Feedback Loop Control System

Posted by PITHOCRATES - October 30th, 2013

Technology 101

Living through Winters became easier with Thermostats

When man discovered how to make fire it changed where we could live.  We no longer had to follow the food south when winter came.  We could stay through the winter.  And build a home.  As long as we could store enough food for the winter.  And had fire to stay warm.  To prevent our dying from exposure to the cold.

There’s nothing like sitting around a campfire.  It’s warm.  And cozy.  In large part because it’s outside.  So the smoke, soot and ash stayed outside.  It wasn’t always like that, though.  We used to bring that campfire inside the home.  With a hole in the roof for the smoke.  And families slept around the fire.  Together.  Even as some fornicated.  To propagate the species.  But that wasn’t the worst part about living around an indoor campfire.

Your distance from the fire determined how hot or cold you were.  And it was very hot by it.  Not so hot away from it.  Especially with a hole in the roof.  Worst, everyone got colder as the fire burned out.  Meaning someone had to get up to start a new fire.  The hard way.  Creating an ember.  Using it to start some kindling burning.  Then adding larger sticks and branches onto the kindling until they started to burn.  Which was a lot harder than turning the thermostat to ‘heat’ at the beginning of the heating season and forgetting about it.  Then turning it to ‘off’ at the end of the heating season.

A Feedback Loop Control System measures the Output of a System and Compares it to a Desired Output

Replacing the indoor campfire with a boiler or furnace made life a lot simpler.  For with a supply of fuel (natural gas, fuel oil, electricity, etc.) the fire never burned itself out.  And you never had to get up to start a new one.  Of course, that created another problem.  Shutting it off.

Boilers and furnaces are very efficient today.  They produce a lot of heat.  And if you let them run all day long it would become like a hot summer day inside your house.  Something we don’t want.  Which is why we use air conditioners on hot summer days.  So heating systems can’t run all day long.  But we can’t keep getting up all night to turn it off when we’re too hot.  And turning it back on when we’re too cold.  Which is why we developed the feedback loop control system.

We did not develop the feedback loop control system for our heating systems.  Our heating systems are just one of many things we control with a feedback loop control system.  Which is basically measuring the output of a system and comparing it to a desired output.  For example, if we want to sleep under a cozy warm blanket we may set the ‘set-point’ to 68 degrees (on the thermostat).  The heating system will run and measure the actual temperature (at the thermostat) and compare it to the desired set-point.  That’s the feedback loop.  If the actual temperature is below the desired set-point (68 degrees in our example) the heat stays on.  Once the actual temperature equals the set-point the heat shuts off.

The Autopilot System includes Independent Control Systems for Speed, Heading and Altitude

Speed control on a car is another example of a feedback loop control system.  But this control system is a little more complex than a thermostat turning a heating system on and off.  As it doesn’t shut the engine off once the car reaches the set-point speed.  If it did the speed would immediately begin to fall below the set-point.  Also, a car’s speed varies due to terrain.  Gravity speeds the car when it’s going downhill.  And slows it down when it’s going uphill.  The speed controller continuously measures the car’s actual speed and subtracts it from the set-point.  If the number is negative the controller moves the vehicle’s throttle one way.  If it’s positive it moves the throttle in the other way.  The greater the difference the greater the movement.  And it keeps making these speed ‘corrections’ until the difference between the actual speed and the set-point is reduced to zero.

Though more complex than a heating thermostat the speed control on a car is pretty simple.  It has one input (speed).  And one output (throttle adjustment).  Now an airplane has a far more complex control system.  Often called just ‘autopilot’.  When it is actually multiple systems.  There is an auto-speed system that measures air speed and adjusts engine throttles.  There is a heading control system that measures the aircraft’s heading and adjusts the ailerons to adjust course heading.  There is an altitude control system that measures altitude and adjusts the elevators to adjust altitude.  And systems that measure and correct pitch and yaw.  Pilots enter set-points for each of these in the autopilot console.  And these control systems constantly measure actual readings (speed, heading and altitude) and compares them to the set-points in the autopilot console and adjusts the appropriate flight controls as necessary. 

