Meeting Minutes - OST STDT Bi-Weekly Telecon - December 15, 2017

Subject:OST STDT Bi-Weekly TeleconDate: 
Purpose:To discuss science activities for OST.Facilitator:Margaret Mexiner 

Telecon: WebEx Online

Meeting Number:

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Access code: 194 170 917

Note Taker:Sydney Jones

Discussion Items 

 Mission Concept 2:  Instrument Prioritization: focus on FIP and HERO (see Mexiners PowerPoint here: ) / Continuum mapping:  FIP vs. MRSS – Meixner and Staguhn

  • See PowerPoint presentation for this here: Continuum-FIP-MRSS.pptx
  • Why is FIP thousands of time faster than MRSS? Mapping speed is faster. Get latest updates from Matt. FIP is an array; it is broadband, the spectral resolution is lower; detectors for MRSS have to be better to achieve these numbers. Detectors have to be background limited. FIP is a conservative instrument with higher impact. Not summing over spectroscopic pixels? correct.
  • Confusion limit is due to noise to to sources that are uncatalogued due to....
  • 8 square degrees can be scanned in an hour; 100 arc seconds per second 
  • Do we need a 40 micron channel in FIP, can this number be dropped? That is probably not a useful channel and should be discussed. FIP has polarimetry. 
  • Continuum mapping science cases include:
    • 1) Solar System, TNO, Bauer
    • 2) Time Variable Star Formation (uses slower mapping speed, the size of the field. Just need to solve dynamic range and stability of detectors to do relative measurements.) Lower background, dynamic range will be depend of lower background but not spectral resolution. 
      • MRSS for continuing mapping will be at 100 km size range. 
      • Margaret Meixner may arrange a meeting with GW counterparts to discuss discovery space (in ranking FIP 3rd), and is something to consider for the extra galactic group. Takes advantage of sensitivity gains of a cold aperture. 
  • May be useful to have a detector array instead of the solar array, longest dimension of array sets some parameters. 
  • Telescope scans are super important 
Thoughts of ranking FIP as 3rd
Speaker Comments/Feedback
Karin Sandstrom50%-%50 split between FIP and Hero. Informative, using polarization to continue with FIP puts it one step higher. Working on instruments, the extragalatic case, polarization is key. Choosing FIP, transformative thing with continuing mapping is important.
Lee ArmusFIP is a must have for OST, not politically, but in having the capability similar to other telescopes, is unique. Having this ability is a must have
Desika NarayananDoesn't feel qualified to answer. 
Asantha CoorayWould like to hear the case for Hero. 
Gary MelnickHas bias for spectroscopy because one area that OST covers that is lacking in Luvoir and HaBex is following water. They may not be able to trace the water through clouds and exoplanets like OST. The high spectral resolving power can do this. FIP has a high selling point. Still leaning towards HERO; helps us with the water program that is a big part of OST.
David LeisawitzRequiring HRS and MRSS provide a mode that gives a spectral resolution of three times tent to the five, would this change Gary Melnick answers? Gary Melnick responded indicating that if we received a velocity of 3 km per second at 50 microns; this is not that great. Should sharper hypothetical and discuss what would be achieved in the case of water. Spectrometer teams should say what they can achieve at the water lines at longer wavelengths. Can't toss out spectral resolving powers. If we insist on spectral resolving power at longer wavelengths. Asantha Cooray would be useful for Ted and Klauss to sit down and define requirements (spectral resolving power requirements). Thought about using MRSS and HERO in detecting water lines where HERO would go in and get exact line...
Margaret MeixnerEveryone will have to trim back science; these discussions (water lines and resolutions); we won't be able to have everything we had in Concept 2. With respect to relative sizes, for MRSS it is hard to make direct detection spectrometer as a MISC instrument. STDT needs to understand the relative ranking for who gets priority in terms of total real estate. Was hoping to establish consensus; will send out doodle poll.
Ruth CarterConcept 1 was over 10 billion. In order to accommodate instruments and prioritization; FIP is the only one, don't know for MRSS and HERO. The requirements will dictate how much volume and mass is available for higher priority instruments.Need clear understanding of what can go first and what instruments have higher priority. 
Douglas Scottwe have to have a camera; fast continuing mapping that cannot fall off the list of priority instruments. 
Thomas L. RoelligA lot of advantages give us rapid mapping speed. If we need to descope, could have a smaller array which would take longer time to scan the sky. Johannes Staguhn only option is to reduce the array; pixel number results will be half the size and half the weight. HERO is pretty conservative in technical requirements

