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Docking Maneuver

Docking maneuver

A space rendezvous between two spacecraft, often between a spacecraft and a space station, is an orbital maneuver where the two arrive at the same orbit, make the orbital velocities the same, and bring them together (an approach maneuver, taxiing maneuver); it may or may not include docking. Examples:
- A visit to the International Space Station (manned) by:
- Soyuz spacecraft (manned)
- Space Shuttle (manned)
- Progress spacecraft (unmanned)
- Visit to the Hubble Space Telescope (unmanned), for servicing, by Space Shuttle (manned), and possibly in future by the Hubble Robotic Vehicle (HRV) to be developed (unmanned)
- a small unmanned spacecraft, the CX-OLEV, to be launched as a secondary payload, is being developed for rendez-vous with a geosynchronous satellite that has run out of fuel, to take over orbital stationkeeping and/or finally bring it to a graveyard orbit, after which the CX-OLEV can possibly be reused for another satellite; gradual transfer from the geostationary transfer orbit to the geosynchronous orbit will take a number of months, using Hall effect thrusters.[http://www.orbitalrecovery.com/news15.html]
- Moon landing crew returning from the Moon in the ascent stage of the Apollo Lunar Module (LM), to the Apollo Command/Service Module (CSM) orbiting the Moon (Project Apollo) (both manned)
- The STS-49 crew attached a rocket motor to the Intelsat VI (F-3) communications satellite to allow it an orbital maneuver Alternatively the two are already together, and just undock and dock in a different way:
- Soyuz spacecraft from one docking point to another on the ISS
- in the Apollo spacecraft, an hour or so after Trans Lunar Injection of the sequence third stage of the Saturn V rocket/ LM inside LM adapter / CSM (in order from bottom to top at launch, also the order from back to front with respect to the current motion), with CSM manned, LM at this stage unmanned:
- the CSM separated, while the four upper panels of the LM adapter were disposed of
- the CSM turned 180 degrees (from engine backward, toward LM, to forward)
- the CSM connected to the LM while that was still connected to the third stage
- the CSM/LM combination then separated from the third stage Another kind of "rendezvous" was in 1969, when the Apollo 12 mission involved a manned landing on the Moon within walking distance of the unmanned Surveyor 3, which had made a soft landing in 1967. Parts of the Surveyor were brought back. Later analysis showed that bacteria had survived their stay on the Moon. On August 12, 1962 Vostok 3 and Vostok 4 were placed into adjacent orbits and passed within several kilometers of each other, but did not have the orbital maneuvering capability to perform a space rendezvous. This was also the case on June 16, 1963 when Vostok 5 and Vostok 6 were launched into adjacent orbits. The first space rendezvous took place on December 15, 1965 when Gemini 6 came within 30-cm of Gemini 7. The spacecraft were not equipped to dock and no physical contact took place. The first space rendezvous and docking took place on March 16, 1966 when Gemini 8 rendezvoused and docked with the uncrewed Agena 8 target vehicle. An example of an undesired rendezvous in space is an uncontrolled one with space debris. Anti-satellite weapons partly fall under the category of hostile rendezvous. "Non-energy weapons" are those which do not use explosives or radiation, but just collide. Category:Astrodynamics

Spacecraft

, 2004.]] A spacecraft is a vehicle that travels through space. Spacecraft include robotic or unmanned space probes as well as manned vehicles. The term is sometimes also used to describe artificial satellites, which have similar design criteria.

Overview

The term spaceship is generally applied only to spacecraft capable of transporting people. A space suit has at times been called a miniature spacecraft or spaceship, emphasizing its purpose of keeping its wearer alive while traveling in the vacuum of outer space. The spacecraft is one of the primal elements in science fiction. Numerous short stories and novels are built up around various ideas for spacecraft. Some hard science fiction books focus on the technical details of the craft, while others treat the spacecraft as a given and delve little into its actual implementation.

Examples of past or existing spacecraft

Manned
- Apollo Spacecraft
- Gemini Spacecraft
- International Space Station
- Mir
- Mercury Spacecraft
- Shuttle Buran
- Shenzhou Spacecraft
- Space Shuttle
- Soyuz Spacecraft
- SpaceShipOne
- Voskhod Spacecraft
- Vostok Spacecraft Unmanned
- Cassini-Huygens
- Cluster
- Deep Space 1
- Genesis
- Mars Exploration Rover
- Mars Global Surveyor
- Mars Pathfinder
- Pioneer 10
- Pioneer 11
- Progress
- SOHO
- Stardust
- Viking 1
- Viking 2
- Voyager 1
- Voyager 2
- WMAP

Spacecraft under development

- Crew Exploration Vehicle
- Kliper
- Automated Transfer Vehicle
- H-II Transfer Vehicle
- Ansari X Prize (incl. a list of spacecraft in various stages of completion as of 2005) The US Space Command, according to its "Long Range Plan", is currently planning to develop a weaponized spaceship, which has yet to be announced.[http://www.fas.org/spp/military/docops/usspac/]

External links

- [http://science.hq.nasa.gov/missions/phase.html NASA: Space Science Spacecraft Missions]
- [http://www.skyrocket.de/space/ Gunter's Space Page - Complete information on spacecraft]
- [http://www.cinespaceships.net/ Cinespaceships - Database on spaceships in movie]
- ja:宇宙船

Space station

A space station is an artificial structure designed for humans to live in outer space. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities — instead, other vehicles are used as transport to and from the station. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years. Space stations are used to study the effects of long-term space flight on the human body as well as to provide platforms for greater number and length of scientific studies than available on other space vehicles. Since the ill-fated flight of Soyuz 11 to Salyut 1, all manned spaceflight duration records have been set aboard space stations. The duration record of 437.7 days was set by Valeri Polyakov aboard Mir from 1994 to 1995. As of 2005, 3 astronauts have completed single missions of over a year, all aboard Mir.

Past and present space stations

- Salyut stations: Salyut 1, Salyut 2 (failed on-orbit, never occupied), Salyut 3, Salyut 4, Salyut 5, Salyut 6, Salyut 7
- Skylab
- Mir
- International Space Station (ISS) Following the controlled deorbiting of Mir in 2001, the International Space Station is the only one of these currently in orbit; it has been continuously manned since October 30, 2000. A second Skylab unit (Skylab B) was manufactured, as a backup article; due to the high costs of providing launch vehicles, and a desire by NASA to cease Saturn & Apollo operations in time to prepare for the Space Shuttle coming into service, it was never flown. The hull can now be seen in the National Air and Space Museum, in Washington DC, where it is a popular tourist attraction. A number of additional Salyuts were also produced, as backups or as flight articles which were later cancelled. The International Space Station evolved from the American Space Station Freedom program, which - despite being under development for ten years - was never launched; it incorporated elements of a Mir replacement station ("Mir 2") which was also never constructed. Other cancelled space station programs included the United States Air Force Manned Orbiting Laboratory project, cancelled in 1969 about a year before the first planned test flight; this was unusual in being an explicitly military project, as opposed to the Soviet Almaz program, which was heavily intertwined with - and concealed by - the contemporaneous Salyut program. Currently, Bigelow Aerospace is commercially developing inflatable habitat modules, derived from the earlier Transhab concept, intended to be used for space station construction.

