MISSION SPACECRAFT
Tathagat Nawadia
Overview
Aerospace engineering is the branch of engineering behind the design, construction and science of aircraft and spacecraft. It is broken into two major and overlapping branches: aeronautical engineering and astronautical engineering. The former deals with craft that stay within Earth's atmosphere, and the latter deals with craft that operates outside of Earth's atmosphere.
Space Shuttle, spacecraft designed for transporting humans and cargo to and from orbit around Earth. The United States National Aeronautics and Space Administration (NASA) developed the shuttle in the 1970s to serve as a reusable rocket and spacecraft. This objective differed significantly from that of previous space programs in which the launch and space vehicles could be used only once. After ten years of preparation, the first space shuttle, Columbia, was launched on April 12, 1981. Today NASA has three space shuttles: Discovery, acquired in 1983; Atlantis, which arrived in 1985; and Endeavour, which joined the fleet in 1991. The Union of Soviet Socialist Republics (USSR) started a shuttle program in 1988 with the Buran space shuttle, but the program was halted in 1993.
The space shuttle was initially used to deploy satellites in orbit; to carry scientific experiments such as Spacelab, a modular arrangement of experiments installed in the shuttle's cargo bay; and to carry out military missions. As the program matured, the space shuttle was also used to service and repair orbiting satellites, to retrieve and return to Earth previously deployed spacecraft, and to help build and maintain the International Space Station.
The space shuttle carries a wide range of equipment, known as the payload, into space, ranging from communication, military, and astronomical satellites; space experiments for studying the apparent weightlessness (called microgravity) experienced aboard a shuttle flight; and human experimental facilities. Often, NASA collaborates with other countries by allowing them to use shuttle cargo space for special projects.
Contents
1.) Space Shuttle
1.1) Crew
1.2) Components of space mission
1.3) Orbiter Vehicle (OV)
1.3.1) Remote manipulator system (RMS)
1.3.2) Thermal protection system or (TPS)
1.3.3) Landing in earth’s atmosphere
1.3.3.1) Challenges during landing
1.3.3.2) Heating by the Plasma
1.3.3.3) Process of Reentry
1.3.4) Reaction control systems (RCS)
1.3.5) Pressurized cabin
1.3.6) Propulsion
1.3.6.1) Physics involved
1.3.6.2) SRBs (SOLID ROCKET BOOSTERS)
1.3.6.3) SSMEs (SPACE SHUTTLE MAIN ENGINE)
1.3.6.4) OMS (ORBITAL MANEUVERING SYSTEMS)
1.3.6.5) EFT (EXTERNAL FUEL TANK)
1.3.7) Hydraulic Systems
1.3.8) Reason for the space shuttle to remain stable earth’s orbit
1.3.9) Docking
2.) Space Events
3.) Living in Space
3.1) Challenges
3.2) Solutions
3.3) Space suits
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| 1. | )Space Shuttle |
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The space shuttle is designed to leave Earth as a vertically launched rocket weighing up to 2.0 million kg (4.5 million lb) with 3 million kg (7 million lb) of thrust from its multiple propulsion systems. The orbiter segment returns from space—withstanding the intense heat when entering Earth's atmosphere. Flown by the shuttle crew much like an aircraft, the shuttle lands horizontally on a conventional airport runway.
1.1) Crew
The crew of the shuttle is an integral part of the system and is critical to the success of each mission. The flight crew is led by the commander and backed up by the pilot—both are professional astronauts and proven pilots with extensive space systems and operations training. Their primary responsibility is to fly the shuttle as a launch vehicle, spacecraft, and aircraft.
The remaining crew members—up to five more people—are responsible for the unique aspects of a particular space mission. The mission specialist is the lead astronaut and ensures that the mission meets all the objectives. Payload specialists are experts in that mission's objectives and cargo, which are usually space experiments or artificial satellites. Often the payload specialists are astronauts from other countries on board to help with a project in which their country has an interest.
1.2) Components of an space mission
The space-shuttle system, called the Space Transportation System (STS), remains the most technologically advanced and complex machine in the world. It consists of the orbiter, propulsion systems—two solid rocket boosters (SRBs) and three main engines—and an external fuel tank.
