A Half-second Microgravity
Instructor’s Manual

December 2012

Kibo-ABC

Contents
1.0 Introduction ..................................................................................................... 1
2.0 Examples of Microgravity Phenomena under the Simple Free-Fall .............. 2
2.1 Candle flame ................................................................................................ 2
2.2 Two Rubber balloons .................................................................................... 2
2.3 Diamagnetic levitation ................................................................................. 3
2.4 Collision of water drops ............................................................................... 3
2.5 Air bubbles in water ..................................................................................... 43.0 Fabrication of Simple Free-Fall Apparatus .................................................... 53.1 Drop box ....................................................................................................... 53.2 Clutch and release mechanism .................................................................... 63.3 Camera ......................................................................................................... 7
3.4 Supporting Structure ................................................................................... 83.5 Cushion....................................................................................................... 103.6 Hoist ........................................................................................................... 104.0 Tips for Obtaining Better Results ................................................................. 11
4.1 Camera installation ................................................................................... 114.2 Mitigating disturbances by g-jitter ............................................................ 11Disclaimer ............................................................................................................ 12

1.0 Introduction
Constant microgravity condition is one of the most unique and usefulfeatures of the space environment provided on board the International Space
Station. Although the microgravity, or zero-gravity, in space is widely known
through the activities of astronauts today, general understanding tomicrogravity is not very accurate, because it is hard to be experienced. Thus,
it will be very effective to show some typical phenomena under microgravity
by utilizing a simple free-fall method, and have the people witness theoccurrences.
A simple free-fall method was first applied to serious research purposes
by Seiichiro Kumagai of the University of Tokyo in 1950s. The purpose of his
experiment was to scrutinize the burning process of fuel mist particles forbetter efficiency of internal combustion engines. Theoretically the burning
processes of larger droplets and fine mist particles are indistinguishable.
While it is technically easier to observe larger ones, holding a large droplet isdifficult. In addition the flame is deformed by buoyancy convection. The
solution of these problems was to remove the gravitation from the system.
Kumagai utilized a simple free-fall system with a portable clay cooking stove
fitted with a Nikon motor drive camera, newly developed at that time andcapable of 250 frames a second shooting, dropped from the ceiling to the floor.
This pioneering microgravity experiment opened a new realm forinvestigation of the fundamental nature of combustion, as well as
microgravity sciences in general.
Today, there are large-scale free-fall facilities for microgravity research insome countries. Short-time microgravity condition can be achieved byparabolic maneuver of an aircraft. Simple half a second free-fall , however, isstill useful for education and outreach purposes to facilitate theunderstanding of the importance of microgravity sciences and spacedevelopment activities.
Not only students and general public can acquire knowledge from thesimple free-fall, but also performers of the demonstration can learn a great
deal from the activity. Thus, researchers or engineers in the field of spaceenvironment utilization are recommended to perform this simple free-falldemonstration as a part of outreach activity, irrespective to one’s ownspecialty. Since we all live under the constant gravity and usually do notcare about it, even an experienced space engineer could be surprised by
unexpected finding12.0 Examples of Microgravity Phenomena under the Simple Free-Fall

2.1 Candle flame
Candle flame is one of the most impressive and easy-to-observe subject
under microgravity. The flame shrinks right after the beginning of the fall.
This is due to the suppression of buoyancy convection around the flame
under microgravity. But the rest of air in the drop box, however, is still
moving by inertia. The flame is buffeted by the residual air flow. The gradual
return of gravity due to aerodynamic drag also causes disturbance.
μG

1G

2.2 Two Rubber balloons
Put two rubber balloons in a box; one is filled with water (right corner) and theother with air (left corner). When the box is falling, the balloon at the right corner
goes up while the other at the left corner stays. The water balloon is slightly

squashed by the weight of water, or hydrostatic effect. When gravity
disappears, the water balloon is restored to its normal near spherical shape.
μG

1G

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2.3 Diamagnetic levitation
Diamagnetism is the property of any material to create a magnetic fieldin opposition to an externally applied magnetic field. The contribution of thediamagnetism is usually negligibly small and hard to be observed.
Place a small neodymium magnet with 6 mm diameter on a 100 gramsilver bar (left). During a free-fall, the magnet floats apart from the silverbar (right).
μG

1G

2.4 Collision of water drops
Small amount of water was ejected simultaneously from two nozzles
facing each other and collide to form one larger droplet.

A next photo shows a droplet formation system. The spring is shortenedwith the weight of a clay lump under normal gravity. When gravity
disappears, the spring extends and a droplet is pushed out from the nozzle by
the extruded air with the power of spring.

32.5 Air bubbles in water
Air bubbles generated in a small jar by air pump continues to come up to
the water surface under normal gravity. Under microgravity, bubbles stop
rising and become spherical.

