by alter-ego » Sun Jan 22, 2012 6:54 am
Flase wrote:
Interesting. It seems to be both a pinhole and a "starshade". Such a thing has always seemed a good idea to me; the use of a shade to block out a star's glare so you can see its planets. They use one already in the SOHO solar observatory.
I believe the the link(s) presented have led to some confusion. The 2005 article on Dr. Cash's New World Imager approach for imaging exoplanets does utilize a 10-m pinhole, but not a starhade. Although a physical aperture includes a block of some sort to creat an aperture, the pinhole "perfect lens" has ≈10 milliarcsecond resolution (10 meters in the image plane) and is meant to isolate an exoplanet with it's narrow field of view. Whereas with Cash's 2010
NWO proposal, the flagship New World Observer uses a starshade WITHOUT a pinhole with the JWST. On the starshade, the petal-looking perimeter is a special "apodized" design which significantly (many orders of magnitude) supresses diffracted light in the regions of interest. Specifically, modeling predicts central startlight supression to 10
-10 within 75 milliarcseconds. I'm not sure, but I believe that today, the starshade may be the primary path of interest.
- Starshade only
I'm startled by this claim, though:
http://www.nasa.gov/vision/universe/newworlds/new_worlds_imager.html wrote:Finally, the NWI would swing into imager mode, the two collector spacecraft executing a complicated
dance around the combiner craft to build up an image of another world. With the ability to resolve distant objects about 100 kilometers (60 miles) across, New Worlds Imager should be able to see clouds, continents, and oceans, giving us the first true pictures of a planet far from our own solar system. Not bad for the old pinhole camera.
I'm not sure how far away such a planet could be. The obvious candidate in the search for planets would be Alpha Centauri and it would truly be an event if we could take such images. What about Pluto and the asteroids for starters?
Another bit that needs some clarification. Not stated is that an array of
two starshades and
two primary collecting telescopes (~4-meter class) are needed to achieve the quoted resolution. Their light is combined at the "combiner craft" Assuming a visible wavelength of 500nm, and using two telescopes (and two starshades) separated by 1500km,
100km would be the limiting resolution at 10 parsecs (~33lyr) Note, that corresponds to
≈60 nanoarcseconds, or ≈ 1600x higher resolution than the single starshade/collector.
(See left)
Lastly, implimenting these tools for objects in our solar system may be feasible in that we always find new, unplanned ways to use new tools. However, a key goal today for NWO is to look for life by way of finding oxygen on planets in the habitable zone. That pretty much puts pluto and asteroids at the bottom of the priority list, and given the physical expanse of these planet-hunting systems, tracking solar system objects could be problematic as they move very fast relative to planets light years away.
[quote="Flase"][quote="neufer"][quote=" http://en.wikipedia.org/wiki/Pinhole_camera"]
<<NASA has funded initial research into the [url=http://en.wikipedia.org/wiki/New_Worlds_Mission]New Worlds Mission project[/url], which proposes to use a pinhole camera with a diameter of 10 m and focus length of 200,000 km to image earth sized planets in other star systems.
[/quote][/quote]
Interesting. It seems to be both a pinhole and a "starshade". Such a thing has always seemed a good idea to me; the use of a shade to block out a star's glare so you can see its planets. They use one already in the SOHO solar observatory.[/quote]
I believe the the link(s) presented have led to some confusion. The 2005 article on Dr. Cash's New World Imager approach for imaging exoplanets does utilize a 10-m pinhole, but not a starhade. Although a physical aperture includes a block of some sort to creat an aperture, the pinhole "perfect lens" has ≈10 milliarcsecond resolution (10 meters in the image plane) and is meant to isolate an exoplanet with it's narrow field of view. Whereas with Cash's 2010 [url=http://newworlds.colorado.edu/documents/.../cash_jwststarshades_ppp.pdf]NWO proposal[/url], the flagship New World Observer uses a starshade WITHOUT a pinhole with the JWST. On the starshade, the petal-looking perimeter is a special "apodized" design which significantly (many orders of magnitude) supresses diffracted light in the regions of interest. Specifically, modeling predicts central startlight supression to 10[sup]-10[/sup] within 75 milliarcseconds. I'm not sure, but I believe that today, the starshade may be the primary path of interest.[attachment=0]NWO - Starshade + JSWT.JPG[/attachment]
[quote]
I'm startled by this claim, though:
[quote="http://www.nasa.gov/vision/universe/newworlds/new_worlds_imager.html"]Finally, the NWI would swing into imager mode, the two collector spacecraft executing a complicated [color=#0040FF]dance around the combiner craft[/color] to build up an image of another world. With the ability to resolve distant objects about 100 kilometers (60 miles) across, New Worlds Imager should be able to see clouds, continents, and oceans, giving us the first true pictures of a planet far from our own solar system. Not bad for the old pinhole camera. [/quote]
I'm not sure how far away such a planet could be. The obvious candidate in the search for planets would be Alpha Centauri and it would truly be an event if we could take such images. What about Pluto and the asteroids for starters?[/quote]
[float=left][attachment=1]NWI - Starshade Interferometer.JPG[/attachment][/float]Another bit that needs some clarification. Not stated is that an array of [u]two[/u] starshades and [u]two[/u] primary collecting telescopes (~4-meter class) are needed to achieve the quoted resolution. Their light is combined at the "combiner craft" Assuming a visible wavelength of 500nm, and using two telescopes (and two starshades) separated by 1500km, [color=#0040FF]100km would be the limiting resolution at 10 parsecs (~33lyr) [/color] Note, that corresponds to [color=#0040BF]≈60 nanoarcseconds[/color], or ≈ 1600x higher resolution than the single starshade/collector. [url=http://event.arc.nasa.gov/aresv/ppt/Saturday/10-Hyde/10Hyde.pdf](See left)[/url]
Lastly, implimenting these tools for objects in our solar system may be feasible in that we always find new, unplanned ways to use new tools. However, a key goal today for NWO is to look for life by way of finding oxygen on planets in the habitable zone. That pretty much puts pluto and asteroids at the bottom of the priority list, and given the physical expanse of these planet-hunting systems, tracking solar system objects could be problematic as they move very fast relative to planets light years away.