SpaceTEC® Resource Blog for Aerospace Technicians

Archive for January, 2011

Magic Triangles

“Hey Guys! Was it V over I or I over V?” Credit NASA

Electronics is a major part of some aerospace technician’s workday.  As an aerospace technician, it is considered a basic skill to be able to calculate voltage, current (amps), power (watts), and resistance (ohms), but remembering the formulas that go into those calculations can be difficult.  This is where a “magic triangle” can help.

The first thing you need to remember is the correct formula sign.  What letter or symbol represents each of these values.  The table below should help and can be cut out and kept in your badge holder if you want.

Name Formula sign Unit Symbol
voltage V or E volt V
current I ampere (amp) A
resistance R ohm Ω
power P watt W

To calculate power (watts), voltage, and current you can try to memorize three different formulas depending on which value your looking for or you can use a Power Triangle.

Power Triangle Credit sengpielaudio.com

To find the value your looking for, just cover up the formula sign on the triangle and do the calculation you see.  Let’s say you have measured the volts and current with your multimeter, you can cover the P up on the triangle with your thumb and see that you need to multiply volts by current to get the wattage (power) that is being passed over the line.  Or, say you want to find out the volts and all you can measure is the watts (P) and current (I).  You cover up the V on the triangle and discover you need to divide P by I to get the answer.  It’s really not that difficult using the Power Triangle and sure beats trying to remember three separate formulas.

Credit sengpielaudio.com

To calculate resistance using the Ohms law, there is another magic triangle called the Ohms Law Triangle.  This triangle will help you calculate resistance, current (I), and voltage.  This can also help you figure out how large of a resistor you want to place in a circut to obtain a specified current and voltage.

Ohms Law Triangle Credit sengpielaudio.com

To calculate what type of resistor you need to obtain the proper resistance in a circuit, you would cover the R on the triangle and see that you need to divide Volts by Current.  If you already have a resistor on the circuit and wish to know the current, you can divide volts by the resistance to get the answer after you cover up the R on the triangle.  Not too hard is it?

For more advanced calculations, you might also find this Power Wheel handy.

Power Wheel Credit sinclair.edu

Overall, power calculations don’t have to keep you up at night or calling your former electronics instructor right in the middle of a job.  All it takes is just a couple “magic triangles” to help you through.

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Friday, January 28th, 2011 Basic Electricity Comments Off on Magic Triangles

SpaceTEC Featured on Syndicated News

Recently, Dr. Al Koller, Principal Investigator of SpaceTEC, appeared on Syndicated News, a web based journalist site.  You can listen to the 15 minute interview below.

You can discuss the SpaceTEC interview or any other aerospace subject on our forum.

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Thursday, January 27th, 2011 SpaceTEC Comments Off on SpaceTEC Featured on Syndicated News

Clean Your Room Young Man!

Mars Rover Clean Room

How many times have we heard out parents bellow out to clean our rooms?  Probably far more than we care to count, but cleanliness does not end with childhood.  Cleanliness is essential to good health and a safe environment.  That not only applies to humans, but to spacecraft as well.

Spacecraft of course range from satellites to planetary probes to manned spacecraft.  Each type of spacecraft has its own unique reasons as to why it needs to be kept in a clean environment.  Specialized equipment can be contaminated by material that is less than 100 microns big.  (A human hair is about 100 microns in width)  Also some planetary probes must be microbe free so that the probe will not contaminate another world and possibly endanger life on that planet or give us a false reading of life on that particular planet.  If you think trying to bring a plant through customs after visiting a foreign country is a big deal, just try sending a contaminated lander to Mars and making the mistake of announcing to the world that you found life on Mars!

