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Hubble space telescope (abbreviated as HST)

brief introduction

This is a telescope orbiting the earth in the name of astronomer Hubble. It is located above the earth's atmosphere, so it has the advantages that ground-based telescopes do not have-the image will not be disturbed by atmospheric turbulence, the visibility is excellent, there is no background light caused by atmospheric scattering, and ultraviolet rays absorbed by the ozone layer can be observed. 1990 became the most important instrument in the history of astronomy after its launch. He filled the gap in ground observation, helped astronomers solve many basic problems and gained more knowledge of astrophysics. Hubble's ultra-deep field of view is the deepest (clearest) optical image obtained by astronomers.

From his initial conception in 1946 to the launch, the plan to build a space telescope has been postponed continuously and is plagued by budget problems. Immediately after launching, he found that there was spherical aberration in the main mirror, which seriously reduced the observation ability of the telescope. Fortunately, after the maintenance task of 1993, the telescope recovered the planned quality and became the most important tool for astronomical research and public relations. Hubble Space Telescope, Compton Gamma-ray Observatory, Chandra X-ray Observatory and Spitzer Space Telescope are all part of NASA's Large Orbit Observatory program. The Hubble Space Telescope is jointly managed by NASA and the European Southern Observatory.

Hubble's future depends on the success of subsequent maintenance tasks. Several stable gyroscopes have been damaged. In 2007, even the spare ones have been used up, and the function of another pointing telescope is also declining. Gyroscope must be repaired manually. On June 30th, 2007, the main advanced sky camera (ACS) also stopped working. Before manual maintenance, only the ultra-violet channel can be used. On the other hand, if there is no lift to increase the orbital height, the drag will force the telescope to re-enter the atmosphere at 20 10. Since the unfortunate incident of the space shuttle Columbia in 2003, astronauts lack safe haven in an emergency because the International Space Station and Hubble are not at the same height. Therefore, NASA believes that it is unreasonable and dangerous to repair the Hubble telescope through manned space missions. After re-examination by NASA, CEO Mike Griffin decided to carry out the last Hubble maintenance mission in Atlanta from June 5 to1October 36, 2006. This mission will be arranged on September 6, 2008. For safety reasons, Discovery will be on standby at LC-39B launch pad to provide rescue in case of emergency. The planned maintenance will enable the Hubble Space Telescope to work continuously until 20 13. If successful, the subsequent James Webb Space Telescope (JWST) should have been launched and can be connected to the mission. Weber Space Telescope has far more functions than Hubble in many research projects, but it can only observe infrared rays, so it can't replace Hubble's functions in the visible and ultraviolet fields of the spectrum.

[Edit this paragraph] "Hubble" faces elimination

The Hubble Space Telescope is old. During more than ten years in space, it has undergone four overhauls, namely 1993, 1997, 1999 and 200 1 year. Although Hubble has taken on a brand-new look after each overhaul, especially in the fourth overhaul of the space shuttle Columbia in 200 1 year, scientists installed a mapping camera for it, replaced the solar panel, replaced the power control device that had been working for 1 1 year, and activated the near-infrared camera and multi-target spectrometer in the "dormant" state.

In the near future, NASA will gather experts and astronauts from all walks of life to discuss "when and how to make NASA proud" and "Hubble" die. Although people are still reluctant to part with it, there is not much time left for Hubble, and it may be replaced by the "first line" this year or later.

[Edit this paragraph] Concept, design and indicators

1, Planning and Pre-operation

The history of Hubble Space Telescope can be traced back to the paper entitled "Advantages of Extraterrestrial Astronomical Observation" put forward by astronomer Lyman Spitzer in 1946. In the article, he pointed out that the space observatory has two advantages over the ground observatory. First of all, the limit of angular resolution (the minimum separation angle that can clearly distinguish an object) will mean that it is limited by diffraction, not the visibility caused by starlight flicker caused by turbulent atmosphere. At that time, the resolution of ground-based telescope was only 0.5- 1.0 arc seconds. In contrast, a telescope with a diameter of 2.5 meters can reach the theoretical diffraction limit of 0. 1 arc second. Secondly, telescopes in space can observe infrared rays and ultraviolet rays absorbed by the atmosphere.

