:: wikimiki.org ::

Advanced Space Vision System

Advanced Space Vision System

The Advanced Space Vision System (also known as the Space Vision System or by its acronym SVS) is a laser based computer generated three dimensional vision system used to manipulate any object within or without the Space Shuttle bay using the Canadarm or assemble International Space Station (ISS) components and do any maintenance work, using Canadarm2 on the Mobile Servicing System. Because of the small number of viewing ports on the station and on the shuttle most of the assembly and maintenance is done using cameras, which do not give stereoscopic vision, and thus do not allow a proper evaluation of depth. In addition the difficult conditions created by the particular conditions of illumination and obscurity in space, make it much more difficult to distinguish objects, even when the assembly work can be viewed directly, without using a camera. For instance, the harsh glare of direct sunlight can blind human vision. Also, the contrasts between objects in black shadows and objects in the solar light are much greater than in Earth's atmosphere, even where no glare is involved. The Advanced Space Vision System scans objects and constructs three dimensional models of all of them, showing their exact relative positions in real time. Although some militarised earthside relatives of this system can be used without preparing the scanned objects, the space based version requires that 4 inch target disks be placed, before launch, at several exact pre-defined points on the surface of any space bound object. The target disks are composed of thin films of silicon dioxide layered with inconel to form an inconel interference stack. A stack like this has nearly no reflectivity in the Electromagnetic spectrum . The result is a black color that appears even blacker than the flattest black paint. In photos the disks look like small black dots, and a minimum of three are needed, so they are quite unobtrusive on most payloads. The basic elements of the system were devised at the National Research Council of Canada in the 1970s, to study car collisions. In 1990 development was transferred to Neptec, a small commercial enterprise located in Kanata, a suburb of Ottawa. The entire system runs on any of the portable computers which are standard on the ISS, though two redundant networked IBM Thinkpads are reserved for it. The operating system is the Unix-like and POSIX compliant QNX Real-time operating system running the Photon windowing interface. The Photon implementation here was optimized to be the most worry free direct manipulation interface possible for the particular needs and work habits of the astronauts. The Canadian Space Agency was involved at several stages in the development and deployment of the space vision system. Training for the system takes place in the simulators located at the agency's headquarters at the John H. Chapman Space Centre near Montreal. The system was first tested in its early form on STS-52 in October 1992, and used in subsequent missions. The advanced version was first tested on STS-74 in November 1995. The system has been used with success on shuttle flights since then, and with equal success for the assembly and maintenance of the station since 1997. Category:International Space Station Category:Spacecraft components

Laser

glass lasers (bottom) used for inertial confinement fusion.]] A LASER (Light Amplification by Stimulated Emission of Radiation) is an optical source that emits photons in a coherent beam. Laser light is typically near-monochromatic, i.e. consisting of a single wavelength or hue, and emitted in a narrow beam. This is in contrast to common light sources, such as the incandescent light bulb, which emit incoherent photons in almost all directions, usually over a wide spectrum of wavelengths. Laser action is understood by application of quantum mechanics and thermodynamics theory (see laser science). The verb "to lase" means "to produce coherent light" or possibly "to cut or otherwise treat with coherent light", and is a back-formation of the term laser.

Physics

back-formation A laser is composed of an active laser medium and a resonant optical cavity. The gain medium is a material of controlled purity, size, and shape, which uses a quantum mechanical effect called stimulated emission (discovered by Einstein while researching the photoelectric effect) to amplify the beam. For a laser to operate, the gain medium must be "pumped" by an external energy source, such as electricity or light (from a classical source such as a flash lamp, or another laser). The pump energy is absorbed by the laser medium to produce excited states in the medium. When the number of particles in one excited state exceeds the number of particles in some lower state, population inversion is achieved. In this condition, an optical beam passing through the medium produces more stimulated emission than stimulated absorption so the beam is amplified. An excited laser medium can also function as an optical amplifier. The light generated by stimulated emission is very similar to the input signal in terms of wavelength, phase, and polarization. This gives laser light its characteristic coherence, and allows it to maintain the uniform polarization and monochromaticity established by the optical cavity design. The resonant cavity (see also cavity resonator) contains a coherent beam of light between reflective surfaces so that each photon passes through the gain medium multiple times before being emitted from the output aperture or lost to diffraction or absorption. As light circulates through the cavity, passing through the gain medium, if the gain (amplification) in the medium is stronger than the resonator losses, the power of the circulating light can rise exponentially. However, each stimulated emission event returns a particle from its excited state to the ground state, reducing the capacity of the gain medium for further amplification. When this effect becomes strong, the gain is said to be saturated. The balance of pump power against gain saturation and cavity losses produces an equilibrium value of the intracavity laser power which determines the operating point of the laser. If the pump power is chosen too small (below the "laser threshold"), the gain is not sufficient to overcome the resonator losses, and the laser will emit only very small light powers. The beam in the cavity and the output beam of the laser, if they occur in free space rather than waveguides (as in an optical fiber laser), are often Gaussian beams. If the beam is not a pure Gaussian shape, the transverse modes of the beam may be analyzed as a superposition of Hermite-Gaussian or Laguerre-Gaussian beams. The beam often has a very small divergence (highly collimated), but a perfectly collimated beam cannot be created, due to the effect of diffraction. Nonetheless, a laser beam will spread much less than a beam of incoherent light. The distance over which the beam remains collimated increases with the square of the beam diameter, and the angle at which the beam eventually diverges varies inversely with the diameter. Thus, a beam generated by a small laboratory laser such as a helium-neon (HeNe) laser spreads to approximately 1 mile (1.6 kilometres) in diameter if shone from the Earth's surface to the Moon. By comparison, the output of a typical semiconductor laser, due to its small diameter, diverges almost immediately on exiting the aperture, at an angle that may be as high as 50°. However, such a divergent beam can be transformed into a collimated beam by means of a lens. In contrast, the light from non-laser light sources cannot be collimated by optics as well or much. lens at Univ. Paris 6. The glowing ray in the middle is an electric discharge producing light in much the same way as a neon light; though it is the gain medium through which the laser passes, it is not the laser beam itself which is visible there. The laser beam crosses the air and marks a red point on the screen to the right.]] The output of a laser may be a continuous, constant-amplitude output (known as CW or continuous wave), or pulsed, by using the techniques of Q-switching, modelocking, or gain-switching. In pulsed operation, much higher peak powers can be achieved. Some types of lasers, such as dye lasers and vibronic solid-state lasers can produce light over a broad range of wavelengths; this property makes them suitable for the generation of extremely short pulses of light, on the order of a femtosecond (10^-15 seconds). It should be understood that the word light in the acronym LASER is meant in the expansive sense, as photons of any energy; and is not limited to photons in the visible spectrum. Hence there are X-ray lasers, infrared lasers, ultraviolet lasers, etc. Because the microwave equivalent of the laser, the maser, was developed first, devices that emit microwave and radio frequencies are usually called masers. In early literature, particularly from researchers at Bell Telephone Laboratories, the laser was often called the optical maser. This usage has since become uncommon, and as of 1998 even Bell Labs uses the term laser [http://www.bell-labs.com/about/history/laser/].

