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with the link in the description After spending 7 days in orbit around the
earth, the Space Shuttle Orbiter now has arguably the most difficult portion of
its mission to complete. A hell blazing journey through the earth’s upper atmosphere.
Where it will travel so fast that it will rip air molecules apart, forming a layer of
superheated plasma around the aircraft. Re-Entry is where the Space Shuttle
truly became a one of a kind spacecraft. The Space Shuttle was a radical
new idea. A spacecraft capable of not only surviving the immense heat of
re-entry, but capable of transitioning to aerodynamic flight, which required
careful moulding of its wings and tail, balancing the needs of unpowered glider
with the needs of a re-entry vehicle This is the Insane Engineering of the Re-Entry The Re-entry procedure begins with a 2-4 minute
burn of the orbital manoeuvring system engines while the space shuttle is upside
down and travelling backwards. With an orbital speed of around 7 kilometres
per second, the OMS pods need to reduce the orbiter's speed by just 0.1 kilometre per
second. 1.3% of its velocity, to lower its orbit enough to bring it into a collision
course with the earth’s upper atmosphere. A precise manoeuvre; bleed too little
speed and the orbiter will overshoot its narrow window for success, skimming through
the thin upper atmosphere and potentially bouncing back into space. The orbiter
has wings that generate lift, after all. Bleed too much speed and the orbiter will
descend through the atmosphere too fast, reaching the thick lower atmosphere
before enough speed has been leached away, resulting in catastrophic overheating. This narrow
entry window was called the entry flight corridor. Once the delicate retrofiring sequence has
been completed. The next phase of re-entry begins. The reaction control system flips
the shuttle around and places it into a 40 degree upwards pitch angle, ready
to meet the earth’s atmosphere. [REF] Entering the upper atmosphere at 30 times the
speed of sound. The speed is so great that it begins to rip air molecules apart, creating a
glowing cloud of charged plasma around the lower surface of the orbiter. With peak temperatures
reaching 1650 degree celsius (3000 F). Nothing like this had ever been attempted.
A blunt body capsule, like every other re-entry capsule to date, designed purely for
thermal protection is an engineering challenge, but tack on the needs of an aircraft
and the task gets vastly more difficult. Thankfully NASA had a test run in 1959
with the X-15. The fastest plane in the history of humankind, and it advanced
our understanding of hypersonic flight, providing many lessons that were
incorporated into the space shuttles design. However the X-15 had one major advantage over the
Space Shuttle. It didn’t need to launch itself to orbit. It didn’t even launch from the ground.
Instead launching from the belly of a B-52. This allowed the X-15 to use a state of the
art advanced heat resistant aerospace metal, inconel X, with a max operating temperature of 980 degrees celsius (1800 F). The Space
Shuttle could not use this metal. Inconel X is too heavy, about 180%
heavier than an equivalent aluminium airframe. A massive issue for an aircraft
designed to be carried to orbit. [REF] The Space Shuttle’s airframe therefore is not
made from inconel X. It is composed of lightweight aluminium, which has a max operating temperature
of just 177 degrees. 5 times lower than Inconel X. The orbiter would experience temperatures 10 times greater than this for extended
periods of its re-entry flight. To make matters worse, one of the
principle lessons learned during the X-15 program was that the hot pink foam
ablative coating sprayed onto the plane for top speed flights was completely
unsuitable for the space shuttle. An ablative coating is a sacrificial
material designed to gradually burn and fall away from the aircraft,
pulling the heat away with it. However, the ablative coating of the X-15 had a
nasty habit of burning away from the nose of the plane, and begin attaching itself to the cockpit
windows, rendering the pilots completely blind. Which presented a bit of a problem. At one
point the engineers of the X-15 considered attaching a small explosive to the window, and
intentionally exploding the outer pane of glass to remove the ablative stained window,
leaving only the inner pane for landing. Thankfully they came up with the much less
risky solution of installing a mechanical eyelid to the left window that remained
closed until the high speed portion of the flight concluded. Providing the pilot
one clean window to land with. An extremely primitive solution that created stability
issues as the open eyelid acted like a canard, causing the plane to pitch
up, roll right and yaw right. Even more terrifyingly, this coating
became explosive when mixed with liquid oxygen and could be triggered by even a
slight impact. A massive safety concern for a plane that required a liquid oxygen
oxidizer to operate. A danger that would be multiplied many fold with a vehicle filled
with half a million litres of liquid oxygen. The ablative was also not reusable, which
would drastically increase the cost of refurbishing the shuttle between flights.The
space shuttle would need to be better. As the space shuttle descended
through the atmosphere its nose and wings bore the brunt of the re-entry heat. The high pressure shock waves forming around
them have created a layer of superheated plasma, if this heat managed to find its way into the
delicate aluminium framework inside the orbiter, it would be game over. This is exactly
what happened to the Columbia shuttle as a result of damage to the
leading edge of these wings. The first step to protect the
orbiter's surface was to keep this super heated plasma as far away
from the surface as possible. The nose, wings and belly of the orbiter was carefully
crafted to ensure shockwaves were kept at bay. We can see how using schlieren imaging.
