Hubble's mirror
Donald H. Locker
how the Hubble mirror contractor messed up the figure of the main
mirror. I understand it has spherical aberration, but wonder how
[Rockwell?] managed to do that.
Thanks for any info.
--
Donald. Speaking only for myself.
"You can't set glasses or a book on a door or a bathroom!" - djl
Gerard M. Foley
It wasn't Rockwell (I forget axactly who it was, but it was an
otherwise reputable New England outfit) and put briefly, they
fouled up the test, performing it incorrectly, and never
checked by any independent method.
ge...@bluemoon.rn My amateur radio callsign is K8EF, and my
packet radio address is K8...@W8CQK.OH.USA.NA
Dan Pechonis
>> how the Hubble mirror contractor messed up the figure of the main
>> mirror. I understand it has spherical aberration, but wonder how
>> [Rockwell?] managed to do that.
>
>otherwise reputable New England outfit) and put briefly, they
>fouled up the test, performing it incorrectly, and never
>checked by any independent method.
>
I believe it was Perkin-Elmer Corporation. Sorry I don't know the details.
Dan Pechonis
da...@mammoth.sps.mot.com
Doug S. Caprette Bldg. 28 W191 x3892
>d...@mrdog.msl.com (Donald H. Locker) writes:
>
>> Now that I know a little about mirror-making, I'd like to hear again
>> how the Hubble mirror contractor messed up the figure of the main
>> mirror. I understand it has spherical aberration, but wonder how
>> [Rockwell?] managed to do that.
>>
>> Thanks for any info.
>> --
>> Donald. Speaking only for myself.
>>
>> "You can't set glasses or a book on a door or a bathroom!" - djl
>
>It wasn't Rockwell (I forget axactly who it was, but it was an
>otherwise reputable New England outfit) and put briefly, they
>fouled up the test, performing it incorrectly, and never
>checked by any independent method.
>
independent method, and found the error. Then, the difference was handwaved
away.
Also Kodak, which made the backup mirror, wanted the two of them to be
closely compared and the best of the two used. They were turned down on
this idea.
William H. Jefferys
#Now that I know a little about mirror-making, I'd like to hear again
#how the Hubble mirror contractor messed up the figure of the main
#mirror. I understand it has spherical aberration, but wonder how
#[Rockwell?] managed to do that.
The Hartford Courant had a Pulitzer Prize winning
series of reports that go into gory detail on this.
They may still have copies available. It's entitled
"Hubble error: Time, money and millionths of an inch."
Write the Hartford Courant, 285 Broad St., Hartford
CT, or call Corporate Affairs Manager Sylvia Levy
at (203) 241-6431.
Bill
jcj
>mirror. I understand it has spherical aberration, but wonder how
>[Rockwell?] managed to do that.
>
Although Rockwell is my competitor in some areas, I must point out it was
Perkin-Elmer that blew the figuring.
--
j...@tellabs.com
aal...@hamp.hampshire.edu
>
> According to Dr. Steve Maran, who works on the HST project at the
> Goddard Flight Center, and who was recently a guest lecturer at my college,
> none of the above is true. The company that ground the mirror did it
> exactly to the specs they were given.
>
> The specs were wrong.
>
>
According to what I have heard from my optics professor, this is the
proper account. The Hubble mirror is the most precise mirror ever made wrong.
--
Adam Alpern * "All that is gold does not glitter, not all *AAl...@hamp.hampshire.edu * those who wander are lost." - JRR Tolkien * * "When I look in the mirror I see the days to * * come, and my face is just a trace of where * * I'm coming from." - Ani DiFranco *
Claudio Egalon
article in Physics Today- which explained very nicely the real messed
up-, I still recall that there was three diferent instruments that were
used to measure the curvature of the primary mirror. Two of them
used refraction principle and one of them used the reflection
principle (don't remember the details so I may commit some
mistakes. If so, I apologize). The results of the other two instruments
that used the refraction principle to measure the mirror curvature
matched up but... the measurements produced by the one that used
reflection, reflective null corrector, was different and, since it was
thought to be superior to the other two, no one bottered about
finding out why the discrepancy between the measurements... of
course untill they found out that there was something wrong with
Hubble.
*However* as I recall (and I may be wrong) the error in the RNC
came along because the WRONG surface in the instrument was
providing the reflection and not that because the instrument was
built improperly. Aparently there was an scratch in a surface that was
suposed to be black, for absorbing incoming radiation, and it was this
scratch that worked as the WRONG reflecting surface. So, that how
the wrong prescription came about. Another reference for the
investigation on the problem of the mirror was the report put out by
Lew Allen's review board (I guess I have a copy of it at home and I
am confindent that you people can get one from NASA but I do not
know whether they will charge you or not). Maybe, not oddly
enough, there were other complaints about the handling of the
project like people did not like to be bothered with criticism (read
peer review)... So aparently, the problem was both technical and
arrogance.
Claudio O. Egalon
Henry Spencer
>>... put briefly, they
>>fouled up the test, performing it incorrectly, and never
>>checked by any independent method.
>
>Goddard Flight Center, and who was recently a guest lecturer at my college,
>none of the above is true. The company that ground the mirror did it
>exactly to the specs they were given.
You're sure that's what he said? It's *not* what Lew Allen's review board
found (and documented in detail). The grinding people at Perkin-Elmer did
indeed produce an essentially perfect mirror to the wrong spec. But it was
Perkin-Elmer that botched the spec, by mis-building the reflective null
corrector that was used to measure the mirror shape, and Perkin-Elmer that
ignored three successive hints that something was wrong with the RNC.
(First, the error made it impossible to build the RNC without a slight
design change; the change was made without anyone asking why it was
necessary. Second and third, results from two other measurements were
disregarded because the RNC was thought to be superior.)
