Overall view with tower up all the way (not nested)

 

An issue with telescoping towers is that they are not safe to climb, even when retracted.  It you are on the tower when the cable snaps the sections will crash down and cut off your fingers and toes in the process.  I suspect it would be very difficult to avoid falling once the toes and fingers are gone.   The idea here is to provide a "landing platform" for each tower section when it is in the fully retracted position.  This is fairly easily done by mounting some 2x4's vertically.  Two 2x4s are cut to the right length to "catch" each section of the tower.   Here is a view of the fixture from the side. It's not totally clear from the picture, but the 2x4's are bolted together and clamped to the fixed portion of the tower.  It is very important that each board be just the right height so that the weight of each section comes fully to rest on it at the same instant that all the other sections come to rest on their boards,  or "platforms".  This sounds more difficult than it is.  Just start with the outer section, which is the one that goes down the farthest, and trim one pair of boards until they are perfect - with no other beams in place.  Then put in the next taller board, which will support the next section of the tower and get it trimmed to just the right size.  Then move to the next higher one, etc. If you attempt to duplicate this design in metal, be sure you use thick wall tubing that will not buckle under a longitudinal compression load of considerably more than 1000 pounds. I inserted each 2x4 into the tower by itself and then bolted them all together.  It is not possible to get the fully assembled unit in or out of the tower.  You must unbolt them and take the individual 2x4's out one at a time.  Again, this sounds harder than it is.

Overall view with the tower retracted and nested

Here you can see the tower retracted and resting on the nesting fixture.  The base of each telescoping section is recognizable by the flat horizontal steel piece that is about 16 inches wide and 4 inches high.  There are three sections of the tower that retract and each one is resting on two 2x4's.  The boards are holding all of the weight of the retracted sections, so the cable could snap and nothing would move.  This makes it safe to climb.

The lowest "platform", for the outer-most telescoping section

Here's a close up view of the lowest landing platform, which catches the outer-most telescoping section.  You are looking at two 2x4's that are about 18 1/2 inches long that are held vertically by the (admittedly rather ratty) clamps that fasten it to the tower itself.  Since all four 2x4's are bolted together, these clamps hold the entire nesting structure in place.  The tops of these two 2x4's hold the outer-most telescoping section of the tower when it is retracted, as seen in the next photo below.  I cut these 2x4's to exactly the length required to take the whole weight of this section just as the limit switch de-energizes the electric winch.

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The middle "platform", for the middle of the three telescoping sections

Here's a close up view of the second landing platform, which catches the middle of the three telescoping sections.  You are looking at two 2x4's that are about 44 inches tall.  The tops of these two 2x4's hold the middle section of the tower when it is retracted, as seen in the next photo below.  As before, I cut these 2x4's to exactly the length required to take the whole weight of this section just as the limit switch de-energizes the electric winch.

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The top "platform" holding the inner-most section

These two 2x4's are about 67 inches tall and are shown holding the inner-most of the three telescoping sections.  As with the other "platforms", I cut these to the exact length necessary to take the weight of the inner section just as the limit switch de-energizes the electric winch.  The pull down cable still has some tension at this point.  So I "pulse" the winch upward for an instant and the pull-down cable unloads but the pull-up cable is still slightly slack.  At that point, there is no load on either cable and all of the weight of the tower sections is being transferred to the concrete base through the 2x4 beams, which are in longitudinal compression.  The wooden 2x4's are quite strong and there is, I believe, at least a 10X margin of safety.