HUBBLE: CURIOSITIES AND SUCCESSES OF THE TELESCOPE WITH GLASSES

Over the years humanity has managed to achieve incredible goals and some of these have been so sensational and spectacular that even today - in 2021 - we wonder how they were possible. The answer is always the same: dedication, perseverance, ingenuity . It is no secret, however, that among the greatest achievements of man there is certainly having plowed, albeit briefly, the extraterrestrial spaces that surround our planet. All this was possible thanks to the knowledge of humanity.

If there's one thing we can't do without, it's that staggering amount of photos and images of the Universethat come to us constantly from the various space agencies around the world, allowing us to dream of alien realities and worlds of which, for sure, we will never be a part. Among the most important "smiths of cosmic dreams" it is right to mention the Hubble Space Telescope , an instrument that since 1990 represents the primary eye that humanity uses to scrutinize the Universe (but not the only one).  techbizcenter

We hear about him very often, yet not everyone knows the most unique aspects of his mission: did you know, for example, that the Hubble Telescope has vision problems and "wears glasses" ? No, we are not fooling you! Let's continue the (re) discovery of this fantastic tool together, and everything will be revealed.

Where it all started

The idea of a telescope entered into space, capable of observing the depths of the universe without any kind of atmospheric interference, did not arise with Hubble. Already in the 1950s and 1960s the need was felt to enhance the data acquisition capabilities of radiation from the cosmos: ever-larger telescopes on Earth began to suffer too much from problems such as "atmospheric seeing", pollution, and similar. The first observatory that managed to successfully enter Earth's orbit dates back to 1968, a year before the Apollo 11 moon landing.

Many instruments have been launched over the years - each with the ability to work in a certain frequency of the spectrum. electromagnetic - butno one has equated the "fame" and successes achieved by the Hubble Space Telescope , which was launched at the end of the last millennium, in 1990.

For example, if we cited the Orbiting Astronomical Observatory 2 (OAO-2, nicknamed "Stargazer") only the experts or the most hardened enthusiasts could know what we are referring to, the same if we cited the Hipparcos or the more recent Kepler Space Telescope . The secret of Hubble lies not only in its exceptional qualities and instruments , but also (and above all) in the possibility of easily varying the type of object studied, that is, it does not focus on exclusive celestial bodies (Kepler, for example, was dedicated to discovery of exoplanets in a specific portion of the Milky Way).

The numbers you don't expect

The Hubble Space Telescope is an incredible record holder to date: its data has been used by astronomers in approximately 18,000 scientific papers , making it one of the most productive space instruments ever built. In addition, those documents have been cited in other documents over 900,000 times ... and this over a span of 31 years.

But Hubble also hides thousands of other curiosities of which little is said and which we believe deserve attention, as they are also easily understood, and can reveal more about how much incredible engineering there is behind equipment like this. Here are a couple of examples:

 

• According to estimates provided by NASA, Hubble generates approximately 150GB of raw data every week.which are then processed to Earth and sent through the "NASA Space Network";

• Hubble has made more than 1.4 million observations since the beginning of his career, and shows no signs of stopping;

• Hubble continuously completes several orbits of the Earth at a relative speed of about 27,000km / h (very similar to the speed of the International Space Station), at an altitude of about 547km. The telescope in total has traveled more than 6 billion km since it was in operation (the same distance at which the "Pale Blue Dot" photo was taken by the Voyager 1 probe );

• Hubble lacks thrusters or engines, yet is capable of changing its angle as needed . This happens thanks to the simple Third Law of Newton (" to every action corresponds an equal and opposite reaction "). Hubble uses this principle by means of four reaction wheels, large and massive that run under the control of the on-board computer. If a wheel turns clockwise, the Hubble tilts counterclockwise and so on.

• Aiming accuracy is guaranteed by magnetic sensors and gyroscopes, which detect the solar magnetic field and "instruct" the telescope on its correct orientation. In this way, without using any type of propellant, Hubble has a pointing accuracy of 0.007 arc seconds, which is about the width of a human hair seen at a distance of 1.6 km.

Vision problems

Although these numbers make Hubble appear to be a perfect instrument in all respects, in reality it should be noted that the Telescope was born "crippled" , and in a rather serious way. To make an immediate comparison we could say that "Hubble wears glasses" (or the monocle, since it is a cyclops): shortly after its launch in 1990, the operators discovered that the observatory's primary mirror provided less image cleanliness. than estimated through the simulations, then an investigation was opened to find out what was wrong. The mirror was found to suffer from an annoying spherical aberration, which heavily affected the clarity of the images .

