Telescopes for the 21st century
The last week of september, I attended a meeting at Nice Observatoire. The Observatoire was founded in 1881 thanks to Raphaël Bischoffsheim generous sponsorship, XIXth century Mr. Keck. The dean of the observatory old instrumentation is a refractor accommodated within a building designed by Mr. Charles Garnier. The original dome was a clever device designed by Mr. Eiffel, (yes!, the same engineer that built a rather well known tower in Paris) - at the time the telescope was built the electric power supply at the Observatoire was not enough to support moving a dome over wheels, instead Mr. Eiffel designed a system based on supporting the dome on a channel so the whole structure was floating on water.
The meeting passed unattended for a large fraction of the European Astronomical Community however, it was an important meeting for astronomical instrumentation. Telescopes are optical instruments that magnify the image of far objects; they also are designed to collect as much radiation as possible. In fact, the current technological challenge is to increase the capability of telescopes to collect light (basically, to increase their size). Space telescopes are the most challenging ones. Some human beings love challenges. Laurent Koechlin is a French instrumentalist working in Toulouse; he is working very hard in the attempt to form astronomical images by difraction (from the infrared to the ultraviolet). Fresnel interferometry allows imaging of astronomical objects using a perforated screen as radiation collector.
At first sight, a mirror seems a better option than a perforated screen to collect radiation; mirrors are very efficient in reflecting radiation and a screen always occults partially the radiation however,
1. Current technology makes easier to unfold in space big screens than 10 m telescopes.
2. Mirrors are not as efficient in the ultraviolet as in the optical range.
Fresnel telescopes ought to be long since the distance between the radiation collector (the screen) and the imaging instrumentation is larger than in conventional telescopes. This is the reason why we travelled to Nice. The old refractor (with a long tube) was used by Laurent ’s team with Jean-Pierre’s assistence to accommodate the telescope to work under a Fresnel scheme.
76cm refractor telescope at the Nice Observatoire with the Fresnel optics on it.
At the end of the image, at the end of the tube, there is a grating which is shown magnified below:
This is the first prototype to form image of astronomical objects. What next?
A team is being created to present the project to the next call by the European Space Agency. A device with a 3m screen/membrane and an optics alike that of a 40cm telescope will allow to achieve a spatial resolution of 8 milliarcseconds in the ultraviolet. This high resolution, ten times better than HST, would allow mapping the evolution of disks around stars and the environment around black holes.
This is an artists view of the instrument with the two spaceships: the spacecraft hosting the membrane and the spacecraft hosting the optics. Check here for more technical details.
