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The math of ground-based telescopes v. space-based telescopes v. interstellar probes

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  • #31
    Originally posted by DanS
    Balloon telescopes suck for the same reasons that rockoons suck. They're much harder to handle than they appear and they aren't that stable.
    From University of Pennsylvania

    An international team of researchers has launched the most highly sensitive telescope of its kind to be carried by balloon. The Balloon-borne Large Aperture Sub-millimeter Telescope or BLAST will take a five to nine-day journey along the upper reaches of Earth's atmosphere. BLAST will collect images of objects in our solar system as well as the distant light that details the formation of stars and the evolution of whole galaxies.

    The balloon launched on June 11th from the Swedish Space Corporation facility in Kiruna, Sweden and follow the atmospheric currents toward Canada where it will be recovered.

    Suspended by a massive (37 million cubic foot) unmanned helium balloon, the BLAST will float 126,000 feet up, to the edge of space -- past the pollution and atmospheric conditions that hamper the abilities of even the best Earthbound telescopes. When fully inflated, the balloon would fill a football stadium.

    "While BLAST won't become a permanent fixture in the sky, balloon-based astronomy offers many of the perks of space-based telescopes at a fraction of the cost of actually putting a telescope in orbit and maintaining it," said Mark Devlin, principle investigator for the BLAST project and associate professor in Penn's Department of Physics and Astronomy.

    The telescope's mirror measures two meters (6.5 feet) in diameter and will be capable of surveying a patch of sky about four times the size of the moon to look for faint stellar objects. The entire telescope weighs 2000 kilograms (about 4400 pounds).

    On board, 260 detectors, about 20 times as many ever used on a balloon telescope flight, will convert photons from the observed objects into heat. A rise in temperature would thereby measure the number of photons from galaxies formed 5 to 12 billion years ago, when the universe was one-tenth its current age. The detectors will capture light at three separate wavelengths. By measuring the number of photons at each wavelength of light from an object, the astronomers could determine how far away the object is as well as its luminosity.

    The goal of the project is to conduct a series of experiments to help accurately theories of the formation of stars within our own galaxy as well as the formation of other galaxies. Chief among those is a series of extra-galactic surveys to identify the distant galaxies responsible for producing the background levels of light and radiation that we see throughout the Universe. In addition, BLAST will survey the molecular clouds associated with the earliest stages of star formation. Closer to home, BLAST will observe features of our own Solar System including planets, and large asteroids.

    "Not only are we collecting some unique and interesting information about the universe, but we are also pioneering technologies that will pave the way for other planned balloon projects," Devlin said. "Of course, once we have our data, the real hard part comes in figuring out what all this information means.

    Along with Devlin, the Penn BLAST contingent is comprised of Ed Chapin, Simon Dicker, Jeff Klein, Marie Rex and Chris Semisch. In its entirety, the BLAST project is a collaboration between Penn researchers and colleagues at Brown University, the University of Toronto, the University of British Columbia, the University of Miami, the Jet Propulsion Laboratory, Cardiff University and the Instituto Nacional de Astrofisica of Mexico.

    Support for the research was provided by NASA, the Canadian Space Agency and the United Kingdoms Particle Physics and Astronomy Research Council (PPARC).

    Technical details about BLAST can be found online at: http://chile1.physics.upenn.edu/blas...c/index.shtml.

    Ongoing details about the launch can be found at the blog of University of British Colombia graduate student Gaelen Marsden (http://www.physics.ubc.ca/~gmarsden/kiruna_2005/) and the blog of University of Toronto graduate student Don Weibe (http://gimli.physics.utoronto.ca/Kiruna_2005/).

    Global positioning system tracking of BLAST can be found at NASA's National Scientific Balloon Facility's website:


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    • #32
      Originally posted by DanS
      Look 'em up, bathroom boy.
      I've heard of them, just not by that name.

      Comment


      • #33
        Balloon telescopes

        The fact that they suck doesn't stop people from trying. Who knows, maybe one day they'll get it to work well? Unfortunately, today is not that day.
        “It is no use trying to 'see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.”

        ― C.S. Lewis, The Abolition of Man

        Comment


        • #34
          Re: Unfolding

          Originally posted by pchang
          works great for collectors of long waves (radar, radio, etc.) - it is how the deathstars worked
          we don't have the technology to unfold optic collects and have them come together at the tolerances necessary.
          Is that why JWST isn't optical, for instance? IIRC, that's contemplated as an unfolding telescope. 36 mirror segments. 6.5 meter diameter total.
          I came upon a barroom full of bad Salon pictures in which men with hats on the backs of their heads were wolfing food from a counter. It was the institution of the "free lunch" I had struck. You paid for a drink and got as much as you wanted to eat. For something less than a rupee a day a man can feed himself sumptuously in San Francisco, even though he be a bankrupt. Remember this if ever you are stranded in these parts. ~ Rudyard Kipling, 1891

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          • #35
            reasoning backwards

            It is why they think they can make it unfold. They picked infrared because that was what they wanted to look at.
            “It is no use trying to 'see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.”

