Hubble's megapixels

Discussion in 'Casual Photo Conversations' started by wildflower art, Jul 8, 2012.

  1. The visual imager of Hubble is three large format 1024 x 1024 array sensors, the STSI.
    Am I correct in saying that the Hubble has a megapixel equivalent of about three? Three megapixels?
    http://www.stsci.edu/hst/stis/design/detectors/
    That's pretty good for 1990!
    They have to keep the camera steady, accounting for the rotation of Hubble around the Earth and Earth around the Sun. This is called Astrometry.
    What would they do now? Like with Jim Webb? Could they put an image stabilizer that moves the chip to account for that rotation instead of moving the how telescope?
    How would you do the Hubble 2 (Jim Webb)? Like a quartz reflex lens that lets in all UV and IR light?
    Would you put a new digital chip in Hubble now? Three square large format chips? Can you image Kodak working on a digital chip for large format (four by five inches)? How many megapixels would that be?
    I wonder how long it takes them to send a three megapixel picture that far away... I used a wi-fi connection to send a picture from camera to computer, ten minutes and low battery power and that was two feet!
    Matt
     
  2. Hubble is am interesting topic. It allows us to consider techology that we consumers think of as new. Consider how long spy satellites have been in orbit. To my knowledge, no satellite that ever stayed in orbit used film. Satellites have been shooting digital pictures and transmitting them to Earth longer than many of us have been alive. (Cuban missile crisis, anyone?) Yet we think of digital cameras as a fairly new concept.
    My understanding is that Hubble is a Keyhole satellite turned around to look up instead of down. So the working platform for telemetry and image stability was already figured out long before it became a scientific telescope.
     
  3. John, it appears the early satellite images were analogue video transmissions; makes sense considering digital technology and integrated circuits were primitive even in the 70s.
    http://en.wikipedia.org/wiki/Satellite_imagery#History
    There was a PBS documentary on the Hubble service mission described in my second link above. It's well worth watching and available on-line to certain countries:
    http://www.pbs.org/wgbh/nova/space/hubbles-amazing-rescue.html
    What amazed me most about the program was that contractors who built the Hubble were still using Phillips-head screws as fasteners. I would have thought any variety from the Torx family of screws would have been much preferred, especially after the problems astronauts encountered from servicing the Hubble and their experience with broken and stripped screw-heads.
     
  4. What would they do now? Like with Jim Webb? Could they put an image stabilizer that moves the chip to account for that rotation instead of moving the how telescope?​
    They would likely do the exact same thing! Remember, you're not talking so much about "the jitters" humans have when holding a camera. Hubble exposures are many seconds long (if not minutes or longer...), and to image a specific object requires a lot of work to keep it on target, especially when orbiting at 17,500 MPH!. Hubble's sole method of pointing is by the use of gyroscopes. Hubble (Webb, too) has to be able to point in any given direction, so you could not have it always pointing in one direction, and still image the entire universe.
     
  5. I recall reading about a processor upgrade in the late 90's where they were installing the equivalent of a i486 25mhz processor. The explanation was that it was a proven technology - no need to be cutting edge in space if that meant an increased potential for failure.
     
  6. To my knowledge, no satellite that ever stayed in orbit used film.​
    Then you need to update your knowledge. The Gambit and Hexagon series satellites all used film. The film was rolled up in canisters that were parachuted back to earth and recovered using an airplane by snagging the parachutes. The Hexagon series had 60 miles of film onboard. They were programmed to make four film drops over the life of the satellite. The Hexagon series were used through the mid 1980's.
    The surveillance of the Cuban missiles was done using both U-2 aircraft and Navy A-6 aircraft with aerial film cameras.
     
  7. Gyroscopes in space? I wonder how they work without gravity!
    Matt
     
  8. Michael, I share your hatred for Phillips head screws. Why on earth we still use any fastener that won't stay on the end of the screwdriver is beyond me. I have torn more components out of backplanes to find dropped screws than I want to remember. I can't imagine the frustration those astronauts faced. Especially now that almost everyone is using apex bits the use of slotted and phillips head screws is fairly maddening.
     
  9. In the mid 90s I remember reading a one page editorial in Scientific American about the dropping of that mirror. It suggested a constellation of satellites; but, "keyhole" if I remember right, was of a class gone by. Who knows what's up there now.
    How about what we didn't know was up there back when? PBS' "Nova: Astrospies." It described the use of film cameras in space. I think there is a segment in there describing cosmonauts developing film and sending it back to earth by video.
     
