3D printing technologies experienced a huge evolution both in techniques and applications since its invention in the early 1980s. Fused Deposition Modelling (FDM) was the first term used to describe an additive manufacturing technique and from that point on, many different ways of 3D printing have been developed to fulfil a variety of needs.
Nowadays, 3D printing has become more accessible to the general public because of the big drop in prices caused by the big technical developments. As a result of that, a community of “makers” has been taking shape internationally making access to designs and advice easier.
3D printing is without a doubt one of the key developments of the last decades and covers from highly technical research fields (like medicine-related investigations) to individual makers or even educational programs to encourage young people to create.
As a result of that, it can be seen daily that the so-called 3D printing has gained a big amount of fame between fabrication processes for its accessibility and ease of use, it only takes a computer, a 3D printer and time. On behalf of that, an idea for a final degree thesis was proposed: designing and printing using fused deposition modelling a telescope for astronomical and educational purposes.
The main goal of the project is to, first check the capabilities of the 3D printing technology to build telescopes for amateur astronomers, comparing its performance with the current commercial products, and secondly, to develop a set of educational resources that permit the easy construction of low-cost custom instruments for the teaching and diffusion of Astronomy and Space Science. The set of resources derived from this project will be an interesting tool for Astronomy beginners, Engineering and Science students, teachers, and makers.
In this work, we summarise the current status of the project and the results obtained with the first built prototype, as well as the design and choices made to fulfil our needs in a practical and feasible way. Last but not least, a list of possible educational activities to be carried out with the developed resources will be exposed.Peer ReviewedPostprint (published version