Unlike a car or an airplane a building doesn’t move from point A to point B.  Yet they often have more complex control systems than autopilot systems on airplanes.  With thousands of inputs and outputs.  For example, in the summer there’s chilled water temperature, heating hot water temperature (for the summer boiler), supply air pressure, return air pressure, outdoor air pressure, indoor air pressure, outdoor temperature, outdoor humidity, indoor temperature (at numerous locations), indoor humidity, etc.  Thousands of inputs.  And thousands of outputs.  And unlike an airplane these are all integrated into one control system.  To produce a comfortable temperature in the building.  Maintain indoor air quality.  Keep humidity levels below what is uncomfortable and possibly damaging to electronic systems.  And prevent mold from growing.  But not keep it too dry that people suffer static sparks, dry eyes, dry nasal cavities that can lead to nose bleeds, dry and cracked skin, etc.  To prevent a blast of air hitting people when they open a door.  To keep the cold winter air from entering the building through cracks and spaces around doors and windows.  And a whole lot more.  Far more than the thermostat in our homes that turns our heating system on and off.

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Aircraft De-Icing Systems

Posted by PITHOCRATES - October 23rd, 2013

Technology 101

A build-up of Ice on Airfoils causes a Reduction of Lift and a Loss of Stability

In the classic movie Airport (1970) after the guy pulled the trigger on his briefcase bomb the plane suffered a massive decompression.  When Dean Martin got back to the cockpit he told the flight engineer to give them all the heat they had.  Because it’s very cold flying above 10,000 feet without pressurization.  That’s why World War II flight crews wore a lot of heavy clothing and thick mittens in their bombers.  As well as oxygen masks as the air was too thin to breathe.  The B-17 even had open windows for the waste gunners.  Making it very cold inside the plane.  Because the air is very, very cold at altitude.

There is another problem at altitude.  Because of these very frigid temperatures.  Water droplets in the air will freeze to any surface they come into contact with.  They can reduce engine power for both propeller and jet engines.  They can freeze on ports used for instrumentation and give inaccurate readings of vital aircraft data (such as engine pressure ratio, aircraft speed, etc.).  And they can freeze on airfoils (wings, rudder, tail fin, etc.).  Disturbing the airflow on these surfaces.  Causing a reduction of lift and a loss of stability.

Ice and airplanes are two things that don’t go together.  As ice forms on a wing it disturbs the airflow over the surface of the wing.  Increasing drag.  And reducing lift.  Causing the plane to lose speed.  And altitude.  If the ice continues to form on the wing eventually it will stall the wing.  And if the wing stalls (i.e., produces no lift) the plane will simply fall out of the sky.  In the early days of aviation pilots were highly skilled in flying their planes where there were no icing conditions.  Flying over, under or around masses of air containing water droplets in subfreezing temperatures.  Today we have anti-icing systems.

The most common Anti-Icing System on Commercial Jets is a Bleed Air System

One of the most common anti-icing systems on turboprop aircraft is the use of inflatable boots over the leading edge of the wing.  Basically a rubber surface that they can pump air into.  When there is no ice on the wing the boot lies flat on the leading edge without interrupting the airflow.  When ice forms on the leading edge of the wing the boot inflates and expands.  Cracking the ice that formed over it.  Which falls away from the wing.

Commercial jets have larger airfoils.  And require a larger anti-icing system.  The most common being a pneumatic manifold system that ducts hot air to areas subject to icing.  Which works thanks to a property of gas.  If you compress a gas you increase its temperature.  That’s how a diesel engine can work without sparkplugs.  The compressed air-fuel mixture gets so hot it ignites.  This property comes in handy on a jet plane as there is a readily available source of compressed air.  The jet engines.

