CAJ 9: The Look into the Future of Space Telescopes/ The James Webb Space Telescope

Now we know about the two famous space telescopes that changed our notion of the Universe and helped many astronomers around the world in analyzing phenomena like the black hole, dark matter, or planets orbiting other stars. But how does the future look for space telescopes. Hubble had already five servicing missions and the Kepler Mission will also only work for maybe this decade and not longer. What will come after that? Considering that the technologies that these telescopes are using are considered to be outdated compared to the  technological advancements already existing, the question occurs what will the future space telescopes be like?

The answer to this question is The James Webb Space Telescope (JWST), or formerly known as The Next Generation Space Telescope (NGST). The Primary funding bodies are the NASA, The European Space Agency (ESA) and the Canadian Space Agency (CSA). Supposedly it will be launched in 2018 (approximately when the Kepler Mission's current mission status is over). It's Mission is to observe the Universe and study its origins and the first galaxies. From the Big Bang to the formation of solar systems and the planets in those solar systems, it will give us insight into the history of our Universe. It will be the successor of Hubble but technologically it will be much more advanced.

The Telescope itself will be enormous in size. Alone the sunshield will approximately be the size of a tennis court. The Mirror of the telescope will be 6.5 meters in diameter. This is nearly three times bigger than that of Hubble (2.4 m). As the size of the sunshield is bigger in width than the rocket used that launches it, the telescope, with its shield will only be unfolded when it has arrived in space.


The observatory itself consists of three main parts. The Integrated Science Instrument Module (ISIM) which is responsible for housing the cameras and the instruments. The Optical Telescope Element (OTE), which is the Eye of the Observatory. It comprises two mirrors one primary and one secondary mirror and a backplane which is the spine of the mirrors. These mirrors collect the sunlight and direct it towards the science instruments. The primary mirror consists of 18 hexagonal parts that are connected to each other and will only unfold when the observatory is in space. The Mirror itself is made of metal beryllium and is coated with gold. The second mirror, similarly like the Hubble Telescope, is reflecting the sunlight collected by the primary mirror and concentrates it towards the science instruments.  The third main part is the spacecraft bus, which is responsible for supporting functions. The six subsystems that keep the telescope functioning are located in the spacecraft bus. The Electrical Power Subsystem, the Attitude Control Subsystem, the Communication Subsystem, the Command and Data Handling Subsystem, the Propulsion Subsystem, and the Thermal Control Subsystem are all essential for the telescope to function properly.

These are only the main parts of the observatory. However, the Telescope consists of many more other elements.

The Telescope observes mainly the infrared light that comes from very distant objects, but by simply functioning, the System itself emits infrared light. For this reason the Spacecraft is also applied with a sunshield that protects it from overheating and from swamping the incoming light with infrared light emitted from the systems of the telescope. 


The already mentioned ISIM will be the heart of the telescope and includes four elements: 

Near-Infrared Camera - primary imager

Near-Infrared Spectrograph - disperses incoming light into a spectrum to analyze

Mid-Infrared Instrument - has both a camera and a spectrograph that sees light in the mid-infrared region of the electromagnetic spectrum

Fine Guidance Sensor - allows the telescope to point precisely All of these systems are the most sophisticated technologies that are currently known. This telescope will help humanity discover things that we do not even know about yet. Maybe even life on another planet. Take care, Harald

PS: Looks like Star Wars is becoming reality huh? :D

CAJ 8: The Hubble Telescope - Optics (part 3)

How is it possible that a telescope can view stars that are more hundred or even thousand light-years away? What optical device is capable of picturing galaxies that are so far away that we cannot even conceive the enormous distances?

It is not only the fact that it does not have to look through our polluted atmosphere, but also the "eyes" of Hubble. The eyes of Hubble have also a real name that is the Optical Telescope Assembly. This system is designed to offer the widest possible field of view. The system consists of two main mirrors, apertures and supporting trusses.

As the light strikes the telescope, it enters the tube, which prevents stray light to enter the telescope. After it entered the tube it passes the first optical glass. Than it strikes the first mirror that is shaped like an upside down bowl. This mirror is called the concave. Because of the shape of the mirror, it diverts the light and reflects it to the centre of the optical glass in which the second convex shaped mirror can be found. This mirror directs the light again to the first mirror. The first mirror has a hole in the Center where the light can enter and can reach its focal point right where the science instruments are placed. This basic model is called the

Ritchey-Chretien Cassegrain. 

The main mirror measures 2.4 meters in diameter. The smaller mirror that redirects the light towards the science instruments is only 0.3 meters in diameter. The focal plane where the light gets picked up is roughly the size of a dinner plate. 

The mirrors are developed in a very special way. They are treated with abrasives so that the surface of the mirrors is perfectly smooth. The mirrors are designed so that they do not deviate from a perfect curve by more than 1/800,000th of an inch. To help you understand this I use an example. The mirrors are so smooth that if the mirror were as big as the Earth in Diameter, the biggest bump would be 6 inches tall. 
The mirrors are made of ultra-low expansion glass and are kept constantly at the same temperature. This prevents the glass from cracking or warping. The surfaces are coated with a very thin layer of aluminum and a similarly thin layer of protecting magnesium-fluoride. The magnesium-fluoride allows the mirrors to be even more reflective to ultraviolet light. 

In the first post I already mentioned the first problems of the telescope with the mirrors and blurry images. This was because of the primary mirror. After the telescope was launched and the first images were sent to Earth, it became apparent that something is wrong with the telescope as the images are all very blurry. This was because the primary mirror had a flaw called spherical aberration. The outer edge of the mirror was four microns flatter than intended. Four microns equal approximately one-fiftieth of a single human hair.

During the first servicing mission this problem was solved by putting small corrective mirrors on the primary mirror. After this the images became much sharper and the telescope could start to function properly. During the fourth servicing mission the corrective mirrors were replaced by an instrument called Cosmic Origins Spectrograph. This device breaks down the light reaching the telescope. By analyzing these light waves, scientists can determine the density and chemical components of a planet. This technology was a major development and improved the telescope's sensitivity up to 10 times, especially the sensitivity to ultra-violet light.