Types of space station

Broadly speaking, the space stations so far launched have been of two types; the earlier stations, Salyut and Skylab, have been "monolithic", intended to be constructed and launched in one piece, and then manned by a crew later. As such, they generally contained all their supplies and experimental equipment when launched, and were considered "expended", and then abandoned, when these were used up. Starting with Salyut 6 and 7, a change was seen; these were built with two docking ports, which allowed a second crew to visit, bringing a new spacecraft (for technical reasons, a Soyuz capsule cannot spend more than a few months on orbit, even powered down, safely) with them. This allowed for a crew to man the station continually. The presence of a second port also allowed Progress supply vehicles to be docked to the station, meaning that fresh supplies could be brought to aid long-duration missions. This concept was expanded on Salyut 7, which "hard docked" with a TKS tug shortly before it was abandoned; this served as a proof-of-concept for the use of modular space stations. The later Salyuts may reasonably be seen as a transition between the two groups. The second group, Mir and the ISS, have been modular; a core unit was launched, and additional modules, generally with a specific role, were later added to that. (On Mir they were usually launched independently, whereas on the ISS most are brought by the Shuttle). This method allows for greater flexibility in operation, as well as removing the need for a single immensely powerful launch vehicle. These stations are also designed from the outset to have their supplies provided by logistical support, which allows for a longer lifetime at the cost of requiring regular support launches. These stations have various issues that limit their long-term habitability, such as very low recycling rates, high radiation levels and a lack of gravity. Some of these problems cause discomfort and long-term health effects. In the case of solar flares, most current habitats even have an acute danger of radiation poisoning. Some space habitats address these issues, and are intended for long-term occupation. Some designs might even accommodate large numbers of people, essentially "cities in space" where people would make their homes. No such design has yet been constructed, because even for a small station, the extra equipment is too expensive to place in orbit at current (2005) launch costs.

List of occupied space stations, with statistics

-
- ISS stats as of August 28, 2005.
-
- ISS stats as of October 6, 2005.

In fiction

A large amount of science fiction is set on space stations. A notable example is Babylon 5, a series set on a space station by that name far into the future. Similarly, Deep Space 9 is a prominent space station in the Star Trek story line. It was built by the Cardassians around Bajor and later staffed by Federation personnel. The film (and novel) 2001: A Space Odyssey contains a large space station, built as a revolving ring; this has proven to be one of the iconic images of a space station in popular culture. The James Bond film Moonraker featured a space station which serves as Hugo Drax's lair and a base to nerve-gas Earth. The Star Wars films A New Hope (Star Wars) and Return of the Jedi each feature a heavily armored space station known as the Death Star, which is capable of destroying a planet. Some may dispute the usage of the term space station to describe the Death Stars because they are capable of traveling great distances. Category:Space stations ja:宇宙ステーション

Orbital maneuver

An orbital maneuver is a change from one orbit to another, accomplished by applying thrust. In deep space it is called deep-space maneuver (DSM).

Impulsive maneuvers

An impulsive maneuver approximates a finite thrust maneuver by adding an instantaneous velocity change to an ephemeris record while maintaining the position. During the planning phase of most space or rocket missions, designers will first calculate orbital changes using impulsive maneuvers. This greatly reduces the complexity of finding the correct orbital transitions. The instantaneous changes in velocity are referred to as delta-v (

\Delta\mathbf\,

), the total delta-v for all maneuvers required in the mission is called a delta-v budget. With a good approximation of the delta-v budget designers can estimate the fuel to payload requirements of the spacecraft. Using these approximations are most useful when finite thrusts are to be executed in short bursts. Finite maneuvers like these are possible with high thrust-to-weight propulsion systems, e.g. chemical rockets. However, even for long burns, impulsive maneuver approximations remain very accurate outside the Earth's atmosphere.

Non-impulsive maneuvers

Applying a low thrust over longer periods of time is referred to as non-impulsive maneuvers (even though any thrust can be said to produce an amount of impulse). They are less efficient as energy can be lost due to gravity drag. However those maneuvers can be the only option when efficient but low thrust-to-weight propulsion systems are used (e.g. ion engines). They are not possible for a launch.

Finite Burn Trajectories

For a few space missions high fidelity models of the trajectories are required to meet the mission goals. Calculating a finite burn requires a detailed model of the spacecraft and its thrusters. The most important of details include: mass, center of mass, moment of inertia, thruster positions, thrust vectors, thrust curves, specific impulse, thrust centroid offsets and fuel consumption.

Orbital velocity

The orbital speed of a body, generally a planet, a natural satellite, an artificial satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body. It can be used to refer to either the mean orbital speed, the average speed as it completes an orbit, or instantaneous orbital speed, the speed at a particular point in its orbit. The orbital speed at any position in the orbit can be computed from the distance to the central body at that position, and the specific orbital energy, which is independent of position: the kinetic energy is the total energy minus the potential energy. Thus, under standard assumptions the orbital speed (

v\,

) is:
- in general:

v=
\sqrt

- elliptic orbit:

v=
\sqrt

- parabolic trajectory:

v=\sqrt

- hyperbolic trajectory:

v=\sqrt

where:
-

\mu\,

is the standard gravitational parameter
-

r\,

is the distance between the orbiting body and the central body
-

\epsilon\,

is the specific orbital energy
-

a\,\!

is the semi-major axis Note:
- Velocity does not explicitly depend on eccentricity but is determined by length of semi-major axis (

a\,\!

Radial trajectories

In the case of radial motion:
- if the energy is non-negative: the motion is either for the whole trajectory away from the central body, or for the whole trajectory towards it. For the zero-energy case, see escape orbit and capture orbit.
- if the energy is negative: the motion can be first away from the central body, up to r=μ/|ε|, then falling back. This is the limit case of an orbit which is part of an ellipse with eccentricity tending to 1, and the other end of the ellipse tending to the center of the central body.

Transverse orbital speed

The transverse orbital speed is inversely proportional to the distance to the central body because of the law of conservation of angular momentum, or equivalently, Kepler's second law. This states that as a body moves around its orbit during a fixed amount of time, the line from the barycenter to the body sweeps a constant area of the orbital plane, regardless of which part of its orbit the body traces during that period of time. This means that the body moves faster near its periapsis than near its apoapsis, because at the smaller distance it needs to trace a greater arc to cover the same area. This law is usually stated as "equal areas in equal time."

Mean orbital speed

For orbits with small eccentricity, the length of the orbit is close to that of a circular one, and the mean orbital speed can be approximated either from observations of the orbital period and the semimajor axis of its orbit, or from knowledge of the masses of the two bodies and the semimajor axis. :

v_o \approx

v_o \approx \sqrt

where

v_o

is the orbital velocity,

a

is the length of the semimajor axis,

T

is the orbital period,

m

is the mass of the other body, and

G

is the gravitational constant. Note that this is only an approximation that holds true when the orbiting body is of considerably lesser mass than the central one, and eccentricity is close to zero. Taking into account the mass of the orbiting body, :

v_o \approx \sqrt

where

m_1

is now the mass of the body under consideration,

m_2

is the mass of the body being orbited, and

r

is specifically the distance between the two bodies (which is the sum of the distances from both to the barycenter). This is still a simplified version; it doesn't allow for elliptical orbits, but it does at least allow for bodies of similar masses. For an object in an eccentric orbit orbiting a much larger body, the length of the orbit decreases with eccentricity

e

, and is given at ellipse. This can be used to obtain a more accurate estimate of the average orbital speed: :

v_o = \frac\left[1-\frac-\frac - \dots \right]

