Re: Proof that macintosh is better than VMS

On Mar 13, 12:40 pm, koeh...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (Bob
Koehler) wrote:
In article <88a389f1-7231-4f3d-b3f9-7c996b10d...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, AEF <spamsink2...@xxxxxxxxx> writes:

Even if it fails to be exact, certain aspects will survive. NASA still
uses Newtonian gravity to calculate orbits. There is no need to use GR
for that.

NASA's Messenger mission might not orbit Mecrury so well without some
relatavistic considerations. After all, Mercury's orbit of the
Sun disagrees with Newton, you have to bring in GR to get it right.

I assume you mean getting to Mercury, not orbiting it. Orbiting it
doesn't require GR.

Well, all the planets' orbits disagree with Newton. Mercury's
disagreement is the largest and is the one that is most easily
measured. It means that the orbit precesses an extra 43 seconds of arc
per century. (Venus, 8.63; Earth, 3.84; Mars, 1.35; Jupiter, 0.06 --
Marion, Classical Physics, Table 8.2 on page 271)

Now how much difference does that make?

43"" 1 deg 1 radian 36000000 miles
-------- ----- -------- --------------- = 75 miles / year
100 yrs. 3600" 57.3 deg 1 radian

(assuming a circular orbit, which is rather wrong, but should be good
enough for this purpose)

Now, the spacecraft will approach Mercury along an orbit that is
tangential to Mercury's orbit. So that 75 miles is a timing issue.
Since the craft is going faster than Mercury, and Mercury goes approx.
36000000*2pi/88days=30miles/sec, that 75 miles amounts to probably
somewhere between 0.5 and 1 second. That's assuming a year since your
last careful observation of Mercury.

Is that enough to screw things up? I don't know enough about how the
calculations are done for the spacecraft's orbit, what it takes to
steer it, how precisely it must be steered, etc. You tell me. Does it
really get down to a matter of seconds? I don't know for sure.

For the most part, GR is not needed. The only use I know of outside of
basic physics research is GPS.

AEF
.

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