As the air enters the jet it goes through a series of fast-spinning rotors.  As the air moves through the engine these rotors push this air into smaller and smaller spaces.  Compressing it.  Through a low-pressure compressor.  And then through a high-pressure compressor.  At which time the air temperature can be in excess of 500 degrees Fahrenheit.  It is in the high-pressure compressor that we ‘bleed’ off some of this hot and pressurized air.  We call this a bleed air system.  The air then enters a manifold which ducts it to at-risk icing areas.  From the engine cowling to the wings to the instrumentation ports.  Using the hot air to raise temperatures in these areas above the freezing temperature of water.  Thus preventing the formation of ice.

The Drawback of a Bleed Air System is Reduced Engine Efficiency

The bleed air system does more than just anti-icing.  It also pressurizes the cabin.  As well as keeps it warm.  Which is why we don’t have to dress like a crewmember on a World War II bomber when we fly.  It also powers the air conditioning system.  And the hydraulic system.  It provides the pressure for the water system.  And it even starts the jet engines.  With the source of pressurized bleed air coming from the auxiliary power unit mounted in the tail.  Or from an external ground unit.  Once the jets are running they disconnect from the auxiliary source and run on the bleed air from the engines.

There is one drawback of a bleed air system.  It bleeds air from the jet engine.  Thus reducing the efficiency of the engine.  And a less efficient engine burns more fuel.  Raising the cost of flying.  With high fuel costs and low margins airlines do everything within their power to reduce the consumption of fuel.  Which is why pilots don’t top off their fuel tanks.  They’d like to.  But extra fuel is extra weight which increases fuel consumption.  So they only take on enough fuel to get to their destination with enough reserve to go to an alternate airport.  Even though it seems risky few planes run out of fuel in flight.  Allowing the airlines to stay in business without having to raise ticket prices beyond what most people can afford.

To help airlines squeeze out more costs Boeing designed their 787 Dreamliner to be as light as possible by using more composite material and less metal.  Making it lighter.  They are also using a more efficient engine.  Engines without a bleed air system.  In fact, they eliminated the pneumatic system on the 787.  Converting the pneumatic components to electric.  Such as using electric heating elements for anti-icing.  Thus eliminating the weight of the bleed air manifold and duct system.  As well as increasing engine efficiency.  Because all engine energy goes to making thrust.  Which reduces fuel consumption.  The key to profitability and survival in the airline industry.

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Air, Low Pressure, High Pressure, Lateen Sail, Flight, Wing, Lift, Drag, Leading Edge Slats, Trailing Edge Flaps and Angle of Attack

Posted by PITHOCRATES - October 10th, 2012

Technology 101

There’s more to Air than Meets the Eye even though it’s Invisible

When you take a shower have you noticed how the shower curtain pulls in towards you?  Have you ever wondered why it does this?  Here’s why.  Air has mass.  The water from the showerhead sends out a stream of water drops that also has mass.  So they fall to the floor of the shower.  Pushing air with it.  And pulling air behind it.  (Like drinking through a straw.  As you suck liquid out of the straw more liquid enters the straw.)  So you not only have a stream of water moving down alongside the shower curtain.  You also have a stream of air moving down alongside the shower curtain.

As the falling water sweeps away the air from the inside of the shower current it creates a low pressure there.  While on the outside of the curtain there is no moving water or air.  And, therefore, no change in air pressure.  But there is a higher pressure relative to the lower pressure on the inside of the shower curtain.  The low pressure inside pulls the curtain while the high pressure outside pushes it.  Causing the shower curtain to move towards you.

There’s more to air than meets the eye.  Even though it’s invisible.  It’s why we build modern cars aerodynamically to slice through large masses of invisible air that push back against cars trying to drive through it.  Making our engines work harder.  Consuming more gas.  And reducing our gas mileage.  While race cars will use spoilers to redirect that air up, forcing the weight of the car down on the tires.  To help the tires grip the road at higher speeds.  We even design skyscrapers to be aerodynamic.  To split the prevailing winds around the buildings to prevent large masses of air from slamming into the sides of buildings, minimizing the amount buildings sway back and forth.

