Risk Assessment Used to Prevent Accidents on Mission to Saturn
Reprinted with permission from Scientific Computing and Automation (June 1997)
Frank Kampas has been very busy for the last two years. And he plans to
keep on furiously working at least until October 6. On that day, if
everything goes according to plan, his work will prove to be for nought.
Kampas is a senior staff system engineer for the Lockheed Martin Missiles
and Space Company, a leading supplier of satellites to military, civil
government, and commercial communications organizations around the world.
For the past several months, he has been part of a five-person team that is
working with the National Aeronautics and Space Administration (NASA) on
the Cassini Orbiter mission, which will explore Saturn and its dark,
cloud-laden moons. But if all goes well, Kampas's contribution to the
mission will go unnoticed.
He and his team are responsible for probabilities risk assessment. His
objective--to manage the risk in the project and prevent accidents. "It's a
matter of looking at every aspect of the mission and making sure nothing
goes wrong," he explained.
NASA's Cassini Orbiter's goals are to determine the three-dimensional
structure and dynamic behavior of the giant planet's rings, determine the
composition of the satellite surfaces and the geological history of each
object, and determine the nature and origin of the dark material on one of
Saturn's 17 moons, Iapetus. It will also study how the icy satellites--all
the moons except Titan--interact with the planet's magnetosphere.
To explore the moons, Cassini will deploy the Huygens probe, which is
provided by the European Space Agency (ESA). Cassini itself will remain in
orbit around Saturn to explore its rings and satellites. The Cassini
spacecraft, the orbiter and its probe, will rank as one of the most
complex, bulky missions sent into space. When all the propellants are
added, the craft will weigh 5,600 kilograms (12,346 pounds). Supporting the
explorers functions are 1,630 interconnect circuits, 22,000 wire
connections, and more than 14 kilometers (8.7 miles) of cabling.
Cassini will be carried into space by the Titan IV/Centaur launch vehicle,
but once it nears Saturn the usual solar array panel power system will be
inadequate because of diminished sunlight. The orbiter will be powered by
three radioisotope thermoelectric generators (RTGs), which use heat from
the natural decay of plutonium to generate direct current electricity. The
RTG design is currently used on the wandering Galileo and Ulysses spacecrafts.
One of Kampas's responsibilities is to determine the likelihood of power
failure and engine failure onboard the spacecraft. As a result, he says,
simulation programs and probability equations are essential to his work.
Even though Kampas, who received a Ph.D. in physics from Stanford
University, runs most final-version programs in Fortran, Mathematica from
Wolfram Research (Champaign, Illinois) plays a crucial role in his work.
"I use Mathematica mostly for postprocessing. It's a very compact,
powerful programming language that let's me organize and plot my data
before I convert to Fortran," Kampas said. Mathematica is a symbolic
computer language that can manipulate a large number of technical computing
functions using fewer programming lines.
For example, Kampas sometimes needs to write a piece of program to
calculate a sine of a function. In typical programs, the complete
calculation would take five or six lines to operate whereas Mathematica
takes only one, using a vector function. In addition to Fortran and
Mathematica, Kampas often works with visualization software like PV-Wave
from Visual Numerics in Houston, Texas.
Kampas has been programming on Mathematica for about four to five years and
currently runs Version 3.0 on Windows 95. By the time he left the solar
energy industry two years ago and joined Lockheed Martin, Kampas had had
experience in a number of similar languages like APL, which was developed
by employees at IBM. "Mathematica is like APL in that it's so compactable
and powerful," said Kampas. APL is also best known for its general purpose
functionality and its use of non-ASCII symbols. The Lockheed team
eventually chose to use Mathematica because of its integrative features
and is not planning to add any new software, at least not until after the
orbiter launch. "We're very happy with it (Mathematica) so far," he added.
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