            ― C.S. Lewis, The Abolition of Man

            Comment


            • #36
              It's all about wallpaper

              NASA made a poor PR decision. The flagship telescope has to be optical. People like to see what their billions are getting them.
              I came upon a barroom full of bad Salon pictures in which men with hats on the backs of their heads were wolfing food from a counter. It was the institution of the "free lunch" I had struck. You paid for a drink and got as much as you wanted to eat. For something less than a rupee a day a man can feed himself sumptuously in San Francisco, even though he be a bankrupt. Remember this if ever you are stranded in these parts. ~ Rudyard Kipling, 1891

              Comment


              • #37
                That's what

                false color is for
                “It is no use trying to 'see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.”

                ― C.S. Lewis, The Abolition of Man

                Comment


                • #38
                  OK, so it looks like near-term, the max diameter for an optical telescope will be 8 or 9 meters, given that's what the Ares V will be, if they ever get the damn thing built...



                  What can you see with a diameter of 8 or 9 meters?

                  You could probably make an oversized fairing. Might get you a couple extra meters.
                  I came upon a barroom full of bad Salon pictures in which men with hats on the backs of their heads were wolfing food from a counter. It was the institution of the "free lunch" I had struck. You paid for a drink and got as much as you wanted to eat. For something less than a rupee a day a man can feed himself sumptuously in San Francisco, even though he be a bankrupt. Remember this if ever you are stranded in these parts. ~ Rudyard Kipling, 1891

                  Comment


                  • #39
                    U-huh, just use false color. The people who care only about optical telescopes will never realize that the pretty images they get are false color. Chances are that they don't even understand the concept of false color.
                    http://www.hardware-wiki.com - A wiki about computers, with focus on Linux support.

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                    • #40
                      AFAIK, false color only gets you so far. The Earth is more beautiful than anything you would paint. The goal is to put something in orbit that would replace an interstellar probe. You want full visual impact.

                      How big would a telescope need to be to replace an interstellar probe? Are we talking miles? Meters? AUs?
                      I came upon a barroom full of bad Salon pictures in which men with hats on the backs of their heads were wolfing food from a counter. It was the institution of the "free lunch" I had struck. You paid for a drink and got as much as you wanted to eat. For something less than a rupee a day a man can feed himself sumptuously in San Francisco, even though he be a bankrupt. Remember this if ever you are stranded in these parts. ~ Rudyard Kipling, 1891

                      Comment


                      • #41
                        Regarding unfolding, let's pretend that we can assemble the telescope by hand in orbit. Would the needed tolerances still disallow optical telescopes? Would we always need monolithic mirrors for optical telescopes?
                        Last edited by DanS; February 19, 2007, 15:21.
                        I came upon a barroom full of bad Salon pictures in which men with hats on the backs of their heads were wolfing food from a counter. It was the institution of the "free lunch" I had struck. You paid for a drink and got as much as you wanted to eat. For something less than a rupee a day a man can feed himself sumptuously in San Francisco, even though he be a bankrupt. Remember this if ever you are stranded in these parts. ~ Rudyard Kipling, 1891

                        Comment


                        • #42
                          Do you know how color really works?

                          Originally posted by DanS
                          AFAIK, false color only gets you so far. The Earth is more beautiful than anything you would paint. The goal is to put something in orbit that would replace an interstellar probe. You want full visual impact.

                          How big would a telescope need to be to replace an interstellar probe? Are we talking miles? Meters? AUs?
                          What our brains perceive as color is just the assignment of a particular color to a range of EM Wavelengths. False color is just an artificial shift of the color to EM Wavelength range matching.

                          If we didn't tell you it was false color, how would you ever know the difference?
                          “It is no use trying to 'see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.”

                          ― C.S. Lewis, The Abolition of Man

                          Comment


                          • #43
                            Sure

                            Originally posted by DanS
                            Regarding unfolding, let's pretend that we can assemble the telescope by hand in orbit. Would the needed tolerances still disallow optical telescopes? Would we always need monolithic mirrors for optical telescopes?
                            The problem is that working by hand in space is pretty tough. Last time I tried the spacesuit gloves, it was very hard for me to manipulate tools (compared to no gloves). Perhaps they have made advances in spacesuits since then.

                            Anyway, the real answer is to have self adjusting mirror segments controlled by computer controlled actuators. This is not here currently, but should not be too far away.
                            “It is no use trying to 'see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.”

                            ― C.S. Lewis, The Abolition of Man

                            Comment


                            • #44
                              That an unfair question, considering that we don't often see side-by-sides. We either see optical pictures of Earth or we see false color images of the stars. Do interplanetary probes use false color liberally?
                              I came upon a barroom full of bad Salon pictures in which men with hats on the backs of their heads were wolfing food from a counter. It was the institution of the "free lunch" I had struck. You paid for a drink and got as much as you wanted to eat. For something less than a rupee a day a man can feed himself sumptuously in San Francisco, even though he be a bankrupt. Remember this if ever you are stranded in these parts. ~ Rudyard Kipling, 1891

                              Comment


                              • #45
                                You better believe it

                                Originally posted by DanS
                                That an unfair question, considering that we don't often see side-by-sides. We either see optical pictures of Earth or we see false color images of the stars. Do interplanetary probes use false color liberally?
                                Once you get past Jupiter, its too dark to use real color.
                                “It is no use trying to 'see through' first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To 'see through' all things is the same as not to see.”

                                ― C.S. Lewis, The Abolition of Man

                                Comment

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