We put the Engines on, and the Fuel in, the Wings to Counteract the Lifting Force on an Aircraft’s Wings

Air can be annoying.  Such as when the shower curtain sticks to your leg.  As it steals miles per gallon from your car.  When it shakes the building you’re in.  But it can also be beneficial.  As in early ship propulsion before the steam engine.  Large square-rigged sails that pushed ships along the prevailing winds.  And triangular lateen sails that allowed us to travel into the wind.  By zigzagging across the wind.  With the front edge of a lateen sail slicing into the wind.  The sail redirects the wind on one side of the sail to the rear of the boat that pushes the boat forward.  While the wind on the other side follows the curved sail creating a low pressure that pulls the boat forward.  Like the inside of that shower curtain.  Only with a lot more pulling force.

Harnessing the energy in wind let the world become a smaller place.  As people could travel anywhere in the world.  Of course, some of that early travel could take months.  And spending months on the open sea could be very trying.  And dangerous.  A lot of early ships were lost in storms.  Ran aground on some uncharted shoal.  Or simply got lost and ran out of drinking water and food.  Or fell to pirates.  So it took a hearty breed to travel the open seas under sail.  Of course today long-distant travel is a bit easier.  Because of another use for air.  Flight.

Like a lateen sail an aircraft wing splits the airflow above and below the wing.  And like the lateen sail an aircraft wing is curved.  The air pushes on the bottom of the wing creating a high pressure.  While the air passing over the curve of the top of the wing creates a low pressure.  Pulling the wing up.  In fact, it’s the wind passing over the top of the wing that does the lion’s share of lifting airplanes into the air.  The low pressure on top of the wing is so great that they put the engines on the wings, and the fuel in the wings, to counteract this lifting force.  To prevent the wings from curling up and snapping off of the plane.  Planes with tail-mounted engines have extra reinforcement in the wings to resist this bending force.  So those lifting forces only lift the plane.  And not curl the wing up until it separates from the plane.

To make Flying Safe at Slow Speeds they add Leading Edge Slats and Trailing Edge Flaps to the Wing

Sails can propel a ship because a ship floats on water.  The wind only propels a ship forward.  On an airplane the wind moving over the wings provides only lift.  It does not propel a plane forward.  Engines propel planes forward.  And it takes a certain amount of forward speed to make the air passing over the wings fast enough to create lift.  The faster the forward air speed the greater the lift.  Today jet engines let planes fly high and fast.  In the thin air where there is less drag.  That is, where the air has less mass pushing against the forward progress of the plane.  At these altitudes the big planes cruise in excess of 600 miles per hour.  Where these planes fly at their most fuel efficient.  But these big planes can’t land or take off at speeds in excess of 600 miles per hour.  In fact, a typical take-off speed for a 747-400 is about 180 miles per hour.  Give or take depending on winds and aircraft weight.  So how does a plane land and take off at speeds under 200 mph while cruising at speeds in excess of 600 mph?  By changing the shape of the wing.

We determine the amount of lift by the curvature and surface area of the wing.  The greater the curvature the greater the lift.  However, the greater the curvature the greater the drag.  And the greater the drag the more fuel consumed at higher speeds.  And the more stresses placed on the wing.  Also, current runways are about 2 miles long for the big planes.  That’s when they land and take off at speeds under 200 mph.  To land and take off at speeds around 600 mph would require much longer runways.  Which would be extremely costly.  And dangerous.  For anything traveling close to 600 mph on or near the ground would have a very small margin of error.  So to make flying safe and efficient they add leading edge slats to the front edge of the wing.  And trailing edge flaps to the back edge of the wing.  During cruise speeds both are fully retracted to reduce the curvature of the wing.  Allowing higher speeds.  At slower speeds they extend the slats and flaps.  Greatly increasing the curvature of the wing.  And the surface area.  Providing up to 80% more lift at these slower speeds.

