Oops. I should have learnt by now that I stray into the whole 'Physics' domain at my peril. I've redacted this post in response to comments (which I have left in place) - thanks to Drew and anonymous for those.
On a recent visit to Washington DC I managed a quick look at the Smithsonian's National Air and Space Museum, which was great. Unfortunately I didn't get out to the Udvar-Hazy Annex near Dulles airport, but that's for another time. Anyway, downtown one of the exhibits I saw was a Hubble space telescope. It was placed in between the Skylab Orbital Workshop, and a linked pair of Apollo and Soyuz command modules.
It prompted a number of thoughts:
- first, scale: when you have an opportunity to see things like the early Gemini re-entry capsules, the Apollo command/re-entry module, the lunar lander, the space telescope and the Skylab section (in order of increasing size), it reinforces the impression that the Hubble is big. It's on the same general scale as the other large exhibits, but of course they had the additional design requirement of being able to contain human beings. With the Hubble, it's all machine. [The Hubble was launched using the Space Shuttle, as Drew points out. The US National Reconnaissance Office is apparently a bit reticent about how/when Keyhole-type satellites are launched, but according to howstuffworks.com, both the Shuttle and Titan-4 rockets are viable vehicles. The Spaceflight Now site maintains that the Keyhole has an optical resolution down to about 10cms/4ins - though one could expect the resolution of imaging released to Google to be significantly lower than that retained for intelligence purposes. In terms of size, the Hubble is about 40 feet long and has a telecope barrel of 10ft diameter. The 'fairing' mounted on a Titan-4 rocket for presumed Keyhole launches is about 66ft long.]
- second, the Soyuz command module reminded me irresistibly of the Starbug from Red Dwarf.
- third: did you know that the Hubble space telescope is essentially the same as the Keyhole surveillance telescopes from which (among other things) Google gets its satellite pictures of your roof? It's just pointed inwards rather than outwards. [anonymous casts doubt on this - but I refer you to Prof. Mark Monmonier's 2002 book "Spying With Maps", in which he explains the shared heritage of Hubble and Keyhole, and the different techniques used by surveillance satellites for 'straight down' and 'oblique' imaging. The 'How Stuff Works' site, among others, confirms the similarity. Drew - in my defence, I did say that the Keyhole mapping is just one of Google Maps' imaging sources...]
[A further update as of Tuesday Sept 4th., on the question of the maximum theoretical clarity of trans-atmospheric imaging: this BBC article describes how scientists from Caltech and Cambridge have used software to 'sharpen' the images captured by a 200-inch telescope at Mount Palomar Observatory by compensating for atmospheric distortion. The article points out the conflicting factors of atmospheric distortion and telescope size...]
So it makes sense, I suppose, that the current version of Google Earth includes a "Sky" button which you can use to get your own virtual planetarium.
Well - that's your productivity ruined for a few hours... I'm off to do some work.
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Hubble was launched from the Space Shuttle, NOT a Saturn 5. If Wilton can't get that public fact right, how can you possibly believe his conjecture that the Hubble is the same as a Keyhole?
Posted by 71.178.189.252 on September 04, 2007 at 02:17 AM GMT+00:00 #
Robin, ye gods man! Two factual errors in one post! What is the world coming too? The astronomer in me can't let those go...
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The HST was launched from a space shuttle in 1990, not a Saturn 5. The last thing launched from a Saturn 5 was the ill fated Skylab in 1973 as I recall, bits of which got ripped off on the way up, and bits of which were showered over Australia on the way down... (for which the americans were sent a littering invoice they never paid!)
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Secondly, Google Earth is a composite of satellite imagery (resolution 15metres) and aerial photography (down to .5 metres or so)
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Interestingly, satellite imagery, under perfect conditions in a low orbit has a theoretical resolution of 10cm, so contrary to conspiracy theories it will never be possible to read number plates or newspapers from space...
Posted by Drew Wagar on September 04, 2007 at 08:32 AM GMT+00:00 #