1.3) Orbiter
The orbiter is a reusable winged "space-plane", a mixture of rockets, spacecraft, and aircraft. This space-plane can carry crews and payloads into Earth orbit, perform on-orbit operations, then re-enter the atmosphere and land as a glider, returning her crew and any on-board payload to the Earth. A total of six Orbiters were built for flight: Atlantis, Challenger, Columbia, Discovery, Endeavour and Enterprise all made by the Rockwell International Company . Challenger was destroyed in an accident after launch. Endeavour was built as Challenger's replacement, and was first launched in 1992. In 2003, Columbia was destroyed during re-entry , leaving just three remaining Orbiters. Two were to be used for the last time in flights during 2010, Atlantis in May, Discovery in November. Endeavour is scheduled to make its final flight in January 2011. The orbiter structure is made primarily from aluminum alloy, although the engine thrust structure is made from titanium alloy. The windows are made of aluminum silicate glass and fused silica glass, and comprise an internal pressure pane, a 1.3-inch-thick (33 mm) optical pane, and an external thermal pane.
An orbiter has three sections
(i) Flight deck-commander and pilot control the whole craft and are surrounded by switches computer and controls. In a seven member crew 2 astronauts are positioned just behind the pilot and commander to control the craft in case of emergency. The other three astronauts are positioned in the mid deck
(ii) Mid deck-It is below flight deck. The galley, toilet, sleep stations, and storage and experiment lockers are found in the mid-deck. Also located in the mid-deck are the side hatches for passage to and from the vehicle before and after landing. Simplified Aid for EVA Rescue, or SAFER, are units strap on an astronaut's back over the space suit and allow an astronaut to move about in space without being tethered to the shuttle or to facilate them to space walk.
(iii) Utility area-it has air and water tanks. Cargo bay carries satellites, spacecraft, and scientific laboratories. It also is a workstation for astronauts to repair satellites, a foundation from which to erect space structures, and a storage area for satellites retrieved from space to be returned to Earth.
1.3.1) Remote manipulator system (RMS)
It was developed and funded by the Canadian government is a robotic arm of 15m and run along the cargo bay area. The RMS can move anything from satellites to astronauts to and from the cargo bay or to different points in nearby space. It is also known as Canadarm.
1.3.2) Thermal protection system or (TPS)
The orbiter's aluminum structure cannot withstand temperatures over 175 °C (350 °F) without structural failure. Aerodynamic heating during reentry would push the temperature well above this level in areas, so an effective insulator is needed.
Thermal tile insulation and larger flexible sheets of insulating material. Cover the underbelly, bottom of the wings, and other heat-bearing surfaces of the orbiter and protect it during its fiery reentry into Earth's atmosphere. Now asbestos is used for better insulation. In space even small sand like particle can damage the metallic body of the craft. Withstands -250 °F cold space and 3000 °F heat of reentry.
.the shuttle's silicate fiber tiles were designed to be used for 100 missions before requiring replacement so as to sustain the heat when the craft reenters the earth’s atmosphere. These tiles are incredibly lightweight and dissipate heat so quickly that a white-hot tile with a temperature of 1260°C (2300°F) can be taken from an oven and held in bare hands without injury.
1.3.3) Landing in earth’s atmosphere
The shuttle faces as high temperatures of 3000°F during reentry.
There are four elevons mounted at the trailing edges of the delta wings, and the combination rudder and speed brake is attached at the trailing edge of the vertical stabilizer. These, along with a movable body flap, control the Orbiter during her later stages of descent through the atmosphere and her landing. Elevons, rudder and the delta wings are effective only in the earth’s atmosphere.
Generally the crafts land in areas that have been specially-cleared by both the Federal Aviation Administration and the Air Force. The Orbiter nearly always lands at either Edwards Air Force Base (California) or near to the Patrick Air Force Base (Florida).
