i want to paraphrase these papers. urgent its due 12 hours

James Webb Space Telescope (JWST):

The JWST idea was first launched for scientific purposes that included knowing what happened after the big bang. The main goals of JWST can be concluded as follows:

1. Reionization and first light.

2. Knowing how galaxies formed and the assembly of galaxies.

3. To know and get more details about the birth of stars and planets.

4. To know more about planets and the origin of life and if life is possible on other galaxies and planets.

5. To know what and where other earth-like planets are there.

The mission drives basic requirements can be concluded as recognizing the faint objects, distant -old- objects, and through dust clouds. This can be achieved using a telescope that has the following properties in sequence:

A high redshift is when galaxies move in respect together with low velocity and at high speed in relative to themselves.

Requirements of JWST:

To make this mission a successful one, several requirements were set as requirements. The requirements include the following:

· Large Light-Collecting Area:

· Deployable system (Deformable).

· Lightweight materials (thin mirrors, films and membranes, and composites).

· Stable structures and materials (beryllium mirrors &low creep composites).

· Infrared observations:

· A cryogenically compatible system (beryllium mirrors & carbon fiber composites).

· Cryogenic telescope and science instrument:

· Deformable beryllium mirrors (can deform in 6° of freedom).

· Bonded carbon fiber campsites structures.

· Four infrared optimized science instruments.

Composites were chosen for this mission because they are basically plastics that can deform under load and retain their original shape and dimensions upon unloading them. Carbon fiber, however, was chosen because its unique properties that include the high strength-to-weight ratio and extreme temperatures resistance.

Components of the JWST:

· The Sunshield:

A multi-layer sunshield was developed for this very mission and consisted of light-tight materials that are capable of resisting the damage that might be caused by sunlight (which is not filtered like the sunshine on earth). Also, the membranes are infrared-tight; which means that they won’t develop damages when an IR beam hit them. Note that the membranes are deployable.

The sunshield was coated with aluminum on both sides in layers 3, 4, & 5. However, layers 1 and 2 were coated with aluminum on top and silicon on bottom. It is worth mentioning that the size of the shield is almost the size of a tennis court. Two of the biggest challenges in the design of the sunshield are coming up with a concept to fold it in the rocket and the wide temperature range between the top and bottom.

The membranes are coated with kapton to withstand the high temperature range. The calculation of the temperature difference between the top and bottom resulted in realizing that the temperature on top (away from sun) is around 50 K (= -370 °F) and on bottom (facing sun) is around 360 K (=185 °F).

To make sure that the sunshield will be fine in space, several tests were performed that include the abrasion test, which resulted in less than 0.03& damage in shield. Also, a meteoroid impact test was performed and it was successful (a tear was developed but didn’t really affect the performance of the shield).

· Warm Spacecraft Bus:

Another interesting part in JWST is the “Warm Spacecraft Bus”. This part works as the brain of the telescope. It also generates power for the structure and launches vehicle interface.

· The Mirror:

Mirrors can be made of glass, however, since glass is very heavy, fragile, and hard to produce in big dimensions, it was replaced by beryllium. Basically, JWST mirror is bigger than the Hubble mirror. The mirror consists of 18 hexagonal segments that are 6.5 m (21.4 ft.) across; each of is 1.34 m (4.4 ft.) flat to flat. There are 6 motors that are responsible for adjusting the curvature of the mirror with 6° of freedom (correctable structure). Also, there is a 7th motor in the center to make sure that the mirror is in the correct curvature.

Beryllium is one of the strangest elements on earth. It is very toxic and causes lung cancer on the long term of being exposed to it. Also, this element is hard to handle; however, its unique properties qualified it for manufacturing the mirror. Beryllium is very light and has high melting point (around 1280 °C).

The process by which the mirrors were manufactured is that they were first consolidated (HIP), then machined and polished, and afterwards, they were gold coated. Note that the mirror is gold coated because gold is the only element that is capable of reflecting all of the infrared beams that might cause damage to the telescope.

How to Make Sure That Mirrors Survive Launch & Mission:

Several test were developed specifically to make sure that the mirror is capable of withstanding the harsh conditions in space. Those tests include:

1. Cryogenic temperature cycling.

2. Iterative polishing.

3. Vibration testing.

And afterwards, the mirrors were checked to notice any imperfections of deformation in the materials.

Note that the impact of radiation is very important. The optical absorption and emissivity is performance critical; because radiation may cause changes, which will affect the performance negatively. The samples were exposed to low speed electrons and low speed neutrons. The JWST shield was tested in a 7-year storage simulation and the coating remained well adhered and the optical properties didn’t degrade significantly.

Also, a high temperature exposure was performed under a temperature of 600 K. the results showed that the coating remained well adhered and the optical properties didn’t degrade significantly.

The Plan:

The JWST is planned to be launched in 2018. The observatory time is estimated to be 5 years knowing that the fuel is supposed to last long for 11 years.

Large Collecting Area

Long Observations

High Redshift

Infrared Observations