It wasn't just an assassination, it was a cataclysmic event that claimed 3,000 lives. At the Indira Gandhi Memorial Friday, where India's only woman prime minister lived and died 24 years ago, it may be business as usual but memories of the dark days following her killing still cast shadows in the afternoon sun.
The crowds come chattering in through the metal detector that takes them to the sprawling white bungalow in the heart of the Indian capital that Indira Gandhi had made her home -- 1 Safdarjung Road where she lived while she was information and broadcasting minister in the 1960s and during her two stints as prime minister.
It was during her second term as prime minister of the country that Indira Gandhi fell to a hail of bullets from her Sikh bodyguards as she was walking from home to office in the next bungalow on Oct 31, 1984, unleashing a frenzy of mob violence that saw an estimated 3,000 Sikhs being killed in three days in the Indian capital.
Some called them anti-Sikh riots, many others a pogrom that is still blamed on the Congress government led by Indira Gandhi's son Rajiv who was sworn in as prime minister just hours after his mother's assassination.
Twenty-four years later, the charisma of the Gandhis pulls in the crowds by the thousands everyday to the museum dedicated to Indira Gandhi and her son (who lived there for a while with his family).
Friday was no different.
From near and far, from all corners of the world and distant reaches of India they enter the museum, quite unmindful of the import of the day. They make their way through the sepia tinted photographs chronicling the heady days of Mahatma Gandhi and Jawaharlal Nehru, India's first prime minister and Indira Gandhi's father, through her book-lined study and elegant dining room, through the memorabilia that made up her life.
And a hush begins to descend.
The mustard, black bordered handloom sari she wore when she was killed is displayed, a little blotchy and with some holes, along with simple black sandals and an embroidered cloth bag.
That's where people pause to take a look. Like the young schoolboy from Mizoram who stands in a corner, perhaps taking it all in and remembering lessons learnt in textbooks.
Another turn and the visitor is face to face with the tattered remains of Rajiv Gandhi's kurta pyjama and the sneakers he was wearing when a suicide bomber killed him in Tamil Nadu in May 1991.
The chatter slowly dies down.
As visitors step out of the bungalow and walk towards the connecting bungalow - 1 Akbar Road - that was Indira Gandhi's office the conversation gets more muted.
"I think we are going towards the place she was killed," Mamta, a young girl from Pune, tells her sister and mother hesitantly.
The last walk down the pathway to her office that Gandhi took is laid with crystal, to freeze into the memory of the nation that one moment that felled her - and with her many thousands. Just short of a sentry gate, where Beant Singh and Satwant Singh stood waiting for her to gun her down, is a clear sheet of glass where she slumped to the ground.
Some walk past the spot - covered with flowers - maybe in a hurry to get home or to the next stop on their itinerary. But many stop, try to read the words of a speech inscribed in glass and suddenly realise -- hey, this is her death anniversary.
Moved by the solemnity of the occasion, a couple from Nepal bend down and touch the flowers in reverence. Seeing them, a young boy follows suit and then his mother, father and grandmother too.
Dressed in a pink silk sari with her hair covered, Indira Gandhi smiles down from a portrait. The sun filters through the trees and a gentle breeze rustles the rose petals. Perhaps someone is also mourning the deaths of the 3,000 Sikhs who died as retaliation for her.
In 1954 the United Nations General Assembly suggested that all nations should observe a Universal Children's Day as a day of worldwide fraternity and understanding between children and of activity promoting the welfare of the world's children.
The date of 20 November marks the day in 1959 when the Assembly adopted the Declaration of the Rights of the Child, and the Convention on the Rights of the Child in 1989, and is often the day chosen by countries as their own designated day to observe Universal Children's Day.
State governments are responsible for passing legislation providing a day and name appropriate for their compliance with the United Nations General Assembly resolution. United Nations Office of the High Commissioner for Human Rights / UN Committee on the Rights of the Child
In India, Children's Day is celebrated on November 14 every year. This date marks the birth anniversary of independent India’s first Prime Minister, Pandit Jawaharlal Nehru as he was very fond of children. Children's day is celebrated on this day in recognition of his lifelong passion and work for children.
