Re: SPACE: Cassini Mission Consequences

Richard Plourde (rplourde@andesign.mv.com)
Mon, 22 Sep 1997 13:00:16 -0400


At 06:23 PM 9/21/97 -0500, Eliezer S. Yudkowsky wrote:

>As a simple example: How can the chances of the probe
malfunctioning be a
>million to one? Do you really believe NASA on this one?

I don't think that the million-to-one estimate refers to a generic
malfunction of the probe. I think that it refers to the specific
malfunction of a course error during a specific time window of the
mission. That estimate, for example, explicitly does *not*
include launch failure, where re-entry friction does not represent
a factor.

A course error during that specific window-of-vulnerability would
represent a malfunction, while only a very small set of possible
course errors would result in a high-speed re-entry. From space,
the earth is a very small target. The velocities involved exceed
earth escape velocity, and so "decaying orbit" considerations
don't enter into the calculations.

I don't know the algorithm or the data used to calculate the
million-to-one estimate. The "roundness" of the number (a million
and not 500,000 or 2 million) leads me to suspect that the
algorithm involved inequalities, and represents a "not to exceed"
value rather than an exact value. When considered from the
perspective of the entire mission profile, it sounds pessimistic,
and not optimistic, to me.

-R

Richard Plourde .. rplourde@andesign.mv.com

"The word is not the thing, the map is not the territory"
http://www.crl.com/~isgs/isgshome.html
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