From Launch to Flyby

The current risks for Cassini

by Russell D. Hoffman

Today, the significance of Cassini is something that concerns the world's future far more than its past; this is not something that is "behind us now". Furthermore, if an injustice has indeed been done to the public (and I believe the STOP CASSINI movement has shown quite clearly that that has happened), it is never too late to at least set the record straight. Most people appreciate the danger of letting wrongs go unpunished, undetected, and unspoken.

But worse still, is that the bigger crime does not really concern Cassini at all, it concerns the militarization of space, and Cassini's nuclear payload has held open a floodgate in that regard. We all wish to support space exploration. But our dreams of space colonization are NOT being fulfilled by the current policies of NASA. More public support is not what NASA needs right now. More public control would be a better first step. Then, I'm sure appropriate levels of public financial support will also come. But first, NASA must be reigned in.

On August 18th, 1999 Cassini is scheduled to do a flyby of Earth, in which it will pass less than 800 km from the surface of the Earth, at a speed of over 42,000 miles per hour. Originally it was scheduled to fly just 500 km above Earth, but some time after the anti-Cassini side pointed out that the atmosphere, in the event of a solar flare (which are not entirely predictable) might actually go out that far, NASA raised the flyby height to 800 km. (We don't know if our voice had anything to do with the altitude change, we only know the order of the events).

Cassini will do this maneuver -- the Earth flyby -- for what is known as a "gravity assist", which imparts additional relative speed ("kinetic energy" or "inertia") to the probe for the final flight out to Saturn, its final destination. The theory of how this maneuver works and why it is necessary is well understood by the physicists involved, and there is little doubt that it can be reasonably accurately calculated.

However, whether it can be accurately executed is another matter entirely. Any mistake, be it from a miscalculation of the trajectory to a malfunction of the equipment due to poor workmanship (it happens) or a collision with interplanetary space debris, can put the probe on a collision course with Earth, which can have dire consequences. This viewpoint is held by many responsible and qualified scientists who stake their reputations upon their every word (as do we all). The full potential consequences of such an event should concern us all. This is no time to be turning a blind eye. Deaths from leukemia and lung cancer (the primary health effects from vaporized Pu 238) are slow, premature, painful, tragic and degrading. This is what the efforts against Cassini seek to avoid. We are not against space exploration and certainly not against science. Indeed it is seeing honorable scientists be silenced on this issue that irks many of us most of all.

There is nothing inherently dangerous in a flyby maneuver. It is only because Cassini carries such vast quantities of Plutonium that it is dangerous. NASA could have avoided the danger by using a solar-based power source. There is no doubt that either now or in the very near future this mission could have been nearly, or even completely nuclear-free. Even many, if not all, of the "RHU's", the small heater units, could probably have been replaced with solar parabolic heat sources. Sure, the sun is far away from Saturn and Saturn gets only about 1% of the light that Earth gets. But look at the "plus" side: The sun is nearly a million miles in diameter, its mass is 99.86% of the mass of the entire solar system, and it is a sustained thermonuclear fusion reaction producing temperatures in the corona as hot as 3,600,000 degrees F (2,000,000 degrees C).

There's enough energy being put out by THAT nuke, which is a comfortable 92.9 million miles away from Earth, to create nearly all the light and heat we have here on Earth. Saturn, at less than 10 times our distance from the sun, gets enough solar energy to power NASA's little science experiment. There were, are, and will always be, solar solutions for missions as far out as Saturn, and probably quite a bit further.

To have avoided the flyby maneuver, NASA would have needed either more thrust available at takeoff, or a lighter payload, either of which could (in theory) be converted into more additional speed for the probe as it circles the sun and does its flybys of Venus. The Titan used to launch Cassini is our most powerful operational rocket, so more thrust was not readily available (Saturn 5's are out of service), but the number of experiments might have been reduced, which would have been in keeping with NASA's "faster, smaller, cheaper" philosophy. There were alternatives to Cassini and even now, there are alternatives. Avoiding the flyby maneuver would have been possible, but far better would have been to avoid the danger by eliminating the RTG's and RHU's from the probe in the first place. Then, the flyby would not be dangerous even if it did fail.

And the flyby is not the only danger being posed by Cassini. Regarding the Cassini flight path, even a malfunction AFTER the Earth "swingby" (another name for the "flyby" or "gravity assist") could in fact result in a collision with Earth at a later date, perhaps as much as 1000 years (or more) later. So this poison pill is NOT "past history"! Things we do now can make a difference.

For reference, see NASA's own 1995 Environmental Impact Statement for the Cassini Mission. To be fair, one can add that NASA's calculations do "tend" (NASA's word) to indicate a failure would NOT cross Earth's path if it occurred after the flyby, but that is hardly a definitive conclusion. It is impossible to calculate the exact trajectory of a lost probe. Furthermore, the same paragraph of the 1995 NASA EIS clearly points out that "failures on legs targeted toward Earth or Venus" (that is, prior to the final Earth flyby) "would tend to result in spacecraft trajectories that remain in the vicinity of Earth's orbit". The page number is B-4, first paragraph.

Thus, if Cassini goes dead, like the communications satellite Galaxy 4 did recently, it will pose a threat to Earth for centuries to come. And, if it goes dead and we can no longer communicate with it, it is too small and going to fast to be found again and recovered. We will simply have to leave the speeding hunk of junk out there on its own and hope for the best. This is proper science? There were, and are, safe alternatives to this madness.

Cassini remains at this time, a threat to humanity on Earth. It should never have been launched, and NASA should be instructed to redirect the probe into a trajectory that will cause it to fall towards the sun and be engulfed there. Launching plutonium into outer space will NEVER be a proper disposal method because of the inherent risks involved at launch (not to mention the expense), but as long as this particular pile of poison is past that point, we might as well keep it there. While we still are able to communicate with it at all (we could loose that ability at any time), we should direct it to use it's remaining fuel in such a way as to slow it down and cause it to fall into the sun.

Cassini should be destroyed, and if NASA won't undo its dirty deed, then I have no choice but to recommend that NASA should be dismantled, and a new agency, one truly dedicated to the peaceful exploration of space (and the peaceful observation of Earth from space) for the benefit of all humanity, be resurrected in its place.

Written May, 1998 by
Russell D. Hoffman

Note: Numerical values for the sun and solar system distances are based on The New York Public Library Science Desk Reference, 1995 edition.


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First published online June 15th, 1998.
Last modified September 21st, 1998.
Webwiz: Russell D. Hoffman
Copyright (c) Russell D. Hoffman