"... So the pressure was on us to reduce costs. We had some actual points to use as targets. And the coming out to 2.4 meters was the right decision. We had things that we generally didn't expect, like this business about 2.4 meters being just about the largest size you could package with a low moment of inertia, a point I made in the review panel. That was really the driver, on 2.4 meters. That's what kept the costs down. That was the big break on the costs. The uncertainty of cost in making 3 meter optics was great, but very hard to define, whereas the certainty of the difference in cost between reaction wheels and control moment gyros was clear. That was black and white".https://www.aip.org/history-programs/niels-bohr-library/oral-histories/4802-1
I was interested in the comment about reaction wheels versus CMGs and the general pointing/stability/structure issue. Do I infer from the interview that @hoku quoted that CMGs are newer and better than reaction wheels but were not used on Hubble for cost reasons ? Bit I've bolded seems to imply that ? This squares with fact that reaction wheels appear in Noordung whereas CMGs are mentioned in one of the NRO pioneer's citations.Quote from: hoku on 10/01/2021 05:31 pm "... So the pressure was on us to reduce costs. We had some actual points to use as targets. And the coming out to 2.4 meters was the right decision. We had things that we generally didn't expect, like this business about 2.4 meters being just about the largest size you could package with a low moment of inertia, a point I made in the review panel. That was really the driver, on 2.4 meters. That's what kept the costs down. That was the big break on the costs. The uncertainty of cost in making 3 meter optics was great, but very hard to define, whereas the certainty of the difference in cost between reaction wheels and control moment gyros was clear. That was black and white".
"... So the pressure was on us to reduce costs. We had some actual points to use as targets. And the coming out to 2.4 meters was the right decision. We had things that we generally didn't expect, like this business about 2.4 meters being just about the largest size you could package with a low moment of inertia, a point I made in the review panel. That was really the driver, on 2.4 meters. That's what kept the costs down. That was the big break on the costs. The uncertainty of cost in making 3 meter optics was great, but very hard to define, whereas the certainty of the difference in cost between reaction wheels and control moment gyros was clear. That was black and white".
Quote from: LittleBird on 10/06/2021 07:07 amI was interested in the comment about reaction wheels versus CMGs and the general pointing/stability/structure issue. Do I infer from the interview that @hoku quoted that CMGs are newer and better than reaction wheels but were not used on Hubble for cost reasons ? Bit I've bolded seems to imply that ? This squares with fact that reaction wheels appear in Noordung whereas CMGs are mentioned in one of the NRO pioneer's citations.Quote from: hoku on 10/01/2021 05:31 pm "... So the pressure was on us to reduce costs. We had some actual points to use as targets. And the coming out to 2.4 meters was the right decision. We had things that we generally didn't expect, like this business about 2.4 meters being just about the largest size you could package with a low moment of inertia, a point I made in the review panel. That was really the driver, on 2.4 meters. That's what kept the costs down. That was the big break on the costs. The uncertainty of cost in making 3 meter optics was great, but very hard to define, whereas the certainty of the difference in cost between reaction wheels and control moment gyros was clear. That was black and white".WikiCMGs differ from reaction wheels. The latter apply torque simply by changing rotor spin speed, but the former tilt the rotor's spin axis without necessarily changing its spin speed. CMGs are also far more power efficient. For a few hundred watts and about 100 kg of mass, large CMGs have produced thousands of newton meters of torque. A reaction wheel of similar capability would require megawatts of power.[3]
CMGs weren't used on HEXAGON
Quote from: Blackstar on 10/01/2021 08:27 pmIn that 1985 interview he references what he says is a pretty good Sky & Telescope article. Maybe that's what I was thinking of (not Scientific American). I wonder if I can find that. I have access to a research librarian, but I need to give them more specifics. I'll have to go digging.Found it in the "dungeons" of our archive (see attachment). While there, I also scanned a few pages of an Oct 1990 article, which includes a photo of the polishing set-up for HST's 94.5 inch primary at Perkin-Elmer (as well as a famous cartoon reflecting the public opinion at that time.