--
MS-DOS is the OS/360 of the 1980s. | Henry Spencer @ U of Toronto Zoology
-Hal W. Hardenbergh (1985)| he...@zoo.toronto.edu utzoo!henry
Rick Kirchhof
>
>>d...@mrdog.msl.com (Donald H. Locker) writes:
>
>>> Now that I know a little about mirror-making, I'd like to hear again
>>> how the Hubble mirror contractor messed up the figure of the main
>>> mirror. I understand it has spherical aberration, but wonder how
>>> [Rockwell?] managed to do that.
>>>
>>otherwise reputable New England outfit) and put briefly, they
>>fouled up the test, performing it incorrectly, and never
>>checked by any independent method.
>
>Goddard Flight Center, and who was recently a guest lecturer at my college,
>none of the above is true. The company that ground the mirror did it
>exactly to the specs they were given.
>
>
>
That is not the case. The primary mirror was produced by Perkin-Elmer.
This has been the subject of MUCH investigation by NASA. The end result
is that Perkin-Elmer manufactured a large primary mirror to exceedingly
accurate standards obtained from a incorrectly manufactured optical test
cell they also made. The "smoking gun" is in their mirror lab, as NASA
requested all relevant project materials mothballed upon project
completion.
To be fair, the quality of the mirror was extremely good as tested by
their rig. If the test cell had been correct, the mirror would have been
correct. Perkin-Elmer just did not produce what NASA asked for.
It is ironic that several other types optical tests could have shown a
gross error such as this. They were never used. In addition, Eastman
Kodak, who also made a primary mirror to the design specs, requested
that the better of the two mirrors be used. This was never done.
For independent verification of all of this, see several issues of SKY &
TELESCOPE. The subject has been reported several times there.
--
Rick Kirchhof Austin, Texas | Experience is what you
Domain: ri...@posms.cactus.org | get when you don't
Bang path: ...!cs.utexas.edu!peyote!posms!rick | get what you want.
===========================================================================
Gary Coffman
>In <yssPTB...@bluemoon.rn.com> ge...@bluemoon.rn.com (Gerard M. Foley) writes:
>
>>> Now that I know a little about mirror-making, I'd like to hear again
>>> how the Hubble mirror contractor messed up the figure of the main
>>> mirror. I understand it has spherical aberration, but wonder how
>>> [Rockwell?] managed to do that.
>>>
>>otherwise reputable New England outfit) and put briefly, they
>>fouled up the test, performing it incorrectly, and never
>>checked by any independent method.
>
>Goddard Flight Center, and who was recently a guest lecturer at my college,
>none of the above is true. The company that ground the mirror did it
>exactly to the specs they were given.
>
> The specs were wrong.
According to the NASA investigation of the Hubble mirror problem, there
was nothing wrong with the specs. The backup mirror built to the same
specs by Kodak is *perfect*. The problem was that Perkin-Elmer bollixed
up the testing of the figure of the mirror and ignored the results of
a Foucault test that showed the mirror to have spherical abberations
because their primary test was supposed to give more accurate results.
Unfortunately, they installed a fixture backwards when making the
primary measurements and got the *wrong* result.
Gary
William H. Jefferys
#
#>d...@mrdog.msl.com (Donald H. Locker) writes:
#
#>> Now that I know a little about mirror-making, I'd like to hear again
#>> how the Hubble mirror contractor messed up the figure of the main
#>> mirror. I understand it has spherical aberration, but wonder how
#>> [Rockwell?] managed to do that.
#>>
#>It wasn't Rockwell (I forget axactly who it was, but it was an
#>otherwise reputable New England outfit) and put briefly, they
#>fouled up the test, performing it incorrectly, and never
#>checked by any independent method.
#
# According to Dr. Steve Maran, who works on the HST project at the
#Goddard Flight Center, and who was recently a guest lecturer at my college,
#none of the above is true. The company that ground the mirror did it
#exactly to the specs they were given.
#
# The specs were wrong.
If my friend Steve Maran really said this, then he's
incorrect. The specs were fine. What happened was that
Perkin-Elmer mis-manufactured a critical piece of
equipment, a reflective null corrector, that was used
to figure the mirror. A field lens was located 1.3 mm
out of its proper position. The reasons for this having
happened are rather complex and involved. They are
described in gory detail in the Hartford Courant
report series that I posted information about earlier.
I personally attended many days' worth of reviews where
these events were found out, so I have reason to believe
that what I say is accurate.
The poster to whom you responded had it essentially right.
I don't think that Steve would be as far off base as
this, and I suspect that you have misunderstood him.
Bill Jefferys
Brian Stuart Thorn
simply return Hubble to Earth and replace the faulty mirror?
I know, I've read many times that returning Hubble to Earth is *not* an
option, but I can't figure out WHY. At 24,000 lbs, Hubble is well within
the Shuttle's landing cargo capacity, and since the only part of Hubble
likely to suffer damage during a 3g return is primary mirror (which
will be replace anyway) I don't understand why NASA doesn't simply swap
mirrors. NASA has already spent a fortune building COSTAR and ESA is
building replacement (no wobble) solar panels. With three spacewalks, the
Shuttle crew will be hard pressed to get all the work done.
Doesn't bringing Hubble home for repairs make more sense than jerry-rigging
and dangerous EVAs on orbit?
-Brian
William H. Jefferys
#Henry Spencer is right. Although it was sometime ago that I read an
#article in Physics Today- which explained very nicely the real messed
#up-, I still recall that there was three diferent instruments that were
#used to measure the curvature of the primary mirror. Two of them
#used refraction principle and one of them used the reflection
#principle (don't remember the details so I may commit some
#mistakes. If so, I apologize). The results of the other two instruments
#that used the refraction principle to measure the mirror curvature
#matched up but... the measurements produced by the one that used
#reflection, reflective null corrector, was different and, since it was
#thought to be superior to the other two, no one bottered about
#finding out why the discrepancy between the measurements... of
#course untill they found out that there was something wrong with
#Hubble.
