CASSINI:
A look at NASA's own documents

With comments by Russell D. Hoffman

This document contains the entire text in order, at the time we found it, of NASA's own document which can be found at the following URL:
http://www.jpl.nasa.gov/cassini/MoreInfo/spacepwr.html

We have added our comments and italicized NASA's original statements. I'm sure I hardly need to add the we would welcome an attempt by NASA to refute the assertions made in this article. If they do we will be happy to add a link to it, and then tear it apart as well.

Spacecraft Power for Cassini

February 1996

Cassini's electrical power source - Radioisotope Thermoelectric Generators (RTGs) - have provided electrical power for some of the U.S. space program's greatest successes, including the Apollo lunar landings and the Viking Landers that searched for life on Mars. RTGs made possible NASA's celebrated Voyager explorations of Jupiter, Saturn, Uranus and Neptune, as well as the Pioneer missions to Jupiter and Saturn. RTG power sources are enabling the Galileo mission to Jupiter and the international Ulysses mission studying the Sun's polar regions.

While they may have had some successes, they have also had some dismal failures, including Apollo 13. Although not mentioned in the recent Hollywood movie, there was plutonium onboard the lunar lander, plutonium which was supposed to be left on the moon but instead was brought back to Earth in a fireball somewhere near New Zealand. We currently buy our Plutonium 238 for our RTGs from Russia which means its use involves unlicensed and unregulated (by U.S. agencies) nuclear sources and transport halfway around the world prior to use. Dismal as our nuclear safety record has been, Russia's is far worse.

And as for using it on our Ulysses mission to the Sun -- doesn't it seem strange that NASA could not even find a solar alternative for that?

The fact that RTGs provided the power for past missions does not mean it was the only solution that NASA could have used, and even if it were, it no longer is. Solar power works.

Extensive studies conducted by NASA's Jet Propulsion Laboratory (JPL) have shown that NASA's Cassini mission, given its science objectives, available launch systems, travel time to its destination and Saturn's extreme distance from the Sun, requires RTGs.
Freedom of Information Act documents obtained by Karl Grossman show that even NASA knows it has viable solar alternatives. That makes this statement a lie, and even if it were true, technology is improving as such a rate that it is inconceivable that a solar-powered solution would not be available within the next few years -- if only NASA would look for it.

What Are RTGs?

"RTGs are 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-weaponsgrade 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 be infeasible. They remain unmatched for power output, reliability and durability by any other power source for missions to the outer solar system."

This paragraph contains several falsehoods. First of all, there is no "natural" radioactive decay of plutonium. The term in inappropriate. Plutonium does not exist in nature! Every ounce of plutonium, the most dangerous substance known to man, was created by man. Hard to believe, isn't it? So while other radioactive substances have a "natural" decay rate, plutonium's radioactive properties should not be thus described. It's a little thing, to be sure. Pure semantics. But why do the semantics always seem to fall "their" way?

Second, it is simply not true that solar energy would not work. Additionally, new developments in computer and machine and micromachine technology are reducing the required power consumption of virtually every component on board Cassini. In fact, considering how long Cassini has been in development, it is probable that more modern off-the-shelf components would use much less power than the RTG's are designed to deliver!

Safety Design

The United States has an outstanding record of safety in using RTGs on 23 missions over the past three decades. While RTGs have never caused a spacecraft failure on any of these missions, they have been on-board three missions which experienced malfunctions for other reasons. In all cases, the RTGs performed as designed.
The fact that they performed as designed is irrelevant. The fact is that in just 23 missions, 3 were failures. (Or, as NASA puts it, "experienced malfunctions", but don't forget what an explosion like the Challenger is to NASA: a "malfunction.") That's a lousy percentage. Why put humanity at such risk for those lousy odds?

