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Subject: SPACE Digest V12 #618

SPACE Digest                                     Volume 12 : Issue 618

Today's Topics:
          Re: HST images via anonFTP and SPAN/HEPnet
            Re: sts35 orbital data
           NASA Prediction Bulletin Format
              Re: Photon engine
          Re: HST images via anonFTP and SPAN/HEPnet
             Magellan terminology

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

Date: 1 Dec 90 20:50:52 GMT
From: usc!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!ohstpy![e-mail]
Subject: Re: HST images via anonFTP and SPAN/HEPnet

In article <[e-mail]>, [e-mail] (Doug McDonald) writes:
> In article <[e-mail]> [e-mail] (Paul A. Scowen) writes:
>>If the Saturn image you're all talking about is the one that was distributed
>>on the first GTO tape then only the first plane has anything on it: they only
>>used one WFPC frame to take the shot.  That may make extracting it easier for
>>the dabbler.
>>
> It is not difficult to extract all four. What is, apparently,
> at least as far as I can tell, is figuring out EXACTLY where each one
> is on the sky. I have tried and failed to do so by using the published
> FITS papers. There are some parameters that are not listed in the papers.
>

   Not surprising, FITS really only specifies the image format and
standardizes the header keywords that tell programs how to decode the data
records. Very few header keywords are "required", some are "recommended" (and
are standard out of expediency, and they are sensible), the rest are up to the
person creating the file.  This lack of a fixed lexicon of header cards is on
purpose, it endows the format with a fair degree of flexibility ("Flexible
Image Transport System...").  Each observatory and reduction package (VISTA,
IRAF, Figaro, MIDAS, you name it) has their own families of specialized
keywords.  HST is no exception.  You'll have to go to the documents for the
WF/PC to get the meanings of most of the header keywords.  Though the on-line
comments do give most of the info, the fine details are in the relevant
documents.  You'll have to write to STScI for those.

  Please bear in mind that this HST image distribution was intended for people
who have HST time assigned, and was set out in an anon-ftp space with the
assumption that those for whom they are primarily intended already have both
the basic knowledge and/or relevant documents at their disposal. Recreational
access to these images by the interested members of the general public is
incidental.

> DOES ANYBODY KNOW HOW TO DO THIS? If so, please tell me!
>
> Doug McDonald

Hmm, OK Doug, let me see.  You could mean one of 2 things.

1) Where the HST was pointed when the image was taken?

      That's in the FITS header.  Here's the section of the Saturn
      header that has that info

RA      =        0.2910366E+03 / right ascension of the target (degrees)
DEC     =       -0.2201969E+02 / declination of the target (degrees)

      there are other header cards which give more detailed pointing info,
      like:

PSANGLV3=        0.2492861E+03 / position angle of v3 axis of HST
RTASCSUN=  0.1550832672119E+03 / right ascension of the sun
DECLNSUN=  0.1035161304470E+02 / declination of the sun
EPOCHSUN=        0.2000000E+04 / epoch of the sun
MTFLAG  =                    F / moving target flag
EQRADTRG=        0.6033000E+05 / equatorial radius of target
FLATNTRG=        0.1076209E+00 / flattening of target
NPDECTRG=        0.8354000E+02 / north pole declination of target
NPASNTRG=        0.2236000E+03 / north pole right ascension of target
ROTRTTRG=        0.2840832E+09 / rotation rate of target

   etc.  You'll have to consult the relevant HST FITS documents for
   details on what all this means.  I haven't got a set handy, or
   I'd pass along the document numbers.

2)  How to position the 4 images so that they form one 1600x1600 image?

  (this is not definitive, or official...)

How to Merge WF/PC Images Into One Large Image
==============================================

   The key point to remember is that the fiducial pixel is always the first
pixel of each image.  All four fiducial pixels must surround the
"four-corners" intersection of the set.  This means that after the first image
is laid down, the next three must be first rotated by 90, 180, and 270 degrees
(respectively) before merging into the full 1600x1600 image.  The origin is
set by the order in which the pixels were read out, hence the rotations, as
each CCD chip has to be positioned so that the on-chip amplifiers and shift
registers are on the outside of the mosaic).  This gives the odd appearing
order.

NB: the windows below are for WF images.  The PC images have different
    boundaries.  I don't know what the PC boundaries are yet.

Step 0:  Create a 1600x1600 array to hold the final merged image

Step 1:  Window each image to the sizes given below:

            Image 1:  nx=782 ny=772 x0=19 y0=29
            Image 2:  nx=788 ny=776 x0=13 y0=25
            Image 3:  nx=780 ny=776 x0=21 y0=25
            Image 4:  nx=782 ny=772 x0=19 y0=29

         This cuts out the residual flat-field crud between the images.

Step 2:  Translate the windowed images so that the origin of each
         image segment is [1,1] in array coordinates.  This step is
         to help keep the bookkeeping simple.  Another translation
         must follow the rotations (below) prior to merging the
         images.