A pointed missile-like vehicle pierces through the air with efficiency and
in doing so creates a shock wave, attached to its nose at an angle
determined by its mach number. This shockwave is simply a region
of incredibly high pressure, and with that pressure comes
incredibly high temperatures This can have disastrous effects, as DARPA
experienced twice in 2010 and 2011 when testing their sharp nosed hypersonic
reentry vehicle. The HTV-2. Within 9 minutes of re-entering earth's atmosphere,
both vehicles disintegrated as a result of the 1930 degree heat penetrating their
metallic skin. The HTV-2 completed its mission of collecting hypersonic flight
data, but the space shuttle needed to not only survive this mode of flight, but to
do it repeatedly with minimal refurbishment. A good portion of this heat could be
kept away from the aircraft skin with blunt body design.Which creates a rounded
bow shock wave with a layer of insulating lower pressure air between the vehicle and
the shockwave. Reducing heat transfer rates. For this reason the Space Shuttles surface is
carefully moulded to take advantage of this phenomenon. The rounded nose cross section
gradually transitions to a blunted triangle. This shape minimised the heat reaching the
less protected side wall of the shuttle, which used lower temperature insulation. We are now 7 minutes into the re-entry procedure,
having descended 50 kilometres in altitude, but only shedding 0.5 kilometres per second
off our velocity, we have entered the period of maximum reentry heat. A confluence
of speed and atmospheric density. The layer of superheated plasma surrounding
the shuttle is blocking communication to the computers and astronauts inside. A result
of free electrons in the plasma interfering with electromagnetic communication techniques. A
problem that would last for the next 12 minutes. For now the shuttle is operating on its own
telemetry data. Ensuring that a 40 degree angle of attack is maintained. Managing that angle with
a velocity of 6.5 kilometres per second was no easy task. A massive control surface was needed.
The elevons on the outer wing would not suffice. This is where the rear body flap came into
play. It was a massive control surface underneath the shuttle's main engines,
covered in high temperature insulation. The body flap doubled as a
heat shield for the shuttles main engines. With no cooling liquid
hydrogen running through the nozzle, the flap was needed to shield the
engines from the heat of re-entry. On the Space Shuttle’s third flight the Kuiper
Airborne Observatory flew underneath the orbiter as it re-entered and captured an infrared image of
its searing hot belly. An experimental program to validate NASA’s newly developed computational
calculations and experimental testing. This is what it saw [REF] The nose and leading
edges are a scorching 1500 degrees celsius. Far beyond what the Aluminium airframe
underneath is capable of enduring. These leading edges, experiencing the hottest
temperatures, needed the most heat resistant material on the entire shuttle, a reinforced
carbon-carbon composite. One of the amazing materials created in the years between the
development of the X-15 and the Space Shuttle. A carbon composite manufactured
with a special post processing step. It was initially manufactured like any
other carbon fibre part. A carbon fibre weave moulded into shape and bound
together with a resin. However, the heat of re-entry would
set the hydrocarbon resin on fire without special treatment. The post
processing step would solve this problem. The carbon composite is placed in a
vacuum chamber and heated, causing the hydrocarbon resin to decompose, releasing
the hydrogens, leaving layers of pure carbon behind. Graphite. Carbon fibres bound together
by a maze of graphite. Strong, and capable of withstanding 1510 degrees celsius. They face
head on into the inferno of hypersonic flight. The leading edge of the orbiter's wings
is composed of 22 of these carbon carbon panels. With sealing strips covering
expansion gaps between each panel, an essential solution to a lesson hard
won during the development of the X-15. To investigate the heat of hypersonic
flight the X-15 was painted with a special kind of paint that reacts to heat,
and after one flight the X-15 returned with strange wedge shaped patterns emanating
from the leading edge expansion joints. Small gaps in the leading edge to allow the
inconel skin to bend and contort with the wing without buckling. This localised heating
was happening as a result of turbulent flow, increasing the rate of heat transfer to
the metallic skin of the aircraft. To fix this small floating strips of inconel
were placed over the expansion gaps.. These strips of reinforced carbon
carbon serve the very same purpose. However, there was one more problem. Carbon is a thermally conductive material,
not ideal for a heat shield. The space shuttle has been travelling