The mean orbital speed decreases with eccentricity. See also examples. Category:Celestial mechanics ja:軌道速度

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]

External links

- [http://science.nasa.gov/Realtime/JTrack/3D/JTrack3D.html NASA 3D Java Tracker for ISS and other Satellites]
- [http://www.space.gc.ca/asc/eng/iss/default.asp International Space Station — CSA Site]
- [http://www.energia.ru/english/energia/iss/iss.html International Space Station — Energia site]
- [http://www.esa.int/esaHS/iss.html International Space Station — ESA site]
- [http://www.jaxa.jp/missions/projects/iss_human/index_e.html International Space Station — JAXA site]
- [http://samba.aeb.gov.br/conteudo.php?ida=28&idc=118 International Space Station — AEB site]
- [http://www.nasa.gov/mission_pages/station/main/index.html International Space Station — NASA site]
- [http://stream1.euronews.net:8080/ramgen/mag/space-issquovadis-en.rm?usehostname International Space Station — EuroNews report (Real player video stream)]
- [http://www.astronautix.com/craft/intation.htm International Space Station] from Encyclopedia Astronautica
- [http://spd.nasa.gov/ NASA Space Partnership Development]
- [http://spacelink.nasa.gov/NASA.Projects/Human.Exploration.and.Development.of.Space/Space.Product.Development/.index.html Spacelink — Space Product Development]
- [http://www.planetarysociety.org/ The Planetary Society]
- http://www.seds.org/pub/seds/National/misc/why-space
- [http://esa.heavens-above.com/esa/iss_step1.asp See the ISS from your home town]
- [http://www.heavens-above.com/ Heavens Above] — locate ISS, and find when to view it, from any location.
- [http://spaceflight.nasa.gov/shuttle/future/index.html NASA Human Spaceflight - ISS Assembly Sequence webpage]
- [http://www.sworld.com.au/steven/space/shuttle/manifest.txt Unofficial Shuttle Launch Manifest]
- [http://gmaps.tommangan.us/spacecraft_tracking.html Track the ISS] with Google Maps
- http://www.issfanclub.com Category:International Space Station Category:Space stations Category:Manned spacecraft Category:Big Science ja:国際宇宙ステーション

Soyuz spacecraft

Soyuz (Soyus, Союз, union) is a series of spacecraft designed by Sergey Korolev for the Soviet Union's space program. The Soyuz succeeded the Voskhod spacecraft design and were originally built as part of the Luna program. The spacecraft are launched by the Soyuz launch vehicle, as part of the Soyuz program and the later missions of the Zond program. They were later used to carry cosmonauts to and from the Salyut and Mir space stations and are now used for transport to and from the International Space Station. The first unmanned launch of the Soyuz was on November 28 1966. The first manned launch of the Soyuz was on April 23 1967.

Spacecraft design

A Soyuz spacecraft consists of three parts. From front to back, a roughly spherical orbital module, a small smooth reentry module, and a cylindrical service module with solar panels attached. The first two portions are habitable living space. By moving as much as possible into the orbital module, which does not have to be shielded or decelerated during atmospheric reentry, the Soyuz is both larger and lighter than the Apollo spacecraft's command module. The Apollo command module had 6 cubic meters of living space and a mass of 5000 kg; the 3-part Soyuz provided the same crew with 9 cubic meters of living space, an airlock, and the service module for the mass of the Apollo capsule alone. Soyuz can carry up to three cosmonauts and provide life support for them for up to 3.2 days. The life support system provides a nitrogen/oxygen atmosphere at sea level partial pressures. The atmosphere is regenerated through KO₂ cylinders which absorbs most of the CO₂ and water produced by the crew and regenerates the oxygen, and LiOH cylinders which absorb leftover CO₂. The vehicle is protected during launch by a nose fairing, which is jettisoned after passing through the atmosphere. It has an automatic docking system. The ship can be operated automatically, or by a pilot independently of ground control. The forepart of the spacecraft is the orbital module. It houses all the equipment that will not be needed for reentry, such as experiments, cameras or cargo. It also contains the docking port and can be isolated from the descent module to act as an airlock if needed. This separation also lets the orbital module be customized to the mission with less risk to the life-critical descent module. The descent module is used for launch and the journey back to Earth. It is covered by a heat-resistant covering to protect it during re-entry. It is slowed initially by the atmosphere, then by a braking parachute, followed by the main parachute which slows the craft for landing. At 1 metre above the ground, solid-fuel braking engines mounted behind the heat shield are fired to give a soft landing. One of the design requirements for the reentry module was for it to have the highest possible volumetric efficiency (internal volume divided by hull area). The best shape for this is a sphere, but such a shape can provide no lift, which results in a purely ballistic reentry. Ballistic reentries are hard on the occupants due to high deceleration and can't be steered beyond their initial deorbit burn. That is why it was decided to go with the 'headlight' shape that the Soyuz uses - a hemispherical forward area joined by a barely angled cone (7 degrees) to a classic spherical section heat shield. This shape allows a small amount of lift to be generated due to the unequal weight distribution. The nickname was thought up at a time when nearly every headlight was circular. At the back of the vehicle is the service module. It has a pressurized container shaped like a bulging can that contains systems for temperature control, electric power supply, long-range radio communications, radio telemetry, instruments for orientation and control. A non-pressurized part of the service module contains the main engine and a spare: liquid-fuel propulsion systems for maneuvering in orbit and initiating the descent back to Earth. The ship also has a system of low-thrust engines for orientation. Outside the service module are the sensors for the orientation system and the solar array, which is oriented towards the sun by rotating the ship.

The many incarnations of the Soyuz

propulsion system The first manned version of the Soyuz was called 7K-OK. It could support up to three crewmembers in a shirt-sleeve environment. Although it could feature a docking fixture, this was passive and only allowed the two spacecraft to be joined, with no facility for internal transfer. Cosmonauts had to spacewalk to the other spacecraft, as done on Soyuz 4 and 5. This spacecraft was also designed to fly to the moon. The 7K-L1 was designed to launch men from the Earth to circle the moon. It was based on the 7K-OK with several components stripped out to reduce the vehicle weight. The most notable modifications included the removal of the orbital module (extra space for living quarters or equipment) and reserve parachute. It was the primary hope for Soviet circumlunar flight. Tests in the Zond program from 1968-1970 produced multiple failures in the 7K-L1's re-entry systems. The goal was scrapped, along with the two remaining 7K-L1s. The next manned version of the Soyuz was the 7K-OKS. This was designed for space station flights and now had a docking port that allowed internal transfer between spacecraft. It flew only twice manned. During the reentry of the second flight, Soyuz 11, the crew were killed when the capsule depressurised during the re-entry phase. The complete redesign that resulted led to the 7K-T. It deleted one crew space so that all cosmonauts could wear spacesuits during launch and reentry. The replacement of solar panels with batteries limited it to about two days of undocked flight. A modified version of this spacecraft flew on Soyuz 13 where instead of the docking system was a large Orion 2 astrophysical camera for imaging the sky and Earth. Another modification was the 7K-T/A9 used for the flights to the military Almaz space station. This featured the ability for remote control of the space station and a new parachute system but other than that the changes are still classified and unknown. The Soyuz ASTP spacecraft was designed for use during the Apollo Soyuz Test Project. It featured design changes mandated by the Americans to make the spacecraft safer. The Soyuz ASTP featured new solar panels for increased mission length, an androgynous universal docking mechanism instead of the standard male mechanism and modifications to the environmental control system to lower the cabin pressure to 0.68 atmospheres (69 kPa) prior to docking with Apollo. The last flight of this version, Soyuz 22 again replaced the docking port with a camera. The next major redesign was the Soyuz T version. It featured solar panels allowing longer missions, a revised Igla rendezvous system and new translation/attitude thruster system on the Service module. The Soyuz TM crew transports were introduced in 1986 to service the Mir space station. It added to the Soyuz T new docking and rendezvous, radio communications, emergency and integrated parachute/landing engine systems. The new Kurs rendezvous and docking system permitted the Soyuz TM to maneuver independently of the station, without the station making "mirror image" maneuvers to match unwanted translations introduced by earlier models' aft-mounted attitude control. A slightly modified Soyuz TMA is now also being used. This features several changes to accommodate requirements requested by the American space agency NASA, including more latitude in the height and weight of the crew and improved parachute systems. It is also the first expendable vehicle to feature "glass cockpit" technology. The unmanned Progress spacecraft were derived from Soyuz and are used for servicing space stations. The Chinese Shenzhou spacecraft is also heavily influenced by the design of the Soyuz. In 2004, Russian space officials announced that the Soyuz will be replaced by early 2011 with the new Kliper spacecraft. See also:
- Sokol space suit
- space exploration