Spitzer takes space telescope as his career and devotes himself to the promotion of space telescope. 1962, the National Academy of Sciences recommended the space telescope as a part of the space development plan. 1965, Spitzer was appointed as the chairman of a scientific committee whose purpose was to build a space telescope.

During World War II, while developing rocket technology, scientists tried space-based astronomy on a small scale. 1946, the ultraviolet spectrum of the sun was observed for the first time. As part of the Aryan space program, Britain launched a solar telescope in orbit in 1962. 1966, NASA carried out the first mission of the Orbital Observatory (OAO), but the battery of the first OAO failed three days later and the mission was terminated. The second OAO observed the ultraviolet rays of stars and galaxies from 1968 to 1972, which was one year more than originally planned.

The mission of orbital observatory shows the important role of space-based observatory in astronomy. Therefore, in 1968, NASA decided to build a reflecting telescope with a diameter of 3 meters in space. At that time, its temporary name was Large Orbital Telescope or Large Space Telescope (LST), and it was expected to be launched in 1979. This plan emphasizes the need for someone to go into space for maintenance to ensure that this expensive plan can last long enough; At the same time, we will develop reusable space shuttle technology to turn the previous plan into a feasible plan.

2, the demand for funds

The success of the orbiting observatory project has encouraged more and more people to support that large space telescopes should become an important goal in the field of astronomy. 1970, NASA set up two committees, one for planning the space telescope project and the other for studying the scientific objectives of the space telescope mission. After that, the next obstacle that NASA needs to remove is the funding problem, because it is many times more expensive than any observation station on the ground. The US Congress has raised many questions about the budget requirements for space telescopes. In order to meet the budget for disarmament, the hardware requirements of the telescope and the instruments needed for subsequent development are listed in detail. 1974, at the instigation of cutting government expenditure, Gerald Ford cancelled all the budgets of the space telescope.

In response, astronomers coordinated a nationwide lobbying campaign. Many astronomers personally visited members of the House of Representatives and senators to conduct large-scale letters and text propaganda. The report published by the National Academy of Sciences also emphasizes the importance of space telescope. Finally, the Senate decided to restore half of the budget originally deleted by Congress.

The reduction of funds leads to the reduction of target projects, and the mirror diameter is also reduced from 3 meters to 2.4 meters, so as to reduce the cost and configure the hardware of the telescope more effectively and closely. As a preliminary test, the 1.5-meter space telescope placed on the satellite was also cancelled, and the European Space Agency, which was worried about the budget, became a partner. The European Space Agency agreed to provide funds and some instruments needed for the telescope, such as solar cells as power supply. In return, European astronomers can use no less than 15% of the telescope observation time. 1978, the U.S. congress allocated $36 million to start designing a large-scale space telescope, which is scheduled to be launched in 1983. 1980, the telescope was named Hubble to commemorate the astronomer Edwin Hubble who discovered the expansion of the universe in the early 20th century.

3. Structure and engineering

Once the space telescope project was approved, it was divided into many sub-plans and assigned to various institutions for implementation. Marshall Space Flight Center (MSFC) is responsible for the design, development and construction of telescopes, while Jinshi Space Flight Center (GSFC) is responsible for the overall control of scientific instruments and the mission control center on the ground. Marshall Space Flight Center entrusts Perkin Elmer to design and manufacture optical components of space telescope and precision positioning sensor (FGS), and Lockheed is entrusted to build spacecraft with telescope.

4. Optical telescope combination

The mirror and optical system of the telescope are the most critical parts, so there are strict specifications in the design. Generally, the precision of the polished mirror surface of a telescope is about one tenth of the wavelength of visible light. However, since the observation range of a space telescope is from ultraviolet to near infrared, the resolution is ten times higher than that of previous telescopes, and the polished mirror surface is about one twentieth of the wavelength of visible light, that is, about 30 nanometers.

