Re: Centre of mass change of melting ice + tray sys. in gravity-free hall?

Greetings Kaushani:

References:

1) NASA Microgravity Interactive web site, Fluid Physics

http://microgravity.msfc.nasa.gov/education/FluidPhysics/fluid.htm

2) A300 Zero-G Airbus Experiments

http://w ww.esa.int/export/esaHS/SEM8WZ8YFDD_research_0.html

3) Government of India, Department of Space, Annual Report 2002- 2003

http://www.isro.org/rep2003/in dex.htm

Thank you for your interesting question. The center of gravity (CG) for an ice
block is fairly simple to determine; however, scientists and engineers do not yet
fully understand the problem of liquids in a free fall environment and the impact
these liquids have on the CG of vehicles. Research on this problem continues in space
programs in the USA, Europe and India.

Your questions are related to what engineers call Sloshing. Sloshing is a
branch of the Physics of Fluids, in which we are trying to understand how
fuel and other equipment using cryogenic solids and liquids impact the CG and the
control stability of aircraft, missiles, rockets and spacecraft. On the ground the
CG location can be determined with considerable accuracy. However in space flight,
fuel slosh, fuel usage, uncertainties in the deployment of appendages and bending
of the booms all result in movement of the vehicle CG.

For spacecraft, which in orbit are in a zero-G free fall environment, NASA has set a
tentative research goal of 2.5mm accuracy in the location of the CG. This goal
requires that a sophisticated method of CG control be developed. Options for control
of CG include, multiple fuel tanks with the ability to control fuel usage from
individual tanks, movable masses within the spacecraft or control over boom lengths.
Also, metal diaphragms in the storage containers should be used to minimize the
effects of sloshing instead of less controllable elastomeric diaphragms currently
used to minimize fuel slosh.

In a free fall zero-G environment, such as in your question, the surface tension of
liquids produced by melting solids, such as water, and the absence of a gravitational
force, causes the liquid to break up and to form into small spherical liquid
balls. These balls them move in all directions within the container in an uncontrolled
manner causing unwanted movement of the vehicles CG. This problem was responsible for
the loss of control stability of several satellites early in the space program.

To this day there is not a clear understanding of liquid behavior in a zero G - microgravity
environment. NASA uses the term microgravity because in
a continuous free fall environment, such as experienced by satellites in orbit,
various small forces caused by atmospheric drag, local changes in the earth's
gravitational field, and variation in solar radiation pressures, produce microforces
on the vehicle. These microforces produce a microgravity environment.

Reference 1 is a NASA Microgravity interactive web site that discusses this
problem and has some video clips that show the phenomena of water behavior in a
microgravity environment.

The problem of understanding liquids in a free fall, microgravity environment are
also being studied by the European Space Agency (ESA) using an A300 Airbus
aircraft laboratory to study zero - G environments. Reference 2 is an ESA interactive
web site that describes their program and the Airbus laboratory.

Closer to your home in India, Reference 3 is a web site containing the
Government of India, Department of Space, Annual Report 2002- 2003. This
very detailed report indicates that under the topic of Sponsored Research
in Space Technology, during 2004 Project (7) will study liquid sloshing
in spherical tanks under microgravity conditions. Information in this very detailed
report may be able to put you in touch with engineers and scientists working in
India's space program.

If you search the web for the topics "sloshing" AND "satellite" you will
find dozens of references to groups addressing this problem.

Best regards Your Mad Scientist
Adrian Popa