#
#*However* as I recall (and I may be wrong) the error in the RNC
#came along because the WRONG surface in the instrument was
#providing the reflection and not that because the instrument was
#built improperly. Aparently there was an scratch in a surface that was
No, the reflective null was built improperly. Here's what
happened: The field lens was supposed to be aligned to the
cell by using a precisely machined Invar rod, whose length
was traceable to NBS standards. A laser was used to align
the end of the bar to the cell. In order to guarantee that
the laser was reading just the end of the bar (which was
rounded), an end cap with a small hole was placed over the
end of the bar. The end cap extended 1.3 mm further than
the end of the bar, and was painted black so that there
would be no return to the laser from the end cap. Unfortunately,
as it turned out, a fleck of the black paint got scraped off,
and a significant return from the end of the bar was obtained.
Thus, the bar was positioned too far away from the laser, and
the other end of the bar (which was positioned against the
field lens) was 1.3 mm from where it should have been.
In order to misposition the field lens, they people who did
this _had to shim out the lens cell with washers_!!! The
cell had been properly built, but when the lens didn't fit
where they thought it should (in the wrong position), they
kludged it to _make_ it fit.
You are right that the refractive null and the inverse null
agreed with each other, but not with the reflective null. Why
the engineers didn't see the red flag waving by 2 out of
3 vote, and the fact that they had to shim out the lens position
in the cell, is beyond me.
#suposed to be black, for absorbing incoming radiation, and it was this
#scratch that worked as the WRONG reflecting surface. So, that how
#the wrong prescription came about. Another reference for the
#investigation on the problem of the mirror was the report put out by
#Lew Allen's review board (I guess I have a copy of it at home and I
#am confindent that you people can get one from NASA but I do not
#know whether they will charge you or not). Maybe, not oddly
#enough, there were other complaints about the handling of the
#project like people did not like to be bothered with criticism (read
#peer review)... So aparently, the problem was both technical and
#arrogance.
#
#Claudio O. Egalon
Bill
William H. Jefferys
#as it turned out, a fleck of the black paint got scraped off,
OF THE END CAP
#and a significant return from the end of the bar
not the bar, the END CAP
#was obtained.
#Thus, the bar was positioned too far away from the laser, and
#the other end of the bar (which was positioned against the
#field lens) was 1.3 mm from where it should have been.
Bill
Michael V. Kent
>If there is a perfect mirror presumably sitting at Kodak, why doesn't NASA
>simply return Hubble to Earth and replace the faulty mirror?
There is no perfect mirror sitting at Kodak. The "mirror" at Kodak is a blank
that would need to be ground and polished at considerable expense.
>At 24,000 lbs, Hubble is well within
>the Shuttle's landing cargo capacity, and since the only part of Hubble
>likely to suffer damage during a 3g return is primary mirror (which
>will be replace anyway) I don't understand why NASA doesn't simply swap
>mirrors. NASA has already spent a fortune building COSTAR and ESA is
>building replacement (no wobble) solar panels. With three spacewalks, the
>Shuttle crew will be hard pressed to get all the work done.
The expense of grinding and polishing a new mirror from the blank and the
expense of launching two Shuttle missions (one for retrieval, another for
relaunch) is far in excess of the expense of COSTAR and one Shuttle mission.
It is also much more time-consuming, and time is science. Meanwhile, while
Hubble is on the ground, it is doing *no* science, while considerable cutting-
edge work can be done even with the faulty mirror. Add in the possibility
that unforseen problems may arise during retrieval, storage, and relaunch, and
the sum is that the retrieval option is costlier and riskier than the COSTAR
option. At least that's NASA's opinion.
If the gyro's, solar panels, and COSTAR can all be fixed, then Hubble should
be back up to about 80% planned capability. It is about 15% now.
Note to astronomers: I realize one number is not sufficient to decribe all of
the qualities of a telescope, but if these figures are true, they give a sense
of the magnitude of improvement this revisit should bring. Hopefully all will
work as planned.
Mike
--
Michael Kent ke...@rpi.edu
McDonnell Douglas Rensselaer Polytechnic Institute
Tute Screwed Aero Class of '92 Apple II Forever !!
Bob Pendleton
> From article <69...@cup.portal.com>, by Bri...@cup.portal.com (Brian Stuart Thorn):
>> If there is a perfect mirror presumably sitting at Kodak, why doesn't NASA
>> simply return Hubble to Earth and replace the faulty mirror?
>
>> and dangerous EVAs on orbit?
>>
>> -Brian
>
> where between $100,000,000 US and $250,000,000 US.
>
> Repair on orbit requires 1 launch. Repair on the the ground requires 2
> launches.
>
> Thus, repair on orbit, saves somewhere between $100 and $250 million
> dollars. As the US is rapidly approaching it's legal debt limit of
> roughly $4,100,000,000,000 dollars (your share, if you are a US
> citizen, is roughly $16,000) we really can afford to piss away
^^^
That's supposed to be "CAN'T"
> $250,000,000 for the convenience of some astronauts and astronomers.
> Especially when we are borrowing the money to fix it.
>
> As much as I value the information that we can get from Hubble. I'm
> not willing to go $0.01 US more than is needed to fix it.
>
> I think it is time to face the simple fact that as long as we are
> paying $300,000,000,000 US in interest on the Debt we (US) are not
> going to be spending money on large, long term, space programs.
>
> The interest on the Debt is the single largest item in the US Federal
> budget.
>
> Bob P.
>
> P.S.
>
> What we pay in interest on the Debt, if spent on education, would just
> about double what we spend per student in the K-12 grades.
>
>
> P.P.S
>
> Do we need nuclear weopons anymore? Or can we destroy the worlds
> economy by just defaulting on the our loans?
> --
> Bob Pendleton | As an engineer I hate to hear:
> bo...@hal.com | 1) You've earned an "I told you so."
> Speaking only for myself. | 2) Our customers don't do that.
> <<< Odin, after the well of Mimir. >>>
--
Bob Pendleton | As an engineer I hate to hear:
bo...@hal.com | 1) You've earned an "I told you so."
