By Corey S. Powell in Discover
Magazine
If you are old enough to remember
news stories from 1990 (or if you are a devoted student of astronomy), you’ll
recall that the Hubble Space Telescope was not always regarded as the
technological triumph that NASA is loudly celebrating today, on its 25th
anniversary. The orbiting observatory debuted as a king-size disaster: the
telescope that couldn’t see straight, built with a mirror that was ground
perfectly…but perfectly incorrect.
The story of how the error was discovered
and ultimately fixed has been told many times, most recently in a beautiful retrospective
by my colleague Ian Sample at The Guardian. But today it is hard to
appreciate the magnitude of Hubble’s turnaround–the depth of the scientific
despair right after launch, and the many resurrections that transformed Hubble
into the most famous and productive observatory in history. Since Hubble may not live
to celebrate a 30th anniversary, there is no time like the present to tell the
tale.
The Unbelievable Truth
Astronomers knew there was something
wrong with Hubble from the moment they saw the first data downloads. It was
obvious even in the so-called first light snapshot
that NASA unveiled on May 20, 1990. That image, showing a section of star
cluster NGC 3532, should have presented a set of crisp dots of light. Instead
the stars are notably blurred and distorted. Mission scientists were in denial
at first, assuming (or hoping) that they were dealing with a simple problem of
fine-tuning Hubble’s optics. The reality was initially too shocking to grasp.
In retrospect, the NASA press
release accompanying the first-light image reads like a mixture of farce and
tragedy, bragging about the quality of the image (without acknowledging its
readily visible flaw) and applauding the sharpness of the view “even at this
early stage of the focusing task.” Behind the scenes, though, the Hubble team
was finding that their focusing adjustments did not help, because the problem
was built directly into the telescope’s 2.4-meter primary mirror.
It is a tribute to Hubble’s optical
engineers that once they understood the true severity of the blunder, they
almost immediately recognized ways to correct it. By the time NASA held a press conference
on June 27, 1990, acknowledging the problem, Hubble chief scientist Ed Weiler
insisted that “we are deferring science, not canceling science.” He was
frustrated and embarrassed but, by this point, confident that his claim was
truthful.
NASA had designed Hubble so that it
could be serviced and upgraded by astronauts aboard the Space Shuttle. That
meant the telescope could also be repaired–assuming the engineers could figure
out what the repairs should entail. In the case of Hubble’s signature
wide-field camera, it was soon clear that the fix meant installing a whole new
camera containing corrective optics. For Hubble’s other instruments, the
problem was more complicated.
Unlikely as it may seem, the
solution emerged in a Hollywood-style flash of inspiration that took place
while engineer James Crocker was taking a shower.
He realized that a set of optical adapters (mounted on arms resembling the
controls on a European shower) could intercept light beams and reshape them
before they entered Hubble’s three other primary instruments, restoring them
nearly all of their function.
Even as the Hubble team grew
increasingly confident about these solutions, they had to face the hard reality
that NASA would not be able to send a service mission to the space telescope
until 1993. That left three long years to salvage good science out of Hubble’s
impressive but distorted data–and three long years to convince the public that
NASA was not a bunch of bumbling fools who just spent $1.5 billion on a
telescope that could not even take clear pictures of the stars.
Make no mistake, the public attitude
toward NASA was poisonous during that time. The Hubble telescope was the butt
of caustic cartoons, late-night monologue jokes, and Congressional ridicule.
The movie Naked Gun 2 1/2, released in 1991, contained a satirical scene
set in a bar that featured photographs of famous disaster on its walls. The
Hubble Space Telescope was there, right alongside the Edsel, the 1906 San
Francisco earthquake, and Michael Dukakis.
The scientific attitude toward
Hubble was more generous, but not by much. In off-the-record conversations at
the time, several prominent astronomers told me that the money lavished on
Hubble was a waste, and would have been better spent on new telescopes on the
ground. Members of the Hubble team worked feverishly on computer
image-correction algorithms to extract more value from Hubble’s images, which
required considerable additional effort and still did not match the originally
intended results.
