Goodbye to Hubble? – Magazine ?

600 kilometers from the Earth’s surface, circling the planet every 97 minutes, the Hubble Space Telescope moves. But its journey, which began in 1990, could be approaching its end if the maintenance services that this instrument requires are not performed.

When we enjoy the majestic photographs taken by the Hubble Space Telescope, we may not imagine the amount of effort necessary to reach such an amazing result. Hubble is the product of 50 years of pursuing an ideal and more than 20 of international work and collaboration, with the intervention of experts in areas such as astronomy, astrophysics, optics and engineering.

It can be said that it all began in the early 1920s, when the German scientist Hermann Oberth published an article speculating about the possibility of putting a telescope into orbit. At first many called him deluded, but around that time another visionary, Robert Goddard, began his first tests with rockets, and little by little the topic of launches into space became more respectable.

The development of technology in the 20th century facilitated the construction of increasingly larger and more powerful telescopes to peer into the depths of space. However, the time came when the increase in size of telescopes was no longer proportional to the clarity of their images. This is because Earth’s atmosphere distorts the light passing through it. This distortion is what makes stars appear to twinkle. With the idea of ​​improving telescopic images, the American astrophysicist Lyman Spitzer Jr. proposed, in 1946, designing a space observatory to avoid atmospheric distortion.

In 1962, the United States National Academy of Sciences recommended that the new space agency NASA build and launch a space telescope. That was enough for Spitzer to devote much of his time to advocating for the creation of the telescope, both in the US Congress and before the scientific community.

NASA launched its first space observatory into orbit in 1968. It was called OAO-II (the first OAO, launched in 1966, failed to enter orbit, apparently because its batteries exploded). The small device operated successfully for four and a half years, during which it measured ultraviolet emissions from galaxies, stars, planets and comets.

The success of OAO-II encouraged the National Academy of Sciences, which published a report on the “Scientific Uses of the Large Space Telescope” in 1969, granting its approval to the project. The design and construction of the telescope began in the 1970s, with the participation of the European Space Agency. After the space shuttle explosion Challenger in 1986, which delayed the launch of the instrument, finally on April 25, 1990 the shuttle discovery It took off from the Kennedy Space Center with a crew of five astronauts and the Hubble Space Telescope, named in honor of astronomer Edwin Powell Hubble, who, in 1929, discovered the expansion of the Universe.

Attributes of a giant

The Hubble Space Telescope is a cylinder 13.2 meters long, with a diameter of 4.2 meters and weighing more than 11 tons, which rotates in orbit around our planet at a speed of more than 28 thousand kilometers per hour. It obtains electrical energy through two solar panels that measure 7.6 meters each. The device also has navigation systems that allow it to be directed and maintain its orientation while capturing images. The mechanical instruments that allow it to rotate to observe various points in the sky are six gyroscopes (rotating disks). The laws of physics indicate that an object that rotates without external influences, such as the Hubble telescope, must always rotate at the same speed and in the same orientation. As the speed of the gyro wheels increases or decreases, the telescope reacts by turning in the opposite direction to compensate for the change. This way you can orient the telescope.

Capturing light from the Cosmos, converting it into digital data and transmitting it to Earth also requires other tools. Before the space telescope can carry out any observations, it must locate a pair of “guide stars.” These stars, which serve as a reference, are previously selected with the help of a catalog that contains the precise location of more than 15 million stars.

Hubble is the first space observatory capable of capturing light from the entire electromagnetic range between infrared and ultraviolet, passing through visible light. Originally the telescope carried five scientific instruments. After almost three decades, some of them have been replaced by more advanced ones, as happened with the camera for dim objects (Faint Object Camera), replaced in 2002 by the advanced prospecting camera, whose tasks include observing the most remote and ancient events in the Universe.

Other important instruments for Hubble’s work are: the planetary and wide-angle camera, mainly responsible for the most famous images of the space telescope; the near-infrared camera and multi-object spectrometer, whose high sensitivity to infrared light allows it to observe objects obscured by interstellar gas and dust and thus peer into the depths of space; and the imaging spectrograph, which acts similar to a prism, separating the light from the objects it observes into its different colors to carry out chemical composition analysis.

There is no camera to photograph the “natural color” of the stars on board Hubble. All your digital cameras take grayscale photos. Although attempts are often made to give the final images a color close to natural, this does not have an artistic motivation, but rather more practical purposes for science, such as showing the distribution of chemical elements in clouds of gas and dust or highlighting some important features. To reconstruct the color, the images formed with blue, green and red fi lters are electronically processed and added to obtain tinted images.

The centerpiece of the Hubble telescope is the optical system formed by the primary mirror, 2.4 meters in diameter, and the secondary mirror, 0.3 meters, whose combined weight is close to a ton. The primary mirror is a concave mirror that captures light and reflects it towards the secondary (convex) mirror, which in turn returns it by passing it through an opening in the center of the primary mirror. There the light is concentrated in an area called the focal plane, where it is collected by the instruments.

The Hubble glasses

Hubble has revealed the Universe to us in a level of detail previously unimaginable, but it was not like that at first. In May 1990, when Hubble transmitted the first images from space, scientists discovered to their horror that the instrument’s primary mirror had a curvature flaw; In other words, he was shortsighted.

Although being myopic is no tragedy for those on Earth who can order corrective lenses at any time, in the case of a space telescope it represents a real drama. The “spherical aberration,” as the defect in Hubble’s mirror is called, was actually just a four-micron deviation at the outer edge, but it produced blurry images.

Scientists and engineers immediately set about making some kind of corrective “glasses” that could give Hubble perfect vision. The apparatus consisted of a series of small mirrors designed to be placed in front of the telescope’s instruments. Now all that was left was the most difficult part: installing it in weightless conditions and at 600 kilometers above sea level.

In December 1993 the space shuttle Endeavor took the astronauts of the first service mission for Hubble into space. The astronauts installed Planetary Camera 2 and the corrective system to compensate for the failure of the primary mirror. The maneuvers were very difficult for the astronauts because they had to be performed at night (when the Sun was on the other side of the Earth) to protect the telescope instruments from sunlight. As if that were not enough, they should not leave even the slightest trace on the mirror.

The astronauts prepared for several weeks. In addition to theoretical training, they carried out repair simulations in a swimming pool, with a model of the telescope, to simulate weightlessness. After capturing the telescope and placing it in the cargo area of ​​the Endeavorthe astronauts carried out five “space walks”, one per night, to adjust Hubble’s new “glasses”, which could finally see with complete clarity.

Since then, the telescope has transmitted about 120 gigabytes of data every week, information that has allowed impressive advances in our knowledge of the Cosmos. Members of the international astronomical community compete each year for observing time on Hubble. Because the demand far exceeds the time available, scientists must submit their observation proposals to committees of astronomers in charge of making decisions. When a proposal is accepted, observations are meticulously planned. This is done by the experts at the Space Telescope Scientific Institute, founded in 1981 on the campus of Johns Hopkins University, in Maryland, United States, as Hubble’s operations center.

All observations are stored on an optical disk. The data is sent to the researcher in charge of each observation. After a year of…