keithl@vice.UUCP (Keith Lofstrom) (12/01/83)
I mostly agree with Lew Mammel's comments on Sundiver ( I liked Startide
Rising much better ), but I couldn't let his comment on solar buffeting
go without comment.
If the density is 1e-6 g/cm3 (though it sounds too high), that is about
0.001 that of the Earth's atmosphere. Aerodynamic forces are proportional
to the density times the relative wind velocity squared; the solar velocities
would only have to be 30 times higher for an equivalent force. Hurricane
velocities in the Earth's atmosphere are around 100 m/sec; an indication of
the solar velocity scale is the solar wind, which comes off the sun at
>300 Km/sec! For this crude analysis, the buffeting forces would be
9,000 times greater than an Earth hurricane!
Of course, the real situation is dependent on the velocities in the deeper
layers of the Sun, the actual turbulence, and the "wind shear". The actual
buffeting could be orders of magnitude larger or smaller, but the important
point is that even a "vacuum" can have a strong wind if it moves fast enough.
The Sun is a powerful machine...
--
Keith Lofstrom
uucp: {ucbvax,decvax,chico,pur-ee,cbosg,ihnss}!teklabs!vice!keithl
CSnet: keithl@tek
ARPAnet:keithl.tek@rand-relaylew@ihuxr.UUCP (Lew Mammel, Jr.) (12/03/83)
I finished reading Sundiver over the weekend and I have a few bones to pick with Brin's solar physics. First, he depicts the chromosphere as being rather more substantial than it is. He has the ship being buffeted by turbulence and being obscured by filaments. Actually, the chromosphere has a density of less than 1e-6 g/cm3 - laboratory vacuum level. Second, he depicts the spicules as being a feature of the photoshpere. They actually rise above the chromosphere and have a length scale equal to the thickness of the chromosphere, about 10,000 km. He has the people (and others) in the ship looking down on them as though they were looking at an earth based photo of the sun.. Even if you displace a spicule so that its base was in the photoshpere, the ship's entire field of view would be encompassed by that single spicule. I thought these were pretty basic misconceptions to be perpetrated by someone with a Ph.D. in Astrophysics. I don't think it's necessarily true that Brin holds these misconceptions himself, but I'm hard put to make up excuses for him. I'm no authority myself, mind you, but all you have to do is look this stuff up and keep your length scales in mind. I happen to have a copy of "The New Sun", a NASA publication summarizing the solar findings of Skylab. I also have a problem with his "refrigerator laser", although I'm more inclined to grant poetic license here (I'm not sure Brin applied for one, though) Anyway, as Brin notes in the book, the laser has an extreemly high effective temperature. This begs the question of how to pump heat out of the ship, since you have to raise its temperature (schematically speaking) to that of the laser. This is just as hard as pumping to the solar atmosphere. I posted a comment a while ago comparing the sundiver refrigeration to the "gas refrigerator" based on an absorption cycle. On reflection I think the laser is incompatible with this scheme. It is effectively an "entropyless" sink. That is, running it is equivalent to doing work. As I said, using it to "dump heat" begs the question of how to drive the laser. As far as the story goes, I thought it was a typical SF potboiler, even if the plot machinations were intriguing enough to hold my interest. I thought the solarians were a little silly. Brin's pastoral metaphor was rather uninspired. They could have been fun, though, but he never went anywhere with them. Maybe in "Startide Rising" ... ? Incidentally, for some reason, I couldn't help picturing Culla as Admiral Ackbar (the reddish brown bug-eyed guy with the white uniform) in ROTJ. Ok, Sundiver fans, tune up those x-ray flame lasers. I'm ready! Lew Mammel, Jr. ihnp4!ihuxr!lew