Missions

See List of manned space missions as well as the Zond program

External references

- David S.F. Portree, [http://spaceflight.nasa.gov/history/shuttle-mir/references/r-documents-mirhh.htm Mir Hardware Heritage], NASA RP-1357, 1995
- [http://www.astronautix.com/craftfam/index.htm Information on Soyuz spacecraft] (search for Soyuz on that page for links to every spacecraft imaginable)
- [http://www.io.com/~o_m/ssh_forgotten_astp.html OMWorld's ASTP Docking Trainer Page] Category:International Space Station Category:Manned spacecraft Category:Soyuz programme

Progress spacecraft

The Progress is a Russian expendable unmanned freighter spacecraft; it was derived from the Soyuz spacecraft, and is launched with the Soyuz launch vehicle. It is currently used to supply the International Space Station, but was originally used to supply Russian space stations for many years. There are three to four flights of the Progress spacecraft to the ISS per year. Each spacecraft remains docked until shortly before the new one arrives. Then it is filled with waste, disconnected, deorbited, and destroyed in the atmosphere. It has carried fuel and other supplies to all the space stations since Salyut 6. The idea for the Progress came from the realisation that in order for long duration space missions to be possible, there would have to be constant source of supplies. It had been determined that a cosmonaut needed 30 kg of consumables a day; this equates to 5.4 tonnes over a 6 month stay. It was impractical to launch this along with cargo of the Space Shuttle missions, or in the small space available in the Soyuz.

Design

Progress is of much the same size and shape as Soyuz. It consists of three modules:
- A pressurised forward module. This carries the supplies for the crew such as scientific equipment, clothes, prepackaged and fresh food, and letters from home. The docking drogue is similar to that of the Soyuz but features ducting for the UDMH fuel and N₂O₄ oxidiser.
- A fuel compartment. The reentry module of the Soyuz was replaced with an unpressurized propellant and refueling compartment with ducting along the outside of the spacecraft. This meant that if a leak occurred, the poisonous gas would not enter the station's atmosphere. The fuel was carried in two tanks.
- A propulsion module. The propulsion module, at the rear of the spacecraft, remained unchanged and contains the orientation engines used for the automatic docking. It may be used to boost the orbit of the station once docked. Reduction in weight was possible because the Progress was designed to be unmanned and disposable. This means that there is no need for bulky life support systems and heat shields. The spacecraft also has no ability to split into separate modules. After undocking, the spacecraft performs a retrofiring and burns up in the atmosphere.

Versions

There were many small variations between the different flights, but the major upgrades are reflected in the change of name.

Progress

There were 42 spacecraft under the name Progress, the last one being launched in May 1990. The bureau in charge of designing the freighter was TsKBEM (now RKK Energia). They began work on the design in mid-1973, assigning Progress the rather cryptic designation 11F615A15. The design was complete by February, 1974, and the first production model was ready for launch in November 1977. Progress 1 launched on January 20, 1978 aboard the same rocket used to launch the Soyuz. It still featured the same launch shroud as the Soyuz, though this was purely for aerodynamic purposes as the launch escape system had been deactivated. This first version of Progress had a mass of 7,020 kg and carried 2,300 kg of cargo, or 30% of its launch weight. It had the same diameter as the Soyuz at 2.2 metres, but was 8 metres in length—slightly longer. The autonomous flight time was 3 days, the same time as that of the Soyuz ferry. It could spend one month docked. Progress always docked to the aft port of the station it was resupplying.
- Launch weight 7,020-7,249 kg
- Weight of cargo (Progress 1-24) ~2,300 kg
- Weight of cargo (Progress 24-42) ~2,500 kg
- Length 7.94 m
- Diameter of cargo modules 2.2 m
- Maximum diameter 2.72 m
- Volume of cargo compartment 6.6 m³

Progress M

The upgrade Progress M was first launched in August 1989. The first 43 flights all went to Mir; following Mir's re-entry, there have been about 10 flights to the International Space Station, and more are scheduled. It is essentially the same spacecraft as the Progress, but it features improvements from the Soyuz T and Soyuz TM. It can spend up to 30 days in autonomous flight and is able to carry 100 kg more to Mir. Also, contrary to the old Progress crafts, it can return items to Earth. This is accomplished by using the Raduga capsule, which can carry up to 150 kg of cargo. It is 1.5 m long and 60 cm in diameter and has a "dry weight" of 350 kg. Progress M can dock to the forward port of the station and still transfer fuel. It uses the same rendezvous system as the Soyuz, and it features solar panels for the first time.
- Launch weight 7,130 kg
- Cargo weight 2,600 kg
- Dry cargo weight 1,500 kg
- Liquid cargo weight 1,540 kg
- Length 7.23 m
- Solar array span 10.6 m
- Dry cargo compartment volume 7.6 m³
- Diameter of cargo modules 2.2 m
- Maximum diameter 2.72 m

Progress M1

Progress M1 was another variant, capable of carrying more propellant (but less total cargo) to the stations. There have been 11 of these flights.
- Mass: 7,150 kg
- Capacity cargo: 2,230 kg
- Capacity propellant: 1,950 kg
- Capacity dry cargo: 1,800 kg

Current status

This spacecraft is still in use today for the International Space Station. Between February 1, 2003 and July 26, 2005, it was the only spacecraft available to transport large quantities of supplies to the station, as the Space Shuttle fleet was grounded after the breakup of the Columbia at the end of STS-107. For ISS missions, the Progress M1 variant is used, which moves the water tanks from the propellant and refueling module to the pressurized section, and as a result is able to carry more propellant. Like the Soyuz (and unlike most American space ships), the Progress has an autonomous navigation system that usually allows for automatic docking with the space station. It can be manually overridden if necessary. The European Space Agency (ESA) is planning its own supply freighter called the Automated Transfer Vehicle. The first of these, the Jules Verne, is due for launch in August 2006. It will be able to carry up to 7.5 tonnes of cargo into space, roughly three times as much as the Progress, and will be launched every 12 months by an Ariane 5 rocket.

