1946, an astrophysicist named Lyman Spitzer Jr. proposed that the telescope in space would display the images of distant objects more clearly than any ground telescope. Sounds logical, doesn't it? But this is an outrageous idea, because no one had launched rockets into outer space at that time.
With the maturity of American space program in 1960s and 1960s, Spitzer lobbied NASA and Congress to develop space telescope. 1975, the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) of the United States began to draft a preliminary plan for it. 1977, Congress approved the necessary funds. NASA appointed Lockheed Missile Company (now Lockheed Martin Company) as the contractor to build the telescope and its supporting system, and assembled and tested it.
This famous telescope is named after American astronomer Edwin Hubble. His observation of variable stars in distant galaxies confirmed that the universe was expanding and supported the Big Bang theory.
Due to the Challenger disaster of 1986, the Hubble Space Telescope was put into orbit by the space shuttle Discovery on April 24th, 1990 after a long delay. Since the launch, Hubble has reshaped our view of space. Scientists have written thousands of papers based on the clear discovery of important things by telescopes, such as the age of the universe, the appearance of huge black holes or the death of stars.
In this article, we will discuss how Hubble records outer space and the instruments that allow it to do so. We will also discuss some problems encountered by ancient telescopes/spacecraft in this process.
Co-stars saved the world.
After the deployment of 1990, astronomers discovered the problem of their beloved1500 million 43.5-foot telescope almost immediately. Their new tractor trailer-sized eyes can't focus correctly in the air. They realized that the primary mirror of the telescope had been ground to the wrong size. Although the defect in the mirror-about one fiftieth of the thickness of human hair-seems small to most of us, it causes the Hubble Space Telescope to suffer from spherical aberration and produce blurred images. Of course, astronomers didn't spend years studying telescopes, just to satisfy the humble snapshot of outer space.
Scientists have proposed an alternative "invisible" lens called COSTAR (Axial Replacement of Corrected Optical Space Telescope) to repair the defects in HST. COSTAR consists of several small mirrors, which will intercept the light beam from the defective mirror, repair the defect, and transmit the corrected light beam to the scientific instrument at the focus of the mirror.
NASA and its staff spent 1 1 month preparing for one of the most challenging space missions ever. Finally, in199365438+February, seven people on the space shuttle Endeavour launched rockets into space to perform the first maintenance task of HST.
It took the crew a week to carry out all necessary maintenance. When the telescope was tested after the maintenance task, the image was greatly improved. Now all instruments placed in HST have built-in optical components to correct mirror defects, and COSTAR is no longer needed.
However, there are more Hubble telescopes than COSTAR, and we will discuss some key parts of them next.
HST analysis
Like any telescope, HST has a long tube with one end open to let light in. It has a mirror to collect light and focus it on the eyes. There are several types of "eyes" in HST, which appear in the form of various instruments. Just as insects can see ultraviolet rays, or we humans can see visible light, Hubble telescope must also see all kinds of light falling from the sky.
Specifically, the Hubble telescope is a seglin reflecting telescope. This simply means that light enters the device through the opening and is reflected from the primary mirror to the secondary mirror. The secondary mirror reflects the light to the focus behind the primary mirror through the hole in the center of the primary mirror. If you draw the path of incoming and outgoing light, it will be like the letter "W", except that there are three downward bumps instead of two.
At the focal point, small semi-reflective and semi-transparent mirrors distribute the incident light to various scientific instruments. (We will discuss these tools in detail in the next section. As you may have guessed, these are not just ordinary mirrors. You can stare at them and admire your reflection.
The mirror of HST is made of glass and coated with pure aluminum (three millionths of an inch thick) and magnesium fluoride (one millionth of an inch thick) to make it reflect visible light, infrared light and ultraviolet light. The primary mirror is 7.9 feet (2.4 meters) in diameter and the secondary mirror is 1.0 feet (0.3 meters) in diameter.
Next, we will discuss how Hubble handles all the light that enters the telescope.
Hubble's scientific instruments: WFPC2, NICMOS and STIS
By observing the different wavelengths or spectra of celestial bodies, you can distinguish many of their properties. To this end, HST is equipped with several scientific instruments. Each instrument uses a charge-coupled device (CCD) instead of photographic film to capture light. The light detected by CCD is converted into digital signals, which are stored in the onboard computer and relayed to the earth. Then turn the digital data into amazing photos. Let's look at how each instrument forms these images.
