Features:
 Dual-purpose liner thermally insulates the wall, and absorb scattered light.
Fits inside aluminum tubes sold by Hastings Pipe.
Economical solution compared to separate cork, glue, and flocking.
Less weight than separate cork and flocking.
Other applications include cores for carbon fiber lay-ups, and light trap cylinders.
The ProtoStar tube liner solves two traditional problems with aluminum telescope tubes. The first function is to thermally insulate the interior of the tube from the aluminum tube wall. Under clear night skies, the aluminum wall is several degrees cooler than the ambient temperature. If the wall is not insulated, air will churn within the tube continuously through the night, and visibly degrade high-resolution image quality. The liner insulates the interior of your telescope by creating an air gap between the liner and aluminum tube. Air is an excellent insulator, and weighs almost nothing.
The liner is also flocked on the inside wall to suppress stray light from reaching the focal plane, and eliminates the need to apply the light trap material separately.
The liner fits aluminum tubing available from Hastings Pipe Company (Hastings, NE; e-mail: abeirow@hipco-ne.com; phone: 402-463-6633). We offer tube liners for the Hastings 8", 10", and 12" OD tubes (for 6”, 8”, and 10” mirrors, respectively). Most aluminum tubes offered by other astronomy vendors originate from Hastings. If so, our liners will fit their tubes as well.
Important note: Hastings offers an optional inward fold on the ends of their tubes called "rolled ends". We don't recommend choosing this option with our liner. The ID reduction makes it difficult to insert the liner.
How the air-spaced tube liner works
Because of continuous heat loss and the high thermal conductivity of aluminum, the inside wall of the tube will drop several degrees below the ambient air temperature when exposed to a clear, night, sky. (This is due to radiative heat loss from the outside tube surface directly to outer space, and is the same phenomenon causes dew on the grass before sunrise.) The cooler, denser, air on the upper tube wall will spill downward throughout the night, adversely affecting image quality.
(click to enlarge)
Temperatures recorded from 8:30 PM to 3:30 AM on
a clear night showing the temperature of the upper inside wall.
The traditional fix for this problem is to line a metal tube with an insulating material like cork or cardboard. This works, but it is a time-consuming job and doesn't always look good. It also adds a surprising amount of weight when you add up the cork, adhesive, and layer of flocking or paint.
The air-spaced tube liner solves the thermal problem by exploiting the low thermal conductivity of air. The air gap created between the liner and aluminum wall is an effective thermal barrier, and the liner wall will track the ambient temperature within a few tenths of a degree all night long.
The air gap created by the liner can be exploited for other purposes. Electrical wiring and small screws and nuts can be hidden by the liner to eliminate light scatter, and for a cleaner appearance. The liner is not glued in place, so it can be removed if you need to do future work on the telescope. Made in the U.S.A.
Each kit includes:
tube liner
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foam spacer material
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instructions
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Specifications
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TL-8
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TL-10
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TL-12
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Inside diameter
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7.65 in.
(194 mm)
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9.65 in.
(245 mm)
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11.45 in.
(291 mm)
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Outside diameter
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7.71 in.
(196 mm)
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9.71 in.
(247 mm)
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11.53 in.
(293 mm)
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Wall thickness
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0.03 in.
(0.8 mm)
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0.03 in.
(0.8 mm)
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0.04 in.
(1.0 mm)
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Total weight (48" length)
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15 ozs
(420 g)
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19 ozs
(550 g)
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26 ozs
(730 g)
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Inside wall reflectivity
(Avg visible @ 0º AOI)
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<0.4%
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Inside wall reflectivity
(Avg visible @ 80º AOI)
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<0.7%
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