External link

- [http://www.nasa.gov/mission_pages/station/structure/elements/progress.html NASA - Russian Progress Spacecraft] - NASA page discussing the Progress spacecraft, updated May 2005. Category:International Space Station Category:Unmanned resupply spacecraft

Hubble Space Telescope

The Hubble Space Telescope is a telescope in orbit around the Earth. Its position outside the Earth's atmosphere allows it to take extremely sharp images, and since its launch in 1990, it has become one of the most important telescopes in the history of astronomy. It has been responsible for many ground-breaking observations and has helped astronomers achieve a better understanding of many fundamental problems in astrophysics. From its original conception in 1946 until its launch, the project to build a space telescope was beset by delays and budget problems. Immediately after its launch, it was found that the main mirror suffered from spherical aberration, severely compromising the telescope's capabilities. However, after a servicing mission in 1993, the telescope was restored to its planned quality and became a vital research tool as well as a public relations boon for astronomy. The future of Hubble is currently uncertain. Though the United States Congress has appropriated funds to repair the telescope in July 2005, it is possible that a servicing mission may be cancelled again. Without intervention it will re-enter the Earth's atmosphere some time after 2010. Its successor telescope, the James Webb Space Telescope, is due to be launched in 2013.

Conception, design and aims

Proposals and precursors

2013 The history of the Hubble Space Telescope can be traced back as far as 1946, when astronomer Lyman Spitzer wrote a paper entitled Astronomical advantages of an extra-terrestrial observatory. In it, he discussed the two main advantages that a space-based observatory would have over ground-based telescopes: First, the angular resolution (smallest separation at which objects can be clearly distinguished) would be limited only by diffraction, rather than by the turbulence in the atmosphere which causes stars to twinkle and is known to astronomers as seeing. Ground-based telescopes are typically limited to resolutions of 0.5–1.0 arcseconds, compared to a theoretical diffraction-limited resolution of about 0.1 arcsec for a telescope with a mirror 2.5 m in diameter. The second major advantage would be that a space-based telescope could observe infrared and ultraviolet light, which are strongly absorbed by the atmosphere. Spitzer devoted much of his career to pushing for a space telescope to be developed. In 1962 a report by the US National Academy of Sciences recommended the development of a space telescope as part of the space program, and in 1965, Spitzer was appointed as head of a committee given the task of defining the scientific objectives for a large space telescope. Space-based astronomy had begun on a very small scale following World War II, as scientists made use of the developments in rocket technology that had taken place. The first ultraviolet spectrum of the Sun was obtained in 1946. An orbiting solar telescope was launched in 1962 by the UK as part of the Ariel space program, and 1966 saw NASA's launch of the first Orbiting Astronomical Observatory (OAO) mission. OAO-1's battery failed after three days, terminating the mission, but OAO-2 carried out ultraviolet observations of stars and galaxies from its launch in 1968 until 1972, well beyond its original planned lifetime of one year. The OAO missions demonstrated the important role space-based observations could play in astronomy, and 1968 saw the development by NASA of firm plans for a space-based reflecting telescope with a mirror 3 m in diameter, known provisionally as the Large Orbiting Telescope or Large Space Telescope, with a launch slated for 1979. These plans emphasised the need for manned maintenance missions to the telescope to ensure such a costly program had a lengthy working life, and the concurrent development of plans for the reusable Space Shuttle indicated that the technology to allow this was soon to become available .

The quest for funding

The continuing success of the OAO program encouraged increasingly strong consensus within the astronomical community that the LST (Large Space Telescope, the original name) should be a major goal. In 1970 NASA established two committees, one to plan the engineering side of the space telescope project, and the other to determine the science goals of the mission. Once these had been established, the next hurdle for NASA was to obtain funding for the instrument, which would be far more costly than any Earth-based telescope. The US Congress questioned many aspects of the proposed budget for the telescope and forced cuts in the budget for the planning stages, which at the time consisted of very detailed studies of potential instruments and hardware for the telescope. In 1974, public spending cuts instigated by Gerald Ford led to Congress cutting all funding for the telescope project. In response to this, a nationwide lobbying effort was co-ordinated among astronomers. Many astronomers met congressmen and senators in person, and large scale letter-writing campaigns were organised. The National Academy of Sciences published a report emphasising the need for a space telescope, and eventually the Senate agreed to a budget half that originally refused by Congress. The funding issues led to something of a reduction in the scale of the project, with the proposed mirror diameter reduced from 3 m to 2.4 m, both to cut costs and to allow a more compact and effective configuration for the telescope hardware. A proposed precursor 1.5m space telescope to test the systems to be used on the main satellite was dropped, and budgetary concerns also prompted collaboration with the European Space Agency. ESA agreed to supply some of the instruments for the telescope as well as the solar cells which would power it and contribute approximately 15% of the costs, in return for European astronomers being guaranteed at least 15% of observing time on the telescope. Congress eventually approved funding of US$36,000,000 for 1978, and the design of the LST began in earnest, aiming for a launch date of 1983. During the early 1980s, the telescope was named after Edwin Hubble, who made one of the greatest scientific breakthroughs of the 20th century when he discovered that the universe was expanding.

Construction and engineering

universe 1979]] Once the Space Telescope project had been given the go-ahead, work on the program was divided between many institutions. Marshall Space Flight Center was given responsibility for the design, development and construction of the telescope, while the Goddard Space Flight Center was given overall control of the scientific instruments and ground control centre for the mission. Marshall commissioned optics company Perkin-Elmer to design and build the Optical Telescope Assembly (OTA) and Fine Guidance Sensors for the space telescope. Lockheed were commissioned to construct the spacecraft in which the telescope would be housed.

Optical Telescope Assembly (OTA)

The mirror and optical systems of the telescope were the most crucial part, and were designed to exacting specifications. Telescopes typically have mirrors polished to an accuracy of about a tenth of the wavelength of visible light, but because the Space Telescope was to be used for observations ranging from ultraviolet to near-infrared with ten times better resolution than the best previous telescopes, its mirror needed to be polished to an accuracy of 1/20 of the wavelength of visible light, or about 30 nanometres. Perkin-Elmer intended to use extremely sophisticated computer-controlled polishing machines to grind the mirror to the required shape, but in case their cutting-edge technology ran into difficulties, Kodak was commissioned to construct a back-up mirror using traditional mirror-polishing techniques. Construction of the mirror began in 1979, using ultra-low expansion glass. To keep the mirror's weight to a minimum it consisted of inch-thick top and bottom plates sandwiching a honeycomb lattice. Mirror polishing began in 1979 and continued until May 1981. NASA reports at the time questioned Perkin-Elmer's managerial structure, and the polishing began to slip behind schedule and over budget. To save money, NASA halted work on the back-up mirror and put the launch date of the telescope back to October 1984. The mirror was completed by the end of 1981 with the addition of a reflective coating of aluminum 75 nm thick and a protective coating of magnesium fluoride 25 nm thick, which increased the mirror's reflectivity in ultraviolet light. However, doubts continued to be expressed about Perkin-Elmer's competence on a project of this importance as their budget and timescale for producing the rest of the OTA continued to inflate. In response to a schedule described as "unsettled and changing daily," NASA postponed the launch date of the telescope until April 1985. Perkin-Elmer's schedules continued to slip at a rate of about one month per quarter, and at times delays reached one day for each day of work. NASA was forced to postpone the launch date until first March and then September 1986. By this time the total project budget had risen to $1.175 billion .