Step 3:  Rotate the images to the correct orientation.  The sense
         the rotations are COUNTERCLOCKWISE.

            Image 1:  Theta = 0 degrees
            Image 2:  Theta = 90
            Image 3:  Theta = 180
            Image 4:  Theta = 270

Step 4:  Merge the images with the 1600x1600 array.  The origin of
         each image must correspond to these locations in the
         final grand array:

            Image 1:  X=801  Y=801
            Image 2:  X=25   Y=801
            Image 3:  X=21   Y=25
            Image 4:  X=801  Y=19

The final mosaic will look like this:

                 +-------+-------+
                 |       |       |
                 |   2   |   1   |
                 |       |       |
                 +-------X-------+
                 |       |       |                     Y
                 |   3   |   4   |                     |
                 |       |       |                     |
                 o-------+-------+     orientation:    +----> X

where "o" is the origin [1,1] of the 1600x1600 array, and "X" is the
four-corners point where the first pixel of each image segment must touch.
Given this, it is easy to see how the sense of each rotation goes, and the
amount of translation required.

The actual N-S/E-W orientation of the images depends on the rotation angle of
HST when the images were taken.  I haven't rummaged through the header info
enough to find out, but it is certainly not the usual North=Up/East=Left
orientation a priori.

Interested VISTA users can email for a .PRO procedure script that will
do the merger.  It is based on a more special purpose procedure written
by Jon Holtzman.

---------------------------------------------------------------------
Richard Pogge             |  Internet: [e-mail]
Dept. of Astronomy        |  Bitnet:   pogge@ohstpy
The Ohio State University |  Snail:    Columbus, OH  43210 USA
---------------------------------------------------------------------

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

Date: 1 Dec 90 14:34:05 GMT
From: nuchat!buster!lescsse![e-mail]  (Gary A. Morris)
Subject: Re: sts35 orbital data

In <[e-mail]> [e-mail] (Troy T. Pummill) writes:

>Could someone please post the new orbital elements for sts35....

These are the preliminary elements for launch at 0628 UCT on Dec 2,
1990.  A new set will be posted after we have get a post OMS burn state
vector, sometime Sunday morning.

This information and more was posted on Nov 27 in rec.ham-radio,
Message-ID: [e-mail], Subject: STS-35 Shuttle Amateur Radio
Experiment (SAREX).

--GaryM

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

Keplerian Element Set

STS-35
1 00035U          90336.32152778  .00031000  00000-0  22174-3 0    66
2 00035  28.4690 359.2943 0005720 246.6067 119.6564 15.71792660    23

Satellite: STS-35
Epoch time:      90336.32152778
Element set:     JSC-006
Inclination:       28.4690 deg          Space Shuttle Flight STS-35
RA of node:       359.2943 deg           Pre-launch flight profile
Eccentricity:     .0005720                   Keplerian Elements
Arg of perigee:   246.6067 deg         Launch:   2 DEC 90   06:28 UTC
Mean anomaly:     119.6564 deg
Mean motion:   15.71792660 rev/day                 W5RRR
Decay rate:       3.10E-04 rev/day^2      NASA Johnson Space Center
Epoch rev:               2

============================================================
Gary Morris                    Internet: lobster!lescsse![e-mail]
Lockheed (LESC), A22           UUCP:     lobster!lescsse!gamorris
Space Station Freedom          NASAmail: gmorris/jsc/nasa
Houston, Texas                 Internet: [e-mail]
N5QWC - PP/ASEL                Phone:    [phone]
--
Gary Morris                    Internet: lobster!lescsse![e-mail]
Lockheed (LESC), A22           UUCP:     lobster!lescsse!gamorris
Space Station Freedom          NASAmail: gmorris/jsc/nasa
Houston, Texas                 Internet: [e-mail]

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

Date: 1 Dec 90 22:23:42 GMT
From: ncis.tis.llnl.gov!blackbird![e-mail]  (TS Kelso)
Subject: NASA Prediction Bulletin Format


As a service to the satellite user community, the following description
of the NASA Prediction Bulletin's two-line orbital element set format is
uploaded to sci.space on a monthly basis.  The most current orbital elements
from the NASA Prediction Bulletins are carried on the Celestial BBS, (513)
427-0674, and are updated several times weekly.  Documentation and tracking
software are also available on this system.  The Celestial BBS may be
accessed 24 hours/day at 300, 1200, or 2400 baud using 8 data bits, 1 stop
bit, no parity.

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

Data for each satellite consists of three lines in the following format:

AAAAAAAAAAA
1 NNNNNU NNNNNAAA NNNNN.NNNNNNNN +.NNNNNNNN +NNNNN-N +NNNNN-N N NNNNN
2 NNNNN NNN.NNNN NNN.NNNN NNNNNNN NNN.NNNN NNN.NNNN NN.NNNNNNNNNNNNNN

Line 1 is a eleven-character name.

