Selecting the Right Inflatable Planetarium I: Dome Capacity/Size

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Inflatable planetariums came on the market in the late 1970s, and anyone who has been around since their beginning can appreciate the refinements to the product over the years. Many of the improvements are innovations pioneered by Go-Dome, makers of the world’s finest portable planetariums.

Looking back at these refinements, I thought it might be helpful to provide this primer on inflatable planetarium features. Potential customers can use it as a guide in selecting the right product (from any manufacturer) for their needs.

First, let’s look at the dome, which is, of course, the essence of the thing. Safety should be the first concern of anyone hosting educational programs in a portable planetarium dome, or anywhere else for that matter.  We proudly state that our Go-Dome cloth meets the rigid requirements of the National Fire Protection Association’s NFPA 701:2010 Standard Methods of Fire Test for Flame Propagation of Textiles and Films. We post our documentation online. Other reputable manufacturers should be able to supply similar documentation on request.

Now we can consider the things that anyone planning an astronomy program–or any educational program–for an inflatable dome venue should be thinking about. These are not listed in any priority since everyone’s needs are different, but they are all worthy of careful consideration.

Let’s start with capacity.

What is your ideal class size? I know, the question belongs in the “how long is a piece of string?” category. If you are buying an inflatable dome for a school, or if you have an educational business that takes your program to various locations, you should settle on your target for a class size. That will tell you how big a dome you need.

Let’s say that your ideal class size is 25-30 (just to pick a number). Most inflatable dome manufacturers will say you should be looking for a five-meter (roughly16.5 feet) diameter dome. That capacity is probably based on young students sitting on the floor. The size/age of students or having them sitting on chairs will impact the capacity.

When the dome sits directly on the floor, the curve starts at the point of contact, creating a zone that cannot be occupied until the curve of the dome reaches sufficient clearance height. This affects capacity as well. Of course, simple domes are basically hemispherical, so a five-meter dome will be roughly 2.5 meters (8.25 feet) high. (Note that dimensions are rarely precise when you are dealing with any inflatable product, and some inflatable planetaria are not designed to be perfect hemispheres.) Younger audiences siting on the floor typically need a lower clearance height so they can occupy areas of this zone that are not useable for taller audience members or people sitting on chairs.

Inflatable rings are a Go-Dome innovation that raises the level of dome off the floor by providing sidewalls. These allow the audience to sit on folding chairs, which is often attractive for older age groups. See our specifications chart for details and options on our rings and how they affect overall height and diameter.

Again, I just threw the 5-meter dome size out there to start the discussion. It is a popular size for a number of reasons. One needs to remember that larger diameters and options like rings add to the overall weight of the product, which may be a consideration when transporting and handling. If you are planning on one person transporting your dome by car, and setting up alone on site—keep that in mind. Large domes are far more viable if you are only moving them by cart within a building such as a school, or have two or three people on hand to set up. 

Related to capacity is overall size, which is another primary consideration. Obviously, the larger the dome, the larger the space needed. If you are setting up in a school gymnasium, you probably aren’t too limited for space. Other areas, such as a cafeteria or library, may have lower ceiling clearance or limited floor space. In any case, the dome needs to stand free of objects and obstructions when inflated. Care must be taken to avoid contact or close proximity with light fixtures that can singe the cloth. Additional space surrounding the inflated dome should be left open for access, the entrance system, the inflator fan, etc.

Durability is a factor, too.

Inflatable planetarium domes need to be rugged to withstand repeated transportation, inflation, use, deflation and storage. They need to be light safe, so that your program projection is as vibrant as it can be.

Go-Domes come with a one-year guarantee against defects, and seams are sealed to prevent light seepage through stitch holes. Exposure to direct sunlight, excessive heat (over 40° C/100° F) or freezing will void the warranty. Allowing the dome to become wet will void it also, and a wet dome should be inflated and remain that way until the cloth is thoroughly dry to avoid mildew.

All that said, we are proud to say that some of our Go-Domes are still in use after ten years, with only minor repairs made by the owners. (We include extra cloth for repairs when we ship the product.)

My future blogs on Inflatable planetarium features will cover entrance systems, dome screens and more!

 

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Gary Young is President of Go-Dome since 2005 and President and CEO of Avela Corporation, the parent company to Go-Dome.