Speaking only for myself. | 2) Our customers don't do that.
<<< Odin, after the well of Mimir. >>>
Bob Pendleton
> simply return Hubble to Earth and replace the faulty mirror?
> Doesn't bringing Hubble home for repairs make more sense than jerry-rigging
> and dangerous EVAs on orbit?
>
> -Brian
Depending on whose figures you believe a shuttle launch costs some
where between $100,000,000 US and $250,000,000 US.
Repair on orbit requires 1 launch. Repair on the the ground requires 2
launches.
Thus, repair on orbit, saves somewhere between $100 and $250 million
dollars. As the US is rapidly approaching it's legal debt limit of
roughly $4,100,000,000,000 dollars (your share, if you are a US
citizen, is roughly $16,000) we really can afford to piss away
Phil Fischer
>simply return Hubble to Earth and replace the faulty mirror?
>
There is another wrinkle to this. Apparently the Kodak mirror is in a sealed
box which they will not allow anyone to open. Hmm? Is it possible that
Kodak is no longer in possession of the mirror. I wonder who might have
purchased it?
--
Phil Fischer | Hamilton, Ont.
fis...@crocus.physics.mcmaster.ca | Canada
Dept. of Physics and Astronomy | L8S 4M1
McMaster University | 416-525-9140 X 4574
Thomas Clarke
> From article <69...@cup.portal.com>, by Bri...@cup.portal.com (Brian Stuart
Thorn):
> > If there is a perfect mirror presumably sitting at Kodak, why doesn't NASA
> > simply return Hubble to Earth and replace the faulty mirror?
>
> > Doesn't bringing Hubble home for repairs make more sense than jerry-rigging
> > and dangerous EVAs on orbit?
> >
> > -Brian
>
> Depending on whose figures you believe a shuttle launch costs some
> where between $100,000,000 US and $250,000,000 US.
>
> Repair on orbit requires 1 launch. Repair on the the ground requires 2
> launches.
a Hubble retrieval with another light-payload mission like the recent
LAGEOS launch? The Hubble could be retrieved with little extra
cost over the repair mission, but with a much higher probability
of success.
Actually, we should forget Hubble and spend the money needed
for the repair mission on building a half-dozen Keck-type telescopes.
> P.P.S
>
> Do we need nuclear weopons anymore? Or can we destroy the worlds
> economy by just defaulting on the our loans?
Paraphrasing the comedian Emo Phillips:
When the international bankers come to the US and ask for
their money, we'll just have to say "Aw shucks. We spent all the
money on these here nuclear weapons."
Whereupon the bankers will say: "That's OK. We'll just
renew your loans for another decade."
> --
> Bob Pendleton | As an engineer I hate to hear:
> bo...@hal.com | 1) You've earned an "I told you so."
> Speaking only for myself. | 2) Our customers don't do that.
> <<< Odin, after the well of Mimir. >>>
--
Thomas Clarke
Institute for Simulation and Training, University of Central FL
12424 Research Parkway, Suite 300, Orlando, FL 32826
(407)658-5030, FAX: (407)658-5059, cla...@acme.ucf.edu
Dave Jones
> If there is a perfect mirror presumably sitting at Kodak, why doesn't NASA
> simply return Hubble to Earth and replace the faulty mirror?
>
It would take two missions to return, fix and re-launch Hubble. You
could probably rebuild Hubble on the ground and launch it for less.
The extended portions of Hubble are almost certainly not designed to
retract, and would have to be cut off in orbit. This has never been
done before.
If one aspect of securing Hubble for the return mission fails, you're
screwed. The mission would fail and Hubble would likely be disabled
permanently.
Hubble is doing valuable work right now. Removing it from orbit, probably
for months, would damage astronomy far more than a mirror whose defects are
known and correctable by image-processing techniques.
--
||Dave Jones (d...@ekcolor.ssd.kodak.com)|Eastman Kodak Co. Rochester, NY |
riv...@mdcbbs.com
The error was introduced into the main mirror because the setup used to
test it was missing some spacers which were planned to locate the
test rig at the correct focal point. Because the spacers were not present,
the mirror was figured perfectly, but to the wrong focal point, outside
the range of the Hubble's focusing apperatus. This error would have shown
up had the entire telescope been tested as a whole prior to launch. Sadly,
due to budget constraints, this was never done.
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
| Michael Rivero riv...@mdcbbs.com "Middle-aged Mutant Ninja Animator" |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| If Thomas Jefferson were alive today, he'ld be ASSASSINATED! |
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
I. Neill Reid
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
--
>||Dave Jones (d...@ekcolor.ssd.kodak.com)|Eastman Kodak Co. Rochester, NY |
Agreed to all except the last sentence. Let's be under no illusions -
the Hubble telescope is SERIOUSLY harmed for imaging programmes. It is
possible to apply sophisticated image-reconstruction algorithms, but only at
high signal-to-noise (at least a 2 magnitude reduction in the limiting
magnitude) and only if the field is populated relatively sparsely, and
predominantly by point sources. (And UV spectroscopy also demands
longer integrations since less light gets down the slit.)
Neill Reid - i...@eccles.caltech.edu
hath...@stsci.edu
> From: d...@ekcolor.ssd.kodak.com (Dave Jones)
>
>>Brian Stuart Thorn (Bri...@cup.portal.com) wrote:
>
>>Hubble is doing valuable work right now. Removing it from orbit, probably
>>for months, would damage astronomy far more than a mirror whose defects are
>>known and correctable by image-processing techniques.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> --
>>||Dave Jones (d...@ekcolor.ssd.kodak.com)|Eastman Kodak Co. Rochester, NY |
>
> Agreed to all except the last sentence. Let's be under no illusions -
> the Hubble telescope is SERIOUSLY harmed for imaging programmes. It is
^^^^^^^^^ ^^^^^^
Compared to what? You got anything on earth that can touch it???