  10. John, thanks for the ink to Astrospies. Most interesting.
    The attempts in the 60s to use film was apparently not very successful. The satellite was named Corona and the mission log described many of its challenges:
    http://en.wikipedia.org/wiki/Corona_(satellite)
    Photo of the Pentagon from Corona:
    http://upload.wikimedia.org/wikipedia/commons/2/27/Corona_pentagon.jpg
    It was replaced by the KH-11 Kenna in 1976 which used video sensors:
    http://en.wikipedia.org/wiki/KH-11
    Pretty crude pictures compared to what everyone can get today on Google Earth:
    http://upload.wikimedia.org/wikipedia/commons/2/20/Janeskh11leakedphoto.jpg
     
  11. John (Wilson), an old engineering joke about Phillips screwdrivers: Normally used to stab the vacuum seals under lids, but it excels at converting screws into non-removable screws. :)
     
  12. Gyroscopes in space? I wonder how they work without gravity!
    Matt
     
  13. It's not clear if you saw Michael's reply to your earlier, identical post, however, let me clarify his response: Gyros have absolutely nothing to do with gravity. They don't need it, they don't use it, they don't benefit from it.
    Here's a simpler article on the subject: http://en.wikipedia.org/wiki/Gyroscope . Note that gravity is never mentioned once in this article w.r.t. the principle of operation of these devices.
    Tom M
     
  14. Sorry for the repeat.
    My initial post shows my ignorance.
    Hubble doesn't use lenses, it is a giant mirror.
    It does use CCD sensors like in a Nikon digital camera.
    Since the camera takes UV-IR pictures, the sensor must be like a S2 UV/IR picture.
    Since the Hubble is a giant mirror, larger sensors or more megapixels don't make sense because the telescope focuses light to a pinhole beam.
    Aiming the telescope is a huge issue, they say it is like pointing a laser beam at a target 100 miles away. This may be done in flight, but not by booster, because I don't think Hubble used fuel. The electricty can only power the circuits. How does it fly?
    Hubble takes thousands of images and transmits 120 gigabytes a week. This is a 20 kilabtye/second wi-fi connection spend, based on transmitting a signal by light waves.
    The telescope is powered by rechargeble batteries. Recharged by the sun(!) Which communicates with Earth, powers the camera, sends the pictures, and takes aiming instructions.
    The Jim Webb is also a giant mirror which will take very few optical pictures of the early universe, mostly IR.
    I guess if I were to rephrase my question, what would the ISO of Hubble be? Would a newer, higher ISO sensor be better?
    Matt
     
  15. I guess I have a camera user's joke:
    it would just have to focus at infinity! There is no gradiation between 1,000 miles and infinity on our lenses!
    Matt
     
  16. "what would the ISO of Hubble be? Would a newer, higher ISO sensor be better?"
    I'll take a stab at this, Matt, but only guesses.
    It's really cold up there, but that good for reducing sensor and general electronics noise down to near theoretical minimum. ISO will simply be post-sensor gain once photons have been converted to electrons so I imagine they can apply as much gain until just before it dominates as a primary noise source.
    Given the already large pixel area, I think the only way they can increase performance is to further increase chip/pixel size but probably impractical because the optics and associated electronics is fixed.
    The Hubble apparently transmits digital data to a selected communications satellite which is then resent to a relay station on earth, in New Mexico if I'm not mistaken.
    Hubble has on-board computers and software to lock on to a "guide star" within its field of view then auto-guiding takes over. It manipulates its own position to follow its imaging target as it orbits the earth by way of a reaction wheel explained here:
    http://en.wikipedia.org/wiki/Reaction_wheel
     
  17. "How does it fly?"
    Forgot to add. I think satellites use small chemical thrusters for propulsion to correct its orbital position. Its useful life ends when propellant runs out which causes it to fall back to earth.
    I've always been fascinated by the Lockheed-Martin Multiple-Kill Vehicle demonstration video; I imagine it's how satellites are propelled, but keep in mind that the video shows it hovering on earth which needs to overcome gravity. It's intended to be space-based:
    http://www.youtube.com/watch?v=KBMU6l6GsdM
     
  18. On the subject of screw head types, I have used almost all of them and nothing compares to the Robertson type. It is such a shame he got burnt in buisness in the UK and subsequently severely restricted the licensing of them. They are so workable, never slip, you can undo them when they have been painted over etc etc. I have worked on several Canadian built projects and love it when Roberson fasteners are the fixings used, from a job time perspective they save hours.
     
  19. The visual imager of Hubble is three large format 1024 x 1024 array sensors, the STSI.
    Am I correct in saying that the Hubble has a megapixel equivalent of about three? Three megapixels?​
    The wide field imager stared at a spot in space for 3 months to come up with Hubble's most famous photograph. I would hate to see the noisy mess the iphone 4s' 8 megapixel censor would make of the same image. Megapixels aren't everything. Anyway I'm pretty sure at least one of the current sensors is 16 megapixels.
    The high sensitivity to light of the 16 megapixel UVIS CCD, combined with a wide field of view (160x160 arcseconds), yields about a 35-times improvement in discovery power versus HST’s current most sensitive ultraviolet imager, the ACS High Resolution Channel.​
     
  20. Michael,
    The Corona satellites were not replaced by the KH-11 series. They were replaced by the film-based KH-8 Gambit from 1966-1984 and the KH-9 Hexagon series from 1971-1986. Those were eventually replaced by the KH-11 series.
     

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