SALT

Technology

Development

Lisa CrauseIndia-South Africa Astronomy

Workshop – SAAO

6 August 2012

SALT Image Quality

Large focus gradient, bifurcated stars seen in out of focus images, all seemed to be randomly

variable as well

Traced to problematic

interface ring transmitting

forces into the corrector &

disrupting the 4 SAC mirrors

The SAC Fix

Brought SAC down Replaced interface

with a pair of collars Developed Clean Room

Washed M5 & M3

SAC Alignment & Testing

Optically aligned & tested the mirrorsChecked system

performance at angle & over temp range

Re-installed SAC

On-Sky Testing

Used a bare CCD on an XY stage to tile the focal plane &

check the post-fix performance (also for direct comparison with

images taken before the fix)

SALTICAM was re-installed after its upgrade & it too

produced beautiful, uniform images over the full 10

arcmin field

Inductive Edge Sensors• Capacitive edge sensors were unsuitable

due to their sensitivity to humidity & dust• Contract signed with Fogale Nanotech in June

2012 for their inductive edge sensors• Excellent results obtained: insensitive to

humidity & consistent behaviour with temperature changes

• Maximum deviation of 30 nm over 5 days

• To be installed in situ & phased in, starting with the central 7 segments

Inductive Edge Sensors• 12 sensors/segment, each mounted to a

Clearceram L-bracket for a 3.5 mm gap• Primary mirror alignment should hold for

at least 5 days, longer if ΔT <20 C • Expect a substantial increase in

observing efficiency due to the alignment time saved & better overall IQ

• Full installation to take ~2 years

• Pathfinder for ELTs

RSS: Our Insane Spectrograph

Robert Stobie Spectrograph (RSS)

• Various problems with optics, mostly due to troublesome lens fluid

• Major overhaul of all mechanisms by SALT while the optics were being repaired

• Latest throughput issue traced to the collimator optics

• Keen to tackle the repair/replacement ourselves this time

RSS Near Infrared Arm• Being built by the University of Wisconsin• NIR to have most of RSS-Vis

functionality, but will operate from 0.8 to 1.7 microns

• Semi-warm design is an economical way to extend optical instruments into the near infrared

• Pre-dewar part kept @ -40 C & & dewar @ 120 K

RSS Near Infrared Arm• RSS spectroscopy from the atmospheric

cut-off (320 nm) to the H-band, in 1 shot!• Tracker weight budget is already being

exceeded so will need to upgrade its load capacity to make provision for NIR

• Tracker upgrade project is funded & will be carried out by SALT & SAAO staff

• Timescale: late 2014?

High Resolution Spectrograph• SALT HRS: fibre-fed echelle

spectrograph under construction at Durham’s Centre for Advanced Instrumentation

• Commissioning due to start towards the end of this year

• Blue & red beams to cover 370-555 nm & 555-890 nm

• λ/Δλ from 16000 to 67000 via 4 different modes

High Resolution Spectrograph• Pair of object & sky fibres for each

mode• Optics to be housed in a vacuum tank

& the whole instrument will be sealed in a thermally stabilised enclosure in the spectrometer room below the telescope

• Payload Fibre Instrument Feed for HRS designed & built at the SAAO

Conclusion

We have grown the most from

the biggest challenges

SALT’s presented so far & we have much more to learn!