>
> Neill Reid - i...@eccles.caltech.edu
Wm. Hathaway
David Adams
one to launch a brand new one? (Or wait 5 or 10 years and launch
a brand new one.)
---
--David C. Adams Statistician Cray Research Inc. dad...@cray.com
___________________________________________________________________
Old Sourdoughs never die. They just ferment away.
I. Neill Reid
Actually, yes - we can get a resolution of 0".07 (that's about twice
the HST) using speckle interferometry on the 200-inch. Image-sharpening
techniques have been used on many other 4-5 metre telescopes to
recover images near the diffraction limit of those telescopes (which,
at twice the diameter of HST, give twice the resolution). The catch,
of course, is that most of the current techniques can only recover
the diffraction limit with lots of signal (we can't go much fainter
than K = 9 (2.2 microns) on the 200-inch with speckle). But there are
many experiments going on at present with more sophisticated
techniques using laser guide stars, `rubber mirrors', tip-tilt
systems (Laird Thompson was one of the first with such a system and
has achieved image-sizes of 0.4 arcsecs (I think) from Mauna Kea).
These systems can go much (10+ magnitudes) fainter than speckle.
There will probably always be atmospheric limitations as to how large
a solid angle these systems can cover, but against that there is
the advantage of more time on a larger telescope.
A _working_ HST with diffraction limited images would certainly beat
the current ground-based activity in depth. But the main problem with
Hubble is that it spreads about 85 % of the light of a given point source
over an enormous area - take a relatively crowded field (say, the core of
a globular cluster; a region in the Magellanic clouds or M31; or a field
towards the Galactic Bulge) and these overlapping halos around the individual
stars combine to wash out the fainter objects. That's where you lose
the sensitivity, and that's where you lose at least 2 magnitudes in
depth, and that's what hampers many of the projects which were the
main justifications for ST - and that's what makes it such a
disappointment.
Yes - you can go some way towards reconstructing the distribution of the
brighter images, where the central core of the image is identifiable
(you can even get spectacular pictures of something really bright, like
Jupiter, as Bill Gawne pointed out) - but the fainter stars in a
complicated image are lost. That's why you lose so much in limiting magnitude,
and that's also why the magnitudes that are derived from HST pictures are
much wobblier than you'd like. One of the key projects was monitoring
Cepheid variables in various galaxies to get a better estimate of the
extragalactic distance scale. While the project is still feasible, it
requires more integration time, which means fewer (and more sparsely
populated) fields, which means fewer Cepheids, which means greater
uncertainties in any distances derived. Similarly, resolving the stellar
populations of Virgo galaxies is that much more difficult (shading
towards impossible).
Obviously, there are still areas where ST is ahead of ground-based
telescopes - mainly involving UV work or imaging sparse fields - but
the incorrectly-figured mirror means that the imaging performance has
been reduced to a state where (larger) ground-based telescopes are
getting close.
William H. Jefferys
#
#According to the NASA investigation of the Hubble mirror problem, there
#was nothing wrong with the specs. The backup mirror built to the same
#specs by Kodak is *perfect*. The problem was that Perkin-Elmer bollixed
#up the testing of the figure of the mirror and ignored the results of
#a Foucault test that showed the mirror to have spherical abberations
#because their primary test was supposed to give more accurate results.
#Unfortunately, they installed a fixture backwards when making the
#primary measurements and got the *wrong* result.
I'm pretty sure there was never a Foucault test; that
there hadn't been one became an issue after the mistake
was discovered. This was brought up at NASA reviews I
attended. After all, the interferometric test was supposed
to be so accurate that a crude test such as the Foucault
test wouldn't tell you anything you didn't already know
(or so they thought).
The "fixture" that was used backwards was the Invar rod;
It was indeed used backwards, but that was not the chief
reason for the mis-manufactured null corrector. This was,
as I posted earlier, the laser return from the end cap,
which had had a fleck of black paint scraped off.
Bill
Greg Hennessy
#This is rapidly becoming a contender for Technological Myth Of The Decade.
Err, correcting Dr. Jefferys on something to do with HST is best done
very carefully. Dr. Jefferys is the PI on the Fine Guidance Sensors of
HST, and has forgotten more about HST then most people have learned in
their lives.
--
-Greg Hennessy, University of Virginia
USPS Mail: Astronomy Department, Charlottesville, VA 22903-2475 USA
Internet: gs...@virginia.edu
UUCP: ...!uunet!virginia!gsh7w
Henry Spencer
>#This is rapidly becoming a contender for Technological Myth Of The Decade.
>
>Err, correcting Dr. Jefferys on something to do with HST is best done
To the best of my knowledge, the only statement in my posting which is
not a solidly-established fact -- verifiable by reference to the Allen
panel's report -- is my opinion that P-E management, having ignored two
indications of trouble (actually three, if you count the fact that the
reflective null corrector unexpectedly required extra spacing washers),
would have disregarded the results of other simple tests too, unless
they were absolutely unmistakable (i.e. an end-to-end imaging test).
If I am in error -- certainly possible -- I'd appreciate hearing about
it, preferably with enough detail so I can verify it.
Greg Hennessy
#To the best of my knowledge, the only statement in my posting which is
#not a solidly-established fact . . .
I was referring to your statment implying that Dr. Jefferys was
contributing to the "technological myth of the century." Correcting
Dr. Jefferys on matters of the HST is like correcting Dennis Ritchie
on matters of C.
While certianly a very expensive end to end test would have caught the
trouble, assuming that such a test is even possible (which I'm not
convinced of given the difficulty), the set of tests that you develop
to test a mirror BEFORE you know it has a certian problem is not
necessarily the same as the set of tests that you develop AFTER you
know it has a problem. PE developed a system of testing that they
THOUGHT would be good enough. Unfortunately it was not. At least we
can be pretty sure that this blunder won't be repeated.
John F. Woods
>PE developed a system of testing that they
>THOUGHT would be good enough. Unfortunately it was not.
