JST/T250 progress report

The Javalambre Survey Telescope (JST/T250) is an 250cm Ritchey Chrétien telescope with a large field of view of 3 deg diameter, particularly defined for carrying out large sky photometric surveys like J-PAS. Click here for a detailed technical description of the JST/T250.
February
 
 

The Centro de Estudios de Física del Cosmos de Aragón (CEFCA) has proceeded with the final acceptance of the JST/T250 telescope at the Observatorio Astrofísico de Javalambre. Optical fine tuning of the system during Final Acceptance tests provides images of 0.15” FWHM using “lucky imaging” techniques.

 
October
 
 

Last September 2015, the JST/T250 telescope at the Observatorio Astrofísico de Javalambre passed successfully the Provisional Acceptance test review. This milestone represents a big step forward for the completion of the project, only pending the Final Acceptance tests that shall be completed in the next weeks.

 
September
 
 

JST/T250 completely integrated with the final optical elements. Dummies, used to previously verify telescope mechanics and control, have been replaced by the primary mirror (M1) (2.6m diameter), the secondary mirror (M2) (1.2m diameter) and the field corrector composed by three lenses with 50-60cm diameters and aspherical surfaces with steep slopes. A lifting platform has been used to transport the optical elements and their mechanical supports from the OAJ loading dock, located in the basement of the JST/T250 building below the ground level of the observatory, where dismantling and integration tasks were done, to the telescope plant. This platform, integrated in the JST/T250 building, has a capacity up to 10 tons and has been specially designed and made to this task.

 
June
 
 

JST/T250 completely integrated and verified, with dummies for the optical elements and the verification camera for engineering first light.

M1 primary mirror of the JST/T250 telescope arrives at OAJ.

 
April
 
 

M2 secondary mirror of JST/T250 after being alluminized.

 
March
 
 

The JST/T250 telescope assembled at OAJ's dome. Still lacking M1 rotator and M1 cell. The image shows the JST/T250 assembled with the dummy optics awaiting the arrival of the final optical elements.

Barrel of JST/T250 field corrector lenses. The field corrector is totally finished, including anti-reflecting covering of the three lenses' surfaces. First image shows the barrel opened. It displays the first lens of the field corrector L1, which has a 60 cm diameter with a complex aspheric geometry on both surfaces. The serrurier support structure provides the anchorage to the system of the two other lenses, L2-L3, which are closer to each other and, in this case, inside the barrel. Second image shows the field corrector completely closed, as it will be installed in the optical path of JST/T250.
 
February
 
 

JST/T250 primary mirror M1 during the process of glueing of the support pads on its lower surface in the factory (AMOS, Belgium). The mirror is in the latest computer-controlled polishing phase (CCP), very close to achieve the optical quality requirement.

Support pads fixed to the non optical mirror surface. Those pads are the point of contact with the whiffle tree, which keeps the position of the mirror once assembled in its cell.
JST/T250 secondary mirror M2, 1.2 m diameter, finished at AMOS (Belgium), still not aluminized. The image displays the mirror and its cell with (6x3) 18 points of contact of the whiffle tree structure.
 
November
 
 

Integration tasks of JST/T250 telescope in the interior of its dome. Principal parts of the telescope were brought into the dome through the main slit with a 25 m crane. The images show the sequence of introduction of the interphase structure and anchoring with the telescope's concrete pier.

 
June
 
 

L3 lens of JST/T250 field corrector (the closer one to Cassegrain focus) finished and assembled in its support. L3, which is 50 cm aproximately, is concave with big curvature. It can be observed the serrurier's structure in the support of the lens. It will be connected to the support of L2, thus guaranteeing a better stability of the system.

 
December
 
 

JST/T250 during the mechanical acceptance test.

 
September
 
 

JST/T250 fully assembled, with the verification camera counterweight and dummies simulating the optical elements.

 
June
 
 

JST/T250 during the rotator and general cabling integration. The telescope is integrated with dummies that simulate the shape and weight of the mirrors.

 
May
 
 

L3 during optical tests.

 
April
 
 

JST/T250 under integration process, during a progress review meeting with CEFCA staff members.

 
March
 
 

JST/T250 during the assembly phase at AMOS' headquarters. In the center of the image, the telescope ground interface structure, the fork, the centerpiece, the serrurier structure, the M2 top ring and the altitude and azimuth drives and bearings are already in place. At the right bottom of the image, the M1 cell completely assembled before integration under the centerpiece.

 
December
 
 

The M2 hexapod, manufactured by Symétrie (France).

L2, one of the three lenses of the JST/T250 field corrector, at the testing optical bench. The field corrector is being manufactured by L3-Tinsley (USA).

 
October
 
 

M2 at the Hindle sphere optical metrology test tower setup, at L3-Brashear (USA) premises. The M2 mirror is located at the bottom loaded on the metrology support. The interferometer assembly with the null lens is located above it at the top of the tower. The Hindle sphere is located at mid-height pointing downward toward the M2 mirror. A laser tracer, at the right of the picture, is used to monitor spacings between the various optics and test optical axis alignment.

The JST/T250 alt-azimuthal fork.

Parts of the M1 whiffle tree.

 
December
 
 

The M1 blank under polishing process at AMOS headquarters.

 
November
 
 

The M1 blank arrives AMOS headquarters in Liege (Belgium). The blank is made of Zerodur, a glass ceramic by SCHOTT (Germany) with nearly null thermal expansion. The blank weights 2.4 tons and has an outer diameter of 2.64m.