Project
Manager's Corner: Scheduling TMT I Last month I discussed adjustments to the design of TMT and to its estimated cost. I described our progress into the last phase of TMT design. By May 2008 we plan to complete the site-independent Preliminary Design of TMT. This means that we will have fully defined the design that we intend to build and that this design can be shown to meet the design requirements. Following that phase, we will have selected the TMT site and will proceed to complete site-specific elements of the design, such as different foundations for different local geology. Final design, where detailed construction documents are completed for industry, follows and this initiates construction. Science
Nugget—Observatory
Operations: Setting the Stage
Technology
Nugget—APS The Alignment and Phasing System, or APS, is the TMT instrument that is responsible for the precision optical alignment of the telescope. Perhaps its most challenging task is the proper phasing of the segments: in order for the TMT to achieve its ultimate theoretical resolution, the 492 segments of its primary mirror must form a continuous optical surface, with the steps between adjacent segments no larger than 6 nanometers (nm) high, or less than one one-hundred-millionth of a segment diameter. By contrast, a poorly phased TMT would have an angular resolution no better than that of a 1.2 meter telescope! Q & A with George Angeli
George sat down recently for an interview with Doug Isbell to talk about the systems engineering challenges of the TMT project. Download
George Angeli Interview Focus
On—Deployment of the IRMA Infrared Water Vapor Radiometers Previous Issues View the TMT Newscast Archive. |
As
described elsewhere in this Newscast, the TMT project is already
running small observatories every night on five different mountaintops.
These observatories operate robotically, picking out target stars
under automated control, collecting data and relaying the information
to local and remote archives. When systems fail or degrade, TMT
personnel must journey, often on short notice, over long distances
to make repairs or adjustments. This continuous, night-after-night
operation must meet demanding reliability standards and produce
scientifically reliable data, suitable for any reputable scientific
journal. The figure shows an interesting byproduct of this program—an
image of Comet McNaught caught by one of our all-sky cameras. (For
more on site testing, see the 
George
Angeli is the Head of Systems Engineering for the TMT project.
He has been involved in the design of Extremely Large Telescopes
since 2001. Before formally joining the project he was working
on the Giant Segmented Mirror Telescope (GSMT) at NOAO and chaired
the Integrated Modeling Working Group for the collaborative efforts
of CELT, GSMT, and VLOT. 
The
higher you go, the drier it gets. That is the rule
of thumb concerning the average amount of precipitable
water vapor (PWV) above an astronomical site. It
works pretty well as a guideline, but there are many
aspects of PWV that are of interest for TMT in a
more quantitative way. How often is the PWV content
of the atmosphere above the site lower than a certain
value? What are the conditions one gets during the
best 10% of the time? Are there diurnal or seasonal
patterns that are specific to a site? And so on.
The answers to these questions will not only affect
site selection, but might also determine certain
TMT operations strategies. For example, if the PWV
is always high during a certain time of the year,
you would not schedule mid infrared observations
for that time. Operation of a PWV monitor on the
TMT candidate sites was therefore always considered
highly desirable.