Telescope Aperture

50 cm

Optical Design

Modified Ritchey-Chrétien with 4 channels: FUV & NUV Imaging, FUV & NUV Spectroscopy. FUV & NUV obtained simultaneously using dichroic beam splitter also acting as a field aberration corrector.

Field of View

1.2 degrees, circular

Focal Length

3 m

Telescope coatings

Al+MgF₂

Imaging/Grism Modes

Optics wheel with

 (1) CaF₂ Imaging window, (2) CaF₂ transmission grism; (3) Opaque position.

Grism Rotation

Grism position angle may be selected with a resolution of 0.3 degrees, independent of S/C roll

Dichroic/Corrector

Aspheric astigmatism corrector

Ion-etched fused silica (aspheric surfaces on both sides)

Dichroic beam splitter with dielectric multilayer coating on input side

FUV Channel

NUV Channel

Band

1350-1750 Å

1750-2800 Å

Beam path

Reflected from dichroic

Transmitted through dichroic

Filters

Blue edge filter

(blocks OI, Ly a - transmission)

Red block filter/Fold mirror

 (blocks red Zodaical light)

Detectors

Sealed tube Z-stack microchannel plate with crossed delay-line anodes

Detector Window

MgF_2, includes power for field flattering

Fused Silica

includes power for field flattering

Detector Photocathode

CsI, opaque, repeller grid on window

Cs₂Te, semitransparent

300 mm proximity gap

Detector peak QE

12%

8%

Detector maximum local countrate w/o temporary saturation within PSF

~100 c/s

~1000 c/s

System angular resolution

6.0 arcsec (80% EE diam)

4.0  arcsec (FWHM)

8.0 arcsec (80% EE diam)

5.6 arcsec (FWHM)

Spectral Resolution

250-300

80-150

Imaging Effective Area

25 cm²

44 cm²

Photometric Zero Point [1 ct/s] m_AB

18.8

20.1

Spectroscopy Effective Area

20 cm²

39 cm²