Casamor Martinell, Oriol

Fernández, Daniel

Macías Macías, Raúl

Marzoa Domínguez, Antonio

Soler Ruiz, Juan

English

Macías Quesada, Roger

UPCommons. Portal del coneixement obert de la UPC

4th Symposium on Space Educational ActivitiesBarcelona, April 20223D printed telescopes: an interesting tool for teaching Astronomy,Science and TechnologyRoger Macías1*, Antonio Marzoa1, 2, Oriol Casamor1, 2, Joan Soler1, Daniel Fernández3__________________________________________________________________________Abstract3D printing technologies experienced a huge evolution both in techniques and applicationssince its invention in the early 1980s. Fused Deposition Modelling (FDM) was the first termused to describe an additive manufacturing technique and from that point on, many differentways of 3D printing have been developed to fulfil a variety of needs.Nowadays, 3D printing has become more accessible to the general public because of the bigdrop in prices caused by the big technical developments. As a result of that, a community of“makers” has been taking shape internationally making access to designs and advice easier.3D printing is without a doubt one of the key developments of the last decades and coversfrom highly technical research fields (like medicine-related investigations) to individualmakers or even educational programs to encourage young people to create.As a result of that, it can be seen daily that the so-called 3D printing has gained a big amountof fame between fabrication processes for its accessibility and ease of use, it only takes acomputer, a 3D printer and time. On behalf of that, an idea for a final degree thesis wasproposed: designing and printing using fused deposition modelling a telescope forastronomical and educational purposes.The main goal of the project is to, first check the capabilities of the 3D printing technology tobuild telescopes for amateur astronomers, comparing its performance with the currentcommercial products, and secondly, to develop a set of educational resources that permit theeasy construction of low-cost custom instruments for the teaching and diffusion of Astronomyand Space Science. The set of resources derived from this project will be an interesting toolfor Astronomy beginners, Engineering and Science students, teachers, and makers.In this work, we summarise the current status of the project and the results obtained with thefirst built prototype, as well as the design and choices made to fulfil our needs in a practicaland feasible way. Last but not least, a list of possible educational activities to be carried outwith the developed resources will be exposed.Keywords3D printer, Additive manufacturing, Astronomy, Education, Telescope_______________________________________________________________________1* Corresponding author: roger.macias@estudiantat.upc.edu1 Departament de Física, Universitat Politècnica de Catalunya, Spain2 SENER Aeroespacial, S.A., Spain3 Agrupació Astronòmica de Sabadell, SpainPage 1 of 64th Symposium on Space Educational ActivitiesBarcelona, April 2022Acronyms/AbbreviationsCAD Computed Aided DesignFDM Fused Deployment ModellingFFF Fused Filament FabricationSLA Stereolithography1. Introduction3D printing is a technology that has beenaround us for more than four decades [1].The pioneering 3D printing works date from1981 and were carried on by the Japaneseautomobile designer Hideo Kodama.Kodama invented a new manufacturingtechnique that consisted of the addition oflayers using resin polymerized under UV lightirradiation. However, Kodama’s invention didnot fit the requirements for patent claiming, andhe was not officially recognized as the inventorof the procedure.In 1986, a group of French investigators failedto file a patent for a monomer curing system bymeans of a laser. That same year, a patent forSLA by Charles Hull, who was searching for afabrication technique that let him build smallparts for furniture in an easy way, waspublished. Hull’s technique consisted of asystem that cured resin by exposing it to UVlight, layer by layer.Later on, in 1988, Charles Hull founded theenterprise 3DSystems [2], a companydedicated to the development of 3D printersand related technology.At that same time, the first iteration of the mostfamous 3D printing method was patented.Scott Grump submitted the patent for FusedDeposition Modelling (FDM) or Fused FilamentFabrication (FFF), which was a printing methodthat consisted of extruding material through apre-heated nozzle in order to melt it.During the 1990 decade, the industry benefitedfrom the emerging different CAD software,increasing the ability of both individuals andcompanies to mass-produce designs that couldbe easily exportable to 3D printing formats thatexisted at that time.Later on, in the first decade of the 2000s, twomajor milestones of 3D printing were achieved.The first of them, achieved in 2005 being thecreation of the RepRap Project [3], whichconsisted in designing an OpenSource printerthat could be mainly built using piecespreviously printed with another 3D printer,basically a “self-replicating manufacturingmachine” (as told by RepRap themselves).This, in fact, opened the doors of amateur 3Dprinting by enabling the general public to printtheir own print farms.The second major accomplishment of thistechnology was achieved in 2008 when thefirst fully printed prosthetic leg was unveiledgiving 3D printing a big media coverage andhelping it expand all over the world.Since then, 3D printing has done nothing lessthan keep expanding through the globe andbecoming key in technological developments infields such as medicine, fabrication methods oreven in the aerospace industry with the designand fabrication of new rockets with many of itscomponents 3D printed.As an example, a recent work [4] has shownthe possibilities of the practical implementationof 3D print optomechanical hardware withhigh-performance rates and with a cost muchlower than if conventional commercialhardware was bought. This reference is anillustrative example (among many others) onhow 3D printing technologies can be agame-changer in research and development inmany areas of the optical industry.2. Contextualization of the project:Amateur AstronomyAmateur Astronomy is a field in which differenttechnical skills and needs converge. Theamateur astronomical community is formed bythousands of motivated people that want toknow more about the Cosmos and to transmitthat knowledge. Furthermore, a huge fractionof that community