Wide Field of View and Planetary Camera 2 (WFPC2) is Hubble's main "eye" or camera. It captures light with the help of four CCD chips arranged in an "L" shape-three low-resolution and wide-field CCD chips and a high-resolution planetary camera CCD chip. Four chips simultaneously expose the target, and the target image is centered on the required CCD chip. This eye can see visible light and ultraviolet light, and can take images through various filters to make natural color pictures, such as this well-known eagle nebula image.
Usually, interstellar gas and dust will block our view of visible light of various celestial bodies. No problem: Hubble telescope can see the infrared light or heat of objects hidden in dust and gas. In order to see this infrared light, HST has three sensitive cameras, consisting of a near-infrared camera and a multi-target spectrometer (NICMOS).
In addition to illuminating a celestial body, the light emitted by an object can also reveal its composition. A specific color tells us which elements exist, and the intensity of each color tells us how many elements exist. Space telescope imaging spectrometer (STIS) separates the colors of incident light, just like a prism forms a rainbow.
In addition to describing chemical composition, spectra can also convey the temperature, density and motion of celestial bodies. If the object is moving, the chemical fingerprint may move to the blue end (moving towards us) or the red end (moving away from us) of the spectrum. Unfortunately, STIS lost power in 2004 and has been inactive since then.
Read on to see what other scientific instruments are on the telescopic sleeve of Hubble telescope.
Hubble's scientific instruments: ACS and FGS
During a maintenance mission in February 2002, astronauts added an advanced measuring camera (ACS), which doubled the field of view of Hubble telescope and replaced the dark object camera as the HST telephoto lens.
ACS can see visible light, and its installation helps to map the distribution of dark matter, detect the farthest objects in the universe, find massive planets and check the evolution of galaxy clusters. Scientists estimate that it will last for five years. In June 2007, two of its three cameras were paralyzed due to power shortage.
Schematic diagram of the Hubble Space Telescope. Hover over Telescope Features to check each feature. Note: In 2002, "weak object camera" was replaced by "advanced measuring camera".
The last instrument on HST is its fine guidance sensor (FGS), which points to the telescope and accurately measures the position and diameter of the constant star and the distance between the two stars. Hubble always has three such sensors. Two pointing telescopes are fixed on the target, looking for "guiding" stars in the HST field near the target. When each FGS finds a guiding star, it will lock it and feed back the information to the HST steering system to keep the guiding star in its field of vision. When two sensors are operating the telescope, one sensor can freely carry out astrometry (star position). Astrometry is very important for detecting planets, because orbiting planets will cause the parent star to swing when it is in air movement.
It is planned that these instruments will be repaired several times and supplemented in the next maintenance task in early 2009.
Now you know how Hubble took these photos. Next, we will learn about Hubble's other life as a spaceship.
Hubble Spacecraft System: Power Generation and Dialogue with Ground Control
Hubble is more than just a telescope with highly specialized scientific instruments. It is also a spaceship. Therefore, it must have strength, be able to communicate with the ground and change its attitude (direction).
All instruments and computers on HST need electricity. Two large solar panels fulfill this responsibility. Each wing panel can convert solar energy into 2800 watts of electricity. When HST is in the shadow of the earth, the energy stored in the onboard battery can last the telescope for 7.5 hours.
In addition to power generation, HST must be able to communicate with controllers on the ground to relay data and receive commands from the next target. For communication, HST uses a series of relay satellites called Tracking and Data Relay Satellite (TDRS) system. At present, there are five TDRS satellites in different positions in the sky.
The communication process of Hubble telescope is also assisted by two main computers, which are installed around the telescope tube above the scientific instrument cabin. A computer communicates with the ground, transmitting data and receiving commands. Another computer is responsible for controlling HST and various housekeeping functions. Hubble also has a spare computer in case of emergency.
But what is used to retrieve data? What will happen after collecting this information? The four antennas on the telescope send and receive information between Hubble and the flight operation team at Goddard Space Flight Center in Greenbelt, Maryland. Goddard received the information and sent it to the Space Telescope Science Research Institute (STScI) in Maryland, where it was translated into scientific units such as wavelength or brightness.
Next, learn how the Hubble telescope navigates.
