■ BY L. PAUL VERHAGE
THE NEAR SPACE GEIGER
COUNTER TELESCOPE — Part 2
THIS MONTH’S COLUMN wraps up the Geiger Counter Telescope (GCT) and discusses
a transistor experiment I performed. This article covers the GCT’s field-of-view, a ground
test of the GCT, and flight software that operates the GCT. There is a small note to clear
up the RM- 60 instructions in chapter eight of my near space book at the
Parallax website and a transistor experiment which includes a competition for readers.
The GCT is launched on near
spacecraft with a BASIC Stamp 2p
based flight computer. With luck, its
first flight will be NearSys 06A which
takes place in Grand Island, NE. My
plan is to eventually launch from every
state, and Nebraska is one that is still
on my list. You can read about the
CNNSP at their website: http://web
What’s the field-of-view of the
GCT? Here are the pertinent measurements needed to calculate its field-of-view; the size of its Geiger-Muller (GM)
tubes, and the distance between them.
In Figure 1, the rays shown passing through both GM tubes represent
the cone of cosmic ray paths that will
intersect both GM tubes. Cosmic rays
traveling outside this cone will not be
detected because they don’t trigger a
near simultaneous detection on both
■ FIGURE 1. The physical arrangement
of the GM tubes inside the GCT.
GM tubes. Note that I’m ignoring any
cosmic ray flux from beneath the GC T
since Earth should block cosmic rays
approaching from below.
From this arrangement of GM
tubes, I used trig to calculate that the
GCT will only detect cosmic rays
approaching within a 19. 7 degree field-of-view. However, that 19. 7 degree
field-of-view is the GCT’s maximum
range and it represents any cosmic ray
passing through any part of the two GM
tubes, even through their outer edges.
The GCT is more likely to detect
cosmic rays that pass through the
maximum volume of the GM tubes (as
opposed to just nicking their edges).
So the GC T is more sensitive to cosmic
GCT Angular Sensitivity
■ FIGURE 2
- 5 0 5
Off Center Axis (degrees)