Why We Should Stop Cassini
by Russell D. Hoffman
Soon, NASA plans to launch a space probe called Cassini. Cassini is
designed to go to Saturn by way of Venus, Earth, and Jupiter. It will use
each planet in one or more "gravity assist maneuvers" to attain the speed
necessary to make it all the way to Saturn. When Earth is used for the
Gravity Assist (EGA), NASA will fly Cassini just 496 miles above the surface
of the Earth, at about 43,000 miles per hour (19.4 Kilometers per second, or
63,600 feet per second). The actual stated height above Earth which NASA
will use has changed many times, and was 312 miles for several years prior
to the latest published number.
Taken by Hubble.
To say Cassini is a risky mission is an understatement. It will contain
over 72 pounds of Plutonium Dioxide consisting of over 60 pounds of pure
plutonium 238. This is a health risk of virtually unprecedented
proportions. In the past, all the weapons testing, which the world felt it
was necessary to do, put an incredible amount of plutonium in the
atmosphere. But that was a WAR -- albeit, a cold (blooded) one, but it was
If such actions were inexcusable (and this writer and many others believe
that the vast majority of past nuclear weapons testing was certainly
inexcusable) then it surely is inexcusable to risk the same sort of
contamination of our home turf (Earth) for NASA's next science experiment.
But that is just what Cassini is capable of if an accident occurs during the
launch, late launch, or during the gravity assist.
This is not a peaceful use of the mighty atom (if indeed there can be such a
The purpose of 99% of the plutonium on board Cassini is to provide merely
745 watts (nominal) to power the science experiments. It is not for
propulsion, it is not a "fuel" for attitude control or anything like that:
it is just a small heat source used to create a very modest amount of
electrical power via thermocouples. Is it necessary? No. While NASA
claims that the current mission objectives would be severely hampered by
insistence on a reliance on solar, in truth, there is little doubt that one
of the following solutions would work:
1) NASA could reduce the mission objectives to power requirements that could
be supplied by solar.
2) NASA could work harder on perfecting solar options -- with continuance of
the Cassini mission, and the benefits to mankind of better solar technology,
as two powerful incentives.
3) NASA could realize that mankind, while we love the quest for knowledge,
does not want to take unnecessary risks, and Cassini is too risky RIGHT NOW.
Therefore, in addition to perfecting the solar option, NASA should redesign
the scientific tools to be used on the mission to have even lower power
requirements. Probably within 10 years NASA would be able to fly the exact
same mission with one tenth or at most half the power requirements -- then
they could use solar options. We have waited over two decades to return to
the moon -- we can wait for NASA to perfect its tools. Cassini is not
necessary RIGHT NOW.
Cassini, if it is not stopped, will be launched some time in October or
November of this year (1997), with a number of backup launch opportunities
extending to the year 2001. Holding up Cassini will not do. It must be
permanently prohibited until it can be launched with solar alternatives.
In 1964 NASA had a mission abort of a nuclear-packed mission that resulted
in 17,000 Curies of plutonium being intentionally incinerated in the upper
atmosphere. Opposition estimates range to hundreds of thousands of people
-- or more -- who may have died from that one accident, known as SNAP-9A.
In 1967, in response to a worldwide atmospheric test ban treaty, NASA
changed its policy of intentional incineration of nuclear fuel packs, so
that their newest RTG (Radioisotope Thermoelectric Generator) design does
not intentionally incinerate.
But now, NASA is carrying many times more plutonium. Cassini is scheduled
to carry about 406,000 Curies of plutonium! In an EGA reentry accident
during the Earth Gravity Assist (EGA) maneuver of Cassini, NASA estimates
that 4/5ths of the time there will be a fuel release. According to NASA, in
an EGA reentry accident, 3/4's of the time about 13,000 Curies of the fuel
will be released at high altitude, and several times more than that will be
released near Earth's surface if the plutonium pellets impact on hard
surfaces. But unlike the SNAP-9A, this time, somehow, it will be considered
an accident! Yet virtually the same amount is EXPECTED to be released in a
flyby reentry accident as was released in the SNAP-9A intentional
incineration! That's some accident!
How does this work? What NASA does is it puts the plutonium into 108
separate units called GISs (Graphite Impact Shells). These units are then
placed in pairs into 54 units called GPHSs (General Purpose Heat Sources).
18 of these are packed into each of 3 RTGs.