History

In 1916, Albert Einstein laid the foundation for the invention of the laser and its predecessor, the maser, in a ground-breaking rederivation of Max Planck's law of radiation based on the concepts of spontaneous and induced emission. The theory was forgotten until after World War II. In 1953, Charles H. Townes and graduate students James P. Gordon and Herbert J. Zeiger produced the first maser, a device operating on similar principles to the laser, but producing microwave rather than optical radiation. Townes' maser was incapable of continuous output. Nikolay Basov and Aleksandr Prokhorov of the Soviet Union worked independently on the quantum oscillator and solved the problem of continuous output systems by using more than two energy levels. These systems could release stimulated emission without falling to the ground state, thus maintaining a population inversion. Townes, Basov and Prokhorov shared the Nobel Prize in Physics in 1964 "for fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser-laser principle." In 1957 Charles Townes and Arthur Leonard Schawlow, then at Bell Labs, began a serious study of the infrared maser. As ideas were developed, infrared frequencies were abandoned with focus on visible light instead. The concept was originally known as an "optical maser". Bell Labs filed a patent application for their proposed optical maser a year later. Schawlow and Townes sent a manuscript of their theoretical calculations to Physical Review, which published their paper that year (Volume 112, Issue 6). Simultanously, Gordon Gould, a graduate student at Columbia University, was working on a doctoral thesis on the energy levels of excited thallium. Gould and Townes met and had conversations on the general subject of radiation emission. After that meeting, Gould made notes about his ideas for a "laser" in November 1957. In 1958, Prokhorov proposed an open resonator which became an important ingredient of future lasers. The first introduction of the term "laser" to the public was in Gould's 1959 paper "The LASER, Light Amplification by Stimulated Emission of Radiation". Gould intended "aser" to be a suffix, to be used with an appropriate prefix for the spectra of light emitted by the device (e.g. X-ray laser = xaser, UltraViolet laser = uvaser). None of the other terms became popular, although "raser" is sometimes used for radio-frequency emitting devices. Gould's notes included possible applications for a laser, such as spectrometry, interferometry, radar, and nuclear fusion. He continued working on his idea and filed a patent application in April 1959. The U.S. Patent Office denied his application and awarded it to Bell Labs in 1960. This sparked a legal battle that spanned three decades, with scientific prestige and much money at stake. Gould won his first minor patent in 1977, but it was not until 1987 that he could claim his first significant patent victory when a federal judge ordered the government to issue a patent to him for each of the optically pumped and the gas discharge laser. The first working laser was made by Theodore H. Maiman in 1960 at Hughes Research Laboratories in Malibu, California, beating several research teams including those of Townes at Columbia University, and Arthur L. Schawlow at Bell Labs. Maiman used a solid-state flashlamp-pumped synthetic ruby crystal to produce red laser light at 694 nanometres wavelength. Maiman's laser, however, was only capable of pulsed operation due to its three energy level transitions. Later in the same year the Iranian physicist Ali Javan, together with William Bennet and Donald Herriot, made the first gas laser using helium and neon. Javan later received the Albert Einstein Award in 1993. The concept of the semiconductor laser was proposed by Basov and Javan; and the first laser diode was demonstrated by Robert N. Hall in 1962. Hall's device was constructed in the GaAs material system and produced emission at 850 nm, in the near-infrared region of the spectrum. The first semiconductor laser with visible emission was demonstrated later the same year by Nick Holonyak, Jr. As with the first gas lasers, these early semiconductor lasers could be used only in pulsed operation, and indeed only when cooled to liquid nitrogen temperatures (77 K). In 1970, Zhores Alferov in the Soviet Union and Hayashi and Panish of Bell Telephone Laboratories independently developed continuously operating laser diodes at room temperature, using the heterojunction structure. The first application of lasers visible in the daily lives of the general population was the supermarket barcode scanner, introduced in 1974. The laserdisc player, introduced in 1978, was the first successful consumer product to include a laser, but the compact disc player was the first laser-equipped device to become truly common in consumers' homes, beginning in 1982.

Recent innovations

1982 Since the early period of laser history, laser research has produced a variety of improved and specialized laser types, optimized for different performance goals, including
- new wavelength bands
- maximum average output power
- maximum peak output power
- minimum output pulse duration
- maximum power efficiency and this research continues to this day.
Lasing without maintaining the medium excited into a population inversion, was discovered in 1992 in sodium gas and again in 1995 in rubidium gas by various international teams. This was accomplished by using an external maser to induce "optical transparency" in the medium by introducing and destructively interfering the ground electron transitions between two paths, so that the likelihood for the ground electrons to absorb any energy has been cancelled. In 1985 at the University of Rochester's Laboratory for Laser Energetics a breakthrough in creating ultrashort-pulse, very high-intensity (terawatts) laser pulses became available using a technique called chirped pulse amplification, or CPA, discovered by Gérard Mourou. These high intensity pulses can produce filament propagation in the atmosphere.

Uses of lasers

At the time of their invention in 1960, lasers were called "a solution looking for a problem". Since then, they have become ubiquitous, finding utility in thousands of highly varied applications in every section of modern society, including consumer electronics, information technology, science, medicine, industry, law enforcement and the military. They have been widely regarded as one of the most influential technological achievements of the 20th century. The benefits of lasers in various applications stems from their properties such as coherency, high monochromaticity, capability for reaching extremely high powers. For instance, a highly coherent laser beam can be focused down to its diffraction limit, which at visible wavelengths corresponds to only a few hundred nanometers. This property allows a laser to record gigabytes of information in the microscopic pits of a DVD. It also allows a laser of modest power to be focused to very high intensities and used for cutting, burning or even vaporizing materials. For example, a frequency doubled neodymium yttrium aluminum garnet (Nd:YAG) laser emitting 532 nanometer (green) light at 10 watts output power is theoretically capable of achieving an intensity of megawatts per square centimeter. In reality however, perfect focusing of a beam to its diffraction limit is very difficult. square centimeter In consumer electronics, telecommunications, and data communications, lasers are used as the transmitters in optical communications over optical fiber and free space. They are used to store and retrieve data from compact discs and DVDs, as well as magneto-optical discs. Laser lighting displays (pictured) accompany many music concerts. In science, lasers are employed in a wide variety of interferometric techniques, and for Raman spectroscopy and laser induced breakdown spectroscopy . Other uses include atmospheric remote sensing, and investigation of nonlinear optics phenomena. Holographic techniques employing lasers also contribute to a number of measurement techniques. Lasers have also been used aboard scientific spacecraft. In medicine, the laser scalpel is used for laser vision correction and other surgical techniques. Lasers are also used for dermatological procedures including removal of tattoos, birthmarks, and hair; laser types used in dermatology include ruby (694 nm), alexandrite (755 nm), pulsed diode array (810 nm), Nd:YAG (1064 nm), Ho:YAG (2090 nm), and Er:YAG (2940 nm). In industry, laser cutting is used to cut steel and other metals. Laser line levels are used in surveying and construction. Lasers are also used for guidance for aircraft. Lasers are used in certain types of thermonuclear fusion reactors. In law enforcement the most widely known use of lasers is for lidar to detect the speed of vehicles. Military uses of lasers include use as target designators for other weapons; their use as directed-energy weapons is currently under research. Laser weapon systems under development include the airborne laser, the airborne tactical laser, the Tactical High Energy Laser, the High Energy Liquid Laser Area Defense System, and the MIRACL, or Mid-Infrared Advanced Chemical Laser.

Popular misconceptions

The representation of lasers in popular culture, especially in science fiction and action movies, is generally very misleading. For instance, contrary to their portrayal in movies such as Star Wars, a laser beam is never visible in the vacuum of space. In air the ray can hit dust and other particles in its path and scatter producing a glowing "ray", in much the same way that a sunbeam glows in dusty air. This effect can be intensified to make the beam more visible by increasing the amount of suspended particles in the air. Very high intensity beams can be visible in air due to Rayleigh scattering or Raman scattering. With even higher intensity beams, the air can heat up to the point where it becomes a plasma, which would be visible. This would however cause a loud explosion, and will cause a reflection of the ray back into the laser, probably damaging it (depending on the laser design). Furthermore, science fiction film special effects often depict laser beams propagating at only a few metres per second—i.e., slowly enough to see their progress, in a manner reminiscent of conventional tracer ammunition—whereas in reality a laser beam travels at the speed of light, and would be instantly visible along its entire length. Some action movies depict security systems using red lasers (and being foiled by the hero, typically using mirrors); the hero may see the path of the beam by sprinkling some white dust in the air. It is actually easier and cheaper to build infrared laser diodes rather than visible light laser diodes, therefore such systems would almost certainly not use visible light.

Laser safety

Even low-power lasers with only a few milliwatts of output power can be hazardous to a person's eyesight. At wavelengths which the cornea and the lens can focus well, the coherence and low divergence of laser light means that it can be focused by the eye into an extremely small spot on the retina, resulting in localised burning and permanent damage in seconds or even faster. Lasers are classified into safety classes numbered I, inherently safe, to IV, even scattered light can cause eye and/or skin damage. Laser products available for consumers, such as CD players and laser pointers are usually in class I, II, or III.

