"Do-it-yourself" instructions for making a

HUBBLE SPACE TELESCOPE MODEL


Max Mutchler
Space Telescope Science Institute
July 1995


1. INTRODUCTION

I wanted a set of Hubble Space Telescope (HST) models for use during presentations to elementary school students. I needed several durable models so that each student could have a chance to handle and explore them (rather than just looking at one fragile model from afar).

Before I started this project, these are the other HST models that I was aware of:

1. At the Institute, there are several very accurate (professionally made) models that can be borrowed temporarily. These are best if you want one model for display, but not good if you want to give each student in a large group an opportunity to examine the model closely -- they are limited in number, and must be treated as fragile/expensive.

2. A laser-cut paper HST model (assembly required) by Space Craft International, PO Box 61027, Catalina Station, Pasadena, California, 91116-7027. Cost is $16 each. This company also offers models of Voyager, Galileo, Magellan, etc. The work involved in assembling these models, coupled with the fragile nature of the finished product, made these infeasible for my purposes.

3. A paper HST model (assembly required) available from any of NASAs Teacher Resource Centers. These are less detailed than the laser-cut paper model described above, but they are free. They also take several hours to assemble, and are also not durable enough for students to handle. However, I did make use of this model to add exterior detail to my models. Also, I have handed out these kits to students who expressed an interested in making their own model of HST.

4. A snap-fit plastic injected HST model (assembly required) by SkilCraft. Cost is about $10 each. While accurate, the model is relatively fragile and not easily repairable. Since none of these models would satisfy my requirements, I set out to make some models from readily available materials. The following instructions describe how to make a model of HST that is moderately accurate, highly durable, and relatively inexpensive. These instructions were written after I built 14 models, so they reflect what I've learned through some trial and error.

2. MATERIALS AND PARTS

For reference, this diagram shows the basic parts of the Hubble Space Telescope:

 
               solar panel    aperture
                              door
                [][][][][]
               _____|      /                                     *     *
        aft   |     |------   forward                 light        *     *    *
     shroud   |_____|------   shell               <----------   *   stars    *
                    |                                              *     *
                [][][][][]                                           *

               solar panel                                                
The aft shroud is the back end of the telescope, where the scientific instruments reside. The forward shell is the the front tube that light enters into. The primary mirror collects the light at the bottom of forward shell tube.

The aperture door is a hinged door at the end of the forward shell. The two solar panels collect sunlight for power -- the is one on each side. The two high-gain antennae are for communication. They are orthogonal to the solar panels (i.e. in the diagram above, one would be sticking out of this page, and one would be sticking into this page). It may be helpful to find a good picture or diagram of the telescope for reference.

Item                 	Specifications      	Model part    		Cost 
----------------------- ----------------------- ----------------------- ------
1 PVC pipe		3" diameter* x 2.75" 	Aft shroud		$ 1.00 
1 PVC pipe		2" diameter* x 6.75"	Forward shell		$ 1.00 
1 PVC bushing		2" - 3" diameter	Midsection		$ 2.50
1 PVC snap drain	3" diameter		Aft shroud		$ 2.00
1 PVC cement 		8 ounce can		Midsection		$ 6.00 

1 circular mirror	2" diameter	       	Primary mirror         	$ 1.00
2 dowel rods (wood)	3/16" diam. x 8"  	Panels + antenna 	$ 0.25
2 wooden beads		1" diam. with hole      Antenna "dish"		$ 0.25
4 posterboards		1.5" x 9"    		Solar panels   		$ 0.25
These last few items are not absolutely essential:
1 black paper    	1 sheet			Door + baffle 		$ 0.10
1 can spray paint	silver/metallic		Rods + antennae  	$ 3.00
1 paper HST model   	from NASA		Exterior detail  	Free

Total cost of materials per model (estimated): $10

Some helpful tools and materials to have handy: saw, mitre box, scissors, file, sandpaper, drill, hammer, wood glue, clear plastic tape, and duct tape. Note that the 8 ounce can of PVC cement was much more than is required to make even 14 models -- each model required only a few dabs of cement (but this is the usually the smallest can size available).

Since I bought many of these materials in bulk (I made 14 models at once), the costs listed are averages or estimates. To make just one model, you can probably use scrap materials to save money. For example, you can often get free "samples" of PVC pipe from your vendors scrap heap.

PVC is a plastic used often in plumbing. PVC supplies can be found at hardware stores, home improvement stores, or plumbing supply outlets. Dowel rods, wooden beads, posterboard, and colored paper can be found at arts and crafts stores or fabric stores.

I found cheap circular mirrors at an auto parts store (sold as "blindspot mirrors"). These mirrors are convex rather than concave (which would be more appropriate), but they do the trick. Heck, even the real primary mirror onboard HST has the wrong curvature! If you can't find these mirrors locally, here are the names of two companies that sell them:

  • CIPA, 1125 12th Avenue, Port Huron, Michigan, 48060 (part number 49102)
  • Cobbs Manufacturing Company, Des Moines, Iowa, 50309 (model number 421x)
  • This design creates a model of HST which is 10.5 inches long (or 13" long with the aperture door open), with a "wingspan" of 8.5 inches. This amounts to a 1/47 scale model -- the real HST is over 42 feet long! The scale of the model is set primarily by the diameter of PVC pipe that is generally available. I used 2" and 3" PVC pipe for the forward shell and the aft shroud, respectively. Presumably, you could use 1.5" and 2" pipe to make a smaller model, and scale all the other parts accordingly.