If a reentry accident occurs, the RTGs are expected to melt away and release
the GPHSs. Then, the GPHSs are expected to slow down, and also melt a bit,
but not entirely. Most of the time. But it's not expected to work 100% by
If the GPHSs are cracked or smashed in some way while still traveling at
high speed (for example, by smacking into each other or other pieces of the
disintegrating spacecraft) then the GISs and the plutonium within will
probably melt and be released. Every one of those 54 GPHS's must remain
intact, since each one contains over a pound of deadly plutonium. But even
NASA admits that it is unlikely that all of them will remain unbroken.
Current NASA estimates are that 1.7 of the GPHSs will crack or "ablate"
(melt away) sufficiently to release their GISs (two in each GPHS). Those
GISs are expected to release their plutonium contents as vapor and small
What does NASA do about this? While they could give up and go to a solar
option, instead they consider this to be okay! And how do they do that?
NASA does not think that a slight increase in radioactivity is anything to
worry about. Since "background radiation" is already about 360 millirem per
year per person, adding a fraction of a millirem to everybody is A-OKAY.
But it isn't.
Plutonium 238 is a highly radioactive (i.e. "hot") substance. It is 280
times more radioactive than plutonium 239. This means that a given weight
of Plutonium 238 emits about 280 times more "alpha particles" per second
than the same amount of Plutonium 239 does. So a given mass of Plutonium
238 is much more dangerous, especially when inhaled, than the same mass of
Plutonium 239. A Cassini reentry accident can create literally billions and
billions of respirable pieces, and both sides -- pro and con -- agree that
inhaling even a millionth of a gram of plutonium is a fatal dose. But NASA
would risk spreading anywhere from several pounds to many pounds of this
stuff in an accident. The half-life of Plutonium 238 is 87.75 years; while
the half-life of Plutonium 239 is about 24,400 years. About 10% of the
nuclear fuel will be plutonium 239 and most of the rest will be plutonium 238.
NASA claims that the chance of a reentry accident is less than one in one
million -- but NASA bases this number on complex mathematical estimates
based on "educated guesses". Past NASA flight experience suggests a much
greater danger. Yet every time NASA figures out what it did wrong on a
previous disaster, it discounts the obvious fact -- that they blew it again!
For example, the Titan booster rocket that NASA plans to use for the Cassini
launch has successfully been used just 18 times -- and failed
catastrophically once. Yet NASA's estimate of a Titan launch failure is one
in several hundred -- not one in 19!
Furthermore, they have based their guess that usually only 1.7 of the GPHS
units will break apart on studies done with very, very few actual units and
a lot of simple computer modeling. (While very time consuming to run, the
actual programs do not appear to be terribly complicated.)
When Boeing or Airbus do computer simulations prior to launching a new
airplane, they risk their businesses and they risk the lives of perhaps 500
people in an accident -- both high risks. But NASA numbers, if in fact 3.4
GPHS's will desintegrate rather than 1.7 of them, would mean hundreds of
thousands more deaths! This is a much greater risk! Also, the possible
deviation from this number is quite high depending on many accident scenario
factors. In reality, no one knows what will happen if a flyby reentry
occurs. It could be that only a few pounds will be vaporized in the upper
atmosphere as NASA suggests, but then again it could be more like 10 or 20
pounds -- it could even be more. And it would be very hard to tell what
actually had happened, even if over the years millions of deaths were to
occur from the accident.
There are many things that need to be done to stop this madness, because
NASA is in no mood to stop it themselves. We have made many attempts to
present NASA with an alternative viewpoint to what they consider "acceptable
risk". But NASA intends to launch.
People need to learn about this awful thing. This writer is personally
shocked by how surprised even the staunch environmentalists he talks to are
when they learn what NASA is trying to do. The average person, today, might
know what PATHFINDER is and what planet it whet to, but they are sure to say
"What's Cassini?" if you ask them about NASA's upcoming mission.
The public needs to hear the truth. Anyone reading this message should feel
free to republish it as they see fit. President Clinton needs to be
contacted, so that he knows that people care about today's Earth more than
they care about NASA's weak scientific arguments for the Cassini mission.
People need to contact their congresspeople and ask for their help in
stopping Cassini as the mission is presently planned, with its deadly
People need to stand up and say they ARE AWARE of Cassini, and they want it
stopped -- "what is Cassini?" is not a sufficient answer for the general
public who funds this sort of thing. NASA loves to promote its successes,
but has an amazing ability to hide its failures behind complex scientific
jargon, and a dearth of press releases. We the public should not be able to
say later: "Who knew?"
People need to shout: "NASA IS PLANNING TO LAUNCH 72+ POUNDS OF PLUTONIUM IN
OCTOBER, 1997 -- AND WE HAVE TO STOP IT."
For more information and more "to do" ideas, please visit our web site at:
Russell D. Hoffman