1.3.3.1) Challenges during landing
In order to make a safe landing, a returning spacecraft has to lose nearly all of that orbital speed. The operation is basically a reversal of the launch phase, and this means that the returning craft must sink as much kinetic energy. Theoretically speaking, there are four fundamentally different methods of doing this:
· Powered Deceleration:
This can be achieved by rocket thrust opposed to the direction of motion. The shuttle does this at the very beginning of its re-entry, to trim the speed and so initiate the descent from orbit but it doesn’t really make a difference during reentry. In addition the craft will have to carry even more fuel.
· Energy Exchange
This ingenious braking method requires the conversion of kinetic energy into potential energy. But at present it is much beyond mechanical feasibility to attain such mechanism.
· Mass Shedding
This method is conceptually exemplified by a pilot ejecting from his damaged plane by smaller portable shuttle which ejects from the main one - most of the system's energy remains invested in the part that carries on and crashes. Though the idea works, the shuttle program's fundamental premise of orbiter re-usability precludes it. The shuttle program, though, is bound by the principle that everything that enters earth orbit comes home again.
· Energy Dissipation
This method differs from energy exchange in that the kinetic energy is progressively (and wastefully) converted to another form, such as heat, as the descent proceeds. The amount of energy that must be dissipated is very large. Stopping a one hundred tonne craft from a speed of 8 km per second in eighty minutes requires nearly 2,000 megawatts of power.
1.3.3.2) Heating by the Plasma
It's usually assumed that the mechanism of heating in re-entry is by friction i.e., viscous drag in the atmosphere. In fact this is the predominant mechanism only at lower altitudes, as air density increases.
The energy density is sufficient to cause atmospheric molecules to dissociate, and their component atoms to become ionized. The vehicle thus descends in a superheated shroud of incandescent plasma. Plasma, known as the fourth state of matter has proportionality to pressure and temperature.
The formation of the pressure wave, therefore, also creates extreme temperatures. The plasma stream is electrostatically-charged too and causes intense local heating in the acute contours of the shuttle's body.
1.3.3.3) Process of re-entry
The space has altitude of 150 kms and a total velocity of 29000 kmph. A speed trim of about 300 kmph is sufficient to initiate descent. Shedding around one percent of the momentum of a vehicle might seem like a gentle touch on the brakes, but it's a complex operation for the shuttle. Small thrusters are sufficient to alter its attitude, but a reduction of speed requires the firing of relatively large rocket motors pointing forward, opposite to the sense of travel.
Thrusters flip the orbiter right over about its pitch axis, so that its tail now points towards the earth. The main engines are then fired for about twenty seconds. The thrusters fire again in a different configuration, rotating the craft on its yaw axis. It emerges from this sequence in the descent attitude, nose forward and slightly upward, and belly facing downward. This process utilizes all available fuel on the craft. At an altitude of around 120 km, the orbiter enters a discernable atmosphere. Though still extremely rarefied (containing little oxygen), there is now enough external matter to undergo ionization, and the plasma flare begins to form. From this point, the angle of attack is critical, and is maintained at 40 degrees by automatic and continuous thruster trims. Any shallower, and the orbiter will experience excessive lift and overfly its destination. Any steeper and it will burn up. At an altitude of 85 km, the flight surfaces of the orbiter become usable. Under automatic control, a series of four S-bend turns is now performed, with the craft banking through 80 degrees at the fullest extent of the roll. The object is to lose speed more quickly.
The enclosure of plasma is never complete over the shuttle and so there is always a communication maintained with the NASA space control. When the shuttle is still at an altitude of 40 kms it has speed of 10000 kmph.
Plasma flaring has ceased, and has now been replaced by reactive hypersonic flow. Drag on the craft increases greatly, and deceleration takes place more rapidly. The pilot takes control and reduces the speed to 4000 kmph into a stable supersonic regime by using airbrakes which become effective now. With still a 40 kms range from the runway, the pilot adjusts the nose of the shuttle in a landing direction and releases the landing gears (i.e. wheels).The speed of touchdown is 350 kmph. The parachutes are released and wheel brakes are employed to lower the speed to 150 kmph and the shuttle finally comes to a halt.