NASA's Space Shuttle, officially called the Space Transportation System (STS), is the spacecraft currently used by the United States government for its human spaceflight missions. At launch, it consists of a rust-colored external tank (ET), two white, slender Solid Rocket Boosters (SRBs), and the orbiter, a winged spaceplane which is the space shuttle in the narrow sense.
The orbiter carries astronauts and payload such as satellites or space station parts into low earth orbit, into the Earth's upper atmosphere or thermosphere. Usually, five to seven crew members ride in the orbiter. The payload capacity is 22,700 kg (50,000 lb). When the orbiter's mission is complete it fires its Orbital Maneuvering System (OMS) thrusters to drop out of orbit and re-enters the lower atmosphere. During the descent and landing, the shuttle orbiter acts as a glider, and makes a completely unpowered ("dead stick") landing.
The shuttle is the first orbital spacecraft designed for partial reusability. It carries payloads to low Earth orbit, provides crew rotation for the International Space Station (ISS), and performs servicing missions. The orbiter can also recover satellites and other payloads from orbit and return them to Earth, but this capacity has not been used often. However, it has been used to return large payloads from the ISS to Earth, as the Russian Soyuz spacecraft has limited capacity for return payloads. Each Shuttle was designed for a projected lifespan of 100 launches or 10 years operational life. The man responsible for the design of the STS was Maxime Faget, who had also overseen the Mercury, Gemini and Apollo spacecraft designs. The crucial factor in the size and shape of the Shuttle Orbiter was the requirement that it be able to accommodate the largest planned commercial and classified satellites, and have the cross-range recovery range to meet classified USAF missions requirement for a one-around abort for a polar launch. Factors involved in opting for 'reusable' solid rockets and an expendable fuel tank included the desire of the Pentagon to obtain a high-capacity payload vehicle for satellite deployment, and the desire of the Nixon administration to reduce the costs of space exploration by developing a spacecraft with reusable components.
Six air-worthy shuttles have been built; the first orbiter, Enterprise, was not built for space flight, and was used only for testing purposes. Five space-worthy orbiters were built: Columbia, Challenger, Discovery, Atlantis, and Endeavour. Challenger disintegrated 73 seconds after launch in 1986, and Endeavour was built as a replacement. Columbia broke apart during re-entry in 2003.
Each Space Shuttle is a partially reusable launch system that is composed of three main assemblies: the reusable Orbiter Vehicle (OV), the expendable external tank (ET), and the two partially-reusable solid rocket boosters (SRBs). The tank and boosters are jettisoned during ascent; only the orbiter goes into orbit. The vehicle is launched vertically like a conventional rocket, and the orbiter glides to a horizontal landing, after which it is refurbished for reuse.
At times, the orbiter itself is referred to as the space shuttle. Technically, this is a misnomer, as the actual "Space Transportation System" (space shuttle) is the combination of the orbiter, the external tank (ET), and the two partially-reusable solid rocket boosters. Combined, these are referred to as the "Stack".
The orbiter resembles an aircraft with double-delta wings, swept 81° at the inner leading edge, and 45° at the outer leading edge. Its vertical stabilizer's leading edge is swept back at a 50° angle. The four elevons, mounted at the trailing edge of the wings, and the rudder/speed brake, attached at the trailing edge of the stabilizer, with the body flap, control the orbiter during descent and landing. The orbiter has a large payload bay measuring 15 feet (4.6 m) by 60 feet (18.3 m) comprising most of the fuselage.
Three Space Shuttle Main Engines (SSMEs) are mounted on the orbiter's aft fuselage in a triangular pattern. The three engines can swivel 10.5 degrees up and down, and 8.5 degrees from side to side during ascent to change the direction of their thrust and steer the shuttle as well as push. The orbiter structure is made primarily from aluminum alloy, although the engine thrust structure is made from titanium (alloy).
Solid Rocket Boosters
Two solid rocket boosters (SRBs) each provide 12.5 million Newtons (2.8 million lbf) of thrust at liftoff, which is 83% of the total thrust needed for liftoff. The SRBs are jettisoned two minutes after launch at a height of about 45.7 km (150,000 feet), and then deploy parachutes and land in the ocean to be recovered. The SRB cases are made of steel about 1.3 cm (½ inch) thick.
Early shuttle missions took along the GRiD Compass, arguably one of the first laptop computers. The Compass sold poorly, as it cost at least US$8000, but offered unmatched performance for its weight and size. NASA was one of its main customers.
