MAXAT ISSUES FOR FURTHER CONSIDERATION
The final session of the workshop consisted of a group discussion of major points that came up during the Workshop.
SCIENCE CASE: our initial explorations suggest that strong science cases can be developed, but to do so a clearer understanding of technical issues is required.
1. Future studies need to cross cut across wavelengths to properly develop the multiple dimensions of interesting scientific problems, and thereby better define the role of MAXAT in addressing them.
COMPLEMENTARITY: The focus during the Workshop was on NGST with the conclusion that the combination of MAXAT and NGST would be extremely powerful.
- MAXAT operating as a high sensitivity, high angular resolution imaging spectrograph system in the optical and IR terrestrial windows would complement NGST (spectroscopy of objects it images and takes low resolution spectra of; lower background a major advantage in thermal IR for NGST if optics are cooled) and MMA (infrared characteristics of dense regions, observed with comparable angular resolution).
- Consideration needs to be given to scientific interactions with the full suite of planned space observatories; e.g. MAP, PLANCK, SIM.
- Similar issue arises for future ground-based observatories; e.g., VLA upgrades, square kilometer array, advanced VLBI, etc.
- MAXAT should be designed to take advantage of continuing technological advances during its lifetime (e.g. detectors).
- The relationship between MAXAT and O/IR interferometers will benefit from experience with prototype systems.
TECHNOLOGY: Major technical uncertainties exist. The Workshop saw several opportunities to develop basic capabilities as steps towards a better-defined concept for a MAXAT.
- Primary Mirror.
- Fully active and adaptive optics-friendly
- Structural issues; segmented design with segment sizes of <8-m to allow transportation
- Studies of mirror phase control important
- Wind loading on the mirror and structure major issues for mechanical control of MAXAT
Adaptive Optics (AO)
- Natural guide stars (NGS) technologically "reasonable" for this time frame, but limited to optical mag=15.
- scientific specifications definition required
- use of K-band guide stars? (Experience needed)
- tomography with natural guide stars, opportunity area?
- Laser Guide Stars (LGS)
- "stitching" of LGS to obtain wider corrected field with AO is an issue specific to MAXAT or mirror D>8-10m and for smaller apertures in the optical.
- Need low cost, high performance sodium lasers?
- LGS is viewed by some as a potential "show stopper" for MAXAT.
- Primary gains seen in imaging spectroscopy over small fields corrected with AO for moderate-to-high spectral resolution.
- Spectrograph sizes are fixed with f-ratio for diffraction-limited telescopes; reasonable size instruments seem feasible with AO.
- "National Light Bucket" version of NGST potentially scientifically useful, but requires huge spectrographs; a serious problem.
- Explore alternate technologies, could be less difficult than multiple LGS systems.
Other Technical Issues
- Not clear how to specify systems aspect of MAXAT so as to yield a clear prediction of cost, performance and risk.
- Need to explore the path of technology -> capabilities -> science.
OPERATIONS SUPPORT: A successful MAXAT will work in concert with other highly capable astronomical facilities. Since it will not be able to replace all other US OIR ground-based facilities, we must be extremely careful about operating costs:
- Large capital investment suggests high operating costs that would reduce cost-benefit ratio of MAXAT; e.g. $300 M instrument at 10% per year operating cost would require NOAO's total budget to operate.
- Need to develop specialized operations models
- Consider campaigns and other ways to minimize configuration changes
- Upfront effort in telescope design to minimize operations costs