NASA’s PR machine engaged in awkward
contortions to put the best possible spin on the situation. In 1991, when NASA
released a Hubble movie of a huge storm on Saturn,
the agency acknowledged the issue with a weak boast: “Each of the 24 frames was
processed to largely remove instrumental artifacts and the effects of the HST
spherical aberration.”
The Resurrections and the
Rehabilitation
As we know now, the 1993 service
mission was a huge success, giving Hubble the clear vision it was built to
achieve and initiating a remarkable 22-year run of incredible science and
breathtaking images. The latter were essential to redeeming the space telescope
in the public eye, but they were equally crucial in selling it (or rather,
re-selling it) to a skeptical scientific community. Just as Hubble’s disgrace
was held in public, so was its rehabilitation, which played out through a
series of press conferences and media releases.
There is a notable sense of
catharsis in the first few sets of images that NASA issued after the 1993 fix.
At last, the Hubble team was allowed–even encouraged–to admit how compromised
Hubble’s images had been. The before-and-after comparisons took on the tone of
a bad weight-loss infomercial, emphasizing the sheer awfulness of the “before”
in order to heap praise on the “after.” Now NASA could cite the “dramatic
improvements” that came with the optics upgrade. A 1993 press release
heaped scorn on a pre-repair image of the 30 Doradus nebula: “It is very hard
to do quantitative measurements on such an image because of the way the light
from many stars overlaps.”
Today the story of Hubble’s repair
feels like dredging up ancient history, which the truest possible testament to
the mission’s success. NASA fixed not only Hubble itself, but also the
telescope’s image in the public and professional communities. Perhaps no single
picture did more in that regard than the iconic 1995 Pillars of Creation
view of the Eagle Nebula, a visually and scientifically stunning look at how
stars are born and emerge from their gaseous cocoons.
But there is more to the story of
Hubble’s resurrection, much more. Crucial though the 1993 repair mission was,
it merely salvaged Hubble’s reputation; it did not secure it. What has made
Hubble such a lasting success is its continued evolution. Every instrument
aboard has been replaced and drastically upgraded.
The new wide-field camera and
corrective optics package (called COSTAR) are themselves long gone, swapped out
for better instruments. Over the course of three additional service missions,
Hubble has been rebuilt from the inside out. The telescope orbiting Earth today
is a totally different instrument than the one launched in 1990. The primary
mirror is the only major element that remains the same.
Hubble’s new instruments pushed its
vision into the infrared wavelengths needed to study galaxies in the extremely
distant universe; allowed the kind of fine spectroscopy needed to study the
properties of planets around other stars; and provided the high-resolution,
high-sensitivity imaging essential to mapping gravitational lenses and
indirectly tracing the distribution of the universe’s invisible dark matter.
In short, Hubble’s most outstanding
scientific successes have come from observations that lay beyond the
capabilities of the original telescope, even if it had functioned perfectly
right out of the box. It took four service missions–four
different resurrections–to make Hubble the scientific triumph we know today.
One of the most surprising
perspectives on Hubble’s evolution comes from Massimo Robberto, an observatory
scientist at the Space Telescope Science Institute. Reflecting back on the
ridicule heaped on the buggy Version 1.0 of Hubble, Robberto zeroes in on a
cartoon by Ralph Dunagin. Although the cartoon is nominally one more jab at
Hubble’s failure, it centers on the scientists trying to come to terms with the
problem and wondering, absurdly, if maybe the fault lies in the stars, not in
the telescope itself.
As it turned out, Hubble was not
what we expected, but the universe was not what we expected either. Hubble has
been hard at work collecting data on planets around other stars and measuring
the properties of dark energy, two things that were utterly unknown when the
telescope launched. And as Robberto points out,
Hubble was out of focus but the universe is out of focus, too, full of regions
where gravity warps and bends the light of distant galaxies. Dunagin’s
absurdity was not so absurd after all.
That is perhaps the final and
strangest resurrection of all: In forcing astronomers to keep revising the way
they look at the cosmos, Hubble has forced them to revise the way they think
about it as well.
The
entire link with images can be found at: http://blogs.discovermagazine.com/outthere/2015/04/24/the-many-resurrections-of-the-hubble-space-telescope/#.VTtGL5PRV2I
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