NASA's space shuttle

SPACE SHUTTLE

The vehicle which is responsible to transport the payloads and human to outer-space. But very few people know the working and engineering behind a space shuttle.

NASA stands for National Aeronautics and Space Administration. NASA's space shuttle is the most complicated and complex machine ever build, making it one of the world's most expensive vehicles. It travels 25 times more faster than a speeding bullet and carries cargo worth million's of dollars. Its the world's first reusable space shuttle. On each mission it travels 6.5 millions kilometers. The launching of space shuttle is being done at Kennedy's space center. A new space shuttle cost around 1.7 billion dollars and take it for a spin can cost around 450 million dollars. Because of huge expense, NASA had to reduce its cost by reusing the space shuttle for its next program. And the best thing about space shuttle - "It has to be part plane and part rocket".

But before we get started, let's get introduced with the main components of  space vehicle.

The two white booster's are called SRB's which stands for 'Solid Rocket Booster'. They play very important role during initial minutes of flight and produces very large thrust to lift off this giant vehicle. After burnout they are parachuted into Atlantic Ocean. The orange tank is space shuttle external tank which consist of liquid oxygen and liquid hydrogen. The main part in middle looking like a aircraft is actually called 'orbiter' which takes the payload and humans to space. 

The initial spark that you see above before combustion has also a reason. This is hydrogen burn-off system which eliminates free hydrogen present prior to main engine ignition. Hydrogen vapours are exhausted into main engine nozzles during the start sequence, if ignited when the engines ignite ,a small explosion could happen which can damage engine bells. The six hydrogen burn-off pre-igniters are initiated at T-10 seconds on launch countdown clock. They throw off thousands of hot,luminescent balls into the area below the engine bells , igniting the free hydrogen and precluding a rough combustion when main engine starts. These pre-igniters are Radial Outward Firing Initiators(ROFIs). the ROFIs were designed to provide safe ignition source for any unburned GH2 during space shuttle engine start period.This was done by the use of small rocket motors in the ROFIs that fired zirconium particles outward into the aft engine area and flooded the area between the main engine nozzles and the exhaust duct entrance with hot zirconium sparklers.

The orbiter's three main engine burns furiously during shuttle's 8.5 minute ascent into orbit. They are extremely powerful- 37 million horse-power approximately, and they propel 2000 tonnes shuttle upto 650 kilometers above earth surface.This engines not only travel at enormous distances but also they have to withstand extreme temperatures. Without protection, they would not only melt like an ice-cream melting at room temperature, but would vaporize at such extreme temperature. The temperature in the engines can exceed upto 3300°C or 6000°F. That is the problem-"Engines that melt can never do the job they are suppose to do !! "
So, how is this achieved ?

These are not some random design inside the shuttle's nozzle. But they are small distribution tubes, 1080 to be precise, to pass the super-cooled hydrogen fuel to the engine thereby keeping nozzle cool.

Actually hydrogen which is used as a fuel, works as a coolant. Inside the giant orange tank,the super-cooled liquid hydrogen at -253°C is passed through this tubes, keeping the temperature below the melting point of the material. Hence with one arrow two targets achieved - that is with one hydrogen fuel, it is used as both fuel as well as coolant. And that's how the nozzle don't melt even at such high temperature.

But even the thrust produced by the orbiter isn't enough to lift the shuttle. Thus, along with the orange tank filled with liquid hydrogen and liquid oxygen, two solid rocket booster are required. More engines, more fuel required, and also the weight will increase. But NASA don't want weight to be increased along with increasing number of engines. So, they used SRB's(Solid Rocket Booster), and name itself suggest that, the fuel used is solid. Solid have the least volume compared to liquid and gas. Hence huge amount of fuel can be stacked within small volume with great power to weight ratio. Booster are very large in size- height of a 15 storey building, these are the largest solid rocket booster ever flown producing about 1300 tonnes of thrust, equal to  17000 F1 car engines. To get that amount of power, the fuel has to burn at incredible temperature and incredibly faster. The rocket propellent mixture in each solid rocket motor consisted of ammonium perchlorate(Oxidizer 69.6% by weight) atomized aluminium powder(fuel 16%), iron oxide (catalyst 0.4%),PBAN (binder,also acts as fuel 12.04%) and an epoxy curing agent(1.96%). This propellent is commonly referred to as Ammonium Perchlorate Composite Propellent or APCP. 
 At launch each booster is burning fuel at the unbelievable rate of 5 tonnes every second(5tons/sec). They burn for about two minutes and then they jettison( Drop from shuttle).  See the below GIF for complete illustration.

They get jettisoned 49 kms up, come back to earth and crash land into Atlantic ocean. The beauty of these system is - They are used again after maintenance ready for its next journey.