At takeoff and landing pilots elevate the nose of the aircraft to increase the angle of attack of the wing.  Forcing more air under the wing to push the wing up.  And causing the air on top of the wing to turn farther away for its original direction of travel as it travels across the top of the up-tilted wing.  Creating greater lift.  And the ability to fly at slower speeds.  However, if the angle of attack it too great the smooth flow of air across the wing will break away from the wing surface and become turbulent.  The wing will not be able to produce lift.  So the wing will stall.  And the plane will fall out of the sky.  With the only thing that can save it being altitude.  For in a stall the aircraft will automatically push the stick forward to lower the nose.  To decrease the angle of attack of the wing.  Decrease drag.  And increase air speed.  If there is enough altitude, and the plane has a chance to increase speed enough to produce lift again, the pilot should be able to recover from the stall.  And most do.  Because most pilots are that good.  And aircraft designs are that good.  For although flying is the most complicated mode of travel it is also the safest mode of travel.  Where they make going from zero to 600 mph in a matter of minutes as routine as commuting to work.  Only safer.

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Corduroy Roads, Positive Buoyancy, Negative Buoyancy, Carbon Dioxide, Crush Depth, Pressurization, Rapid Decompression and Space

Posted by PITHOCRATES - May 9th, 2012

Technology 101

Early Submarines could not Stay Submerged for Long for the Carbon Dioxide the Crew Exhaled built up to Dangerous Levels

People can pretty much walk anywhere.  As long as the ground is fairly solid beneath our feet.  Ditto for horses.  Though they tend to sink a little deeper in the softer ground than people do.  Carts are another story.  And artillery trains.  For their narrow wheels and heavy weight distributed on them tend to sink when the earthen ground is wet.  Early armies needing to move cannon and wagons through swampy areas would first build roads through these areas.  Out of trees.  Called corduroy roads.  It was a bumpy ride.  But you could pull heavy loads with small footprints through otherwise impassable areas.  As armies mechanized trucks and jeeps with fatter rubber tires replaced the narrow wheels on wagons.  Then tracked vehicles came along.  Allowing the great weights of armored vehicles with large guns to move across open fields.  The long and wide footprints of these vehicles distributing that heavy weight over a larger area.  Still, nothing can beat the modern rubber tire on a paved road for a smooth ride.  And the lower resistance between tire and road increases gas mileage.  Which is why trucks like to use as few axles on their trailers as possible.  For the more tires on the road the more friction between truck and road.  And the higher fuel consumption to overcome that friction.  Which is why we have to weigh trucks for some try to cheat by pulling heavier loads with too few axles.  When they do the high weight distributed through too few wheels will cause great stresses on the roadway.  Causing them to break and crumble apart.   

Man and machine can move freely across pretty much anything.  If we don’t carry food and water with us we could even ‘live off the land’.  But one thing we can’t do is walk or drive on water.  We have to bridge streams and rivers.  Go around lakes.  Or move onto boats.  Which can drive on water.  If they are built right.  And are buoyant.  Because if a boat weighed less than the water it displaced it floated.  Much like a pair of light-weight, spongy flip-flops made out of foam rubber.  Throw a pair into the water and they will float.  Put them on your feet and step into the deep end of a pool and you’ll sink.  Because when worn on your feet the large weight of your body distributed to the light pair of flip-flops makes those flip-flops heavier than the water they displace.  And they, along with you, sink.  Unlike a boat.  Which is lighter than the water it displaces.  As long as it is not overloaded.  Even if it’s steel.  Or concrete.  You see, the weight of the boat includes all the air inside the hull.  So a large hull filled with cargo AND air will be lighter than the water it displaces.  Which is why boats float. 

