Posted 8/6/1999 12:12:56 AM
Cassini Mission False and True - NoFlyby's Rebuttal
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Re: http://www.jpl.nasa.gov/cassini/rtg/intro2true.htm
[Last Updated by NASA: December 1997]
FROM NASA/JPL:
Cassini Mission False and True
There are people who are making incorrect statements about NASA's
Cassini mission to Saturn. Some of the statements are either
misinterpretations or misrepresentations of NASA and European Space Agency
(ESA) documents. The purpose of this fact sheet is to address some of the
technically incorrect descriptions of potential launch and reentry
accidents, and unsubstantiated health impact predictions.
FALSE:
The Cassini mission could use solar power instead of RTGs.
TRUE:
A Cassini spacecraft equipped with the highest efficiency solar
cells available, or even the new high-efficiency cells under development by
ESA, would make Cassini too massive for launching to Saturn.
The ESA scientists who developed the high-efficiency cells have
stated that their cells would not enable a solar powered Cassini mission.
NASA's primary choice of electrical power for planetary missions has
historically been solar. The Mars Observer, Viking Orbiters, and six Mariner
missions to Mars all used solar-powered spacecraft.
RTGs were developed by the Department of Energy (DOE) in response to
a need for a compact, reliable source of electrical power for NASA deep
space missions. RTGs are used when solar power or other technologies are not
feasible.
NASA has safely used RTGs for three decades on its Apollo, Pioneer,
Viking, Voyager, Galileo, and Ulysses missions.
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FROM NOFLYBY:
Dr. Michio Kaku, Professor of Nuclear Physics, City University of
New York, said in an interview on EnviroVideo's "Nukes in Space 2,
"..I happen to agree with the NASA estimate. I did the calculation
myself. Cassini cannot go solar." but he continues: "It is one percent
overweight. Therefore, you cannot shoot Cassini into outer space with solar.
I agree with NASA. But, if you go to the store and you want to put on a
favorite dress and you are one percent overweight, you simply say, 'Well, I
can't do it. I can't do it.' Or you simply lose that one percent. It is 130
pounds overweight by NASA's own estimates."
When the current administrator of NASA first assumed his post,
NASA's chief scientist stated that Mr. Goldin would have preferred to cancel
the Cassini project because of "enormous risk factors" (Space News, March
1994, p. 3).
Three out of the 26 known U.S. space missions involving nuclear
power have met with accidents, as have six of 41 known Russian missions,
reported by the Christian Science Monitor on December 17, 1996.
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FROM NASA/JPL:
FALSE:
The Titan IV rocket that Cassini was launched on has been involved
in many accidents.
TRUE:
As of February 1997, there have been 23 Titan IV launches, of which
22 have been successful.
The single failure in August, 1993 was due to a flaw in one of the
solid rocket motors (SRMs) which was induced by a post development repair
procedure. This problem has been fixed.
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FROM NOFLYBY:
NASA is slow in updating this very misleading statement, before they
had a 12% failure rate with the Air Force Titan 4 rocket missions. Since the
Cassini launch, three consecutive failures have occurred! NASA agrees now,
they have a big problem.
http://www.nonviolence.org/noflyby/ref/another.htm
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FROM NASA:
FALSE:
No failure probability of NASA spacecraft can be as low as one in
one million.
TRUE:
NASA has designed the Cassini mission trajectory to ensure that the
spacecraft will successfully swingby Venus twice, Earth, and then Jupiter to
attain the required velocity to reach Saturn.
The accidental swingby reentry probability of less than I in I
million may be surprising to some people (at first) since it is difficult to
prove that failures of any system, particularly spacecraft, can be that small.
The result is driven by two factors: First, for most of the Cassini
trajectory it is very hard to hit the Earth. In fact, until about 50 days
before Earth swingby, the probability of hitting the Earth is much less than
one in one million regardless of the spacecraft failure (this is because of
the vastness of space, the smallness of the Earth as a target, and the
randomness of a spacecraft failure or micrometeoroid hit leading to a
velocity change).
Second, JPL has "biased" the trajectory for Earth swingby.
This scheme further limits the time and events that could cause inadvertent
reentry by eliminating all failures except those that give the spacecraft
the proper velocity magnitude and direction to impact the Earth. The
spacecraft is biased 5,000 kilometers (3,106 miles) or more away from the
swingby altitude (about 1,160 km) for all but about 7 days prior to the
swingby.
Additionally, the navigation accuracy of NASA spacecraft is better
than 20 km.
The biasing strategy effects, coupled with redundant spacecraft
system design, built-in fault detection and correction systems, and
controlled operation (via sending commands to the spacecraft), particularly
during the limited time when failures could cause impact, lead to the
exceedingly small probability of Earth impact.
In addition, these analyses are constantly being reviewed and
refined, and revisions made in spacecraft design to ensure that the design
requirement will not be exceeded.
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FROM NOFLYBY:
[The following three paragraphs are from "Nukes in Space 2: Unacceptable
Risks:"]
Dr. Michio Kaku:
And now Cassini is coming back. And now they say the probability of misfire
is one-in-a million. I looked at the "Final Environmental Impact Statement."
I zeroed in on the precise sentence where they calculate this
one-in-a-million failure. Where do they get this number?
