A Mission to Study Water in the Local Universe Paul F. Goldsmith Jet Propulsion Laboratory California Institute of Technology Pasadena CA With thanks to Darek Lis, Imran Mehdi, Jose Sile, and Adrian Tang 29 th IAU General Assembly, Focus Meeting FM 15: Water Throughout the Universe Tuesday August 4 th 2015

The Importance of Water (Vapor) Important coolant of “warm” interstellar clouds having T > 100 K Significant reservoir of oxygen in the interstellar medium (ice and gas-phase water together) Valuable tracer of the motions of interstellar clouds including OUTFLOWS and COLLAPSING CORES Tracer of thermo-chemical history of diffuse gas via ortho-to-para ratio (OPR) Critical source of information on origin of Earth’s oceans from icy objects in solar system (HDO/H 2 O ratio) Critical for life on Earth and other planets

Tracing Gas Phase Water High spectral resolution is essential for realizing potential of H 2 O as a probe of conditions and history Rich spectrum throughout Submillimeter and Far-Infrared – Need to make choices! Transitions of H 2 O and isotopologues observed in NGC6334 with Herschel HIFI (Emprechtinger+ 2013) Quiescent Clouds: Water frozen on dust grains Outflows: Shocks & radiation clean grain mantles – water returned to gas phase

Water as Tracer of Dense Core Kinematics Water: demanding excitation => tracers innermost, densest regions C 18 O: easy to excite--traces overall core and its motions Cold (8-12 K), compact (0.1 pc) dense( cm -3 ) Precursors to new stars; should be collapsing What is the velocity field in collapsing cores? All models have ~same n(r) but vastly different v(r) Keto, Caselli, Rawlings 2015 Larson-Penston Singular Isothermal Sphere Unstable B-E Sphere

H2OH2O C 18 O Only the Quasi- Equilibrium Bonnor-Ebert Sphere model reproduces observations of L1544 L1544 H 2 O 557 GHz data from Herschel HIFI Note velocity resolution Theoretical Models

Water Emission in Orion Offset (arc seconds) Ground State (557 GHz) Emission Dominated by Broad Outflow Herschel Excited State – Thermal & Maser Emission

Hartogh et al. (2010) Comet C/2008 Q3 (Garradd) Deuterated Water Comet 103P/Hartley (para) 1113 GHz (ortho) 1670 GHz Water & Heavy Water in Comets: Origin of Earth’s Oceans D/H ratio varies significantly within the solar system Earth’s D/H ratio does NOT match that of Oort Cloud (very distant) comets D/H ratio DID match that of first Jupiter- Family comet in which water observed Narrow lines require high spectral resolution Kuiper Belt P < 20yr >10,000 AU P ~ 10,000 yr Hartogh et al. (2011)

Evolution of Level Populations in Cometary Comae Bockelee-Morvan+ (1998) Upper level of 557 GHz Upper level of 987 GHz Ground states of Ortho & Para Important Transitions of HDO Important Transitions of H 2 O – 1 01 (o-18) – 1 01 (o-16) – 1 11 (p-16) – 1 11 (p-18) – 0 00 (p-17) – 0 00 (p-16)

Water in the Local Universe: Mission Concept Heterodyne spectroscopy does NOT require cold optics: translate cost savings of ambient optics to larger telescope Larger aperture => higher angular resolution AND higher sensitivity Increase data rate by using FOCAL PLANE ARRAYS and SIMULTANEOUS MULTIBAND OBSERVATIONS Utilize recent advances in submm receiver technology Baseline cryocoolers rather than cryogens for receiver cooling Exploit Digital Signal Processing breakthroughs

Telescope Concept Deployable, segmented telescope to fit within shroud of low-cost launch vehicle Falcon 9 Heavy – direct launch to L2 6m dia telescope (6.8m diameter possible) 12.5” FHWM beam 1 THz (λ = 300 μm) 6.5” FWHM at λ = 158 μm 36 hexagonal segments Two folds (as JWST) plus secondary deployment Overall surface accuracy ~ 10 μm rms Various panel technologies – CFRP honeycomb, Al honeycomb, hybrid designs 1 o C temperature gradient across deployed antenna Orbital LEOstar-3 bus with upgraded dual star trackers for required 1” pointing accuracy (possibly Ball HAST) Enhanced propulsion system for orbital insertion and orbit maintenance Total spacecraft mass 7000 kg (probably will be less)

