Lensless space telescope could be 1,000 times stronger than Hubble

 

Artist's concept of the Aragoscope deployed The Hubble space telescope has given us decades of incredible images, but it's reaching the end of its service life and the question is, what will come after? One possibility is the Aragoscope from the University of Colorado Boulder, which uses a gigantic orbital disk instead of a mirror to produce images 1,000 times sharper than the Hubble's best efforts. The Aragoscope is named after French scientist Francois Arago who first noticed how a disk diffracted light waves. The principle is based on using a large disk as a diffraction lens, which bends light from distant objects around the edge of the disk and focuses it like a conventional refraction lens. The phenomenon isn't very pronounced on the small scale, but if the telescope is extremely large, it not only becomes practical, but also extremely powerful. When deployed the Aragoscope will consist of an opaque disk a half mile in diameter parked in geostationary orbit behind which is an orbiting telescope keeping station some tens to hundreds of miles behind that collects the light at the focal point and rectifies it into a high-resolution image. "The opaque disk of the Aragoscope works in a similar way to a basic lens," says CU-Boulder doctoral student and team member Anthony Harness. "The light diffracted around the edge of the circular disk travels the same path length to the center and comes into focus as an image." He added that, since image resolution increases with telescope diameter, being able to launch such a large, yet lightweight disk would allow astronomers to achieve higher-resolution images than with smaller, traditional space telescopes. The Aragoscope is similar to the starshade being developed for NASA, which uses the same telescope and giant floating disk architecture. But where starshade uses the disk to create artificial stellar eclipses to aid planet hunting, the Aragoscope turns the disk into a gigantic diffraction lens. According to the team, the similarity is no coincidence, since starshade was developed by members of the Aragoscope team. The new orbital telescope was selected last June by NASA as one of 12 proposals for its NASA Innovative Advanced Concept (NIAC) program – each of which received US$100,000 to fund nine-months of research for projects ranging from capturing asteroids to sending submarines to the lakes of Titan. The Aragoscope is now up for being one of six projects that will receive an additional US$500,000 in April. The team sees the Aragoscope as a way to penetrate farther into the universe to observe phenomena like black hole event horizons, or turned on the Earth to pick out objects the size of a rabbit. The next phase of the project involves testing the concept. This will involve laboratory work using a one-meter disk set several meters from a telescope. If this is successful, a more dramatic demonstration will use a disk set on a mountain top while a telescope mounted on a helicopter tries to focus on the star Alpha Centauri. Source: University of Colorado Boulder

Time to think big: A call for a giant space telescope

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An artist’s concept of the ATLAST telescope under construction in space. This design has a segmented mirror 20 metres across.

In the nearly 25 years since the launch of the Hubble Space Telescope (HST), astronomers and the public alike have enjoyed ground-breaking views of the cosmos and the suite of scientific discoveries that followed. The successor to HST, the James Webb Telescope should launch in 2018 but will have a comparatively short lifetime.

Now Prof Martin Barstow of the University of Leicester is looking to the future. In his talk at the National Astronomy Meeting (NAM 2014) in Portsmouth on Tuesday 24 June, he calls for governments and space agencies around the world to back the Advanced Technologies Large Aperture Space Telescope (ATLAST), an instrument that would give scientists a good chance of detecting hints of life on planets around other stars.

ATLAST is currently a concept under development in the USA and Europe. Scientists and engineers envisage a telescope with a mirror as large as 20 m across that like HST would detect visible light and also operate from the far-ultraviolet to the infrared parts of the spectrum. It would be capable of analysing the light from planets the size of the Earth in orbit around other nearby stars, searching for features in their spectra such as molecular oxygen, ozone, water and methane that could suggest the presence of life. It might also be able to see how the surfaces of planets change with the seasons.

Within the vision "Cosmic birth to living Earths," ATLAST would study star and galaxy formation in high definition, constructing the history of star birth in detail and establishing how intergalactic matter was and is assembled into galaxies over billions of years.

If it goes ahead, ATLAST could be launched around 2030. Before this can happen, there are technical challenges to overcome such as enhancing the sensitivities of detectors and increasing the efficiencies of the coatings on the mirror segments. Such a large structure may also need to be assembled in space before deployment rather than launching on a single rocket. All of this means that a decision to construct the telescope needs to happen soon for it to go ahead.

Prof Barstow is the President of the Royal Astronomical Society, but is speaking in a personal capacity. He sees ATLAST as an ambitious but extraordinary project. He commented:

"Since antiquity human beings have wondered whether we really are alone in the universe or whether there are other oases of life. This question is one of the fundamental goals of modern science and ATLAST could finally allow us to answer it.

'The time is right for scientific and space agencies around the world, including those in the UK, to take a bold step forward and to commit to this project."