I
electrical storms are one of nature's
most spectacular and unpredictable
phenomenal despite our technology we
remain poems to control this awesome
force nevertheless the conditions that
cause lightning are at the very heart of
a groundbreaking experiment at NASA
Lewis Research Center in Cleveland the
solar array module plasma interaction
experiment or Sam p is an essential step
toward the development of future
high-voltage power systems for space
exploration dr. Dale Ferguson is
principal investigator of the santee
project he and his team are nearing the
most critical phase of the experiment
flight testing in low-earth orbit before
earth-based technologies are used for
space applications they must be
thoroughly tested to ensure that they
will perform as needed in the space
environment flight testing is crucial to
the engineering process historically
electric power generation in space has
relied on photovoltaic solar arrays
Volta voltaic cells commonly made of
silicon are semiconductors that convert
visible light into direct electrical
current the cells are covered with a
transparent housing that allows light to
easily penetrate them excess current is
stored in batteries photovoltaic power
is routinely used in such low voltage
items as calculators the amount of
current created by photovoltaic cells is
a direct function of surface area the
greater the surface the greater the
power cells are connected in small units
called coupons and coupons are strung
together in larger sheets known as solar
array modules photovoltaics has proven
to be a reliable source of electricity
for the 28 volt power systems in Paris
from the aviation industry however
future space exploration will require
higher voltages as much as 160 volts DC
on earth when you want to increase the
power of a photovoltaic array you
increase the number of cells and as the
number of cells goes up so does the
power in space adding more cells
increases the voltage that the system
will operate at and and a high voltage
in space can be a problem for a
spacecraft when we think of the space
environment we immediately think of zero
gravity however what poses the gravest
problem to designers of a high voltage
power system is space plasma plasma is
created when a gas is subjected to high
temperatures or bombardment by
ultraviolet rays from the Sun the
electrons are literally stripped away
from their normal orbits around the
nucleus when this happens the gas which
is normally an excellent insulator
becomes a fairly good conductor of
electricity this chart depicts the
density of the plasma relative to the
altitude above the earth the density
decreases as we increase in altitude for
low voltages plasma does not present
much of a problem but in high voltages
in low-earth orbit it's a stumbling
block when the electric potential
between two points is great enough the
gas between them ionizes creating a path
of low resistance for electricity and
when that happens arcing takes place an
undesirable and destructive current is
unleashed it's lightning with all of its
hazards and unpredictability only on a
smaller scale arcing can destroy or
degrade most materials it contacts from
the delicate solar arrays to such
durable materials as anodized aluminum
which is used as the primary structural
material for satellites and other space
payloads arcing can also cause current
disruptions that could hamper in space
operations of every time
among the important questions the sappy
flight test will help answer are at what
voltage does arcing occur at what rate
does arcing occur at what intensity and
specifically what effect will arcing
have on all the various materials and
geometries currently designated not only
for the solar arrays but for the whole
space station all other materials need
to be found how can we protect them and
ultimately what steps can be taken to
eliminate or minimize argue the sappy
payload consists of an electronics
enclosure with an experiment plate fixed
to the top surface it will be mounted
directly to the top of a hitchhiker M
carrier the instruments and electronics
that run the experiment and record data
are located inside the enclosure the
experiment plate will expose more than a
dozen different materials geometries and
technologies to conditions identical to
those the space station will encounter
extensive ground testing is always
conducted first and is critical to
research but certain conditions are
simply impossible to simulate on the
ground such as pressure plasma flow and
electron temperature for example results
from previous flight tests of silicon
solar cells differ radically from the
ground tests of those cells the sappy
experiment plate will flight test
leading-edge technologies but more
familiar materials are also represented
all u.s. spacecraft that have flown to
date have used silicon solar cells they
therefore will provide a baseline for us
to allow us to compare our data with
data that has been taken in the past
even though other technologies are more
efficient silicon is still the cheapest
and is still the most commonly used we
have to take a look at what happens to
silicon them also to be tested is a
coupon of advanced photovoltaic solar
array or absa cells
these cells hold great promise because
they are much thinner and lighter than
silicon Sampey will also test the impact
of arcing on several state-of-the-art
alloys being considered for use on the
space station when the sappy experiment
completes its set of flight tests the UH
norbit data collected will be brought
back and analyzed by scientists and
engineers at the Lewis research center
this flight data will provide the
foundation for developing future high
voltage space power systems for NASA
into the 21st century and beyond
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