Technologies for Future Far-IR Telescopes and Interferometers Dave Leisawitz, NASA GSFC SPICA SPIRIT CALISTO

Future Far-IR Missions SPICA – the Space Infrared Telescope for Cosmology and Astrophysics, led by Japan SPIRIT – the Space Infrared Interferometric Telescope, studied as a candidate Origins Probe (comparable to FIRI – the Far- Infrared Interferometer in Europe) SAFIR – Single Aperture Far-IR Telescope. A refined version, CALISTO, the Cryogenic Aperture Large Infrared Space Telescope Observatory, was proposed for technology devopment to the Decadal Survey 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 2192 The Far-IR Community is unified in its endorsement of US involvement in these missions.

NWNH Recommendations Science goals that require more capable far-IR missions than any developed to date US participation in SPICA (budget caveat) Technology development for single-aperture (SAFIR/CALISTO) and interferometric (SPIRIT) far-IR missions 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 2193

Compelling Science Goals 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 219 How do the conditions for planetary habitability arise during planet formation? (“follow the water”) Find and characterize exoplanets by imaging and measuring the structures in protoplanetary and debris disks. How did high-redshift galaxies form and merge to form the present-day population of galaxies? (How did a hot, smooth universe give rise to the Milky Way?) When and how did the first stars form and enrich the intergalactic medium? 4 SAFIR/ CALISTO SPIRIT

8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 219 Water, water everywhere! (Some gaseous, some solid.) How do the conditions for planet habitability arise during planet formation? 5

8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 219 Kuchner et al. Eps Eri model scaled to 30 pc Jang-Condell protoplanetary disk structure Find and characterize planets by detecting lumps of gravitationally trapped dust in debris disks. Detect and characterize newborn planets in protoplanetary disks. 14 May 20116D. Leisawitz - Far-IR Space Opportunities and SPIRIT 6

8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 219 How did high-z galaxies form and merge to form the present-day population of galaxies? 7

Herschel GOODS-N Deep Field 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 2198

Derived Requirements (SPIRIT) Sub-arcsecond angular resolution over the wavelength range 25 – 400  m (between JWST and ALMA) – Image protostellar and debris disks – Resolve the far-IR extragalactic background ~10  Jy continuum, W/m 2 line sensitivity – Detect low surface brightness debris disks – Measure SEDs and spectral lines of high-z galaxies >1 arcmin instantaneous FOV Spectral resolution, R ~ 3000 (integral field spectroscopy) 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 2199

8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 219 To image protoplanetary and debris disks and definitively distinguish the emissions of individual high-z galaxies requires sub-arcsecond angular resolution. This capability is sorely lacking in the far-IR, where these objects are bright and their information content is great. 10

8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS Sub-arcsecond angular resolution Astronomical background-limited sensitivity Technology: Detectors Cryocoolers Wide-field spatial-spectral interferometry Low aereal density, possibly deployable primary mirror Technology: Detectors Cryocoolers Wide-field spatial-spectral interferometry Low aereal density, possibly deployable primary mirror Measurement requirements drive technology requirements

8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS Technology Roadmap (SPIRIT)* * A large single-aperture telescope also requires: large format, lower NEP detectors, though they needn’t be as fast (see Paul Goldsmith’s presentation), and a low aereal density primary mirror, possibly deployable.

Cooling FIR Telescopes: Past and Future Past: IRAS COBE Spitzer Akari WISE Herschel 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 219 Past missions used expendable cryogens 13 Future: SPICA SAFIR/CALISTO SPIRIT Future missions will use cryocoolers

Why use cryocoolers? Much less mass to launch Greatly reduced volume relative to cryostat Lower mass and volume means lower cost to launch or more room for science payload Mission lifetime not limited by expendable cryogen 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 21914

Technology Readiness 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS With straightforward modifications, the JWST cryocooler (left) and the IXO CADR (right) will reach TRL 6 for SPIRIT.

How much cooling power? 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS (Left) Heat loads and cryocooler requirements are based on high-fidelity thermal models like this 106-node model of a SPIRIT telescope. (Right) Subscale cryothermal testing in a LHe shroud was used to validate the model. Dipirro et al. (2007)

Cooling Requirements (SPIRIT)* For optical components, extend JWST cryocooler technology to enable cooling to 4 K with 180 mW heat lift at 18 K and 72 mW at 4K. For focal plane, need an ADR cryocooler operating from a base temperature of ~4K and cooling to 30 mK with a continuous heat lift of 5µW at 50 mK and 1 mW at 30 mK. Compactness, high efficiency, low vibration, and other impact-reducing design aspects are desired. * More stringent requirements may pertain to a large single-aperture far-IR telescope with much larger focal plane arrays. 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 21917

Wide-field Spatial-Spectral Interferometry something old and something new 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 21918

8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 219 Wide-field Spatial-Spectral interferometry We’ve been developing and gaining practical experience with this technique in the lab for the past decade 19

Low aereal density mirror 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS ~10 kg/m 2 ~4 K CALISTO

Summary In the far-IR, the drive toward sub-arcsecond angular resolution coupled with the need for astronomical background-limited sensitivity translates into technology requirements for: – Far-IR detectors (Paul Goldsmith’s presentation) – Cryocoolers – Wide-field spatial-spectral interferometry – Low aereal density mirrors Most of the technology requirements are well understood Recommendation: future investments in the technologies listed above should be coordinated, sustained, and tied to the needs of studied single aperture and interferometric mission concepts 8 Jan 2012D. Leisawitz - COPAG Workshop - Austin AAS 21921