Single –layer sunshield supported by 4 astromasts Sunshade geometry will be optimized but want to preserve ability to point relatively close to sun (especially for Solar System objects) Solar array on opposite side of sunshield Secondary reflector supported by tripod Telescope & Sunshade Deployed

Submillimeter Receiver Status Focal plane arrays are critical for imaging – C/Hartley2 resolved with 3.4m dia Herschel at 557 GHz, as are most astronomical (ISM) sources Technology for mixers (SIS & HEB) is mature; cooling to 4K is required. SIS to 1400 GHz and HEB above InP MMIC amplifiers available to 500 GHz but not yet competitive in terms of noise, but operate at 15 K Frequency-multiplied tunable local oscillators Local oscillators have made major advances since Herschel HIFI in terms of power output, efficiency, and tunability. Designs and configurations for THz and more at lower frequencies are available Low-power broadband digital signal processing Custom CMOS ASICs have transformed capability to analyze broad bandwidths in many pixels (including different bands) simultaneously Beam Model

4-Pixel 1.9 THz Local Oscillator Subsystem 20 cm x 20 cm x 10 cm More than 10 uW per pixel measured

California Institute of Technology Extending Array Architecture to 16 Pixels GHz tripler module 1.9 THz GHz tripler modules THz GHz GHz GHz Flange adapter HRL GaN Power Amplifiers (x4) Coax-WR28 Adapters 4-way waveguide power-divider JPL GaAs W- band PreAmp P out > 5 uW/pixel GHz J. Siles & Imran Mehdi

Simultaneous Multiband Observations 1.Calibration system 2.Polarization divider (wire grid) 3.Cascade of high-pass perforated plate filters Highest frequency dropped first Beam recollimated by ellipsoidal reflector Next lowest frequency band dropped …. Arrays for each band 16 to 64 pixels Configuration to be optimized – depending on mission profile

Spectrometer for Heterodyne Receivers This has been an issue at mm/submm wavelengths because of required large bandwidth and multiplicity of lines Solutions have included filterbanks (typically used on atmospheric sounders), chirp spectrometers (low power; used on planetary missions), and acousto-optical spectrometers (complex, heavy; used on SWAS (SMEX) and Herschel/HIFI) Digital signal processing, offering many advantages, is now feasible but FPGA approach is relatively power hungry (~4W/GHz BW) Ideal technology is custom VLSI using technology developed for cell phones and other communications systems Dr. Adrian Tang at JPL has unique partnership with UCLA team and Qualcomm for development of CMOS VLSI chips for NASA applications “SPECTROCHIP II” has 750 MHz bandwidth, 512 spectral channels, includes digitizer, data accumulator, and USB output interface 5x10cm size on board with support circuitry; 200mW DC power Next generation (Dec 2015) will have ≥ 2 GHz bandwidth, 8K channels

Spectrochip II  A Full 1.5 GS/s spectrum analyzer chip in advanced 65nm CMOS was developed by UCLA’s high speed electronics lab.  Integrated 7b digitizers, offset and interleaving calibration functions, clock management system and vector accumulation.  256dsb/512ssb channel quadrature output with integrated USB 2.0 controller Full SoC Die Photo Full SoC Block Diagram Module Assembly

Water Mission Summary A heterodyne-only mission devoted to study of water in the local universe can provide dramatically enhanced capabilities compared to Herschel/HIFI 6 – 6.8 m diameter aperture provides 3 to 4 times greater collecting area and thus this factor higher sensitivity for pointlike sources 22” FWHM beam width at 557 GHz; 6.5” FWHM at 1900 GHz Frequency bands 500 – 570 GHz (H 2 O, H 2 18 O, HDO) 890 – 1150 GHz (H 2 O, H 2 18 O, HDO, OH +, H 2 O +, H 3 O GHz (H 3 O +, [CII], [OI], HeH +, CO) 20% to 50% reduction in noise temperature for individual pixels 16 – 64 pixel arrays for observations of extended sources – up to 100 X faster imaging than Herschel HIFI Simultaneous observations with all (3 or more) bands