1GμG

1G

μG

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3.0 Fabrication of Simple Free-Fall Apparatus
A simple free-fall experiment requires just the following materials: a dropbox or a capsule, a camera, a clutch and release mechanism, a bufferingcushion, and objects to be observed such as a candle.
In addition to the above, a structure to hold the clutch about 2 meters
above the floor is required. Utilizing existing commodity such as tall shelves,
step ladders or ceiling hooks may be used for this purpose.
Clutch and release mechanism
Drop boxCamera
Test object
Buffering cushion

In other cases, using collapsible support structure shown here will beconvenient. Although such a little tower structure itself is a kind of the least
essential elements of this system as a matter of fact, it may attract muchattention and tends to cost some labor to fabricate.

3.1 Drop box
Plastic storage box containers for home use are suitable for this purpose.

53.2 Clutch and release mechanism
The simplest way of free-fall experiment is just to hold and release a dropbox by human hands. Another simple method is to cut a string hanging adrop box. Many other mechanical clutch-and-release systems can be madewith household parts such as door latches. However, subtle/slight but
disturbing swing at the moment of release is inevitable for the most ofmechanical systems. To avoid disturbance at the release, electromagneticsystems is thus preferable. Commercially available door magnets which
operate with 12 V DC and generate about 500 to 2000 N of holding force withmatching armature is one of the best choices.

63.3 Camera
Capturing image data is one of the key functions of the system. Driverecorders, or windshield video cameras, may be the easiest choice for thispurpose. A drive recorder is a small digital video camera to be attached to thewindshield of an automobile to record events on the road. The picture quality
tends to be not very good, but it is still acceptable for experiments by younger
students. Average models have an accelerometer, or G-sensor, andautomatically save video clips right before and after an impact exceeding
preset level is detected. Viewing the results is also easy with PC using
included software. The only modification needed is to its 12V DC powersupply. The power should be supplied with a battery placed in theexperiment box, otherwise with the cable from the outside. GPS sensors
contained in the camera is unnecessary for the microgravity experiment.

Among the consumer products, Casio High Speed EXILIM(R) series offers
practical performance. However, these models are not designated for roughhandling; careful protection from landing impact is required.
With Eye-Fi(R) memory cards which can transfer photos and videos
wirelessly to Wi-Fi network, it will be easy and efficient for data collection
without demounting a camera from the box. In addition, many extra
functions of current digital cameras such as image stabilization should beturned off.
Considering the specifications its low prices, USB cameras or web
cameras is also suitable. However those are not recommended, since theirpoor capability to record moving objects.

73.4 Supporting Structure
Small, light-weight, and easy-to-use free-fall apparatus is needed in doing
microgravity demonstration for education and outreach purposes. Several
types of collapsible support structure have been developed.

The example shown next page is one of the simplest yet reliablesupporting part of the tripod which is shown above pictures circled by a redline. This supporting part is cited from a private website with permission. It
is designed to be made with commercially available materials shown pictures
under the design drawing.

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3.5 Cushion
A drop box hits the ground at about the speed of 16 km/h in 1-meter fall.
When its drop distance extends to 2 meters, the speed increases to about 22.5km/h. Choice of an appropriate buffering material is essential to mitigatedamages caused by the impact. Highly elastic materials, however, should be
avoided because it may cause secondary damages by rebound andsubsequent upsetting. Among commercially available materials, cushions orpillows stuffed with polystyrene foam micro beads seems the easiest
selection, since they make only minimum rebound.

3.6 Hoist
Hoist is not essential but convenient and fancy. This example utilizes
sailboat parts.

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4.0 Tips for Obtaining Better Results

4.1 Camera installation
Drive recorder or windshield video camera can be directly installed insidewall of a drop box since it is designed impact proof. Careful protection fromlanding impact is required for other standard cameras. An example offriction based shock absorbing camera mount is shown below.

4.2 Mitigating disturbances by g-jitter
In class room physics, every object except materials like a spring is
considered as an ideal rigid body. In reality, almost everything is elastic anddistorted by the weight of itself. Such distortion is negligible in ordinal daily
life, but it often does matter in simple free-fall experiments. Actually,distortion of a drop box and other elements causes vibrations right after it isreleased and affects the observation.
The figure below shows an example of acceleration profile during afree-fall. Considerable degree of vibration is observed right after release andthen it decreases gradually. This vibration is thought to be generated mainlyby the mass of the recorder to measure the acceleration and a foam rubbercushion to protect the device.

11Some of the factors which cause vibration are illustrated in an
exaggerated manner below. It is very hard to eliminate all these factors but
try to avoid these for better experiment.

Disclaimer
None of the authors nor other members of Kibo-ABC are responsible toany damage or misconception resulted from the information provided in thisdocument. All users should conduct their operation at their own risk.

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