After a long investigation by the engineers it was found that the problem was due to badly calibrated equipment during the manufacture of the mirror, which showed a difference in height of 2.2 micrometers between the center and the edges (equivalent to one twelfth of the diameter of a human hair). However, although Hubble was easily reachable from the Shuttle missions, replacing the components was too risky (and expensive), so it was decided to build and assemble adaptive tools, capable of canceling the "deflection" of the mirror ... real glasses. .

The corrective optics and the new instruments were installed on Hubble by the astronauts who took part in the STS-61 mission, in 1993. The image of the galaxy M100 (or NGC4321) that we have reported above speaks for itself: on the left we see the photo acquired by the WFPC-1 camera before correction , on the right instead the same celestial object but captured by the WFPC-2 installed during the maintenance mission, demonstrating that the corrective optics completely compensated for the errors in the Hubble primary mirror.

Time goes by and the Universe is evil

The greatest masterpieces can arise from small inconveniences, and our favorite space telescope is certainly a prime example. But Space is an insidious place, despite being "empty" ... a thousand dangers are around the corner and, you know, nothing lasts forever. Hubble in these many years of activity has risked his life several times, especially due to copious fragments of dust, micro-asteroids and fragments that travel at crazy speeds around our planet (sure you are thinking of the scene of the movie "Gravity" in which Hubble is torn apart by a swarm of fragments but don't worry, nothing like this will ever happen). However, it is true that the telescope is occasionally hit by space debris, but so far no serious damage has ever been found.

NASA engineers had tangible proof of its unfortunate encounters when - thanks to maintenance missions - its solar panels were replaced several times and promptly returned to Earth for analysis.

Close examination of these showed many small cracks and chips on the surface , caused mainly by tiny particles hitting Hubble. Even today on the Space Telescope there is also a small hole (about a centimeter in diameter) on one of the high-gain satellite dishes (called HGAs), caused by an unknown object.

Among the dangers of the Universe, there is something even more insidious and omnipresent than the "banal" debris and that is radiation. Hubble is not located in deep space, so it still suffers from a weak defense from the Sun's harmful rays thanks to the Earth's magnetic field, but it is not completely shielded from it.

The telescope undergoes constant degradation by radiation . Thankfully, the maintenance missions we've often talked about have made it possible to mitigate collateral damage, replacing the most degraded tools over time.

The big hits and the "Hubble Deep Fields" photos

Among the many achievements and impressive images that Hubble has given us, certainly we will never forget the so-called "Hubble Deep Fields" , photos of spectacular beauty in which thousands of galaxies sprout in every single pixel of the frame. These particular images were acquired with a technique very similar to the "long exposure" that photographers and amateurs use : while with our cameras we are now able to expose for long periods of hours (always if you want to kill the poor sensor in your camera / SLR), Hubble acquired HDFs with week-long exposures , captured multiple times and then merged together.

For example, between 18 and 28 December 1995 - the period during which Hubble made about 150 orbits around the Earth - 342 images of the selected area were taken

. Also using different filters, the exposure times for each wavelength were 42.7 hours (at 300 nm), 33.5 hours (at 450 nm), 30.3 hours (at 606 nm) and 34.3 hours (at 814 nm).

To infinity and beyond!

Although Hubble is still in good health (excluding the little scares he makes us take from time to time ), he too will have to retire sooner or later: it is estimated that the Telescope can still operate for several years, but its orbit is no longer corrected. since 2009 and could face serious problems after 2030, the year in which NASA and ESA could also decide to deorbit it in a controlled manner. We said before, however, that Hubble is devoid of any engine or thruster, so it is not possible to "control" it, at least not directly.

 

Fortunately, the aerospace engineers are foresight (and they knew that the Shuttle program was coming to an end) so, also in 2009, the space agencies decided to mount a small block on Hubble, called "Soft Capture and Rendezvous System" (SCM), which allows future generation shuttles ( maybe even Elon Musk's Starship? ) to be able to bring Hubble to a controlled reentry into the atmosphere.

The space observatory is too big to let it burn free, and dangerous pieces would risk falling to the surface. For now - we repeat - there are no plans for how and when to put an end to Hubble's service, and all in all that's fine with us: we will still be able to enjoy wonderful images and photos without remorse and melancholy.

 

Meanwhile, NASA is not idle, and is preparing to launch a brand new and powerful "half-brother" of Hubble, named James Webb Telescope : the latter will have totally different characteristics and we have talked about it in depth in the past . It cannot be considered a true replacement, so it can be said that the Hubble Space Telescope will be an observatory that will last forever, and its legacy will never be forgotten or replaced.

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