Japanese astronaut Akihiko Hoshide holds up a sign for the camera as he enters the Kibo lab for the first time. Note the mask and goggles.  Photo credit: NASA TV

Human spacecraft also require a clean environment.  Dust and other contaminates will not just sit idly on the floor as they do on Earth, but float in a micro-gravity environment getting into equipment, the astronaut lungs, eyes, mouth, etc.  Depending on the material floating around, it can be an irritant to an astronaut or something that could be life threatening such as breathing in microscopic metal shavings.  This is why you always see astronauts wearing goggles and sometimes masks as they open a new module to the International Space Station until they can confirm that the filters have completely cleaned the air of all contaminants.

As an aerospace technician, you may find yourself working in a clean room environment.  Some space hardware cannot risk exposure to dust, microbes, or any other contaminant.  Humans, no matter how fastidious they are in their hygiene, are the dirtiest objects to enter a clean room.  So, since you are a hazard, precautions must be taken.

At the Jet Propulsion Laboratory or JPL, “The default clean room settings are determined by the project with the most stringent cleanliness requirements. Both high bays are class 100,000. This means that in every cubic foot (about 28 liters) of air there must be no more than 100,000 particles at one-half of a micron and no more than 700 particles at five microns or larger. This may sound like many particles, but they are incredibly minute; for example, one strand of human hair measures 100 microns. A typical home or school usually measures in the 200,000-300,000 class.”  But it can be even more stringent.  During the assembly of the Genesis spacecraft, “engineers and scientists at NASA’s Johnson Space Center in Houston, Texas, built a class ten clean room exclusively for the spacecraft to ensure that no contaminants from Earth accompanied the Genesis spacecraft to its destination in space. That means that a mere ten particles (one micron in size) are present per cubic foot of air per minute.”  Genesis used “collector plates” to capture particles from a comet’s tail and return them to Earth.  To ensure that only comet particles were being viewed once the collector plates were returned and examined, extraordinary efforts were made to keep the plates and spacecraft as sterile as possible.

So, as an aerospace technician, what precautions would you be required to take?  Well first of all, good hygiene is a nice thing to do.  (Your co-workers will thank you for that step!)  Next would be collecting a “bunny suit” from logistics that is sealed in an air tight bag.  This suit will end up covering your head, face, and entire body including your feet ensuring that any particles such as hair or exfoliated skin that falls off your body is contained within the suit.

Your next step would be to stop by a clerk or person that is responsible for keeping track of everyone and everything that enters and exits the clean room.  For the Space Shuttle Program, these people are called Orbiter Integrity Clerks or OIC’s.  You will bag up all unnecessary items on your person and place them in a bag to be kept by the clerk, sign in all tools and materials you will be taking inside with you to do your job, and of course sign yourself in too.  When you exit the clean room, you will go over the list of all the items you took inside with you with the clerk and ensure you brought everything back out.  You cannot leave any FOD behind in the clean room.

Air Shower

Once you’re done checking in with the clerk, it’s time to take a shower.  Not a water shower, but an air shower.  You will enter a doorway, close it behind you, and raise your arms in the air while a blast of air blows over you from several nozzles.  This air blast is to knock loose any particles that may be on your clothes and tool bag.  The particles are then sucked up into a filter.  After the shower ends its cycle, you will exit the other door into the dressing area.

The dressing area will have a “sticky mat” (sometimes there will be sticky mats outside before you enter the air shower) that will cause your shoes to stick to the floor removing any particles that may be on the bottom of your shoes. In the dressing area you will put on your bunny suit and prepare to enter the clean room.  Make sure you inspect the bunny suit for any tears or holes.  There should be no openings that could possibly allow contaminants to fall out.

While in the cleanroom good work practices become even more important.  Did you bring a waste bag that seals to put all your trash in?  Are you practicing “clean as you go?”  These things are important outside the clean room and much more so inside.  You should never leave anything behind that shouldn’t be there.

Now you know how to work in a clean room.  Your parents sure will be proud of you.

Goddard Space Flight Center clean room used for the Hubble Telescope

More information can be found about clean rooms at JPL’s website.

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Thursday, January 13th, 2011 Introduction to Aerospace Comments Off on Clean Your Room Young Man!