1.3.4) Reaction control systems (RCS)
The Reaction Control System (RCS) is composed of 44 small liquid-fueled rocket thrusters and their very sophisticated computerized (fly-by-wire) The RCS system provides the fine-pointing control of the Orbiter by the 12 primary and two vernier RCS rockets. It is used for attitude during re-entry along the pitch, roll, and yaw axes during all of the flight phases of launching, orbiting, and re-entry. It is used for station keeping in orbit. It monitors the conservation of limited fuel in spacecraft.
1.3.5) Pressurized cabin
The whole craft is pressurized at around 1 atm. There is an airlock which depressurizes the spacesuits before a walk in space and repressurizes before the astronomer enters the craft. The airlock mechanism doesn’t allow the craft to lose pressure to the outer space while the astronauts make movements from and to the space.
1.3.6) Propulsion
1.3.6.1) Simple Physics involved in rocket propulsion systems
In Earth’s Atmosphere
In a rocket engine some type of (usually) chemical reaction spits the burned rocket fuel out of the back of the rocket. Via this chemical reaction, the rocket exerts a strong backward force on the burned rocket fuel. According to Newton's third law the required reaction is that the burned rocket fuel exerts an equal forward force on the rocket. This force accelerates the rocket forward.
Outside Earth’s Atmosphere
An object's momentum is its mass multiplied by its velocity: momentum equals mass times velocity. Momentum, like velocity, is a vector quantity. It includes direction. If an object changes the direction of its motion, its velocity and momentum both change. The law of conservation of momentum applies only to isolated systems, which have no external forces acting on them. Momentum conservation states that the total momentum of an isolated system must remain constant. If the rocket and the fuel inside the rocket is an isolated system, then the total momentum of the rocket and fuel must remain zero as the rocket launches. When the rocket ignites, violent chemical reactions in the rocket fuel thrust the burned rocket fuel out the back of the rocket at a high rate of speed. This burned rocket fuel has a large backwards momentum. However the total momentum of the rocket fuel system must be conserved and remain zero. If the burned fuel has a backwards momentum, the rocket must have an equal forward momentum. The rocket must accelerate forward to get the needed forward momentum. The backward and forward momenta add up to zero because momentum is a vector. The two momenta have opposite signs. If the forward momentum is positive, the backward momentum is negative. The equal positive and negative numbers add to zero. The rocket has a forward momentum so that the rocket and fuel system keep the zero total momentum when the burned fuel has a backward momentum. These principles apply to any rocket from a toy water rocket to the launch of the space shuttle. They also apply to more than rocket propulsion. For example, a gun recoils when fired because of the same principles.
A) SRBs (SOLID ROCKET BOOSTERS)
They are located on either side of the rusty or orange-colored external propellant tank. The two SRBs, with their combined thrust of some 26 million Newton (about 5.8 million lb), provide most of the power for the first two minutes of flight. The SRBs take the space shuttle to an altitude of 45 km (28 mi) and a speed of 4,973 km/h (3,094 mph) before they are separated by the booster separator motors and fall back into the ocean to be retrieved, refurbished, and prepared for another flight. Each SRB produces 80% more liftoff thrust than one F-1 engine, the most powerful single-chamber liquid-fueled rocket engine ever flown.
B) SSMEs (SPACE SHUTTLE MAIN ENGINE)
It is manufactured by rocket dyne. A total of 42 reusable SSME engines have been part of the STS program, after each flight, the three SSMEs are removed from the Space Shuttle orbiter, inspected and refurbished in preparation for reuse on a subsequent flight.
After the boosters fall away, the three main engines of the orbiter continue to provide thrust .Three Space Shuttle Main Engines (SSMEs) are mounted on the Orbiter's aft fuselage in the pattern of an equilateral triangle. These engines are clustered at the rear end of the orbiter and have a combined thrust of almost 5.3 million Newton (almost 1.2 million lb).They use the liquid hydrogen and oxygen from the external fuel tank in earth’s atmosphere and use the liquid fuel in the craft in space. The space shuttle's liquid-propellant engines are the world's first reusable rocket engines. They fire for only eight minutes for each flight, just until the shuttle reaches orbit, and are designed to operate for 55 flights. The engines are very large—4.2 m (14 ft) long, and 2.4 m (8 ft) in diameter at the wide end of the cone-shaped nozzle at the rear of the orbiter. These three liquid-fueled engines can be swiveled 10.5 degrees vertically and 8.5 degrees horizontally by the hydraulic system during the rocket-powered ascent of the Orbiter in order to change the direction of their thrust.
