options. First, you can
cancel the launch and
reschedule it for next week
(I don’t like this one).
Second, you can change
the amount of helium inside
the balloon to change its
climb rate and maximum
altitude. Or third, you can
move to a new launch site.
Let’s look at each program
in more detail.
■ FIGURE 2
THE ASCENT
RATE CALCULATOR
The first ascent rate calculator
program was written by Hank Riley.
His program calculated the maximum
altitude and climb rate for a balloon
given its type, initial fill of helium, and
payload weight (which you can find
at the Edge of Space Science website
at www.eoss.org)
When you run the CAPnSPACE
version of the Ascent Rate Calculator,
you’re presented with the screen
shown in Figure 2.
The Balloon Wgt field asks for the
size of the balloon. When you
purchase a weather balloon from
Kaymont ( www.kaymont.com), you
order it by weight. Examples of the
balloons I’ve flown in the past are
300, 1,000, 1,200, 1,500, and 3,000
grams. The weight of the balloon
(grams is actually a measure of mass
and not of weight — but we’ll ignore
that) is an indication of the balloon’s
maximum volume and the altitude it
can reach before bursting.
The Nozzle Lift field asks how
much lift the balloon will have after
being filled. The greater the lift of the
balloon, the faster the balloon will
climb. At the same time that its ascent
rate is greater, its maximum altitude is
lower, but only slightly. A lift of three
pounds greater than the payload weight
is my minimum preferred amount of lift.
The Payload Wgt field asks for the
weight of the near spacecraft sans
parachute. In most cases, this won’t
be greater than 12 pounds. You can
launch a payload heavier than 12
pounds, but additional rules will apply
to your launch. Check Federal
Aviation Regulation 101
(FAR 101) for the additional
requirements. You can consult my book — Near Space
(available from Parallax;
www.parallax.com/html_
pages/resources/cust
apps/ app_nearspace.asp)
— for its chapter on FAR
101 or consult with other
ARHAB groups.
The Parachute Wgt field
asks for the weight of the
parachute in ounces.
Click the CALCULATE
button to calculate the
Estimated Ascent Rate
based on your values. Remember this
ascent rate, because it’s one of the
inputs to the next program, Balloon
Track. Just a note here — the minimum
ascent rate I accept for a flight is 1,000
feet per minute. When the ascent rate
is too low, there’s a chance the
balloon will become neutrally buoyant
and stop rising. In a future article, I’ll
explain how you can prevent this from
ruining your near space mission.
■ FIGURE 3
WEB BASED
BALLOON TRACK
Balloon Track has a long history in
the ARHAB community. It was
originally written by Bill Brown as a
Basic program that ran under MS-DOS
(remember that operating system?).
Later, Rick Van Glahn of Edge of Space
Science in Denver rewrote Balloon
■ FIGURE 4
May 2007 87