Early sail ships had great range.  As long as the wind blew.  Their range only being limited by the amount of food and fresh water they carried.  Later steam engines and diesel-electric engines had greater freedom in navigation not having to depend on the prevailing winds.  But they had the same limitations of food and water.  And when we took boats under the water we had another limitation.  Fresh air.  Early submarines could not stay submerged for long.  For underwater they could not pull air into a diesel-electric engine.  So they had to run on batteries.  Which had a limited duration.  So early subs spent most of their time on the surface.  Where they could run their diesel engines to recharge their batteries.  And open their hatches to get fresh air into the boat.  For when submerged the carbon dioxide the crew exhaled built up.  If it built up too much you could become disoriented and pass out.  And die.  If a sub is under attack staying under water for too long and the levels of carbon dioxide build up to dangerous levels a captain has little choice but to surface and surrender.  So the crew can breathe again.

Rapid Decompression at Altitude can be Catastrophic and Violent

Being in a submarine has been historically one of the more dangerous places to be in any navy (second to being on the deck of an aircraft carrier).  Just breathing on a sub had been a challenge at times while trying to evade an enemy destroyer.  But there are other risks, too.  Some things float.  And some things sink.  A submarine is somewhere in between.  It will float on the surface when it has positive buoyancy.  And sink when it has negative buoyancy.  But submarines operate in the oceans.  Which are very deep.  And the deeper you go the greater the pressure of the water.  Because the deeper you go there is more ocean above you pressing down on you.  And oceans are heavy.  If a sub goes too deep this pressure will crush the steel hull like a beer can.  What we call crush depth.  Killing everyone on board.  So a sub cannot go too deep.  Which makes going below the surface a delicate and risky business.  To submerge they flood ballast tanks.  Replacing air within the hull with water.  Making it sink.  Other tanks fill with water as necessary to ‘trim’ the boat.  Make it level under water.  When under way they use forward propulsion to maintain depth and trim with control surfaces like on an airplane.  If everything goes well a submarine can sink.  Then stop at a depth below the surface.  And then resurface.  Modern nuclear submarines can make fresh water and clean air.  So they can stay submerged as long as they have food for the crew to eat.

An airplane has no such staying power like a sub.  For planes have nothing to keep them in air but forward propulsion.  So food and water are not as great an issue.  Fuel is.  And is the greatest limitation on a plane.  In the military they have special airplanes that fly on station to serve as gas stations in the air for fighters and bombers.  To extend their range.  And it is only fuel they take on.  For other than very long-range bombers a flight crew is rarely in the air for extended hours at a time.  Some bomber crews may be in the air for a day or more.  But there are few crew members.  So they can carry sufficient food and water for these longer missions.  As long as they can fly they are good.  And fairly comfortable.  Unlike the earlier bomber crews.  Who flew in unpressurized planes.  For it is very cold at high altitudes.  And there isn’t enough oxygen to breathe.  So these crew members had to wear Arctic gear to keep from freezing to death.  And breathe oxygen they carried with them in tanks.  Pressurizing aircraft removed these problems.  Which made being in a plane like being in a tall building on the ground.  Your ears may pop but that’s about all the discomfort you would feel.  If a plane lost its pressurization while flying, though, it got quite uncomfortable.  And dangerous. 

Rapid decompression at altitude can be catastrophic.  And violent.  The higher the altitude the lower the air pressure.  And the faster the air pressure inside the airplane equals the air pressure outside the airplane.  The air will get suck out so fast that it’ll take every last piece of dust with it.  And breathable air.  Oxygen masks will drop in the passenger compartment.  The flight attendants will scramble to make sure all passengers get on oxygen.  As does the flight crew.  Who call in an emergency.  And make an emergency descent to get below 10 thousand feet.  Almost free falling out of the sky while air traffic control clears all traffic from beneath them.  Once below 10 thousand feet they can level off and breathe normally.  But it will be very, very cold.