through the atmosphere for 15 minutes, but is still travelling at 6 kilometres
per second and contact has not been reestablished through the cloud of
plasma surrounding the aircraft. This is a sustained heat, and
with carbon being conductive, this heat could make its way to the
aluminium airframe over this period of time. If these carbon carbon shields were attached
directly to the airframe the heat would come into direct contact with the metal, raising
it above its max operating temperature. To prevent this the panels were fitted with
inconel attachment points that attached to the aluminium airframe with inconel bolts.
Inconel, being mostly made of steel, is a poor conductor of heat and could handle
the heat the carbon parts transferred to it, without easily transferring
that heat to the aluminium. This wasn’t enough to protect the
interior of the shuttle however, a layer of insulating tiles were placed
underneath the carbon carbon shield too. The same insulation that was used on
the underside of the entire orbiter. The Space Shuttle Columbia had 32000 of these
tiles, in two flavours, low temperature and high temperature, white and black. Both of these
tiles were made from the same base material. Silica fibres just a few millimetres thick,
which by volume made up just 10% of the tile, the remaining 90% was nothing by air.
An excellent insulating material, a thick and light tile, composed of a
material with a high operating temperature. The coating is where the tiles differ. The black
tiles, installed on the lower portion of the shuttle, were covered in a black borosilicate
and tetraboron silicide glass coating. This black coating helps dissipate heat
before it can conduct into the vulnerable inner structure. Black for the same reason the
SR-71 is black. Kirchoff’s Rule of Radiation. This rule tells us a good infrared heat absorber, basically any black object, is also an equally
effective heat emitter. With the heat gained from hypersonic flight vastly higher than
the heat gained from solar radiation, it’s preferable to prioritise outward heat radiation,
than minimising heat gained from solar radiation. So why isn’t the entire space
shuttle black, like the SR-71? The shuttle has one important difference with the
SR-71, it exited earth’s atmosphere. Once outside the earth's atmosphere the intensity of solar
radiation increases drastically, with the longest orbiter mission at 17 days, this heat had plenty
of time to conduct through to the people inside. The orbiter did have huge radiator panels to
reject heat to space, but to minimise their size we want to reflect as much of that heat back
into space, and for that reason they are white. These tiles were coated with
a similar glass coating, but with an aluminium oxide additive
to provide the white colouring. The coatings also helped to waterproof
and strengthen these porous tiles. The tiles were assembled like a giant precisely
engineered puzzle with 32,000 pieces. Each tile assigned a serial number that corresponded
to their location, shape and thickness. The tiles were created by mixing cotton like
silica fibres with water, this mixture was then cast into large blocks, and were then
dried in a microwave oven. Once dried they could be cut into smaller sheets. [Footage]
The tiles varied from 25 millimetres to 127 millimetres thick. With the 127 millimetres
tiles insulating up 1280 degrees celsius. These sheets were then into their precise shapes, according to their assigned serial numbers,
using a computer controlled milling machine. We are now coming through the end of
the communication blackout, and enough of the heat of re-entry has reached the aluminium
airframe to cause it to expand. A major problem as these tiles are not flexible in the slightest,
and are quite fragile. The expanding airframe could easily break the tiles and open up a path
for the superheated gas to penetrate inside. The engineers needed a way
to allow the structure to move beneath the tiles without
causing the tiles to pop off. To do this, the tiles were first glued in
groups to a layer of flexible nomex felt. This nomex fabric allowed the structure beneath
to flex, expanding the lower side of the felt, without transferring that strain to
the upper layer attached to the tiles. These tiles and felt were then attached
to the shuttle using the same adhesive. A commercially available high temperature RTV
adhesive. A bright red silicone based adhesive. To prevent collisions between tiles, gaps between 0.64 millimetres and
1.9 millimetres were included. Thankfully the issue of turbulent flow created
by expansion gaps primarily affected the leading edges of the wing, so these gaps were not
covered on the exterior of the shuttle. In areas exposed to lesser temperatures flexible
heat shields were used. Constructed from high temperature silica and nomex fibres to create
a flexible fabric which were sewn together with the same fibres, giving a quilted blanket
