Asked by: @KrnSidez via twitter to @patricknorton

The quick answer is that the Hubble Space Telescope is about 40 feet long and has an Earth weight of about 12 tons. We often say that it is about the size of a large school bus. See the Hubble Essentials: Quick Facts page at HubbleSite for other basic figures.

The more detailed answer? Well, that involves negotiations with the low Earth orbit delivery service.

Shipping and Handling

The real answer to the question is that the Hubble Space Telescope is as large as astronomers could make it, while still fitting in the space shuttle cargo bay and not being too heavy for launch. Those constraints are the practical considerations that guided the design of the telescope.

I encountered a similar constraint when buying a barbecue grill a few years ago. The largest one I could buy was the largest that could fit into the back of my minivan. There were many that would not even have come close to fitting. Fortunately, my needs did not exceed my transportation space.

Astronomers, however, want the largest telescope possible. The larger the mirror, the finer the resolution. And resolution is Hubble's key characteristic. Being above Earth's atmosphere meant that the telescope would not suffer the blurring effects of the atmosphere that interfere with observations from ground-based telescopes. Hubble is what we call "diffraction limited", and that limit depends directly on the size of the mirror.

The maximum size that fit into the shuttle cargo bay is roughly a cylinder about 43.5 feet long and about 14.5 feet in diameter (at its base, which is wider than the top). It is interesting that I see the length quoted in lots of places, but the diameter is not. If you search on "Hubble diameter" you will get references to the primary mirror diameter, which is 94.5 inches.

That mirror diameter, combined with the instruments that record the light, give Hubble a resolution of 1/20th of an arc second per pixel in its highest resolution images. For scale, 1/20th of an arc second is what you get when you divide a circle into about 26 million pieces.

The accompanying image shows the cargo bay of the Shuttle Atlantis. And before you say anything, yes, I know that Hubble was carried up by the Shuttle Discovery, not Atlantis. You can see how a big cylinder would fill the cargo bay nicely. Perfect for telescopes.

Hand-Held Hubble

If you want to examine the relative dimensions of Hubble for yourself, there are instructions available to make your own Hubble model. That web page describes three versions; one made from PVC and two made from paper. The advanced paper one is supposed to be really detailed and difficult. You have been warned.

Also on those pages is a comparison of the model dimensions to the real Hubble dimensions. Here you will some of the terminology about the naming of Hubble parts that is extremely important for those working with the telescope, but which I often forget and have to look up. Here's a glossary of terms and abbreviations for those who need all the details. NASA is overly fond of TLAs (three letter acronyms).

Ms. Frizzle

One last point is a joke I often make to school children. If the Magic School Bus went to visit  Hubble, the bus and the telescope would be about the same size. Space is a popular topic for the Magic School Bus series, but one might worry about what dramatic event the writers would invent as a reason for visiting Hubble. Still, the kids could get a great lesson in optics, imaging, and data processing.

Here's an idea: they could follow the path of the information that makes up a Hubble image,starting out as the light from a galaxy, bouncing around the mirrors of Hubble, recorded as digital data by the detectors, downloaded through the TDRS satellites, transferred across the internet, and then cleaned, combined, and processed into an image. This question is often asked, and a cartoon version of the answer would be great for kids. Somebody point Scholastic to this paragraph. I'll make myself available as a consultant.