Perkin Elmer used an extremely complicated computer-controlled polishing machine to polish the mirror, but the most advanced technology also had problems. Kodak was commissioned to use traditional polishing technology to make spare mirrors (Kodak's mirrors are now permanently preserved at the Smithsonian Institution). 1979, Perkin Elmer began to grind lenses, using ultra-low expansion glass. In order to reduce the weight of the mirror as much as possible, a honeycomb grid is used, the surface is only one inch, and the bottom is only one inch of thick glass.

Mirror polishing started at 1979 and lasted until 198 1 in May. The polishing progress has fallen behind and exceeded the budget, and then the NASA report began to question Perkin Elmer's management structure. In order to save money, NASA stopped supporting the production of lenses and postponed the listing date to 1984 10. The lens was completed at the end of 198 1, and was coated with 75 nm thick aluminum to enhance reflection and 25 nm thick magnesium fluoride protective layer.

Due to the expanding budget of the optical telescope combination and the backward progress, doubts about Perkin Elmer's competence in the follow-up work continue to exist. In response to the daily report described as "uncertain and changeable", NASA extended the release date to April 1985. However, Perkin Elmer's progress continues to increase by one month every quarter, and the time delay has reached the point where it continues to fall behind every working day. Nasa was forced to postpone the launch date, first to March 1986 and then to September 1986. At this point, the total cost of the whole plan has reached1175 million dollars.

5. Spacecraft system

Spacecraft equipped with telescopes and instruments is another major engineering challenge. It must be able to withstand the temperature changes caused by frequent access between sunlight and the earth's shadow, and it must be extremely stable and can accurately aim the telescope at the target for a long time. The shelter made of multi-layer heat insulation materials can keep the temperature inside the telescope stable, and the lightweight aluminum shell surrounds the telescope and the support of the instrument. Inside the shell, the graphite epoxy resin frame firmly fixes the calibrated working instrument.

For a time, the spacecraft used to install instruments and telescopes was built more smoothly than the combination of optical telescopes, but Lockheed still experienced insufficient budget and backward progress. 1before the summer of 985, the spacecraft was several months behind schedule and the budget exceeded 30%. Marshall Space Flight Center reported that Lockheed did not take the initiative in the construction of spacecraft and relied too much on the guidance of NASA.

6. Mine support

1983, the Space Telescope Science Association (STScI) was founded after the power struggle between NASA and the scientific community. The Space Telescope Science Association is affiliated to the American University Astronomical Research Alliance (AURA), which is a unit composed of 32 American universities and 7 international members and headquartered in John F.? On the campus of Hopkins University.

The Space Telescope Science Association is responsible for the operation of space telescopes and providing data to astronomers. The National Aeronautics and Space Administration (NASA) once wanted to use it as an internal organization, but scientists planned to establish it as a research unit according to the practice of the scientific community. NASA's Space Telescope Science Association, Goddard Space Flight Center and contractors located 48 kilometers south of Green Dam, Maryland provide engineering support. Hubble telescope operates 24 hours a day, and four working groups take turns to operate.

The European Space Telescope Coordination Agency was established in Garching bei München, near Munich, Germany, in 1984, providing similar support for European astronomers.

7. Challenger accident

As early as 1986, the Hubble Space Telescope was planned to be launched in June of that year. However, the Challenger accident stopped the American space program, and the suspension of the space shuttle forced the launch of the Hubble Space Telescope to be delayed for several years. Telescopes and all accessories must be stored in clean rooms in different categories until the launch date, which also makes the total cost of overspending even higher.

Finally, with the shuttle launching again at 1988, the telescope is planned to launch at 1990. In the final preparation before launch, the mirror was sprayed with nitrogen to remove the dust that might accumulate, and all systems were extensively tested. Finally, on April 24th, 1990, the space shuttle Discovery successfully put the telescope into the scheduled orbit on STS-3 1 voyage.

From its initial total budget, about 400 million dollars, to the current cost of more than 2.5 billion dollars, Hubble's cost is still accumulating and increasing. The US government estimates that the expenditure will be as high as $4.5 billion to $6 billion, and the capital injected from Europe will be as high as € 600 million (estimated 1.999).