Spacecraft systems

$ The spacecraft in which the telescope and instruments were to be housed was another major engineering challenge. It would have to adequately withstand frequent passages from direct sunlight into the darkness of Earth's shadow which would generate major changes in temperature, while being stable enough to allow the extremely accurate pointing of the telescope that would be required. A shroud of multi-layered insulation keeps the temperature within the telescope stable, and surrounds a light aluminium shell in which the telescope and instruments sit. Within the shell, a graphite-epoxy frame keeps the working parts of the telescope firmly aligned. While construction of the spacecraft in which the telescope and instruments would be housed proceeded somewhat more smoothly than the construction of the OTA, Lockheed still experienced some budget and schedule slippage, and by the summer of 1985, construction of the spacecraft was 30% over budget and three months behind schedule. An MSFC report said that Lockheed tended to rely on NASA directions rather than take their own initiative in the construction .

Ground support

In 1983, the Space Telescope Science Institute (STScI) was established after something of a power struggle between NASA and the scientific community at large. STScI is operated by the Association of Universities for Research in Astronomy (AURA) and is physically located on the Homewood campus of Johns Hopkins University in Baltimore, which is one of the 32 U.S. universities and 7 international affiliates that comprise the AURA consortium. STScI is responsible for the scientific operation of the telescope and delivery of data products to astronomers, a function which NASA had wanted to keep 'in-house', but which scientists were keen to see based in an academic establishment. Engineering support is provided by NASA and contractor personnel at the Goddard Space Flight Center in Greenbelt, Maryland, 30 miles south of the STScI. Hubble's operation is monitored 24 hours per day by four teams of flight controllers who make up Hubble's Flight Operations Team. The Space Telescope European Coordinating Facility was established at Garching bei München near Munich in 1984 to provide similar support primarily for European astronomers.

Challenger disaster

In early 1986, the planned launch date of October that year looked feasible, but the Challenger disaster brought the US space program to a halt, grounding the Space Shuttle fleet and forcing the launch of Hubble to be postponed for several years. All telescope parts had to be kept in clean rooms until a launch could be rescheduled, a costly situation which pushed the overall costs of the project still higher. Eventually, following the resumption of Shuttle flights in 1988, the launch of the telescope was scheduled for 1990. In preparation for its final launch, dust which had accumulated on the mirror since its completion had to be removed with jets of nitrogen, and all systems were tested extensively to ensure they were fully functional. Finally, on 24 April 1990, shuttle mission STS-31 saw Atlantis launch the telescope successfully into its planned orbit. From its original total cost estimate of 435 million dollars (in FY77 funds), the telescope had by now cost over US$2.5 billion to construct. Hubble's cumulative costs to-date are approximately 14 billion dollars (inflation adjusted to the buying power of FY2005).

Instruments

Atlantis When launched, the HST carried five scientific instruments: the Wide Field and Planetary Camera (WF/PC), Goddard High Resolution Spectrograph (GHRS), High Speed Photometer (HSP), Faint Object Camera (FOC) and the Faint Object Spectrograph (FOS). WF/PC was a high-resolution imaging device primarily intended for optical observations. It was built by NASA's Jet Propulsion Laboratory, and incorporated a set of 48 filters isolating spectral lines of particular astrophysical interest. The instrument contained four CCD chips, three of which were 'wide field' chips while the fourth was the 'planetary camera' (PC). The PC took images at a longer effective focal length than the WF chips, giving it a greater magnification. The GHRS was a spectrograph designed to operate in the ultraviolet. It was built by the Goddard Space Flight Center in conjunction with Ball Aerospace, and could achieve a spectral resolution of 90,000 . Also optimised for ultraviolet observations were the FOC and FOS, both of which were also capable of the highest spatial resolution of any instrument on Hubble. Rather than CCDs these three instruments used photon-counting digicons as their detectors. FOC was constructed by ESA, while the Martin Marietta corporation built the FOS. The final instrument was the HSP, designed and built at the University of Wisconsin. It was optimised for visible and ultraviolet light observations of variable stars and other astronomical objects varying in brightness. It could take up to 100,000 measurements per second with a photometric accuracy of about 2% or better .

Flawed mirror

Within weeks of the launch of the telescope, the images returned showed that there was a serious problem with the optical system. Although the first images appeared to be sharper than ground-based images, the telescope failed to achieve a final sharp focus, and the best image quality obtained was drastically lower than expected. Images of point sources spread out over a radius of more than one arcsecond, instead of having a point spread function concentrated within a circle 0.1 arcsec in diameter as had been specified in the design criteria . Analysis of the flawed images showed that the cause of the problem must be that the primary mirror had been ground to the wrong shape. Although it was probably the most accurately figured mirror ever made, with variations from the prescribed curve of no more than 1/20 of the wavelength of light, it was too flat at the edges. The mirror was barely 2 micrometres out from the required shape, but the difference was catastrophic, introducing severe spherical aberration, a flaw in which light reflecting off the edges of a mirror reaches a different focus to the light reflecting off the centre. The aberration meant that images from the Space Telescope were only marginally better than the best images obtainable from the ground.

Origin of the problem

focus Working backwards from images of point sources, astronomers determined that the conic constant of the mirror was −1.0139, instead of the intended −1.00229. The same number was also derived by analysing the null correctors (instruments which accurately measure the curvature of a polished surface) used by Perkin-Elmer to figure the mirror, as well as by analysing interferograms obtained during ground testing of the mirror. A commission was established to determine how the error could have arisen and was headed by Lew Allen, director of the Jet Propulsion Laboratory. The Allen Commission found that the null corrector used by Perkin-Elmer had been incorrectly calibrated, as a spot on a metering scale where an end cap had worn away was wrongly believed to be a valid scale. The null corrector had then been wrongly spaced by 1.3 mm. During the polishing of the mirror, Perkin-Elmer had analysed its surface with two other null correctors, both of which (correctly) indicated that the mirror was suffering from spherical aberration. These tests were specifically designed to eliminate the possibility of major optical aberrations. Against written quality guidelines the company ignored these test results as it believed that the two null correctors were less accurate than the primary device which was reporting that the mirror was perfectly figured. The commission blamed the failings primarily on Perkin-Elmer. Relations between NASA and the optics company had been severely strained during the telescope construction due to frequent schedule slippage and cost overruns. NASA found that Perkin-Elmer had not regarded the telescope mirror as a crucial part of their business and were also secure in the knowledge that NASA could not take its business elsewhere once the polishing had begun. While the commission heavily criticised Perkin-Elmer for these managerial failings, NASA was also criticised for not picking up on the quality control shortcomings such as relying totally on test results from a single instrument.

Design of a solution

The flaw meant that Hubble could obtain data about as good as that achievable with a large ground-based telescope on a night of good seeing, but at a vastly greater cost. NASA and the telescope became the butt of many jokes, and the project was popularly regarded as a white elephant. However, the design of the telescope had always incorporated servicing missions, and astronomers immediately began to seek potential solutions to the problem which could be applied at the first servicing mission, scheduled for 1993. While Kodak had ground a back-up mirror for Hubble, it would have been impossible to replace the mirror in orbit, or bring the telescope temporarily back to Earth for a refit. Instead, the fact that the mirror had been ground so precisely to the wrong shape led to the design of new optical components with exactly the same error but in the opposite sense, to be added to the telescope at the servicing mission, effectively acting as 'spectacles' to correct the spherical aberration. Because of the way the instruments were designed, two different sets of correctors were required. The design of the Wide Field and Planetary Camera (WFPC) included four relay mirrors to direct light onto the four separate charge-coupled device (CCD) chips making up the camera, and so the relay mirrors on the replacement Wide Field and Planetary Camera 2 could be figured to correct the aberration. However, the other instruments lacked any intermediate surfaces which could be figured in this way, and so required an external correction device.

