A Mission to Study Water in the Local Universe Paul F. Goldsmith Jet Propulsion Laboratory California Institute of Technology Pasadena CA With thanks to.

A Mission to Study Water in the Local Universe

Paul F. GoldsmithJet Propulsion Laboratory

California Institute of TechnologyPasadena CA

With thanks to Darek Lis, Imran Mehdi, Jose Sile, and Adrian Tang

29th IAU General Assembly, Focus Meeting FM 15: Water Throughout the UniverseTuesday August 4th 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/H2O ratio)

• Critical for life on Earth and other planets

Tracing Gas Phase WaterHigh spectral resolution is essential for realizing potential of H2O as a probe of

conditions and history

Rich spectrum throughout Submillimeter and Far-Infrared – Need to make choices!

Transitions of H2O and isotopologues observed in NGC6334 with Herschel HIFI (Emprechtinger+ 2013)

Quiescent Clouds: Water frozen on dust grainsOutflows: Shocks & radiation clean grain mantles – water returned to gas phase

Water as Tracer of Dense Core Kinematics

Water: demanding excitation => tracers innermost, densest regionsC18O: easy to excite--traces overall core and its motions

Cold (8-12 K), compact (0.1 pc) dense(103-107 cm-3)Precursors to new stars; should be collapsingWhat is the velocity field in collapsing cores?

All models have ~same n(r) but vastly different v(r)

Keto,Caselli,Rawlings2015

Larson-PenstonSingular Isothermal Sphere

Unstable B-E Sphere

H2O C18O

Only the Quasi-Equilibrium Bonnor-Ebert Sphere model reproduces observations of L1544

L1544 H2O 557 GHz datafrom Herschel HIFINote 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 2

111-000(para) 1113 GHz 212-101 (ortho) 1670 GHz

Water & Heavy Water in Comets: Origin of Earth’s Oceans

D/H ratio varies significantly within the solar systemEarth’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 BeltP < 20yr

>10,000 AUP ~ 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 509.3 110 - 101

599.9 211- 202

893.6 111- 000

919.3 202- 101

1009.9 211- 101

Important Transitions of H2O 547.7 110 – 101 (o-18) 556.9 110 – 101 (o-16) 987.9 202 – 111 (p-16) 994.7 202 – 111 (p-18)1107.2 111 – 000 (p-17)1113.3 111 – 000 (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 width @ 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• 1o 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 tripodTelescope &

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 oscillatorsLocal oscillators have made major advances since Herschel HIFI in terms of power output, efficiency, and tunability. Designs and configurations for 16 pixels @ 1.9 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 14

Extending Array Architecture to 16 Pixels

225 GHz triplermodule

1.9 THz + 650 GHz tripler modules

1.9-2.06 THz

633-686 GHz

211-229 GHz

70-76 GHz

Flange adapter

HRL GaN Power Amplifiers (x4)

Coax-WR28Adapters

4-way waveguide

power-divider

JPL GaAs W-band PreAmp

Pout > 5 uW/pixel

70-76 GHz

J. Siles & Imran Mehdi

Simultaneous Multiband Observations

1. Calibration system2. Polarization divider (wire grid)3. Cascade of high-pass perforated plate filters

Highest frequency dropped firstBeam recollimated by ellipsoidal reflectorNext lowest frequency band dropped….

Arrays for each band16 to 64 pixelsConfiguration 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 systemsDr. 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 interface5x10cm 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 SummaryA 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 (H2O, H218O, HDO)

890 – 1150 GHz (H2O, H218O, HDO, OH+, H2O+,

H3O+

1700 - 2100 GHz (H3O+, [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