The shuttle was one of the earliest craft to use a computerized fly-by-wire digital flight control system. This means no mechanical or hydraulic linkages connect the pilot's control stick to the control surfaces or reaction control system thrusters.
A primary concern with digital fly-by-wire systems is reliability. Much research went into the shuttle computer system. The shuttle uses five identical redundant IBM 32-bit general purpose computers (GPCs), model AP-101, constituting a type of embedded system. Four computers run specialized software called the Primary Avionics Software System (PASS). A fifth backup computer runs separate software called the Backup Flight System (BFS). Collectively they are called the Data Processing System (DPS).
The design goal of the shuttle's DPS is fail operational/fail safe reliability. After a single failure, the shuttle can still continue the mission. After two failures, it can still land safely.
The four general-purpose computers operate essentially in lockstep, checking each other. If one computer fails, the three functioning computers "vote" it out of the system. This isolates it from vehicle control. If a second computer of the three remaining fails, the two functioning computers vote it out. In the rare case of two out of four computers simultaneously failing (a two-two split), one group is picked at random.
Atlantis deploys landing gear before landing on a selected runway just like a common aircraft.
The Backup Flight System (BFS) is separately developed software running on the fifth computer, used only if the entire four-computer primary system fails. The BFS was created because although the four primary computers are hardware redundant, they all run the same software, so a generic software problem could crash all of them. Embedded system avionic software is developed under totally different conditions from public commercial software, the number of code lines is tiny compared to a public commercial software, changes are only made infrequently and with extensive testing, and many programming and test personnel work on the small amount of computer code. However in theory it can still fail, and the BFS exists for that contingency. And while BFS will run in parallel with PASS, to date, BFS has never been engaged to take over control from PASS during any shuttle mission.
The software for the shuttle computers is written in a high-level language called HAL/S, somewhat similar to PL/I. It is specifically designed for a real time embedded system environment.
The IBM AP-101 computers originally had about 424 kilobytes of magnetic core memory each. The CPU could process about 400,000 instructions per second. They have no hard disk drive, and load software from magnetic tape cartridges.
In 1990, the original computers were replaced with an upgraded model AP-101S, which has about 2.5 times the memory capacity (about 1 megabyte) and three times the processor speed (about 1.2 million instructions per second). The memory was changed from magnetic core to semiconductor with battery backup.
Space Shuttle program insignia
Typography and graphic design
The typeface used on the Space Shuttle Orbiter is Helvetica. On the side of the shuttle between the cockpit windows and the cargo bay doors is the name of the orbiter. Underneath the rear of the cargo bay doors is the NASA insignia, the text 'United States' and a flag of the United States. Another United States flag appears on the right wing.
During STS-101, Atlantis was the first shuttle to fly with a glass cockpit.
Internally, the shuttle remains largely similar to the original design, with the exception of the improved avionics computers. In addition to the computer upgrades, the original vector graphics monochrome cockpit displays were replaced with modern full-color, flat-panel display screens, similar to those of contemporary airliners like the Airbus A380 and Boeing 777. This is called a glass cockpit. Programmable calculators are carried as well (originally the HP-41C). With the coming of the ISS, the orbiter's internal airlocks have been replaced with external docking systems to allow for a greater amount of cargo to be stored on the shuttle's mid-deck during station resupply missions.
The Space Shuttle Main Engines (SSMEs) have had several improvements to enhance reliability and power. This explains phrases such as "Main engines throttling up to 104%." This does not mean the engines are being run over a safe limit. The 100% figure is the original specified power level. During the lengthy development program, Rocketdyne determined the engine was capable of safe reliable operation at 104% of the originally specified thrust. They could have rescaled the output number, saying in essence 104% is now 100%. To clarify this would have required revising much previous documentation and software, so the 104% number was retained. SSME upgrades are denoted as "block numbers", such as block I, block II, and block IIA. The upgrades have improved engine reliability, maintainability and performance. The 109% thrust level was finally reached in flight hardware with the Block II engines in 2001. The normal maximum throttle is 104%, with 106% and 109% available for abort emergencies.
