What INDEPENDENT EXPERTS are saying about the

Cassini - Huygens mission to Saturn 

'A fantastic group of worlds await us at Saturn with much to teach us and
Our children. Saturn's complex system of rings and satellites, not to
mention the planet itself, awaits exploration with a treasure trove of new
discoveries. The search for understanding our solar system, the planets,
the chemical and physical conditions and processes that shape our
environment, and the origin and evolution of life are the greatest
adventures in our lifetimes."
 
Dr. Louis Friedman
The Planetary Society, Pasadena1 CA
626/793-5100
 
"Radioisotope Thermoelectric Generators (RTGs) are tested under more
severe shock, temperature, and pressure conditions than any component ever
built. The best example of the success of their design was when the worst
imaginabie accident did happen: a Titan rocket carrying a payload
containing an RTG blew up seconds after launch. .the RTG not only wasn't
damaged, it was fished out of the bay, polished up a bit, and launched on
a subsequent mission. RTGs are designed to prevent dispersal of the fuel
even under the most severe conditions of an exploding launch vehicle or an
uncontrolled reentry into the Earth's atmosphere from space.. The value of
the knowledge gained by these missions, and the consequent benefits to
humanity, far outweigh the tiny risk involved."
 
Jerry Grey, PhD
Director Of Science and Technology Policy, AIAA
Visiting Professor of Mechanical and Aerospace
Engineering, Princeton University
212/595-7102
 
"Contrary to some outlandish claims of horrible consequences associated
with the use of RTG power supplies in the Cassini probe, there is actually
little risk to anyone from accidental releases of plutonium. Accidental
re-entry into the earth's atmosphere could lead to the release and
dispersion into the atmosphere of up to about I % of the plutonium-238
contained within the RTG. There is no known or expected risk associated
with such small radiation exposures."
 
Prof. Otto G. Raabe, Ph.D., CHP
Professor of Radiation Health Biophysics and Radionuclide
Toxicology at the Institute of Toxicology and Environmental
Health, and President, Health Physics Society, Institute of
Toxicology & Environmental Health (ITEH) Univ. of Calif.,
Davis 916/752-7754
 
"...Opponents of RTGs are expected to take last-minute legal steps to
block the Oct. 6 launch. There is concern that demonstrators might even
attempt to physically interfere with the launch... There is more at stake
than Cassini... It could set a precedent that would effectively end
exploration of the outer reaches of the solar system-- there simply is no
practical substitute for RTGs at this point... Pioneer 10 was powered by
an RTG for 25 years until it was abandoned more than six billion miles
from Earth."
 
Dr. Robert L. Park
American Physical Society, Washington, DC
202/662-8700
 
"Saying 'no' to Cassini would be saying 'no' to knowledge. Cassini,
planned for years to reveal the secrets of Saturn, its rings and
mysterious system of satellites, will provide invaluable data and another
unforgettable rendezvous with images we've never seen before. Saying 'no'
to Cassini would jeopardize years of international preparation and
investment. Misinformation and exaggerated claims of risk should not be
arlowed to slam the door on deep space discovery. Cassini's RTGs, which
occupy the center of current debate, have proven their safety and
capability in 23 prior missions, including human missions. RTGs are the
only realistic option for sending probes great distances from the Sun and
will certainly play a part in future human missions. The National Space
Society fully supports the launch of Cassini."
 
Charlie Walker
President, National Space Society, Washington, DC
202/543-1900

Other experts available for Interviews

Contacts for the Media 

	Douglas Isbell       Policy/Program Management     202/358-1753
	Headquarters,
        Washington, DC
 
	Donald Savage        Cassini Nuclear Safety        202/358-1727
        Headquarters,
	Washington, DC
 
	Franklin O'Donnell   Cassini Mission               818/354-5011
	Jet Propulsion Laboratory,
	Pasadena, CA
 
	Mary Beth Murrill                 Cassini Mission      818/354-6478
	Jet Propulsion Laboratory,	  and Nuclear Safety
        Pasadena, CA
 
	George Diller                     Launch Operations    407/867-2468
	Kennedy Space Center, FL
 
