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.
solar panel aperture door  _____| / * * aft | |------ forward light * * * shroud |_____|------ shell <---------- * stars * | * *  * solar panelThe 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 $ 0.25These 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
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:
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
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.
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.
Max Mutchler Internet: firstname.lastname@example.org Space Telescope Science Institute NSI/DECnet: stscic::mutchler 3700 San Martin Drive Telephone: 410-338-1321 Baltimore, Maryland USA 21218 Fax: 410-338-5085