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Subject: SPACE Digest V12 #44

SPACE Digest                                      Volume 12 : Issue 44

Today's Topics:
        Ray tracing and optical simulation...
            Re: NASA's lobbying on the net
            Re: Investing in NASA
              Re:  SPACE Digest V12 #38
           Re: grim tidings for the future

Administrivia:

    Submissions to the SPACE Digest/sci.space should be mailed to
  [e-mail].  Other mail, esp. [un]subscription notices,
  should be sent to [e-mail], or, if urgent, to
             [e-mail]

----------------------------------------------------------------------

Date: 10 Jul 90 22:08:09 GMT
From: skipper![e-mail]  (Al Bowers)
Subject: Ray tracing and optical simulation...


Hi folks,

With all this talk about optical simulation and aberrations I thought
I'd dig up an old program that I had.  I got this from Sky &
Telescope, April 1981.  The original is in BASIC, but as most of the
machines I work on are FORTRAN literate, I made the conversion.  It
only works for parallel rays to the axis prior to the entrance pupil.
The example given is for a Schmidt corrector Cassegrain camera (see
the above mentioned issue of S&T).  Now all I need is a descrption of
a Ritchey-Chretien and we (here on the net) can bastardize it to see
how badly we (NASA) `screwed the pooch'.

The example input and output follows the program.

=============================================================================
      program ray
c  ...  ray trace program
c  ...
c  ...  algorithm from Sky and Telescope, April 1981
c  ...  fortran conversion by Al Bowers, Jul 06, 1990
c  ...
c  ... ep ray ht    = entrance pupil ray height
c  ... ep-s3 dist   = entrance pupil to surface 3 distance
c  ... k5           = 0, new optical system
c  ...              <> 0, uses the previously entered optical system
c  ...
c  ... cv           = curvature, reciprocal of the radius
c  ... th           = thickness or air space
c  ... index        = refractive index for the wavelength of light
c  ... skode        = surface code
c  ...              = -1, for a plane
c  ...              = 0, spherical
c  ...              = 1, aspheric, program will ask for more if selected
c  ... surfn0       = surface number
c  ...
c  ... conc         = conic constant
c  ...              > 0, oblate spheroid
c  ...              = 0, sphere
c  ...              = 0>-1, ellipsoid
c  ...              = -1, parabola
c  ...              < -1, hyperboloid
c  ... asph4,6,8,10 = coefficients of even powers of distance from optic axis
c  ...
      dimension l(20,8),k(20),y(20)
      real l,l1,l2,m1,m2
      do 80 i=1,2
      do 60 j=1,8
      l(i,j)=0
  60  continue
      k(i)=0
  80  continue
      l(1,3)=1
      l(2,3)=1
 100  print(6,*) 'enter ep ray ht, ep-s3 dist, and k5'
      read(5,*) y(2),l(2,2),k5
      if(k5.ne.0) goto 260
      print(6,*) 'enter cv, th, index, skode, surfn0'
      do 230 i=3,20
      read(5,*) l(i,1),l(i,2),l(i,3),k(i),s1
      if(k(i).le.0) goto 200
      print(6,*) 'enter conc, asph4,6,8,10'
      read(5,*) l(i,4),l(i,5),l(i,6),l(i,7),l(i,8)
      if(l(i,4).le.0) goto 200
      l(i,4)=l(i,4)-1
 200  if(s1.ne.0.) goto 230
      l5=i
c  ...  l5 = last surface number
      goto 240
 230  continue
 240  if(l(3,3).eq.0) goto 1160
      do 250 m=1,l5
 245  l(m,4)=l(m,4)+1
 250  continue
 260  k(i)=-1
      k(2)=-1
      l(1,2)=1.000000e+20
      y(1)=0
      y2=y(2)
      z=0
      m2=1
      t1=0
      m1=1/sqrt(1+t1*t1)
      l1=t1*m1
      g1=m1
      j=2
 360  d=(l(j,2)-z)/m1
      y1=y2+l1*d
      j=j+1
      if(k(j).ge.0) goto 460
      y2=y1
      z=0
      l2=z
      m2=1
      g3=m1
      goto 850
 460  t1=l(j,1)*(1+(l(j,4)-1)*m1*m1)
      t2=m1-l(j,1)*y1*l1
      t3=l(j,1)*y1*y1
      t4=t2*t2-t1*t3
      if(t4.le.0.) goto 1070
      g3=sqrt(t4)
      if(t2.ge.0.) goto 540
      g3=-1.*g3
 540  d1=t3/(t2+g3)
      y2=y1+l1*d1
      z=m1*d1
      if(k(j).lt.0) goto 850
      if(k(j).eq.0) goto 830
      m2=1
      i=0
 610  t1=y2*y2
      t2=1-l(j,4)*l(j,1)*l(j,1)*t1
      if(t2.le.0.) goto 1090
      t3=sqrt(t2)
      t4=l(j,1)/(1+t3)
      t5=l(j,1)/t3
      s=z-((((l(j,8)*t1+l(j,7))*t1+l(j,6))*t1+l(j,5))*t1+t4)*t1
      f=(((10*l(j,8)*t1+8*l(j,7))*t1+6*l(j,6))*t1+4*l(j,5))*t1
      f=f+t5
      l2=-1.*(y2*f)
      g3=l2*l1+m1
      d1=d1-s/g3
      y2=y1+l1*d1
      z=m1*d1
      t6=abs(s)
      if(t6.le.1.0000e-07) goto 850
      i=i+1
      if(i.le.1000) goto 610
 790  print(6,*)'aspheric test failed in trace ',k2
      goto 1160
      t1=y2*y2
      y(j)=y2
 830  l2=-1.*l(j,1)*y2
      m2=1-l(j,4)*l(j,1)*z
 850  t1=y2*y2
      y(j)=y2
      if(j.eq.l5) goto 1110
      g2=l2*l2+m2*m2
      r1=l(j-1,3)/l(j,3)
      if(r1.ge.0.) goto 950
      g1=-1.*g3/g2
      r=1.
      g4=g1+g1
      goto 1040
 950  r=r1
      t1=r*g3/g2
      t2=(r*r-1)/g2
      t3=t1*t1-t2
      if(t3.le.0.) goto 1090
      g1=sqrt(t3)
      if(t1.ge.0.) goto 1030
      g1=-1.*g1
1030  g4=g1-t1
1040  l1=r*l1+g4*l2
      m1=r*m1+g4*m2
      goto 360
1070  k2=-1.*j
      goto 790
1090  k2=j
      goto 790
1110  print(6,*) 'curvature      thickness     index         y'
      do 1140 i=2,l5
      print(6,1130) l(i,1),l(i,2),l(i,3),y(i)
1130  format(4f14.7)
1140  continue
      goto 100
1160  stop
      end
=============================================================================