For the first two missions, STS-1 and STS-2, the external tank was painted white to protect the insulation that covers much of the tank, but improvements and testing showed that it was not required. The weight saved by not painting the tank results in an increase in payload capability to orbit. Additional weight was saved by removing some of the internal "stringers" in the hydrogen tank that proved unnecessary. The resulting "light-weight external tank" has been used on the vast majority of shuttle missions. STS-91 saw the first flight of the "super light-weight external tank". This version of the tank is made of the 2195 aluminum-lithium alloy. It weighs 3.4 tons (7,500 lb) less than the last run of lightweight tanks. As the shuttle cannot fly unmanned, each of these improvements has been "tested" on operational flights.
The SRBs (Solid Rocket Boosters) have undergone improvements as well. Design engineers added a third O-ring seal to the joints between the segments after the Space Shuttle Challenger disaster.
The three nozzles of the Main Engine cluster with the two Orbital Maneuvering System (OMS) pods, and the vertical stabilizer above.
Several other SRB improvements were planned in order to improve performance and safety, but never came to be. These culminated in the considerably simpler, lower cost, probably safer and better performing Advanced Solid Rocket Booster. These rockets entered production in the early to mid-1990s to support the Space Station, but were later canceled to save money after the expenditure of $2.2 billion. The loss of the ASRB program resulted in the development of the Super LightWeight external Tank (SLWT), which provides some of the increased payload capability, while not providing any of the safety improvements. In addition, the Air Force developed their own much lighter single-piece SRB design using a filament-wound system, but this too was cancelled.
STS-70 was delayed in 1995, when woodpeckers bored holes in the foam insulation of Discovery's external tank. Since then, NASA has installed commercial plastic owl decoys and inflatable owl balloons which must be removed prior to launch. The delicate nature of the foam insulation has been the cause of damage to the Thermal Protection System, the tile heat shield and heat wrap of the orbiter, during recent launches. NASA remains confident that this damage, while linked to the Space Shuttle Columbia disaster on February 1, 2003, will not jeopardize the objective of NASA to complete the International Space Station (ISS) in the projected time allotted.
A cargo-only, unmanned variant of the shuttle has been variously proposed, and rejected since the 1980s. It was called the Shuttle-C, and would have traded re-usability for cargo capability, with large potential savings from reusing technology developed for the space shuttle.
On the first four shuttle missions, astronauts wore modified U.S. Air Force high-altitude full-pressure suits, which included a full-pressure helmet during ascent and descent. From the fifth flight, STS-5, until the loss of Challenger, one-piece light blue nomex flight suits and partial-pressure helmets were worn. A less-bulky, partial-pressure version of the high-altitude pressure suits with a helmet was reinstated when shuttle flights resumed in 1988. The Launch-Entry Suit ended its service life in late 1995, and was replaced by the full-pressure Advanced Crew Escape Suit (ACES), which resembles the Gemini space suit worn in the mid-1960s.
To extend the duration that orbiters can stay docked at the ISS, the Station-to-Shuttle Power Transfer System (SSPTS) was installed. The SSPTS allows these orbiters to use power provided by the ISS to preserve their consumables. The SSPTS was first used successfully on STS-118.
Space Shuttle Atlantis transported by a Boeing 747 Shuttle Carrier Aircraft (SCA), 1998 (NASA).
Space Shuttle Endeavour being transported by a Boeing 747.
Space Shuttle Orbiter and Soyuz-TM (drawn to scale).
An overhead view of Atlantis as it sits atop the Mobile Launcher Platform (MLP) before STS-79. Two Tail Service Masts (TSMs) to either side of the orbiter's tail provide umbilical connections for propellant loading and electrical power.
Water is released onto the mobile launcher platform on Launch Pad 39A at the start of a rare sound suppression system test in 2004. During launch, 300,000 US gallons (1,100 m³) are poured onto the pad in only 41 seconds.
Main engines: Three Rocketdyne Block IIA SSMEs, each with a sea level thrust of 1.75 meganewtons (MN) (393,800 pounds-force (lbf))
Maximum payload: 25,061 kilograms (55,250 lb)
Payload bay dimensions: 4.6 m (15 ft) by 18 m (59 ft)
Operational altitude: 100 to 520 nmi (185 to 960 km)
Speed: 7,743 m/s (27,875 km/h, 25,404 ft/s, 17,321 mi/h)
Crossrange: 2,009 km (1,085 nmi)
Crew: Varies. The earliest shuttle flights had the minimum crew of two; many later missions a crew of five. Today, typically seven people fly (commander, pilot, several mission specialists, and rarely a flight engineer). On two occasions, eight astronauts have flown (STS-61-A, STS-71). Eleven people could be accommodated in an emergency mission (see STS-3xx).