        Matthew Donughue                 Public Affairs        202/586-0619
        Dept of Energy

Cassini's Nuclear Safety 

	The Cassini spacecraft derives its electrical power from
radioisotope thermoelectric generators (RTGs), lightweight, compact
spacecraft power systems that are extraordinarily reliable. RTGs are not
nuclear reactors and have no moving parts. They use neither fission nor
fusion processes to produce energy. Instead, they provide power through
the natural radioactive decay of plutonium (mostly Pu-238, a
non-weapons-grade isotope). The heat generated by this natural process is
changed into electricity by solid-state thermoelectric converters.
 
	RTGs enable spacecraft to operate at significant distances from
the Sun or in other areas where solar power systems would not be feasible.
They remain unmatched for power output, reliability and durability by any
other power source for missions to the outer solar system.
 
	The United States has an outstanding record of safety in using
RTGs on 23 missions over the past 30 years. While RTGs have never caused a
spacecraft failure on any of these missions, they have been onboard three
missions which experienced malfunctions for other reasons. In all cases,
the RTGs performed as designed.
 
	More than three decades have been invested in the engineering,
safety analysis and testing of RTGs. Safety features are incorporated into
the RTG design, and extensive testing has demonstrated that they can
withstand physical conditions more severe than those expected from most
accidents.
	
	First, the fuel is in the heat-resistant, ceramic form of
plutonium dioxide, which reduces its chance of vaporizing in fire or
reentry environments. This ceramic-form fuel is also highly insoluble, has
a low chemical reactivity, and primarily fractures into large,
non-respirable particles and chunks. These characteristics help to
mitigate the potential health effects from accidents involving the release
of this fuel.
 
	Second, the fuel in each RTG is divided among 18 small,
independent modular units, each with its own heat shield and impact shell.
This design reduces the chances of fuel release in an accident because all
modules would not be equally impacted in an accident.
 
	Third, multiple layers of protective materials, including iridium
capsules and high-strength graphite blocks, are used to protect the fuel
and prevent its accidental release. Iridium metal has a very high melting
point and is strong, corrosion-resistant and chemically compatible with
plutonium dioxide. These characteristics make iridium useful for
protecting and containing each fuel pellet. Graphite is used because it is
lightweight and highly heat-resistant.
 
	Potential RTG accidents are sometimes mistakenly equated with
accidents at nuclear power plants. It is completely inaccurate to
associate an RTG accident with Chernobyl or any other past radiation
accident involving nuclear fission. RTGs do not use either a fusion or
fission process, and could never explode like a nuclear bomb under any
accident scenario. Neither could an accident involving an RTG create the
kind of radiation sickness associated with nuclear explosions.
 
	NASA and the Department of Energy, the producer of the RTGs, place
the highest priority on assuring the safe use of plutonium in space.
Thorough and detailed safety analyses are conducted before launching
spacecraft with RTGs, and many prudent steps are taken to reduce the risks
involved in missions using RTGs. In addition to NASA's internal safety
requirements and reviews, NASA missions that carry nuclear material also
undergo an extensive external safety review involving detailed testing and
analysis. Further, an independent safety evaluation of the Cassini mission
has been performed as part of the nuclear launch safety approval process
by an Interagency Nuclear Safety Review Panel (INSRP), which is supported
by experts from government, industry and academia.

Alternatives 

	Studies conducted by NASA's Jet Propulsion Laboratory (JPIJ) have
concluded that neither fuel cells nor spacecraft batteries demonstrate the
operational life needed for planetary missions, whose duration can exceed
10 years from launch. In addition, the large mass of batteries that would
be needed to power a mission such as Cassini exceeds current launch
vehicle lift capabilities.
 
	JPL's rigorous analysis has also taken into account the advances
in solar power technologies that have occurred over the last decade. The
conclusion reached by JPL researchers is
that solar technology is still not capable of providing sufficient and
reliable electrical power for	the Cassini mission. The mass of solar
arrays required would make the spacecraft too heavy for available launch
vehicles. Even if a sufficiently powerful launch vehicle were available
for an all-solar Cassini, other limitations exist with current and
near-term solar technologies.
 