Following is a sample run.  The lines that are typed in by the user
(_YOU_) are followed by a `<='.  All others are from the program.  To
terminate the run simple type in zeros for all prompted inputs.

=============================================================================

 enter ep ray ht, ep-s3 dist, and k5
107.39  0  0                                              <=
 enter cv, th, index, skode, surfn0
.00005807  9.525  1  3                                    <=
 enter conc, ashp4,6,8,10
0  -1.87279e-09  -7.97425e-15  3.13145e-21  0             <=
0  536.43  1  -1  4                                       <=
-.00181663  -149.123  -1  1  5                            <=
 enter conc, ashp4,6,8,10
1.0943768  0  0  0  0                                     <=
-.00181663  225.864  1  0  6                              <=
0  0  1  -1  0                                            <=
 curvature     thickness     index         y
      .0000000      .0000000     1.0000000   107.3899990
      .0000581     9.5249996     1.4632000   107.3899990
      .0000000   536.4299920     1.0000000   107.4011300
     -.0018166  -149.1230010    -1.0000000   108.3070670
     -.0018166   225.8639980     1.0000000    49.6727600
      .0000000      .0000000     1.0000000      .0064888
 enter ep ray ht, ep-s3 dist, and k5
85  0  1                                                  <=
 curvature     thickness     index         y
      .0000000      .0000000     1.0000000    85.0000000
      .0000581     9.5249996     1.4632000    85.0000000
      .0000000   536.4299920     1.0000000    84.9996337
     -.0018166  -149.1230010    -1.0000000    84.9692001
     -.0018166   225.8639980     1.0000000    38.8188095
      .0000000      .0000000     1.0000000     -.0022316
 enter ep ray ht, ep-s3 dist, and k5
60  0  2                                                  <=
 curvature     thickness     index         y
      .0000000      .0000000     1.0000000    60.0000000
      .0000581     9.5249996     1.4632000    60.0000000
      .0000000   536.4299920     1.0000000    59.9945297
     -.0018166  -149.1230010    -1.0000000    59.5428047
     -.0018166   225.8639980     1.0000000    27.1187400
      .0000000      .0000000     1.0000000     -.0025940
 enter ep ray ht, ep-s3 dist, and k5
0  0  0                                                   <=
 enter cv, th, index, skode, surfn0
0  0  0  0  0                                             <=
=============================================================================

Just thought it might be of interest.  Another opinion...

--
Albion H. Bowers  [e-mail]  ames!elxsi.dfrf.nasa.gov!bowers

------------------------------

Date: 10 Jul 90 02:14:59 GMT
From: bfmny0![e-mail]  (Tom Neff)
Subject: Re: NASA's lobbying on the net

I wish I could agree with Nick on this, but a lot of the stuff that
could be considered pro-NASA lobbying from people at Lewis, Ames etc,
also contains bits of information (sometimes carefully selected!) about
what's going on, and I would hate to lose that.  One might like to be
able to say "only factual postings you humps," but in practice I think
NASA people would just clam up completely, and that'd be no fun.

Also keep in mind that many of the non-NASA postings are from places,
like observatories, that do NASA related work -- are they wrong too?

