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Subject: SPACE Digest V11 #596

SPACE Digest                                     Volume 11 : Issue 596

Today's Topics:
         Re: Bringing the HST down -- even possible?
Re: NASA announces next steps in Space Exploration Outreach Program (F
            Re: HST focus problem
         Re: human combustion, (Was Re: none)
         Re: Hubble Space Telescope Update - 06/28/90
        Re: The HST was risky from square one
           Re: NSS protests Chinese launch pricing
       Re: RE  Hubble Space Telescope Update - 06/28/90

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

Date: 30 Jun 90 03:56:09 GMT
From: cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Bringing the HST down -- even possible?

In article <[e-mail]> [e-mail] (Tim Maroney) writes:
>Everyone seems quite sure that the HST will not be brought down to the
>ground for repair.  Granted it's a very costly operation, involving two
>flights of the space shuttle.  My question:  Can it be done?  Does the
>HST have the standard shuttle satellite-retrieval handles? ...

Yes.  There is no problem, in principle, with the actual retrieval.

>...what would be the estimated cost of the whole repair
>operation?

Two dedicated shuttle missions.  (You won't be able to piggyback another
payload for a maximum-altitude mission, and HST fills the *whole* payload
bay for all practical purposes.)  New solar arrays, because I think the
existing ones cannot be re-furled for return.  (I would think the design
capable of it, but I have seen statements saying that it's not.)  A bundle
for fixing the mirror(s).  Another bundle, of very uncertain size, for
repairing equipment and perhaps structural damage done during reentry
and landing.  A vast array of overhead costs during (probably) a couple
of years of downtime.

I can't put numbers on all of this... but we're clearly talking about
a fair fraction of a billion dollars.  Repair in orbit, if practical,
would be very strongly preferred.
--
"Either NFS must be scrapped or NFS    | Henry Spencer at U of Toronto Zoology
must be changed."  -John K. Ousterhout |  [e-mail]   utzoo!henry

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

Date: 30 Jun 90 03:46:36 GMT
From: usc!venera.isi.edu![e-mail]  (Craig E. Ward)
Subject: Re: NASA announces next steps in Space Exploration Outreach Program (F

In article <[e-mail]> [e-mail] (Craig E. Smith) writes:
>
>    Speaking of history, if you compare space exploration with the
>European colonial expansion, which I think is a fair analogy....

Right so far (but beware of analogies: look to differences also).

>...expansion of English power was at least in part based
>on the plundering, and exploitation of these other colonies....

The part that played was very small.  The real reason English colonies were
stronger, and why most North Americans speak English, is that the English
sent families.  When England and France fought over the Northeast, the
English won primarily because the birth rate had put many, many more
Englishmen than Frenchmen on the continent.  (The Dutch didn't have many
colonies -- New Amsterdam became New York -- and many Germans were allowed to
emigrate because after 1714, the King of England was also Elector of
Hanover.)
--
Craig E. Ward <[e-mail]>     Slogan:    "nemo me impune lacessit"
USPS:    USC/Information Sciences Institute
    4676 Admiralty Way, Suite 1100
    Marina del Rey, CA 90292

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

Date: 30 Jun 90 05:33:47 GMT
From: uvaarpa!murdoch!fits![e-mail]  (Don Wells)
Subject: Re: HST focus problem

In article <[e-mail]>
    [e-mail] writes:
>[e-mail] (Greg S. Hennessy) writes:
>> [nice description of MEM, etc deleted]
>...spherical abberation will... produce radial variations in the shape of the
>PSF outward from the intersection of the optical axis with the image plane.
>...MEM methods would have a hard time with this...

And, in article <[e-mail]>
    [e-mail] (Kevin William Ryan) writes:
>...the spherical abberation... distortion function is shift-variant.

Essentially *all* real-world imaging systems are shift-variant at some
level, but that does not prevent deconvolution from being a valuable
technique in many important real-world cases in astronomy. The
question always is: how big is the effect? Each CCD of WFPC has a
field of only about 1.5arcmin at the Cass focus of the f/24(?)
2.4meter telescope.  I will be surprised if radial variation of the
geometrical image across 1arcmin proves to be a significant difficulty
for the deconvolution.  Anyway, computer power gets cheaper and
cheaper every year; shift-variant PSF deconvolution is not necessarily
impractical even now.

 [e-mail] (Kevin William Ryan) also referred to:
>...Standard Fourier techniques...

Astronomers make almost no use of simple *linear* deconvolution
techniques like Fourier division (Wiener filtering).  But *nonlinear*
deconvolution is standard procedure in some fields of astronomy,
especially radio astronomy, where state-of-the-art science depends
critically on deconvolution technology. The principal algorithms used
are variations on the CLEAN theme and variations on the Maximum
Entropy theme. These two general approaches to the problem are
complementary, suitable for different classes of target sources. I
assure you that the data analysis specialists at the STScI in
Baltimore are quite aware of the technology and literature of
non-linear deconvolution in astronomy.

and he also referred to:
>... certain spacial frequencies will not be recorded well...
> I suspect that the higher frequencies will be lost entirely...