    *Note that PVC pipe is specified according to its inner diameter, but for our purposes, it is the outer diameter that is most relevant. For 3" PVC pipe, the outer diameter is about 3.5", and for 2" PVC pipe, the outer diameter is about 2.5". It is these outer diameters that actually set the scale for the whole model. I used a spreadsheet to calculate the dimensions of each part. By entering the diameter of the aft shroud using only values that are readily available (i.e. in stock at the hardware store), all other model dimensions were automatically calculated based on the real dimensions of HST. In the end, the dimensions didn't come out exactly as listed here, but they were close:

    					Actual HST	Model HST
    
    Aft shroud diameter			163.3"		 3.50"
    Forward shell diameter			116.3"		 2.50"	
    Forward shell length			268.0"		 5.75"
    Aft shroud + equipment length		240.5"		 5.15"
    Solar panel length			452.8"		 9.70"	
    Solar panel width			 98.4"		 2.1"
    Antenna rod length			565.0"		12.11"
    Primary mirror diameter			 94.5"		 2.03"
    
    Total length				508.5"		 10.9"
    Total weight				25500 lbs	 0.25 lbs
    

    3. ASSEMBLY INSTRUCTIONS

    Step #1: Preparing and assembling the PVC (plastic) parts

  • Cut the 3" diameter PVC pipe into 2.75 inch long pieces (for the aft shroud).
  • Cut the 2" diameter PVC pipe into 6.75 inch long pieces (for the forward shell).
  • Remove any rough edges with a file and/or sandpaper.
  • Wash the pieces in soapy water and dry them thoroughly.
  • The forward shell fits snugly into the narrower end of the PVC bushing. It slides in about 0.75 inches. Apply PVC cement to the bushing and/or the forward shell and slide them together. Apply cement to the bottom rim of the PVC bushing and attach the aft shroud. Allow the cement to cure for several hours.

    Step #2: Drill 4 holes for the solar panels and antennae

  • Drill 2 holes on opposite sides of the forward shell with a 3/16" drill bit. These 2 holes should be roughly 1/4" away from the edge of the bushing.
  • Drill 2 more holes at 90 degrees from (in between) the first 2 holes, but an additional 1/4" further away from the edge of the bushing (so that when you push the dowel rods through later, the 2 rods don't hit each other).
  • Step #3: Inserting the primary mirror and attaching the aft base

    The mirror can be inserted into the midsection of the telescope where the aft shroud meets the forward shell. The reflective surface should be facing out the forward shell, so that it is visible when you look down into the forward shell. Secure the mirror using tape. Insert the PVC snap drain into the end of the aft shroud. It should fit very snugly -- use tape to secure it, rather than PVC cement. I used tape to secure the mirror and snap drain so that I can get access to the mirror in the future (to wipe it clean or adjust/repair it).

    Step #4: Adding exterior detail to the telescope

    I made use of the paper model (from NASA) to add accurate detail to the exterior of the model (such as access doors, ports, handrails, etc). I made appropriately enlarged copies of the paper model parts, and wrapped them around the exterior of the PVC parts, securing them with clear plastic tape. The paper model parts must be enlarged by the following amounts:

  • The circular base of the aft shroud must be enlarged by 55%.
  • The aft shroud must be enlarged by 52%
  • The forward shell must be enlarged by 47%
  • The baffle (inside of forward shell) must be enlarged by 12%
  • The solar panels must be enlarged by 20%
  • Note the NASA model incorrectly identifies the Fine Guidance Sensors (FGSs) as "FSG" on the aft shroud. A simpler alternative way to add detail to the exterior of the model is to wrap it in aluminum foil. The meticulous model maker can add as much detail as time and creativity allows, by hand-painting the model, and/or attaching handrails, etc.

    Step #5: Assembling the solar panels

    Spray paint all the wooden dowel rods and the wooden beads (silver, gray, or black). Insert one rod into the pair of holes you drilled that are closest to the aft shroud. Attach the posterboard strips to both sides of the rod using duct tape. Wrap the paper (i.e. detailed) solar panel over the posterboard and secure it with clear plastic tape.

    Step #6: Assembling the antennae

    Insert another dowel rod into the other pair of holes you drilled in the forward shell. Slide the wooden beads onto both ends of the rod and use a small drop of wood glue to secure it. These beads are the antenna dish. I chose round beads for safety and durability -- you may wish to attach something that looks more like a dish.

    Step #7: Assembling the aperture door and light baffle

    The aperture door can be cut from paper. By leaving a tab, it can be slid in between the plastic surface of the forward shell and the paper that covers the forward shell. A more solid aperture door could be cut from a sheet of PVC plastic, and cemented to the end of the forward shell, or better yet, attached with a working hinge. I curled up a small sheet of black paper and inserted it into the foward shell to act as the light baffle (which minimizes scattered light inside the telescope optics).

    All of these steps can be expanded upon or simplified, depending on the qualities you want your HST model to have. Your imagination and time are the only limits.

    GOOD LUCK!


      Max Mutchler                              Internet:  mutchler@stsci.edu
      Space Telescope Science Institute       NSI/DECnet:  stscic::mutchler
      3700 San Martin Drive                    Telephone:  410-338-1321
      Baltimore, Maryland USA 21218                  Fax:  410-338-5085