Common laser types

For a more complete list of laser types see list of laser types. list of laser types

Color	Wavelength interval	Frequency interval
red	~ 625 to 740 nm	~ 480 to 405 THz
orange	~ 590 to 625 nm	~ 510 to 480 THz
yellow	~ 565 to 590 nm	~ 530 to 510 THz
green	~ 520 to 565 nm	~ 580 to 530 THz
cyan	~ 500 to 520 nm	~ 600 to 580 THz
blue	~ 430 to 500 nm	~ 700 to 600 THz
violet	~ 380 to 430 nm	~ 790 to 700 THz

- Gas lasers
- HeNe (543 nm and 633 nm)
- Argon-Ion (458 nm, 488 nm or 514.5 nm)
- Carbon dioxide lasers (9.6 µm and 10.6 µm) used in industry for cutting and welding, up to 100 kW possible
- TEA Laser (UV Light, 337.1 nm)
- Nitrogen laser
- Carbon monoxide lasers, must be cooled, but extremely powerful, up to 500 kW possible
- Chemical lasers
- Chemical oxygen iodine laser (1315 nm)
- Hydrogen fluoride laser (2700-2900 nm)
- Deuterium fluoride laser (3800 nm)
- Excimer gas lasers, producing ultraviolet light, used in semiconductor manufacturing and in LASIK eye surgery; F₂ (157 nm), ArF (193 nm), KrCl (222 nm), KrF (248 nm), XeCl (308 nm), XeF (351 nm)
- Semiconductor lasers
- Laser diodes produce wavelengths from 405 nm to 1550 nm. Low power laser diodes are used in laser pointers, laser printers, and CD/DVD players. More powerful laser diodes are frequently used to optically pump other lasers with high efficiency. The highest power industrial laser diodes, with power up to 10 kW, are used in industry for cutting and welding.
- External-cavity semiconductor lasers have a semiconductor active medium in a larger cavity. These devices can generate high power outputs with good beam quality, wavelength-tunable narrow-linewidth radiation, or ultrashort laser pulses.
- VCSELs are semiconductor lasers whose emission direction is perpendicular to the surface of the wafer. VCSEL devices can achieve better beam quality and higher output power than conventional laser diodes, and potentially could be much cheaper to manufacture. The technology is not (as of 2005) as well developed, however.
- VECSELs are external-cavity VCSELs.
- Quantum cascade lasers are semiconductor lasers that have an active transition between energy sub-bands of an electron in a structure containing several quantum wells.
- Solid-state lasers
- Neodymium-doped YAG lasers (Nd:YAG), a high-power laser operating in the infrared spectrum at 1064nm, used for cutting, welding and marking of metals and other materials also used in spectroscopy and for pumping dye lasers. Can be frequency doubled from 1064nm to 532nm to produce a green laser.
- Ytterbium-doped lasers with crystals such as Yb:YAG, Yb:KGW, Yb:KYW, Yb:SYS, Yb:BOYS, Yb:CaF2, or Yb-doped glasses (e.g. fibers); typically operating around 1020-1050 nm; potentially very high efficiency and high powers due to a small quantum defect; extremely high powers in ultrashort pulses can be achieved with Yb:YAG
- Erbium-doped YAG, 1645 nm, 2940 nm
- Thulium-doped YAG, 2015 nm
- Holmium-doped YAG, 2097 nm; an efficient laser operating in the infrared spectrum, it is strongly absorbed by water-bearing tissues in sections less than a millimeter thick. It is usually operated in a pulsed mode, and passed through optical fiber surgical devices to resurface joints, remove rot from teeth, vaporize cancers, and pulverize kidney and gall stones.
- Titanium-doped sapphire (Ti:sapphire) lasers, a highly tunable infrared laser, used for spectroscopy
- Erbium-doped fiber lasers, a type of laser formed from a specially made optical fiber, which is used as an amplifier for optical communications.
- Dye lasers
- Hollow cathode sputtering metal ion lasers, generating deep ultraviolet wavelengths, of which there are two examples; Helium-Silver (HeAg) 224 nm and Neon-Copper (NeCu) 248 nm. These lasers have particularly narrow oscillation linewidths of less than 0.01 cm^-1 making them good candidates for use in fluorescence suppressed Raman spectroscopy.

External links

- [http://www.repairfaq.org/sam/lasersam.htm Sam's Laser FAQ] by Samuel M. Goldwasser
- [http://www.rp-photonics.com/encyclopedia.html Encyclopedia of laser physics and technology] by [http://www.rp-photonics.com/paschotta.html Dr. Rüdiger Paschotta]
- [http://www.aip.org/pnu/2002/596.html Liquid Light] by Phil Schewe, James Riordon, and Ben Stein
- [http://www.newscientist.com/article.ns?id=dn2497 Light turns into glowing liquid] by Eugenie Samuel
- [http://www.aip.org/pt/vol-54/iss-8/p17.html Experiments Detail How Powerful Ultrashort Laser Pulses Propagate through Air]
- [http://www.nrl.navy.mil/content.php?P=03REVIEW59 Filamentation and Propagation of Ultra-Short, Intense Laser Pulses in Air]
- [http://www.aip.org/pnu/1992/physnews.100.htm Lasing Activity without Population Inversion] by Phillip F. Schewe and Ben Stein
- [http://www.aip.org/pnu/1995/physnews.240.htm Lasing without Inversion] by Phillip F. Schewe and Ben Stein Category:Optical devices Lasers Category:Lighting Category:Acronyms ko:레이저 ms:laser ja:レーザー

Space Shuttle

). For the first two missions only, the external fuel tank spray-on foam insulation (SOFI) was painted white. Subsequent missions have featured an unpainted tank thus exposing the orange/rust colored foam insulation. This resulted in a weight saving of over 1,000 lb (450 kg), a savings that translated directly to added payload capacity to orbit.]] : This article is about the NASA Space Shuttle. For information on the Soviet Space Shuttles, see the articles Shuttle Buran, Ptichka, Shuttle 2.01, Shuttle 2.02 and Shuttle 2.03. NASA's Space Shuttle, officially called Space Transportation System (STS), is the United States government's sole manned launch vehicle currently in service. The Space Shuttle orbiter was manufactured by North American Rockwell, now part of the Boeing Company. Martin Marietta (now part of Lockheed Martin) designed the external fuel tank and Morton Thiokol (now part of Alliant Techsystems (ATK)) designed the solid rocket boosters. The Shuttle is the first orbital spacecraft designed for partial reusability. It carries large payloads to various orbits, provides crew rotation for the International Space Station (ISS), and performs servicing missions. While the vehicle was designed with the capacity to recover satellites and other payloads from orbit and return them to Earth, this capacity has not been used often; it is, however, an important use of the Space Shuttle in the context of the ISS program, as only very small amounts of experimental material, hardware needing to be repaired, and trash can be returned by Soyuz. Each Shuttle was designed for a projected lifespan of 100 launches or 10-years operational life. The program started in the late 1960s and has dominated NASA's manned operations since the mid-1970s. According to the Vision for Space Exploration, use of the Space Shuttle will be focused on completing assembly of the ISS in 2010, after which it will be replaced by the yet-to-be-developed Crew Exploration Vehicle (CEV). However, following the STS-114 return-to-flight mission in August 2005, the Shuttle program is currently grounded pending repairs and the solution of outstanding safety issues. Further aggravating the shuttle's return to space, also in August 2005, the Space Shuttle external tank construction site, Michoud Assembly Facility located in New Orleans, Louisiana was damaged by Hurricane Katrina, with all work shifts cancelled up to September 26, 2005. This could potentially set back further Shuttle flights by more than two months. The NASA Chief Administrator Michael Griffin has recently suggested the decision to develop the Space Shuttle and International Space Station was a mistake by saying, "It is now commonly accepted that was not the right path. We are now trying to change the path while doing as little damage as we can." [http://www.usatoday.com/printedition/news/20050928/1a_bottomstrip28.art.htm]