In that 1985 interview he references what he says is a pretty good Sky & Telescope article. Maybe that's what I was thinking of (not Scientific American). I wonder if I can find that. I have access to a research librarian, but I need to give them more specifics. I'll have to go digging.
Interesting btw to see Lew Allen popping up again as chair of enquiry board.
Quote from: LittleBird on 10/07/2021 06:56 amInteresting btw to see Lew Allen popping up again as chair of enquiry board.You don't read about him much these days, but he was well-regarded at the time. He played a key role in GPS in addition to his NRO work.After he left the Air Force he ran JPL during the 1980s:https://en.wikipedia.org/wiki/Lew_Allen
He certainly had an interesting and rich career. Few people can boast having worked altogether, for the NRO, Air Force, NASA-JPL, and NSA (among others).
This is a bit of a sidenote, but it's worth understanding when we look at the history of science and technology, that most technologies have a very long development time and are rarely ever suddenly developed. This was something that struck me when I was first researching Samos back in the 1990s. I thought that the "flying spot scanner" that scanned the developed film and sent it out electronically was a new thing, invented for the satellite. Nope, some version of that technology--essentially equivalent to a fax machine--had been around since the 1940s. Newspapers used to transit photographs over telephone lines using that kind of technology. I don't know of a good source on that, but the tech was around. (There are probably photos of the early news photo machines used for this somewhere on the internet, but I've never gone looking for them.)
A technician is talking on the phone to another technician who is sending the photo over the phone line--his machine is scanning the image, then it's going through the analog phone line, and the technician at the other end turns on his machine which has a spinning drum. Inside the spinning drum is a piece of light sensitive paper.
QuoteA technician is talking on the phone to another technician who is sending the photo over the phone line--his machine is scanning the image, then it's going through the analog phone line, and the technician at the other end turns on his machine which has a spinning drum. Inside the spinning drum is a piece of light sensitive paper.Used to have a fax machine in my office that did that, but it was thermal paper.
Quote from: Blackstar on 10/04/2021 05:03 pmThis is a bit of a sidenote, but it's worth understanding when we look at the history of science and technology, that most technologies have a very long development time and are rarely ever suddenly developed. This was something that struck me when I was first researching Samos back in the 1990s. I thought that the "flying spot scanner" that scanned the developed film and sent it out electronically was a new thing, invented for the satellite. Nope, some version of that technology--essentially equivalent to a fax machine--had been around since the 1940s. Newspapers used to transit photographs over telephone lines using that kind of technology. I don't know of a good source on that, but the tech was around. (There are probably photos of the early news photo machines used for this somewhere on the internet, but I've never gone looking for them.)Yeah, I'm replying to my own post.Somebody tipped me off to the 1948 movie "Call Northside 777" starring Jimmy Stewart (yes, the nice Jimmy Stewart). <snip>
Just noticed this NRO press release page:https://www.nro.gov/News/News-Articles/Article/2803800/nro-celebrates-60-years/The one useful thing it has there is a collection of all the new links for declassified documents. It's a good shortcut page.
Quote from: hoku on 10/05/2021 05:34 pmQuote from: Blackstar on 10/01/2021 08:27 pmIn that 1985 interview he references what he says is a pretty good Sky & Telescope article. Maybe that's what I was thinking of (not Scientific American). I wonder if I can find that. I have access to a research librarian, but I need to give them more specifics. I'll have to go digging.Found it in the "dungeons" of our archive (see attachment). While there, I also scanned a few pages of an Oct 1990 article, which includes a photo of the polishing set-up for HST's 94.5 inch primary at Perkin-Elmer (as well as a famous cartoon reflecting the public opinion at that time. I don't want to send you back to the bowels of some dusty library, but having got to the end of page 353 I am now hooked ... I want to know if the butler did it ;-)<snip>
Here is the laser scanner that I mentioned earlier. I wonder if there was any commercial laser scanning equivalent in the 1960s/70s?