External tank specifications (for SLWT)
Length: 46.9 m (153.8 ft)
Diameter: 8.4 m (27.6 ft)
Propellant volume: 2,025 m³ (535,000 US gal)
Empty weight: 26,535 kg (58,500 lb)
Gross liftoff weight: 756,000 kg (1,667,000 lb)
Solid Rocket Booster specifications
Length: 45.6 m (149.6 ft)
Diameter: 3.7 m (12.14 ft)
Empty weight (per booster): 63,272 kg (139,491 lb)
Gross liftoff weight (per booster): 590,000 kg (1.3 million lb)
Thrust (sea level, liftoff): 12.5 MN (2.8 million lbf)
System Stack specifications
Height: 56 m (183.7 ft)
Gross liftoff weight: 2 million kg (4.5 million lb)
Total liftoff thrust: 30.16 MN (6.781 million lbf)
All Space Shuttle missions are launched from Kennedy Space Center (KSC). The shuttle will not be launched under conditions where it could be struck by lightning. Aircraft are often struck by lightning with no adverse effects because the electricity of the strike is dissipated through its conductive structure and the aircraft is not electrically grounded. Like most jet airliners, the shuttle is mainly constructed of conductive aluminum, which would normally shield and protect the internal systems. However, upon takeoff the shuttle sends out a long exhaust plume as it ascends, and this plume can trigger lightning by providing a current path to ground. The NASA Anvil Rule for a shuttle launch states an anvil cloud cannot appear within a distance of 10 nautical miles. The Shuttle Launch Weather Officer will monitor conditions until the final decision to scrub a launch is announced. In addition, the weather conditions must be acceptable at one of the Transatlantic Abort Landing sites (One of several Space Shuttle abort modes) to launch. While the shuttle might safely endure a lightning strike, a similar strike caused problems on Apollo 12, so for safety NASA chooses not to launch the shuttle if lightning is possible (NPR8715.5).
The Shuttle has not been launched if its flight will take it from one year to the next (December to January), a year-end rollover (YERO). Its flight software, designed in the 1970s, was not designed for this, and would require the orbiter's computers be reset through a change of year, which could cause a glitch while in orbit. In 2007, NASA engineers devised a solution to this, allowing Shuttle flights to cross the year-end boundary.
On the day of a launch, after the final hold in the countdown at T minus 9 minutes, the Shuttle goes through its final preparations for launch, and the countdown is automatically controlled by a special computer program at the Launch Control Center. This is known as the Ground Launch Sequencer (GLS), which stops the count if it senses a critical problem with any of the Shuttle's on-board systems. The GLS hands off the count to the Shuttle's on-board computers at T minus 31 seconds, in a process called auto sequence start.
At T minus 16 seconds, the massive sound suppression system (SPS) begins to drench the Mobile Launcher Platform (MLP) and SRB trenches with 300,000 U.S. gallons (1,100 m³) of water to protect the Orbiter from damage by acoustical energy and rocket exhaust reflected from the flame trench and MLP during liftoff.
At T-minus 10 seconds, hydrogen igniters are activated under each engine bell to quell the stagnant gas inside the cones before ignition. Failure to burn these gases can trip the onboard sensors and create the possibility of an overpressure and explosion of the vehicle during the firing phase. The main engine turbopumps are also commanded to begin charging the combustion chambers with liquid hydrogen and liquid oxygen at this time. The computers reciprocate this action by allowing the redundant computer systems to begin the firing phase.
