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I

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electrical storms are one of nature's

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most spectacular and unpredictable

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phenomenal despite our technology we

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remain poems to control this awesome

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force nevertheless the conditions that

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cause lightning are at the very heart of

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a groundbreaking experiment at NASA

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Lewis Research Center in Cleveland the

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solar array module plasma interaction

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experiment or Sam p is an essential step

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toward the development of future

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high-voltage power systems for space

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exploration dr. Dale Ferguson is

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principal investigator of the santee

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project he and his team are nearing the

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most critical phase of the experiment

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flight testing in low-earth orbit before

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earth-based technologies are used for

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space applications they must be

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thoroughly tested to ensure that they

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will perform as needed in the space

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environment flight testing is crucial to

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the engineering process historically

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electric power generation in space has

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relied on photovoltaic solar arrays

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Volta voltaic cells commonly made of

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silicon are semiconductors that convert

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visible light into direct electrical

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current the cells are covered with a

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transparent housing that allows light to

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easily penetrate them excess current is

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stored in batteries photovoltaic power

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is routinely used in such low voltage

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items as calculators the amount of

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current created by photovoltaic cells is

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a direct function of surface area the

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greater the surface the greater the

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power cells are connected in small units

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called coupons and coupons are strung

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together in larger sheets known as solar

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array modules photovoltaics has proven

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to be a reliable source of electricity

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for the 28 volt power systems in Paris

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from the aviation industry however

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future space exploration will require

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higher voltages as much as 160 volts DC

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on earth when you want to increase the

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power of a photovoltaic array you

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increase the number of cells and as the

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number of cells goes up so does the

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power in space adding more cells

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increases the voltage that the system

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will operate at and and a high voltage

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in space can be a problem for a

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spacecraft when we think of the space

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environment we immediately think of zero

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gravity however what poses the gravest

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problem to designers of a high voltage

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power system is space plasma plasma is

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created when a gas is subjected to high

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temperatures or bombardment by

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ultraviolet rays from the Sun the

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electrons are literally stripped away

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from their normal orbits around the

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nucleus when this happens the gas which

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is normally an excellent insulator

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becomes a fairly good conductor of

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electricity this chart depicts the

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density of the plasma relative to the

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altitude above the earth the density

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decreases as we increase in altitude for

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low voltages plasma does not present

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much of a problem but in high voltages

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in low-earth orbit it's a stumbling

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block when the electric potential

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between two points is great enough the

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gas between them ionizes creating a path

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of low resistance for electricity and

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when that happens arcing takes place an

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undesirable and destructive current is

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unleashed it's lightning with all of its

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hazards and unpredictability only on a

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smaller scale arcing can destroy or

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degrade most materials it contacts from

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the delicate solar arrays to such

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durable materials as anodized aluminum

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which is used as the primary structural

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material for satellites and other space

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payloads arcing can also cause current

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disruptions that could hamper in space

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operations of every time

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among the important questions the sappy

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flight test will help answer are at what

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voltage does arcing occur at what rate

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does arcing occur at what intensity and

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specifically what effect will arcing

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have on all the various materials and

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geometries currently designated not only

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for the solar arrays but for the whole

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space station all other materials need

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to be found how can we protect them and

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ultimately what steps can be taken to

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eliminate or minimize argue the sappy

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payload consists of an electronics

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enclosure with an experiment plate fixed

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to the top surface it will be mounted

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directly to the top of a hitchhiker M

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carrier the instruments and electronics

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that run the experiment and record data

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are located inside the enclosure the

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experiment plate will expose more than a

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dozen different materials geometries and

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technologies to conditions identical to

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those the space station will encounter

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extensive ground testing is always

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conducted first and is critical to

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research but certain conditions are

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simply impossible to simulate on the

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ground such as pressure plasma flow and

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electron temperature for example results

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from previous flight tests of silicon

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solar cells differ radically from the

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ground tests of those cells the sappy

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experiment plate will flight test

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leading-edge technologies but more

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familiar materials are also represented

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all u.s. spacecraft that have flown to

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date have used silicon solar cells they

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therefore will provide a baseline for us

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to allow us to compare our data with

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data that has been taken in the past

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even though other technologies are more

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efficient silicon is still the cheapest

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and is still the most commonly used we

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have to take a look at what happens to

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silicon them also to be tested is a

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coupon of advanced photovoltaic solar

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array or absa cells

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these cells hold great promise because

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they are much thinner and lighter than

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silicon Sampey will also test the impact

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of arcing on several state-of-the-art

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alloys being considered for use on the

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space station when the sappy experiment

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completes its set of flight tests the UH

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norbit data collected will be brought

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back and analyzed by scientists and

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engineers at the Lewis research center

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this flight data will provide the

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foundation for developing future high