Linking soap bubbles to satellites

From: Amara Graps (
Date: Thu May 10 2001 - 14:49:11 MDT

>From SCNewsline issue 39, May 2001


Computers the link between soap bubbles and satellites

A computer model originally applied to understanding the
formation of soap bubbles has been used to gauge how much fuel
is left to manoeuvre communications satellites - a development
potentially worth millions of dollars for the companies that
operate the satellites.

As a bonus, the technique, developed by engineers at Purdue
University in Indiana USA, uses temperature data that is already
collected routinely, so it does not requires any additional
hardware and can be applied to existing spacecraft. Satellites
are maintained in geostationary orbit about 22,500 miles above
Earth by firing small rocket thrusters, and they have to be
replaced before they run out of fuel and lose position. In
addition, enough fuel must remain to get the old satellite out
of orbit to make room for its replacement.

Since a single satellite may earn annual revenues in the
billions of dollars, companies have an interest in avoiding its
premature retirement.

More accurate fuel-gauging methods are needed so that companies
can better determine when to replace a satellite. For satellites
that send signals to pagers or residential TV dishes, just one
pound of hydrazine rocket fuel translates into about $2.5
million in revenue so the hydrazine is worth more than its
weight in gold.

Precisely measuring the amount of propellant in a satellite's
fuel tank is not so easy. Steven Collicott, an associate
professor of aeronautics and astronautics at Purdue and one of
the authors of the new system, pointed out that 'it's not like a
car's fuel tank, which has a little float that floats on top of
the gasoline and moves a lever. Floats don't work in space
because everything is floating.'

Conventional methods involve estimating fuel consumption from
the number and duration of all rocket firings since launch.
However, the Purdue engineers used a model created in the early
1990s by Kenneth Brakke, a mathematics professor at Susquehanna
University, initially to describe the mathematics behind such
phenomena as the formation of soap bubbles.

Collicott's application of the model uses routine temperature
data from the satellite to monitor how much fuel is left in the
tank. Heaters are needed to keep the fuel from freezing, and
those areas of the tank that contain fuel take longer to heat,
while portions of the tank that are empty heat up faster. The
more fuel that is present, the longer it takes to heat.

The model uses the temperature information to provide a
detailed, three-dimensional understanding of where fuel is
located inside the tank. That information can, in turn, be used
to calculate how much fuel remains in the tank. The technique
may be improved in the future, as researchers gain a better
understanding of how fluids behave in weightlessness.

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********************************************************************* Amara Graps | Max-Planck-Institut fuer Kernphysik Interplanetary Dust Group | Saupfercheckweg 1 +49-6221-516-543 | 69117 Heidelberg, GERMANY * ********************************************************************* "Never fight an inanimate object." - P. J. O'Rourke

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