According to the report, the system of testing *was* good enough. Two of the
three tests indicated the mirror was mis-figured. Perkin-Elmer gave exactly
the attention to those tests that a CERTAIN OTHER manufacturer of space
hardware gave to the tests indicating routine damage to a CERTAIN O-ring in
the Shuttle...
All the managers who approved ignoring those tests (who were probably rewarded
with bonuses for bringing the mirror in on-time) ought to be billed the repair
costs. (and whoever thought to add random spacing washers to a piece of
*precision* equipment, instead of asking why it didn't fit like it was supposed
to, ought to have boxing gloves surgically attached to his hands so he won't
be tempted to screw up any *other* pieces of equipment...)
Henry Spencer
>#To the best of my knowledge, the only statement in my posting which is
>#not a solidly-established fact . . .
>
>I was referring to your statment implying that Dr. Jefferys was
>contributing to the "technological myth of the century." Correcting
>Dr. Jefferys on matters of the HST is like correcting Dennis Ritchie
>on matters of C.
Since I've been known to do the latter, I don't see why I shouldn't do
the former. :-) Actually, I don't immediately remember having had
occasion to correct Dennis on the net, but I have found bugs in both
his code and his book.
Mario Wolczko
> The *only* test that would have detected the error [an end-to-end test]
> [would have been difficult due to problems]
> like gravitational distortion of the primary
I've seen this mentioned a few times, and it has me confused.
Any idea why an end-to-end test would have been more susceptible to
gravitational problems than the null corrector test? Couldn't both be
performed with the primary flat on its back? And why are there
more risks of surface contamination?
robert.f.casey
>All the managers who approved ignoring those tests (who were probably rewarded
>with bonuses for bringing the mirror in on-time) ought to be billed the repair
>costs. (and whoever thought to add random spacing washers to a piece of
>*precision* equipment, instead of asking why it didn't fit like it was supposed
Whoever did the above adding washers to the test jig probably felt a lot of
time pressure from management to get it done NOW! and don't waste time
about it. He also probably figured the designer made an error overlooking
a small mounting detail, and he could "correct" it easy enough with the
washers, and deliver it as done. And his boss won't be on his ass.
Hell, in my job, I have to deal with a lot of bad documentation, missing
info, lack of proper training, time pressure, bad bosses, not enough time,
and other problems (excuses my boss calles them). Odds are, given time
pressure and bad management, I might have hacked the above mirror tester
to get it done myself. And probably I would have figured I had to make
the "correction" with the washers. And not be able to ask the designer
about it ("he's in a meeting all day", "he's out of town", or some such,
or "can't you figure it out yourself, you idiot").
William H. Jefferys
#In article <83...@ut-emx.uucp> bi...@bessel.as.utexas.edu (William H. Jefferys) writes:
#>I'll agree, the error would have been caught if the primary
#>and secondary mirrors had been tested together. There are
#>lots of simple tests that would have caught the error.
#>None were used.
#
#This is rapidly becoming a contender for Technological Myth Of The Decade.
#If you look at what actually happened, rather than the popular mythology,
#the fact is that three independent tests were run, and TWO OF THEM DETECTED
#THE ERROR. At which point, Perkin-Elmer management decided that the third
#was more trustworthy than the other two, and ignored the two failed tests.
The tests to which you refer are the refractive null and
the inverse null, in addition to the faulty reflective null.
All three of them are based on the same basic interferometric
technology, and are not independent in the sense that I
meant. You are correct, had P-E decided to investigate the
discrepancies between the reflective null and the other two
devices (which agreed with each other) the problem would have
been discovered. Had the optics people who built the reflective
null realized that there was a problem when they found themselves
shimming out the lens cell for the field lens with washers, the
problem would have been found. Had they measured the position of
the field lens with a PLASTIC RULER, it would have been found.
There were lots of red flags flying, and they were all ignored.
By an independent test, I meant a geometric-optics test such as a
Hartmann test that could have, fairly cheaply, detected the problem.
I certainly don't want to be accused of promoting a Technological
Myth; I am personally quite cognizant of the technical issues involved,
owing to my long association with the HST project. But I am using
'independent' in a different sense than you.
Bill
Mario Wolczko
> I would guess that the null-corrector tests were done with the mirror
> flat on its back; it would seem the obvious approach. The problem with
> gravitational distortion -- I would think -- is simply that it requires
> doing the test in a vertical orientation, which considerably complicates
> the test facility (if for no other reason, because you need a vertical
> shaft of considerable height to mount everything in).
I don't know what the spacing between primary and corrector(s) was,
but I would be surprised if it was substantially less than the
primary-secondary spacing. So maybe there was a setup in use for the
corrector tests that didn't need a huge amount of change for a
primary-secondary test. Of course, this is all easy to say in
hindsight. The real problem is that the existing tests should have
caused alarm bells to ring, but the bells were ignored.
As they say, you can make something foolproof, but not bloody
foolproof..
William H. Jefferys
#In article <1992Nov1...@cs.man.ac.uk> ma...@cs.man.ac.uk (Mario Wolczko) writes:
#>Any idea why an end-to-end test would have been more susceptible to
#>gravitational problems than the null corrector test? Couldn't both be
#>performed with the primary flat on its back? And why are there
#>more risks of surface contamination?
#
#Adding tests means moving the mirrors around and doing work in their
#vicinity, which automatically increases the risk of contamination.
#The problem there isn't the nature of the test, but simply the fact that
#it's yet more fiddling with the mirrors, when you would really like to
#handle them as little as possible between manufacturing and launch.
Contamination was a major concern because even a small
amount of organic contamination (a little oil, human
evaporant, or whatever) would seriously degrade UV
performance.
#I would guess that the null-corrector tests were done with the mirror
#flat on its back; it would seem the obvious approach. The problem with
#gravitational distortion -- I would think -- is simply that it requires
#doing the test in a vertical orientation, which considerably complicates
#the test facility (if for no other reason, because you need a vertical
#shaft of considerable height to mount everything in). That is, it's not
#something you could expect the P-E optics shop to be able to rig up with
#equipment on hand; it might even need a special building (although there
#are reports that the USAF already has one).