History

The Shuttle decision

NASA had conducted a series of paper projects throughout the 1960s on the topic of reusable spacecraft to replace their expedient "one-off" systems like Mercury, Gemini, and Apollo. Meanwhile, the U.S. Air Force had a continuing interest in smaller systems with more rapid turn-around times, and were involved in their own spaceplane project, the X-20 Dyna-Soar. In several instances groups from both worked together to investigate the state of the art. With the major Apollo development effort winding down in the second half of the 1960s, NASA started looking to the future of the space program. They envisioned an ambitious program consisting of a large space station being launched on huge boosters, served by a reusable logistics "space shuttle", both providing services for a permanently manned Lunar colony and eventual manned missions to Mars. However, in reality, NASA found itself with a rapidly plunging budget. Rather than trying to adapt their long-term future to their dire financial situation, they attempted to save as many of the individual projects as possible. The mission to Mars was rapidly dismissed, but the Space Station and Shuttle conserved. Eventually only one of them could be saved, so it stood to reason that a low-cost Shuttle system would be the better option, because without it a large station would never be affordable. A number of designs were proposed, but many of them were complex and varied widely in their systems. An attempt to re-simplify was made in the form of the "DC-3" by one of the few people left in NASA with the political importance to accomplish it, Maxime Faget, who had designed the Mercury capsule, among other vehicles. The DC-3 was a small craft with a 20,000-pound (9 tonne) (or less) payload, a four-man capacity, and limited maneuverability. At a minimum, the DC-3 provided a baseline "workable" (but not significantly advanced) system by which other systems could be compared for price/performance compromises. Mercury The defining moment for NASA was when they, in desperation to see their only remaining project saved, went to the Air Force for its blessing. NASA asked that the USAF place all of their future launches on the Shuttle instead of their current expendable launchers (like the Titan II), in return for which they would no longer have to continue spending money upgrading those designs — the Shuttle would provide more than enough capability. The Air Force reluctantly agreed, but only after demanding a large increase in capability to allow for launching their projected spy satellites (mirrors are heavy). These were quite large, weighing an estimated 40,000 pounds (18 tonnes), and needed to be put into polar orbits, which require higher energies than lower inclination orbits; and since the Air Force also wanted to be able to abort after a single orbit (as did NASA), and in addition land at the launch site (unlike NASA), the spacecraft would also require the ability to maneuver significantly to either side of its orbital track to adjust for launch-point rotational drift while in polar orbit — for example, in a 90-minute orbit, Vandenberg AFB would drift over 1,000 miles (1,600 km), whereas in more equatorially aligned orbits, the required cross-range would be less than 250 mi/400 km. This large "cross-range" capability for polar orbits meant the craft had to have a greater lift-to-drag ratio than originally planned, requiring the addition of bigger, heavier wings. The result was that the simple "DC-3" was clearly irrelevant because it had neither the cargo capacity nor the cross-range the Air Force demanded. In fact, all existing designs were far too small, as a 40,000-pound (18 tonnes) delivery to polar orbit equates to a 65,000-pound (29 tonne) delivery to an eastwardly launched orbit with typical 28-degree inclination. Additionally, any design using simple straight or foldout wings was not going to meet the cross-range requirements, so any future design would require a more complex, heavier delta wing. Of further concern, any increase in the weight of the upper portion of a launch vehicle, which had just occurred, required an even bigger increase in the capability of the lower stage used to launch it. Suddenly, the two-stage system had grown in size to something larger than the Saturn V, and the complexity and costs to develop it soared. While all of this was going on, others were suggesting a completely different approach to the future. They stated that NASA would fare better using the existing Saturn to launch their space station, supplied and manned using modified Gemini capsules on top of the Air Force's newer Titan II-M. The cost of development for this looked to be considerably less than the Shuttle alone, and would have a large space station in orbit earlier. In reply, advocates of the Shuttle answered that given enough launches, a reusable system would more than pay for the cost of development when compared with the launch costs of disposable rockets. Another factor in the cost-benefit analysis was inflation, and in the 1970s this was high enough that the payback from the development had to happen very quickly to see a positive return. Hence, a high launch rate was needed to make the system economically feasible. But it was infeasible that a space station or Air Force payloads could demand such rates (roughly one or two a week), so they insisted and suggested that all future U.S. launches would take place on the Shuttle, once built. In order to do this, the cost of launching the Shuttle would have to be lower than any other system, with the exception of very small rockets, ignored for practical reasons, and very large boosters, which were rare and excessively expensive in any case. With a baseline project now gelling, NASA started to work through the process of obtaining stable funding for the five years the project would take to develop. Once again, they found themselves in an increasingly deplorable situation. With the budgets being pressed by inflation in the U.S. and the Vietnam War abroad, Congress and the Administration were generally uninterested in long-term projects such as space exploration. Some members were therefore looking to further cut NASA's budget; but with a single long-term project confirmed, they could do little in terms of cutting whole projects — the Shuttle was the single one left, and its cancellation would mean that there would be no U.S. manned space program by 1980. Instead, they looked to reduce the year-to-year costs of development to a stable figure. That is, they wished to see the development budgets spread out over several more years. This was somewhat impractical and in conflict with the planned funding and development. The result was another intense series of redesigns in which the reusable booster was eventually abandoned due to its high price. Unsurprisingly, some designs for reusable boosters amounted to vehicles the size of the then-new Boeing 747, which would have to fly faster than the record-holding — and considerably smaller — X-15 rocket plane. Instead, a series of simpler rockets would launch the system and then drop away for recovery. Another change was that the fuel for the Shuttle itself was placed in an external tank instead of internal tanks as in the previous designs. This allowed a larger payload bay in an otherwise much smaller craft, although it also meant throwing away the tankage after each launch. The last remaining debate was over the nature of the boosters. NASA had been looking at no less than four solutions to this problem: one a development of the existing Saturn lower stage, another using simple pressure-fed liquid-fuel engines of a new design, and finally either a large, single solid rocket, or two (or more) smaller ones. The decision was eventually made on the smaller solids due to their lower development costs (a decision that had been echoed throughout the whole Shuttle program). While the liquid-fueled systems provided better performance and enhanced safety, delivery capability to orbit is much more a function of the upper-stage performance and weight than the lower; the money was hence spent elsewhere.

Development

Vietnam War The Shuttle program was launched on January 5, 1972, when President Richard M. Nixon announced that NASA would proceed with the development of a reusable, low-cost Space Shuttle system. The project was already to take longer than originally anticipated due to the year-to-year funding caps. Nevertheless, work started quickly and several test articles were available within a few years. Most notable among these was the first complete Orbiter, originally to be known as Constitution. However, a massive write-in campaign from fans of the Star Trek television series convinced the White House to change the name to Enterprise. Amid great fanfare, the Enterprise was rolled out on September 17, 1976, and later conducted a successful series of glide-approach and landing tests that were the first real validation of the design. The first fully functional Shuttle Orbiter, built in Palmdale, California, was the Columbia, which was delivered to Kennedy Space Center on March 25, 1979, and was first launched on April 12, 1981—the 20th anniversary of Yuri Gagarin's space flight—with a crew of two. Challenger was delivered to KSC in July 1982, Discovery was delivered in November 1983, and Atlantis was delivered in April 1985. The Shuttle was meant to visit Space Station Freedom, announced in 1984, an ambitious and much-delayed project later downsized and merged into the International Space Station program. Challenger was destroyed in an explosion during launch on January 28, 1986, with the loss of all seven astronauts on board. Endeavour was built to replace it (using spare parts originally intended for the other Orbiters) and delivered in May 1991. Columbia was lost, with all seven crew members, during reentry on February 1, 2003, and has not been replaced.

Description

2003 The Shuttle has a large 60 by 15 ft (18 by 4.6 m) payload bay, filling most of the fuselage. The payload bay doors have heat radiators mounted on their inner surfaces, and so are kept open for thermal control while the Shuttle is in orbit. Thermal control is also maintained by adjusting the orientation of the Shuttle relative to Earth and Sun. Inside the payload bay is the Remote Manipulator System, also known as the Canadarm, a robot arm used to retrieve and deploy payloads. Until the loss of Columbia, the Canadarm had been used only on those missions where it was needed. Since the arm is a crucial part of the Thermal Protection Inspection procedures now required for Shuttle flights, it will probably be included on all future flights. The Space Shuttle system has undergone numerous improvements over the years. The Orbiter has changed its thermal protection system several times in order to save weight and ease workload. The original silica-based ceramic tiles need to be removed for inspection for damage after every flight, and they also soak up water and thus need to be protected from the rain. The latter problem was initially fixed by spraying the tiles with Scotchgard, but a custom solution was adopted. Later, many of the tiles on the cooler portions of the Shuttle were replaced by large blankets of insulating feltlike material, which means huge areas (notably the cargo bay area) no longer have to be inspected as often. Internally the Shuttle remains largely similar to the original design, with the exception that the avionics continue to be improved. The original systems were "hardened" IBM 360 computers connected to analog displays in the cockpit similar to contemporary airliners like the DC-10. Today the cockpits have been replaced with "all glass" systems and the computers themselves are many times faster. The computers use the HAL/S programming language. In the Apollo-Soyuz Test Project tradition, programmable calculators are carried as well (originally the HP-41C). In addition to the "glass cockpit," several improvements have been made for safety reasons after the Challenger explosion, including a crew escape system for use in a narrow range of situations that require the Orbiter to "ditch." With the coming of the Space Station, the Orbiter's internal airlocks are being 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. HP-41C The Space Shuttle Main Engines have had several improvements to enhance reliability and power. This is why during launch you may hear curious phrases such as "Go to throttle-up at 106%." This does not mean the engines are being run over limit. The 100% figure is the power level for the original main engines. The actual engine contract requirement was for 109%. The original flight engines could handle 102%. The 109% number was finally reached in flight hardware with the Block II engines in 2001. For 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. This saved considerable weight, and thereby increases the payload the Orbiter can carry into 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 7,500 lb (3.4 t) less than the last run of lightweight tanks. As the Shuttle cannot fly unmanned, each of these improvements has been "tested" on operational flights. And, of course, the SRBs (Solid Rocket Boosters) have undergone improvements as well. Notable is the adding of a third O-ring seal to the joints between the segments, which occurred after the Challenger accident. A number of 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 which was to have entered production in the early to mid-1990s to support the Space Station, but was later cancelled to save money after the expenditure of $2.2 billion. The loss of the ASRB program forced the development of the 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 design using a filament-wound system, but this too was cancelled. A cargo-only, unmanned variant of the Shuttle has been variously proposed and rejected since the 1980s. It is called the Shuttle-C and would trade re-usability for cargo capability with large potential savings from reusing technology developed for the Space Shuttle.

