NASA has successfully tested an alternative rocket fuel
that may increase operational safety and reduce costs over
current solid fuels. The new paraffin-based fuel could
eventually be used in Space Shuttle booster rockets.

Two years of collaboration between Stanford University, Palo
Alto, Calif., and NASA’s Ames Research Center, Moffett
Field, Calif., have led to the development of a non-toxic,
easily handled fuel made from a substance similar to what is
used in common candles. The by-products of combustion of the
new fuel are carbon dioxide and water; unlike conventional
rocket fuel that produces aluminum oxide and acidic gasses,
such as hydrogen chloride.

“There is great cost in making, handling and transporting
traditional solid rocket fuels, but the new paraffin-based
fuel is less expensive, non-toxic and non-hazardous,” said
Greg Zilliac of Ames. “Because the fuel is very stable and
environmentally friendly, a hybrid rocket could be fueled at
the launch site rather than at the factory, thereby saving
money,” he added.

The main goal of the NASA test program is to determine if
the promising results of earlier bench-top experiments
conducted at Stanford will scale up to the combustion
chamber conditions required for space launch operational
systems. “The NASA combustion tests have been very promising
and indicate the burn rate for the larger-scale apparatus is
as high as that achieved in the small-scale Stanford tests,”
Zilliac continued. “This new fuel could significantly impact
the future of space transportation,” he said.

“A hybrid rocket equivalent to the Space Shuttle’s solid
rockets would be about the same diameter, but would be
somewhat longer,” said Stanford University Professor Brian
Cantwell. “Hybrid rockets, using the paraffin-based fuel,
can be throttled over a wide range, including shut-down and
restart. That’s one reason why they could be considered as
possible replacements for the Shuttle’s current solid rocket
boosters that cannot be shut off after they are lit,” he
said. “One design concept being considered is a new hybrid
booster rocket that is able to fly back to the launch site
for recharging,” he added.

A hybrid rocket uses a liquefied oxidizer that is gasified
before being injected into the combustion chamber containing
the solid fuel. Upon ignition, a flame develops over the
fuel surface causing the solid to evaporate, thereby
sustaining the combustion. Because current hybrid fuels,
other than paraffin-based fuels, cannot sustain a high
combustion rate, they have found only limited application
and are not commercially viable for space applications.
Tests at Stanford and Ames have shown the new paraffin-based
fuel has a burn rate that is three times greater than that
of other hybrid fuels.

Scientists are testing the new fuel at the Ames Hybrid
Combustion Facility. The first successful test in the series
took place on Sept. 24, 2001. The heavy-duty test chamber
can accommodate pressures up to 60 atmospheres.

The first phase of the program included approximately 40
runs. A new combustion chamber with sapphire windows will
soon be installed to allow researchers to observe the
combustion process using optical instruments. Scientists
will study the underlying physical processes that produce
the fuel’s high performance.

NASA engineers will conduct roughly 200 test runs during the
lifetime of the project. A maximum of one test will take
place per day, each lasting 20 seconds or less.

The concept of a fast-burning, low-cost, paraffin-based fuel
was originally conceived by Dr. Arif Karabeyoglu of
Stanford, Dr. David Altman, president of Space Propulsion
Group Inc., Menlo Park, Calif. and Cantwell. Karabeyoglu
developed the theory in his doctoral thesis that was
partially supported by Stanford and NASA. He leads the
Stanford contribution to the fuel research.

Images and more information is available on the Internet at:

http://amesnews.arc.nasa.gov/releases/2003/03images/paraffin
/paraffin.html