C) OMS (ORBITAL MANEUVERING SYSTEMS)
Space shuttle’s main engines shut down as the ship approaches the altitude at which it will begin orbiting around Earth, known as the orbital insertion point. The Space Shuttle Orbital Maneuvering System, or OMS is a system of 44 rocket engines designed and manufactured by Aerojet for use on the space shuttle orbiter for orbital injection and modifying its orbit. It consists of a reaction control system(RCS) which uses fuel monomethylhydrazine (MMH), which is oxidized with nitrogen tetroxide (N2O4).RCS is clustered at the nose of the shuttle and either side of the tail. The orbital insertion point has to be tampered to facilate shuttle's important work of retrieving, launching, and repairing satellites in orbit.
D) EFT (EXTERNAL FUEL TANK)
They are the giant, cylindrical, external fuel tank, with a length of 47 m (154 ft) and a diameter of 8.4 m (27.5 ft), is the largest single piece of the space shuttle. It weight 27000kg without fuel. It contains the liquid hydrogen fuel and liquid oxygen oxidizer. It fuels the orbiter's three main engines or the SSMs which use 450 kgs of fuel each per second. During launch, the external tank also acts as a support for the orbiter and SRBs to which it is attached.. During lift-off and ascent it supplies the fuel and oxidizer under pressure to the three space shuttle main engines (SSME) in the orbiter. Unlike the SRBs external tanks can’t be re-used. After its 1.99 million liters (526,000 gallons) of fuel are consumed during the first 8.5 minutes of flight, the external tank is jettisoned from the orbiter and breaks up in the upper atmosphere.
1.3.7) Hydraulic Systems
The aft of the fuselage also houses three auxiliary power units (APU). The APUs burn hydrazine to provide hydraulic pressure for all of the hydraulic system, including the ones that point the three main liquid-fueled rocket engines, under computerized flight control. The hydraulic pressure generated is also used to control all of the Orbiter's "aero surfaces" (the elevons, rudder, air brake, etc.), to deploy the gear of the Orbiter, and to open and close the cargo bay's large main doors.
1.3.8) Reason for the space shuttle to remain stable earth’s orbit
The stability of the shuttle in an earth’s orbit is based on the principle of centripetal and centrifugal force. The craft has to maintain a critical velocity and altitude to prevent it from descending to the earth’s atmosphere under gravity. It has to move at a speed 30 times that of sound or approx. 8 kms/s.
1.3.9) Docking
At times the shuttles need to dock or join with artificial satellites or space station to update it or to replace its damaged component or add new sections or set up new aerials and solar panels. They join the satellites at previously made joint with the help of RMS.
2) Space events
Terminal Count
Extends from T minus 20 minutes through SRB ignition.
First Stage
Extends from SRB ignition through SRB separation.
Second Stage
Begins at SRB separation and extends through main engine cutoff and ET separation.
Ascent Abort Modes
Abort may become necessary if there is a failure that affects vehicle performance.
Return-to-Launch-Site
Designed to allow return of orbiter and crew to KSC launch site.
Transatlantic Landing
Available if a main engine fails after last RTLS opportunity, but before AOA can be accomplished.
Abort to Orbit
Used to boost the orbiter to a safe orbital altitude if it is impossible to reach the planned altitude.
Abort Once Around
Vehicle orbits the Earth once and lands at Edwards AFB or KSC.
Contingency Abort
Maintains orbiter integrity for in-flight crew escape if landing cannot be made.
Manual Thrust Vector Control
Substitutes inputs from RHC for automatic commands from Guidance.
Orbit Insertion
Following MECO, one or two propulsive thrusting periods move the vehicle to the desired orbital altitude
On Orbit
Guidance, navigation and control during orbit phase.
On-Orbit Checkout
The day before deorbit, the crew performs a checkout of systems used during entry.
Deorbit
Phase includes deorbit burn preparation through descent to 400,000 feet.