Components

The Space Shuttle consists of three main components: the reusable Orbiter itself, a large, brown, expendable external fuel tank, and a pair of white, reusable solid-fuel booster rockets. The fuel tank and booster rockets are jettisoned during ascent, so only the Orbiter goes into orbit.
- The reusable Orbiter Vehicle (OV), with a large payload bay and three main engines (fed from the external tank) and an orbital maneuvering system with two smaller engines (used after jettisoning the external tank). There are currently three orbiters, rotated between missions.
- A large expendable external fuel tank (ET) containing liquid oxygen and liquid hydrogen (at the forward and aft ends, respectively) for the three main engines of the Orbiter; it is discarded 8.5 minutes after launch at an altitude of 60 nautical miles (111 km) and breaks up in the atmosphere upon reentry. The pieces fall in the ocean and are not recovered.
- A pair of reusable solid-fuel rocket boosters (SRB); the propellant consists mainly of ammonium perchlorate (oxidizer, 70% by weight) and aluminum (fuel, 16 %); they are separated two minutes after launch at a height of 36 nautical miles (67 km) and are recovered after landing in the ocean, their fall slowed by parachutes. Initial plans for the so-called Space Transportation System included space tugs and extra fuel tanks for the orbital-maneuvering-system engines, among many other concepts. None of this hardware has actually ever been built.

Technical data

parachute Shuttle Carrier Aircraft (SCA), 1998 (NASA)]]
- System stack height: 184.2 ft (56.14 m)
- Orbiter length: 122.17 ft (37.236 m)
- Wingspan: 78.06 ft (23.79 m)
- Gross liftoff: 4.5 million lb (2,040,000 kg)
- ET: 1.7 million lb (751,000 kg)
- SRBs: 1.3 million lb (590,000 kg) each (x 2)
- Orbiter: 240,000 lb (109,000 kg)
- Total liftoff thrust: 7.82 million lbf (34.8 MN)
- SSMEs: 400,000 lbf (1.8 MN) each (x 3) = 1.2 million lbf (5.3 MN)
- SRBs: 3.30 million lbf (14.7 MN) each (x 2) = 6.61 million lbf (29.4 MN)
- Maximum landing: 230,000 lb (104,000 kg)
- Maximum launch payload: 63,500 lb (28,800 kg)
- Operational altitude: 100 to 520 nmi (185 to 1000 km)
- Speed: 25,404 ft/s (7743 m/s, 27 875 km/h, 17 321 mi/h)
- Passenger capacity: 10 Astronauts (crews other than 5 to 7 are uncommon)

Normal ascent

Initially the main engines are lit and checked out; if successful, the SRBs are lit and the vehicle is then committed to takeoff. At takeoff the vast majority (~90%) of the thrust is provided by the SRBs. Shortly after clearing the tower the Shuttle rotates so that the vehicle is below the main tank and SRBs. The vehicle climbs in a progressively flattening arc, accelerating as the weight of the SRBs and main tank reduces. To reach orbit, the vehicle needs to reach high altitude, but more importantly it needs to achieve mach 25 sideways, and so must spend as much time as possible accelerating horizontally. 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 vulnerable parts such as the wings). 126 seconds after launch, the SRBs thrust reduces and then explosive bolts release them from the vehicle and they fall 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 reduces, the ever-lighter vehicle produces more and more acceleration until the thrust to weight ratio exceeds 1 again and the vehicle can hold itself up. 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 whilst it accelerates horizontally towards orbit. Finally, in the last tens of seconds towards the end of the main engine burn, the mass of the vehicle is low enough, that the acceleration is throttled back to keep the vehicle accelerating at no more than 3g, largely for astronaut health and comfort. Before complete depletion of propellant (running dry would destroy the engines) the main engines are shutdown, and the empty main tank is released by firing explosive bolts. The tank then falls to largely burn up in the atmosphere, with some fragments falling into the Indian Ocean. At this point the Shuttle is still slightly suborbital, since the trajectory intersects the atmosphere. The Shuttle then fires the OMS engines to circularize the orbit and avoid reentry.

Ascent abort modes

There are five abort modes available during ascent, classified as intact aborts and contingency aborts [http://www.shuttlepresskit.com/STS-93/REF86.htm]. The choice of abort mode depends on estimates of what the orbiter's situation would be at the time of main engine cutoff (TMECO). The abort modes cover a wide range of potential problems, but the most common expected problem is that the orbiter failing to achieve orbital speed by TMECO, technically known as "MECO underspeed".

Intact abort modes

There are four intact abort modes. Intact aborts are designed to provide a safe return of the orbiter to a planned landing site.
- Return To Launch Site (RTLS) — has never been tried, but would involve turning the Shuttle around while continuing to burn the SSMEs, jettisoning the ET, and gliding to a landing at Kennedy Space Center.
- East Coast Abort Landing (ECAL) — involves landing at predetermined locations on the east coast of North America in the U.S. and Canada. This has never occurred.
- Transoceanic Abort Landing (TAL) — involves landing at predetermined locations in Africa and western Europe. This has never occurred.
- Abort to Orbit (ATO) — occurs when the intended orbit cannot be reached but a stable alternate orbit is possible. This occurred on STS-51-F mission; required mission replanning, but the mission was nevertheless declared a success.
- Abort Once Around (AOA) — occurs when entering a stable orbit is not possible. This has never occurred.

Contingency abort mode

Contingency aborts are designed to permit flight crew survival following more severe failures when an intact abort is not possible. A contingency abort would generally result in a ditch operation. To the extent that the hydrogen and oxygen are not needed, they are used up deliberately to allow the ET to be discarded safely. The designated sites for ECAL are Bangor, Maine, Wilmington, North Carolina; MCAS Cherry Point, North Carolina; NAS Oceana; Wallops Flight Facility; Dover Air Force Base; Atlantic City, New Jersey; Gabreski, New York; Otis ANGB; Pease International Airport (all USA); Halifax; Stephenville; St John's; Gander; and Goose Bay (all Canada). A TAL would be declared between roughly T+2:30 minutes (liftoff plus 2 minutes, 30 seconds) and Main Engine Cutoff (MECO), about T+8:30 minutes. The Shuttle would then land at a predesignated friendly airstrip in Africa or Europe. Potential sites include Istres Air Base in France; Banjul International Airport in The Gambia; and Zaragoza Air Base and Morón Air Base in Spain. Prior to a Shuttle launch, two of them are selected depending on the flight plan, and staffed with standby personnel in case they are used. The list of TAL sites has changed over time; most recently Ben Guerir Air Base in Morocco was eliminated due to terrorism concerns. Past TAL sites have included Kano, Nigeria; Easter Island (for Vandenberg launches); Rota, Spain; Casablanca, Morocco; and Dakar, Senegal. Emergency landing sites for the Orbiter include Lajes, Beja, (both Portugal), Keflavik (Iceland), Shannon International Airport (Ireland), RAF Fairford (UK), Köln Bonn Airport (Germany), Ankara (Turkey), Riyadh (Saudi Arabia), Diego Garcia (British Indian Ocean Territory). Were the Orbiter unable to reach a runway, it could ditch in water, or could land on terrain other than a landing site. It would be unlikely for the flight crew still on board to survive. However, if the Orbiter ascent were aborted in a narrow set of circumstances in which controlled gliding flight could be achieved, the In-flight Crew Escape System would allow the crew to escape with parachutes. A special Escape Pole would take each crewmember on a trajectory beneath the Orbiter's left wing. In the two disasters, things went wrong so fast that little could be done. In the case of Challenger, the SRBs were still burning as they tore free from the rest of the stack. The orbiter disintegrated almost instantly because of aerodynamic stresses as the stack broke up. The Columbia disaster occurred high in the atmosphere during reentry. Even if the crew had been able to bail out, they would have been killed by the heat generated by the friction of the air.