Also, even if every previous mission had been a success, that would prove nothing (but NASA would make big of it, you could be sure.) For even I do not argue that the odds are against the worst-case scenario. But look, if you do something that has a 1 in a million chance of killing a million people, those are simply bad odds. No two ways around that fact! NASA argues that various Cassini failure modes have such long odds, but they are just speculating. The fact is, in 23 missions, 3 "malfunctions". So what if the RTG's weren't to blame? They were there, and they didn't have to be. It's like the guy that brings a weapon to a crime scene. Even if he doesn't use it, bringing the weapon makes it much more of a crime. A bar fight, and a bar fight where weapons are drawn, are very different criminal cases. NASA should put its weapons away. There's no fight going on.

More than 30 years have been invested in the engineering, safety analysis and testing of RTGs. Safety features are incorporated into the RTG's 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.

From most accidents. Not all accidents. Just most of them. What does that mean--51 out of 100 accidents? That's most. NASA, can you possibly be any less clear on what you really think the odds are? There is no way NASA has engineered a solution to the problems of a shallow accidental reentry or that of a random collision with space debris. Neither of these are "remote possibilities". The future space station is expected to be hit by a major piece of space debris -- one too big to build in protection against -- once every 50 years. That's not remote. That's a dangerous mission. But Cassini is endangering us all, not just the highly paid and highly trained adventurers and risk-takers we all admire called astronauts.
Second, the fuel 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.
When you are dealing with a substance so deadly that less than 1/70 of the Cassini load is enough to kill everyone on Earth "if properly distributed" and high-altitude incineration is just the ticket to proper distribution, dividing it into 18 smaller groups is hardly comforting! Dividing 72.3 pounds of plutonium into 18 "small" units means four pounds of plutonium in each one, and that's not small and that's no safety feature at all--each module can kill everybody at least four times over! Not one of these "modules" should be risked in upper-atmosphere incineration!
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 is a metal that 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.
43,000+ miles an hour is how fast Cassini will be traveling on the flyby -- the fastest object man has ever buzzed earth with. At that speed, passing too close to Earth during the flyby could result in friction temperatures which would demolish the spacecraft and quite possibly damage the plutonium cargo. Collision at that speed with any of the millions of pieces of space debris which man has already placed in orbit can pulverize the RTGs protective covering. NASA knows this and they aren't mentioning it. They have decided that any hazard they cannot fix is irrelevant. To NASA, "unlikely" and "impossible" are the same thing. They aren't. Cassini is a game of chance in which the winners are the nuclear space industry and the losers are you and I and every other living thing on Earth.
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 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 acute radiation sickness similar to that associated with nuclear explosions.
It is presumably true that RTG's cannot explode. But they absolutely can burn up on reentry. The plutonium will then disperse throughout Earth's atmosphere. If it does this, cancers and other sicknesses will occur throughout the world. Acute Radiation Sickness would not occur. So what? No one is mistaking anything here, except NASA. Plutonium spread in fine particles throughout the upper atmosphere not only CAN happen, it HAS happened. And if we don't stop the madness, it WILL happen again, and again, and again. Not just Cassini, but every nuclear mission is a crapshoot.

Additionally, it is hardly comforting that NASA has endeavored so hard to ensure that the plutonium pods will be intact upon impact. If these intact pods are found by terrorist groups they could be used for a number of hostage and ransom purposes, even if you could not make a nuclear weapon with them. If found by children or other living things, they could certainly be mishandled. Even if they do survive the burning reentry, final impact could still break them into thousands of irretrievable pieces even if they are not "vaporized". Any confined area would surely be devastated by the needless introduction of 72.3 pounds of plutonium chunks -- cities, lakes, rivers, reservoirs, stadiums, schools...