The three Space Shuttle Main Engines (SSMEs) start at T minus 6.6 seconds. The main engines ignite sequentially via the shuttle's general purpose computers (GPCs) at 120 millisecond intervals. The GPCs require that the engines reach 90% of their rated performance to complete the final gimbal of the main engine nozzles to liftoff configuration. When the SSMEs start, the water from the sound suppression system flashes into a large volume of steam that shoots southward. All three SSMEs must reach the required 100% thrust within three seconds, otherwise the onboard computers will initiate an RSLS abort. If the onboard computers verify normal thrust buildup, at T minus 0 seconds, the SRBs are ignited. At this point the vehicle is committed to takeoff, as the SRBs cannot be turned off once ignited. After the SRBs reach a stable thrust ratio, pyrotechnic nuts are detonated by radio controlled signals from the shuttle's GPC's to release the vehicle. The plume from the solid rockets exits the flame trench in a northward direction at near the speed of sound, often causing a rippling of shockwaves along the actual flame and smoke contrails. At ignition, the GPC's mandate the firing sequences via the Master Events Controller, a computer program integrated with the shuttle's four redundant computer systems. There are extensive emergency procedures (abort modes) to handle various failure scenarios during ascent. Many of these concern SSME failures, since that is the most complex and highly stressed component. After the Challenger disaster, there were extensive upgrades to the abort modes.
Shuttle launch of Atlantis at sunset in 2001. The sun is behind the camera, and the plume's shadow intersects the moon across the sky.
STS mission profile
SSLV at Mach 2.46 and 66,000 feet (20,000 m). The surface of the vehicle is colored by the pressure coefficient, and the gray contours represent the density of the surrounding air, as calculated using the OVERFLOW codes.
After the main engines start, but while the solid rocket boosters are still clamped to the pad, the offset thrust from the Shuttle's three main engines causes the entire launch stack (boosters, tank and shuttle) to pitch down about 2 m at cockpit level. This motion is called the "nod", or "twang" in NASA jargon. As the boosters flex back into their original shape, the launch stack pitches slowly back upright. This takes approximately six seconds. At the point when it is perfectly vertical, the boosters ignite and the launch commences.
Shortly after clearing the tower the Shuttle begins a roll and pitch program to set its orbital inclination and so that the vehicle is below the external tank and SRBs, with wings level. The vehicle climbs in a progressively flattening arc, accelerating as the weight of the SRBs and main tank decrease. To achieve low orbit requires much more horizontal than vertical acceleration. This is not visually obvious, since the vehicle rises vertically and is out of sight for most of the horizontal acceleration. The near circular orbital velocity at the 380 km (236 statute miles) altitude of the International Space Station is 7.68 kilometers per second (27,650 km/h, 17,180 mph), roughly equivalent to Mach 23 at sea level. As the International Space Station orbits at an inclination of 51.6 degrees, the Shuttle has to set its inclination to the same value to rendezvous with the station.
Around a point called Max Q, where the aerodynamic forces are at their maximum, the main engines are temporarily throttled back to avoid overspeeding and hence overstressing the Shuttle, particularly in vulnerable areas such as the wings. At this point, a phenomenon known as the Prandtl-Glauert singularity occurs, where condensation clouds form during the vehicle's transition to supersonic speed.
126 seconds after launch, explosive bolts release the SRBs and small separation rockets push them laterally away from the vehicle. The SRBs parachute back to the ocean to be reused. The Shuttle then begins accelerating to orbit on the Space Shuttle main engines. The vehicle at that point in the flight has a thrust-to-weight ratio of less than one – the main engines actually have insufficient thrust to exceed the force of gravity, and the vertical speed given to it by the SRBs temporarily decreases. However, as the burn continues, the weight of the propellant decreases and the thrust-to-weight ratio exceeds 1 again and the ever-lighter vehicle then continues to accelerate toward orbit.
The vehicle continues to climb and takes on a somewhat nose-up angle to the horizon – it uses the main engines to gain and then maintain altitude while it accelerates horizontally towards orbit. At about five and three-quarter minutes into ascent, the orbiter rolls heads up to switch communication links from ground stations to Tracking and Data Relay Satellites.
Finally, in the last tens of seconds of the main engine burn, the mass of the vehicle is low enough that the engines must be throttled back to limit vehicle acceleration to 3 g (30 m/s²), largely for astronaut comfort.
The main engines are shut down before complete depletion of propellant, as running dry would destroy the engines. The oxygen supply is terminated before the hydrogen supply, as the SSMEs react unfavorably to other shutdown modes. Liquid oxygen has a tendency to react violently, and supports combustion when it encounters hot engine metal. The external tank is released by firing explosive bolts and falls, largely burning up in the atmosphere, though some fragments fall into the Indian Ocean. The sealing action of the tank plumbing and lack of pressure relief systems on the external tank helps it break up in the lower atmosphere. After the foam burns away during reentry, the heat causes a pressure buildup in the remaining liquid oxygen and hydrogen until the tank explodes. This ensures that any pieces that fall back to Earth are small.