Shuttles

Columbia disaster, Discovery, Atlantis and Endeavour. Not illustrated: Enterprise and Pathfinder.]] Individual Orbiters are both named, in a manner similar to ships, and numbered using the NASA Orbiter Vehicle Designation system. Whilst all three are externally very similar, they have minor internal differences; new equipment is fitted on a rotating basis as they are maintained, and the newer Orbiters tend to be structurally lighter.
- Handling test article designed with no spaceflight capability whatsoever:
- Pathfinder (Orbiter Simulator, no series number)
- Main propulsion test article, with no spaceflight capability whatsoever:
- MPTA-ET (External Tank) which is now attached to Pathfinder
- MPTA-098 suffered major damage due to engine failure.
- Structural test article, with no spaceflight capability:
- STA-099 which became Challenger
- Test vehicle suitable only for glide/landing tests, with no spaceflight capability without major refit:
- Enterprise (OV-101)
- Lost in accidents (see below):
- Challenger (OV-099, ex-STA-099) - destroyed after liftoff - January 28, 1986
- Columbia (OV-102) - destroyed during reentry February 1, 2003
- In use:
- Atlantis (OV-104)
- Discovery (OV-103)
- Endeavour (OV-105)

Applications

- Crew rotation of the ISS
- Manned servicing missions, such as to the Hubble Space Telescope (HST)
- Manned experiments in LEO
- Carry to LEO:
- Large satellites — these have included the HST
- Components for the construction of the ISS
- Supplies
- Carry satellites with a booster, the Payload Assist Module (PAM-D) or the Inertial Upper Stage (IUS), to the point where the booster sends the satellite to:
- A higher Earth orbit; these have included:
- Chandra X-ray Observatory
- Many TDRS satellites
- Two DSCS-III (Defense Satellite Communications System) communications satellites in one mission
- A Defense Support Program satellite
- An interplanetary orbit; these have included:
- Magellan probe
- Galileo spacecraft
- Ulysses probe

Flight statistics (as of August 25, 2005)

† Satellites deployed

- This was flight STS-80, during November 1996.

Accidents

Two Shuttles have been destroyed in 114 missions, both with the loss of the entire crew of seven:
- Challenger — lost 73 seconds after liftoff, January 28, 1986; see STS-51-L.
- Columbia — lost during reentry, February 1, 2003; see Space Shuttle Columbia disaster. This gives a 2% death rate per astronaut per flight. While the technical details of the accidents are quite different, the organisational problems show remarkable similarities. In both cases events happened which were not planned for or anticipated. In both cases, instead of dealing with the issue as unexpected and in need of complete explanation, at significant cost in time and money, the lazy attitude was to allow the unexpected events to happen as the damage done was not deemed to endanger the shuttle, although this was not actually known to be the case. In the case of Challenger, an O-ring which should not have eroded at all did, in fact, erode on earlier shuttle launches. Instead of finding out why, it was noted that it had not eroded by more than 30%, and the assumption was made was that this was not a hazard as there was a safety margin of a factor of 3. Despite repeated pleas by NASA's engineers to cancel or reschedule the launch, the managers allowed the shuttle to launch. Challenger's O-ring eroded right through, fatally, shortly after its last launch. Columbia failed as a consequence of damage caused by being struck by a piece of foam which broke off from the bipod during ascent. The foam had not been designed or expected to break off, but had been observed in the past to do so without incident.

Retrospect

Space Shuttle Columbia disaster

Costs

While the Shuttle has been a reasonably successful launch vehicle, it has been unable to meet its goal of radically reducing flight launch costs, as the average launch expenditures during its operations up to 2005 accumulates to $1.3 billion [http://sciencepolicy.colorado.edu/prometheus/archives/space_policy/], a rather large figure compared to the initial projections of $10 to $20 million. The total cost of the program has been $145 billion as of early 2005 ($112 billion of which was incurred while the program was operational) and is estimated at $174 billion when the Shuttle retires in 2010. NASA's budget for 2005 allocates 30%, or $5 billion, to Space Shuttle operations. [http://www.space.com/news/shuttle_cost_050211.html] The original mission of the Shuttle was to operate at a high flight rate, at low cost, and with high reliability. It was intended to improve greatly on the previous generation of single-use manned and unmanned vehicles. Although it did operate as the world's first reusable crew-carrying spacecraft, it did not improve on those parameters in any meaningful way, and is considered by some to have failed in its original purpose. Although the design is radically different from the original concept, the project was still supposed to meet the upgraded USAF goals, and to be much cheaper to fly in general. One reason behind this apparent failure appears to be inflation. During the 1970s the U.S. suffered from severe inflation, driving up costs about 200% by 1980. In contrast, the rate between 1990 and 2000 was only 34% in total. This magnified the development costs of the Shuttle. The original process by which contractors bid for Shuttle work has also inflated overall project costs as there were political and industrial pressures to spread Shuttle work around. For instance, the need for a single-piece SRB design was dismissed as only one company, Aerojet, was located close enough to the launch site to make this viable. The company that secured the SRB contract, Morton Thiokol, is based in Utah, necessitating the modular design that contributed to the Challenger loss. Ironically, the U.S. aerospace mergers of the 1990s mean that the vast majority of the STS contracts are now held by a single company (Boeing). However, this does not explain the high costs of the continued operations of the Shuttle. Even accounting for inflation, the launch costs on the original estimates should be about $100 million today. The remaining $400 million arises from the operational details of maintaining and servicing the Shuttle fleet, which have turned out to be tremendously more expensive than anticipated. Some of this can be attributed to operating beyond the 10-year anticipated lifespan of each Shuttle. The main reasons for higher costs can be ascribed to:

the reentry tiles turned out to be very expensive (averaging about 1 person week to replace a tile, with hundreds damaged with each launch)

engines were highly complex and marginal necessitating removal and maintenance after each flight

launch rate is much lower than ideal (studies showed that launching 50 times per year would have dramatically cut costs- the current shuttle launches about 4 times per year- the written record shows that NASA never installed any infrastructure to launch more than 12 times per year)

original costs of $118/lb were marginal costs, not total costs

Shuttle operations

When originally conceived, the Shuttle was to operate similarly to an airliner. After landing, the Orbiter would be checked out and start "mating" to the rest of the system (the ET and SRBs), and be ready for launch in as little as two weeks. Instead, this turnaround process takes months. Decisions to cut short-term development costs have resulted in a continued high-cost maintenance schedule. The documentation requirements have become extremely thorough. Dramatically increasing the number of support personnel needed to launch also caused a significant increase in costs. This was exacerbated in the aftermath of the Challenger disaster. Even simple changes require significant amounts of documentation. This paperwork results from the fact that, unlike current expendable launch vehicles, the Space Shuttle is manned and has no escape systems mode for most of the flight regime, and therefore any accident which would result in the loss of a booster would also result in the loss of the crew. Because loss of crew is unacceptable, the primary focus of the Shuttle program is to return the crew to Earth safely, which can conflict with other goals, namely to launch payloads cheaply. Furthermore, because there are cases where there are no abort modes — no potential way to prevent failure from becoming critical — many pieces of hardware simply must function perfectly and so must be carefully inspected before each flight. The result is a massively inflated labor cost, with around 25,000 workers in Shuttle operations and labor costs of about $1 billon per year. Initially NASA hoped the Shuttle's manned capacity would be justified as a "space taxi" to a revived Skylab or a Saturn V-launched "Skylab 2". With the go-ahead for the large, modular "Freedom" Space Station proposal the Shuttle appeared to have a continued justification with the prospect of a 6- to 10-crew outpost only being serviceable by the Shuttle. The scale back of the Space Station concept in the 1990s ultimately made the utility of the Shuttle as a manned ferry obsolete. NASA's justification of the STS for its own unmanned science missions has also declined. Following the Challenger disaster, use of the powerful Centaur upper stages required for interplanetary probes was ruled out. The Shuttle's history of unexpected delays also makes it liable to miss the narrow launch windows. Advances in technology over the last decade have made probes smaller and lighter, and as a result it is possible to reach Mars using a relatively cheap and reliable Delta launcher. Another possible impediment to the Shuttle system was the politically required participation of the United States Air Force. To receive the funding required, Congress mandated that the Shuttle replace all other launch vehicles in the national inventory as a cost-cutting measure. This requirement dramatically altered the size and scope of the program as the Air Force needed significant capabilities to allow it to meet national defense objectives. Ironically, neither NASA nor the Air Force got the system they wanted or needed, and the Air Force eventually returned to their older launch systems and abandoned their Vandenberg shuttle launch plans; many of the Air Force-imposed capabilities that most seriously hobbled the Shuttle system have never been used. Opinions differ on the lessons of the Shuttle. In general, however, future designers look to systems with only one stage, automated checkout and, in some cases, overdesigned (more durable) low-tech systems. Another consideration for future manned space flight is to pursue the construction and operation of "space planes", which could fly up to the edge of the atmosphere and then rocket out into Earth orbit, thereby being more efficient and versatile than such vehicles as the space shuttle.