Right. The interferometric tests with the null corrector were
done with the mirror horizontal, in a large vacuum chamber.
The mirror was mounted on a special "metrology mount" that
compensated for gravitational effects by specially adjusted
weights. I doubt that an _in vacuuo_ two-mirror test could
have been performed[*]. A crude "sanity check" test could have
been done; such a test, if planned (it was not) would have
given the whole test process more visibility & might have
forced the powers that be to recognize that there was a
problem. The problems with the null correctors were too
easily swept under the rug.
Bill
[*] for reasonable cost, that is.
Joe Dellinger
|> the set of tests that you develop
|> to test a mirror BEFORE you know it has a certian problem is not
|> necessarily the same as the set of tests that you develop AFTER you
|> know it has a problem. PE developed a system of testing that they
|> THOUGHT would be good enough. Unfortunately it was not. At least we
|> can be pretty sure that this blunder won't be repeated.
But... PE's system of testing WAS good enough. They had three
redundant tests, so that if one test gave a false OK the other
two could catch it.
One test gave a false OK, and the other two caught it. The system worked!
The blunder was that they _ignored_ the test results that indicated
something was wrong.
The blunder was that the people paying for it weren't checking
over the shoulders of the ones being paid.
Human nature being what it is, I expect we will see these blunders repeated
again and again and again!
/\ /\ /\/\/\/\/\/\/\.-.-.-.-.......___________
/ \ / \ /Hawaii Institute of Geophysics, Honolulu\/\/\.-.-....__
___/ \/ \/Joe Dellinger, Internet: j...@montebello.soest.hawaii.edu\/\.-.__
Bill Higgins-- Beam Jockey
> In article <1992Nov16.0...@murdoch.acc.Virginia.EDU>, gs...@fermi.clas.Virginia.EDU (Greg Hennessy) writes:
> |> PE developed a system of testing that they
> |> THOUGHT would be good enough. Unfortunately it was not. At least we
> |> can be pretty sure that this blunder won't be repeated.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> But... PE's system of testing WAS good enough. They had three
> redundant tests, so that if one test gave a false OK the other
> two could catch it.
>
> The blunder was that the people paying for it weren't checking
> over the shoulders of the ones being paid.
Ah, but "the system was designed to work this way." NASA was trying
to build an inherently expensive and high-performance system, the
Space Telescope, as cheaply as possible, so they cut a lot of corners.
In this case they kept the NASA staff supervising the project small
and gave the contractors a lot of autonomy.
People on the Net, and in the general press, often praise streamlined,
low-paperwork project management... the popularity of the phrase
"skunk-works" is one example. When it works, the results are
wonderful and great value for the money. Fermilab's construction was
supervised by a cowboy physicist, and his gang finished the Main Ring
ahead of schedule and under budget.
When it goes wrong, though, the risks of this approach become
apparent. Hubble ran into big management troubles in the early
Eighties, long before the mirror problem was detected. It was
finished pretty much by throwing massive amounts of money at the
problems, which negated the penny-pinching efforts of its early years
and ended up costing way over a gigabuck by launch day. See Robert
Smith's history *The Space Telescope*. (But wait a bit. It's coming
out in paperback soon, in a revised post-launch, post-spherical-
aberration edition which includes more Tales of Woe and Intrigue.)
O~~* /_) ' / / /_/ ' , , ' ,_ _ \|/
- ~ -~~~~~~~~~~~/_) / / / / / / (_) (_) / / / _\~~~~~~~~~~~zap!
/ \ (_) (_) / | \
| | Bill Higgins Fermi National Accelerator Laboratory
\ / Bitnet: HIG...@FNAL.BITNET
- - Internet: HIG...@FNAL.FNAL.GOV
~ SPAN/Hepnet: 43011::HIGGINS
John David Regehr
week or so. I'm writing a paper contrasting manned and unmanned spaceflight.
I'm in the middle of a couple of books, but I haven't been able to come up
with a good thesis statement yet. I would appreciate hearing from people who
have opinions on the subject, or who can suggest some good reference material.
I am trying to approach this from a practical and philosophical standpoint,
rather than detailing the historical controversy on whether the focus of space
exploration should be on manned or unmanned flights. Thanks.
-----------------------------------------------------------------------
John Regehr jre...@matt.ksu.ksu.edu
Kansas State University
-----------------------------------------------------------------------
Henry Spencer
>#THE ERROR. At which point, Perkin-Elmer management decided that the third
>#was more trustworthy than the other two, and ignored the two failed tests.
>
>The tests to which you refer are the refractive null and
>the inverse null, in addition to the faulty reflective null.
>All three of them are based on the same basic interferometric
>technology, and are not independent in the sense that I
Okay, point taken -- more diversity in tests is desirable. However...
>...Had they measured the position of
>the field lens with a PLASTIC RULER, it would have been found.
>There were lots of red flags flying, and they were all ignored.
>
>By an independent test, I meant a geometric-optics test such as a
>Hartmann test that could have, fairly cheaply, detected the problem...
Ah, but would it have been believed? That's the crucial problem. My
impression is that it wasn't "we've got three similar tests, and the
best one says we're okay", but rather "we've got three tests, and the
best one says we're okay". The trick was not detecting the error --
after all, it *was* detected -- but detecting it in a way that would
have been sufficiently emphatic and unmistakable to make P-E doubt
their beautiful reflective null corrector.
The point of an end-to-end imaging test, in this context, is not that
it's an easy way to detect the problem, but that it's so hard to
argue with.
David M. Palmer
>The point of an end-to-end imaging test, in this context, is not that
>it's an easy way to detect the problem, but that it's so hard to
>argue with.
How do you do an end-to-end imaging test? The depth of field of
an instrument with Hubble's aperture is such that a point source
must be thousands of kilometers away in order to be in focus.
