* Posts by trsanford

6 publicly visible posts • joined 24 Jul 2017

Hubble Space Telescope sails serenely on in safe mode after efforts to switch to backup memory modules fail

trsanford

Re: Wishful thinking...

Right. Wonderful things appear on the leading edge, and for some reason are not duplicated before they wear out or disappear from view.

NASA awarded the Hubble Telescope objective-mirror contract to Perkin-Elmer; the losing bidder was Kodak. This all was discussed in considerable depth when the winning mirror, built into the instrument and shot off into orbit, turned out to have an aberration. As it happened, the Hubble instrument's accessibility to astronauts enabled the agency to calculate, assemble and install an optical corrector.

There is great demand for viewing-time on pretty nearly all astronomical telescopes, even ones of much more modest specification than Hubble. The Kodak mirror is on display at a museum, from which it could be retrieved. NASA now knows how to build successful space telescopes. The only really serious expense would be a launch vehicle, but surely the people planning joyrides for billionaires could be persuaded to lend a hand ... perhaps by way of apologizing for all the shiny space litter.

T.R. Sanford

Behold, the Ultimately Large Telescope: A revived proposal for a 100-metre liquid-mirror star scanner on the Moon

trsanford

Worth pursuing

I dimly recall a science-fiction story from (I think) the late '50s, perhaps by Arthur C. Clarke, in which a large reflecting telescope is constructed on the moon by filling a large, shallow cylindrical container (like a cake pan) with mercury. The metal is maintained at a temperature above its melting-point while the container is rotated. When it is spinning steadily, the surface of the liquid is made concave by centrifugal force. The apparatus is allowed to cool, so the metal solidifies to form the telescope's objective.

I always wondered whether this would work. Would the concave surface be spherical? If so, there are a good many variations of the Cassegrainian telescope design that place a small secondary lens and/or mirror group on the optical axis to correct spherical aberration.

It had not occurred to me that changing the mercury's phase might alter the geometry of the mirror.

Answering those questions should be straightforward enough. If the answers were affirmative, I think the project would be worth doing. If you did it on one of the lunar poles, a simple altazimuth mount would let you point the instrument at anything in about half of the sky. The task of designing a structure capable of accommodating a 330-foot-diameter mirror and the necessary optics and electronics should be simplified by the much lower gravity of the moon, and the absence of weather. Rotating and tilting it might be about as difficult as aiming the main battery of a World War II battleship.

Has anyone looked for sources of mercury on the moon?

Nine million logs of Brits' road journeys spill onto the internet from password-less number-plate camera dashboard

trsanford

Re: Brownie?

I wondered too. It looks like a single-lens reflex with internal vertical rollfilm transport (e.g., Curt Bentzin Primar), but those didn't use bellows focusing. The designers of those little glyphs enjoy a good deal of artistic license.

Mirror mirror on sea wall, spot those airships, make Kaiser bawl

trsanford

Many reference works available to a child in 1950 (like me) carried detailed accounts of pre-WWII weaponry. I remember seeing pictures of a good many exponential horns, often mounted on wheels, for use as acoustic detectors and direction finders. Your article is the first mention I've ever seen of paraboloidal reflectors used for that purpose.

I do hope someone is documenting all this stuff thoroughly, before it vanishes and is completely forgotten.

This surf-and-turf robot swims using ribbon-like fins. And it's floated for US Navy approval

trsanford

Possible Precursor

I recall seeing an illustration of a boat constructed by the Tissandier brothers in the late 19th century that was designed to test a propulsion system inspired by the way fish swim. The thing had a central longitudinal well, above which was mounted a fore-and-aft horizontal rod. On this rod were pivoted a series of vertical shafts attached to a long strip of stout fabric. Shafts and fabric extended through the well into the water. The drive train caused each shaft to swing back and forth in sequence, causing the fabric to undulate rhythmically and drive the vessel forward. It is said to have worked well, though it has obvious disadvantages for many of the purposes for which you'd want a boat.

I ran into this in an ancient bound volume of Scientific American, a long time ago. I'm surprised that it has not made its way into Wikipedia, which recognizes Gaston and Albert Tissandier primarily for their contributions to aerostatics.

US vending machine firm plans employee chip implant scheme

trsanford

Re: Vending machines?

They aren't vending machines, although many operators of vending machines offer micromarkets to their larger clients. A micromarket works pretty much like the self-checkout line in a supermarket customers pick their items from those shelves and coolers, then scan them and pay at a "kiosk." I'm not sure how many patrons will want to have an NFC chip implanted in order to streamline the payment process, but then, I can't understand why so many people use Twitter, either.