COSTAR

The system designed to correct the spherical aberration for light focussed at the FOC, FOS and GHRS was called the "Corrective Optics Space Telescope Axial Replacement" (COSTAR) and consisted essentially of two mirrors in the light path, one of which would be figured to correct the aberration . To fit the COSTAR system onto the telescope, one of the other instruments had to be removed, and astronomers selected the High Speed Photometer to be sacrificed. During the first three years of the Hubble mission, before the optical corrections could be fitted, the telescope still carried out a large number of observations. Spectroscopic observations in particular were not too badly affected by the aberration, but many imaging projects were cancelled as the space telescope no longer gave decisive advantages over ground-based observations. Despite the setbacks, the first three years saw numerous scientific advances as astronomers worked to optimise the results obtained using sophisticated image processing techniques.

Servicing missions and new instruments

image processing

Servicing mission 1

The telescope had always been designed so that it could be regularly serviced, but after the problems with the mirror came to light, the first servicing mission assumed a much greater importance, as the astronauts would have to carry out extensive work on the telescope to install the corrective optics. The seven astronauts selected for the mission were trained intensively in the use of the hundred or so specialised tools which would need to be used. The mission (STS-61) took place in December 1993, and involved installation of several instruments and other equipment over a total of 10 days. Most importantly, the High Speed Photometer was replaced with the COSTAR corrective optics package, and WFPC was replaced with the Wide Field and Planetary Camera 2 (WFPC2), with its internal optical correction system. In addition, the solar arrays and their drive electronics were replaced, as well as four of the gyroscopes used in the telescope pointing system, two electrical control units and other electrical components, and two magnetometers. The onboard computers were upgraded, and finally, the telescope's orbit was boosted, having been slowly decaying for three years due to drag in the tenuous upper atmosphere. drag On January 13, 1994, NASA declared the mission a complete success and showed the first of many much sharper images . The mission had been one of the most complex ever undertaken, involving five lengthy periods of extravehicular activity, and its resounding success was an enormous boon for NASA, as well as for the astronomers who now had a fully capable space telescope.

Subsequent servicing missions

Subsequent servicing missions were less dramatic, but each gave the space telescope new capabilities. Servicing Mission 2 (STS-82) in February 1997 replaced the GHRS and the FOS with the Space Telescope Imaging Spectrograph (STIS) and the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), replaced an Engineering and Science Tape Recorder with a new Solid State Recorder, repaired thermal insulation and again boosted Hubble's orbit. NICMOS contained a heat sink of solid nitrogen to reduce the thermal noise from the instrument, but shortly after it was installed, an unexpected thermal expansion resulted in part of the heat sink coming into contact with an optical baffle. This led to an increased warming rate for the instrument and reduced its original expected lifetime of 4.5 years to about 2 years. Servicing Mission 3A (STS-103) took place in December 1999, replaced all six gyroscopes (one had failed and rendered the telescope unusable just weeks before the mission), replaced a Fine Guidance Sensor and the computer, installed a Voltage/temperature Improvement Kit (VIK) to prevent battery overcharging, and replaced thermal insulation blankets. The new computer was based on a space-qualified Intel 486 and permits some computing tasks that were previously performed by computers on the ground to be handled on board the spacecraft. Servicing Mission 3B (STS-109) in March 2002 saw the installation of a new instrument, with the FOC being replaced with the Advanced Camera for Surveys (ACS), and also saw the revival of NICMOS, which had run out of coolant in 1999. A new cooling system was installed which reduced the instrument's temperature enough for it to be usable again, although it was not as cold as its original design called for. The mission replaced the solar arrays for a third time, with the new arrays being smaller but generating more power. The new arrays were derived from those built for the Iridium comsat system and were only two-thirds the size of the old arrays, resulting in less drag against the tenuous reaches of the upper atmosphere, while providing 30% more power. The additional power allowed all instruments on board the Hubble to be run simultaneously, and reduced a vibration problem that occurred when the old, less rigid arrays entered and left direct sunlight. Hubble's Power Distribution Unit was also replaced in order to correct a problem with sticky relays, a procedure that required the complete electrical power down of the spacecraft for the first time since it was launched. The completion of this servicing mission considerably enhanced Hubble's capabilities. The two instruments primarily affected by the mission, ACS and NICMOS, together imaged the Hubble Ultra Deep Field in 2003 to 2004.

Scientific results

Important discoveries

Hubble Ultra Deep Field] Hubble has helped to resolve some long-standing problems in astronomy, as well as turning up results that have required whole new theories to explain them. Among its primary mission targets was to measure distances to Cepheid variable stars more accurately than ever before, and thus constrain the value of the Hubble constant, the measure of the rate at which the universe is expanding, which is also related to its age. Before the launch of Hubble, estimates of the Hubble constant typically had errors of up to 50%, but Hubble measurements of Cepheid variables in the Virgo cluster and other distant galaxy clusters provided a measured value with an accuracy of 10%, which is consistent with other accurate measurements made since Hubble's launch using other techniques. While Hubble helped to refine the age of the universe, it also threw doubt on its future. Astronomers using the telescope to observe distant supernovae uncovered evidence that far from decelerating under the influence of gravity, the universe may in fact be accelerating. This acceleration was later confirmed by other ground-based and space-based telescopes, but the cause of this acceleration is currently very poorly understood. The collision of Comet Shoemaker-Levy 9 with Jupiter in 1994 was very fortuitously timed for astronomers, coming just a few months after Servicing Mission 1 had restored Hubble's optical performance. Hubble images of the planet were sharper than any taken since the passage of Voyager 2 in 1979, and were crucial in studying the dynamics of the collision of a comet with Jupiter, an event believed to occur once every few centuries. Other major discoveries made using Hubble data include proto-planetary disks (proplyds) in the Orion Nebula; evidence for the presence of extrasolar planets around sun-like stars; and the optical counterparts of the still-mysterious gamma-ray bursts.

Impact on astronomy

gamma-ray burst Many objective measures show the enormous impact of Hubble data on astronomy. Over 4,000 papers based on Hubble data have been published in peer-reviewed journals, and countless more have appeared in conference proceedings. Looking at papers several years after their publication, about one-third of all astronomy papers have no citations, while only 2% of papers based on Hubble data have no citations. On average, a paper based on Hubble data receives about twice as many citations as papers based on non-Hubble data. Of the 200 papers published each year which receive the most citations, about 10% are based on Hubble data . Although the HST has clearly had a significant impact on astronomical research, the financial cost of this impact has been very large. A study on the relative impacts on astronomy of different sizes of telescopes found that while papers based on HST data generate 15 times as many citations as a 4 m ground-based telescope such as the William Herschel Telescope, the HST cost about 100 times as much to build and maintain . The development of adaptive optics in recent years means that ground-based telescopes can take images approaching the sharpness of Hubble images, at much lower cost, and this has been a key consideration in the debate about the future of space telescopes (see below).