To prevent the shuttle from following the external tank back into the lower atmosphere, the Orbital maneuvering system (OMS) engines are fired to raise the perigee higher into the upper atmosphere. On some missions (e.g., missions to the ISS), the OMS engines are also used while the main engines are still firing. The reason for putting the orbiter on a path that brings it back to Earth is not just for external tank disposal. It is one of safety; if the OMS malfunctions, or the cargo bay doors cannot open for some reason, the shuttle is already on a path to return to earth for an emergency abort landing.
Re-entry and landing
Simulation of the outside of the Shuttle as it heats up to over 1,500 °C during re-entry.
Two space shuttles sit at launch pads. This particular occasion is due to the final Hubble servicing mission, where the International Space Station is unreachable, necessitating having a shuttle on standby for a possible rescue mission.
A space shuttle model undergoes a wind tunnel test in 1975. This test is simulating the ionized gasses that surround a shuttle as it reenters the atmosphere.
Almost the entire space shuttle re-entry, except for lowering the landing gear and deploying the air data probes, is normally performed under computer control. However, the re-entry can be flown entirely manually if an emergency arises. The approach and landing phase can be controlled by the autopilot, but is usually hand flown.
The vehicle begins re-entry by firing the Orbital maneuvering system engines, while flying upside down, backside first, in the opposite direction to orbital motion for approximately three minutes, which reduces the shuttle's velocity by about 200 mph (90 m/s). The resultant slowing of the Shuttle lowers its orbital perigee down into the upper atmosphere. The shuttle then flips over, by pulling its nose up (which is actually "down" because it's flying upside down). This OMS firing is done roughly halfway around the globe from the landing site.
The vehicle starts encountering more significant air density in the lower thermosphere at about 400,000 ft (120 km), at around Mach 25 (8.2 km/s). The vehicle is controlled by a combination of RCS thrusters and control surfaces, to fly at a 40 degree nose-up attitude, producing high drag, not only to slow it down to landing speed, but also to reduce reentry heating. In addition, the vehicle needs to bleed off extra speed before reaching the landing site. This is achieved by performing s-curves at up to a 70 degree roll angle.
The orbiter's maximum glide ratio/lift-to-drag ratio varies considerably with speed, ranging from 1:1 at hypersonic speeds, 2:1 at supersonic speeds and reaching 4.5:1 at subsonic speeds during approach and landing.
In the lower atmosphere, the orbiter flies much like a conventional glider, except for a much higher descent rate, over 10,000 feet per minute (50 m/s).
At approximately Mach 3, two air data probes, located on the left and right sides of the orbiter's forward lower fuselage, are deployed to sense air pressure related to the vehicle's movement in the atmosphere.
Columbia touches down at Kennedy Space Center at the end of STS-73.
When the approach and landing phase begins, the orbiter is at a 3,000 m (10,000 ft) altitude, 12 km (7.5 miles) from the runway. The pilots apply aerodynamic braking to help slow down the vehicle. The orbiter's speed is reduced from 682 km/h (424 mph) to approximately 346 km/h (215 mph), (compared to 260 km/h (160 mph) for a jet airliner), at touch-down. The landing gear is deployed while the Orbiter is flying at 430 km/h (267 mph). To assist the speed brakes, a 12 m (40 ft) drag chute is deployed either after main gear or nose gear touchdown (depending on selected chute deploy mode) at about 343 km/h (213 mph). The chute is jettisoned once the orbiter slows to 110 km/h (69 mph).
After landing, the vehicle stands on the runway for several minutes to permit the fumes from poisonous hydrazine, used as a propellant for attitude control, to dissipate, and for the shuttle fuselage to cool before the astronauts disembark.
Conditions permitting, the space shuttle will always land at Kennedy Space Center; however, if the conditions make landing there unfavorable, the shuttle can touch down at Edwards Air Force Base in California or at other sites around the world. A landing at Edwards means that the shuttle must be mated to the Shuttle Carrier Aircraft, and returned to Cape Canaveral, costing NASA an additional 1.7 million dollars. Space Shuttle Columbia (STS-3) also landed once at the White Sands Space Harbor in New Mexico, but this is often a last resort, as NASA scientists believe that the sand could cause damage to the shuttle's exterior.