NASA places the highest priority on assuring the safe use of plutonium in space. Thorough and detailed safety analyses are conducted prior to launching NASA spacecraft with RTGs, and many prudent steps are taken to reduce the risks involved in NASA missions using RTGs. In addition to NASA's internal safety requirements and reviews, missions that carry nuclear material also undergo an extensive safety review involving detailed verification testing and analysis. Further, an independent safety evaluation of the Cassini mission will be 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.
NASA uses the nuclear option in the first place. That's the mistake. Any other plan for safety is going to fall short of the goal of flying the safest possible missions. True safety is achievable. Plutonium does not belong in space. The so-called experts are people from the nuclear government, the nuclear industry, and the engineering academia who want to see their little science experiments fly. I believe most physicians who have studied the issue are required by their own Hippocratic Oath ("First, do no harm") to oppose risking the spread of plutonium throughout the environment when there is no significant benefit to mankind.

Non-Nuclear Alternatives to RTGs

JPL studies 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 greatly exceeds current launch vehicle lift capabilities.
As mentioned previously, power requirements of computer and mechanical devices are dropping rapidly due to improvements in ceramics, chip design, and wiring techniques (many of these improvements, of course, are coming right out of NASA!) If we could wait a mere decade and do this safely, why not? Why not put the scientists to work on low-energy, high-efficiency devices that would ease power consumption requirements not just for NASA, but for everyone else? NASA can do this. They know they can do this and we want them to do this. Part of NASA's original and ongoing purpose has always supposedly been to create technology we can use on Earth. Plutonium-powered RTGs have no use on Earth, and will never be used on Earth. If NASA would help develop solar technology, on the other hand, that would have great usefulness here.

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 the researchers at JPL 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, including:

  1. 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.
  2. The size of solar arrays that would be needed, about one-quarter the area of a football field, would not only be difficult to deploy reliably, but would significantly increase the orbiter's moments of inertia, making turns and other timely maneuvers extraordinarily difficult to perform This would severely inhibit Cassini's ability to achieve its science objectives.
  3. 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.
  4. Large arrays could generate serious electromagnetic and electrostatic interference, which would adversely impact the operation of the science experiments and the spacecraft's communications equipment and computers.
So these are things you work on, NASA -- not things you give up on! All of these problems are solvable in due time -- not one is an insurmountable wall. There is no need to risk the use of plutonium for these excuses. If you folks over at NASA are so inventive and such geniuses, why did you give up so easily? Even the Ulysses mission to the Sun wasn't solar powered--are we supposed to believe you are even trying? If the behavior of solar cells at vast distances from the sun is not well understood, then that's what your next mission should study! Low power consumption devices and low light solar cells are needed by everyone -- NASA could be the heroic knight in shining armor coming to save us through technology -- but they aren't even trying. Instead they are trying to get away with stuff they know is dangerous. We give them billions of dollars and this is their response -- secrecy, obfuscation, lies. I challenge NASA, in the interest of free inquiry and presenting a balanced view, to link to our site as we have linked to theirs!!

Cassini's Earth Swingby

By aiming a spacecraft so that it passes very close to a planet or moon, it is possible to boost the spacecraft on to still more distant destinations with greater velocity. Called the "slingshot effect" or, more properly, a gravity-assist swingby, this maneuver has become an established method of launching massive, instrument-laden spacecraft to the outer planets. Cassini plans to make use of this technique when it swings by Venus twice, then the Earth and Jupiter to reach its ultimate destinaton 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 approximately 500 kilometers (310 miles).

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 10 days before the Earth swingby, the spacecraft is on a trajectory that, without any further maneuvers, would miss the Earth by thousands of kilometers. The biased trajectory also strictly limits the possibility that random external events (such as a micrometeoroid puncture of a spacecraft propellant tank) might lead to Earth impact.

Aiming off to the side until ten days before the Earth swingby sounds like a safety procedure, and to some extent it is, but the fact is that doing it this way can actually increase the danger to mankind. How? Simply this: To make the swingby work, they will HAVE TO perform a manuever which forces Cassini towards Earth. If they fire the rocket for even a second or two longer than they should, the Cassini probe will be forced towards an upper Earth atmosphere incineration. Understeer can be just as deadly as oversteer. This is not a safe manuever at all but is presented as such to give us the impression that they have done all they can. They haven't.