8. Tools

At the time of launch, the Hubble Space Telescope carried the following instruments:

Wide area and planetary camera (WF/ PC)

Goddard high resolution spectrograph (GHRS)

High speed photometer (HSP))

Dark object camera (FOC)

Dark celestial spectrograph

WF/PC was originally designed as a high-resolution camera for optical observation. Made by NASA's Jet Propulsion Laboratory, with a set of 48 optical filters, it can screen special bands for astrophysical observation. The whole instrument uses 8 CCDs and two cameras, each with 4 CCDs. "Wide-area camera" (WFC) loses its resolution because of its wide field of vision, while "Planetary camera" (PC) has a longer imaging focal length than WFC, so its magnification is higher.

GHRS is a spectrometer made by Goddard Space Center for ultraviolet band. It can achieve a spectral resolution of 90,000, and can also select suitable observation targets for FOC and FOS. FOC and FOSS are the highest resolution instruments on the Hubble Space Telescope. These three instruments all give up CCD and use digital photon counter as detection device. FOC is made by the European Space Agency, and FOS is made by Martin marietta.

The last instrument is HSP designed and manufactured by the University of Wisconsin-Madison, which is used to observe the brightness changes of variable stars and other shielded celestial bodies in visible and ultraviolet light bands. Its photometer can detect 100000 times per second with an accuracy of at least 2%.

The navigation system of Hubble Space Telescope can also be used as a scientific instrument. Its three fine guide star sensors (FGS) are mainly used to keep the pointing accuracy of the telescope during observation, but they can also be used for very accurate celestial measurement, with the measurement accuracy reaching 0.0003 arc seconds.

[Edit this paragraph] Lens defects

A few weeks after the telescope was launched, the pictures returned showed that there were serious problems in the optical system. Although the first image looks better than the Ming Rui of the ground-based telescope, it is obvious that the telescope has not reached the best focusing state, and the quality of the best image obtained is far lower than originally expected. The point source image spreads into a circle with a radius greater than 1 arc second, which is not the standard in the design criteria: the point spread function images of concentric circles are concentrated in the diameter range of 0. 1 arc second.

The analysis of pattern defects shows that the root of the problem is the wrong shape of the main mirror. Although, this difference is less than 1/20 wavelength light, but the edge is a little too flat. The mirror is only 2 microns away from the required position, but this difference has caused disastrous and serious spherical aberration. The reflected light from the edge of the mirror cannot be focused on the same focus as the reflected light from the center.

The influence of mirror defects is that in the core observation of scientific observation, the PSF of core aberration should be Ming Rui enough to achieve high resolution, but it is not affected by bright celestial bodies and spectral analysis. Although, the loss of light in a large area of the periphery will cause vignetting because it can't converge to the focus, which will seriously damage the telescope's ability to observe dark objects or Gao Fancha images. This means that almost all cosmological research projects cannot be carried out because they are very dim observation objects. NASA and the Hubble Space Telescope have been the targets of many jokes, and they are considered as huge white elephants.

1, the root of the problem

Looking back from the image of the point light source, astronomers determined the conic constant of the mirror. 1.0 139, not as expected? 1.00229。 By analyzing Perkin Elmer's zero corrector (an instrument for accurately measuring the polished surface) and the interferogram image of the mirror tested on the ground, the same value is obtained.

The committee headed by Aaron, director of the Jet Propulsion Laboratory, determined how the mistake happened. Allen Committee found that the zero corrector used by Perkin Elmer made an error in assembly, and its field mirror position deviated from 65438 0.3 mm.

In the process of polishing the mirror, Perkin Elmer used two other zero correctors, both of which showed spherical aberration. These tests are aimed at eliminating spherical aberration. Regardless of the guidance of quality control documents, the company thinks that the accuracy of these two zero calibrators is not as good as that of the main equipment, and ignores the test results.

The Committee pointed out that the main reason for the failure was Perkin Elmer. Due to the losses caused by frequent schedule changes and the cost overrun of telescope manufacturing, the relationship between NASA and Optical Company is extremely tense. NASA found that Perkin Elmer didn't think making mirrors was a key and difficult task in their business, and NASA didn't do its duty before polishing. While the Committee deeply criticized Perkin Elmer's improper management and shortcomings, NASA was also criticized for failing to fulfill its responsibility of quality control and should not rely solely on the test results of one instrument.

