The maximum altitude that a
near spacecraft will reach is
influenced by the weight of the
near spacecraft, the original volume
of helium in the balloon, and
variations in the balloon’s manufacture. So the numbers I’ve given
you are just rough estimates. You
can experiment with changing lift
amounts and payload weights with a
program called Lift Win. This program
is available from the website of
the Edge of Space Science (www.
eoss.org) as a free download.
■ FIGURE 5
Track as a Windows application. Now,
Troy Campbell has created an online
version of the software that takes you
through the entire process of making a
flight prediction (see Figure 3).
Currently, you don’t have to enter
information in the General section. In
the future, you’ll want to enter this
information because of
the planned enhancements to the
The Launch Site section asks for
the latitude and longitude of the
planned launch site. This information
is used to map the mission’s predicted
flight path and recovery zone. The
elevation field is not very important
because the effects of launch
■ FIGURE 6
elevation are usually swamped by
inaccuracies in the predicted winds
aloft, precision of the balloon’s helium
fill, and manufacturing variations in
the balloon. One exception may be
when the balloon is launched from
the top of a tall mountain.
The Flight Parameters section asks
for the predicted ascent rate, descent
rate, and burst altitude of the balloon.
Here’s where you need the result from
the Ascent Rate Calculator. In my
experience, the descent rate is between
1,000 and 1,200 feet per minute. If the
parachute is larger or the payload
lighter, the descent speed is lower. You’ll
get a better feel for the proper descent
rate after you’ve flown a mission or two.
As a rule of thumb, I expect to reach
50,000 feet with a 300 gram balloon,
80,000 feet with a 1,000 gram balloon,
85,000 feet with a 1,200 gram balloon,
93,000 feet with a 1,500 gram balloon,
and over 100,000 with a 3,000 gram
balloon (see the note in the sidebar).
There’s one data entry field and
three buttons in the Data Source
section. The Wx Station (weather station)
field asks for the station ID for the
weather station closest to your launch
site. Since very few people know the
three letter designation of their local
weather station, there’s an option to
look it up in the Station List link. You’ll
find weather stations sorted by state
and listed in alphabetic order. Next to
each weather station is its three letter
designation. I discovered that the Boise
weather station has a station ID of BOI.
After entering the station’s ID,
click one of the three buttons below
■ FIGURE 7 the Wx Station field.