appearance. With the nomex fabric capable of resisting temperatures up to 370 degrees and the
silica fabric capable of tolerating temperatures up to 650 degrees. These were lighter and
easier to replace than the tiles. Being bonded directly to the structure once again
with that bright red silicone RTV adhesive. We are now out of the communication black out
and approaching 4 km/s or mach 12 in velocity and are about 45 kilometres in altitude. About
4 times the cruising altitude of an airliner. The orbiter has maintained that 40
degree angle of attack this entire time. [Page 239]. Being forced to hold an
angle of attack this large comes with some control problems. The orbiter needs to
land precisely on a landing strip from orbit. Managing its trajectory while being
stuck with its nose up would be difficult. Especially for a glider with no way to add
energy once its been bled away by drag. If the Space Shuttle wanted
to lower its lift and lower its altitude faster it could
not lower its angle of attack, So the shuttle needed a special way to adjust
its trajectory to target its landing area. Instead the orbiter decreased
its lift by banking. This split the lift into vertical and horizontal
components. Reducing the lift keeping the shuttle in the air and trading
it for lift that moved it sideways. This is what a typical re-entry flight profile
looked like. This line is the angle of attack, keeping steady up until Mach 12
and then gradually reducing as it descends through the thick lower
atmosphere. And this is the bank angle. As the orbiter crashes down from
orbit, it banks wildly from side to side. The astronauts inside, who are already
pointed 40 degrees up, are not tilted on their sides up 70 degrees. The orbiter is
essentially doing the fastest drift in history. There are some quirks of flying this high
in the atmosphere at hypersonic speeds. The bank angle controls actually work in reverse
to normal. If we deflect the right elevon down, it should increase lift on the
right wing and cause that wing to rise, banking the aircraft
anti-clockwise, but it doesn’t. When the elevon is deflected downwards, into the
already compressed hypersonic air it causes drag to rise on the outer wing. This causes the
orbiter to turn its nose in that direction. As the nose turns in the direction of the
deflected elevon, it shields that wing and causes a decrease in lift, causing
the shuttle to bank in that direction. So, where a downwards deflecting elevon would
typically cause an increase in lift on the wing, here, through a series of events, it
causes a decrease. Working in reverse. Ofcourse this bank angle causes
the Orbiter to drift off target for its landing and to correct
it needs to bank the other way. The orbiter has now slowed down to Mach 3, and at this point flight crew deploy air data
sensors to aid in the final approach. [Page 418] Two probes rotate from underneath the
heat shield on either side of the nose, providing air speed, angle of attack and
temperature data to the flight computer. At this point the orbiter is flying like a
plane, but it’s not a plane, it's a glider and the flight crew needed to carefully
manage the remaining energy to land safely. Especially as the orbiter is not built like
a traditional glider. Balancing the need to survive reentry, while maximising lift efficiency
was a unique engineering challenge, made more difficult by Air Force funding causing the design
to skew closer to a plane than a re-entry vehicle. Early concepts of the shuttle
drew inspiration from the X-15, with much smaller wings. More than enough to
land the original smaller orbiter on a runway. The air force wanted a larger payload capacity, and they had one more specific requirement
that required bigger wings. They wanted the Space Shuttle to be able to take off
from Cape Canaveral, complete its mission, and land back at Cape Canaveral after
a single orbit. Essentially treating the space shuttle like a military operation
to avoid Soviet attention, fast and elusive This came with some issues. A single orbit took 90 minutes, in which
time the earth rotated below the shuttle’s orbit by 2000 kilometres. So, to return
to its launch location the orbiter would need to be capable of flying laterally by
at least 2000 kilometres. This is called crossrange. The original X-15 inspired design
was capable of just 370 kilometres of crossrange. North American Rockwell proposed this huge
blended body delta wing concept in 1970 which would have given the orbiter 2800
kilometres of crossrange (1500 nautical miles). The full reusable concept,
with its crewed booster rocket and internal fuel tanks were not to be,
but the large delta wings endured. These delta wings provided enough lift in both
hypersonic, supersonic and subsonic flight regimes to provide the cross range needed to reach
the original launch site after a single orbit. Despite that, the space shuttle was an
unwieldy aircraft, and with no powered flight, the commander had one shot to land it safely.
