■ BY L. PAUL VERHAGE
A MARTIAN NEAR SPACE LAUNCH
BALLOONS ARE POTENTIALLY THE BEST way to study large areas of Mars.
They can travel across the Martian surface
faster than rovers and they won’t be stopped
by every boulder or canyon that gets in the
way. Also, since balloons are closer to the
Martian surface than satellites, their
cameras resolve far smaller surface features.
With this in mind, let’s look at what it would
take to launch a near spacecraft on Mars.
Later, we’ll briefly look at launching a near
spacecraft on Titan.
Mars Pathfinder Surface Weather Report
I’ll address three factors in this
month’s column. The first is the
surface winds and their effect on filling and launching a weather balloon.
The second factor is how the atmospheric composition and pressure
on the surface will affect the initial
volume of a weather balloon. The last
factor is how atmospheric pressure
changes with altitude. This factor is
important because it determines the
maximum altitude that a weather
balloon will reach before bursting.
FILLING A WEATHER
BALLOON ON MARS
Refer to the weather report above.
When a near space group fills a weather balloon, they prefer a surface wind
of zero knots. Since a balloon acts like
a kite sail, it blows around even in the
slightest wind. A balloon can successfully be filled in winds of a few knots (a
knot is equal to 1.15 miles per hour),
but the measurement of the balloon’s
lift is less accurate. This reduction in
accuracy is a minor problem, but it
does result in a less predictable
ascent speed and maximum altitude
for the balloon. Wind speeds greater
than 10 knots will make filling a balloon nearly impossible and possibly
dangerous. If the balloon doesn’t
bounce around and burst during the
■ FIGURE 1. Open house at the National
Weather Service. It’s surprising how
many people will line up to look inside
a balloon filling shed. And I ought to
know, I was one of them.
filling, then it will yank the balloon
crew around and possibly give someone a string burn as a result.
One benefit of filling a balloon on
Mars is that the air pressure is much
lower than it is on Earth. This is
because the wind creates a force that
scales by the square root of the air
pressure. This means if the air pressure
is reduced by 75% to only one quarter
its original pressure, then the wind
feels like it’s only blowing half (the
square root of one quarter) as fast.
Average air pressure on the surface
of Mars is just under seven millibars
(mb). On Earth at sea level, the average
air pressure is 1,013 mb. Therefore,
Mars has an atmospheric pressure that
is 0.7% that of Earth. So winds on Mars
feel like they’re only blowing 1/12th as
fast as they do on Earth. Satellite
measurements indicate that the
strongest winds on Mars are between
67 to 111 mph. This means the maximum winds on Mars only feel like they
are blowing at between 5. 6 to 9. 3 mph.
Wind speeds in the range of 100
mph and higher will create dust storms
on Mars. During a dust storm, visibili-