is also interested indo-it-yourself projectsThis section summarises the different designsof telescopes commonly used by the amateurcommunity and the different approaches inwhich, as far as the authors know, severalmembers of the community have been madewith 3D printing technology.2.1. Types of telescopesTelescopes are basically divided into threetypes: refractors, reflectors and catadioptric.In this subsection, the three main types oftelescopes used by amateur astronomers arebriefly introduced and described.2.1.1. RefractorsThis type of telescope is based on the use ofrefracting elements (lenses). The main designknown as Keplerian telescope is compound byPage 2 of 64th Symposium on Space Educational ActivitiesBarcelona, April 2022two positive (i.e, converging) lenses (theobjective and the eyepiece), and it is theprincipal design used nowadays (despiteoptical corrections such as the use ofachromatic doublets or inversors for the caseof terrestrial telescopes). Another commondesign is the Galilean telescope, which uses anegative (divergent) lens as eyepiece. Anexample of a Keplerian telescope is shown inFigure 1a).Refractors need little to no maintenancebecause of their lenses being static and fixedto the tube. This kind of telescope providessuperb colour contrast and are generallycompact.Even though its simplicity, refractors sufferfrom chromatic aberration, a phenomenoncaused by the different focus points that lightcan have when changing the refractivity indexof the environment depending on thewavelength of the light.2.1.2. ReflectorsA reflector's working principle is based onreflection instead of refraction. In the mostcommon design, parallel beams of light enterthe tube by the top opening and travel throughthe whole telescope until they reach thebottom, where a parabolic (or spherical) mirrorreflects the light to a secondary flat mirrormounted on the spider at the top of thetelescope. This secondary mirror reflects lightto the side eyepiece in which the focal point ofthe primary mirror is re-sended to the infinity.This design is commonly known as Newtoniantelescope and it is one of the most popularreflecting systems used by amateurastronomers. The basic scheme of this type oftelescope is shown in Figure 1b).In comparison to refractor telescopes,reflectors do have the need of somemaintenance, due to the fact that they use two(or more) mirrors and these need to bealigned, a process called collimation — whichconsists in the alignment of the two mirrors —must be done from time to time. Furthermore,eventual dust deposition over the primarymirror could occur, leading to a reflectivity loss,which affects the final quality image.2.1.3. CatadioptricCatadioptric telescopes are a combination ofthe characteristics of both refractors andreflectors because they combine the benefitsof lenses and mirrors at the same time.This type of telescope works by applying acorrection to avoid aberrations to the beam oflight which then is reflected by the primaryspherical mirror that can be found at thebottom of the tube. The beam then travels tothe secondary mirror which finally reflects it tothe eyepiece. It is for this reason thatcatadioptric telescopes are much morecompact than refractors or reflectors.Figure 1. Working principle of a refracting (a))and reflecting (b)) telescope. [5] [6] [7] [8]2.2. Amateur 3D printed telescopes3D printed telescopes are starting to gainpopularity among the maker community. Bylooking at 3D printing websites like Thingiverse[9], many different projects with full guidelinesto print and build a telescope using a 3Dprinter can be found.As an example, one of the most popularprojects is the Pikon telescope [10], a reflectortelescope that uses a Raspberry Pi [11] tocapture images of the observed objects. Apicture of the telescope is shown below.Figure 2. PiKon telescope, extracted from PiKonWebsite. [10]3. Design and specificationsFor this project, a Newtonian design waschosen. For the optical specifications of thesystem, a 152 mm (6 inches) aperture waschosen. Since a 762 mm focal length concavemirror with such aperture diameter wasavailable, thus, an F5 Newtonian telescopedesign was finally proposed.With these main characteristics set, the nextstep is to begin designing the pieces needed tobuild the telescope using CAD. In our case,SolidWorks [12], a software developed byDassault Systems was used. After somePage 3 of 64th Symposium on Space Educational ActivitiesBarcelona, April 2022iterations and a complete assembly of all thepieces, the CAD design resulted in the solidshown in Figure 3.Figure 3. Telescope CAD.Four parts of the design can be differentiatedin Figure 3: the top cap —to the left—, themiddle rings —the two rings at the centre ofthe assembly—, the bottom cap —to theright— and finally the bars that form the trussand unite all the pieces together. We will nowgo into further detail about each part.3.1. Top CapThe top cap is composed of five pieces itself:the top ring, the eyepiece holder (which in thiscase it is a Crayford focuser designedspecifically for this telescope), the searchersupport, the spider and the secondary mirrorcell.Figure 4. Top cap image with all the parts visible.The most important piece of this part is thespider —centrepiece attached to the top cap—,which is basic for holding the secondary mirrorcell to the body of the telescope. The design ofthe spider has to be done with special care,because it is required that it occupies the leastamount of aperture possible, maximising theamount of photons that arrive at the primarymirror. All the pieces are fixed to the top ringwith DIN912 M3 (different length depending onusage) screws that screw into inserts that arecoupled to the ring using heat.It can also be seen that both the eyepiece andsearcher holders have many screw holes. Thatis to ensure the integrity of the system in casethe final user would like to strap a camera totake pictures through the eyepiece.3.2. Middle ringsThe main purpose of the middle rings is to actas interfaces between the truss and theequatorial mount that will be used to point thetelescope to the sky.Figure 5. Middle ring, used as the interfacebetween the mount and the telescope.As it is shown in Figure 5, the middle ring’sdesign presents three plates that screw intothe main ring to ensure a perfect attachment tothe truss of the telescope and a fourth platewhich is different, that is used for fastening thetelescope to the mount with the centre hole.Again, all screws fit