A computer simulation of high velocity air flow around the space shuttle during re-entry.
A list of other landing sites:
Elmendorf Air Force Base, Alaska
White Sands Space Harbor, New Mexico (actual landing site for STS-3)
MCAS Yuma/Yuma International Airport, Arizona
Plattsburgh Air Force Base, New York (Former site; now closed)
Ben Guerir Air Base, Morocco
Morón Air Base, Spain
Banjul International Airport (Yundum), The Gambia
Zaragoza Air Base, Spain
Diosdado Macapagal International Airport, The Philippines (When it was still under U.S. Air Force Control)
Kuala Lumpur International Airport, Malaysia
RAAF Base Amberley, Australia
Andersen AFB, Guam
Amilcar Cabral International Airport, Cape Verde
Hickam AFB, Hawaii
Stockholm-Arlanda Airport, Sweden
Istres AB, France
Bangor International Airport, Maine
Salina Municipal Airport, Kansas
Westover Air Reserve Base, Massachusetts
Gander International Airport, Canada
Shannon International Airport, Ireland
A list of launch abort sites:
Atlantic City International Airport, Atlantic City, New Jersey, USA
RAAF Base Darwin, Darwin Australia
Myrtle Beach International Airport, South Carolina, USA
Dyess Air Force Base, Texas, USA
Marine Corps Air Station Cherry Point, North Carolina, USA
Ellsworth Air Force Base, South Dakota, USA
Naval Air Station Oceana, Virginia Beach, Virginia, USA
Esenboğa International Airport, Ankara, Turkey
Dover Air Force Base, Delaware, USA
Fort Wayne International Airport (Air Guard Station), Fort Wayne, Indiana, USA
International Airport of Gran Canaria-Gando, Gran Canaria (Las Palmas), Canary Islands, Spain
Otis Air National Guard Base, Massachusetts, USA
Grant County International Airport, Washington, USA
Pease ANGB, New Hampshire, USA
Hao Airport, French Polynesia
AFB Hoedspruit, South Africa
Bermuda International Airport (former NAS Bermuda)
King Khalid International Airport, Riyadh, Saudi Arabia
Kinshasa International Airport, Congo-Kinshasa
Cologne Bonn Airport, Germany
Lajes Field, Azores, Portugal
Lincoln Airport, Nebraska, USA
Mountain Home Air Force Base, Idaho, USA
Naval Air Station Bermuda, Bahamas
NSA Souda Bay, Crete, Greece
NSF Diego Garcia, Chagos Archipelago, British Indian Ocean Territory
Orlando International Airport, Florida
RAF Fairford, United Kingdom
Roberts International Airport, Monrovia, Liberia
Lehigh Valley International Airport, Allentown, PA
Mataveri International Airport, Hanga Roa, Easter Island, Chile
Halifax International Airport, Halifax, Nova Scotia, Canada
* Prefer the familiar word/s rather than the far-fetched one/s
* Prefer the concrete word to the abstract.
* Prefer the single word to the circumlocution (the use of unnecessarily wordy and indirect language).
* Prefer the short to the long.
Let’s look at a few examples. In the first case use simple words — Seema did not attend her French class because she was so caught up in the cultural ethos of the superlative progamme that was being aired on the television.
It is best to say: Seema did not attend her French class because she was watching an interesting progamme on television.
The second rule warns against composing sentences like, "The signs of the times all point to the absolute necessity of the modification of the current system of administration."
It is much better to say: It is now becoming clear that the administrative system needs modification.
The third rule says don’t use unnecessarily wordy language. For example don’t say: Students made so many mistakes because of the sheer cramped conditions in which they sat and the next to no ventilation the darkened rooms gave them.
Better to say — Students made mistakes because of the cramped way in which they sat as well as poor ventilation and bad light.
The last rule says use the short word. For example don’t say — After eating all that rich food I had a case of reverse peristalsis. It is better to say: After eating all that rich food I vomited.
The above rules are mere guidelines to show you that writing can be uncluttered yet expressive!