But we have not come across the biggest problem. The exhaust gases generates enormous thrust, which is accompanied with another unwanted energy :- ACOUSTIC ENERGY, that is sound energy. It is so powerful that it can have fatal consequences. Even at very far distances at 3 miles , you can feel the energy pounding in your chest. If this energy is not controlled, it can bounce of the ground straight back to the shuttle and cause disaster. On first ever shuttle mission they ripped the heat resistant tile of the surface of orbiter, fortunately that time orbiter returned to earth safely.

Doubt that how sound energy can be catastrophic? We know that sound travels through a medium and is in a form of vibration. These vibration travel in the medium in form of waves. You might have heard about the glass breaking into pieces when opera singer sings.
I hope you remember the movie 'Back to Future' when Marty Mcfly uses huge amplifier.

From Movie -' Back to Future'

That's the power of sound waves. But wait, shuttle's problem is much bigger. It's exhaust gases jet out in about 4000 km/hr, producing vast amount of sound energy as vibrations. So, engineers needed a way to protect the shuttle from these catastrophic vibrations. So, how NASA managed to get rid of this problem ?

They used very clever technique called Sound Suppression System. Bubbles are great insulator to sound waves. They absorb the sound waves and convert it into heat energy. These same technique was used by Germans during world war-II. The German's wanted their submarines to be untraceable by their ally destroyers from their SONAR system. 

SONAR means Sound Navigation And Ranging that uses sound propagation waves underwater. The SONAR works by sending out sound wave and waiting for the echo or the reflected waves to bounce back from a solid object. These could tell them where the German submarines were and they can destroy it very easily. But if German submarine somehow manage to absorb the sound wave preventing it from bouncing back then, they can be invisible to their allies. 

So German put tiles in their submarine surface. But they were not ordinary tiles, as they were preventing sound waves to bounce back to receiver. These tiles are made of rubber with air bubbles on it. That is, it has dimples on its surface, that traps air and creates many air bubbles. So, when SONAR hits this surface, it absorbs the waves preventing the receiver to receive the signals, and German submarines become invisible to their allies in very clever and effective way. 

In much similar way, NASA's sound supression system work by absorbing the sound/vibration waves through millions of small bubbles. But instead of air bubble in water, they have water vapor in air as shuttle is obviously not under water. Just after 9 seconds of launch,the water flows out, at an unbelievable 900,000 gallons or 3.5 million liters a minute. Releasing so much water, so quickly through rain-birds creates millions of water droplets suspended in air. And these water drops that absorbs the phenomenal sound energy turning into heat energy.

Orbiter is designed to transport astronauts and payloads including satellite and ISS (International space station) components to space.
But, you can't just pop open the back and pull out your cargo especially when its heavy object like satellite or ISS equipment which are very expensive and obviously not the easiest objects to move. So, every shuttle is armed with a helping hand- The Canadian arm. 

The real problem in space is no gravity which not only makes it difficult to hold objects but it knock the objects farther from itself. These is again a problem as there is no air resistance in space, so if an object starts moving it won't stop. Hence they are made from special type of grippers which are 20cm in diameter that holds the object in space with 100% efficiency.

Grab Position

Release Position

So, Canadarm plays very important role for safely moving heavy and expensive components in space.The Canadarm was a remote-controlled mechanical arm, also known as the Shuttle Remote Manipulator  System(SRMS). During its 30-year career with NASA's Space shuttle program, the robotic arm deployed,captured and moved cargo. Canadarm retired in July following the Space shuttle program's final mission. Canadarm could be thought of 15-metre human arm with wrist,elbow and shoulder. each of these joints included a "joint one-degree-of-freedom"(JOD). A JOD was a motor-gearbox that allowed the Canadarm to bend and turn with more flexibility than even a human arm.

Working model of Canadarm

A TV camera located on robotic arm's as well as an optional camera located at its elbow,acted as Canadarm's eyes while one of the five on-board shuttle computers served as its brain. Canadarm weighs 410 kilograms and could not support itself in earth's gravity. Because of this, engineers built a computer based simulation facility-similar to video game-to test the robotic arm and to train astronauts in its use. The facility called SIMFAC, verified canadarm's operation before its first flight. Canadarm could lift over 30,000 kilograms on Earth- or upto 266,000 kilograms in the weightless of space at speeds of upto 60 centi-metres per second(Depending on payload mass). 

But the most difficult condition for space shuttle is Re-entry. A return journey is one of the most dangerous part of shuttle. In 2003, the orbiter Colombia burnt up as it re-entered the earth's atmosphere killing all seven astronauts. The problem is incredible speed. Re-entering, the orbiter travels at an enormous speed of 27000 kilometres an hour. Travelling at very high speed in space is not a problem as there is no atmosphere to resist it and create friction. Aircrafts, automobile, bullets are streamlined in order to reduce this friction so that they can cut through air with minimum resistance. So, early scientist also thought that, this approach could also work for shuttle. But, they were wrong.