2, the design of the solution

The maintenance task was originally planned in the design of the telescope, so when the first maintenance task was arranged in 1993, astronomers immediately began to look for a solution to the problem. It is too expensive and time-consuming to replace Kodak's spare mirror for Hubble in orbit, and it is temporarily impossible to bring the telescope back to the ground for maintenance. Instead, the wrong shape of the lens has been accurately measured, so an optical system with the same spherical aberration but opposite effect can be designed to offset this error. That is, in the first maintenance task, Hubble was equipped with a pair of glasses that can correct the spherical aberration.

Because of the design of the original instrument, it is necessary to have two different calibration instruments. The design of wide-area and planetary cameras includes rotating lens and eight independent CCD chips where light directly enters the two cameras. The main deformation of their surfaces can be completely eliminated by anti-spherical lens. The calibration mirror is fixed in the replaced second-generation wide-area and planetary cameras (due to the pressure of schedule and budget, only 4 CCDs are calibrated instead of 8). However, other instruments lack any intermediate surface on which they can be placed, so additional calibration devices are needed.

3. Co-starring

The instrument designed to correct spherical aberration is called "COSTAR", which basically consists of two mirrors on the optical path. One of them corrects spherical aberration, and the light is focused on the dark celestial camera, dark celestial spectrometer and Goddard analytical spectrograph. In order to provide the required COSTAR position in the telescope, one of the instruments must be removed, and the astronomer's choice is to sacrifice the high-speed photometer.

In the first three years of the Hubble mission, the telescope still made a lot of observations before the optical system was calibrated properly. Spectral observation is not affected by spherical aberration, but the observation of many faint celestial bodies is cancelled or postponed because of the poor performance of the telescope. Despite setbacks, optimistic astronomers skillfully used image processing techniques, such as inversion (image overlapping), and made many scientific progress in these three years.

[Edit this paragraph] Maintenance tasks and new instruments

1, first maintenance task

In design, the Hubble Space Telescope must be maintained regularly, but after the problem of the mirror becomes clear, the first maintenance becomes very important, because astronauts must fully install and correct the telescope optical system. Seven astronauts selected for the mission received intensive training in using nearly 100 special design tools. During the STS-6 1 voyage in February of 1993, Endeavour reinstalled several instruments and other equipment within 10 days.

The most important thing is that the high-speed photometer is replaced by the COSTAR correction optical component, and the wide-area and planetary cameras are replaced by the second-generation wide-area and planetary cameras and the internal optical update system. In addition, solar panels and driving electronics, four gyroscopes for telescope positioning, two control panels, two magnetometers and other electronic components have also been replaced. The calculator carried on the telescope has also been updated and upgraded. Because the upper thin atmosphere still has resistance, the orbit of three-year gradual decay has also been improved.

1994,65438+10, 13 On this day, NASA announced that the mission was a complete success and showed many new pictures. The task performed this time is very complicated. There are five activities outside the space shuttle. Its echo not only gave NASA a high evaluation, but also gave astronomers a telescope fully qualified for space missions.

Subsequent maintenance tasks are not so noticeable, but each time they bring new functions to the Hubble Space Telescope.

2. The second maintenance task

The second maintenance mission was carried out by Discovery on STS-82 in February 1997. Goddard high resolution spectrometer (GHRS) and dark object spectrometer (FOS) were replaced by space telescope image spectrometer (STIS) and near infrared camera and multi-target spectrometer (NICMOS). The engineering and scientific recorders were replaced by new solid-state recorders, the thermal insulation was repaired and the Hubble orbit was upgraded. Near-infrared cameras and multi-target spectrometers contain heat absorbers made of solid nitrogen to reduce the thermal noise of the instrument. However, after installation, part of the heat diffusion of the heat absorber accidentally entered the optical baffle, which shortened the service life of the instrument from the original forecast of 4.5 years to 2 years.