Using the telescope

Anyone can apply for time on the telescope; there are no restrictions on nationality or academic affiliation. Competition for time on the telescope is extremely intense, and the ratio of time requested to time available (the oversubscription ratio) typically ranges between 6 and 9. Calls for proposals are issued roughly annually, with time allocated for a 'cycle' lasting approximately one year. Proposals are divided into several categories; 'general observer' proposals are the most common, covering routine observations. 'Snapshot observations' are those in which targets require only 45 minutes or less of telescope time, including the overheads of acquiring the target and so on; snapshot observations are used to fill in gaps in the telescope schedule which cannot be filled by regular GO programs. Astronomers may make 'Target of Opportunity' proposals, in which observations are scheduled if a transient event covered by the proposal occurs during the scheduling cycle. In addition, up to 10% of the telescope time is designated Director's Discretionary (DD) Time. Astronomers can apply to use DD time at any time of year, and it is typically awarded for study of unexpected transient phenomena such as supernovae. Other uses of DD time have included the observations that led to the production of the Hubble Deep Field and Hubble Ultra Deep Field, and in the first four cycles of telescope time, observations carried out by amateur astronomers (discussed below).

Observation scheduling

Hubble Ultra Deep Field Scheduling observations for Hubble is not a simple matter. It is situated in a low-Earth orbit so that it can be reached by the Space Shuttle for servicing missions, but this means that most astronomical targets are occulted by the Earth for slightly less than half of each orbit. Observations cannot take place when the telescope passes through the South Atlantic Anomaly due to elevated radiation levels, and there is a also a sizable exclusion zone around the Sun, and for some instruments around the Moon and Earth, which cannot be observed. However, there is a so-called continuous viewing zone (CVZ), at roughly 90 degrees to the plane of Hubble's orbit, in which targets are not occulted for long periods. Due to the precession of the orbit, the location of the CVZ moves slowly over a period of eight weeks. Because the limb of the Earth is always within about 30° of regions within the CVZ, the brightness of scattered earthshine may be elevated for long periods during CVZ observations. Because Hubble orbits in the upper atmosphere, its orbit changes over time in a way that is not accurately predictable. The density of the upper atmosphere varies according to many factors, and this means that Hubble's predicted position for six week's time could be in error by up to 4,000 km. Observation schedules are typically finalised only a few days in advance, as a longer lead time would mean there was a chance that the target would be unobservable by the time it was due to be observed .

Amateur observations

The first director of the STScI, Riccardo Giacconi, announced in 1986 that he intended to devote some of his DD time to allowing amateur astronomers to use the telescope. The total time to be allocated was only a few hours per cycle, but excited great interest among amateur astronomers. Proposals for amateur time were stringently peer reviewed by a committee of leading amateur astronomers, and time was awarded only to proposals with genuine scientific merit which did not duplicate proposals made by professionals and which required the unique capabilities of the space telescope. In total, 13 amateur astronomers were awarded time on the telescope, with observations being carried out between 1990 and 1997. After that time, however, budget reductions at STScI made the support of work by amateur astronomers untenable, and no further amateur programs have been carried out .

Hubble data

Transmission to Earth

Hubble data is initially stored on the spacecraft. When launched, the storage facilities were old-fashioned reel-to-reel tape recorders, but these were replaced by solid state data storage facilities during servicing missions 2 and 3A. From the onboard storage facilities, data is transferred to the ground via the Tracking and Data Relay Satellite System, a system of satellites designed so that satellites in low-Earth orbit can communicate with their mission control facilities during about 85% of their orbit. Data is transmitted to the TDRSS ground station and then on to the Goddard Space Flight Center for archiving.

Pipeline reduction

Astronomical data taken with CCDs must undergo several calibration steps before it is suitable for astronomical analysis. STScI has developed sophisticated software which automatically calibrates data when it is requested from the archive using the best calibration files available. This 'on-the-fly' processing means that large data requests can take a day or more to be processed and returned. The process by which data is calibrated automatically is known as 'pipeline reduction', and is increasingly common at major observatories. Astronomers may if they wish retrieve the calibration files themselves and run the pipeline reduction software locally. This may be desirable when calibration files other than those selected automatically need to be used.

Data analysis

Hubble data can be analysed using many different packages, but STScI develops the custom-made STSDAS (Space Telescope Science Data Analysis System) software. The software contains all the programs needed to run pipeline reduction on raw data files, as well as many other astronomical image processing tools, tailored to the requirements of Hubble data. The software runs as a module of IRAF, a popular astronomical data reduction program, which runs only under various flavours of Linux and Mac OS X.

Outreach activities

Mac OS X It has always been important for the Space Telescope to capture the public's imagination, given the considerable contribution of taxpayers to its construction and operational costs. After the difficult early years when the faulty mirror severely dented Hubble's reputation with the public, the first servicing mission allowed its rehabilitation as the corrected optics produced numerous remarkable images. Several initiatives have helped to keep the public informed about Hubble activities. The Hubble Heritage Project was established to produce high-quality images for public consumption of the most interesting and striking objects observed. The Heritage Team is composed of amateur as well as professional astronomers as well as people with backgrounds outside astronomy and emphasises the artistic nature of Hubble images. Hubble has also been used to photograph the Apollo 15 and 17 landing sites in the hope that parts of the lunar landing modules would be visible. In addition, STScI maintains several comprehensive websites for the general public containing Hubble images and information about the observatory. The outreach efforts are coordinated by the Office for Public Outreach, which was established in 2000 to ensure that US taxpayers saw the benefits of their investment in the space telescope program. The Heritage Project is granted a small amount of time to observe objects which, for scientific reasons, may not have images taken at enough wavelengths to construct a full colour image. In 2001, to celebrate the 11th anniversary of the launch of Hubble, NASA polled internet users to find out what they would most like Hubble to observe, and they overwhelmingly selected the Horsehead Nebula [http://heritage.stsci.edu/2001/12/caption.html]. A Heritage Project image of the nebula was released on 24 April 2001, the 11th anniversary of the launch.

Future

Equipment failure

2001]] Past servicing missions have exchanged old instruments for new ones, both avoiding failure and making possible new type

Docking maneuver

Spacecraft

Overview

Examples of past or existing spacecraft

Spacecraft under development

See also

External links

Space station

Past and present space stations

Types of space station

List of occupied space stations, with statistics

In fiction

Orbital maneuver

Impulsive maneuvers

Non-impulsive maneuvers

Finite Burn Trajectories

See also

Orbital velocity

Radial trajectories

Transverse orbital speed

Mean orbital speed

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

Soyuz spacecraft

Spacecraft design

The many incarnations of the Soyuz

Missions

External references

Progress spacecraft

Design

Versions

Progress

Progress M

Progress M1

Current status

See also

External link

Hubble Space Telescope

Conception, design and aims

Proposals and precursors

The quest for funding

Construction and engineering

Optical Telescope Assembly (OTA)

Spacecraft systems

Ground support

Challenger disaster

Instruments

Flawed mirror

Origin of the problem

Design of a solution

COSTAR

Servicing missions and new instruments

Servicing mission 1

Subsequent servicing missions

Scientific results

Important discoveries

Impact on astronomy

Using the telescope

Observation scheduling

Amateur observations

Hubble data

Transmission to Earth

Archive

Pipeline reduction

Data analysis

Outreach activities

Future

Equipment failure