Reports

Abstract: The following report outlines the processes by which an educational project, sponsored by Erik Virre,was manufactured so that it could explain the internal and mechanical workings of the James Webb Space Telescope (JWST). The constructed replica demonstrates how reflective telescopes gather light onto a primary mirror and then reflect onto a secondary lens where individuals will be able to see a magnified image of a desired location or object. For this replica, it was decided to replicate this process through a laser that projects onto a group of mirrors to then reflect onto a smaller mirror that captures the laser’s light. This demonstration is one that will be presented in an exhibit at the UCSD Clarke Center for Human Imagination. To accomplish this goal, it was decided to focus on the replication of the mechanical components and physical appearance to keep the grandeur of the JWST intact. The overall design of the JWST replica can be described under three main components: the mirror base, primary mirrors, and secondary mirror gantry. All three components combined needed to fit the constraint of around $2,500. The final design decided upon was able to meet all desired requisites established by the sponsor and follow engineering principles. 

Background: The James Webb Space Telescope is one of the most recent miracles of space exploration which came to fruition via years of careful, precise engineering. The inspiration for investing 10 billion dollars upon such a structure came from lack of knowledge of both the earliest galaxies formed after the big bang and of stars of distant planetary systems. To make this project possible, multiple private and government entities including Northrop Grumman and the National Aeronautics and Space Administration (NASA) contributed to the manufacture, transportation, and deployment processes. The James Webb is mainly composed of a system of 18 parabolic, hexagon-shaped mirrors (primary mirrors), a parabolic secondary mirror, and a system of infrared sensors/cameras that work together to gather light from all angles, forming images of really distant objects in space. 

Sponsor: Our sponsor Dr. Erik Viirre, Director of the Arthur C Clarke Center for Human Imagination, specializes in neuroscience and is an avid space exploration enthusiast, eager to share/learn new things about the world beyond Earth. With that mission in mind, the main objective of the project is not to build a functional telescope, but to build a replica of the James Webb for the purpose of demonstrating to people outside of the realm of engineering how telescopes similar to it capture amazing images like those that have been released recently. The replica is to reflect laser light from distant locations within a room, sport a similar structure/folding mechanism, and similar looks as the actual one currently in action 1 million miles away from here! 

Design Solutions:

Primary Mirror

The Primary Mirror, as seen in Figure 2., is composed of eighteen gold color mirrors. Three have the capability to reflect light from the light source onto the secondary mirror. The other fifteen mirrors provide a reflective curvature backplane to the overall structure, similar to that of the James Webb. In order to be reflective, lightweight, inexpensive, and easily manufactured, aluminum was chosen as the main raw material for the mirrors. To minimize weight concerns of the primary mirror structure, a thickness of 0.23 cm (0.09 in) was chosen which is readily available at various metal suppliers. In addition, to fit space constraints, the side length of the individual hexagons was decided to be 18.4 cm (7.25 in). To address the gold coloration, a reflective gold film was used as it provides a solution that is inexpensive, provides a smooth reflective surface, and provides ease of application. 

Support Structure

For the Support Structure, it was decided that the replica would require a very sturdy base that would support the entirety of the telescope, refer to Figure 2 for visualization. That is, three 1.27 cm (0.5 in) acrylic plates and 18 aluminum hexagons, and a gantry mechanism that will be mounted onto the structure. The weight of these components is expected to weigh a total of xxx lbs. Ergo, why it was necessary to design and find a material that would not fail against the weight of all required components. The structure's rigidity was especially important because of the necessary angles and placement of each individual aluminum hexagon to effectively reflect a laser light as desired. Any movement or slight vibration could cause the geometric constraints of each laser to be unattainable. Thus, the importance of not only having the structure be as rigid as possible but the placement of each hexagon as well.  

Primary Mirror Mounts

One of the key requirements for this replica was to have the primary mirror plane represent an almost concave large mirror, as shown in Figure 4. To reach this goal it was decided to create separate stilts that would be placed behind each mirror to provide the height required to achieve the illusion of a parabolic primary mirror. To mount these mirrors onto the primary mirror support plane (the ½ “ acrylic plate) it was still necessary to design a mount that would be able to support the total load caused by the aluminum hexagonal plate and the stilts. This led to the design of a square mount that was attached to the primary plane support through the use of four bolts. This ensured that the mount was securely placed onto the acrylic plate without having to worry about any vibrations or deliberate movement that would cause the hexagonal mirror to move out of place [A]. The efficiency of these mounts were modeled through the use of Finite Element Analysis further explained in Ch 3 Primary Mirror Mounts. A stilt and hexagonal plate were then attached to each mount utilizing a high strength industrial use epoxy, as seen in Figure 4.

It is also important to note, that because the aluminum hexagons are not parabolic in shape, as seen in the original James Webb Telescope, the angle to which achieve desired reflections of laser light would have to depend considerably on the user's ability to angle select mirrors to precisely to select locations. This meant the use of two Mount designs that would allow for stationary ‘mirrors’ and precision adjustments.

Secondary Mirror

The secondary mirror is a curved convex mirror. The current design decision is to manufacture an Aluminum disk into the desired shape with the CNC turning machine and apply reflective tints onto its surface to make it able to reflect laser lights better from the primary mirror. After performing geometrical simulation of the laser light paths, the current designed shape for the secondary mirror is an arc with 4 inches in diameter and around 20 cm radius of curvature, as shown in Figure 4 below.

Gantry

The Gantry is composed of three aluminum bars and two ball joints, and a pin support. All of which form a triangle like structure that will be responsible for vertically positioning the secondary mirror. The ball joints were included in the design to enable the aluminum bars to adjust in angle. The pin supports at the top to allow rotation, and a secondary mirror plate that was mounted onto the secondary mirror mount.

100% Completed as of 17 Mar 2023.