Lines 2 and 3 are the standard Two-Line Orbital Element Set Format identical
to that used by NASA and NORAD.  The format description is:

Line 2
Column     Description
 01-01     Line Number of Element Data
 03-07     Satellite Number
 10-11     International Designator (Last two digits of launch year)
 12-14     International Designator (Launch number of the year)
 15-17     International Designator (Piece of launch)
 19-20     Epoch Year (Last two digits of year)
 21-32     Epoch (Julian Day and fractional portion of the day)
 34-43     First Time Derivative of the Mean Motion
        or Ballistic Coefficient (Depending on ephemeris type)
 45-52     Second Time Derivative of Mean Motion (decimal point assumed;
           blank if N/A)
 54-61     BSTAR drag term if GP4 general perturbation theory was used.
           Otherwise, radiation pressure coefficient.  (Decimal point assumed)
 63-63     Ephemeris type
 65-68     Element number
 69-69     Check Sum (Modulo 10)
           (Letters, blanks, periods = 0; minus sign = 1; plus sign = 2)

Line 3
Column     Description
 01-01     Line Number of Element Data
 03-07     Satellite Number
 09-16     Inclination [Degrees]
 18-25     Right Ascension of the Ascending Node [Degrees]
 27-33     Eccentricity (decimal point assumed)
 35-42     Argument of Perigee [Degrees]
 44-51     Mean Anomaly [Degrees]
 53-63     Mean Motion [Revs per day]
 64-68     Revolution number at epoch [Revs]
 69-69     Check Sum (Modulo 10)

All other columns are blank or fixed.

Example:

NOAA 6
1 11416U          86 50.28438588 0.00000140           67960-4 0  5293
2 11416  98.5105  69.3305 0012788  63.2828 296.9658 14.24899292346978

Note that the International Designator fields are usually blank, as issued in
the NASA Prediction Bulletins.

--
Dr TS Kelso                           Assistant Professor of Space Operations
[e-mail]          Air Force Institute of Technology

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

Date: 1 Dec 90 23:03:06 GMT
From: swrinde!zaphod.mps.ohio-state.edu!van-bc!ubc-cs!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Photon engine

In article <[e-mail]> [e-mail] (John Roberts) writes:
>I can think of one exception to this rule. If you use a "pure" energy source
>such as antimatter, and if you have a certain mass budget for fuel plus
>reaction mass, then you get marginally more thrust by dedicating the whole
>mass to equal quantities of matter and antimatter, to be blasted out as
>photons, than by setting aside some additional normal matter as reaction
>mass...

Uh, the matter/antimatter reaction does not yield photons.  Not immediately.
If you are reacting matter and antimatter, what you are blasting out is
mostly either pions or muons, depending on the size of your engine.

Electron plus positron does yield gamma rays.  However, proton plus
antiproton is a much more complex reaction.  The usual immediate result
is pions, both charged and uncharged.  The uncharged ones decay pretty
immediately.  The charged ones last long enough that a small antimatter
engine can collimate them into an exhaust jet using a magnetic nozzle.
They then decay into muons; a big engine would end up collimating the
muons with its nozzle instead.  After a substantial delay (on the order
of a kilometer of travel at the energies involved), the muons too decay.

In the long run, everything ends up as gamma rays and neutrinos, but
fortunately for antimatter propulsion, a lot of that happens long after
the stuff leaves the engine.  Charged particles are *much* easier to
work with.
--
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| [e-mail]   utzoo!henry

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

Date: 1 Dec 90 15:35:27 GMT
From: julius.cs.uiuc.edu!ux1.cso.uiuc.edu!aries![e-mail]  (Doug McDonald)
Subject: Re: HST images via anonFTP and SPAN/HEPnet

In article <[e-mail]> [e-mail] (Paul A. Scowen) writes:
>If the Saturn image you're all talking about is the one that was distributed
>on the first GTO tape then only the first plane has anything on it: they only
>used one WFPC frame to take the shot.  That may make extracting it easier for
>the dabbler.
>
It is not difficult to extract all four. What is, apparently,
at least as far as I can tell, is figuring out EXACTLY where each one
is on the sky. I have tried and failed to do so by using the published
FITS papers. There are some parameters that are not listed in the papers.

DOES ANYBODY KNOW HOW TO DO THIS? If so, please tell me!

Doug McDonald

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

Date: Sat, 01 Dec 90 11:32:06 CST
From: "John Schultz" <[e-mail]>
Subject: Magellan terminology

I have a few questions about the terminology that Ron Baalke (thanks for the fi
ne info!) posts about Magellan.  What is the purpose of the star calibrations a
nd desaturations that he mentions?  I assume that the star calibration is used
to either reference the probe with Venus or with Earth (or maybe both).  As for
 the desaturation, I haven't the foggiest.

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
: John Schultz                      :Disclaimer : I *pay* for this -   :
: University of Missouri - Columbia :do you think the bureaucracy      :
: Bitnet   : [e-mail]  :cares what I say???               :
: Internet : [e-mail] (128.206.1.1)                 :
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
: Don't dream it, be it...  - Frank N. Furter, "RHPS"                  :
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

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

End of SPACE Digest V12 #618
*******************