real challenge for us
but we'll be able to deliver on that
one of the important space flight
experiments for space station is
what we call sampy
that's
solar array module plasma interaction
experiment
that's an experiment that's being built
here at lewis
it's going to be flown on the space
shuttle in the year 1994
and it's being built right now hopefully
when it flies we'll have confirmation
that our ideas are correct
in a room much like this lewis will
monitor the performance of the space
station's electric power system once on
orbit
personal computers such as these are
used daily to design systems and conduct
analyses to verify characteristics of
space station freedom
soon computers will be used to run the
machines that fabricate the various
components
along with sampi work package 4 plans to
conduct a qualification type plasma
interactions test with a flight design
solar array circuit to confirm the
operational characteristics of the solar
arrays in plasma
work package 4 also plans to take
advantage of other space flight
experiments such as pass plus and spear
3 to gain confidence in the array's
operation before it flies
beginning in the mid 90s with the first
element launch of one photovoltaic power
module
and continuing with the remaining
elements
space station freedom will be
constructed in stages to yield a
permanently manned configuration by the
end of the decade
the knowledge that we gain from our
research in tank 5 will enable
technology that will allow us to better
exploit the day star's power
you