3. The third maintenance task (3A)

After three of the six gyroscopes broke down (the fourth one broke down a few weeks before the mission, making it impossible for the telescope to carry out scientific observation), the third maintenance mission was still carried out by Discovery on the February voyage STS- 1999 103. In this maintenance, all six gyroscopes were replaced, as well as a fine guide star sensor and calculator, an assembled voltage/temperature improvement tool (VIK) was installed to prevent the battery from overheating, and the insulating blanket was replaced. The new calculator is Intel 486, which can work under low temperature radiation and perform some spacecraft-related calculations that used to have to be processed on the ground.

4, the fourth maintenance task (3B)

In March 2002, Columbia carried out the fourth maintenance mission on the STS- 109 voyage. The advanced sky camera (ACS) is used to replace the dark celestial camera (FOC), and the near-infrared camera and multi-target spectrometer (NICMOS) in 1999 with exhausted coolant are inspected. After replacing the new cooling system, although it can't reach the expected low temperature in the original design, it is cold enough to continue working.

In this mission, the solar panels were replaced again. The new solar panels are developed for iridium satellites, which are only two-thirds as big as the original ones. In addition to effectively reducing the resistance caused by the thin atmosphere, they can also supply 30% more electricity. This extra power enables all the instruments on the Hubble Space Telescope to work at the same time, and because it is soft, it also eliminates the problem that the old solar panels will vibrate when entering and leaving the sunlight irradiation area. In order to correct the problem of relay lag, Hubble's power distribution system has also been updated. This is the first time that the Hubble Space Telescope can make full use of the power gained after launch. Two of the most influential instruments, advanced sky camera, near infrared camera and multi-target spectrometer, jointly completed the Hubble ultra-deep field of view from 2003 to 2004.

5. Final maintenance task

The last Hubble maintenance mission is scheduled for September 1 1 day, 2008, and astronauts will replace new batteries and gyroscopes. Replace the fine guide star sensor (FGS) and repair the space telescope image spectrograph (STIS). They will also install two new instruments: the origin of the universe spectrometer and the third-generation wide-area camera, but may not reset or replace the advanced survey camera.

[Edit this paragraph] Scientific achievements

Hubble helped solve some problems that have puzzled astronomers for a long time, and derived a new holistic theory to explain these results. One of Hubble's main tasks is to measure the distance of Cepheid variable more accurately than before, which will allow us to determine the numerical range of Hubble constant more accurately, so as to have a more correct understanding of the expansion rate and age of the universe. Before the launch of Hubble, the statistical error of Hubble constant was estimated to be 50%, but after Hubble re-measured the Cepheid variable distance in Virgo cluster and other distant clusters, the accuracy of the measured value can be within 10%. This is consistent with the results measured by other more reliable technologies after Hubble launch.

Hubble has also been used to improve the estimation of the age of the universe, and the future of the universe is also one of the questioned issues. Astronomers from the high redshift supernova search team and the supernova cosmology project used telescopes to observe distant supernovae and found that the expansion of the universe may actually be accelerating. This acceleration has been confirmed by Hubble and other ground-based telescopes, but the reason for the acceleration is still difficult to understand.

Hubble's high-resolution spectra and images clearly confirm the popular theory that black holes exist in galactic nuclei. In the early 1960s, it was only a hypothesis that black holes would be found in the cores of some galaxies. It was not until the 1980s that some galactic cores were identified as candidates for black holes. However, Hubble's work has made it a common and universal cognition that the core of galaxies is black holes. In the future, Hubble's plan will focus on the close relationship between the quality of black holes in the core of galaxies and the properties of galaxies. Hubble's research on black holes in galaxies will have a far-reaching impact on the relationship between the development of galaxies and the central black holes.

For astronomers, it was a surprise that comet Shoemaker-Levi 9 hit Jupiter in 1994. Fortunately, this happened a few months after Hubble completed the first maintenance and repair of the optical system. Therefore, Hubble's image is the clearest since Voyager II flew over Jupiter in 1979. Fortunately, it provides a key learning opportunity for estimating the dynamic events of a comet colliding with Jupiter every few centuries. It is also used to study celestial bodies outside the solar system, including dwarf planets Pluto and Eris.