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The MSE Observatory

The project’s grand vision is to provide a facility that will deliver the wealth and quality of observational data needed to answer the next generation of questions about our universe, and to do this with the least possible impact on the environment of Maunakea and the Big Island of Hawai’i – indeed, we intend to complete this project bringing a net benefit to our local community, as well as an important new facility to the international science community.

Central themes in our construction plans are those of recycling wherever we can during the development of MSE, and minimizing the consumption of resources during operations. MSE will use the same building and pier that CFHT telescope now sits upon, and although it will be necessary to replace the dome with one with a larger opening for our larger telescope, once the project is completed the new facility will be almost indistinguishable to the local community from the current CFHT, while to the astronomical community it will be a completely new and vibrant facility. MSE will build upon CFHT’s pioneering work in remote operation, with no staff at all travelling to the summit at night. We're working to reduce the amount of daytime maintenance activity needed, as well. Since MSE will only perform one single task (and perform it very well), there will no longer be campaigns for instrument changes at the telescope. Electrical consumption should see significant reduction, as the new facility takes advantage of modern analysis techniques to predictably thermalize at night using ambient wind and convection rather than the current electrically-driven cooling systems. With smaller living space at the telescope, water consumption (much of it being used for humidifiers) will also reduce.

The Telescope

Existing telescope main components

CFHT, built in the 1970’s, is a general use telescope with 3.6 meter primary mirror on an equatorial mount. Typical of its day, the telescope primary mirror is “slow” (that is, it has a large F/D ratio): the curvature is shallow and the focal point is a long distance from the mirror.

Existing dome main components
Together, these conditions require a larger dome to move around within than more modern, optically “fast” telescopes on altitude-azimuth mounts. In fact the dome on CFHT is even larger and heavier than the telescope needs, perhaps a monument to when steel was cheaper and engineering calculations were performed conservatively by hand. The CFHT building and foundation are strong enough to support the weight of a Keck 10 meter telescope, indeed the enclosure is very nearly able to fit the entire Keck telescope within it without modification. Some modifications to the dome are necessary: the opening in the dome is sized for a 3.6 meter telescope, it’s too small for our 10-meter class primary aperture.

MSE will leave the central massive concrete pier intact and re-use the surrounding building and structure supporting the dome. We will remove the CFHT 3.6 meter telescope and replace it with a modern 10-meter class telescope.
Cross section views and exterior dimensions of the
proposed MSE facility(left) and current CFHT facility(right)
The dome will be replaced with another that looks similar, with an appropriate opening size and perhaps slightly larger in size. Indeed our initial plans (feasibility study part II) are for a dome that is merely 0.5m (19”) larger in radius. We are continuing to study both the optimum size of telescope and optimum style and size of dome, to find a best compromise in science performance and cost while keeping within the mass limits that the current building and foundation can support and striving for the least visual impact as seen by the local community and other users of the Maunakea summit area.

The Instrument

The single dedicated MSE instrument is a fibre-fed multi-object spectrograph, capable of gathering light from up to 3200 simultaneous objects, each being measured with spectral resolution from R=2000 to about R=20,000. There are three main subassemblies that make up this instrument: 1) the fibre positioner unit, 2) the fibre transmission system, and 3) the spectrographs.

The positioner is an array of 3200 small actuators, each supporting the end of one of the 3200 fibres at a point in the 1.5 degree focal plane of the telescope. The positioner has the ability to move each fibre end independently and to place it precisely upon the image of the object being studied. There are a number of alternatives available for a fibre positioner technology. The technology selection in this area will be one of considerable interest until a decision is reached as part of the Project Office work.

The Cobra fibre positioner unit developed for
Subaru's Prime Focus Spectrograph instrument.

The fibre transmission system transfers the light gathered at the telescope focus to the spectrographs located in the Coudé room, buried within the massive concrete pier for the telescope.

The spectrographs in the MSE Coudé room will certainly be many. We require that the spectrographs can operate in a lower resolution mode of R=2000 with all 3200 fibres and over the entire 370-1300nm wavelength range simultaneously, and in the highest resolution mode of about R=20,000 over a restricted range, perhaps 420-620nm, with 800 of the fibres. There will also be a mid-resolution mode with R=6500, again over a restricted but larger wavelength range. To accomplish all this we will use different spectrographs for the low and for the mid- and high-resolution modes, and the spectrograph for each mode will be made of a banks of smaller spectrographs, each accommodating a smaller number of fibre inputs. The design of the spectrographs is an area rich in choices and alternatives, and again will be an area of considerable interest while the Project Office works toward a baseline decision.

Operations and Data

MSE will primarily be a survey instrument, with most of the observations providing data to create large surveys. Survey designs will be developed under the guidance of the MSE Science Advisory Committee. Some opportunities may exist for non-survey observations by scientists in partner countries, and although the policy for this is still under development, we anticipate the share of non-survey observations will remain small, perhaps 10%, through the life of the observatory. Observations will be performed remotely, from the MSE Headquarters building in Waimea Hawai’i. Raw data will be reduced to calibrated individual spectra and archived in a central archive, released to scientists in the partner organizations in accordance with a still-to-be-developed data usage policy.