	The behavior of solar cells at vast distances from the Sun is not
well understood and would add significant risk to the success of a
solar-powered mission to Saturn. Saturn is located approximately 1.42
billion kilometers (882 million miles) from the Sun, nearly twice as far
from the Sun as Jupiter, the next closest planet.
 
	The size of solar arrays that would be needed, about the size of
two tennis courts, would not only be difficult to deploy reliably, but
would make turns and other critical maneuvers extraordinarily difficult to
perform. This would severely inhibit Cassini's ability to achieve its
science objectives.
 
	The large arrays would seriously interfere with the fields of view
of many of the science experiments and navigation sensors, further
limiting the Cassini mission's ability to achieve the science objectives.
 
	Large arrays could generate serious electromagnetic and
electrostatic interference, which would adversely impact the operation of
the science experiments and the Cassini spacecraft's communications
equipment and computers.

Cassini's Earth Swingby 

	By aiming a spacecraft so that it passes close to a planet or
moon, it is possible to boost the spacecraft on to still more distant
destinations with greater velocity. This gravity-assist maneuver has
become an established method of launching massive, instrument-laden
spacecraft to the outer planets. Cassini will make use of this technique
when it swings by Venus twice, then the Earth and Jupiter to reach its
ultimate destination of Saturn.
 
	The Earth swingby does not represent a substantial risk to Earth's
population because the probability of a reentry during the maneuver is
extremely low, less than one in one million. NASA's robotic planetary
spacecraft have performed numerous similar maneuvers with extraordinary
precision. The redundant design of Cassini's systems and navigational
capability allows control of the swingby altitude at Earth to within an
accuracy of 3 to 5 kilometers (2 to 3 miles) at an altitude of 800
kilometers (500 miles) or higher.
 
	In addition, NASA has taken specific actions to design the
spacecraft and mission in such a way as to ensure the probability of Earth
impact is less than one in one million. For example, until seven days
before the Earth swingby, the spacecraft is on a trajectory that, without
any further maneuvers, would miss the Earth by thousands of kilometers.
This trajectory strictly limits the possibility that random external
events, such as a micrometeoroid puncture of a spacecraft propellant tank,
might lead to Earth impact.

Radiation Hazards of Plutonium-238 

	Plutonium-238 gives off short-range alpha particles, helium nuclei
that usually travel no more than about three inches in air. While the fuel
is contained within its iridium capsule, the alpha radiation does not
present a hazard, and the external dose resulting from the low levels of
gamma and neutron radiation associated with the plutonium dioxide RTG fuel
generally do not represent a significant health hazard. External alpha
radiation would be stopped by clothing, an outer layer of unbroken skin,
or even a sheet of paper. The point at which Pu-238 can become a health
hazard is when it is deposited into the body in tiny particle form and
becomes lodged there.
 
	If an individual were to inhale plutonium dioxide particles of a
sufficiently small size to be deposited and retained in proximity to lung
tissue, the alpha radiation could lead to forms of cancer. The ceramic
form of plutonium used in RTGs, however, is made to inhibit the fuel from
shattering into fine particles that could be readily inhaled.
 
	The ceramic form of plutonium dioxide fuel also has low solubility
in water, so it has little potential to migrate in groundwater or be taken
up by plants. Plutonium dioxide also is highly insoluble in the human
digestive system.
 
	A common misconception is that a small amount of plutonium, such
as one pound, if evenly distributed over the entire world, could induce
lung cancer in every person on Earth. While plutonium can alter or kill
living cells if deposited directly onto sensitive human tissue, the
important point is that it must be in a form that enables environmental
transport and intake by humans. Research has demonstrated that the
mechanisms of plutonium dispersion into and transport through the
environment, and hence into humans, are extremely difficult and
inefficient.
 
	Even in the highly unlikely release of plutonium dioxide from
Cassini's RTGs in the event of an accident, independently reviewed
analysis shows that the radiation hazard to the average exposed individual
would be minuscule, about 1/15,000 of the lifetime exposure a person
receives from natural radiation sources.