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April 29, 2010

Hypertelescope Specifications and Capabilities

Astro Bio looks at the telescope array sizes needed to image other planets and objects on other planets in other solar systems.

* a 100-pixel image of a planet twice the width of Earth some 16.3 light years away would require the elements making up a space telescope array to be more than 43 miles apart. Such pictures of exoplanets could make out details such as rings, clouds, oceans, continents, and perhaps even hints of forests or savannahs. Long-term monitoring could reveal seasonal shifts, volcanic events, and changes in cloud cover.
* To resolve 30 foot objects looking 4.37 light years away the elements making up a telescope array would have to cover a distance roughly 400,000 miles wide, or almost the Sun's radius. The area required to collect even one photon a year in light reflected off such a planet is some 60 miles wide. To determine motion of 2 feet per minute — and that the motion you’re seeing is not due to errors in observation — the area required to collect the needed photons would need to be some 1.8 million miles wide. [NOTE - I do not think there would be enough photons coming off of such a small object at light year distances. This is why the hypertelescope expert talks about massive telescope arrays to resolve neutron stars. They are small but are emitting enough photons for an image]

Hypertelescopes

Hypertelescope paper (11 page pdf)

EXO-EARTH DISCOVERER ( EED)
Flotilllas of satellites are obviously needed for optical arrays in the size range from kilometers to hundreds and thousands of kilometers. Among the possible hypertelescope schemes, those with a concave primary array and focal combiner appeared well suited for space versions with multiple free -flyers . Either spherical ( CARLINA scheme) or parabolo├»dal shapes can be considered for the primary array. Early orbital tests are desirable for developing the techniques of formation flying. Our group investigates the design of nano-satellites driven by solar sails, and plans to test them in geostationary orbit . “Gossamer” free -flyers having a mass as low as 100 grams are considered. With a rigid sail of area 0.1 square meter, driving a membrane stellar mirror of comparable size, accelerations can reach 10 microns per square second, providing motions of 5 m in 1000 seconds.

EXO-EARTH IMAGER (EEI)
Once control techniques for a flotilla of space mirrors will be mastered, it will perhaps not take many years to expand their size from hundreds of meters to hundreds of kilometers. This is the size needed to obtain well resolved visible images of an exo-Earth within a few parsecs . Simulation 37 have shown that visible “portraits” of such planets can be obtained in 30 mn of exposure, using a 150 km hypertelescope with 150 mirrors of 3 meters.

NEUTRON STAR IMAGER ( NSI)
For ever larger optical arrays, sizes will ultimately be limited by the number of photons received per resel. The, number decreases when exploding an array since it shrinks the celestial resels The Crab pulsar , believed to contain a compact neutron star of visual magnitude 18, requires huge baselines beyond 100,000 km to resolve the 20 km neutron star , but its extreme luminance can provide enough photons per resel through such a highly diluted aperture, with sub -apertures of a few meters . A “Neutron Star Imager” hypertelescope, spanning several hundred thousand kilometers is therefore conceivable. It can be similar to the EED or EEI., but requires primary mirror elements as large as 8 meters to concentrate their focal Airy peaks within a comparable size, so that they be collectible with beam-combiner optics of manageable size.

Laser Driven Hypertelescope
Feasibility of a laser-driven hypertelescope flotilla at L2 (28 page presentation)

• Many small mirrors better than few large ones • But how small ? Minimum size about 30mm for tolerable beam spread • 40,000 mirrors of 30mm for same area as JWST ? …. Laser-trapped flotilla ?








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