Dr. Stephen Edberg, NASA's Jet Propulsion Laboratory:
The one-in-a-million chance is, in a sense, a number pulled out of a hat. It
was selected to define what most people would agree is a very tiny risk. So
in that sense it was pulled out of the hat. The question then was: can we
make the trajectory of Cassini safe enough that there is only a
one-in-a-million chance that it will collide with the Earth. The answer is yes.
Dr. Michio Kaku:
The one-in-a-million figure comes from the estimate of impact with a meteor
in outer space. Now give me a break. Yes, the chances of space probe hitting
a meteor in outer space is on the order of magnitude of one-in-a-million. We
can calculate that. We know the density of debris in outer space; we know
the trajectory of these space probes. However, a chain is no stronger than
the weakest link. The weakest link is not meteor impacts from outer space.
We're not talking about "Armageddon" and "Deep Impact" in outer space. The
weakest link, as you probably know, is that we lose contact with our space
probes and they explode and misfire in space. In other words, the real
probability is about ten percent. There's a ten percent chance that we will
either lose radio contact with the Cassini mission or that the rockets will
misfire and it'll go into an incorrect trajectory. Ten percent."
A letter sent to the U.S. president from the interagency panel that
reviewed the nuclear safety on Cassini, dated 23 September 1997, requested a
2 months delay in the launch of Cassini to enable a slower flyby speed and
thereby decrease the health risk by a factor of 30 to 100. This advice for
increasing safety for the flyby was ignored.
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FROM NASA/JPL:
FALSE:
A single spacecraft failure or small misfire of the Cassini engines
would result in an Earth reentry accident.
TRUE:
The probability of an inadvertent earth reentry is extremely
unlikely -- less than one in 1 million -- even in the event of a spacecraft
failure or misfire of Cassini's engines. A swingby accident is conceivable
only if an extremely unlikely sequence of events and failures occurs. The
vast majority of possible spacecraft failures would not alter the
spacecraft's trajectory. A spacecraft failure or micrometeoroid impact would
have to cause a change to the spacecraft's velocity of exactly the proper
magnitude and direction to place it on an impacting trajectory.
Cassini's trajectory will never be pointed directly at the Earth.
Only a very small fraction of the micrometeoroid impacts or failures that
could possibly change Cassini's velocity would ever place the spacecraft on
an Earth-impacting trajectory.
Additionally, if a spacecraft failure did occur, it would have to
be so severe that neither automated on-board systems nor their backup
systems nor flight controllers could take corrective action to place the
spacecraft on a non-impacting trajectory.
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FROM NOFLYBY:
The risk of rocket misfire is not the only chance for another NASA
mistake, a Jet Propulsion Lab report (May 1997) lists 18 different types of
malfunctions that may occur, including electrical short-circuits, meteors
and space debris striking the space probe, and erroneous ground commands. At
the planned Fly-By speed of 10 miles per second, a loss of control lasting
under two minutes could result in the Cassini's re-entry into our atmosphere
where the ship will burn up. NASA is taking many risks in scheduling the
flyby for August 1999 at the high point of solar storm activity? Scientists
expect a violent solar storm, perhaps the worst in a century, to strike
sometime between now and January 2001.
http://www.nonviolence.org/noflyby/alerts/flares.htm
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FROM NASA/JPL:
FALSE:
NASA and DOE have underestimated the potential number of cancer
fatalities from a hypothetical Cassini swingby accident. (This claim has
been put forth by Ernest Sternglass)
TRUE:
In fact, DOE analyses used methods consistent with practices
endorsed by independent, national and international radiation protection
organizations, such as the International Commission on Radiological Protection.
In September, 1995 the Jet Propulsion Laboratory (JPL) formally
asked Ernest Sternglass to document the basis for his claims about the NASA
and DOE analysis. Dr. Sternglass was contacted again in May, 1996, via
registered letter, and asked again to validate his claims. He has not
responded to either letter.
For more information on the Cassini mission and its nuclear safety,
contact Cassini Program Nuclear Safety Information Specialist Sandra M.
Dawson (818) 354-1240. Internet: Sandra.M.Dawson@jpl.nasa.gov
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FROM NOFLYBY:
NASA claimed that almost none of the Plutonium could become airborne
in any accident (FEIS-Supplemental p. E-95). In contrast the U.S.
interagency Safety Evaluation Report (SER) notes that 9 kilograms could
become airborne in respirable form, the only hazardous state (p. 3-19).
NASA continues to claim that the cancer-causing potential of the
Plutonium on board Cassini would be small, because the Plutonium in the
event of a flyby accident would be scattered to give a little bit to a large
population. NASA based its figures on the cancer-causing potential of
Plutonium on the dose from general ionizing radiation. However, a
NASA-funded project in 1997 showed that it takes just one decaying
radioactive atom to produce permanent mutation in a cell's genetic molecules
causing cancer. This was reported in the Proceedings of the National Academy
of Sciences (April 1997) from experiments performed at Columbia University,
yet completely ignored by NASA. The SER suggests that based on this evidence
there could be tens of thousands of fatalities in a fifty year period.
However, the SER omits mentioning that each kilogram of Plutonium contains
trillions of radioactive atoms, and the number of fatal cancers might be
many times greater.
http://www.ratical.org/radiation/CNR/LetterOfConcern.html