I'm afraid that if we removed ALL interested parties from the debate,
and boiled the active membership down to the usual collection of Silicon
Valley net-gnomes and Waco, Texas hobbyists, the fun would be gone.  Go
look at CompuServe SPACEFORUM some time.  "A Libertarian Space Program,
Part 17 of 29, by Luigi Guacamole Jr."  "DERE SYSOP I HERD THAT HUBLE
WAS HIT BY A UFO??"  "Hubble So-called 'Defect' a Communist Media
Conspiracy?"  etc.  Real enlightening stuff.

So, although I wish some of these people would take a break from the net
and use the time to finish remedial 6th grade spelling, on the whole I
want to hear from EVERYONE, including people at NASA.  The ones who
aren't afraid to take up the cudgels for the agency in *this* crowd are
actually the good guys.  It's the silent paper pushers I worry about.
--
"Just when we finally got good at this, we    \_i_/   Tom Neff
run out of planets." - a Voyager scientist   --[o]--  [e-mail]

------------------------------

Date: 10 Jul 90 12:38:16 GMT
From: usc!samsung!umich!umeecs!itivax!vax3.iti.org![e-mail]  (Allen W. Sherzer)
Subject: Re: Investing in NASA

In article <[e-mail]> [e-mail] (David Anderman) writes:
>If investing NASA is not a good idea, where should we invest?

SSI

  Allen
|                          |      In War: Resolution                      |
| Allen W. Sherzer         |      In Defeat: Defiance                     |
|   [e-mail]            |      In Victory: Magnanimity                 |
|                          |      In Peace: Good Will                     |

------------------------------

From: [e-mail]
Date:     Tue, 10 Jul 90  10:46:55 EDT
Subject:  Re:  SPACE Digest V12 #38

> >And another thing, HST has not failed!!!!!!!!  I am tired of hearing
> >this.  We have every reason to beleive in the end most if not all
> >of the science will be done.
>
And I am tired of the people who keep defending the HST, and protecting
whoever is responsible for what happened (just what did happen? did any-
thing actually happen?). The HST was supposed to provide VISUAL images
of the universe of a kind, and at a resolution of detail, never before
seen by man on Earth. NOBODY on the ground really gives a damn about
all of the esoteric science that is going to get done (is it realy going
to get done? can the instruments really make use of sloppy, fuzzy, shaky
images?). I mean NOBODY from among the general public. They wanted to
see spectacular new images of galaxies, distant stars, perhaps even "hot
planets." Instead, they are going to see nothing. And they are gonna be
pissed. They are going to scream bloody murder before they allow any
more money to be "thrown away on space garbage." Hmmm? Perhaps the Hubble
did succeed after all, if its real purpose was to ring the death knell
for civilian NASA.

Or perhaps Hubble really is just a third generation "KH"-type spy satellite,
and it is up there right now working away just the way it was supposed to,
and all the astro-science bull was just a smokescreen. After all, with all
of the stupid things that we the people have been told went wrong with the
$1.5 billion project, even the credulity of the 10-year-olds in this coun-
try is being strained to the breaking point. Hell, even 10-year-olds in
rocket clubs around the country wouldn't have overlooked the things that
the high-level engineers and scientists at the Hubble-bubble are suppos-
ed to have overlooked.

And now they're trying to sell the idea that the Hubble "might" get
fixed in mid-1993, or if that "don't get it" then in 1996. Does anybody
at the Hubble-bubble really expect the american "live-for-the-micro-
second public to sit still and wait three or even six years for the fix
to go up. It is to laugh.

                                              AZM@NIHCU

------------------------------

Date: 10 Jul 90 16:29:06 GMT
From: hao.hao.ucar.edu![e-mail]  (Derek Buzasi)
Subject: Re: grim tidings for the future

In article <[e-mail]> [e-mail] (George William Herbert) writes:
#In article <[e-mail]> [e-mail] (Greg Titus) writes:
#>
#>Doesn't matter what they call it.  They're all experimental.
#>By the time the entire shuttle program is ended, the SMEs will
#>still not have been run for as much aggregate time as the
#>engines on a Boeing 747 on a *single* New York to Tokyo round
#>trip.  Experience with the things NASA flies was, is and will
#>remain for a long time very limited compared with what we know
#>about more mundane objects.
#
#While I agree in general, your example is in error...  The engines run
#8 minutes each in a flight, or 24 engine-minutes.  With the testing that is
#run outside of flights, there are about three times as many off-flight engine
#hours as on-flight, or about 96 engine-minutes (1.5 engine-hours) per flight.
#This totals to about fifty flight hours so far, and with fifty to a hundred
#shuttle flights ahead, another seventy five to one hundred fifty hours of
#operation.
#
#Now, while a 747 has four engines, i doubt that it takes 25 hours to fly
#from New York to Tokyo...
#
#-george

Ah, but round trip, like the man said?

--
******************************************************************************
Derek Buzasi                     *    "History is made at night.
High Altitude Observatory        *     Character is what you are in the dark."
[e-mail]                 *             -- Lord John Whorfin

------------------------------

End of SPACE Digest V12 #44
*******************