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[Phys-l] textbook follies (was: rocket science)



I was flipping through Halliday & Resnick
_Fundamentals of Physics_ second edition (1981).
On page 262 I found a version of the orbital rendezvous problem,
analyzed as an example.

The analysis is terribly wrong, several times over:
a) It is diametrically wrong as to the direction of impulse required.
b) It is qualitatively wrong as to the effect of an impulse, suggesting
that it changes position (as opposed to merely changing momentum), in
violation of the most basic conception of Newton's 2nd law.
c) It is quantitatively wrong as to the relative position of the
spacecraft after the indicated 1.1 hour time lapse, even if you
correct item (a).
*) additional errors, arguably independent of the previous errors,
but perhaps not independent.

To be fair, the analysis does mention some correct physics, notably
the need to get into a lower, faster orbit ... it just doesn't have
the slightest notion of how to achieve that.

You could argue that the analysis is dimensionally correct ... but
there is more to physics than dimensional analysis.

Basically, the analysis is a frightful example of plug-and-chug. It
takes some formulae that could have "some" role to play in a correct
analysis, and then plugs numbers into the formulae with no discernible
regard to the actual _physical_ significance.

I know this is a somewhat counterintuitive problem, but one would
think that after the harsh learning experience of Gemini 4, people
would be a little more careful.