Jupiter- Europa Mission Sub-MM Wave (Terahertz) Payload Technology

1. Jupiter- Europa MissionSub-MM Wave (Terahertz) Payload Technology B. Ellison & B. Thomas - Rutherford Appleton Laboratory, UK P. Irwin - University Oxford, UK Jupiter/Europa Technical Studies Workshop - London

2. Terrestrial atmospheric spectra J-E Sub-mm Wave/THz Observations • Jupiter Orbiter: • Molecular emission/absorption features (HCN, CO, H2O, H2D+ etc.) in Jovian upper atmosphere - high resolution spectroscopy. Measure line intensities, line shapes and Doppler wind velocities globally and with high temporal precision. • Data provides unique information on atmospheric composition, structure, dynamics & evolution • Europa Orbiter: • Potential for Europa surface science and gas evolution measurements. Limb and nadir sounding Jupiter/Europa Technical Studies Workshop - London

3. Heterodyne Technique • Coherent detection (passive radiometry): • Conversion of sub-mm wave signal to much lower frequency with arbitrarily fine resolving power. • Room temp or cryogenic instrumentation (room temp. preferred). • Excellent measurement heritage, e.g. astronomy and terrestrial atmospheric physics. • Key elements: • Primary antenna. • Mixer (semi-conductor or superconductor). • Local oscillator. • Intermediate frequency amplifier. • Spectrometer. Jupiter/Europa Technical Studies Workshop - London

4. Technology Drivers/Studies • Detailed study of required payload parameters is essential and drives payload configuration. E.g.: • Defines frequency range and sensitivity requirements. • Defines bandwidth and spectral resolution. • Defines technology selection (mixer/local oscillator). • Preliminary work assumes >1THz operation  study areas to include: • Antenna structure - low mass, low rms error (~5µm), efficient steering (if necessary). • Enhanced system efficiency - sensitivity (mixer), SB filtering, bandwidth. • Local oscillator power - mW generation in THz range. • Signal processing - lower power and lower mass digital correlation systems. • Substantially enhanced system integration - advanced fabrication, MMIC solutions. • Ultra-efficient cryogenics - if SIS/SHEB mixers to be used. • Focal plane array systems. • Radiation hardening. Jupiter/Europa Technical Studies Workshop - London

5. RAL Photonic Local Oscillator Core Technology Advances • Planar Schottky diode technology (cryogenics avoided): • Demonstrated in fundamental waveguide structures to ~3THz • Either self supporting GaAs membranes or transferred onto quartz • SIS/HEB Technology (requires 4k cooling): • Higher sensitivity than Schottky diode • Operation beyond 1THz (SHEB - limited ∆IF) New types of LO sources: • Quantum cascade lasers (providing ~mW power at frequencies > 2THz) • Photonic local oscillators (down converted IR diode lasers…) • Planar Schottky varactor multiplier chains (Herschel HIFI) Development of wide bandwidth, high resolution, low mass & power spectrometers: • Increased digitisation speed • Improved power consumption. Quantum Cascade Laser(Cologne) Omnisys Correlator RAL Planar GaAs Diode Jupiter/Europa Technical Studies Workshop - London

6. Mixer/LO Array IF Array Feedhorn Array Key Technology: 5-10 Year Vision • Receivers to ≥5THz with low cost, predictable performance : • Silicon machining, computer controlled machining of waveguide cavities, membrane diodes… • LO: varactor or photonic mixing to 1THz, room temp. QCLs > 1THz • Increased circuit integration: • Close integration of mixer with LO and IF plus sideband filtering. • Spectrometers with less mass and power consumption and broader bandwidth (e.g. >10GHz). • Potential benefit from commercial activity - fab. new processes (rad. hard?). • Focal plane array development • LO generation and distribution solutions. • Introduction of novel structures and integration methodologies. Conceptual integrated multi-pixel FPA ‘Push-broom’ imaging Jupiter/Europa Technical Studies Workshop - London

7. Jupiter/Europa Mission Example • Heterodyne receivers designed to target key molecular species: • e.g. CO, CS, H2O, HCN, HDO, H2D+, SO2, etc. • Frequency of operation up to ~5 THz range: • Broad spectral bandwidth, >10GHz, with spectral resolution of ~few MHz (both tbd). • Antenna diameter - 0.5m: • 106km Jupiter orbit (periapsis) gives spatial resolution ~600km @ 1THz. • Scanning antenna, or linear array of receivers with fixed aperture. • Limb or nadir view. • Schottky diode mixer receiver technology preferred: • Avoids requirement for mechanical cooling or liquid cryogens and possesses large ∆IF. • Mass and power: • ~ 3W, 0.5kg per receiver. • ~ 8W, 1Kg for 8GHz DAC spectrometer. NEDT assume 1 sec integration time in 1MHz bandwidth. Passive cooling to 100K gives factor of 2 improvement. Jupiter/Europa Technical Studies Workshop - London

8. Summary • The sub-mm wave/THz spectral region offers a potentially novel and important observation window for planetary science. • ‘In situ’ observations provide a unique opportunity to study the composition, dynamics and evolution of Jupiter’s upper atmosphere. • Recent advances in critical receiver technology now allow the possibility of multi-frequency, multi-pixel probes to be deployed with relatively low mass and power. • Relevant science and technical studies will need to be initiated to ensure appropriate payload definition and key technology enhancement. • A sub-mm wave/THz Jovian/Europa orbiter instrument will build upon European strengths in remote sensing and planetary science, and receiver technology development previously sponsored by ESA. Jupiter/Europa Technical Studies Workshop - London