Cell Growth in Microgravity
309
sea level. Microgravity is experienced by
the astronauts because they are in free-
fall around the planet. This is similar
to the microgravity experienced during
free-fall achieved in microgravity analogs
conducted on Earth, for example, in drop
towers (Fig. 2), parabolic aircraft (Fig. 3),
and sounding rockets (Fig. 4).
To achieve the same level of microgravity
by distance alone that is achieved by free-
fall in orbit, the astronaut would have to
be 17 times as distant from the Earth as
Fig. 2
Drop Tower. Drop
towers offer a way to conduct 5-
to 60-s microgravity analog
experiments in free-fall. This
analog is better suited for fluid
characterization of the culture
environment and rapid cellular
events such as shape change
and signal transduction.
34 000
32 000
30 000
28 000
26 000
24 000
Altitude
[ft]
02
0
Maneuver time
[s]
45
65
350 Kias
1.8
g
1.8
g
Zero-
g
350 Kias
45
°
Nose high
45
°
Nose low
Fig. 3
Parabolic Flight. Parabolic flight, where a
specially modi±ed jet alternates steep climbs
with long drops (much like a roller coaster), and
generates 20 to 30 s of analog microgravity. A
typical mission lasts 2 to 3 h and consists of 30
to 40 parabolas. Multiple parabolas are flown,
allowing repeat experiments to be performed
under the same conditions. Flight maneuvers
can be modi±ed to provide any
g
-force level less
than 1.
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