It depends. If there is any sharp aspect to the impulse response, and
the reports make repeated references to a peak containing 10-20% of
the flux, then it will carry high spatial frequency information. Also,
the outer edges of the main mirror and the secondary are likely to
appear as circularly symmetric step functions in some portions of the
impulse response, depending on how you focus the telescope, and these
*edges* will contain much valuable high frequency detail that a
deconvolution algorithm can exploit. I suspect that it would be a good
thing for somebody to do a little study to find the optimum focus for
deconvolution purposes.

>   Finally, successful inversion requires a well-known distortion function.
>... it will be _hard_ to get an accurate reading of the mirror distortions.

(1) *Non-linear* deconvolution techniques are fairly insensitive to
moderate errors in the PSF estimation. (2) The sky has numerous point
sources in it, so that astronomical imagery often contains (noisy)
images of the PSF.  It is common to derive the PSF empirically.
Indeed, sometimes you can even derive the PSF from an ensemble of
non-point sources in your image if you iterate the solution.  In radio
astronomy this is known as "self-calibration".

Finally, <[e-mail]> concludes that:
>...MEM will be of limited
>applicability to most of the imaging problems HST was hoping to address.  One
>would not, for example, put great trust in crowded-field photometry derived
>from an MEM reconstructed star field.  The MEM reconstruction will almost
>certainly introduce systematic errors that will be most difficult to
>characterize.

Deconvolution specialists are always happy to try their bags of tricks
on images of sets of point sources. It is the easiest case! If an
algorithm conserves flux then systematic errors are improbable, as
long as you realize that shapes are not necessarily conserved,
necessitating flux integration over individual images. The CLEAN
family of algorithms are generally the best choice for deconvolving
images of point sources.

    =-=-=

Deconvolution is generally easier in astronomy than in other sciences.
This is because most of our signals are *positive*, and because many
of our target sources are spatially confined, surrounded by regions of
no flux (except flat background signal).  Non-linear deconvolution
algorithms work well in these cases. Bi-polar signals, or signals with
extended structure at low contrast well above zero level (e.g.
terrestrial imagery) are intrinsically much more difficult to
deconvolve.

    =-=-=

I would be curious to know if the FOC sees diffraction patterns in the
out-of-focus images, especially when using a narrow band filter (e.g.,
H-alpha).  If it does, then those irregular "rings" would be carrying
the *full* spatial frequency range of the 2.4meter aperture! Any such
data would make possible a fascinating, and probably profitable,
deconvolution experiment.

    =-=-=

The hearing held before Al Gore's Senate space committee today was
broadcast on CSPAN earlier tonight, and was interesting. The Deputy
Director of STScI, an astronomer named Stockman, spoke for STScI. He
said that their first quick examination of the planned observing
program showed that at least 50% of it, mainly UV spectroscopy, is
still quite doable in spite of the bad images. In the course of his
presentation he stated quite flatly that deconvolution is going to
work for high contrast (i.e. spatially confined) and bright sources,
i.e.  that most of the originally expected details can be recovered in
such cases. He stated that it will only be necessary to increase
exposure time on such targets (to build S/N).  He spoke in a careful
and precise manner, and therefore I expect that his assertion
represents the consensus of expert opinion from inside the STScI.


Donald C. Wells, Associate Scientist | NSFnet: [e-mail] [192.33.115.2]
National Radio Astronomy Observatory | SPAN:   NRAO::DWELLS    [6654::]
Edgemont Road                        | BITnet: DWELLS@NRAO
Charlottesville, VA 22903-2475 USA   | UUCP:   ...!uunet!nrao.edu!dwells
Lat: 38:02.2N  Long: 78:31.1W        | Tel:[phone] Fax:[phone]

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

Date: 30 Jun 90 13:14:35 GMT
From: eru!luth!sunic!mcsun!ukc!harrier.ukc.ac.uk![e-mail]  (H.A.Shaw)
Subject: Re: human combustion, (Was Re: none)

>In article <[e-mail]> [e-mail] (Commander Krugannal) writes:
>   ...
>   BTW, speaking of stuff like this, can anyone offer a good
>   explanation for spontaneous human combustion?
>
There was a program on British TV some time ago on this subject.  It is well
known to the Fire Bregade and has been explained.  the human body can be
considered as a fat covered bone wick.  Once started combustion can be self
sustaning and you don't need an initial flame.  The fire (no flame) tends to
proceed from hands and feet up the limbs to the trunk, and quite often the
combustion is almost total.  There is *ALWAYS* (my emphasis) a sorce of heat
such as an electric fire, oven etc., nearby and quite often nearby plastic
objects such as TVs, radios, have melted *BUT NO BURN MARKS*.  If the body is
on a carpet (especially Nylon ones) then only where the body was is damaged.
The TV program showed a candle made of fat combust when an electric heater with
a reflector was "shone" at it.  Once started the heater was removed, but the
candle contunued to "burn".  The program was in a science series called EQUINOX
shown here on Channel 4.  They produced information booklets on all their
programs.  Other programs included one on racing car engines, aircraft flight,
plastic replacement joints.  I wrote to...
    Equinox.
    PO BOX 4000
    Belfast.
    Northern Ireland.
... to get my information pack.  The programs were in the middle of 1989.

