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Fixing Hubble
In Honor of Frank Cepollina’s 80th Birthday
Holland Ford
Cepi and General George S.
Patton
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I describe Cepi to my friends as NASA’s General
George S. Patton, and that is meant as a compliment.
Like Patton, when Cepi gets new directives from
above, he is already either on his way, or, he has
already taken the next town.
Now, a short story about Cepi, Carolyn Krebs(ACS
Project Manger), me, and Knickers.
Missions for Ceppi
Spherical Aberration
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After a successful launch and deployment of Hubble, my
first inklings that there might be a problem was hearing
people at lunch in the Institute say, “the engineers are
having trouble focusing the telescope”.
Soon afterward, I heard a rumor that Chris Burrows thought
Hubble’s primary mirror was producing spherical
aberration. I think at first the Perkin Elmer engineers were
in a state of disbelief. This was, after all, the most perfect
mirror ever made. But, if Chris thought it was spherical
aberration, I knew we were in real trouble .
So What Should NASA Do?
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Well, go fix it.
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But how?
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NASA planned to periodically replace old instruments
with newer and more capable instruments.
A replacement for WFPC I was already being built, so
the spherical aberration could be (and was) corrected
inside WFPC II.
Genesis of the HST Strategy Panel I
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I had two concerns about the way NASA was proceeding.
First, there were 4 axial instruments that likely were going
to have to make do with aberrated images until the first
servicing mission, and then be replaced
My second concern was that the institute largely was out of
the loop. I felt strongly that the Institute should be involved.
Part of our charter was to represent the interests of all
astronomers who planned on using Hubble.
I didn’t think we were doing that.
Convincing Giaconni
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At the end of every staff meeting Ricardo would ask, “is there
anything else”. I raised my hand and said, “I think we should
fix Hubble”. I explained that by that I meant we, the Institute,
should convene a Tiger Team, that is, a group of very smart
people, and see if the brainstorming could come up with a
solution that would fix all instruments. This suggestion was
based on my experience as FOS Instrument Scientist. On two
occasions, Tiger Teams helped us solve serious problems with
the FOS Digicon detectors.
The third time I said this at a staff meeting, he said “do it”.
One of my colleagues, Bob Brown, told Ricardo that he
should lead the Tiger Team rather than me. The compromise
was that we would be co-chairs.
That compromise worked very well. The task was more than
one person could do, and, our experiences complemented
each other.
The HST Strategy Panel II
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Rather than a Tiger Team, Bob suggested we call the group
“The HST Strategy Panel’. The name was a good way of
describing the importance of the task ahead of us.
Lessons Learned
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1 Move fast while you have NASA’s attention.
Choose a diverse (optikers, engineers, astronomers,
astronauts) group of the most talented people you can
find.
Have an open brainstorming sessions where every idea
is given consideration.
You can’t a priori predict who will have the best idea.
So, who did we get?
Panel Members
What Does COSTAR Mean?
Corrective Optics Space Telescope
Axial Replacement
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COSTAR was Jim Crocker’s inspiration. Jim had
three ideas, conceptually simple, but brilliant.
First, we could sacrifice one of the axial instruments,
the High Speed Photometer, and use that space for
Costar.
Second, after installation, COSTAR would extend an
optical bench through the cassegrain hole in the
primary, thereby providing access to the front side of
the primary mirror.
Third, it would deploy pairs of mirrors that would
correct the spherical aberration for the three remaining
axial instruments.
Conceptual COSTAR
M1, a spherical mirror intercepts the
aberrated beam and directs it to M2.
M1
M1
M2
M2, an anamorphic fourth-order asphere, has the exact
inverse polishing errors of the HST primary mirror.
COSTAR Schematic
COSTAR Key Requirements
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Obviously, the “bench” had to deploy.
The M2 mirrors, anamorphic fourth-order aspheres fabricated
on toroidal blanks, had to have the exact inverse aberration on
the primary mirror. The first 3 vendors could not make the M2
mirrors. Cepi directed us to go to Tinsely Optics, who
succeeded.
The M1 and M2 mirrors had to be deployed to the correct
positions with a precision of ~0.1 mm. This was not easy.
The deployed arms had to be stiff enough to prevent vibrations
induced by moving parts in HST and other instruments.
COSTAR – Start to Finish I
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The HST Strategy Panel’s findings and recommendations
were presented to Dr. Riccardo Giacconi, Director of the
Space Telescope Science Institute, on October 18, 1990.
Dr. Giacconi endorsed the oral recommendations of the
Panel and took the findings to NASA management. The
Panel made a presentation at NASA Headquarters on
October 26, 1990. In the following weeks, NASA and Ball
Aerospace conducted an intensive study of the feasibility
and costs of COSTAR.
In December 1990, NASA Headquarters authorized the
implementation of the COSTAR program to proceed.
COSTAR – Start to Finish II
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I thought my work was done. However, Jim Crocker asked
me to be the Costar Project Scientist, an offer I accepted.
Ball Aerospace began design and proposal work in
November, and was awarded a contract in January 1991.
Costar was built from start to finish in 28 months.
“On December 2, 1993 following a one-day delay for
weather, Endeavour was launched.”
On the 7th day of the mission, astronauts Kathy Thornton and
Tom Akers removed the High Speed Photometer and
installed Costar in its place.
Kathy Thornton Installing COSTAR
SM1 Was Very Demanding
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In addition to replacing WFC1 with WFC2 and
replacing the High Speed Photometer with COSTAR
they had the replacement tasks below.
SM1 Was a Great Success
FOC Before and After
WFC1 and WFC2
Hubble Transformed Our
Understanding of the Universe
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But, getting there was not an easy.
On Jan 28, 1986, the Space Shuttle Challenger
with a crew of seven, exploded 78 seconds after
launch. The launch was the 25-th Shuttle Launch, and
Challenger’s tenth launch. Before Challenger, based on a
failure rate of roughly one in a hundred solid fuel powered
missile launches from Van Den Berg Air Force, I put the
odds for Shuttle launch failures at one fifty. In 1983, a
study for the Air Force put the odds of a Shuttle loss during
launch at 1 in 35.
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Challenger’s Crew
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Sadly for the crew and school teacher Crista McAuliffe, “Before the
Challenger disaster, agency officials regularly asserted that the chance
of disaster was 1 flight in 100,000”.
Knowing the Challenger’s Commander, Dick Scoby, made Challenger
very personal for me. All I can say about those particular agency
officials is, “they were dammed idiots”.