into inserts put on thepiece using heat.3.3. Bottom capThe bottom cap is the most intricate part todesign because it contains moving pieces thatwill be used to collimate the main mirror.Between the pieces that compose it, we canfind the main mirror cell, the levers thatcompose the collimation system and thebottom cap which is the container of all theprevious pieces.This is a key part for the correct performanceof the whole telescope because it contains themain part of the optical system as well as thealignment components.Page 4 of 64th Symposium on Space Educational ActivitiesBarcelona, April 2022Figure 6. Bottom cap image. Main mirror cell istransparent so the collimation system can bevisible.As illustrated in the previous figure, the cell issupported by the red mechanisms. These formthe collimation system as well as provideattachment to the main mirror cell both radialand longitudinally. These work as levers andare preloaded with a spring (not visible in theCAD - Figure 6 -). Figure 7 shows an image ofa prototype of the collimation system.Figure 7. Prototype of the collimation system,intended to test structural integrity.The whiffletree [13] (lever) is spring-loaded andacts the left arm of the lever when the screwon the right arm is actioned. This allows themain mirror cell to move upwards anddownwards because of the flexibility given bythe flexors.Figure 6 shows how the levers are locatedinside guides, to ensure the structure is stiffenough to support the loads produced by thecollimation system.3.4. Truss barsFigure 8. Truss bar with the interfaces to attachit to both the top and bottom caps.The truss is composed of two different pieces,the bars and the interfaces to connect the topand bottom caps.For the bars, 12 mm aluminium hollow bars areused, since aluminium gives rigidity to the trussand avoids overweight problems because of itslightness.The interfaces are also 3D printed parts andare the key backbone of the structure. Theseare glued together with the aluminium barsusing epoxy glue.Figure 9. The interface of the truss in detail.4. Educational applicationsOne of the aims of this project is mainly tointroduce students of all ages into cosmosexploration, optical design of telescopes basis,and to provide a hands-on experience with 3Dprinting technologies, by means of building atelescope and testing its capabilities. Thisproject is adequate both for upper coursestudents, amateur astronomers and makersmotivated with Astronomy. Focused on moreexperienced engineering students. For doingso, a proposal of activities is given.Students could involve themselves in buildingthe actual telescope by following the guidelinesprovided. The majority of the telescope is builtby 3D printing the pieces and the non-3Dprinted materials are easily bought on theinternet.In addition to telescope fabrication andbuilding, an introductory course into opticsshould be done in order to ensure a betterunderstanding of the physics behind thetelescope.Moreover, as an extra activity, a spaceobservation workshop using the telescopecould be conducted.The application of this project for differentdissemination and educational activities, andthe design of a workshop activity is a currentongoing work. At the final stage of the project,a complete free manual and theoreticalbackground will be provided.5. ResultsAt this point, the telescope has been builtensuring each piece was perfectly printed andeverything fits together precisely and withoutcritical loads. The final assembly is shownbelow.Page 5 of 64th Symposium on Space Educational ActivitiesBarcelona, April 2022Figure 10. Final assembly of the telescope.A commercial equivalent system is availablethanks to COSMOS Mataró (an amateurAstronomy Association) to perform acomparison between the commercial and thecustom 3D printed design. A preliminarycomparison between both telescopes is shownin Figure 11. Authors are currently waiting foran optimal observation night, to obtain fullresults of the telescope's real resolution andcapabilities.Figure 11. Image of a telecommunication towerobtained with the Meade LXD75 telescope (a))from COSMOS Mataró, and with the 3D printedF5 Newtonian (b)). Both images were obtainedusing the same equatorial mount.AcknowledgementsThis project has been partially funded by theEscola d’Enginyeria de Telecomunicacions iAeroespacial de Castelldefels (EETAC) andthe Physics Department of the UniversitatPolitècnica de Catalunya.The authors acknowledge Diego Rodríguezfrom COSMOS Mataró for providing thecommercial Meade telescope.The corresponding author also wants toacknowledge his closest friends and family.Especially his brother, who has always beenone of his biggest supports. And his fathers foralways supporting him without ever losing theirfaith as well as for raising him as they did.Also his uncle, Joan, to whom has alwaysadmired. For he served as an inspiration andencouraged him to become a great engineeras well as a better human.References[1] BCN3D Website:https://www.bcn3d.com , last visited:2nd March 2022.[2] 3DSystems Corporation  Website:https://www.3dsystems.com/, last visited: 2ndMarch 2022.[3] RepRap Project  Website:https://reprap.org/wiki/RepRap, last visited: 3rdMarch 2022.[4] Luis José Salazar-Serrano, Juan P.Torres, Alejandra Valencia, A 3D PrintedToolbox for Opto-Mechanical Components,PLoS ONE, 2016.[5] B. K. Johnson, Optics and OpticalInstruments, Dover Publications Inc., 1960.[6] M. Born, E. Wolf, Principles of Optics:Electromagnetic Theory of  Propagation,Interference and Diffraction of Light,Cambridge University Press, 1999[7] W. J. Smith, Modern OpticalEngineering, McGraw-Hill, 1998.[8] J. Mullaney, A Buyer’s and User’sGuide to Astronomical Telescopes andBinoculars, Springer, 2014.[9] Thingiverse Website:https://www.thingiverse.com/ , last visited: 15thMarch 2022.[10] PiKon telescope Website:https://pikonic.com/ , last visited: 15th March2022.[11] Raspberry Pi Website:https://www.raspberrypi.org/ , last visited: 15thMarch 2022.[12] SolidWorks Website:https://www.solidworks.com/ , last visited: 11thMarch 2022.[13] J. H. Hindle, “Mechanical flotation ofmirrors,” in Amateur Telescope Making, BookOne, Scientific American,1945.Page 6 of 6

3D printed telescopes: an interesting tool for teaching Astronomy, Science and Technology

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3D printed telescopes: an interesting tool for teaching Astronomy, Science and Technology

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