--
David Palmer pal...@alumni.caltech.edu
Robert W Murphree
>Sorry if this is a dead subject, but I've only been reading this group for a
>week or so. I'm writing a paper contrasting manned and unmanned spaceflight.
>I'm in the middle of a couple of books, but I haven't been able to come up
>with a good thesis statement yet. I would appreciate hearing from people who
>have opinions on the subject, or who can suggest some good reference material.
>I am trying to approach this from a practical and philosophical standpoint,
>rather than detailing the historical controversy on whether the focus of space
>exploration should be on manned or unmanned flights. Thanks.
Your really going to get overwhelming pro-manned space from these groups.
Nick Szabo sometimes posts antimanned stuff.
Have you read "and the heavans and the earth" by Walter Mcdougall,
Bruce Murray's new memior Journey to the Planets and his old book, before
he became a politician, navigating the future, there's a new book by
somebody burrows who wrote "deep black" on the politics of satellite
reconaissance. The burrows book, whose title excapes me, is probably the
best single peice. If you haven't read "the right stuff" by Toma
Tom Wolfe on how astonauts became somebody instead of nobody you should
either read it or watch the movie. I have an extensive anti-manned
bibliography that I would be willing to share if you'll give me
your address. Since your in Kansas you might call me, I',m in
oklahoma my number is (405)-447-7590.
I have shared my bibliography with others who have written policy
statements on men vs machines, here at OU. Also, I lobbies against
the space station in 1991.
Henry Spencer
>How do you do an end-to-end imaging test? The depth of field of
>an instrument with Hubble's aperture is such that a point source
>must be thousands of kilometers away in order to be in focus.
I'm not an optics guru... but the test was considered feasible, if costly
and somewhat risky. My guess would be a bit of optics to move a real
source out to a virtual infinity, as is done in head-up displays.
robert.f.casey
>
>>The point of an end-to-end imaging test, in this context, is not that
>>it's an easy way to detect the problem, but that it's so hard to
>>argue with.
Well, they could have said "oh, the reason it's out of focus is the Earth's
gravity field is distorting the mirrors. Has to be that, the big mirror
tested great before!" :-(
Robert S. Hill
>In article <1f0tg2...@gap.caltech.edu> pal...@cco.caltech.edu (David M. Palmer) writes:
>>How do you do an end-to-end imaging test? The depth of field of
>>an instrument with Hubble's aperture is such that a point source
>>must be thousands of kilometers away in order to be in focus.
>
>I'm not an optics guru... but the test was considered feasible, if costly
>and somewhat risky. My guess would be a bit of optics to move a real
>source out to a virtual infinity, as is done in head-up displays.
It's not that hard to set up a collimator: it's just a big parabolic
the size of the telescope aperture, with a very small source of the
appropriate wavelength positioned at the focus. This is good enough
for shimming the overall focus of a small instrument. I don't work on
HST, I don't know what they would have done for it.
Robert S. Hill
bh...@stars.gsfc.nasa.gov
Dave Batchelor, Space Phys. Data Facil. 301/286-2988
A fine article on this subject appeared earlier this year in _American
Scientist_. The title was approximately "An Argument for Manned Space
Exploration." The basic concept was that critics of manned flight say
automated/robotic missions are safer, cheaper means to achieve the same
scientific returns that manned missions can; however, AI and robotics
are acknowledged by professionals in those fields to be primitive and
very modest in their accomplishments, outside the space probe context.
The author of the article highlighted this logical inconsistency. Robots
of today and the near future are DUMB and CLUMSY, compared to astronauts.
Why should we risk getting inconclusive or skimpy results from missions
limited to what robots can do or will be able to do in the next few decades?
Examples: the Viking Mars lander could not answer the burning question of
whether life exists on Mars (rather than strange soil chemistry that
resembles life). Many activities of the astronauts during the lunar
landings would have been far beyond the capabilities of robots then and
in the near future, such as retrieving soil core samples (which happens to
be a very delicate and demanding task). When the Skylab space station was
disabled by loss of half the solar power arrays during launch, the
astronauts were able to restore it to nearly full functioning, saving a
multi-million dollar spacecraft and returning tremendous scientific
advances in solar physics and other disciplines. Also, the Hubble Space
Telescope almost had to be rescued by space walkers during its deployment
from the Space Shuttle.
The article gives such examples and really makes its point well: critics of
manned missions actually propose reliance on some very limited technological
substitutes for a human being with a tool kit or some instruments. And
does anybody explore places like Antarctica with robots?
Enjoy,
])ave
------------------------------------------------------------------------------
Dr. David Batchelor Space Science Data Operations Office Mail Code 632
NASA Goddard Space Flight Center Greenbelt MD 20771 USA
batc...@nssdca.gsfc.nasa.gov == &( personal_opinions && !NASA_policy );
William H. Jefferys
#>Hartmann test that could have, fairly cheaply, detected the problem...
#
#Ah, but would it have been believed? That's the crucial problem. My
#impression is that it wasn't "we've got three similar tests, and the
#best one says we're okay", but rather "we've got three tests, and the
#best one says we're okay". The trick was not detecting the error --
#after all, it *was* detected -- but detecting it in a way that would
#have been sufficiently emphatic and unmistakable to make P-E doubt
#their beautiful reflective null corrector.
I can't argue with that! The tests that were performed
lacked "visibility," that is, adequate oversight by people
not involved with the actual testing to ensure that
the anomalies would have been investigated instead of
ignored. At the time, everybody thought the mirror project
was in good shape. People's attentions were directed
elsewhere, because another telescope component was felt
to be at high risk. Thus it was possible for people at a
fairly low level to dismiss the mirror anomalies as inimportant.
#The point of an end-to-end imaging test, in this context, is not that
#it's an easy way to detect the problem, but that it's so hard to
#argue with.
Absolutely correct. And an end-to-end test would have had
"visibility."
Bill