"JS" == Jonathan Silverlight writes:

NASA STUDIES SPACE RAILWAY TO EXPLORE ORIGINS OF PLANETS, STARS,
AND GALAXIES

A NASA-led team is studying the construction of a railway in space
for a pair of telescopes that will provide views of planet, star,
and galaxy formation in unprecedented detail. The proposed Space
Infrared Interferometric Telescope (SPIRIT) mission will also
examine the atmospheric chemistry of giant planets around other
stars.

SPIRIT will consist of two telescopes at opposite ends of a
[40-meter] beam. The telescopes will move along the beam like cars
on a railway, combing their images using the techniques of
interferometry to achieve the resolving power of a single giant
telescope [40 meters] across.

JS Don't you need at least three mirrors for imaging?

Not necessarily. The important aspect is Fourier plane coverage.
SPIRIT could obtain this by allowing the beam to rotate and taking
"snapshots." Each snapshot, with the beam at a slightly different
angle and with the telescopes at slightly different positions along
the beam, provides effectively a different interferometer pair.
Combining all of the different effective interferometer pairs, one can
then make an image.

In the case of radio interferometers, we (often) use the rotation of
the Earth to provide different effective interferometer pairs. In the
early days of radio interferometry, though, a process similar to what
is planned for SPIRIT was used. Some early interferometers contained
a moveable antenna. So an observation was conducted, the antenna
moved, another observation conducted, etc. Even today, some of the
highest "precision" images (more precisely, highest dynamic range
images) are obtained using multiple configurations of the VLA. In
other words, one makes an observation with the VLA in one
configuration, waits for the antennas to be moved to a new
configuration, makes a new observation, and then combines the data
from the different configurations.

Obviously, a key assumption in all of this is that the structure of
the source does not change appreciably in the time it takes to move
the antenna(s).

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html