Hubble's Spacecraft System: Guiding and Focusing the Eye of the Sky
Hubble revolves around the earth every 97 minutes, so it is difficult to focus on the target. Three airborne systems allow the telescope to be fixed on the object: gyroscope, fine guidance sensor and reaction wheel, which we discussed in the previous section.
Gyroscope tracks the rough motion of Hubble telescope. Like compasses, they sense its motion and tell the flight computer that Hubble has moved away from the target. Then, the flight computer calculates how much and in which direction Hubble must move to stay on the target. Then, the flight computer instructs the reaction wheel to move the telescope.
Hubble's fine guidance sensor helps the telescope to be fixed on the target by aiming at the guiding star. Two of the three sensors find the guiding stars around the target in their respective fields of view. Once found, they will lock the guiding star and send information to the flight computer to keep the guiding star within the field of vision. Sensors are more sensitive than gyroscopes, but the combination of gyroscopes and sensors can make HST fixed on the target within a few hours, even though the telescope is moving in orbit.
HST can't use rocket engines or gas propellers for steering like most satellites, because exhaust gas will hover around the telescope and blur the surrounding vision. On the contrary, the reaction wheel of HST faces three moving directions (x/y/z or pitch/roll/yaw). The reaction wheel is a flywheel, just like the flywheel in the clutch. When the HST needs to move, the flight computer will tell one or more flywheels which direction and speed to rotate, thus providing force. According to Newton's third law of motion (every action has an equal and opposite reaction), HST rotates in the opposite direction of the flywheel until it reaches the target.
Limitations of Hubble telescope
Although HST has brought countless incredible images and discoveries, it also has some limitations.
One of the limitations is that HST cannot observe the sun, because strong light and heat will blow up its sensitive instruments. Therefore, HST always points away from the sun. This also means that the Hubble telescope cannot observe mercury, Venus and some stars close to the sun.
In addition to the brightness of objects, Hubble's orbit also limits what can be seen. Sometimes, astronomers hope that the target observed by Hubble telescope will be blocked by the earth itself when it is in Hubble orbit. This can limit the time spent observing a given object.
Finally, HST passes through a part of the Van Allen radiation belt, and charged particles from the solar wind are captured by the earth's magnetic field. These encounters will lead to high background radiation and interfere with the detector of the instrument. During this period, it is impossible for the telescope to observe.
Next, learn about the future of the huge observatory in the sky.
Hubble Space Telescope Program: Final Maintenance Task and Replacement
At present, the future of Hubble telescope is a little uncertain. The last maintenance task is scheduled for June 2008 10. However, because Hurricane Ike swept through Texas, the mission control center in Houston was forced to evacuate, and NASA lost a week's preparation time.
Then, the space shuttle Atlantis will explode on June 65438+1October 65438+April 2008, carrying seven astronauts to complete the mission-the journey will take 1 1 day, and the life of the telescope will be extended to at least 20 13 years.
However, on September 29th, 2008, due to a serious malfunction, NASA postponed its last mission to early 2009. Hubble's command and data processing instruments have broken down, and it just stopped capturing and sending the data needed to produce the deep space images that we are familiar with and love.
When Atlantis finally launches, NASA may send replacement parts for the faulty parts. Before that, however, NASA must test the replacement part and train astronauts how to install it. At the same time, the agency also tried to activate the standby channel of the command and data processing system so that the telescope could resume transmitting data.
What is the life plan after Hubble?
Hubble's successor, the James Webb Space Telescope (JWST), named after former NASA director james webb, will study every stage of the history of the universe. From an orbit about 6,543.8+00,000 miles (6,543.8+06,000 kilometers) from the Earth, the telescope will reveal the birth of stars, the evolution of other solar systems and galaxies, and the information of our own solar system.
In order to realize these fascinating discoveries, JWST will mainly rely on four scientific instruments: near-infrared (IR) camera, near-infrared multi-target spectrometer, mid-infrared instrument and adjustable filter imager.
JWST, formerly known as "Next Generation Space Telescope", is scheduled to be launched in 20 13, and has been an international cooperation among NASA, European Space Agency and Canadian Space Agency.
But before we turn to JWST and forget about Hubble, maybe the hard-working telescope is worth a try. Thanks to the unparalleled discovery of Hubble telescope, everyone can enjoy the fascinating images outside the earth's atmosphere.