Mission Concept 2:   Telescope size direction:  5 m diameter equivalent collecting area or  JWST 6.5 m collecting area & heritage 

  • See PowerPoint for entire presentation here: OST Study Office 20171215.pptx
  • Engineering thoughts - Carter
    • Brief analysis. STDT discussed this and come up with the assumptions listed on the slides (pg. 2)
    • JWST primary mirror is only 25% larger than the 5 m diameter circle 
    • Thomas L. Roellig what do you mean by Spitzer like configuration similar to JWST? Primary bigger than 5 m in diameter that fits in to monolith launch fairing, have barrel around it like Spitzer; which gives a smaller deployment. Size equivalent for JWST is 5.65 diameter; can possibly fit in a 7 m fairing 
    • Configuration advantages (see PowerPoint) 
JWST Comparison Feedback 
John ArenbergTechnically disagrees. Fundamental motivation for blindy recommending colder for JWST is for a cost requirment. The STDT office should look at a completely new design. Thermal design is starting to close with JWST. Have enough volume in JWST spacecraft to insert cooler. A STDT version of a different telescope adds fidelity to the study; as such, Jon Arenberg respectfully disagrees with the primary mirror size trade. Limited volume for five instruments if using the JWST concept; not building independent ISM structure which may have cooling advantages. I agree with the STDT office. JWST has no requirements to be serviced. There are architectural aspects that allow it to be refueled (study going on at Goddard) allowing it to be refueled on orbit. 
  • Why JWST cold? In oing all of the tasks, obligation is to contribute effort. Small effort is being done by a guy who is committed to JWST. Arenberg is committed to getting an answer. Will not delay JWST in committment to help OST.
  • As starting point for instrument accommodation, should we consider? Should consider taking out ISM structure. The ISM is not a highly efficient design. Need more structurally and thermally efficient design. Starting point would be outer envelope of ISM. 
  • Serviceable configuration is recommending. 
    • Serviceable configuration may come at a low cost; serviceable means it can be refueled. Current design of OST can not be refueled. 
Thomas L. Roellig

Thomas L. Roellig not scared of 7m fairing launch vehicle. Would go for 7 m fairing option. Bigger is better. Should not grow too big; easier to do this than cram into a smaller fairing.

  • Ruth Carter indicated would have a higher risk, but the cost may be less for 7 m fairing. Specifically,  an 8.5 m SLS cost is $650 million, which is $340 m dollars less, a seven meter would be less.
Ned Wright

Ned Wright indicated that we are being to specific. Should be bigger than JWST because of political configuration. The fairing size is also something to think about. Should be a $600 billion thing. 

Gary MelnickNo feedback, may have been muted. 
Kevin Stevenson

Intrigued by large Spitzer fitting JWST design. The advantage of Spitzer's shell could be huge; likes implication of design itself. Having collecting area similar to JWST is important to consider. 

Matt BradfordGather as much info as possible to discuss from STDT. Need depth in the descision making. Would be nice to see how much material the STDT has come up with telescope size. Need clarity for a starting point. 
Margaret MeixnerSuggested revoting on this.


Action ITems 

No.Action Item(s)OwnerTarget Due DateStatus (In progress/Completed)
1Instrument Prioritization Poll: Send out survey monkey or vote on FIP being 3rd (Thomas L. Roellig indicated to make sure to include whether it's a wash to avoid any conflict) 

Margaret Meixner

Asantha Cooray

 In Progress 
2Assemble more information on the JWST comparison, and send something around to STDT (the spreadsheet that Carter summarized)Ruth Carter In Progress