Participants: Baldwin, Blanco, Cecil (chair & minutes), Diaz, McMahan, Simkin

The conversation lasted 1 hr. Blanco had provided concept sketches of the telescope at the MSU SAC website to clarify discussion of instrument volumes and configurations.  Action items are in red.

Extra foci in the requirements document

There was some discussion of the 2-mirror Cass. and prime foci which were being considered by the project. Baldwin outlined the discussion that Sebring had had with the CTIO community during his visit the day before. Baldwin noted that the prime focus did not provide a useful pixel scale on existing detectors. Cecil also noted that the fast primary f/ratio put significant requirements on any corrector that would span an interesting field of view. The SAC was unanimous is agreeing that this focus, if provided, not be instrumented at first light. Baldwin hoped that making the enclosure oversized to accomodate this focus would not increase costs.

The SAC was unenthusiastic about a two-sided or dual M2, preferring that the money be spent elsewhere for more science benefit. Cecil noted that the Cass. focus was there to accommodate polarimetry and coronagraphic work. Diaz will see if Brazilian polarimetrists could live with the Blanco or a 4-mirror folded Cass. focus similar to WIYN. Cecil noted that this or Nasmyth were poor locations for a coronagraph. He asked Simkin to establish MSU's position on a coronagraph.

Gemini compatibility issues

McMahan started  this discussion, saying that he had yet to hear the scientific tradeoffs of Gemini compatibility over the lifetime of the telescope. He felt that the only thing this compatibility buys us now is access to the GIRS. The future Gemini instrument complement and its access by SOAR is undefined. But the act of building the telescope to be compatible with those instruments will be severe. McMahan would like the SAC to consider if the instrument complement currently planned for Gemini is sufficiently plausible on SOAR to warrant the engineering compromises.  Simkin noted that there was this assumption that if we were compatible, then those instruments would be available and they certainly won't be available at the best times because Gemini will have priority!  Moreover, Cecil noted that all SOAR partners already have Gemini access so there is a risk of second-rate science that couldn't compete successfully for Gemini access.

Cecil noted that throughout the SWG phase, Gemini compatibility was always discussed as a goal, not a requirement. So it should probably remain one until the engineers satisfy us that it does not impact image performance (our top requirement).
Simkin asked the SAC o envision a telescope with 3 ports instead of 1 capable of bearing a Gemini instrument. If we built simpler, more specialized IR instruments for these ports, then we would always have these available, not the case for the GIRS.  We would also avoid the problem of putting things on and off. Cecil asked: could we build the full suite of our own IR instruments for the  $1-1.5M + X that NOAO would charge us for fractional access to a clone of the GIRS, where $X might be $ recovered from the SOAR telescope budget if it became a lighter weight structure?  The engineers have indicated that steel costs are an insignificant part of beefing up the telescope structure.

Baldwin pointed out that it was actually a package of 3 instruments that are being discussed, each with modern InSb arrays (the GIRS has 4 alone.) Only Phoenix and the GIRS are the true mass drivers, and Phoenix is only 1250 lbs vs. 4500 for the GIRS.  You'd need to reproduce the direct imaging capability of CCOB as well. Simkin noted that IR instruments change faster than any other types. The question is whether closer to 5 years from now as we near first light, will there be a more compact set of instruments than this suite  which, by then, will be nearly 15-year old?

To return to the topic at hand, Cecil noted that providing Gemini compatibility doesn't commit us to the specific package on the table. The point has been made several times that instruments are getting more massive, although this may simply reflect the arrival of 8-10m telescopes. McMahan agreed that it was impractical for the engineers  (= Blanco) to come up with detailed design for a Gemini compatible and incompatible telescopes, but he thought it would be straightforward to summarize the trades. They may actually prefer the heavier structure.

Cecil noted that the Gemini instrument was being balanced on the other side of the telescope by an instrument cube, and that cube was to populated by  three 700 kg instruments. Do we then propose to significantly reduce the mass of these, or drop the number there from 3 to 2?  Baldwin felt that you do need to separate out Gemini compatibility and buying a copy of the GIRS.  Phoenix is 5 ft long, the GIRS is 7. It would seem that you would at least want the space of the GIRS if not its mass. Mass and moment appeared to be the issue here.

Simkin said her main worry was in fact not mass, it was the problem of trading instruments.  Things break, misalign, etc. when they are moved. Cecil reiterated the science loss that would occur when the GIRS was elsewhere.  Q, synoptic, and target of opportunity work would be seriously compromised, as well as the ability of at least the University partners (because of their limited access) to do quick, multiwave followup observations.

Cecil reminded Diaz that  SOAR would still be an f/16 telescope with identical optics to Gemini (of course its pixels would span 4x the area), but suppose we were to propose a smaller mass requirement and somewhat smaller volume envelope than Gemini, 1200 kg instead of 2100. Please find out how Brazil would feel about building somewhat more compact instruments that would still work on Gemini. What does Brazil want out of Gemini compatibility? Would Brazil be willing to take the ``risk" of conducting its IR spectroscopy on instruments other than the GIRS? Brazil could go ahead & still build Gemini instruments and also use them on SOAR. SOAR would just be unable to support the most extreme instrument.

[Simkin left the telecon here.]

McMahan asked that it be an action item for the engineers to provide the SAC with their assessment of what it means to provide full or partial Gemini compatibility.  He asked of Blanco, what would you have to do to WIYN to beef it up to take the various spectrum of Gemini compatible masses that we had discussed today?  Cecil felt that we also needed to come up with a strawman instrument or instruments that would at least reproduce and hopefully exceed the science performance of the GIRS. This would ensure that there would be no science loss to the project if we opted not to support the GIRS. McMahan felt that the whole thing boiled down to: is a single IR slit worth the engineering exercise? Cecil clarified this to a single slit with potentially an image-slicing IFU.  He felt that we could debate these issues, but we needed to converge by Oct. 1.  Baldwin asked what exactly we were asking Dan to do.  The SAC agreed that Blanco  would look at and report next time on the differences of supporting 2100 kg x 2 vs. 1000 kg x 2.

Baldwin asked Blanco if supporting  the GIRS was unreasonable on our budget.  Blanco felt we could do it within budget. McMahan noted that the issue was whether the engineering effort would benefit science more if it was spent elsewhere. Blanco agreed.  Cecil reiterated that the rewards are optimized instruments that are constantly resident at SOAR, and the risk is that the partners are unable to acquire these instruments or that they may be too expensive.

Baldwin felt that the GIRS, since it evolved from an instrument for Blanco, did accurately reflect the requirements of  IR astronomers in the NOAO community. He felt we should be providing the IR capabilities for the SOAR/Blanco system, but agreed that we didn't need to provide the capabilities for Gemini as well.   McMahan agreed.

Cecil reminded everyone to complete their reviews of the requirements document by the next telecon. We will meet on Wed pm but not on 9/17 because both Baldwin and Elston cannot.