PS: why is this in the Space group.  We need sci.fire !

Email: [e-mail]                         | Howard Allan Shaw.
Phone: [phone] Extn: 3783             | Room 165, Physics Laboratory,
                                             | The University,
Don't ask me... I just wrote it!             | Canterbury, England.  CT2 7NR

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

Date: 30 Jun 90 17:40:36 GMT
From: cs.utexas.edu!titan![e-mail]  (Donald Heskett)
Subject: Re: Hubble Space Telescope Update - 06/28/90

I'm afraid you have been somewhat misinformed.  While it has become
common practice, over the last few years, to apply active compensation
to the figure of the mirror, and while many, if not most, large
telescopes are now designed that way, most existing large telescopes
were designed before active compensation was viable.  Cheap small
computers are one of the main advances that made the active
compensation approach possible.

Also, it seems to me that active compensation it confined to mirrors
larger than 100".  Actually, I don't remember seeing it applied to any
that were smaller than about 150".

"Sky and Telescope" constantly runs articles on new professional
telescopes, and the new technology they employ. A number of these
articles over the last couple of years have mentioned active
compensation of mirror figures.  Some of the best articles have been
in the last few months, so you won't have to search that far back.

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

Date: 30 Jun 90 19:47:27 GMT
From: uvaarpa!murdoch!astsun7.astro.Virginia.EDU![e-mail]  (Greg S. Hennessy)
Subject: Re: The HST was risky from square one

Doug McDonald writes:
#The bozos aren't at Perkin Elmer - they are at NASA itself. It was
#just plain stupid to not test the components that could not be fixed.

I don't want to seem like I disagree with you too much, but it is
still not clear how feasable the testing could have been. If the tests
would have cost a few hundreds of millions of dollars (about 10
percent of the total cost) then whether the test should be done is
debatable. I am not an expert on mirrors, and if the proper tests
could have been done easier then they should have been. I would just
say that at this time it is uncertain how "stupid" NASA and PE were.



--
-Greg Hennessy, University of Virginia
 USPS Mail:     Astronomy Department, Charlottesville, VA 22903-2475 USA
 Internet:      [e-mail]
 UUCP:        ...!uunet!virginia!gsh7w

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

Date: 1 Jul 90 00:11:16 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: NSS protests Chinese launch pricing

In article <[e-mail]> [e-mail] (Craig E. Ward) writes:
>... based on what I know of communist regimes in general and China
>in particular, is that Chinese services are subsidized a lot, that these
>services cost the Chinese *more* than they would a private provider...

A private provider who also provided primitive facilities (the Chinese
basically don't believe in clean rooms, for example) for hardware built
in appliance factories with cheap labor probably would come in cheaper
than the Chinese government.  However, that is not what the real private
providers do.  There is every reason to believe that the real costs to
China are lower than Western commercial costs.  If you claim otherwise,
please provide -->NUMBERS<-- instead of just asserting that rotating a
launch pad with hand cranks can't possibly be cheaper than doing it
with computer-controlled machinery built by US aerospace contractors.
(This is not an imaginary example.)

>A clear distinction but be made here.  NSS has not protested Chinese launch
>costs, it has complained about Chinese pricing of those launches...

Complaints about the pricing being too low always seem to be implicitly
based on the assumption that Chinese costs are similar to those of the
Western suppliers, which is clearly untrue, because they provide poorer
service in simpler ways with lower-cost labor.
--
"Either NFS must be scrapped or NFS    | Henry Spencer at U of Toronto Zoology
must be changed."  -John K. Ousterhout |  [e-mail]   utzoo!henry

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

Date: 30 Jun 90 03:47:00 GMT
From: attcan!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: RE  Hubble Space Telescope Update - 06/28/90

In article <[e-mail]> [e-mail] (Peter Nelson) writes:
>  Did anyone take measurements of the mirror and use computer modeling
>  to try to account for the effects of gravity?

Effects of gravity are not the problem.  (They would have been an obstacle
to testing on Earth, but they are not what's wrong.)

>  ...Did the people who approved the $1.5 billion
>  KNOW they were approving a project which was deliberately not
>  testing certain key components?

The components were tested; they met their specs, or what people thought
the specs were, individually.  The amount and form of testing was, based
on current accounts, comparable to what is normally done for large
Earth-based telescopes.  It is not usual to test the entire optical
system together before telescope installation.  The normal assumption is
that if the components check out, the telescope will work.  It always
has in the past.

This sort of thing has never happened before; making tests specifically
to catch such a never-before-in-history mistake would have been classed
as a waste of money, at a time when HST was having lots of trouble with
budget overruns already.  Hindsight is always 20-20.  Don't lean on
people too hard for not anticipating something they had no reason to
anticipate.

Now that we know it can happen, it is virtually certain that it will
never happen again.  Alas, that's not very comforting just now...
--
"Either NFS must be scrapped or NFS    | Henry Spencer at U of Toronto Zoology
must be changed."  -John K. Ousterhout |  [e-mail]   utzoo!henry

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

End of SPACE Digest V11 #596
*******************