Also, it should not go unmentioned that ten days out, when they start to manuever towards Earth, they will be approximately 10 million miles from Earth. At that distance the target area is something in the neighborhood of about 1/10,000 (one ten thousandth) of a percent of one degree away from Earth itself, whose entire cross-section takes up less than 1/5th of one degree on Cassini's horizon. Talk about putting it in the barrel. This is a knothole at a million paces.

Lastly, to call this "an established method of launching massive, instrument-laden spacecraft to the outer planets" is begging complacency from familiarity. We've done it a few times in the past, it's true. And it's worked those few times. That hardly is an "established method." The shuttle was an "established method of launch" prior to the Challenger disaster which NASA claimed would have a 1 in 100,000 failure rate. Now NASA says about 1 in 73 shuttle missions will fail on average. If you are boldly going where no man has gone before, NASA, you aren't "established" in anything.

Radiation Hazards of Plutonium-238

Isotopes of plutonium such as Pu-238 characteristically give 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 would not represent a significant health hazard, either. 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.

If an individual were to inhale plutonium dioxide particles of a sufficiently small size to be deposited and retained in proximity to living lung tissues, the alpha radiation could alter or kill nearby living cells. Over years or decades, the altered cells could become cancerous and form tumors in the lung. Additionally, some of this material could be dissolved in body fluids and transferred by the blood to be deposited in other organs, generally the liver and skeleton, with similar potential consequences. The ceramic form of plutonium used in RTGs, however, is not likely to shatter into fine particles that could be readily inhaled. Other exposure pathways, such as ingestion, contribute far less to health effects.

The ceramic form of plutonium dioxide fuel also has low solubility in water, so its migration in ground water and potential for uptake by plants is limited. The actual proportion of plutonium released from an RTG that could enter the food chain, if any, is small.

What's wrong here? This: upper-atmosphere incineration is a perfectly plausible possibility. It is only by denying that possibility that they can claim any reduced risk from capsule containment, external doses, or nuclear safety through clothing and unbroken skin. Inhalation is the danger here, NASA, inhalation from incinerated RTG's. Furthermore even if it lands largely intact, we all have broken skin on occasion and do not all wear full-body clothes all the time. Someone should tell NASA this.
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 in to humans, are extremely inefficient.

This is flat-out wrong. First of all, grammatically, they say in the first sentence that this is "a common misconception." What they go on to say is that it is not a misconception at all but rather, they claim they will not disperse the plutonium that way -- "the important point is that is must be in a form that enables environmental transport and intake by humans." So what they actually argue in the paragraph just cited is that they will not disperse the plutonium in a manner which will allow intake by humans --NOT that there are any misconceptions about the hazards of plutonium! These are two very different points!

In fact, NASA can do nothing to ensure prevention of distribution of the plutonium in just about the most efficient means possible short of clinical inhalation or injection -- which of course, the government actual did in the 40's and 50's. NASA has not, can not, and will not be able to guarantee that the RTG's will not incinerate in a shallow descent to Earth, will not be hit by one of the millions of pieces of space debris that they have already placed in Near Earth Orbit on previous missions, and will not be blown to smithereens in a launch explosion. Yes, they have strived to reduce the risks on all of these things. But the one thing they could have done to eliminate the risks they have not done -- which is, of course, to not use plutonium in the first place. Why accept a level of risk at all when the plutonium is absolutely not "mission critical"?

Plutonium has no place in space.

And no place on Earth, either. Stop manufacturing this junk.
Related pages at this web site:
Stop Cassini Home Page
No Nukes In Space! Not now, not ever.
Space Debris Home Page
A series of articles on this shameful problem.
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First placed online February 7th, 1997.
Last modified June 5th, 1997.
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