So they had to go through intensive training. In 1973 NASA created 4 training aircraft by
modifying 4 gulfstream jets to fly like the space shuttle. [REF] In order to mimic the
immense drag the blunt body design of the space shuttle would create, the gulfstreams flew
with their landing gear down, with their engines working in reverse, and flew with their flaps
deflected upwards to decrease lift. [Footage] With flight characteristics like this the
space shuttle needed to carefully manage its energy. Losing too much altitude far
from the runway would be far from ideal. The pilots aim, guided by beacons and
ground control, for a tangential entry into a circular approach path 5800 metres
in diameter just off the runway. The moment they intercept this circle the space
shuttle commences a deep spiralling turn. At this point the space shuttle is still
travelling at about 0.8 mach. Still very fast, and it's at this point the wings are stressed
the most. Hitting a higher max dynamic pressure than at any point during the re-entry process
due the higher air pressure at this altitude. And the shuttle's descent rate increases, now losing altitude rapidly with the knowledge
the runway is within a safe gliding distance, descending to about 3000 metres in
altitude and slowing to about 0.5 mach. At this point the Shuttle enters a straight 20 degree glide approach path.
Much steeper than any airliner. Bleeding speed as needed using the
split rudder speed brake. The rudder on the vertical tail wasn’t just used for
controlling yaw by deflecting left and right, it could split in two, deflecting outwards
to a maximum of 62 degrees on either side. The gear is lowered as late as possible
and in the final moments before touching down the commander will increase the
angle of attack of the shuttle using the elevons in order to slow its
descent rate before touching down. At the moment of main gear touch down
the speed brake is commanded to fully open. At this point the shuttle is still
travelling at 360 kilometres per hour, close to 0.3 mach, and there is
plenty of braking left to do. The runway at Cape Canaveral is 4.6 kilometres
long, much longer than your average runway. With typical 3 kilometres long runways being able to
deal with the heaviest of jumbo jets landing. As the nose gear touches down the
electro-hydraulic brakes in each of the 4 main landing gear wheels are fully engaged
by application of the foot pedals in the cockpit. Each brake assembly had nine
carbon-lined beryllium discs, four rotors, and five stators, which were
pressed together to provide braking force. On STS 49, Bruce Melnicks mission, an
additional braking mechanism was introduced, hidden away underneath the vertical tail speed
brake. The drag shoot. STS 49 was the maiden flight of both the endeavour and the drag
shoot. An explosively deployed parachute, you can even see the parachute door and sabot being
flung from the back of the shuttle on landings. It was designed to allow the Space Shuttle
to land on a shorter 2500 metre runway, a contingency plan in the event
the space shuttle had to abort a launch and land on a runway on
the other side of the atlantic. For each and every launch NASA sent staff
to these predetermined landing locations, like Fairford RAF base in Gloucestershire, England. A large team was needed to assist with
the final moments of each space shuttle mission. And these teams were not once needed in the
entire history of the space shuttle program. A giant fan was even rolled out on the runway
to help disperse any potential toxic chemicals, like the hydrazine fuel, away
from the shuttle. [FOOTAGE] The mission is now over. The crew has disembarked
and the space shuttle will be refurbished and flown back to Florida on the back of a
747 in preparation for its next mission. People often say how incredible it is that
older aerospace and aviation projects like this were designed with pen and paper. Hand
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