Dear Sir,
Thank you for your email (shown below) concerning Cassini's possible fate, and your suggestions for updating my web site, which, however, will not be followed.
Unplanned trajectory changes from outgassing fuels, explosions, impacts, etc. could each or all alter the angle and velocity of the probe, as well as cause, by these changes in trajectory and speed, unplanned gravitational flybys, which could just as well slow Cassini down as speed it up.
A rogue nation or faulty computer program or improper conversion from meters and centimeter to yards and inches could result in instructions to Cassini to use up all its remaining fuel in such a way as to slow itself down so it could circle Saturn once and aim straight (in a manner of speaking) towards Earth.
So these could all cause Cassini to be a hazard to Earth at some time in the future were it to go dead today, tomorrow, or some years from now.
You obviously haven't given the matter all that much thought -- nor have you ever (it would appear) read the Environmental Impact Statement published by NASA (available online at their web site, with selections from it published at mine). These matters are discussed there briefly, and these matters are also already discussed at my web site, and this is an example of why the web site is, should be, and will remain, online.
I find your misuse of the word "impossible" almost fascinating. "Unlikely" is actually the best you can do. I'll admit these scenarios are not the most likely results. But then who would have guessed that NASA's Mars probes would fail immediately after Cassini's flyby, including an orbital insertion failure (which is much like a flyby)?
Cassini and Earth meeting some day in the future is far from impossible, even today. But you are probably comforted knowing it won't very likely be our generation which suffers. It could take Cassini 100 years to impact Earth. Or 1000. The half-life of plutonium 238 is 87.75 years, which means in 100 years nearly half would still be left, and the half-life of Pu 239, of which there is a not-insignificant quantity on board as well, is over 24,000 years.
After Cassini arrives in the vicinity of Saturn, the probe will circle Saturn and its moons, and will be prone to being smashed by the debris in the debris fields around Saturn, and will have been slowed from this "escape velocity" you claim it's reached (and you may be right, in some limited definition, that such a velocity has been reached, but my point is, it doesn't matter. There are other considerations you are ignoring.) Once slowed down, or especially while in the process of slowing down, it might be misdirected into a trajectory which would later impact Earth.
To prevent Cassini from ever possibly impacting Earth, it should be SMASHED INTO SATURN IMMEDIATELY UPON ITS ARRIVAL, or perhaps better, its trajectory should be altered to take fullest advantage of the claim you've made (in other words well away from one which will go anywhere near Saturn or any other planet or asteroid belt or any other known object).
Thank you again for your email.
Sincerely,
Russell Hoffman
Stop Cassini webmaster
Carlsbad, California, USA
At 04:02 PM 2/1/01 +0000, you wrote:
Hello.
Your anti-Cassini website is still online.
It contains a misleading statement -
"NASA in particular is ignoring the fact that ANY accident can leave the probe in an orbit around the solar system that might later intersect ours -- even after the flyby, we might still be "attacked" by this probe!" This is incorrect.
Cassini has now reached solar system escape velocity.
Any malfunction on the spacecraft will cause it to fly by Saturn and head for the stars.
It is impossible - not just improbable - for Cassini to "turn around" and impact Earth.
Please remove this statement from your website.
Thank you!
Edwin Kite
Newcastle-Upon-Tyne, England
rhoffman@animatedsoftware.com