Entry
Phase begins at 400,000 feet and ends at touchdown.
3) Living in Space
3.1) Challenges in space
· Debris (rubbish) from previous space missions and micrometriods posses’ threat.
· Astronauts have to face highly accelerated ascent and descent.
· Basic needs as breathing, eating and drinking, elimination of body wastes, and sleeping.
· Microgravity.
3.2) Solutions
3.2.1) Protection against radiation and mechanical threats
Space vehicles usually have double hulls for protection against impacts. A particle striking the outer hull disintegrates and thus does not damage the inner hull. Usual Missions in earth orbit remain in naturally protected regions, such as the earth's magnetic field. Filters installed on spacecraft windows protect the astronauts from blinding ultraviolet rays.
3.2.2) Thermal Regulation
Aboard a spacecraft, temperatures climb because of the heat given off by electrical devices and by the crew's bodies. A set of equipment called a thermal control system regulates the temperature. The system pumps fluids warmed by the cabin environment into radiator panels, which discharge the excess heat into space.
3.2.3) Microgravity
At the altitude of shuttle orbit the gravity is just a bit less than that of earth but the velocity of the shuttle around the earth counteract the gravitational force and create weightlessness.
Fuel does not drain from tanks in microgravity, so it must be squeezed out by high-pressure gas. Hot air does not rise in microgravity, so air circulation must be driven by fans. About half of all space travelers suffer from persistent nausea, sometimes accompanied by vomiting. Drugs to prevent motion sickness can provide some relief for the symptoms of space adaptation syndrome. Microgravity also confuses an astronaut's vestibular system--that is, the organs of balance in the inner ear--by preventing it from sensing differences in direction. The vestibular system is responsible for sensing the orientation of our body and functions under gravity. Muscles go week and the heart becomes weak because of pumping blood in microgravity. The astronauts use treadmills, bikes to remain healthy. The space program also demineralizes their bones due to the absence of stress and strain.
3.2.4) Basic Needs
· Breathing: A tank containing mixture of nitrogen and oxygen. Fans circulate air through the cabin and over containers filled with pellets of a chemical called lithium hydroxide. These pellets absorb carbon dioxide from the air. Charcoal filters help control odours.
· Eating and Drinking: Astronomers eat ready to eat foods which have high nutritive value. Salt and pepper are available but only in a liquid form and not in a powder form because There is a danger they could clog air vents, contaminate equipment or get stuck in an astronaut's eyes, mouth or nose.
Drinking water is obtained from the dry cell used for providing electric supply to the craft. Dehumidifiers recycle the water exhaled by the astronauts and put it into use in the thermal control system.
· Eliminating body wastes: On small spacecraft, crew members use funnels for urine and plastic bags for solid wastes. While working outside the spacecraft, astronauts wear special equipment to contain body wastes.
3.3) Space Suits
The suit is made from many layers of flexible, airtight materials, such as nylon and Teflon. It is able to keep its occupant alive for 7 hours in space. On the EVA (Extra Vechiluar Activity) is facilated by the spacesuit. The spacesuits should be able to perform functions as-
· Life support Systems provide Breathable cool oxygen at 32kPa ,remove odors humidity and CO2 ,maintains internal spacesuits pressure a little below 1 atm as lower pressure allows mobility, provides communication means among the occupants
· Unlike earth where most heat is transferred by convection, space astronauts lose or gain heat by thermal radiation and conduction. Since the temperature varies a lot in the shady and non shady areas in space thus the space suits are made of highly insulating material. The Apollo/Skylab A7L suit included eleven layers in all: an inner liner, a liquid cooling and ventilation garment, a pressure bladder, a restraint layer, another liner, and a thermal micrometeoroid garment consisting of five aluminized insulation layers and an external layer of white Ortho-Fabric.
· Storage bags for human faeces and excreta which are made up of Maximum Absorbency garment.
· It should be able to protect the occupant from ultraviolet radiation, particle radiation, and micrometeoroids provided by a Thermal Micrometeoroids Cloth.
Scripted and Edited by Tathagat Nawadia
(PowerPoint Presentation of the Project Mission Spacecraft coming soon)
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