Terrestrial transportation vehicles

- The Crawler-Transporter moves the Space Shuttle from the Vehicle Assembly Building to Launch Complex 39
- The Shuttle Carrier Aircraft is a modified Boeing 747 that flies the Space Shuttle from alternative landing sites back to Cape Canaveral.

References

- [http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/stsref-toc.html Reference manual]
- [http://science.howstuffworks.com/space-shuttle.htm How The Space Shuttle Works]
- [http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810022734_1981022734.pdf NASA Space Shuttle News Reference - 1981 (PDF document)]
- [http://science.ksc.nasa.gov/shuttle/resources/orbiters/orbiters.html Orbiter Vehicles]
- [http://www.house.gov/science/hot/columbia/rs21411.pdf Shuttle Program Funding 1992 - 2002]

External links

- [http://www.chrisvalentines.com/sts107/index.html Columbia Disaster Multi-Media]
- [http://spaceflight.nasa.gov/shuttle/ NASA Human Spaceflight - Shuttle] Current status of Shuttle missions
- [http://www.nasa.gov/ntv NASA TV] View live streaming of launch and mission coverage
- [http://www.globalsecurity.org/space/facility/sts-els.htm List of all Shuttle Landing Sites]
- [http://www.srh.noaa.gov/smg/lsitegif.htm Map of Landing Sites]
- [http://gmaps.tommangan.us/spacecraft_tracking.html Track the Shuttle] with Google Maps
- [http://www.idlewords.com/2005/08/a_rocket_to_nowhere.htm "A Rocket To Nowhere"] criticism of the Space Shuttle program
- [http://www.washingtonmonthly.com/features/2001/8004.easterbrook-fulltext.html "Beam Me Out Of This Death Trap, Scotty"] Critical article on the Space Shuttle program, from 1981
- [http://www.theatlantic.com/doc/200311/langewiesche "Columbia's Last Flight"] Article from the Atlantic Monthly on the Columbia disaster and the subsequent investigation
- [http://www.spacedaily.com/news/shuttle-03p1.html "Explaining 30 years of Fudge"] - how the shuttle program was miss-sold to congress and where the $118/lb supposed costs came from ja:スペースシャトル th:กระสวยอวกาศ Category:Spaceplanes Category:Space launch vehicles Category:Space Shuttle program

Canadarm

The Remote Manipulator System (RMS) on the Space Shuttle, also known as the Canadarm, is an electromechanical arm that maneuvers a payload from the payload bay of the space shuttle orbiter to its deployment position and then releases it. It can also grapple a free-flying payload, maneuver it to the payload bay of the orbiter and berth it in the orbiter. It was first used on the second Space Shuttle mission STS-2, launched November 12, 1981. Since the destruction of Space Shuttle Columbia during STS-107, NASA has outfitted the RMS with the Orbital Boom Sensor System - a boom containing instruments to inspect the exterior of the shuttle for damage to the Thermal Protection System. It is expected the RMS will play this role in all future shuttle missions. The RMS arm is 50 feet 3 inches (15 m) long and 15 inches (380 mm) in diameter and has six degrees of freedom. It weighs 905 pounds (410 kg), and the total system weighs 994 pounds (450 kg). The RMS has six joints that correspond roughly to the joints of the human arm, with shoulder yaw and pitch joints; an elbow pitch joint; and wrist pitch, yaw, and roll joints. The end effector is the unit at the end of the wrist that actually grabs, or grapples, the payload. The two lightweight boom segments are called the upper and lower arms. The upper boom connects the shoulder and elbow joints, and the lower boom connects the elbow and wrist joints. The RMS arm attaches to the orbiter payload bay longeron at the shoulder manipulator positioning mechanism. Power and data connections are located at the shoulder MPM. The RMS is capable of deploying or retrieving payloads weighing up to 65,000 pounds (29 t) when in space, though the arm motors are unable to move the arm's own weight under the influence of Earth's gravity. The RMS can also retrieve, repair and deploy satellites; provide a mobile extension ladder for extravehicular activity crew members for work stations or foot restraints; and be used as an inspection aid to allow the flight crew members to view the orbiter's or payload's surfaces through a television camera on the RMS. The basic RMS configuration consists of a manipulator arm; an RMS display and control panel, including rotational and translational hand controllers at the orbiter aft flight deck flight crew station; and a manipulator controller interface unit that interfaces with the orbiter computer. Most of the time the arm operators see what they are doing by looking at the Advanced Space Vision System screen next to the controllers. One flight crew member operates the RMS from the aft flight deck control station, and a second flight crew member usually assists with television camera operations. This allows the RMS operator to view RMS operations through the aft flight deck payload and overhead windows and through the closed-circuit television monitors at the aft flight deck station. Spar Aerospace Ltd., a Canadian company, designed, developed, tested and built the RMS. CAE Electronics Ltd. in Montreal provides electronic interfaces, servoamplifiers and power conditioners. Dilworth, Secord, Meagher and Associates Ltd. in Toronto is responsible for the RMS end effector. Rockwell International's Space Transportation Systems Division designed, developed, tested and built the systems used to attach the RMS to the payload bay of the orbiter.

External links

- http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-caws.html#sts-deploy
- http://www.space.gc.ca/asc/eng/exploration/canadarm/default.asp Category:Spacecraft components Category:Canadian space program Category:Space Shuttle program

International Space Station

The International Space Station (ISS) is a joint project of six space agencies:
- National Aeronautics and Space Administration (United States)
- Russian Federal Space Agency (Russian Federation)
- Japan Aerospace Exploration Agency (Japan)
- Canadian Space Agency (Canada)
- Brazilian Space Agency (Brazil)
- European Space Agency (United Kingdom, Ireland, Portugal, Austria and Finland choose not to participate; Greece and Luxembourg joined ESA later). The space station is located in orbit around the Earth at an altitude of approximately 360 km (220 miles), a type of orbit usually termed low Earth orbit (The actual height varies over time by several kilometres due to atmospheric drag and reboosts ). It orbits Earth in a period of about 92 minutes; by June 2005 it had completed more than 37,500 orbits since launch of the Zarya module on November 20, 1998. In many ways the ISS represents a merger of previously planned independent space stations: Russia's Mir 2, United States' Space Station Freedom and the planned European Columbus. Today it represents a permanent human presence in space, as it has been manned with a crew of at least two since November 2, 2000 (see #ISS Expeditions). It is serviced primarily by the Space Shuttle, Soyuz and Progress spacecraft units. It is still being built, but is home to some experimentation already. At present, the station has a capacity for a crew of three. So far, all members of the expedition crews have come from the Russian or United States space programs. The ISS has however been visited by many more astronauts, a number of them from other countries (and by three space tourists).

Name

The name "International Space Station" (abbreviated MKS in Russian) represents a neutral compromise ending a disagreement about a proper name for the station. The initially proposed name "Space Station Alpha" was rejected by Russia, since it would have implied that the station was something fundamentally new, whereas the Soviet Union already had operated eight orbital stations long before the ISS launch (see Space station). The Russian proposal to name the space station "Atlant" was in turn rejected by the US, which was worried about that name's similarity to "Atlantis", the name of a legendary continent that sank into the ocean. The use of "Atlantis" would also have caused confusion with the US shuttle Atlantis.

