nic scott

Telescope Systems Scientist

Current state of CHARA telescopes & Future plans

The CHARA Science Meeting 2025 - Nice

https://slides.com/nicscott/chara_meeting_2025

Where does CHARA have single point failures....

i.e. where the nightmares lie? 

• aging equipment
• time sinks
• lack of spares
• discontinued components
• supply chains becoming questionable
• other risks

• Mirror recoats
• W1 M5 damage
• Winch system
• New drives
• Stairs & weatherstripping & minions
• Cylinder control
• W1 realignment
• AOB problems and plan for new system
• Tiptilt concerns
• Future

Mirror recoats

• W1 M5 fracture
  • internal mirror stress
  • cross polarization test
• Replaced with flat M4 -lucky
  • no spare M6 or M2
  • have a matched M1/M2 spare
• Chamber is no longer flat
  • teflon standoffs
• Chamber seal
• Want a small chamber for individual mirror recoats 
• Boom truck 
  • Genie/rental stop gap
  • new hoist system
  • needed for AZ drive 

W2 & E2

• Stairs and crypt platform      added for safety
• W2 done, E2 next
• S1 weatherstripping and flashing replaced/repaired
  • needed for all scopes​

• Interface plate done for seeing monitor

• TelAO instead of TAS for alignment
• circle4.py
• speeds and improves EL axis alignment
• predicting circle from 74° of rotation by eye is tricky
• 3 independent fits for any circle
• uses pixel values from acq / Brunson aligncam / any camera

• W1 issue
• Custom pcb's
• Prone to elec. interference
  • particularly at E2 & W2
• Very tricky to diagnose
• Single cable fault may make the whole system not work or work in odd ways
• Differences b/t scopes
• Can cascade

• AOB/TEMA/HUT
  • RPC to control dehumidifiers and heaters based on minions (2/3 voting scheme)
• Cable wrap concerns
  • sharp edges
  • friction welding
  • routes
  • reduced cables in wrap
• Heidenhain encoders/tape
  • some show wear/damage

Impact of SPICA and moving actuators:

• 17 cases of beacon flat/m7 motors stuck / runout
• All required working on the motors and realigning
• All during SPICA runs or eng.
• Each was few hours of work.

cylinder upgrade

• done at S2 & W1
• rest are ready
• fan control added
• same for aob

Drive Upgrade

• S2 done and has been in use for a season, W1 after meeting

• Existing drives are ~25 years old & discontinued

• Reduce vibration, improve tuning

• Prototype assembly and short pivot arm done

• 12 drives and motors (plus spare) in hand from Parker

• Drive assemblies fabrication done (2 done, 10 remaining) - ahead of tariffs
• Spare Dojen obtained

• Install during daytime, but some nights needed for software and tuning

Tiptilt, PZT issues, actuators, hexapods?

• 11cm: spider → back of M2
• adjusting spider could get few more cm
• M2, d=140mm
• may need a piezo tiptilt system b/t hexapod and M2, but depends
• needs to function hanging upside down

• Tiptilt concerns
  • PI PZT's discontinued in 2018, could be sent for repair but limited
  • use DM for TT correction (but can't do on-sky reconstructor in this case)
  • actuators were discontinued in 1992
  • replace PI PZT's with Thorlabs PZT's or newer PI actuators+PZT
  • get one hexapod (~$50k) and then we have spare parts for rest of array

New fiber network (new IP pool)

new spycam system (3 per telescope up to 4k+audio, 3 w/ pan/tilt in lab), more sensors (rh, temp) and control

Plan Outline:

• Phase 0: AC at telescopes
• Phase 0.1: new IR dichroics for beam samplers
  • Improve multi-wavelength performance
  • Wider bandwidth for better STST performance
    • CRED1, bluer for science, WFS on a single chip?
  • Dual-star phase reference mode
• Phase 0.5: upgrades of telAO
  • Redesign M2, go to focal design?
• Phase 1: central 2m + AO + OPLE upgrades
  • LabWFS control new telDM,
  • Longer delay + better metrology or double-decker carts
    • Visible-sensitivity, resolution, stability →  needed for nulling 
• Phase 2: replace 1m's with 2m's
  • Propagate upgrades from central 2m
• Phase 3: full CMA - outer km baseline fiber array

(2024 Meeting on CHARA Future)

Central 2m Telescope

• Vacuum beam transport with fiber option
• Bundled with Delay Line Upgrades

• Review the current state of capabilities & techniques in optical/IR interferometry
• Discuss quantum-enhanced methods for pushing current limitations on spatial resolution
• Establish collaborations between the astronomy & quantum communities to address science requirements and technical challenges

"Performance of the Khabiboulline Configuration of Quantum Enhanced Long Baseline Optical Interferometry"- Mcclinton & Ridgeway (AAS 2025)

"Towards quantum-enhanced long-baseline optical/near-IR interferometry"

Rajagopal et al. (2024)

open-air or quantum-enhanced future beam transport?

Initial HBT experiments planned this yr with BNL

"Towards Quantum Telescopes: Demonstration of a Two-Photon Interferometer for Quantum-Assisted Astronomy" - Crawford et al. (2023)

Risks:

very uncertain US environment

Funding options:

- NSF (66% cut proposed)

- private: Heising-Simons Foundation, Keck, Kavli Instititute, others

- extend the consortium?

- other universities?

- National lab status?

- International partnerships?

• Central 2m telescope
• 1m's → 2m's
• Km+ baselines
• AO/ople/lab upgrades
• Off-target phase tracking
• Nuller
• Future beam transport
• Michelson Array

(bigger future plans)

CHARA in 2040

• Telescope dichroic upgrade
• Automated alignment/tracking
• Upgrade labAO system
• Optimizing multi-wavelength simultaneous observations
• Fibers to all telescopes
• W5 site (1100m)
  • extended/double-pass delay
• Up to 300 nights over three years of open access time via NOIRLab.

(near future plans)