Sending payloads into near space is far less expensive than sending
an identical payload to low earth
orbit (LEO). That doesn’t mean,
however, that near space is cheap. A
near space launch costs about $120,
putting the cost to around $10 per
pound of payload. That compares
favorably with launches to LEO
where the cost is much closer to
$10,000 per pound.
Even at a low $120 per flight,
you want to increase your chances of
a successful mission. This is why
testing payloads prior to a mission is
critically important for anyone
contemplating a near space launch.
One of these tests should be a cold
soak in near space like conditions.
Conditions in
Near Space
If you’re a reader of this column,
you’ll know that near space is a
bitterly cold vacuum. Temperatures
drop to - 60°F on a warm day and
down to -90° during winter. There are
a lot of things you might want to
send into near space that don’t like
these conditions. Here’s an example.
Batteries use a chemical reaction
to create a current. Like all chemical
reactions, a battery’s reaction rates
increase when its temperature is
higher. Operating a payload with the
wrong type of battery is an invitation
to disaster. That’s because once the
battery’s temperature gets too cold,
payload power ceases and the
experiment fails. So, where can you
test a battery prior to a near space
launch? In a thermal vacuum
chamber (TVC).
Thermal Vacuum
Chambers
I wrote a series of articles on
TVCs when the availability of
affordable Chinese vacuum pumps
made them a realistic bench-top test
tool of near space research.
Essentially, the near space TVC I’ve
written about previously is a metal
can connected to a vacuum pump.
The exterior of the can is surrounded
by dry ice and the interior is
evacuated of air. Inside, the item
under test experiences the cold and
vacuum of near space.
The issue I’ve always faced with
my TVC design is the determination
68 May 2014
I'm still in the process of
upgrading my thermal
vacuum chamber (TVC)
design. Part of the current
upgrade is incorporating a
thermometer. The problem
is that I haven't located an
affordable thermometer
that reads below - 50°F.
So, when a product is not
available, we readers of
Nuts & Volts go the DIY
route and make one
ourselves. This month, I'll
discuss the design of my
thermometer for TVCs.
; BY L. PAUL VERHAGE NEAR SPACE
A Thermometer for the Totable
Thermal Vacuum Chamber (t-TVC)
Post comments on this article and find any
associated files and/or downloads at
www.nutsvolts.com/index.php?/magazine/article/
may2014_NearSpace.
; Here’s a recording
thermometer that
operates down to
-99°F. It's just the tool
you'll need when
simulating near
space.