Julian Allen

 In 1950's,space scientist Harry Julian Allen realized that rocket speeds come with their own problem. Travelling at speeds five times and above the sound speed, friction play very vital and different role. No, matter how its designed or material used, nothing can survive that heat. His theory was pretty radical " Rather than make the nose to re-enter the atmosphere sharp , he said to make it blunt,deliberately un-aerodynamic. With blunt design you can  smash the air and get out of the way, and not cut through it.

If the nose is sharp then the heat generated due to friction at nose will also flow through the wings. As shown below from model studies it is evident that sharp nose can cause major harm to the wings of shuttle. The sharp pointed nose cuts through air and the high temperature air moves over wings which damages the wing.

Model study of shuttle having sharp nose

While the blunt nose will not have the same effect. Instead the blunt nose smash through air and avoid the high temperature air passing through wings. The model study of blunt nose is shown below.
As it is shown,the air does not pass through the wings but moves away only because of blunt nose.

Model study of blunt nose

But in order to safeguard wings, the nose has to withstand the tremendous friction of Earth's atmosphere and its high generated temperature. 
The Space Shuttle design presented many thermal insulation
challenges. The system not only had to perform well, it had to integrate with other subsystems. The Orbiter’s surfaces were exposed to exceedingly high temperatures and needed reusable, lightweight,low-cost thermal protection. The vehicle also required low vulnerability to orbital debris and minimal thermal conductivity. NASA decided to bond the Orbiter’s thermal protection directly to its aluminum skin, which presented an additional challenge.
The External Tank required insulation to maintain the cryogenic fuels, liquid hydrogen, and liquid oxygen as well as to provide additional structural integrity through launch and after release from the Orbiter.

  

Image credit: NASA

During re-entry, the Orbiter’s external surface reached extreme temperature up to 1,648°C (3,000°F). The Thermal

Protection System was designed to provide a smooth, aerodynamic surface while protecting the underlying metal structure from excessive temperature.The loads endured by the system
included launch acoustics, aerodynamic loading and associated structural deflections, and on-orbit temperature variations as well as natural environments such as salt fog, wind, and rain. In addition, the Thermal Protection System had to resist pyrotechnic shock loads as the Orbiter separated from the External Tank (ET).

  

Image credit: NASA

NASA used rigid silica tiles or fibrous insulation. Fibrous Refractory Composite Insulation tiles helped reduce the overall weight and later replaced the LI-2200 tiles used around door penetrations. Alumnia Enhanced Thermal Barrier was used in areas in which small particles would damage fragile tiles. As part of the post-Columbia Return to Flight effort, engineers developed Boeing Rigidized Insulation. Overall, the major improvements included reduced weight, decreased vulnerability to orbital debris, and minimal thermal conductivity.  Orbiter tiles were bonded using strain isolation pads and room-temperature vulcanizing silicone adhesives. The inner mold line of the tile was densified prior to the strain isolation pad bond, which aided in the uniform distribution of the stress concentration loads at the tile-to-strain isolation pad interface. The structure beneath the tile-to-tile gaps was protected by filler bar that prevented gas flow from penetrating into the tile bond line. NASA used gap fillers (prevented hot air intrusion and

tile-to-tile contact) in areas of high differential pressures, extreme   aero-acoustic excitations and to passivate over-tolerance step and gap conditions. The structure used for the bonding surface was, for the most part, aluminum; however, several other substrates used included graphite epoxy, beryllium, and titanium.

SPACE SHUTTLE FACTS :

• The Space shuttle retired in  2011 so that NASA could concentrate on cheaper methods for space exploration that includes exploring outside of our solar system.

• There have been six space shuttles which were named Enterprise, Columbia, Challenger, Discovery,  Endeavour and Atlantis.

• All space shuttles launched from the Kennedy Space Center in Florida.

• The Challenger and Columbia were both destroyed in accidents where a total of 14 astronauts lost their lives.

• Before a space shuttle could launch weather conditions such as precipitation, lightning, wind, and humidity were strongly considered.

• Space shuttles were not equipped with software that could handle a year change while in orbit so missions never took place between December and January.

• Although over 600 astronauts have flown to outer space on the space shuttle, only about seven can fly out at one time.

• Most of the launches were preferred during day time. The first space shuttle test flight took place in 1981. The space shuttle completed 135 missions.

• Discovery flew 39 space missions during operational life,the first in 1984 and the last one in 2011. It noticed more space flights than any other space shuttle.

• Discovery launched Hubble space telescope on shutle's STS(Space Transportation System)-31 mission in April 1990. 

Footnotes: Special thanks to GIF's sources,NASA and Google images