Man’s Desire is to Go where no Man has Gone before and where no Human Body should Be

Space flight shares some things in common with both submarines and airplanes.  Like airplanes they can’t fly without fuel.  The greatest distance we’ve ever flown in space was to the moon and back.  The Saturn V rocket of the Apollo program was mostly fuel.   The rocket was 354 feet tall.  And about 75% of it was a fuel tank.  In 3 stages.  The first stage burned for about 150 seconds.  The second stage burned for about 360 seconds.  The third stage burned for about 500 seconds (in two burns, the first to get into earth orbit and the second to escape earth orbit).  Add that up and it comes to approximately 16 minutes.  After that the astronauts were then coasting at about 25,000 miles per hour towards the moon.  Or where the moon would be when they get there.  The pull of earth’s gravity slowed it down until the pull of the moon’s gravity sped it back up.  So that’s a lot of fuel burned at one time to hurl the spacecraft towards the moon.  The remaining fuel on board used for minor course corrections.  And to escape lunar orbit.  For the coast back home.  There was no refueling available in space.  So if something went wrong there was a good chance that the spacecraft would just float forever through the universe with no way of returning home.  Much like a submarine that can’t keep from falling in the ocean.  If it falls too deep it, too, will be unable to return home.

Also like in a submarine food and fresh water are critical supplies.  They brought food with them.  And made their own water in space with fuel cells.  It had to last for the entire trip.  About 8 days.  For in space there were no ports or supply ships.  You were truly on your own.  And if something happened to your food and water supply you didn’t eat or drink.  If the failure was early in the mission you could abort and return home.  If you were already in lunar orbit it would make for a long trip home.  The lack of food and hydration placing greater stresses on the astronauts making the easiest of tasks difficult.  And the critical ones that got you through reentry nearly impossible.  Also like on a submarine fresh air to breathe is critical.  Even more so because of the smaller volume of the spacecraft.  Which can fill up with carbon dioxide very quickly.  And unlike a sub a spacecraft can’t open a hatch for fresh air.  All they can do is rely on a scrubber system to remove the carbon dioxide from their cramped quarters.

While a submarine has a thick hull to protect it from the crushing pressures of the ocean an airplane has a thin aluminum skin to keep a pressurized atmosphere inside the aircraft.  Just like a spacecraft.  But unlike an aircraft, a spacecraft can’t drop below 10,000 feet to a breathable atmosphere in the event of a catastrophic depressurization.  Worse, in the vacuum of space losing your breathable atmosphere is the least of your troubles.  The human body cannot function in a vacuum.  The gases in the lungs will expand in a vacuum and rupture the lungs.  Bubbles will enter the bloodstream.  Water will boil away (turn into a gas).  The mouth and eyes will dry out and lose their body heat through this evaporation.  The water in muscle and soft tissue will boil away, too.  Causing swelling.  And pain.  Dissolved nitrogen in the blood will reform into a gas.  Causing the bends.  And pain.  Anything exposed to the sun’s ultraviolet radiation will get a severe sunburn.  Causing pain.  You will be conscious at first.  Feeling all of this pain.  And you will know what is coming next.  Powerless to do anything about it.  Brain asphyxiation will then set in.  Hypoxia.  The body will be bloated, blue and unresponsive.  But the brain and heart would continue on.  Finally the blood boils.  And the heat stops.  In all about a minute and half to suffer and die.

Man is an adventurer.  From the first time we walked away from our home.  Rode the first horse.  Harnessed the power of steam.  Then conquered the third dimension in submarines, airplanes and spacecraft.  We are adventurers.  It’s why we crossed oceans and discovered the new world.  Why we climbed the highest mountains.  And descended to the oceans’ lowest depth.  Why we fly in airplanes.  And travelled to the moon and back.  When things worked well these were great adventures.  When they did not they were horrible nightmares.  While a few seek this adventure most of us are content to walk the surface of the earth.  To feel the sand through our toes.   Or walk to the poolside bar in our flip-flops.  To enjoy an adult beverage on a summer’s day.  While adventurers are still seeking out something new.  And waiting on technology to allow them to go where no man has gone before.  Especially if it’s a place no human body should be.

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