Radio call sign

It should be noted that, although the space station's name is "International Space Station", the station's call sign is Alpha. This call sign was requested immediately upon the embarkation of Expedition 1, by the crew itself. A clearly stunned NASA Administrator Dan Goldin said "Temporarily, take it as Alpha", but the name stuck. As a result, the ISS is not named as such when hailed. "Discovery, Alpha" is thus a common call during Station-Shuttle docking procedures. Note: there is a ham radio aboard the station that gives reports to an Earth-bound station.

History

Initially planned as a NASA "Space Station Freedom" and promoted by President Reagan, it was found to be too expensive. After the end of the Cold War, it was taken up again as a joint project of NASA and Russia's Rosaviakosmos. On December 1, 1987, NASA announced the names of four U.S. companies who were awarded contracts to help manufacture the US-built parts of the Space Station: Boeing Aerospace, General Electric's Astro-Space Division, McDonnell Douglas, and the Rocketdyne Division of Rockwell. The first section, the Zarya Functional Cargo Block, was put in orbit in November 1998. Two further pieces (the Unity Module and Zvezda service module) were added before the first crew, Expedition 1, was sent. Expedition 1 docked to the ISS on November 2, 2000 and consisted of US astronaut William Shepherd and two Russian cosmonauts, Yuri Gidzenko and Sergei Krikalev. To construct the station, the large components are almost entirely completed on Earth, so that when they are launched into orbit the amount of installation required by the astronauts on the ISS is minimal. The components are usually launched in the large cargo bay of the NASA Space Shuttle. Currently the assembly sequence is just under half complete. As of 2005 the station is only able to accommodate three permanent crew members, compared to the expected seven that the completed station will hold. The ISS has been far more expensive than originally anticipated by NASA. Its construction is also behind schedule, largely due to the halting of all NASA Shuttle flights following the Columbia disaster in early 2003. For the two and a half years that the NASA Space Shuttle fleet was grounded, crew rotation continued on the station through the use of the Russian Soyuz spacecrafts, although the science conducted aboard was very limited. Construction of the station was scheduled to resume in 2006, following a few 'Return to Flight' missions, like STS-114. Unfortunately, the reappearance of the foam debris problem on the STS-114 mission in July 2005, (the same that doomed Columbia) has again delayed the launch sequence, and has even called into question the future of the space station.

Building the ISS

- ISS assembly sequence Building the ISS will require more than 50 assembly and utilization flights. Of these flights, 39 are Space Shuttle flights. In addition to the assembly and utilization flights, approximately 30 Progress spacecraft flights are required to provide logistics. When assembly is complete, the ISS will have a pressurized volume of 1,200 cubic meters, a mass of 419,000 kilograms, 110 kilowatts of power output, a truss 108.4 meters long, modules 74 meters long, and a crew of six. The station consists of several modules and elements: Launched on periodic resupply missions
- Multi-Purpose Logistics Module (MPLM) Scheduled for launch by Shuttle after return to flight
(listed in order of planned launch sequence)
- Node 2 (launch ~12/06)
- Columbus Laboratory (launch ~03/07)
- Japanese Experiment Module (JEM), aka KIBO (launch ~09/07)
- Node 3 - (launch ~05/08)
- Centrifuge Accommodations Module (launch ~7/09)
- Science Power Platform (launch ~10/10)
- Cupola - (launch ~03/09) Scheduled for launch by Proton rocket
- Multipurpose Laboratory Module FGB-2 based - (launch ~2007)
- European Robotic Arm (ERA) (2007),
- Russian Research Module reduced to 1 (launch ~2009) Cancelled elements
- Universal Docking Module - cancelled, replaced by (MLM - FGB2)
- Docking and Stowage Module - cancelled
- Habitation Module - cancelled
- Crew Return Vehicle (CRV) - cancelled
- Interim Control Module - cancelled, no need to replace Zvezda
- ISS Propulsion Module - cancelled, no need to replace Zvezda Visiting spacecrafts
- Soyuz spacecraft for crew rotation and emergency evacuation, replaced every 6 months
- Progress spacecraft - resupply vehicle
- European (ESA) Automated Transfer Vehicle (ATV) ISS resupply spacecraft
- Japanese (JAXA) H-II Transfer Vehicle (HTV) resupply vehicle for KIBO module There is also a large unpressurized truss system partially in place that will eventually support the prominent solar arrays.

Purpose of the ISS

There are many critics of NASA who view the project as a waste of time and money, inhibiting progress on more useful projects: for instance, the estimated $100 billion USD lifetime cost could pay for dozens of unmanned scientific missions. There are many critics of space exploration in general, who argue that the $100 billion USD would be better spent on problems on Earth. Advocates of space exploration hold that such criticisms are at the very least short-sighted, and perhaps deceptive. Advocates of manned space research and exploration claim that these efforts have indeed produced billions of dollars of tangible benefits to people on Earth. In some estimates, it has been held that the indirect economic benefit, made from commercialization of technologies developed during manned space exploration, has returned more than seven times the initial investment to the economy (some conservative estimates put the amount at three times the initial investment). Whether the ISS, as distinct from the wider space program, will be a major contributor in this sense is, however, a subject of strong debate. More cynical advocates have pointed out that even if its scientific value is nil, it would have still served to force international cooperation at a time of tough international politics. The ISS has seen the first space tourist, Dennis Tito, who spent 20 million USD to fly aboard a Russian supply mission and the first space wedding when Yuri Malenchenko on the station married Ekaterina Dmitriev who was in Texas.

Present status of the ISS

Yuri Malenchenko After the breakup of Columbia on February 1, 2003, and the subsequent two and a half year suspension of the US Space program, followed by problems with resuming flight operations in 2005, there remains some uncertainty over the future of the ISS. Due to weight restrictions and design constraints, payloads intended for the Shuttle - even if ready to fly - cannot be launched to the station on any other available launcher. In addition, assembly work is manpower-intensive, making it difficult to do without the assistance of EVA teams brought up by the Shuttle. In the meantime, crew exchange has been carried out using the Russian Soyuz spacecraft. Starting with Expedition 7, two-astronaut caretaker crews have been launched, instead of the previous crews of three. However, Soyuz lacks the raw cargo space of the shuttle, and cannot carry a significant amount of material back to earth; because the ISS had not been visited by a shuttle for an extended period, a large amount of waste accumulated which temporarily hindered station operations. The Space Shuttle Program resumed flight on 26 July 2005 with STS-114, the Return to Flight mission of Discovery. This mission to the ISS was intended to both test new safety measures implemented since the Columbia disaster, and to deliver supplies to the station. Whilst the mission succeeded safely, it was not without risk; foam was shed by the external tank, leading NASA to announce future missions would be grounded until this issue was resolved. Discovery The second Return to Flight mission, STS-121 was planned for September 2005, but has been delayed until at least March 2006.

ISS Expeditions

The International Space Station is the most-visited spacecraft in the history of space flight. As of August 28, 2005, it has had 141 (non-distinct) visitors. Mir had 137 (non-distinct) visitors (See Space station).

References

Herman Potočnik
- [http://www.spaceref.com/iss/ SpaceRef] - Regularly updated detailed status reports of the station.
- [http://vesuvius.jsc.nasa.gov/er/seh/td9702.pdf ISS Familiarization and Training Manual - NASA July 1998 (PDF format)]
- [http://www.spaceflight.nasa.gov/station/isstodate.html Current ISS Vital Statistics]

Advanced Space Vision System

Laser

Physics

History

Recent innovations

Uses of lasers

Popular misconceptions

Laser safety

Common laser types

See also

External links

Space Shuttle

History

The Shuttle decision

Development

Description

Components

Technical data

Normal ascent

Ascent abort modes

Intact abort modes

Contingency abort mode

Shuttles

Applications

Flight statistics (as of August 25, 2005)

Accidents

Retrospect

Costs

Shuttle operations

Terrestrial transportation vehicles

See also

References

External links

Canadarm

See also

External links

International Space Station

Name

Radio call sign

History

Building the ISS

Purpose of the ISS

Present status of the ISS

ISS Expeditions

See also

ISS-related articles

Other

References

External links</