From its original total cost estimate of about US$400 million, the telescope cost about US$4.7 billion by the time of its launch. Hubble's cumulative costs were estimated to be about US$10 billion in 2010, twenty years after launch.[58]Gee, just short of 12x the original cost estimate. NASA has a webpage dedicated to the telescope filled with all sorts of eye-popping pictures.
Probably the thing that the HST is best known for is having a defective primary mirror. HST's optical design is a type of a Cassegrain reflector called a Ritchey-Chrétien. RCs have become the preferred optical configuration in high end research observatories because they provide a wide photographic field with less optical distortion off axis than others. There are three or four types of optical Cassegrain reflectors, which have a concave primary (big) mirror and a convex secondary mirror that typically is around 25% to 30% of the diameter of the primary. In the RC, both mirrors are hyperbolic (a hyperboloid of revolution).
Convex mirrors of all sorts are more difficult to test than concave mirrors, and require another calibrated mirror to test against. It has become common practice in testing optical systems to develop a test system with its own optical surfaces that need to be certified correct and use that to test the system being built. According to a report in New Scientist in 1990, the issue with the HST was because the test system was built incorrectly and yet certified.
NASA has established how a mirror aboard its $1.5 billion Hubble Telescope came to be the wrong shape. The agency said last week that errors in a test instrument apparently led Perkin-Elmer, which fabricated the optics, to finish the 2.4-metre primary mirror of the Hubble Space Telescope incorrectly. Tests by NASA earlier this month showed that a lens in the test instrument, called the ‘reflective null corrector’, is about a millimetre askew. Preliminary analysis indicates that an error of this magnitude could cause the spherical aberration that prevents Hubble from focusing sharply.
For reference, 1mm is just over .039 inch. That's more than 1/32" and thousands of woodworkers could make the fixture to that accuracy. The surface is being judged compared to wavelengths of light, around 20 millionths of an inch. Because of this error, Hubble's primary was made flawlessly to the wrong prescription. It has been said that an amateur with a light bulb and a straight edge - a Foucault tester - could have told them their mirror was wrong. And that amateur would have been ignored because their instrument wasn't certified.
I've mentioned a couple of times that I've made a few telescope mirrors grinding glass and then building the instruments. I've done a lot of Foucault tests. I think I could have told them their mirror was wrong.
Hubble's optical system was corrected by adding more optics; a package called COSTAR, The Corrective Optics Space Telescope Axial Replacement. You can be sure it would have produced better images without the additional optics of COSTAR but they made the best of a bad situation.
And when it (they) were turned toward Earth instead of the stars, they were designated KH12's. And re-tasking them here and there to look at this or that from high orbit was expensive and required a few chops before it could happen.
ReplyDeleteHere's a story for you: 30 years ago I worked at a place I've always called Major Southeast Defense Contractor. They were involved with Hubble as well as Galileo and other NASA satellites - along with the Black world.
DeleteSomeone decided the break room needed a picture of the HST to show what we did. They showed the telescope looking down. Force of habit, I suppose.
Martin-Marietta? Didn't they have a major facility in Orlando? I worked at Sperry Microwave Electronics in Clearwater in the early 80's (they changed their name a half-dozen times before being sent to prison).
DeleteNope, nope, nope. I've driven by the Lock Mart plant in O'do, but that's as close as I've gotten.
DeleteThe Hubble mirror problem? I remember that, they fixed it.
ReplyDeleteWhat I remember the Hubble for are those photographs and the number of times I've read of it described as a huge jump in human knowledge!
Then there is the Hubble Ultra Deep photo! 10,000 galaxies in that small black chunk of space. I do know that a galaxy is really big...
The three Deep Field photos are amazing. They pointed the scope at a spot in the sky with very few stars and just let it collect light.
DeleteThe last one, the Ultra Deep Field from 2004 is over 11 days worth of exposures stacked together.
IIRC, the reason (or one of them...) the flawed optics "slipped by" is that to check them to the required accuracy required using equipment for which none of the Hubble Team had a clearance to use.
ReplyDeleteWhen you closely examine pixels on the background like that, finite element mesh subdivides to provide more detail and it takes more CPU to render. Somewhere a fan is spinning faster on a video card in a zoo's machine room. I hope the zookeepers are keeping the dust vacuumed out of it.
ReplyDeleteThe computer graphics ray tracing implementation of woodgrain inside a volume of arbitrary shape is a subroutine which can return the color of any pixel in the volume. It's easy enough to make that calculation fractal so it can return a self-similar result of "galaxies" and "stars" at any resolution. Cosmologists get invent "dark matter" and "dark energy", because they're assuming an implementation made with formulas which is globally consistent. It's not globally consistent, it's just a hack good enough for the movies; it's a case statement riding on top of a dynamically resizing mesh resolution. Keep building bigger telescopes to explore the fractal, you will see galaxies forever. Unless you hit another implementation limit of word size, like the Planck size, and at a certain resolution it goes black.
ReplyDeletehttps://en.wikipedia.org/wiki/Planck_units
Meanwhile, the political recipe for a few humans to parasitize most other humans was already perfected by the time we have written history, because it's just a cosmology rationalization added to preexisting great ape political instincts. The rulers' employees in the government school/church teaches children the Sky Monster will torture them in another reality for eternity if you don't do what the rulers tell you the Sky Monster is demanding you do. Which is obey and stay on the tax/inflation treadmill and never get ahead.
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ReplyDeleteHubble and the mirror screw-up was the first time that everyone saw NASA's insanity. I mean they should have seen it when Challenger exploded, because of a political agenda. And there was a Mars lander that was lost when a subcontractor didn't get the word that parameters were in international units not English units, but I can't actually remember when that was.
ReplyDeleteHubble could have (should have?) been detected if it had been assembled and tested before it was launched. But NASA didn't need to TEST things! They couldn't make such a simple mistake. They are NASA!
There's an old Heinlein novella or short story. "The Man Who Sold the Moon." As much as I don't like Elon Musk, NASA is not what we need managing space flight. I knew that when they designed the Space Truck, but then later it became clear because they needed a reel-to-reel tape deck to replace one that had gone bad and where searching Ebay or its equivalent for one, because they were incapable of updating even one small part of the original design, even though what they needed was no longer manufactured by anyone anywhere on the planet. Because we had all moved to smaller, recorders.
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